Low-heating-value coal pyrolysis combustion staged conversion and quality-divided utilization process based on power generation

Abstract

The invention belongs to the technical field of coal chemical industry, and particularly relates to a low-calorific-value coal pyrolysis combustion staged conversion and quality-divided utilization process based on power generation. In order to comprehensively utilize tar, coal gas and semicoke generated by a low-temperature pyrolysis process, a circulating fluidized bed boiler and a pyrolysis furnace are tightly combined, and joint production of heat, electricity, tar and coal gas is realized in a set of system through a simple and advanced process. And high-quality coal gas and tar are also produced while steam is generated for power generation. Coal gas (pyrolysis gas) contains coal ash, ammonia, tar, hydrogen sulfide, benzene, carbon disulfide and other impurities, the pyrolysis gas needs to be pretreated and purified firstly, namely, after impurities are removed through ammonium sulfate, benzene elution, wet desulfurization and sulfur recovery procedures, the coal gas enters TSA (temperature swing adsorption) for further refined removal of benzene, naphthalene, tar and the like, organic sulfur and inorganic sulfur are removed through a refined desulfurization unit, CO2 is removed through a decarburization unit, and the pyrolysis gas is recycled. Purified pyrolysis gas enters a low-temperature liquefaction separation device (LNG device).

Description

Technical Field

[0001] The invention belongs to the technical field of coal chemical industry, and in particular relates to a process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal based on power generation. Background Art

[0002] Coal pyrolysis is one of the important processes in coal chemical industry. It refers to the process of heating and decomposing coal in air-tight conditions to produce products such as coke, coal tar and coal gas. According to the different final heating temperatures, coal pyrolysis can be divided into three types: 900℃~1100℃ is high-temperature pyrolysis, i.e. coking; 700℃~900℃ is medium-temperature pyrolysis; 500℃~700℃ is low-temperature pyrolysis.

[0003] Low-temperature pyrolysis coal can be low-rank coal with large reserves and high volatile matter. A considerable amount of tar and coal gas can be recovered during the low-temperature pyrolysis process, and the potential advantage of hydrogen in the coal component structure can be utilized. Through pyrolysis, the hydrogen-rich part of the coal is produced as high-quality liquid and gaseous energy or chemical raw materials, so that coal powder and low-quality coal can be reasonably utilized and resources can be effectively utilized. In addition, the low-temperature pyrolysis process is used to first obtain tar, coal gas and clean coal (semi-coke) from coal. How to comprehensively utilize the by-products produced by these low-temperature pyrolysis processes has become a difficult problem that needs to be solved urgently. Summary of the invention

[0004] In view of the above problems, the present invention provides a low calorific value coal pyrolysis combustion graded conversion and quality-based utilization process based on power generation.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A low calorific value coal pyrolysis combustion graded conversion and quality-based utilization process based on power generation, comprising the following steps:

[0007] Step 1, transporting low calorific value coal for power generation to a circulating fluidized bed boiler and a fluidized bed coal pyrolysis furnace respectively, and the fluidized bed coal pyrolysis furnace produces semi-coke and pyrolysis gas;

[0008] Step 2, the semi-coke produced by the fluidized bed coal pyrolysis furnace is transported to a circulating fluidized bed boiler, in which low calorific value coal, air and semi-coke for power generation are burned to produce high-temperature flue gas, which is divided into two paths through a steam-water system, one of which is purified and discharged to meet the standards, and the other is used for power generation; the pyrolysis gas produced by the fluidized bed coal pyrolysis furnace is subjected to pyrolysis gas pretreatment and tar pretreatment to obtain tar and crude pyrolysis gas;

[0009] Step 3, subjecting the crude pyrolysis gas to crude pyrolysis gas pretreatment, wherein the crude pyrolysis gas pretreatment mainly includes an ammonium sulfate process, a benzene elution process, a desulfurization and sulfur recovery process, a fine desulfurization process, a fine desulfurization process and a decarbonization process;

[0010] Step 4, transporting the purified gas from the decarbonization process to the LNG device to prepare LNG and pipeline gas.

[0011] Further, the pyrolysis gas pretreatment is specifically as follows:

[0012] After the pyrolysis gas comes out of the fluidized bed coal pyrolysis furnace, it passes through the first and second level cyclone dust collectors, the coal gas high temperature reheater, the coal gas electrostatic precipitator, and the coal gas waste heat recovery boiler for tar pretreatment.

