Method for preparing urea (variants), method for enhancing output of process

FIELD: chemical technology.

SUBSTANCE: invention relates to producing urea from ammonia and carbon dioxide. Method involves preparing products of reaction in the synthesis zone as a solution containing urea, ammonium carbamate and unreacted ammonia. Part of solution obtained in synthesis of urea (preferably 10-60 wt.-%) is fed from the synthesis zone to additionally assembled zone of treatment under mean pressure at 1-4 MPa wherein gas flow is separated and subjected for absorption with ammonium carbamate solution of low pressure supplying from the section for isolation and treatment of urea. As a variant of method the invention proposes to use the combined reactor in the synthesis zone representing vertically installed or combined reactor. Enhancement of output of existing processes in synthesis of urea is achieved by feeding part of urea solution synthesized in the synthesis reactor to additionally installed zone for treatment of mean pressure including the dissociation zone, desorption zone of mean pressure and the condensation zone of mean pressure. Invention provides enhancement of output of unit for producing urea being without modification of section of high pressure.

EFFECT: improved method for producing urea.

10 cl, 4 dwg

 

The invention relates to a method for producing urea from ammonia and carbon dioxide.

Urea is produced by the introduction of excess ammonia together with carbon dioxide in the synthesis zone at a high pressure (for example, 12-40 MPa) and high temperature (for example, 160-250° (C)that the first leads to the formation of ammonium carbamate in accordance with the reaction:

2NH3+CO2→H2N-CO-ONH4

The dehydrogenation formed ammonium carbamate then leads to the formation of urea according to the equilibrium reaction:

H2N-CO-ONH4↔H2N-CO-NH2+H2O

theoretical maximum conversion of ammonia and carbon dioxide in the urea is determined by thermodynamic equilibrium and depends on, for example, relationships NH3/CO2(relationship N/C), a relationship of H2O/CO2and on temperature. From the above equations reactions can be concluded that the use of excess water in the synthesis zone has a negative effect on theoretical maximum conversion.

When the conversion of ammonia and carbon dioxide into urea in the synthesis zone get obtained during the synthesis of urea solution as a reaction product containing, essentially, urea, water, ammonium carbamate and unreacted ammonia.

Than that obtained in the synthesis of mocovi the s solution in the synthesis zone may also be formed of a mixture of gases, consisting of unreacted ammonia and carbon dioxide together with inert gases, the so-called synthesis gas. Inert gases present in the synthesis gas, usually formed of air supplied in the equipment to improve its corrosion resistance. Ammonia and carbon dioxide are removed from the synthesis gas in the zone of the scrubber before release into the atmosphere of the synthesis gas. The ammonia and carbon dioxide are preferably returned to the synthesis zone.

The synthesis zone may consist of separate zones for the formation of ammonium carbamate and urea. However, these zones can also be combined in one apparatus. The synthesis can be done in one or two reactors. If using two reactors, the first reactor is carried out, for example, using almost raw source materials, and in the second reactor using raw materials which are fully or partially received at any stage of the technological process, which recycle to the synthesis zone.

The conversion of ammonium carbamate into urea and water in the zone of the synthesis can be accomplished by providing a sufficiently long residence time of the reaction mixture in this zone. During their stay, as a rule, should be more than 10 minutes, preferably more than 20 minutes. Typically, the residence time should be less than 3 hours, preferably less than 1 the Asa.

The equipment for manufacture of urea is designed for a specific performance. Generally, the performance of the existing equipment for urea production can be increased only to a very limited extent by increasing the number of initial substances and increase throughput of the process streams. If it is desirable to increase the productivity by increasing throughput of the process streams, it is necessary to achieve high efficiency with increased technological flows at various stages of the method. This applies, in particular, those stages of the method, which is carried out in a section of high pressure installations for the production of urea.

Section high pressure installations for the production of urea, which is carried out in accordance with the so-called process desorption processing), essentially consists of a synthesis zone, in which the gain obtained in the synthesis of urea solution, desorption zone processing, which is obtained when the urea solution is subjected to desorption in countercurrent with one of the raw materials and/or heat, the condensation zone in which the gases released in the desorption zone processing, condensed, and zone of the scrubber, in which ammonia and carbon dioxide in which laroda removed from the synthesis gas.

