Method of transporting cooled natural gas
FIELD: storage or transporting of natural gas.
SUBSTANCE: method comprises cooling natural gas down to a temperature below the temperature of the ambient air and transporting the cooled natural gas.
EFFECT: enhanced efficiency of storage and transporting.
16 cl, 13 dwg
The technical field to which the invention relates.
The invention relates to the transportation of natural gas in containers under pressure at a certain degree of cooling and uses the advantage of increasing the density of the gas at the pressures and temperatures that are acceptable in the case of using a relatively inexpensive container and vehicles, without the need for excessive cooling or compression when loading or transportation. The invention can be used on Board a ship or other moving transportation systems chilled natural gas. The invention does not apply to pipelines for the transportation of chilled natural gas.
The level of technology
It is well known that the term "natural gas" defines a very wide range of gas compositions. Methane is the main component of natural gas and is usually at least 80% by volume from the gas, known as marketable natural gas. Other components include, in descending order, ethane (3-10%), propane (0.5 to 3%), and butane isomers C4 (0,3-2%), pentane and isomers of C5 (0,2-1%), and hexane+ and all isomers of C6+(less than 1%). Natural gas is also typically contain nitrogen and carbon dioxide in amounts from 0.1 to 10%.
In some gas fields, the content of carbon dioxide of up to 30%. Common what somename, contained in natural gas is isobutane and isopentane. Unsaturated hydrocarbons such as ethylene and propylene, natural gas is not detected. Other impurities include water and sulfur compounds, but their content is usually strive to bring to very low levels before the sale of marketable natural gas, regardless of the transportation system used to deliver natural gas from the wellhead to the consumer.
Secord and Clark in U.S. patent 3232725 (1963) and 3298805 (1965) describe the advantages of storing gas at a temperature and pressure that occur when the gas exists in a dense phase fluid, namely at a pressure only slightly higher than the pressure of the phase transition. This state is shown in the usual phase diagram from the patent 3232725 presented on Fig, and occur within the dotted lines on the chart.
The relationship between pressure, volume and temperature of the gas can be expressed by the equation of state of an ideal gas in the form PV=nRT, where when using English units:
P is the gas pressure in absolute pounds per square inch (abs. pound per square inch),
V - volume of gas in cubic feet,
n is the number of moles of gas,
R is the universal gas constant,
T is the gas temperature in degrees Rankine degrees Fahrenheit plus 460) or when using metric e is the INIC:
P is the gas pressure in grams per square centimeter (g/cm2),
V - volume of gas in cubic centimeters (cm3),
n is the number of moles of gas,
R is the universal gas constant,
T is the gas temperature in degrees Kelvin (degrees Celsius plus 273,15).
The equation of state of an ideal gas requires adjustment when considering under pressure hydrocarbon gases due to the inclusion of intermolecular forces and form molecules. To account for these factors in the equation, you must enter the compressibility factor z: PV=znRT. This z-factor is a dimensionless quantity that reflects the specific compressibility of the gas with the measured parameters at a certain temperature and pressure.
At atmospheric pressure or a pressure close to atmospheric, the z-factor is substantially close to 1, so that for most gases can not be ignored, and the equation of state of an ideal gas can be used without the introduction of the z-factor.
However, in cases when the pressure exceeds a few hundred abs. pounds per square inch, the z-factor is much less than 1, and should be included in the equation of state of an ideal gas to obtain the correct results.
According to theorem of van der Waals deviation of real gas from ideal gas law depends on how far the status is of the gas from its critical temperature and pressure. Thus defined, the terms Tr and Pr (known as given temperature and a given pressure), and
where T is the gas temperature in degrees Rankine (Kelvin)
Tc is the critical temperature of the gas in degrees Rankine (Kelvin)
P is the gas pressure in the abs. pounds per square inch (MPa abs.),
Pc is the critical pressure of the gas in the abs. pounds per square inch (MPa abs.).
The critical pressure and the critical temperature for pure gases calculated and are available in many reference books. For gas mixtures of known composition can be used "pseudocritical temperature" and "pseudocritical pressure applied to the mixture using the average critical temperature and critical pressure of pure gases in the mixture taking into account weighting factors corresponding to the molar fractions of each pure gas. Then you can calculate pseudoprivate temperature and pseudoprivate pressure using respectively pseudocritical temperature and pseudocritical pressure.
If you know pseudoriemannian temperature and pseudoprivate pressure, it is possible to find the z-factor using standard charts. An example of one of them is the publication of "compressibility Factors of natural gas", Fig-3, Mvestments and Dloc, 1942, Technical Guide, Associateprograms.com equipment for gas processing, 10th edition, Tool, Oklahoma, USA, 1987. A copy of this chart is shown in Fig.
One aspect of the art is described in U.S. patent 6217626, "Storage and transportation of natural gas containing additives C2 or C3 or ammonia, hydrogen fluoride or carbon monoxide under high pressure". This patent describes a method of storage and subsequent transportation of gas by pipeline, in which the addition of light hydrocarbons, ethane and propane, or ammonia, hydrogen fluoride or carbon monoxide) - may increase the pipeline capacity or to reduce the power required for pumping over this gas mixture. Claims of the present invention mainly limited to obtaining a mixture by adding propane or ethane, in which the product of the z-factor (z) and molecular weight (MW) of the obtained mixture is less than that of the mixture without the addition of ethane or propane. However, this patent does not mention the presence of fluid, as indicated by only a single phase gaseous steam.
The advantage arises from the patterns expressed in the equation of fluid flow through the pipeline. There are several forms of this equation has the following General features:
Flow = constant1[((P1 2-P2 2)/(S*L*T*z))0,5]*(D2,5),
P2- the final pressure in the pipeline
S is the density of gas (equivalent molecular weight)
L is the length of the pipeline
T - gas temperature,
z is the compressibility factor of the gas,
D - internal diameter of the pipeline.
In this equation there are two multipliers, which vary depending on the composition of the gas, namely the density (or molecular mass) S and the z-factor. They are both in the denominator of the equation. Therefore, if the product of z and MW or S decreases, and all other factors remain constant, the flow through the pipeline increases with a similar pressure difference between the start and end points. This is an advantage when pumping through a pipeline, consisting of either throughput or to reduce the power consumption required to pump a given volume through the pipeline.
The main claims of the invention under the patent 6217626 provide for the addition of C2 or C3 to natural gas to reduce work z and MW (or S) when excessive pressure over 1000 psi (6,9 MPa abs.) and without the formation of visible liquid. The advantages obtained according to this patent relate to the throughput capacity of the pipeline or reduce power consumption.
In this patent is described mixture, for which the main obstacle for increasing benefits is a two-phase state caused by the introduction of gas too many liquids natural gas. This two-phase state causes physical damage to the equipment, piping and flow reductions, and therefore it should be avoided. The following claims of the invention limit the amount of ethane level of 35%, and the number of propane - level 12% to avoid in the pipeline this two-phase state. Some claims refer to the minimum number of added ethane and propane with regard to benefits in the pipeline. In U.S. patent 6217626 not mentioned about adding any hydrocarbons heavier than propane, such as butane or pentane, and it actually describes what you should avoid such heavy hydrocarbons, because they lead to premature emergence of a two-phase state. On page 6, it States: "thus, the C4 hydrocarbons are not additives provided in this invention. Further it is stated that the presence of more than 1% of C4 hydrocarbons in the mixture is not preferred because of C4 hydrocarbons have a tendency to easily liquefied at pressures from 1000 to 2200 abs. psig (6,90-15,18 MPa abs.), and their contents in quantities greater than 1%, and increases the ASO is the capacity allocation of the liquid phase. C4 hydrocarbons also have an adverse impact on the z-factor mixture at pressures below 900 abs. psig (6,21 MPa abs.), it is therefore necessary to ensure that during transportation by pipeline mixtures according to the invention containing C4 hydrocarbons, the pressure did not fall below 900 abs. psig (6,21 MPa abs.), preferably was not lower than 1000 abspoel per square inch (6,90 MPa abs.).
The mechanism of regulation proposed in the patent ′626 to eliminate the two-phase state, is the type and amount of liquids natural gas added to the mixture. This is because in the pipeline temperature and pressure are usually exogenous variables that are not amenable to any precise regulation.
Cooling is mentioned in the patent ′626 only once and in a negative sense. Although some claims and refer to the mixtures at a temperature of -40°F (-40°C), on page 10 of the patent ′626 includes the following statement: "even more preferred is a pressure 1350-1750 abs. pounds per square inch (to 9.32-12,08 MPa abs.), that gives good results, but without tanks that can withstand high pressure, and especially preferred temperature is 35-120°F (1,7-48,9° (C)that does not require excessive cooling. Advantages of the invention are illustrated in the graphs presented in ′ 626, which end at the lower temperature limit of 30-35°F (-1,1 to 1.7°).
Despite the fact that the equation of motion of the fluid in the pipeline shows that pipelines are more efficient at lower temperatures (factor T in the denominator), the analysis for lower temperatures was conducted. This is primarily due to the fact that cooling is impractical for use in pipelines, since the temperature of the pipe should be above the freezing point of water to avoid buildup of ice on the pipe and around it.
