Method of dry desulfurization of exhaust gas

 

(57) Abstract:

The invention relates to a method of dry desulfurization of exhaust gas, wherein the exhaust gas generated in the combustion chamber and the contaminated fly ash, harmful gaseous substances and returned by the particles of solids, partially dedust in the first separator solids, then the exhaust gas is directed into the reactor with a fluidized bed, and to the exhaust gas serves at least one absorption means CaO and/or Ca(OH)2in a reactor with a fluidized bed by adding water set temperature 50 - 90oC, then the exhaust gas containing particulate matter away from the reactor with a fluidized bed and is directed to the second separator solids, with the first part of the solids separated in the second separator is sent to a reactor with a fluidized bed, and the second portion of the solids separated in the second separator, return into a cooled zone of the combustion chamber and the pipeline is removed from the cycle, the solids separated in the first separator. The development of this invention allows the use of more accessible absorption means, the Invention relates to a method of dry desulfurization of exhaust gas, when dedust the exhaust gas generated in the combustion chamber and the contaminated fly ash, and gaseous pollutants, which dedusted exhaust gas is cooled with water to a temperature of from 50 to 90oC, mixed with an absorption medium, consisting of CaO and/or Ca(OH)2and bring in a reactor with a fluidized bed separator and return piping of a circulating fluidized bed, in which solid particles from the separator is partially introduced into the reactor with a fluidized bed, and partly in the area of the combustion chamber having a temperature of from 850 to 1050oC. the Method for desulfurization of waste gases that are released during the combustion of solid and liquid combustible substances, in particular coal and oil, as well as in waste incineration and sludge settling.

From DE-PS 4104180 known method of dry desulfurization of exhaust gases of a boiler plant by adding sorbents containing lime, which coarsely crushed lime (CaCO3) with an average grain size equal to 200 μm, is introduced into the zone of the boiler system, in which the exhaust gases have a temperature of from 800 to 900oC, at which the exhaust gases after the heats is then formed coarse-grained part is subjected to grinding to an average grain size of 5 to 10 μm and segregated part with a medium grit and fine-grained part is removed from the system in which part, milled to 5 µm and 10 µm, down with the water and exhaust gases in the circulating fluidized bed consisting of a reactor with a fluidized bed, a separator and a return line, and wherein the exhaust gases finally dedust the second electrostatic paleolatitude and release into the environment, and spin-off residues containing CaSO3and CaSO4return partially in a reactor with a fluidized bed, and partly to the boiler plant. In this known method, the dust removal is carried out in a first electrostatic cyclone separator included after the boiler at 90 - 160oC, and in the circulating fluidized bed set temperature from 50 to 90oC by supplying an appropriate quantity of water.

In addition, it is known that the method of dry desulfurization transformation absorption means by S02is carried out satisfactorily only when there is a stoichiometric excess absorption means. Relatively low excess absorption means is achieved if the applied absorption means for suhaym. In any case, in particular, in circulating fluidized bed portion of CaO or Ca(OH)2is lost due to the fact that the formed calcium carbonate. This adverse reaction have a negative impact on the stoichiometry of the reaction desulfurization, resulting in absorption means CaO and/or Ca(OH)2when dry desulfurization must be entered in a noteworthy abundance; SO2: Ca (released SO2is practically above 1 : 1,3. Additionally, during the dry desulfurization violation occurs in the work due to the fact that in the reaction of HCl contained in the exhaust gas from the absorption means is formed hygroscopic CaCl2, which are the cause of unwanted burns and buildup in the flue gas.

Therefore, the basis of the invention is to create a method of dry desulfurization, which works reliably with respect to the SO2: Ca (released SO2) is less than 1: 1.2, and absorption means makes the desulfurization reaction is significantly more affordable and also eliminates unwanted burns and buildup in the plant for purification of exhaust gas, in particular, in circulating fluidized bed. In the as well as a sufficient amount of CaCO and dehydrated CaSO4.

The problem is solved in that in the method of dry desulfurization of exhaust gas, wherein the exhaust gas generated in the combustion chamber and the contaminated fly ash, harmful gaseous substances and returned by the particles of solids, partially dedust in the first separator solids, then the exhaust gas is directed into the reactor with a fluidized bed, and to the exhaust gas serves at least one absorption means CaO and/or Ca(OH)2in a reactor with a fluidized bed by adding water set temperature 50-90oC, then the exhaust gas containing particulate matter away from the reactor with a fluidized bed and is directed to the second separator solids, with the first part of the solids separated in the second separator is sent to a reactor with a fluidized bed, and the second portion of the solids separated in the second separator, return into a cooled zone of the combustion chamber and the pipeline is removed from the cycle, the solids separated in the first separator, according to the invention before dedusting exhaust gas is first passed through a cooled zone with temperature spilivaya at a temperature in the range of 100-700oC, while the exhaust gas away from the separator with a solids content of 5-40 g/Nm3.