[0013] Furthermore, the pyrolysis gas pretreatment also includes a coal gas quenching tower, which is arranged before the coal gas waste heat recovery boiler. By spraying, the coal gas quenching tower removes the contained dust while cooling the pyrolysis gas. During the normal operation stage, the coal gas quenching tower is not put into operation and only serves as a high-temperature pyrolysis gas channel.

[0014] Furthermore, the tar pretreatment is specifically as follows:

[0015] The pyrolysis gas after the coal gas waste heat recovery boiler passes through the vertical intercooler and the electric tar collector in turn and then enters the coal gas exhauster, and then is divided into two paths, one is sent back to the fluidized bed coal pyrolysis furnace as a fluidized medium, and the other is directly sent through the coal gas buffer tank for crude pyrolysis gas pretreatment.

[0016] Furthermore, the ammonium sulfate process adopts a wet oxidation desulfurization process of PDS+baked rubber, with PDS+tannin extract as a composite catalyst and soda ash as an alkali source, specifically:

[0017] The pyrolysis gas enters the spray-type ammonium sulfate saturator. In the upper section, the pyrolysis gas is divided into two streams and enters the annular chamber, where it contacts the circulating mother liquor in countercurrent. The ammonia in the gas is absorbed by the sulfuric acid in the mother liquor to generate ammonium sulfate.

[0018] The pyrolysis gas after deammoniation is combined into one stream in the rear chamber of the spray-type ammonium sulfate saturator. After continuous spraying and washing by the small mother liquor circulation pump, it enters the first-stage cyclone acid remover in the spray-type ammonium sulfate saturator along the tangential direction to separate the acid mist entrained in the pyrolysis gas. Then it enters the second-stage acid mist collector outside the spray-type ammonium sulfate saturator to further capture the acid mist entrained in the pyrolysis gas and send it to the benzene elution process.

[0019] Furthermore, the benzene elution step is specifically as follows:

[0020] The pyrolysis gas from the ammonium sulfate process is cooled after heat exchange with the circulating water in the upper section and the cooling water in the lower section in the final cooling tower, and then enters the benzene washing tower from the bottom, and contacts with the circulating washing oil sprayed on the top of the tower from bottom to top in countercurrent. The benzene in the pyrolysis gas is absorbed by the circulating washing oil, and then leaves the benzene washing tower to be sent to the desulfurization and sulfur recovery process after the mist droplets are removed by the mist collection section of the tower.

[0021] Furthermore, the desulfurization and sulfur recovery process is specifically as follows:

[0022] The pyrolysis gas from the benzene elution process passes through the lower part of four series-connected air-spray desulfurization towers and is countercurrently contacted with the desulfurization liquid sprayed on the top to remove part of the hydrogen sulfide. Then, the pyrolysis gas enters the lower part of the turbulent spherical tower and is countercurrently contacted with the desulfurization liquid sprayed from the top of the tower for washing. Then, it enters the lower part of the packed desulfurization tower in series and is countercurrently contacted with the desulfurization liquid sprayed from the top of the tower for washing. After the droplets are removed by the mist capture section, all the gas is sent to the fine desulfurization process.

[0023] Furthermore, the fine desorption process adopts TSA temperature swing adsorption, specifically:

[0024] The pyrolysis gas from the desulfurization and sulfur recovery process is first pressurized by a reciprocating compressor, and then naphthalene and tar are adsorbed by TSA temperature swing adsorption. A multi-tower process is used to remove tar and naphthalene, and then enters the PSA section for benzene removal.

[0025] Furthermore, the fine desulfurization process adopts normal temperature hydrolysis + activated carbon dry process, specifically:

[0026] The pyrolysis gas from the fine desulfurization process, after heat exchange with the product gas in the gas heat exchanger, first enters the hydrolysis desulfurization tank, then is cooled in the hydrolysis gas cooler, and then enters the fine desulfurization tank, and then exchanges heat with the product gas in the gas heat exchanger, and is further heated by the steam heater, and then enters the deoxygenation tank and the dechlorination tank to obtain refined gas. The refined gas recovers heat through the gas heat exchanger, and then is cooled by the water cooler, separated by the gas-liquid separator, and filtered by the gas filter before being sent to the decarbonization process.