"Narrow" places in this section, a high pressure can, in particular, to be desorption processing obtained in the synthesis of urea solution in the area of the desorption process and the condensation in the condensation zone gases obtained desorption treatment. The reason for this is that if too strong increase of the load of the liquid in the zone desorption treatment effect desorption treatment significantly lost due to, among other things, zahlebyvayas. Zaklepywanie means that the liquid film on the inside of the pipe section desorption destroyed and part of the liquid is captured by the outgoing gas stream. This greatly reduces the efficiency of the desorption process. The increase in the number of initial substances has little effect on the performance of the zone of fusion. The shorter the residence time, which is the result of higher throughput, has the consequence that the content of ammonium carbamate obtained in the synthesis of urea solution increases slightly, so you need more steam in the area of the desorption processing for decomposition of ammonium carbamate. Therefore, the limiting factor is the desorption zone of the processing and not the synthesis zone.

It is necessary to preserve the possibility that even with the increased supply of the gas mixture heat released is in the zone of condensation in the condensation of the gas mixture, obtained by desorption processing, can be converted into steam, suitable for use on any area of the technological process of production of urea, using the existing heat exchange surface. Found, however, that the increased supply of gas to be condensation leads to a very low vapor pressure, as a consequence, such pairs can no longer be used on any area of technological process of obtaining urea.

These bottlenecks way are largely responsible for the fact that only a very limited way, you can increase the performance of an existing installation without modification or replacement of expensive equipment, working under high pressure. These bottlenecks arise, in particular, when using the so-called combined reactors to produce urea. Combined reactor is a reactor in which the synthesis zone, and/or the condensation zone and/or area scrubber combined in one vessel. Well-known examples are combined reactor, described in US-A-5767313, US-A-5936122 and WO 00/43358.

NL-A-8900152 discloses a method of producing urea, in which you can increase the productivity of plants for the production of urea, which is carried out in accordance with desorption about what abucay, without modifications section of the high-pressure synthesis of urea.

This is achieved in NL-A-8900152 by obtaining urea in accordance with the way in which obtained during the synthesis of urea solution containing urea, ammonium carbamate and unreacted ammonia are in the area of synthesis from carbon dioxide and ammonia, and the part obtained in the synthesis of urea solution is passed into the treatment area medium pressure. In this treatment area average pressure is the amount obtained during the synthesis of urea solution interacts with a certain amount of carbon dioxide at a pressure of from 1.5 to 3.0 MPa (average pressure). In NL-A-8900152 gas mixture formed in the treatment zone average pressure, condensed with an average pressure in the condensation zone medium pressure, the heat formed during such condensation, is used for evaporation of the urea solution in the extraction of urea. In NL-A-8900152 residual obtained in the synthesis of urea solution coming out of the treatment area medium pressure, is passed into the partition recovery low pressure (0.2-0.6 MPa), which is still present carbamate ammonium substantially decompose and separate the formed gas mixture.

It has been unexpectedly discovered that it is possible to increase plant capacity for production is DSTV urea without the need for any modifications section of the high-pressure installation, and to increase the conversion of urea in the synthesis zone. This becomes even more remarkable, because, as a rule, the performance increase resulting from increase in throughput of the installation for the production of urea, partially lost due to a slight reduction of the conversion of urea.

This advantage is achieved by obtaining urea in accordance with the way in which

obtained during the synthesis of urea solution containing urea, ammonium carbamate and unreacted ammonia, produced from carbon dioxide and ammonia in the synthesis zone

the part obtained in the synthesis of urea solution is passed from the zone of fusion in the treatment area medium pressure, operating at a pressure of 1-4 MPa, preferably from 1.5 to 3.0 MPa, and the method is characterized by the fact that the flow of gas from the zone of treatment medium pressure absorb in a solution of ammonium carbamate, under low pressure, partition recovery urea. Low pressure means a pressure of 0.1-1 MPa, in particular from 0.2 to 0.7 MPa. In particular, 10-60 wt.% obtained during the synthesis of urea solution is fed to the treatment zone average pressure, more specifically, 15-45 wt.% Preferably the flow of the processing zones of medium pressure formed by the absorption of the gas flow from the treatment area average pressure in a solution of ammonium carbamate, Academica under low pressure, from the regeneration section, transferred to the scrubber is operating under high pressure.