It is obvious that the invention according to the patent 6217626 based on the preparation of the fluid during its storage for subsequent transportation by pipeline, no cooling is not provided, and the type and minimum amount of added liquids natural gas is limited by the necessity of obtaining advantages in transportation through a pipeline. In addition, the type and maximum number of added liquids natural gas is limited by the problem associated with the presence of two phases, which can occur during transportation through the pipeline, and the pressure is limited subsequent transmission by pipeline. Although the known solution is meant for advantages such as during storage and during transportation through the pipeline, the aspect of izvestno the solution, related to storage, is limited to an application associated with passage through the pipeline, and does not require storage in containers, which are intended for subsequent transport.
Another aspect of the prior art described in the patent US 5315054 "Liquid fuel solutions of methane and light hydrocarbons". This patent describes a method of storing a liquid product, in which the insulated storage tank serves liquefied natural gas at a temperature of about -265°F (-165°C). The tank serves methane and liquid natural gas, methane and liquefied natural gas dissolved in the hydrocarbon solution of liquid natural gas (usually propane or butane), and the resulting mixture is stored in the form of a stable liquid at moderate pressure. This invention is not to be stored in the form of a dense phase fluid, and the beginning of the process depends on the availability of natural gas liquids in the tank.
Another aspect of the prior art described in U.S. patent 5900515 and 6111154 "Storage of methane with high specific energy in solutions of light hydrocarbons". In this patent, similar to the previous example US 5315054 described the dissolution of gaseous methane at least one light hydrocarbon reservoir storage" and "storage solution". In addition, the solution must be maintained at a tempera is ur below -1° C and a pressure of 8.0 MPa. The solution contains a maximum of 80% methane and has a specific energy of at least 11000 MJ/m
The next aspect of the prior art presented in the above U.S. patent 3298805, which describes the storage of natural gas in the absence of any additives at a pressure equal to or close to the pressure of the phase transition, but at a temperature below the critical temperature of methane -116,7°F (-82,6°C). This patent is a continuation of U.S. patent 3232725, which describes the storage of natural gas, without any additives, under pressure, is equal or close to the pressure of the phase transition at a temperature of 20°F (-6,7°and (C) below the ambient temperature.
Another aspect of prior art presented in U.S. patent 4010622, which describes the addition of hydrocarbons C5-C20 sufficient to liquefy a gas at ambient pressure and keeping it in a liquid form that is given as an example related to the above formula, but not particularly associated with the present invention.
Disclosure of inventions
For storage of natural gas in the container under pressure and subsequent transport of the loaded container and gas, it is preferable to cool the natural gas below ambient temperature, and also to enter into natural gas additive, representing fluid is a natural gas industry, such as hydrocarbon compound C2, C3, C4, C5 or C6+, including all isomers, as well as saturated and unsaturated hydrocarbons, or carbon dioxide, or mixtures of such compounds. Alternatively, methane or poor gas mixture can be removed from the mixture based on natural gas, more rich in its own natural gas liquids, getting the same effect.
In the case of a combination with the storage conditions at the optimum pressure and temperature adding liquids natural gas raises a net density of gas (under "net" refers to the density of the gas except for the added liquid natural gas) is higher than the density of the gas, which would be at the same temperature and pressure, but without added liquid natural gas.
Increasing the density of the gas leads to a reduction in the cost of storage and transportation.
The interval of the working pressure at which the addition of natural gas liquids to natural gas provides advantages for storage and subsequent transport ranges from 75% to 150% of the pressure of the phase transition of the gas mixture, with the greatest advantage can be obtained when the pressure of the phase transition or at a pressure slightly above the pressure of the phase transition.
The pressure of the phase transition is defined as the point at which the pressure increase leads to kerekou specific gas mixture of the two-phase state to a dense phase fluid, without separation into liquid and vapor inside the container. This point is usually also referred to as line point initial boiling point and/or line dew point.
The temperature range in which the addition of natural gas liquids to natural gas provides advantages for storage and subsequent transport, when working under pressure equal to or close to the pressure of the phase transition is from -140°F to +110°F (-95,6 to +43,3°). Because cooling by itself gives the advantage associated with increasing density, and also has a synergistic effect in relation to the benefit obtained by adding liquids natural gas, cooling the gas to a temperature not higher than 30°F (-1,1° (C) is another aspect of the present invention.
In the present invention found that the storage of natural gas in the container and the subsequent transportation of the loaded container and the contained gas, for any normal mixtures based on natural gas, it is preferable to enter into natural gas additives, representing C2, C3, C4, C5 or C6+, carbon dioxide or a mixture of these compounds, and the resulting mixture is stored at a pressure in the range from 75% to 150% of the pressure of the phase transition of the gas mixture and the gas temperature is -140°F to +30°F (-95,6 before -1,1°).
The resulting mixture has the more high is the net density (excluding Supplement) at a lower pressure, what would be the underlying natural gas without additives.
Gas cooling below the ambient temperature increases the benefits associated with the addition of natural gas liquids.
Temperature, pressure, the optimal number and optimal views of additives depend on the particular characteristics supplied to the gas market. These characteristics include achievable in practice, the cooling temperature, the composition of the base gas, the type of trade, which may constitute trade with the return, when the additive is used again, or trade with the supply of natural gas liquids, when the additive supply the market with gas, the efficiency of the transportation system using the invention, for example, on ships, trucks, barges or other modes of transportation, and the pressure of the phase transition of the gas mixture. Because the higher gas density implies greater capacity in the system storage and transportation with limited volume and lower pressure leads to a reduction in the cost of equipment for the preparation and storage, the cost of transporting one unit resulting from the use of the invention is reduced.
Brief description of drawings
Figure 1: total (gross) density depending on the pressure at -40°F (-40°C).
Figure 2: net density of liquefied natural gas p and +60° and -40°F (+15,6°C and -40° (C) and chilled natural gas at a pressure of phase transition and -40°F (-40° (C) with the addition of propane, from 5 to 60%.
Figure 3: the optimal quantity of propane mixture at a pressure of phase transition and -40°F (-40° (C) with the addition of propane from 10 to 60%.
Figure 4: the optimal quantity of butane mixture at a pressure of phase transition and -40°F (-40° (C) with the addition of butane from 5 to 25%.
Figure 5: net density of ethane, propane, butane and pentanol mixtures at a pressure of phase transition and -40°F (-40°C).
6: effect of temperature and add liquids natural gas net gas density.
Fig.7 (a): the optimal introduction of natural gas liquids at -40°F (-40° (C) (including components) storage temperature phase transition.
Fig.7 (b): the optimal introduction of natural gas liquids at -40°F (-40° (C) (including components) storage temperature phase transition.
Fig.7 (b): the optimal introduction of natural gas liquids at -40°F (-40° (C) (including components) storage temperature phase transition.
Fig: the effect of temperature on the pressure of the phase transition and the density of the base gas plus 17.5% of propane.
Figure 9: dependence of pressure on temperature when adding or without adding liquids natural gas.
Figure 10: depending the gas density percentage pressure phase transition when adding or without adding liquids natural gas.
11: dependence of bulk density (liquid + vapor) from the base pressure of the gas plus 11% butane at -40°F (-40°C).
Fig: reproduction characteristic of the phase diagram from U.S. patent 3232725.
Fig: "compressibility Factors of natural gas", Fig-3, Mvestments and Dloc, 1942, Technical Guide, Association of suppliers of equipment for gas processing, 10th edition, Tool, Oklahoma, USA, 1987.
The implementation of the invention
Efficiency gas storage is improved by increasing the density of natural gas and minimize the pressure in the storage system. To maximize the density of the gas at a minimum pressure may, for example, to minimize the compressibility factor z.
In the study of the compressibility factor z of the graph Fig-3" of this guide, Fig obvious are two factors. First, the minimum z-factor occurs when the use of gas, which pseudoriemannian temperature is close to 1. This means that the actual temperature of the gas should be close to pseudocritical the temperature of the mixture. Secondly, if you are an economical way to achieve pseudoprophetes temperature of approximately 1.2, and the resultant z-factor is approximately 0.5 by mere cooling with low cost, the change in the composition of the gas by adding fluid the capacity of natural gas to reduce pseudoprophetes temperature to the value close to 1, can reduce the coefficient of z approximately to 0.25.
Thus, the reduction pseudoprophetes temperature for 16% can reduce the coefficient of z by 50% and increase the density of the gas at 200%. Add liquids natural gas reduces pseudoprivate temperature. If the liquid natural gas is added in a smaller amount, do not provide the specified density increases, increasing net density of the base gas. In addition, since the inflection point of the curve of the coefficient of z is at a lower pressure as it approaches pseudoprophetes temperature to 1, then the increase of the density in the system when adding liquids natural gas may be at a lower pressure, which increases the achieved advantage.
The following example illustrates this principle of increasing density under reduced pressure while cooling to -40°F (-40°C).