[0027] Furthermore, the decarbonization process adopts an active MDEA chemical absorption method to remove CO2 purification process, specifically:

[0028] The pyrolysis gas from the fine desulfurization process is sent to the absorption tower after dust is removed by the filter. The pyrolysis gas enters from the bottom of the absorption tower, and the absorbent active MDEA solution is added from the top of the tower. The pyrolysis gas contacts the active MDEA solution at the top of the tower in the tower, and the purified gas is discharged from the top of the tower. The discharged purified gas is cooled by the top cooler of the absorption tower and then enters the top gas-liquid separator. The purified gas discharged from the upper part of the gas-liquid separator is sent to the secondary booster unit, and the liquid collected at the bottom flows to the rich liquid flash tank for recycling. The rich liquid discharged from the bottom of the absorption tower first enters the rich liquid flash tank, and the flash gas flashed from the top returns to the inlet pipeline of the centrifugal compressor. The rich liquid discharged from the bottom enters the regeneration tower for regeneration after heat exchange with the lean liquid at the bottom of the regeneration tower through the lean-rich liquid heat exchanger. The purified gas enters the LNG device after compression.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1) The circulating fluidized bed boiler and the pyrolysis furnace are closely combined to achieve the combined production of heat, electricity, tar and coal gas in one system through simple and advanced processes. While generating steam for power generation, high-quality coal gas and tar are also produced. The coal gas produced is of high quality and is a high-quality raw material for the production of synthetic natural gas and other chemical products. It can also be used as fuel gas for gas-steam combined cycle power generation. The tar produced can be hydrogenated to produce liquid fuel while extracting high-value chemicals, thereby effectively utilizing various components in coal and realizing the multi-product comprehensive utilization of graded conversion and cascade utilization of coal as raw material.

[0031] 2) Pyrolysis gas (coal gas) contains impurities such as fly ash, ammonia, tar, hydrogen sulfide, benzene, carbon disulfide, etc. It is necessary to pre-treat the pyrolysis gas first, that is, after the impurities are removed through the ammonium sulfate, benzene elution, wet desulfurization and sulfur recovery process, it enters TSA (temperature swing adsorption) for further fine removal of benzene, naphthalene, tar (less than 1mg / Nm 3 ) and then go through the fine desulfurization unit to remove organic sulfur and inorganic sulfur (to a total sulfur content of less than 1 mg / Nm 3 ) and decarbonization units remove CO2 (less than 20PPm), and the purified pyrolysis gas enters the low-temperature liquefaction separation unit (LNG unit). BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of the process of pyrolysis combustion, graded conversion and quality-based utilization of low calorific value coal for power generation;

[0033] Figure 2 Flow chart of pyrolysis combustion staged conversion;

[0034] Figure 3 Flow chart of gas pretreatment and tar pretreatment;

[0035] Figure 4 Flow chart of raw pyrolysis gas pretreatment. DETAILED DESCRIPTION

[0036] In order to further illustrate the technical solution of the present invention, the present invention is further described below through embodiments.

[0037] like Figure 1 As shown, a low calorific value coal pyrolysis combustion graded conversion and quality-based utilization process based on power generation in this embodiment includes the following steps:

[0038] Step 1, transporting low calorific value coal for power generation to a circulating fluidized bed boiler and a fluidized bed coal pyrolysis furnace respectively, and the fluidized bed coal pyrolysis furnace produces semi-coke and pyrolysis gas;

[0039] Step 2, such as Figure 2As shown, the semi-coke produced by the fluidized bed coal pyrolysis furnace is transported to the circulating fluidized bed boiler. In the circulating fluidized bed boiler, the low calorific value coal, air and semi-coke for power generation are burned to produce high-temperature flue gas. The high-temperature flue gas is divided into two paths through the steam-water system, one of which is purified and discharged to meet the standards, and the other is used for power generation. The pyrolysis gas produced by the fluidized bed coal pyrolysis furnace is subjected to pyrolysis gas pretreatment and tar pretreatment to obtain tar and crude pyrolysis gas.

[0040] Step 3, the crude pyrolysis gas is subjected to crude pyrolysis gas pretreatment, and the crude pyrolysis gas pretreatment mainly includes an ammonium sulfate process, a benzene elution process, a desulfurization and sulfur recovery process, a fine desulfurization process, a fine desulfurization process and a decarbonization process (such as Figure 4 shown);

[0041] Step 4, transporting the purified gas from the decarbonization process to the LNG device to prepare LNG and pipeline gas.

[0042] Among them, pyrolysis gas pretreatment:

[0043] After the pyrolysis gas comes out of the fluidized bed coal pyrolysis furnace, it passes through the first and second level cyclone dust collectors, the coal gas high temperature reheater, the coal gas electrostatic precipitator, and the coal gas waste heat recovery boiler for tar pretreatment.