It was found that in the process of condensation of the gas stream from the treatment area average pressure in a solution of ammonium carbamate from section regeneration of urea in this zone, condensing medium pressure solution of ammonium carbamate from section regeneration urea, having a water content of 25-35 wt.%, you can concentrate to the solution of ammonium carbamate, having a water content of 10 wt.% below, for example, 15-25 wt.%. Since the solution of ammonium carbamate served in the synthesis zone through the zone of the scrubber operating at high pressure, and the condensation zone operated at high pressure, this means that less water will recycle to the synthesis zone, thereby increasing the efficiency zone of the synthesis. In the condensation zone medium pressure, heat is produced as a result of the formation of ammonium carbamate in the area. Through direct or indirect heat transfer this heat can be disposed on any other part of the technological process for heating process streams or for regeneration by evaporation of the urea solution in the regeneration section of the urea. This heat can also be released when the cooling water.

The application of the method in accordance with the invention unexpectedly has made possible the increase of p is poizvoditelnosti existing plants for the production of urea to about 120-150% of the original performance without increasing power or modifications to the equipment section of the high pressure while the conversion in the course of the synthesis of urea is increased by 0.5 to 3% depending on other conditions. This increase in performance requires additional cleaning zones with appropriate piping, but the necessary equipment is relatively inexpensive compared to the cost of the equipment section of the high pressure. This additional purification zone essentially consists of an area of dissociation medium pressure, the desorption zone of the treatment medium pressure and the condensation zone medium pressure. The possibility of placing two or three of these zones in a single tank. The application of the method of the present invention provides the ability to avoid the above-mentioned bottlenecks, that is, "zahlebyvayas" in the area of the desorption process and the risk of too low pressure steam generated in the condensation zone.

The method according to the present invention can be implemented in the plant for production of urea, which is carried out in accordance with the process of desorption treatment. It is clear that this refers to the fact that the installation for the production of urea, in which the decomposition of ammonium carbamate, which was not transformed into urea, and destruction of normal excess ammonia mainly takes place at a pressure which is essentially in fact, t is some, as the pressure in the synthesis zone. Such decomposition/destruction occurs in the area of desorption treatment, not necessarily adding Stripping gas (Stripping gas). In the desorption process of processing carbon dioxide and/or ammonia can be used as Stripping gas prior to submission of these components in the synthesis zone. Such desorption treatment is carried out in the desorption section, installed along the flow after synthesis reactor, thus obtained in the synthesis of urea solution leaving the synthesis reactor, is subjected to a desorption treatment in countercurrent with the Stripping gas with the supply of heat. You can also use thermal desorption treatment. Thermal desorption processing means for decomposition of ammonium carbamate and removal of ammonia and carbon dioxide contained in the urea solution, use only the supply of heat. Desorption processing also can be performed in two or more stages. For example, there is a method in which first carried out exclusively thermal desorption treatment, after which carried a stage desorption processing using CO2with the additional supply of heat. The gas stream containing ammonia and carbon dioxide coming from the desorption section, returned to the synthesis zone. Decor the information processing obtained in the synthesis of urea solution using desorption environment can be done in more than one desorption section. In ways that use more than one desorption section, obtained during the synthesis of urea solution used for feed in the treatment area medium pressure, can be extracted through the outlet zone of the synthesis or from a liquid solution between the two desorption sections.

In the installation for the production of urea, which is carried out in accordance with the process of desorption treatment, the synthesis reactor operates at a temperature of 160-240°and preferably at a temperature of 170-220°C. the pressure in the synthesis reactor is 12-21 MPa and preferably 12.5 to 19.5 MPa. The ratio of N/C in the synthesis zone setup desorption treatment of urea is between 2.5 and 4. If conversion to urea is carried out in two or more separate areas of synthesis, when fresh raw material is preferably served in a single synthesis zone, and recycled raw materials preferably serves the second synthesis zone, then the invention is particularly suitable for improving the efficiency in this second synthesis zone.

A frequently used variant embodiment of the method of producing urea in accordance with the process of desorption processing is brand desorption process processing Stamicarbon using CO2such as described in Uhlmann,'s Encyclopedia of Industrial Chemistry, Vol.A27, pp.344-346, 1996. A large part of the gas mixtures and, obtained in the desorption process, condense and adsorb together with the ammonia required for the process in the condensation zone, for example in the carbamate condenser high pressure, which formed the ammonium carbamate is passed into the synthesis zone for the formation of urea.