Methane has a critical temperature of -116,7°F (or -82,6°, 343,3 degrees Rankine or 190,6K) and critical pressure 667 abspoel per square inch (4,60 MPa abs.). The minimum temperature that can be achieved currently, cheap single-circuit refrigeration plants based on propane, is approximately -40°F (420 degrees Rankine or -40°C). Pseudoriemannian temperature of methane at -40°F (-40° (C) is 1,223, capoluongo division 420 degrees Rankine (233,2K) 343,3 degrees Rankine (190,6K). From the chart "Fig-3 Fig shows that the minimum of the z-factor for methane is when pseudoprojection a pressure of approximately 2,676 (1785 abs. pounds per square inch or 12,31 MPa abs.). The z-factor is 0,553. The density of the gas is obtained at that, 11.5 pounds per cubic foot (0.18 g/cm3), 272 times higher than the density of gas at normal temperature and pressure, component 0,0423 pounds per cubic foot (0,00068 g/cm3). The density of gaseous methane at a pressure of 1785 abs. psig (12,31 MPa abs.) and an ambient temperature of +60°F (+15,5° (C) (pseudoriemannian temperature 1,515) is of 6.52 pounds per cubic foot (0.10 g/cm3with z-factor, equal 0,787. Thus, the cooling increases the density of methane 1.76 times (11,5 be divided into 6,52).
N-butane has a critical temperature to 305.5°F (765,5 degrees Rankine or 151,9°or 425,1K) and critical pressure 548,8 abs. psig (3,79 MPa abs.). Adding 14% n-butane to 86% methane obtained mixture with pseudocritical temperature equal -57,6°F (402,4 degrees Rankine or -49,8°or 223,4K), and pseudocritical pressure 650,5 abs. psig (4,49 MPa abs.). Pseudoriemannian the temperature of the mixture at -40°F (-40°C or 420 degrees Rankine or 233,2K) is 1,044. The pressure of the phase transition of the mixture at -40°F (-40° (C) is 1532 abs. psig(10,57 MPa abs.) when pseudoprojection pressure of 2.36. Under such conditions, the z-factor is a mixture of equal 0,358, and the density of the gas - 20,84 pounds per cubic foot (0.33 g/cm3). The density of a mixture of methane and butane in the ratio of 86% 14% (molar volume) at normal temperature and pressure is 0,0578 pounds per cubic foot (0,00093 g/cm3), of which 14% is entered Bhutan is 37,06 wt.%, and methane is the rest 62,94%. The net density of methane is 62,94% 20,84 pounds per cubic foot (0.33 g/cm3), or 13.1 pounds per cubic foot (0.21 g/cm3). The process of adding n-butane increases net gas density of 1.14 times (of 13.1 pounds per cubic foot (0.21 g/cm3) divided by 11.5 pounds per cubic foot (0.18 g/cm3)), the pressure is reduced to 253 abs. psig (1,75 MPa abs.) from 1785 until 1532 abs. psig (12,32 to 10.57 MPa abs.).
The combination of these two operations, i.e. cooling from +60°F to -40°F (15.6 to -40° (C) and adding 14% n-butane, increases the net density of the gas is 2.05 times, from 6.52 to 13.1 pounds per cubic foot (from 0.10 to 0.21 g/cm3), when its pressure is reduced by 14%, from 1785 until 1532 abs. psig (12,32 to 10.57 MPa abs.).
Because the critical temperature of methane is -116,7°F (-82,6°C), we should expect that, as we approach the gas temperature to this value, as well as approximation pseudoprophetes temperature of pure methane to 1, the advantage of reducing the coefficient of z is added and liquids natural gas will be reduced or disappear. Considering this together with the fact that the added liquid natural gas occupy a certain volume in the mixture, we can conclude that there is a lower temperature limit below which the addition of liquids natural gas is no advantage.
With the chart Fig-3" from the directory presented on Fig, it is seen that the positive effect associated with the reduction of the z-factor at lower critical temperature, much less at higher critical temperatures. This follows from the chart Fig-3 when calculating the difference of the ratio z between the critical temperatures of 2.2 and 2 (coefficient z decreases to 0.96 to 0.94) and between 1.2 and 1.0 (coefficient z decreases from 0.52 to 0.25 in). Thus, there is an upper temperature limit above which adding liquids natural gas is no advantage.
If not for the influence of the z-factor, the enriched gas liquids natural gas, would show a lower net density than the base gas, as it contains an exogenous component that is refundable and does not contribute to the useful density. Since the gas-enriched liquids natural gas is much less compressible at a pressure above the pressure of the phase transition, there is an upper limit on the pressure at which the density of the cooled base the Aza exceeds the net density of the cooled gas, enriched with natural gas liquids.
There is also a lower limit on the pressure at which the density of the base gas exceeds the net density of the gas-enriched liquids natural gas. This is because the enriched gas liquids natural gas, immediately goes into a two-phase state at a pressure below the pressure of the phase transition and density sharply decreases with decreasing pressure. Such a sharp drop in density caused vaporous component in two-phase condition, the content of which increases rapidly with decreasing pressure. Although it is possible to remove pairs to maintain the fluid container high density, it is accompanied by the removal of methane, a net density of which decreases sharply at a pressure below the pressure of the phase transition. Thus, there is a lower limit pressure, below which the addition of liquids natural gas is no advantage.
For the preparation and storage of natural gas for transportation in ocean-going vessels seagoing use of liquefied natural gas is the only large-scale commercially viable technology available today. When using a liquefied gas preparation works are very expensive because they involve cooling the gas to a temperature of -260°F 162,2° C). However, the transportation of natural gas, already under these conditions, is relatively cheap, since the density is increased 600 times compared to the density of gas at normal temperature and pressure, and the storage is carried out at a pressure equal to or close to atmospheric.
The present invention proposed an alternative to liquefied natural gas for transportation on ships. In the invention, the natural gas can be moderately cooled to an acceptable level in practice, the temperature achieved in the use of inexpensive cooling systems and low-cost storage systems from low carbon steel. Near a source of natural gas in this gas injected liquid natural gas and the resulting gas can be stored at a pressure equal to or close to the pressure of the phase transition. When near a source of natural gas liquids natural gas is not available in large quantities, introduced fluid is extracted at the point of delivery and return back to the source in the same container to add transported to the next party (trade with return). When liquid natural gas exist in abundance near a source of natural gas or the mixture is consumed during transit, you must return only a portion of the liquid natural gas, or return woobine required (trading with the supply of liquid natural gas).
The invention also proposed an alternative to compressed natural gas for small-scale applications, such as cars, buses or rail transport. Compressed natural gas is at ambient temperature, but at very high pressure, in the range of 3000-3600 abs. psig (20,70-to 24.84 MPa abs.). Such high pressures require significant compression in the preparation and storage containers that can withstand approximately three times higher pressure than is necessary when implementing the present invention. To achieve the same density as compressed natural gas, one-third of its pressure provides advantages in the areas where the gas mixture is used to provide fuel for transport, such as cars, buses and railway transport, as well as for overland transportation of natural gas in areas where pipelines are missing or are not economically acceptable.
The benefits of cooling and adding liquids natural gas occur in a wide range of temperature, pressure, composition of natural gas liquids and method of mixing these liquids. The optimal type and amount of added liquids natural gas depend on the composition of the base gas of a given temperature and pressure, as well as the specific the fir trade, such as trade with the return or trade with the supply of natural gas liquids.
In the case of liquefied natural gas to remove carbon dioxide, otherwise it will harden in the process of cooling the gas to a temperature of -260°F (162,2°C). In this invention, carbon dioxide can be left in the gas that may actually have some advantages in the system, for example, if you want the presence of a certain amount of carbon dioxide.
Due to the fact that natural gas is very light (even liquefied natural gas with density, increased 600 times compared to normal conditions, has a specific weight of only 0.4)carrying gas marine transportation system is primarily limited by volume and not by weight. For example, a ship for transporting liquefied natural gas typically contains aluminum spheres with a diameter of 130 feet (39,62 m) and has a draught of 39 feet (11,89 m). Thus, 70% of the vessel is above the waterline. The additional weight of the cargo ship in the use of this invention, due to the weight of the recoil liquids natural gas and steel container, will reduce this to a Deposit to the value of 55% above the waterline that is still quite acceptable for transportation. This extra weight causes minimal economic impact, mainly related to dopolnitelnye fuel and power for to give such a vessel required speed. In the limited volume of the gas transportation system, such as a vessel, the gas density is a key variable and is directly related to the capacity and cost of transportation of the unit.
Operating temperature range based on the efficiency of gas cooling and storing it in containers. In order to clarify all subsequent examples are given at a storage temperature -40°F (-40° (C)unless otherwise stated. This roughly corresponds to the lower limit is reached when cooled propane, based on the boiling point of propane at a temperature of -44°F (-42,2°C).