[0044] 1) After the pyrolysis gas (coal gas) comes out of the fluidized bed pyrolysis furnace, it first passes through the first and second level cyclone dust collectors to initially remove the dust in the coal gas. At this time, the fine particle dust in the coal gas is 10g / Nm 3 The temperature of pyrolysis gas is about 600℃. In order to further reduce the dust contained in the coal gas, obtain tar with low ash content and recover waste heat, a coal gas high-temperature electrostatic precipitator is set. A first-level coal gas high-temperature reheater is set between the coal gas electrostatic precipitators to cool the coal gas to about 500℃. The coal gas after preliminary cooling is further removed from the fine ash particles carried by the coal gas in the high-temperature coal gas electrostatic precipitator. The captured fine ash particles can be collected and sent to the furnace for combustion through pneumatic conveying, or they can be collected and sent to the boiler for combustion through the coal feeding device.

[0045] 2) The coal gas after high-temperature dust removal enters the coal gas cooling waste heat recovery boiler. In order to avoid the related problems caused by dusty coal gas entering the coal gas waste heat recovery boiler during the startup phase, a coal gas quenching tower is set up to remove the dust contained in the coal gas while cooling it by spraying. During the normal operation phase, the coal gas quenching tower is not put into operation and is only used as a high-temperature coal gas channel. After the coal gas enters the waste heat recovery boiler, the coal gas is cooled to about 60°C while heating water to generate steam. The tar and condensed water condensed and separated during the coal gas cooling waste heat recovery process are sent to the oil-water separation device.

[0046] Tar pretreatment:

[0047] The pyrolysis gas after the coal gas waste heat recovery boiler passes through the vertical intercooler and the electric tar collector in turn and then enters the coal gas exhauster, and then is divided into two paths, one is sent back to the fluidized bed coal pyrolysis furnace as a fluidized medium, and the other is directly sent through the coal gas buffer tank for crude pyrolysis gas pretreatment.

[0048] 1) The coal gas cooled to about 60℃ by the waste heat recovery boiler is further cooled and dehydrated by the vertical intercooler, so that the outlet temperature is controlled at about 30℃. The indirect cooling process is adopted. The light oil separated by the electric light oil collector is discharged to the light oil tank. In this link, the condensed part of the phenol-containing wastewater and light tar are sent to the oil-water separation device for oil-water separation to obtain the tar product, which is sent to the tar tank in the tank area for storage.

[0049] 2) To further remove the tar mist in the coal gas, the coal gas coming out of the intercooler uses a honeycomb type electric tar collector to remove the light oil in the coal gas. Most of the tar in the coal gas passing through the electric tar collector is collected and sent to the tar tank.

[0050] 3) After the coal gas leaves the electric light oil collector, it enters the coal gas exhauster to boost the pressure to 20kPa, and then is divided into two paths. One path is boosted to 20kPa and sent back to the pyrolysis furnace as a fluidized medium, while the other path directly enters the subsequent crude pyrolysis gas pretreatment through the coal gas buffer tank.

[0051] 4) Treatment of phenol-containing wastewater

[0052] The wastewater generated by gas cooling and tar recovery is sent back to the semi-coke combustion boiler for incineration. Two treatment schemes can be considered: Scheme 1: If the steam generated by gas waste heat recovery can be used for heating, the wastewater is directly sent to the boiler for incineration after atomization. This scheme will increase the amount of coal due to the heat consumption of wastewater evaporation. Scheme 2: The steam generated by gas waste heat recovery is used to evaporate the wastewater into steam through indirect heat exchange and then sent to the semi-coke combustion furnace for incineration. This scheme does not increase the coal consumption of the boiler system. The present invention adopts Scheme 1.

[0053] Gas pretreatment and tar pretreatment are all negative pressure processes. The simplified process is shown in Figure 3 .

[0054] The pyrolysis furnace is a fluidized bed at normal pressure, which is a mature application equipment. The size of the pyrolysis furnace depends on the residence time of the coal in the bed. It is necessary to ensure that the coal in the bed and the high-temperature ash have sufficient heating time and distillation time to allow most of the volatile components in the coal to precipitate. The fluidized bed has a fast heating speed due to the intense mixing, and the distillation time can be greatly shortened, generally about 3 minutes. The present invention designs a pyrolysis furnace of suitable size (170t / h) based on the existing boiler structure, and then calculates the appropriate coal feed amount for a single pyrolysis furnace based on the amount of circulating materials, the operating speed and residence time of the pyrolysis furnace, thereby obtaining the coal gas yield and tar yield.