The carbamate condenser high pressure, for example, may be designed as so-called "immersion" capacitor, as described in NL-A-8400839. Submersible capacitor can be placed horizontally or vertically. Condensation in horizontal immersion condenser (the so-called modular condenser; see, for example, Nitrogen No. 222, July-August 1996, p.29-31), however, has specific advantages, as compared with other designs of such a condenser, generally provides a longer residence time of fluid in the bulk capacitor. The result is the formation of an additional amount of urea, which increases the boiling temperature so that the temperature difference between containing urea solution of ammonium carbamate and a cooling medium increases and improves heat transfer.

Functions of the reactor, condenser high-pressure carbamate and scrubber high pressure can be combined in one or two vessels of high pressure during the separation of the functions of these stages of the way through the m of the guide walls, designed for a small pressure difference in these vessels working under high pressure. This has the distinct advantage associated with significant cost savings, as it significantly reduces the number of high-pressure pipelines that need to be installed. In addition, it improves the reliability of equipment, because the number is sensitive to the infiltration of the connective elements under high pressure, between the pipeline and the equipment is greatly reduced. Well-known examples are combined reactor, which was already a link, as described in US-A-5767313, US-A-5936122 and WO 00/43358. The preferred embodiment is a combination of precast capacitor with a horizontal reactor, as described in US-A-5767313, which presents the so-called "United" reactor.

After surgery desorption processing desorbed obtained in the synthesis of urea solution increases in volume to a low pressure and restore it when the evaporation section of the recovery of urea, and then release urea, and the flow of ammonium carbamate low pressure recycle in section synthesis. Depending on the type of process, the desorption process of regeneration of the ammonium carbamate can be performed on the same stages with the person or in several stages, working at different pressures. In all variants of the method according to the present invention are achieved advantages.

In a particular embodiment of urea receive in accordance with the manner in which the reactor and the condenser of the high-pressure carbamate provided in a single vessel in the section of high pressure and in which the part obtained in the synthesis of urea solution unloading during machining medium pressure, operating at a pressure of 1-4 MPa, preferably from 1.5 to 3.0 MPa. In this variant embodiment the synthesis zone and the carbamate condenser high pressure can be provided in a horizontal or vertical vessel. Preferably the synthesis zone and the carbamate condenser high pressure can be placed horizontally located the vessel, the so-called United reactor. The advantage of this method according to this invention is that in the section of high pressure benefit associated with cost savings.

In this particular embodiment urea receive in accordance with the way in which

obtained during the synthesis of urea solution containing urea, ammonium carbamate and unreacted ammonia, produced from carbon dioxide and ammonia in the synthesis zone of a combined reactor,

the part obtained in the synthesis of urea solution is passed from the zone of the Intesa urea in the treatment area, working at a pressure of 1-4 MPa, preferably from 1.5 to 3.0 MPa, and the gas flow from the treatment area medium pressure absorb in a solution of ammonium carbamate low pressure section of the recovery of urea. Low pressure means a pressure of 0.1-1 MPa, in particular from 0.2 to 0.7 MPa. In particular, 10-60 wt.% obtained during the synthesis of urea solution is fed to the treatment zone average pressure, more specifically, 15-45 wt.%. Used combined reactor preferably is a vertically placed combined reactor or the combined reactor. It is most preferable to use the combined reactor. Flow from a processing medium pressure formed by the absorption of the gas stream from the treatment area average pressure in a solution of ammonium carbamate low pressure section of the regeneration is preferably passed into a scrubber high pressure.

The method in accordance with the present invention is carried out in the plant for production of urea, operating in accordance with the method desorption process, where

obtained during the synthesis of urea solution containing urea, ammonium carbamate and unreacted ammonia, produced from carbon dioxide and ammonia in the synthesis zone;

part of the ammonium carbamate obtained in the synthesis of urea solution is decomposed in the area on the sorption of high pressure processing as a result of desorption processing the Stripping gas when heated and, at least part formed in the gas mixture is condensed in the condensation zone and the resulting condensate and any unfused portion returned to the synthesis zone;

the ammonium carbamate still present in the remainder obtained when the synthesis of urea solution, at least mostly decomposed in section regeneration of low pressure at the pressure of 0.1-1 MPa, preferably 0.2 to 0.7 MPa, and the resulting gas mixture is separated, and then the rest containing urea solution is subjected to further processing by evaporation to obtain a concentrated solution of urea and, optionally, solid urea;

- formed gas mixture to condense in the section of the low pressure regeneration, receiving a stream of ammonium carbamate low pressure, which returned to the process

the part obtained in the synthesis of urea solution is passed from the zone of fusion in the treatment area, working at a pressure of 1-4 MPa, preferably from 1.5 to 3.0 MPa, and the amount of carbon dioxide and, optionally, ammonia, corresponds to the quantity necessary to obtain the part obtained in the synthesis of urea solution, which serves in this treatment area, and the solution discharged from the treatment area, is subjected to further processing in the regeneration section of low pressure, with the gas flow and the zone of the treatment medium pressure absorb in a solution of ammonium carbamate low pressure section of the regeneration of urea.