The first separator is an electrostatic precipitator, in which the temperature of 100-180oC.

A reactor with a fluidized bed has the grate, while the absorption medium is injected under the grate that is returned from the second separator solids injected under the grate, and water is fed into the reactor with a fluidized bed above the grate.

Into a cooled zone of the combustion chamber enter CaCO3.

As the second separator applied electrostatic precipitator with multiple fields and detachable in the last field of the electrostatic precipitator solids away from the circulation loop.

As the second separator used bag filter, and the filter residue is the content of CaO and/or Ca(OH)2from 2 to 5 wt.%.

Due to the fact that the electrostatic precipitator operates with relatively low performance dedusting, relatively large quantities of particulate matter gets into the circulating fluidized bed, preferably containing CaO or Ca(OH)2. Adelaide only a small fraction of solids and is removed from the circulation circuit as a solid product. This part of the solids consists mostly of dehydrated CaS04and fly ash and CaO. Using this method to achieve the relationship SO2:Ca (released SO2)1: 1,2, and purified gas has more content SO2< 50 mg/Nm3. The electrostatic precipitator has a relatively small power requirement. The product discharged from the electrostatic precipitator, adding water may very well be prosnetsja and used as a building material.

According to the invention, it is also foreseen to replace the electrostatic precipitator inertial separator, in which the exhaust gas containing fly ash, harmful gaseous substances and solid particles that are returned in the cycle, obespylivaetsya at a temperature of 100 - 700oC only until the solids content from 5 to 40 g/Nm3and the absorptive substance harmful gaseous substances is given together with fly ash through the output device of the inertial separator of the circulation circuit of the way. Inertial separator may be preferably made in the form of a cyclone or reflective of the separator. In addition, the inertial separator can be PP>C.

Due to the fact that the inertial separator has a relatively low productivity of dust, a large portion of the solids fall in circulating fluidized bed, preferably containing CaO or Ca(OH)2. This part of the absorption means is fed back to the desulfurization reaction, while in the inertial separator separates only a small portion of the solids and is removed from the circulation circuit of the way as a solid product. This part of the solids consists mostly of anhydrous CaSO4and fly ash and CaO. And when using the inertial separator is provided by the ratio of SO2: Ca (osadovskaya SO2)1 : 1,2, and purified gas there SO2with the content of < 50 mg/Nm3. The product withdrawn from the inertial separator, adding water very hardened and can be used as a building material.

Thus, as the electrostatic precipitator, and an inertial separator used for the removal of the solid product of the way, not containing CaSO3and , therefore, can no longer oxidize additionally, as the product sulfur etc the equipment is if absorption means reaches the average particle diameter d50from 2 to 20 μm. This achieves that the unspent absorption means in the electrostatic precipitator and in the inertial separator is not deposited, and again is supplied in a circulating fluidized bed.

In addition, according to the invention it is proposed that the absorption medium was introduced into a reactor with a fluidized bed below the grate, solid particles returned from the separator, below or above the grate and the water above the grate. Through this complete method reliably prevents the formation of burns, and the fluidity of the particles of solid matter is retained in full.

It is also expedient if the absorption tool CaO and/or Ca(OH)2partially or completely replaced by CaCO3introduced into the area of the combustion chamber having a temperature of from 850 to 1050oC. Due to this can be reduced expenditures on dry desulfurization, with the listed temperatures of CaCO3occurs CaO. By adding CaCO3a reactor with a fluidized bed can work very close to the dew point, but not above it, as if CA is th what is the price of CaCO3significantly lower than that of CaO or Ca(OH)2and absorption of harmful substances in excess of Ca improves.

The method according to the invention both in technological and economic plan is working optimally, if 50 - 80% absorption of the substance replaced by CaCO3.

In addition, according to the invention provides that as a separator for circulating fluidized bed is used, the electrostatic precipitator with multiple fields and that solids are deposited on the last field of the electrostatic precipitator, discharged from the circulation circuit of the way. Due to this event achieved what unburned particles of coal, not saducees in the first precipitator and who therefore, in circulating fluidized bed, are removed from the sweet exhaust gas.

According to the invention, an alternative, it is proposed to use as a circulating fluidized bed separator bag filter, and the filter residue is the content of CaO and/or Ca(OH)2from 2 to ves.%. Due to the alternative implementation of the method provides that the sediment filter has a good degree of purification, as the dust particles in the filter sediment, due to the content C is between the individual cleaning cycles of the bag filter is obtained over a long period of time.