The advantage of using this type of cooling is shown in the following example. Cooling requirements in any system gas storage only approximately correspond to the required temperature changes. For example, liquefied natural gas necessary to decrease the temperature to 320°F (160° (C) for the transition from the 60°F to + 260°F (15.6 to 162,22°). In the proposed system, the temperature drop is 100°F (37,8°C), with 60°F to -40°F (15.6 to -40°C). The proposed system requires approximately 1/3 of cooling required in a comparable system of liquefied natural gas. To achieve temperature -260°F (162,2° (C) installations of liquefied natural gas usually require the Xia 3 refrigeration cycle, includes propane, ethylene and methane as refrigerants. This process is also called "cascade cycle". Each cycle is associated with a loss of efficiency, thus the overall efficiency of the cooling of the liquefied natural gas is approximately 60%. Cooling system propane with one cooling cycle has an efficiency of about 80%. This is even more reduces cooling requirements in the system according to this invention, up to about 1/4 of the requirements for the system for liquefied natural gas. Installation for cooling liquefied natural gas must be constructed of materials which are both cryogenic furthermore, from the base of gas need to remove all of the carbon dioxide. Installation, operating at -40°F (-40° (C)may be made of non-cryogenic materials, and carbon dioxide can remain in the composition of the gas.
Therefore, the total investment in the plant to operate at -40°F (-40° (C) constitute about 15-20% of the investments in the plant for liquefying natural gas, the equivalent size, and fuel consumption is about 1/4 of the fuel installation for liquefying natural gas. Installation for natural gas liquefaction consumes 8 to 10% of the total liquid product and the installation, operating at -40°F (-40° (C)consumes only 2-2,5% of the total number okhlazhdennogo the product. Because the costs of liquefaction of natural gas make up a significant part of the total system cost of transportation of liquefied natural gas, this savings is an important advantage, is able to cover additional costs associated with the construction of ships of a new type, designed for transportation nasizhennoe gas.
For these reasons, the production of liquefied natural gas for cooling necessary for the implementation of the present invention, is not a very effective approach. There are systems with lower cost cooling is well known to specialists.
The heated gas at the point of delivery also reveals the advantages of the proposed system compared to liquefied natural gas. The proposed system consumes about 1/3 to 1/2 of the energy required for liquefied natural gas. Thus, the apparatus for regasification of liquefied natural gas consumes 1.5 to 2% of the product in the form of fuel, and the proposed system uses as fuel from 0.5 to 1% of the product.
For all here thermodynamic calculations used thermodynamic program Kearston developed by Clearstone Engineering Ltd.
Once the selected temperature and prepared gas mixture by adding the liquids the gas to the base gas, optimum storage pressure is at the point where if the pressure gas passes from the two-phase state to a dense phase fluid. This is because in a two-phase state, the mixture is divided into the vapour phase and the liquid phase. Since the density of the vapor phase is very low, the overall density of the entire two-phase state will be low. The increasing pressure to achieve a state of dense phase fluid eliminates the loss of total density. This phenomenon is illustrated in figure 1, which shows the dependence of the total density from pressure at -40°F (-40°C).
Figure 1 and subsequent graphs, it is assumed that the composition of the base gas is the following:
methane is 89.5%,
the enthalpy 1112 British thermal units per cubic foot (41,14 j/cm3),
the critical temperature is 91.5°F (-68,6°C)
critical pressure 668,5 abs. psig (br4.61 MPa abs.),
density 0,0473 pounds per cubic foot (0,00076 g/cm3at a pressure of 14,696 abs. psig (0,10 MPa abs.) and a temperature of 60°F (15,6° (C) (normal temperature).
Three gas mixtures were prepared by adding liquids natural gas to the base gas:
- 35,0% ethane and 65,0% of base gas,
- 17.5% of propane and 82.5% of base gas,
- 11,0% n-butane and 89,0% of base gas.
what a figure 1 shows the total (gross) density mixtures at -40° F (-40°). The density increases sharply with increasing pressure for all three mixtures up to a level of about 21 pounds per cubic foot (0.34 g/cm3), and then with increasing pressure there are almost no further increase in density. This point corresponds to the phase transition point of each mixture between two-phase state and a state of dense phase fluid. Above the phase transition point the gas is incompressible, so that the pressure rise above this point can be obtained only minimal advantage associated with increasing density. Therefore, the optimal storage pressure is at which phase transition occurs between the two-phase state and a state of dense phase fluid.
It should be noted that the phase transition occurs at very different pressures depending on the particular liquid natural gas that is selected to obtain a mixture. The lower carbon number of liquid natural gas, for example carbon number of butane is 4, the lower the pressure at which the phase transition occurs.
This graph illustrates the wide range of selection of the optimal Supplement for any particular type of trade, even after selecting the temperature. The decision on the type and amount of added liquid natural gas is difficult and depends on the economic factors of the different types of trade.
For any particular composition of the mixture of liquid natural gas decision on the amount of additive is relatively simple and is in a narrow interval. For any selected temperature in the storage at a pressure phase transition of a net density of any gas mixture when adding additional quantities of natural gas liquids increases to the point of a sharp bend. Above this inflection point, even though the gross density of adding additional amounts of liquids natural gas continues to increase, the net density begins to decrease along with a decrease in the pressure of the phase transition. Add liquid natural gas are increasingly significant part in the increase in gross density, leaving fewer places for the source gas.
When trading with return (recycle) net density is the main variable, so that the specified sharp inflection of the curve determines the optimal amount of additive liquids natural gas. This feature is shown in figure 2-5.
Figure 2 shows the dependence of net and gross density of the gas from the different quantities of propane added to the base gas, ranging from 5% to 60% of propane, as well as the density of the mixture of base gas at 60°F or -40°F (15.6 and -40° (C) without any additives of natural gas liquids. the while gross density continues to increase with increasing amount of added propane, net density reaches the inflection point adding 15-25% propane and a pressure of 1100 abs. pounds per square inch (to 7.59 MPa abs.). Above this amount is added to propane net density begins to decrease along with a decrease in the pressure of the phase transition. Since the density determines the capacity, pressure value, the minimum value of units in the system, in dollars per unit of volume, requires obtaining the ratio between pressure and density to create the optimal mixture, as can be seen from the figures of the drawings.
This price advantage is shown in figure 3, where the ratio of 3:1 is suitable for cost accounting creating pressure and take advantage of the density in the transport system on ships with recycling. That is, the increase in net density of 30% increases capacity by 30%, while the pressure increases by 30% increases the cost by 10%. In this economic ratio figure 3 shows that the optimal number of added propane is in the range of 15-25%. A similar result was obtained when the ratio of pressure/density equal to 2:1 and 4:1, which is also shown in figure 3.
Figure 4 shows the same characteristics for Bhutan, where the optimal number of Bhutan is in the range of 10-15%. Again it is seen that the sharp point of inflection is not so dependent on the economic relationship between the pressure and p is Amnesty.
Figure 5 shows the same ratio for all four light hydrocarbons that are liquid natural gas, which are ethane, propane, n-butane and n-pentane. Figure 2-5 shows that the choice of inflection point and, accordingly, the amount of a particular additive liquids natural gas is fairly simple, in a narrow interval.
The choice of the type of liquid natural gas to obtain a mixture depends on the economic relationship between pressure and density, as well as the nature of the sale. There are certain barriers pressure, contributing to the increase in value, such as increasing the pressure above 1440 abs. psig (9,94 MPa abs.), therefore, they require the installation of more expensive valves and fittings that meet the standards of ANSI 900. Basic gas also contains a number of natural gas liquids, and the allocation mechanism of these fluids at the point of delivery when trading with recycling, apparently, no differences between the release of liquids contained in the gas, and added liquids natural gas. This means that the mechanism of separation of liquids of natural gas will also affect the optimal form of added liquid.
Figure 6 shows the net density at the point of inflection and the pressure of the phase transition for hydrocarbon liquids natural gas, ethane, propane, n-butane and n-p is ntana. It is also a visible effect in the result of a combination of the two hydrocarbons in the mixture of natural gas liquids, such as mixtures of propane/butane in the ratio of 50% to 50% by molar percent, on net density. In addition, shows a net density of the base gas in the form of compressed natural gas at +60°F or -40°F (15,56 and -40°C), so that it is easier to separate the contribution to the increase in density, the contribution provided by the temperature effect and the effect of the additive liquids natural gas.
Mixing with ethane means receiving system at a pressure of 830 abs. psig (5,73 MPa abs.) with a net density of about 10.8 pounds per cubic foot (0.17 g/cm3). Mixing with propane means receiving system when the pressure 1088 abs. psig (7,51 MPa abs.) with a net density of 13.7 pounds per cubic foot 0,22 g/cm3). Mixing with n-butane means receiving system when the pressure 1305 abs. psi (9 MPa abs.) with a net density of 15.0 pounds per cubic foot (0.24 g/cm3). Mixing with n-pentane means receiving system at a pressure of 1500 abspoel per square inch (10,35 MPa abs.) with a net density of 15.8 pounds per cubic foot (0.25 g/cm3). Mixing with Ethan brings to the pressure outside the ANSI 600, but within ANSI 900. Gross heat content of all these optimal mixtures is within 1330-1380 British thermal units is per cubic SIC ft (49,21-51,g/cm3).