The main advantages are achieved, in particular, in the construction of new capacities for the production of urea ("grassroot plants") and, in particular, high-power. It is clear that under the high-power mean plant with capacity of 1.5·106- 6·106kg of product per day. When applying the method according to this invention, in particular a carbamate condenser high pressure and the desorption pressure in the section of the synthesis unit for production of urea can be designed much smaller compared to conventional design. The high pressure pipeline in this section is also much less when using the method according to the present invention, which also provides savings in capital investment. As for new facilities, this may reduce investment by 5-10%. In addition, the invention implies that in new projects for the high-pressure equipment dimensions are maintained, which allows the manufacturer to easily manufacture such equipment, and this also makes it easy to transport such equipment over long distances.

An additional advantage that has been found is that the method, in particular, is suitable for reduction of consumption of energy in the form of high pressure steam. For new proactivamente saved high-pressure steam is approximately 30-100 kg per 1,000 kg of product produced in comparison with a standard process Stamicarbon desorption processing using CO 2.

Because the coefficient of variation install desorption treatment is determined by the size of the desorption section of the high pressure, flexibility, and hence the coefficient of variation of the installation in accordance with the above method, is much higher than the coefficient of variation standard installations desorption treatment of urea. The coefficient of variation of the installation represents the minimum load at which the plant can operate without the time of failure. Operation at minimum load required when the material is interrupted or severely reduced. In this case, the advantage of this invention is that the treatment zone average pressure is a parallel section, which can be switched off. Plant for urea production capacity of 3·106kg a day and having a coefficient of variation of 60%, can operate, for example, if the minimum performance 1,8·106kg per day. If through the treatment zone average pressure in day 1 is unloaded·106kg, the minimum capacity at which the plant for production of urea, having the same performance and the same coefficient of variation, can still work, 1.2·106kg per day.

With the application of the method according to this izaberete the July increase in performance can be achieved in all existing processes for the production of urea, operating in accordance with the process of desorption processing, by filing a part obtained in the synthesis of urea solution in the secondary zone of the treatment medium pressure, comprising an area of dissociation medium pressure, the desorption zone of the treatment medium pressure and the condensation zone medium pressure.

Examples of processes desorption treatment of urea, which can be used this way include the Stamicarbon process desorption processing using CO2the process of desorption treatment with ammonia, the process of imagesarray, the process of ACES (Advanced process for Cost and Energy Saving (superior way to save money and energy)and IDR process (Isobaric Double Recycle (Isobaric dual recycling)). These processes are described in Uhlmann,'s Encyclopedia of Industrial Chemistry, Vol.A27, 1996, pp.344-350.

The invention is further illustrated with reference to figures 1-4.

Fig. 1 schematically represents a method of producing urea in accordance with the Stamicarbon process desorption processing using CO2.

Fig. 2 schematically represents a method of producing urea in accordance with the Stamicarbon process desorption processing using CO2in which part obtained in the synthesis of urea solution is treated in the treatment zone average pressure through the bypass pipeline.

Fig. 3 schematically presents yet the Stamicarbon process desorption processing using CO 2in the United reactor in accordance with US-A-5767313.

Fig. 4 schematically represents the process of Stamicarbon desorption processing using CO2in the United reactor in accordance with US-A-5767313, in which the part obtained in the synthesis of urea solution is treated in the treatment zone average pressure through the bypass pipeline.