Using the method according to the invention can reliably be achieved with high efficiency desulfurization, if a reactor with a fluidized bed operates at 5 - 20oC above dew point and if the reactor with a fluidized bed sets the velocity of the gas from 3 to 10 m/s, the average processing time solids from 20 to 180 min, and average precipitation of solids from 1 to 10 kg/m3. In such circumstances, the carrying out of the way at high concentrations of SO2in the exhaust gas is reliably observed, the content of SO2in the purified gas < 50 mg/m3. In addition, reliably excluded education of burns and slidenote.

And finally, according to the invention provides that from 90 to 95% of particles of solid substances released in the separator are returned to the reactor with a fluidized bed, while the remaining solid particles enter the combustion chamber. Due to this event ensured that CaSO3obtained by reaction of the absorbent means with SO2due to oxidation in the combustion chamber is formed CaSO4. In addition, CaCO3again it turns out CaO, which is useful for the desulfurization reaction.

The subject invention poasted.

Fine-grained coal is conveyed from the hopper 1 through the pipe 2 into the chamber 3 of the combustion chamber and is burned there with the air supplied into the combustion chamber through the pipeline 4. The combustion chamber 3 is made in the form of a copper, and not shown, the heat exchanger required for heat recovery. Slag receiving the combustion of coal, output from the camera 3 combustion through the pipeline 5. Combustion temperature is from 1200 to 1300oC, therefore, the slag is allocated at least partially in liquid form. As in the upper part of the chamber 3 combustion is made in the form of the boiler, are also heat-exchange surface, where the temperature is less than the combustion temperature. At the entrance to the upper chamber 22 of the boiler flue gas has a temperature of from 850 to 1050oC.

The exhaust gas arising from the combustion of coal, contains the main components of CO2H2O, N2and O2. Since the combustion of coal is carried out with excess oxygen in flue gas CO is present only in trace amounts. The exhaust gas is contaminated, in particular, gaseous compounds SO2HCl and NO. Of sulfur and chlorine compounds contained in coal combustion are formed SO2and HCl. Oxides of nitrogen, about what I nitrogen, contained in the air. The exhaust gas on each Nm3contains 700 mg of SO2, 80 mg HCl 150 mg NO last - in terms of NO2. In the exhaust gas contains, in addition, 20 mg SO3During combustion in the exhaust gas suspendered part of the slag in the form of pulverized fly ash so that the exhaust gas is in the upper chamber 22 of the boiler contents pulverized fly ash, about 10 g/Nm3. Fly ash contains fine-grained, unburned carbon.

On the pipe 6 to the upper chamber 22 of the boiler is served from 5 to 10% solids, which falls on the first field separator 7 made in the form of an electrostatic precipitator is included for reactor 8 fluidized bed. The solid is supplied through the pipe 6, consists of fly ash, as well as from CaSO3that is oxidized in the upper chamber 22 of the boiler, approximately quantitatively to CaSO4from CaCO3from raspodele in the upper chamber 22 of the boiler on CO2and CaO of minor amounts of CaCl2partially disintegrating in the upper chamber 22 of the boiler and unspent CaO and Ca(OH)2and Ca(OH)2in the upper chamber 22 of the boiler turns into CaO. In addition, in line 6 of the storage tank 10 to trouble break up to form CaO. Due to the solids flowing through the pipeline 6, increases the solids content in the exhaust gas flowing from the upper chamber 22 of the boiler, in total, approximately 40 g/Nm3. From the exhaust gas contaminated with harmful gaseous substances, as well as fly ash and particles of solids returned to the cycle, on the surfaces of heat exchangers, located in the upper chamber 22 of the boiler and is not shown in the drawing, is drawn off the heat, and is cooled to 100 - 180oC. At this temperature, cooled exhaust gas flows through the pipe 11 into the electrostatic precipitator 12.

In the electrostatic precipitator 12 is deposited only part of pulverized fly ash and particulate solids so that the pipe 14 from the electrostatic precipitator 12 is diverted flow of exhaust gas, which has a solids content of about 36 g/Nm3that corresponds performance dedusting 10%. The solids removed from the gas stream from the electrostatic precipitator 12 enriched in CaO, while the solid particles deposited in the electrostatic precipitator 12, composed mostly of anhydrous CaSO4and pulverized fly ash. This reaction product is discharged through Truboprovod material. The electrostatic precipitator 12, therefore, has the purpose to separate from the circulation loop absorption medium loaded with harmful gaseous substances, part of pulverized fly ash, while unused absorption means and absorption means, formed in the upper chamber 22 of the boiler are summarized in the circulation loop. This is due to the fact that the electrostatic precipitator 12 operates with relatively low productivity desulfurization, not typical for him.