For mixtures with n-butane density increases from 5.5 pounds per cubic foot (0,088 g/cm3for the base gas at +60°F (15,6°C) and 1305 abs. psi (9 MPa abs.) to 11.5 pounds per cubic foot (0.18 g/cm3under the influence of the cooling gas to -40°F (-40° (C)that is increased to 210% compared to the base gas. Add 11% butane increases the net density of up to 15,04 pounds per cubic foot (0.24 g/cm3), an increase to 273% compared to the base gas. At -40°F (-40° (C) and 1305 abs. psi (9 MPa abs.) and adding 11% n-butane net density, except for the added butane, enthalpy 1112 British thermal units per cubic foot (41,14 j/cm3), 318 times greater than the density of the base of gas under normal conditions. Gross density, including added butane, 445 times higher than the density of the base of gas under normal conditions.
Figure 6 shows that a mixture containing as an additive two adjacent hydrocarbon, are between mixtures of pure hydrocarbons, in accordance with an average carbon number of the mixture of natural gas liquids. Indeed, it is clear that mixtures of different hydrocarbon liquids natural gas act in a similar manner with the addition of pure hydrocarbons in accordance with their average carbon number. A mixture of 11% number is on Bhutan has a net density 15,04 pounds per cubic ft (0.24 g/cm3at a pressure transition 1305 abspoel per square inch (9 MPa abs.). A mixture of 14% supplements containing propane and pentane in a ratio of 50 : 50% molar volumes, has a net density 14,93 pounds per cubic foot (0.24 g/cm3at a pressure transition 1294 abs. psig (8,92 MPa abs.), which is very close to pure butane. A mixture of 12.5% supplements containing propane, butane and pentane in a ratio of 25% to 50% to 25% molar volumes, has a net density 15,01 pounds per cubic foot (0.24 g/cm3at a pressure transition 1298 abs. psig (8,96 MPa abs.), what is also very close to pure butane. Thus, a mixture of additives, liquids natural gas with the same carbon number as the butane working at the same inflection point and the pressure of the phase transition, behaves similarly to pure butane.
Similarly this is the case if the components are isomers of normal liquids natural gas, for example, contain isobutane and normal butane, however, in the case of isomers net density and pressure of the passage below. A mixture of 11% isobutane has a net density 14,42 pounds per cubic foot (0,23 g/cm3at a pressure transition 1241 abs. psig (8,56 MPa abs.). Net density is 4.1% lower than that of n-butane, and the pressure transition below 4.9%. When economic pressure ratio/price - 3:1 n-butane in the system is preferable, h is m isobutane, however, the difference is not so great, to enter any processing isomers.
The same result is observed for mixtures with small amounts of heavier natural gas liquids, even up to Dean With10H22. A mixture of 17.5% of propane and 82.5% of the reference gas has a net density of 13.75 pounds per cubic foot (0,22 g/cm3at a pressure transition 1088 abs. psig (7,50 MPa abs.). A mixture containing 3% octane With8H18and 97% of a mixture of propane and basic gas has a net platnost,12 pounds per cubic foot (0,23 g/cm3at a pressure transition 1239 abs. psig (8.55 MPa abs.). It is between the values obtained in the case of the additive of pure propane and supplements pure butane. A mixture containing 3% decane and 97% of a mixture of propane and basic gas has a gross density 25,74 pounds per cubic foot (0,41 g/cm3and net density 14,15 pounds per cubic foot (0,23 g/cm3at a pressure transition 1333 abs. psig (9,2 MPa abs.).
Very heavy liquid natural gas is transferred into the gas phase at the temperature of phase transition, since they are present in small quantities. This is an important feature for their production of gas condensate or deposits with rich gas, where the liquid condensed from the gas when the pressure is reduced during the production process. If the Dean of the systems is the very as cargo, net density actually would 18,35 pounds per cubic foot (0.29 grams/cm3compared with 14,15 pounds per cubic foot (0,23 g/cm3if the Dean subjected to recycling. On a ship with a displacement of 3000 million cubic feet (84,951 Fuel3contents Dean 3% turns into 131000 barrels (20827428 DM3or about 40 barrels (6359,5 DM3per 1 million cubic feet (0,028 Fuel3). This means that the rich gas can potentially be handed in to the system directly from the reservoir, without the need for large binary liquid systems of work used in the production process.
For the production of motor fuels, this means that a combination of natural gas, liquid natural gas and heavy fuel hydrocarbons in some proportional quantities can be used to obtain a very dense fuel in a state of dense phase fluid, which may have other desired properties, such as octane or cetane number.
On figa, 76 and 7b shows the optimal choice of the type of additive. For this particular illustration, the temperature is -40°F (-40°C), and added the liquid natural gas is expected to be subjected to recycling (return). On figa shows the optimum economic value of the pressure/density - 4:1. On figb optimum is shown in the ratio of 3:1, f is GB - with a ratio of 2:1. The optimum is observed in the pressure range from about 1100 to 1450 abs. pounds per square inch (to 7.59-10,00 MPa abs.), and the range of number of carbon atoms is from 3 (propane) to 4.5 (a mixture of butane/pentane in a ratio of 50% to 50%). The main curve of the pressure/density sufficiently close to the ratio of 3:1 in this interval the number of carbon atoms, so that the choice of any of these mixtures will be very close to optimum.
With reference to the first example above, where it was considered a mixture of methane and butane in the ratio of 86% to 14%, the pressure of the phase transition was 1532 abs. psig (10,57 MPa abs.). To the above mixture 89% of base gas and 11% butane pressure phase transition is 1305 abs. psi (9 MPa abs.). The reason for this difference is that the base gas contains a certain amount of natural gas liquids - 7.5% ethane, 3% propane.
Regardless of whether the liquid natural gas to the most basic gas or added when using this invention, the resulting physical parameters will be identical. Therefore, the option with the addition of 11% butane (carbon number 4) should be considered as the use of liquid natural gas in a mixture, actually containing 6.7% of ethane, 2.7% propane and 11% of Bhutan. The average carbon number of liquids natural the Aza as a whole actually is is 3.21. Thus, the pressure of the phase transition 1305 abs. psi (9 MPa abs.) observed for mixtures having an average carbon number (as added hydrocarbons contained in the gas) is approximately 3.2. Considering the option from 7.5% pentane in the base gas, there is the pressure of phase transition 1500 abspoel per square inch (10,35 MPa abs.) for mixtures with an average carbon number of 3.8. In the example above with a mixture of methane and butane in the ratio of 86% 14% average carbon number of natural gas liquids in General is 4, so the pressure of the phase transition above and is 1532 abs. psig (10,57 MPa abs.).
When trading with the return of the underlying gas probably has a number of natural gas liquids, which will be highlighted together with the added liquids natural gas through a system of fractionation at the point of delivery to return back to the place of production. These extra fluid must at some time be unloaded from the vehicle, otherwise the content of the natural gas liquids will be increasing over time, and the net density to decrease. Thus, regardless of the source of the additive liquids natural gas, over time the composition of the liquid natural gas will be close to the composition of the liquids contained in the base gas and obtained from the fractionation system. Therefore clicks the zoom, the fractionation system can be configured to return thus to return the optimal mixture (instead of having to unload). The selection of propane and heavier hydrocarbons is relatively low cost, and the selection of ethane is relatively expensive. In addition, to find markets for selected liquids, believing that increasing the amount of liquids natural gas is allocated in each cycle and must be disposed of, it will be much harder, if liquids contain ethane, with limited market potential. As most of the gas that contains a C3, C4, C5 and higher in decreasing quantities, the optimal mixture with the number of carbon atoms of 3.5-4 can be obtained by allocating a sufficient amount of propane to compensate for the effect of heavier hydrocarbons in the final mixture. So, if desirable for return of liquid natural gas is the number of carbon atoms 4 and the base gas containing 4% propane, 2% butane and 1% of pentane, the fractionation system set up so as to return 25% of the propane and all of the C4 hydrocarbons+. Regulation of the rate of return of propane in the system fractionation is relatively simple and understandable for specialists.
It is possible to supply the gas was too high enthalpy or heat equivalent is, equal to the square root of enthalpy divided by the density of the gas so that it can be included in subsequent delivery system. In such situations, the allocation of additional liquids natural gas (in the example above - propane) may require the installation of fractionation for gas supply with a lower heat content, and this can lead to less effectiveness of adding fluids. In this case, the presence in the gas of carbon dioxide can have a beneficial effect, as it mostly comes out of the gas supplied from the separation column and reduces the enthalpy and the heat equivalent of the supplied gas.
The influence of the presence of carbon dioxide at a net density of the gas mixture also creates certain advantages, as shown below. A mixture of 82.5% of base gas and 17.5% propane has a net density of 13.75 pounds per cubic foot (0,22 g/cm3) at 1088 abs. psig (7,50 MPa abs.). Mixing 98% of this mixture with 2% carbon dioxide reduces the net density of up to 13,53 pounds per cubic foot (0,22 g/cm3), but also reduces the pressure of the transition to 1072 abs. psig (7,40 MPa abs.). Thus, the decrease in net density of 1.6% leads to a decrease in pressure of 1.5%. Although by itself, the introduction of carbon dioxide is not enough to justify economic pressure ratio/p is otnesti - 3:1, but the decrease in the heat content of gas delivered under some circumstances it may be preferable compared to a system without carbon dioxide.