Fig. 1

Urea solution (USS)leaving the reactor urea (URE), served in the desorption section of the high pressure (HST). In this desorption section of the high pressure unreacted ammonium carbamate is decomposed with high-pressure steam and carbon dioxide with the formation of gaseous Stripping gas (STG), essentially consisting of ammonia and carbon dioxide. The urea solution coming from the desorption section of the high pressure (SUSS), served in the regeneration section of the urea of low pressure (LPR), which is a further purification of the urea solution. Ammonia and carbon dioxide obtained in this section, regeneration, condense and return in the form of a stream of ammonium carbamate low pressure (LPC) in the scrubber high pressure (HSCR) in section synthesis. Gaseous ammonia and carbon dioxide coming from the desorption section of the high pressure (HST), condensed in the condenser of the high-pressure carbamate (HCC). During condensation of amikai of carbon dioxide to form ammonium carbamate heat is released, which is used to produce low pressure steam. The amount of low pressure steam sufficient to meet needs in a pair of low pressure required for the regeneration section of the urea. The carbamate condenser high pressure (HCC) can represent any type of "immersion" of a capacitor or any design type falling film. Both embodiments known to specialists in this field. A solution of ammonium carbamate (LDCs), formed in NSS, together with still present in the free state ammonia and carbon dioxide, is fed into the reactor urea (URE). Fresh NH3also served through the condenser of the high-pressure carbamate. During the synthesis reaction in the reactor to receive the flow of gas, synthesis gas (RG), which is sent to HSCR. Synthesis gas essentially consists of ammonia, carbon dioxide and inert gases supplied to the reaction as a corrosion inhibitor. Such inert gases (air) is usually injected into the process with the supplied carbon dioxide. In the scrubber, high pressure synthesis gas (RG) absorb in the flow of ammonium carbamate low pressure (LPC) of section regeneration of urea. The result is a flow of carbamate (SHPC), which is sent to the condenser of the high-pressure carbamate. From the scrubber high pressure inert substances release the t to the atmosphere, optional after additional removal of any still present ammonia.

Figure 2

Part of the urea solution (USS)leaving the reactor urea (URE), sent to the desorption section of the high pressure (HST). In this desorption section of the high pressure unreacted ammonium carbamate is decomposed using high-pressure steam and part of the feed stream of carbon dioxide with the formation of gaseous ammonia and carbon dioxide. The urea solution coming from the desorption section of the high pressure (SUSS), served in the regeneration section of the low pressure (LPR), which is a further purification of the urea solution. The results obtained in this section regenerate low-pressure ammonia and carbon dioxide condense and return in the form of a stream of ammonium carbamate low pressure (LPC) through the treatment zone average pressure (MCC), located parallel to the desorption section of the high-pressure scrubber high pressure (HSCR) in the synthesis zone. The heat received by condensation, can be used for concentration of the urea solution in the regeneration section. Gaseous ammonia and carbon dioxide coming from the desorption section of the high pressure (HST), the Stripping gas (STG), condensed in the condenser of the high-pressure carbamate (HCC). In the process of condensation of ammonia and carbon dioxide coal is an ode to the formation of ammonium carbamate heat is released, which is used to produce low pressure steam. The amount of low pressure steam sufficient to meet needs in a pair of low pressure required for the regeneration section of the urea. The carbamate condenser high pressure (HCC) can represent any type of "immersion" of a capacitor or any design type falling film. The resulting solution of ammonium carbamate, together with still present in the free state ammonia and carbon dioxide fed into the reactor urea (URE).

Part of the urea solution (USS)leaving the reactor high pressure is directed to the treatment area medium pressure, operating at a pressure of approximately 2 MPa. This treatment area medium pressure includes the area of dissociation medium pressure (MDIS), desorption zone of medium pressure (MST) and the condensation zone of medium pressure (MCC). Unreacted ammonium carbamate in USS decompose to gaseous ammonia and carbon dioxide in the area of dissociation medium pressure (MDIS) when applying heat. The urea solution leaving this zone dissociation medium pressure (DUSS), which contains a relatively large amount of ammonia, can be subjected to desorption processing of fresh carbon dioxide in the section desorption of carbon dioxide medium pressure (MST). The urea solution, vihodiashiy MST, unload section of the low pressure recirculation (LPR). Exhaust gases (MDG) from the dissociation medium pressure (MDIS), together with the exhaust gases (MSG) of section desorption of carbon dioxide medium pressure (MST), condensed in the condenser carbamate medium pressure (MSS) in a stream of ammonium carbamate low davlenie (LPC) of section regeneration, receiving concentrated flow of carbamate ammonium medium pressure (MPC), which is injected into the scrubber high pressure (HSCR). Thus, the ammonium carbamate low pressure (LPC), containing about 30% water, concentrate in the treatment area medium pressure with the formation of ammonium carbamate (IFAS), containing only 20% water. Using these data, calculate the allocation between the amounts of the urea solution supplied to the desorption section of the high pressure (HST) and the area of dissociation medium pressure (MDIS), taking into account the fact that the amount of water fed to the scrubber high pressure through an ammonium carbamate medium pressure below or equal to the quantity of water supplied in such a scrubber high pressure standard unit for treatment of urea. Due to the relatively small amount of urea solution to be processed in the desorption section of the high pressure, the dissociation of urea solution in the area of dissociation medium pressure PR which comes at a lower pressure, therefore, while consuming less energy and at lower or equal to the water supply to the scrubber high pressure through-flow of ammonium carbamate (IFAS), so the consumption of high-pressure steam in installations operating in accordance with this process, lower than in the standard setting desorption purification of urea with a CO2. If desirable, NH3required to process the proportion served through MCC and NCC. The gas mixture, neskondensirovannyh in the carbamate condenser medium pressure is served in the form of a stream of gas (MCG) in the regeneration section of the low pressure, where it is subjected to further processing. Synthesis gas (RG) absorb in the flow of ammonium carbamate medium pressure in the scrubber high pressure so as to form an additional stream of ammonium carbamate. From the scrubber high pressure of this stream of ammonium carbamate (SHPC) is sent to the condenser of the high-pressure carbamate. Inert gases discharged from the scrubber high pressure, optionally after further purification stages, to remove any remaining NH3.