If the electrostatic precipitator 12 replace the inertial separator, it assumes the removal of the reaction products. The inertial separator is made preferably in the form of a cyclone or reflective of the separator and can be located either in the upper part 22 of the boiler or included after the upper part 22 of the boiler, and it depends only on that of the inertial separator operates in the temperature range from 100 to 700oC. Inertial separator also works with a low productivity of the Department.

This flue gas stream containing solid is supplied through the pipeline 14, is introduced into the reactor 8 fluidized bed below the grate 23. This flow of exhaust gas through the pipeline m3. Above the grate 23, through the pipe 17, into the reactor 8 fluidized bed is supplied from 90 to 95% of particles of solid substances, which are deposited on the first fields of the electrostatic precipitator 7. On line 8, part of the nozzle in the reactor 8 fluidized bed, the water is supplied, so that the reactor 8 fluidized bed is set to a temperature of about 65 - 70oC. This temperature is approximately 15 -20oC above the dew point of the exhaust gas. In the reactor 8 fluidized bed gas velocity is about 3 - 5 m/s, and the average processing time of particles in solids is about 60 minutes Average download solid reactor 8 fluidized bed is about 6 kg/Nm3. Gaseous harmful substances SO2and HCl, for the most part, be contacted in the reactor 8 fluidized bed of fine-grained reactive absorption means. Thanks a cart, according to the invention, particles of solids and water in the reactor 8 fluidized bed prevents burns and sintering of solids is not so great that could cause malfunction.

This flue gas stream containing solids, leaves the reactor 8 with p is Kimi fields. This electrostatic precipitator operates with high performance dust control, allowing the pipeline 20 for purified gas leaves the gas flow is cleaned in an electrostatic precipitator 7, containing dust only < 30 mg/Nm3. The purified gas content SO2< 50 mg/Nm3and the content of HCl <5 mg/Nm3. After the separation NO he without further clean-up activity may be emitted into the atmosphere. Solids deposited on the first fields of cleaning electrostatic precipitator 7, fed by pipes 17a and 17b to the return pipe 17. From 92 to 95% of the solids fed into the return line 17, re-enters the reactor 8 fluidized bed, while the remaining solids are fed via the pipeline 6 into the upper chamber 22 of the boiler. Solid particles deposited on the last precipitator 7, via pipe 21. If these solids have a high carbon content, they can be fed to the combustion chamber 3, in addition, they can be stored in the repository, or be mixed with the products of the method, which are discharged from the electrostatic precipitator 12 through the pipe 13.

1. Method of dry desulfurization of exhaust gas, wherein the exhaust gas, widesystem solids, partially dedust in the first separator (12) solids, then the exhaust gas is sent to the reactor (8) fluidized bed, and to the exhaust gas serves at least one absorption means CaO and/or Ca(OH)2and in the reactor with a fluidized bed by adding water (18) set the temperature of 50 - 90oC, then the exhaust gas containing particulate matter away from the reactor (8) fluidized bed and is directed to the second separator (7) solids, with the first part of the solids separated in the second separator (7), send to the reactor (8) fluidized bed, and the second portion of the solids separated in the second separator (7), return to the cooled zone (22) of the combustion chamber and the pipe (13) is removed from the cycle, the solids separated in the first separator (12), characterized in that before dedusting exhaust gas is first passed through a cooled zone (22) with a temperature of 850 - 1050oC, then the exhaust gas is cooled to a lower temperature and cooled exhaust gas dedust at a temperature in the range 100 - 700oC, while the exhaust gas away from the separator (12) with a solids content of 5-nofilter, in which the temperature of 100 - 180oC.

3. The method according to p. 1, characterized in that the reactor (8) fluidized bed has the grate (23), while the absorption medium is injected under the grate (23) that is returned from the second separator (7) solid substances are injected under the grate, and water is fed into the reactor with a fluidized bed above the grate.

4. The method according to p. 1, characterized in that the cooled zone (22) of the combustion chamber enter CaCO3.

5. The method according to p. 1, characterized in that as the second separator (7) apply an electrostatic precipitator with multiple fields and detachable in the last field electrophile solids away from the circulation loop.

6. The method according to p. 1, characterized in that as the second separator (7) apply the bag filter, and the filter residue is the content of CaO and/or Ca(OH)22 to 5 wt.%.

 

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EFFECT: lowered content of carbon, resin and CO in exhaust gases.

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