Carbon dioxide can also be used to increase the net density of methane at a much higher ratios when mixing, when the base gas contains large amounts of carbon dioxide. Adding 10% of carbon dioxide to pure methane is obtained a mixture of 90% methane and 10% carbon dioxide, with a net density (excluding the added carbon dioxide) 7,37 pounds per cubic foot (0.12 g/cm3and the pressure transition 1246 abs. psig (8,60 MPa abs.). Pure methane under these conditions has a density 7,33 pounds per cubic foot (0.12 g/cm3). Thus, these values are the same. A mixture of methane and carbon dioxide in the ratio of 50% to 50% has a net density of methane 9,19 pounds per cubic foot (0.15 g/cm3at a pressure transition 1053 abs. psig (7,27 MPa abs.). Under these conditions, pure methane has a density 5,72 pounds per cubic foot (0,092 g/cm3). Adding carbon dioxide increases the net density of methane up to 160% of the value of the density, which he would have in the absence of carbon dioxide. A mixture of methane and carbon dioxide in the ratio of 60% to 40% has a net density of methane 8,28 pounds per cubic foot (0,13 g/cm3) when pressure is transition 975 abs. psig (6.73 x MPa abs.). Under these conditions, pure methane has a density 5,12 pounds per cubic foot (0.08 g/cm3). This represents an increase in net density of up to 162% of the value of the density, which he would have in the absence of carbon dioxide. This feature would be extremely advantageous for systems where the base gas contains large amounts of carbon dioxide, and its destruction at the site of production would be costly, especially if carbon dioxide can be used at the same commercial route for natural gas.
Unsaturated hydrocarbons such as propylene, provide the same benefits as saturated hydrocarbons with the same number of carbon atoms. For example, the base enriched gas 17.5% of propane, has a net density of 13.75 pounds per cubic foot (0,22 g/cm3at a pressure transition 1088 abs. psig (7,50 MPa abs.). Replacement of propylene to propane in the mixture has little effect on these values. In this case, the net density is 13,74 pounds per cubic foot (0,22 g/cm3at a pressure transition 1085 abs. psig (7,49 MPa abs.).
When trading with the supply of natural gas liquids it is desirable to add fluid received from the available source located near the basic source of natural gas. In a system where the fuel is consumed during the transport of the programme, add liquid natural gas can meet the requirements for fuel, such as octane number for cars. The above calculations optimization net density in this case is unsuitable, because the system will work in a wide range of conditions in order to move the total volume of gas and liquid natural gas with a maximum gross or net density of the mixture at the lowest cost. Any number of added liquids natural gas in this system has the advantage associated with the increase in the gross density of the mixture. If to obtain the desired composition, it is not enough natural gas liquids, the liquids may be returned for increasing the density of the mixture.
On Fig shows how to improve the parameters of the system capacity and pressure at temperatures below -40°F (-40°C). At lower temperatures the efficiency of the system improves as the net density increases, and the pressure of the phase transition decreases. This is shown for mixture with the addition of propane, but similarly observed for all mixtures. For every 5% reduction in temperature below 420 degrees Rankine (233,15K) net density increases by about 10%, and the pressure of the phase transition is reduced by approximately 15%.
However, the reduction in temperature also increases the density is here a basic gas without any added liquids natural gas. For methane, which has a critical temperature -116,7°F (-82,61° (C)closer to the temperature to this limit reduces the benefits associated with the addition of natural gas liquids. You can achieve the same density of the base gas without adding liquids natural gas, and adding these fluids, while the system is running without add fluid at higher pressure than the gas-enriched liquids natural gas. One of the key economic aspects of technology associated with this reduction in pressure is achieved by adding natural gas liquids compared with storage base gas for transportation at the same temperature without the addition of natural gas liquids. This gain in pressure is shown in Fig.9.
Figure 9 shows the gain in pressure at different temperatures for the two gases. Presents the results for rich gas with a heat content 1112 British thermal units per cubic foot (41,14 j/cm3in comparison with a mixture containing 89% rich gas and 11% n-butane, and poor gas enthalpy 1018 British thermal units per cubic foot (37,67 j/cm3containing 99% methane and 1% ethane, compared with a mixture containing 86% of the poor gas and 14% of n-butane. The gain in the pressure maximum at 420 abs. psi (2.9 MPa abs.) and -40°F (-4° C) for a rich gas and at 550 abs. psi (3.8 MPa abs.) and -80°F (-62,2° (C) for the poor gas. The area in which there is a gain in pressure for rich gas is between -120° and +100°F (-84,4 +37,8° (C), and for the poor gas this interval several more from -140° to +110°F (-95,6 +43,3°). This schedule limits the temperature range in which the invention provides an economic benefit.
Although the invention gives the advantage at temperatures above +30°F (-1,1° (C), it is unlikely that the storage system in which this invention will operate at temperatures above +30°F (-1,1°). A large increase in net density and a large reduction in the pressure of the phase transition for small values reduce the temperature means that the most likely way of carrying out the invention is a storage system with some form of cooling. For this reason, the amount of the claims formulated in the disclosure of this invention, is limited by the gas temperatures below +30°F (-1,1°C), which implies the need for cooling.
Figure 10 is used to determine the range of pressure in which the invention gives the benefit. For basic gas enriched 11% n-butane, -40°F (-40° (C) the net density when the pressure of the phase transition 1305 abs. psi (9 MPa abs.) equal 15,04 the fur boots on cubic ft (0.24 g/cm3). Basic gas without adding liquids natural gas should be stored at 1723 abs. psig (11,89 MPa abs.) and -40°F (-40° (C) to achieve the same density, while the gain in pressure is 418 abspoel per square inch (2,88 MPa abs.). Because enriched with butane gas almost incompressible above the pressure of the phase transition, while the base gas is compressible, the net density of the two structures becomes identical at about 2000 abs. psi (13,8 MPa abs.). The gain in the pressure decreases from 418 abs. psig (2,88 MPa abs.) when the pressure of the phase transition to less than 50 abs. psig (0,80 MPa abs.) at pressures above 150% of the pressure of the phase transition.
Therefore, when the pressure is higher than 150% of the pressure of the phase transition invention does not provide tangible benefits. On the contrary, when the pressure below the pressure of the phase transition net density enriched with butane gas is sharply reduced, as shown in figure 10. At a pressure of approximately 1000 abs. psi (6,9 MPa abs.), or 75% of the pressure of the phase transition, the increase in pressure again drops below 50 abs. psi (0.35 MPa abs.) and the invention not provide tangible benefits. Thus, the invention provides advantages at a pressure of from 75% to 150% of the pressure of the phase transition.
Although different compositions actual figures may differ slightly, analogichnye features can be seen for all additives discussed here.
In the transportation system, the gain in pressure manifests itself in the form of at least the following distinct advantages.
The smaller wall thickness of the container of the specified capacity, assumed to be always made of steel. This means lower cost and weight and more competitive conditions of purchase, as many steel enterprises can produce containers with thinner walls.
The larger the diameter of the container, as the production is usually limited by the wall thickness for a given diameter. This means fewer containers for a given size and cost of equipment and headers for connecting containers.
- Lower requirements of ANSI standards for valves and fittings. Typically the system using this invention, require valves and fittings, appropriate ANSI 600 pressure up to 1440 abs. psig (9,94 MPa abs.), while systems for compressed natural gas and higher pressures require more expensive fittings that meet higher standards.
- Less weight means less fuel for the operation of the transport system at a given speed.
- Less pressure means less requirements for the compressors in the preparation of gas for loading into the container.
- For vessels of less weight of the container means is more high draught of the vessel at certain characteristics of the ship's stability. This means more payload.
- For vessels less weight means lower displacement that gives the possibility of entering into a larger number of ports.
Figure 11 shows the shape of the curve decompression in the system cooled natural gas in the discharge gas at the point of delivery. This can be used to provide additional advantages of the invention. This curve is not linear and is shown for the case with 11% n-butane.
Bulk density of the mixture, which represents a single-phase dense fluid medium, at 1305 abs. psi (9 MPa abs.) is 21.06 pounds per cubic foot (0.34 g/cm3). Bulk density of the same mixture in a two-phase state at 650 abs. psi (0.35 MPa abs.) is 5,47 pounds per cubic foot (0.09 g/cm3). Bulk density of the same mixture in a two-phase state at 350 abs. psig (2,42 MPa abs.) is 2,41 pounds per cubic foot (0.04 g/cm3).
Thus, 75% of the cargo can be unloaded at 50% reduced pressure, and 89% of the cargo can be unloaded at 73% pressure decrease, suggesting that simultaneously unloaded proportional amounts of fluid and gas.
As the gas delivery system placed near consumption areas, typically operate at pressures 350-650 abs. psig (2,42-4,49 MPa abs.), this can minimize the article is of compression, necessary for the discharge of gas from the vessel, if the gas pressure in the vessel falls below the pressure required for gas supply to consumers.
Typically, the gas production is carried out at higher pressure close to the pressure storage 1305 abs. psi (9 MPa abs.). Thus, it is seen that this system saves a useful pressure and minimizes the amount of energy required to change the pressure only for transport purposes.