Figure 3

Urea solution (USS), leaving the United reactor urea (URE+HCC), sent to the desorption section of the high pressure (HST). In this desorption section of the high pressure unreacted carbamate, ammo the Oia decompose to gaseous ammonia and carbon dioxide using a high-pressure steam and feed carbon dioxide. A solution of urea (SUSS), emerging from the desorption section of the high pressure, is fed into the regeneration section of the low pressure (LPR), which is a further purification of the urea solution. Ammonia and carbon dioxide obtained in this section recirculation low pressure, condense and return in the form of a stream of ammonium carbamate low pressure (LPC) in the scrubber high pressure (HSCR) in section synthesis. In this scrubber ammonia and carbon dioxide absorb from synthesis gas (RG), and then released a stream of inert gases and the flow of ammonium carbamate high pressure (SHPC), formed in the scrubber, send in the combined reactor. Gaseous stream (STG), mainly containing ammonia and carbon dioxide coming from the desorption section of the high pressure (HST), condensed in the condenser of the high-pressure carbamate (HCC) United reactor. In the process of condensation of ammonia and carbon dioxide with the formation of ammonium carbamate heat is released, which you can use to obtain the low-pressure steam. The amount of low pressure steam sufficient to meet needs in a pair of low pressure required for the regeneration section of the urea. The carbamate condenser high pressure (HCC) represents any type of so-called "immersion" of the capacitor and is located in the joint of the reactor. NH3required for the process, served in the United reactor.

Figure 4

Part of the urea solution (USS), leaving the United reactor urea (URE+HCC), sent to the desorption section of the high pressure (HST). In this desorption section of the high pressure unreacted ammonium carbamate is decomposed to gaseous ammonia and carbon dioxide using a high-pressure steam and part of the supplied carbon dioxide. A solution of urea (SUSS), emerging from the desorption section of the high pressure is directed to the regeneration section of the low pressure (LPR), which is a further purification of the urea solution. Ammonia and carbon dioxide obtained in this section low pressure regeneration, condense and return in the form of a stream of ammonium carbamate low pressure (LPC) through the treatment zone average pressure, located parallel to the desorption section of the high-pressure scrubber high pressure (HSCR) in section synthesis. The treatment area medium pressure includes the area of dissociation medium pressure (MDIS), the desorption zone of the treatment medium pressure (MST) and the condensation zone of medium pressure (MCC). The stream containing the gaseous ammonia and carbon dioxide (STG), emerging from the desorption section of the high pressure (HST), condensed in the condenser carbamate high is anyone pressure (HCC) United reactor. In the process of condensation of ammonia and carbon dioxide with the formation of ammonium carbamate heat is released, which you can use to obtain the low-pressure steam. The amount of low pressure steam sufficient to meet needs in a pair of low pressure required for the regeneration section of the urea. The carbamate condenser high pressure (HCC) represents a type of "immersion" of the capacitor and is located in United reactor. Part of the urea solution (USS), leaving the United reactor high pressure is directed to the treatment area average pressure, which operates at a pressure of about 2 MPa. Unreacted ammonium carbamate is decomposed to gaseous ammonia and carbon dioxide when the heat in the area of dissociation medium pressure (MDIS). The urea solution leaving this zone dissociation medium pressure (DUSS), which contains a relatively large amount of ammonia, can be subjected to a desorption treatment with carbon dioxide desorption section average pressure (MST) using parts of fresh carbon dioxide. The urea solution leaving the section desorption of carbon dioxide medium pressure, relieve in the regeneration section of the low pressure (LPR). Exhaust gases from the zone of dissociation medium pressure (MDG) together with the exhaust gases from succeedingly carbon dioxide medium pressure (MSG), sent to the condenser carbamate medium pressure (MCC) for condensation in the flow of ammonium carbamate low pressure (LPC), obtained in section regeneration. The heat of condensation released in MCC, disposed of by direct heat exchange with a solution of urea in section regeneration, resulting in the concentration of the urea solution. The ammonium carbamate leaving the condenser carbamate medium pressure, is injected into the scrubber high pressure (HSCR). Thus, ammonium carbamate, under low pressure, containing about 30% water, concentrate in the treatment area with medium-pressure receiving ammonium carbamate containing only 20% water. Using these data, calculate the allocation between the amounts of the urea solution supplied to the desorption section of the high pressure (HST) and the area of dissociation medium pressure (MDIS), taking into account the fact that the amount of water fed to the scrubber high pressure through an ammonium carbamate medium pressure below or equal to the quantity of water supplied in such a scrubber high pressure standard unit for treatment of urea. By enhancing the synthesis of a relatively smaller amount of the urea solution can be processed in the desorption section of the high pressure. As a consequence, in the desorption clubs who use less steam. The gas mixture which has not condensed in the condenser carbamate medium pressure (MCC), sent in the form of a gas stream (MCG) in the regeneration section of the low pressure (LPR). In the scrubber high pressure (HSCR) synthesis gas (RG) absorb in the flow of ammonium carbamate medium pressure (IFAS) to produce a concentrated stream of ammonium carbamate (SHPC), which is sent to the combined reactor. Of HSCR inert gases are removed from the system.

1. A method of producing urea from ammonia and carbon dioxide, which is obtained during the synthesis of urea solution containing urea, ammonium carbamate and unreacted ammonia produced in the synthesis zone, the part obtained in the synthesis of urea solution is directed from the zone of fusion in the treatment area medium pressure, operating at a pressure of 1-4 MPa, characterized in that the gas flow from the treatment area medium pressure absorb in a solution of ammonium carbamate low pressure section of the regeneration of urea.

2. The method according to claim 1, characterized in that the pressure in the treatment zone average pressure is from 1.5 to 3.0 MPa.

3. The method according to any one of claims 1 and 2, characterized in that 10-60 wt.% obtained during the synthesis of urea solution is fed to the treatment zone average pressure.

4. The method according to any one of claims 1 and 2, characterized in that the flow of the processing zones of medium pressure generated is the result of absorption of the gas flow from the treatment area medium pressure solution of ammonium carbamate low pressure section of the regeneration, sent to the scrubber high pressure.

5. A method of producing urea from ammonia and carbon dioxide, which is obtained during the synthesis of urea solution containing urea, ammonium carbamate and unreacted ammonia produced in the synthesis zone of a combined reactor, characterized in that the part received in the synthesis of urea solution is directed from the zone of the synthesis of urea in the treatment area, working at a pressure of 1-4 MPa, and in which the flow of gas from the zone of treatment medium pressure absorb in a solution of ammonium carbamate low pressure section of the regeneration of urea.

6. The method according to claim 5, characterized in that the pressure in the treatment zone average pressure is from 1.5 to 3.0 MPa.

7. The method according to any of pp.5 and 6, characterized in that 10-60 wt.% obtained during the synthesis of urea solution is fed to the treatment zone average pressure.

8. The method according to any of pp.5 and 6, characterized in that as a combined reactor used vertically placed combined reactor or the combined reactor.

9. The method according to claim 5 or 6, characterized in that as a combined reactor using the combined reactor.

10. The way to improve the performance of existing processes of urea by submitting in addition established treatment area medium pressure vkluchaushsih dissociation, desorption zone of medium pressure and the condensation zone medium pressure part obtained in the synthesis of urea solution.



 

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EFFECT: increased efficiency of apparatuses designed for decomposition of recycled carbamate solution.

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