System compressed natural gas use a lot of energy to compress the gas for storage, and then a large part of the net pressure is reset when the supply to the consumer market. The pressure of the liquefied natural gas is reset when it is loaded into storage and must be restored when the supply of gas to the market. This system can be designed to operate at a pressure between the pressure of the incoming gas and the pressure of his submission, thus relieving or spending only a small pressure in the process gas for transportation, loading and unloading.
The concept of extracting methane or poor gas to achieve the same results as described above is illustrated as follows.
Because the invention has particular application to gas produced from fields in gas condensate, or gas, southst the subsequent oil extraction, the analysis was performed from the gas field condensate Peru. The raw gas has a heat content 1294 British thermal units per cubic foot (47,88 j/cm3), with approximately 1.7% of the gas consists of C7+. With a daily production 1017,8 million cubic feet of gas (28,821 Fuel3) assumes that 23027 barrels (3660 liters) per day C7+ emit in the form of oil, however, remains 1000 million cubic feet (28,317 Fuel3) per day of gas with a heat content 1199,5 British thermal units per cubic foot (44,38 j/cm3). If this gas is cooled to -70°F (-56,7°C) and place in the evaporating tank at 888 abs. psig (6,13 MPa abs.), will separate into two phases. Steam has a 50 mol.% volume or 500 million cubic feet (14,159 Fuel3with enthalpy 1057,8 British thermal units per cubic foot (39,14 j/cm3). While steam is essentially methane, there are small amounts of ethane and propane. Thus, the invention is directed to the removal of methane or poor gas. The liquid is 50 mol.% volume or 500 million cubic feet (14,159 Fuel3in the day enthalpy 1340,9 British thermal units per cubic foot (49,61 j/cm3). The liquid from the evaporation tank can be compressed to a pressure of 1178 abs. psig (8,13 MPa abs.) and to warm up to -40°F (-40° (C) by heat exchange with the incoming gas, the transition in couples who shaped the state. The pressure of the phase transition of this mixture is 1178 abspoel per square inch (8,13 MPa abs.) at -40°F (-40°C) and the density of each holding 21.25 pounds per cubic foot (0.34 g/cm3). This dense-phase fluid environment can now be submitted to the ship and put on the market without the necessity of returning natural gas liquids. Component C3-C6 this mixture is 41917 barrels (6664300 liters) per day, and the necessity of his return is missing. Vapor from the evaporation tank can either be directed back into the reservoir to maintain pressure, or a plant for liquefied natural gas for delivery on the market. Assuming that steam is supplied to maintain the pressure, the cold can be used by heat exchange with the incoming gas. There is an additional benefit by reducing the heat content of gas injected into the reservoir for pressure maintenance. Considering that the tank temperature is 150°F (65,6°C)a pressure - 2130 abs. psig (14.7 MPa abs.), the z-factor for the crude gas with a heat content 1199,5 British thermal units per cubic foot (44,38 j/cm3) is 0,801 at a density 8,13 pounds per cubic foot (0,13 g/cm3). The z-factor for gas enthalpy 1057,8 British thermal units per cubic foot (39,14 j/cm3) is 0,859 at a density 6,59 pounds per cubic foot (0.11 g/cm3). the thus, the the mass of poor gas component only 81% of the mass of rich gas required to maintain the same pressure that allows you to sell more gas during this stage, maintaining the pressure in the tank. If we assume that the residual gas can be sold as liquefied natural gas, cool pairs continue to pass through an additional cooling system to receive liquefied natural gas. There is a total advantage in the system when submitting the poor gas installation liquefaction of natural gas and rich gas in the system described in this invention. The advantage of the system is that a large volume of gas can be sold on the market at the same price as liquid natural gas are non-refundable. The advantage for liquefied natural gas occurs because the temperature of liquefaction of such a gas is much higher than methane, such as ethane liquefied at minus 127°F (-88,3°C), and propane at minus 44°F (-42,2°C). Essentially spent all the extra work spent on cooling liquids natural gas component of the gas to -260°F (-162,2°C), and may be the best value upon cooling, additional quantities of methane. In addition, there is a problem during transportation or handling of liquefied natural gas, which mo is no limit to the number of natural gas liquids in the system. Usually liquid natural gas as a component of liquefied natural gas is separated after delivery using fractionation and transported to market using transport LPG.
The above description illustrates some specific embodiments of the invention, however, for professionals and other obvious options. Therefore, it is expected that the invention is limited undescribed variants, but only by the attached claims.
1. The method of storing natural gas in the container under pressure for transportation and subsequent transport of the specified natural gas, according to which the cooled natural gas below ambient temperature and add hydrocarbons having 2 to 5 carbon atoms, including all isomers, saturated and unsaturated compounds, at a temperature of from -95,6 to -40°and a pressure of from 75 to 150% of the pressure of the phase transition obtained gas mixture.
2. The method according to claim 1, wherein cooling includes cooling the propane, ethylene and methane.
3. The method according to claim 1, characterized in that the pressure is in the range from 100 to 150% of the pressure of the phase transition obtained gas mixture.
4. The method of storing natural gas in the container under pressure for transportation and subsequent transportation and specified natural gas, according to which the cooled natural gas below ambient temperature and add the hydrocarbons with two carbon atoms, at a temperature of from -95,6 to -40°and a pressure between 75% of the pressure of the phase transition obtained gas mixture and 6.9 MPa abs.
5. The method according to claim 4, wherein cooling includes cooling the propane, ethylene and methane.
6. The method according to claim 4, characterized in that the pressure is between 100% of the pressure of the phase transition obtained gas mixture and 6.9 MPa abs.
7. The method of storing natural gas in the container under pressure for transportation and subsequent transport of the specified natural gas, according to which the cooled natural gas below ambient temperature and add the hydrocarbons with three carbon atoms at a temperature of from -95,6 to -40°and a pressure between 75% of the pressure of the phase transition obtained gas mixture and 6.9 MPa abs.
8. The method according to claim 7, characterized in that the pressure is between 100% of the pressure of the phase transition obtained gas mixture and 6.9 MPa abs.
9. The method according to claim 7, wherein cooling includes cooling the propane, ethylene and methane.
10. The method of storing natural gas in the container under pressure for transportation and subsequent transport of the specified natural gas, according to the who cooled natural gas below ambient temperature and add the hydrocarbons, having 4-10 carbon atoms, at a temperature of from -95,6 to -40°and a pressure in the range from 75% of the pressure of the phase transition obtained gas mixture and 6.9 MPa abs.
11. The method according to claim 10, wherein cooling includes cooling the propane, ethylene and methane.
12. The method according to claim 10, characterized in that the pressure is in the range from 100% of the pressure of the phase transition obtained gas mixture and 6.9 MPa abs.
13. The method of storing natural gas in the container under pressure for transportation and subsequent transport of the specified natural gas, according to which the cooled natural gas below ambient temperature, added to natural gas carbon dioxide and perform subsequent storage at a temperature of from -95,6 to -40°and a pressure in the range from 75% of the pressure of the phase transition obtained gas mixture and 6.9 MPa abs.
14. The method of storing natural gas in the container under pressure and subsequent transportation of natural gas and the container, whereby the cooled natural gas below ambient temperature and remove methane or poor gas from richer natural gas and storage of concentrated rich product gas is carried out at a temperature from -95,6 up -1,1°and a pressure of from 75 to 150% of the pressure of the phase transition obtained gas mixture.
15. With the royals by 14 wherein cooling includes cooling the propane, ethylene and methane.
16. The method according to 14, characterized in that the pressure is in the range from 100% to 150% of the pressure of the phase transition obtained gas mixture.
FIELD: the invention refers to energy-conservation technologies of pipeline transportation of natural gas.
SUBSTANCE: it may be used for controlling the technological process of the main pipeline with simultaneous selection out of gas of valuable ethane, propane, butane components. The technical result of the invention is reduction of energy inputs for maintaining pressure in the main pipeline, provision of stabilization of pressure in the main pipeline. The mode of transportation of natural gas along the main pipeline includes its feeding into the main pipeline on the first and the following compressor stations and giving out natural gas from the main pipeline through gas reducing stations and divide it on two flows one of them is directed into the pipeline of high pressure, and the other into a consumer pipe-bend. At that the gas of consumer pipe-bend is preliminary cooled and cleared from condensed and hard fraction, and then further cooling is executed till the temperature below the point of condensation of methane and division of cryogenic liquid and directed to the user, and out of received cryogenic liquid methane is separated from liquid ethane-propane-butane fraction which is returned into the pipeline of high pressure and further into the main pipeline, and detailed methane is directed into the pipe-bend. At that the gas in the pipeline of high pressure is preliminary additionally cooled, compremirated and returned into the main pipeline.
EFFECT: reduces power inputs.
7 cl, 1 dwg
FIELD: preparation and transportation of petroleum associated and natural gases.
SUBSTANCE: invention relates to preparation of gas for transportation along gas pipeline and separation of heavy fraction condensate from gas. Proposed plant for preparation of petroleum associated gas or natural gas for transportation along gas pipeline and obtaining of liquid hydrocarbons from gas intake line, device to increase and decrease pressure, gas flow line, liquid hydrocarbons extraction line, three-circuit heat exchanger, separator, expansion valve, two regulating valves and swirl pipe whose input is connected through pressure increasing and decreasing device from one side with inlet gas line through first regulating valve and through series-connected second regulating valve and first circuit of heat exchanger, and from other side, with output of expansion valve. Output of cold flow of swirl pipe is connected through second circuit of heat exchangers with gas flow line, output of hot flow of swirl pipe is connected through third circuit of heat exchanger with input of separator whose condensate output is connected with line to remove liquid hydrocarbons, and gas output, with input of expansion valve.
EFFECT: increased degree of separation of condensate of heavy fractions of hydrocarbons from petroleum associated gas or natural gas designed for transportation along gas pipeline.
FIELD: oil and gas industry.
SUBSTANCE: device comprises device for enhancing and reducing pressure, receiving gas line for supplying the plant with the gas, discharging gas line through which the gas after purification is supplied from the plant, two vortex pipes, ejector, and condensate collector. The inlet of the first vortex pipe is connected with the receiving gas line and outlet of the cold gas flow of the second vortex pipe through the device for enhancing or reducing pressure. The output of the hot flow of the first vortex pipe is connected with the inlet of the first separator through the ejector, and the condensate outlet of the separator is connected with the inlet of the second vortex pipe. The outlet of the cold flow of the second vortex pipe is connected with the receiving gas.
EFFECT: enhanced quality of purification.
1 cl, 1 dwg
FIELD: pipeline transport.
SUBSTANCE: method comprises intensifying extraction of low-pressure gas in tanks of oil stabilization due to rarefying gas in the inlet gas collector that connects the tank with the inlet of liquid-gas jet compressors by mixing the pumping product with active agent and increasing initial pressure of the low-pressure gas up to the pressure required by a consumer with simultaneous condensation of C5+ fraction. The gas-liquid mixture is supplied to the air cooling apparatus. After the separation of gas from the active agent, purifying and drying the compressed gas is intensified by supplying the compressed gas into the vortex pipe and, then, to the consumer.
EFFECT: improved method.
FIELD: pipeline transport.
SUBSTANCE: power plant is additionally provided with a turbine expander provided with an electric generator. Power generated by the steam plant is directed to the main gas pipeline, and a part of power is directed to the turbine expander with electric generator to produce electric power.
EFFECT: enhanced reliability and efficiency.
1 cl, 1 dwg
FIELD: cryogenic engineering.
SUBSTANCE: tank comprises vessel with heat insulation made of a polyurethane foam and casing. The vessel is provided with the additional layer made of a polyurethane foam. Between the layers of the polyurethane foam is a shock-absorbing spacer secured with the use of a sealing layer. The layers of the polyurethane foam are provided with compensation joints arranged with a spaced relation one with respect to the other both in the radial and axial directions. The joints are filled with a fiber heat insulation material and are sealed.
EFFECT: reduced heat loss and enhanced reliability.
FIELD: storing or distributing liquid or gases.
SUBSTANCE: method comprises using a water solution of a surface-active agent as a water hydrate-generating material and allowing the water solution to stand at a pressure exceeding the equilibrium pressure to generate pure methane hydrate at a given temperature.
EFFECT: simplified method and reduced power consumption.
FIELD: devices for draining liquefied gases from reservoirs and degassing of reservoir interior.
SUBSTANCE: proposed method consists in pumping inert gas into reservoir for forcing contents of reservoir out of it through at least one outlet pipe. Velocity of gas pumped into reservoir is decreased by means of deflector; inert gas is smoothly distributed over surface of reservoir; pressure and temperature of inert gas is maintained at level ensuring condensation of vapor in reservoir. Plant proposed for realization of this method has device for pumping inert gas into reservoir under pressure which has at least one inlet pipe for inert gas and at least one outlet pipe for draining contents of reservoir. Plant is also provided with deflector mounted inside reservoir and intended for decreasing the velocity of inert gas pumped into reservoir and its smooth distribution over surface of reservoir contents. Reservoir for storage and/or transportation of liquefied gases has housing with loading/unloading neck with cover, pipes for admitting and discharge of gas-and-air mixture and deflector for decreasing the velocity of gas flow and smooth distribution over surface of reservoir contents. Deflector includes reservoir fitted with inlet branch pipe for connection with inlet pipe for pumping inert gas into reservoir and at last two outlet branch pipes for discharge of inert gas into reservoir, thus decreasing the velocity of inert gas flow and smooth distribution over surface of reservoir contents.
EFFECT: avoidance of mixing of inert gas with reservoir contents; possibility of draining and degassing in one stage.
14 cl, 4 dwg
FIELD: equipment for emptying of failed bottles containing compressed, liquefied and dissolved under pressure gases, applicable for discharge of gas from a bottle with a faulty valve.
SUBSTANCE: the device has a frame with a fixture for gripping the bottle, sealing and a gas abstraction system. Two supports with bearings are fastened in the frame, a movable sleeve is installed on the bearings between the supports, the sleeve is made with a radial hole in which a wrench-gripper is placed for motion in the radial direction. The gas abstraction system is positioned on the support distant from the bottle, and a partition with holes is made in the branch pipe of the gas abstraction system.
EFFECT: facilitated servicing due to simplified construction.
2 cl, 1 dwg
FIELD: storage of gases.
SUBSTANCE: proposed multispaced high-pressure bottle containing envelopes mainly, of cylindrical or spherical form, nested one in the other with clearance to keep gas in space formed in between, and filling device to intake/discharge gas providing pressure in spaces reducing in steps from maximum pressure Pmax in central space to minimum pressure in periphery space. Number of envelopes N corresponds to N=(20-100) Pmax/σt where σt is tolerable stress of material of housing, with equal clearances along middle radii of walls of envelopes equal to ratio of middle radius of wall of peripheral envelope to number of spaces. Envelopes are supported at least by one intermediate support made, for instance, in form of disk with possibility of gas passing. Filling device is made for setting equal pressure differentials on envelope walls in filled up bottle equal to Pmax/N.
EFFECT: provision of storage and transportation of gases at very high pressures, improved reliability and simplified technology of manufacture.
2 tbl, 6 dwg
FIELD: high-pressure tanks.
SUBSTANCE: tank comprises hemispherical bottom and is provided with load-bearing shell having seal. The load-bearing shell is made of flexible layer, protective corrosion-protective and sealing layer, and is provided with pole opening. The corrosion-protective and sealing layer of the bottom is made of steel and bronze spirals with a ratio of 2:1 pressed one to the other and to fluoroplastic material whose outer side is additionally pressed to the reinforcing braid made of bronze spirals.
EFFECT: enhanced safety.
FIELD: pressure vessels.
SUBSTANCE: plastic-coating metallic vessel comprises outer load-bearing plastic shell and inner thin-walled welded steel shell whose intermediate section is cylindrical, two bottoms, and connecting pipe. The connecting pipe and at least one of the bottoms are made in block. The method comprises rolling out the rod from its one end thus defining the flange having flat circular surface from one side, working the unrolled section of the rod to form the outer surface and inner passage of the connecting pipe, rotating tension of the flange, moulding the bottom of a given shape, connecting the bottom to the intermediate cylindrical section, and welding the parts.
EFFECT: reduced labor consumption.
4 cl, 3 dwg
FIELD: storing or distributing gases or liquids.
SUBSTANCE: device comprises cylindrical housing with space for supplying and discharging gas, means for directing the drill, and seals. The housing is provided with thread at its one end, longitudinal groove for receiving the slide made for permitting movement along the groove, and with mechanism for fastening. The means for directing the drill is made of a bushing with passage and lid and is secured to the slide. The thread at one of the ends of the housing is made for threaded ring of the vessel neck, and the other end of the housing is provided with seat for the hose for discharging gas.
EFFECT: enhanced reliability.
1 cl, 1 dwg
FIELD: plastic metal working.
SUBSTANCE: invention can be used for making of bottles from sheet blanks. Proposed method includes making of shell, top plate, neck, bottom plate made integral with support ring, flanging and shoe, assembling and connecting the parts by welding. Shell is butt-welded to bottom plate on support ring. Both plates are made of blanks of equal size and in form of bottom plate. When making top plate, support part of shoe is calibrated to bring its diameter to diameter of shell.
EFFECT: reduced labor input.
1 ex, 1 dwg
FIELD: pressure vessels.
SUBSTANCE: multi-chamber tank comprises bank of tubes that bear on the plates provided with parallel rows of openings that can receive the tubes mounted in such a manner that each tube is almost in a contact with the adjacent tubes, frame made of fiber resin that fills all the spaces in the tube bank, ties that connect two covers with tube banks and pass through the spaces in the tube bank and the openings in the plates, outer strengthening layer, outer casing made of sheet aluminum, and standard gas cock mounted in the port made in one of the covers.
EFFECT: enhanced safety.
FIELD: storing or distributing gases or liquids.
SUBSTANCE: pressure vessel has cylindrical shell made of spiral and ring layers which are made of a fiber composite material and bottoms with flanges made of spiral layers and set in openings. The thickness of the cylindrical shell uniformly decreases along the length in the direction to the bottom with greater opening due to the decrease of the thickness of the ring layers.
EFFECT: reduced weight and cost of vessels.