[0055] The present invention adopts recycled coal gas as the fluidizing medium. After the fluidizing gas absorbs heat in the furnace, it is cooled at the tail, so a certain amount of heat loss will be generated. In order to reduce the amount of fluidizing gas, the fluidizing wind speed is as small as possible under the premise of ensuring good fluidization quality in the bed. In addition, a high-pressure head fluidizing gas is used to increase the height of the pyrolysis furnace bed layer, thereby reducing the air distribution area. The entire furnace body can be designed into two sections, with a small lower part and a large upper part, so as to reduce the gas velocity in the upper part and reduce the entrainment loss in the dilute phase zone. The height of the dilute phase zone is determined by the entrainment separation height and the overall layout of the system.

[0056] In the pyrolysis combustion graded conversion polygeneration process, the high-temperature coal gas produced in the pyrolysis furnace carries a large amount of fine particles. The coal gas after the secondary cyclone dust collector also contains a certain amount of fine particles, with a concentration of 10g / m 3 About. Although wet dust removal and cooling can achieve the process of gas cooling and tar recovery for this kind of high-temperature coal gas containing fine particles, there are problems such as high tar ash content and difficulty in recovering waste heat from coal gas. To solve this problem, a coal gas high-temperature dust collector was tested and applied in a 75t / h bituminous coal circulating fluidized bed thermal power tar cogeneration unit. The coal gas high-temperature dust collector used is designed for a coal gas flow rate of 8000Nm 3 / h, and the designed operating temperature is 500°C. The operating results show that the developed high-temperature coal gas electrostatic precipitator can achieve stable operation, and the dust removal efficiency can reach more than 95%, indicating that the high-temperature coal gas dust removal device has the conditions for industrial application and is used in the present invention.

[0057] Ammonium sulfate process: PDS+baked rubber wet oxidation desulfurization process is used, PDS+tannin extract is used as a composite catalyst, and soda ash is used as an alkali source (KOH). Compared with other catalysts, PDS+tannin extract has a catalytic effect on both desulfurization and regeneration processes (the desulfurization process is fully controlled). Therefore, PDS+tannin extract has higher activity and better fluidity than other catalysts. Specifically:

[0058] 1) Desulfurization unit

[0059] The main reactions of pyrolysis gas in the desulfurization tower are as follows:

[0060] H2S(g)→H2S(l)

[0061] H2S+Na2CO3→NaHS+NaHCO3

[0062] NaHS+NaHCO3+(X-1)S→Na2Sx+CO2+H2O

[0063] The main reactions occurring in the regeneration tower are as follows:

[0064] NaHS+0.5O2→S↓+NaOH

[0065] Na2Sx+0.5O2+H2O→2NaOH+xS↓

[0066] 2) Sulfur recovery

[0067] Using the traditional sulfur preparation process, the sulfur foam produced by the desulfurization regeneration tower flows into the sulfur foam tank from the top of the regeneration tower, and is sent to the molten sulfur kettle after stirring and static sedimentation to produce sulfur for sale.

[0068] 3) Deamination

[0069] This process includes two parts: removing ammonia from pyrolysis gas and drying ammonium sulfate. Sulfuric acid is used as an absorbent, and a spray saturator is used to remove ammonia from pyrolysis gas to generate ammonium sulfate, which is then dried to obtain the ammonium sulfate product. The process is simple and the technology is reliable. The drying process uses a vibrating fluidized bed, which is mature in technology and stable in operation. The drying tail gas uses two-stage dust removal, with a dust removal efficiency of more than 99.5%, achieving basically no waste discharge.

[0070] The pyrolysis gas enters the spray-type ammonium sulfate saturator. In the upper section, the pyrolysis gas is divided into two streams and enters the annular chamber, where it contacts the circulating mother liquor in countercurrent. The ammonia in the gas is absorbed by the sulfuric acid in the mother liquor to generate ammonium sulfate.

[0071] The main reactions occurring in the ammonium sulfate saturator are as follows:

[0072] H2SO4+NH3=NH4HSO4

[0073] H2SO4+2NH3=(NH4)2SO4

[0074] NH4HSO4+NH3=(NH4)2SO4

[0075] The pyrolysis gas after deammoniation is combined into one stream in the rear chamber of the spray-type ammonium sulfate saturator. After continuous spraying and washing by the small mother liquor circulation pump, it enters the first-stage cyclone acid remover in the spray-type ammonium sulfate saturator along the tangential direction to separate the acid mist entrained in the pyrolysis gas. Then it enters the second-stage acid mist collector outside the spray-type ammonium sulfate saturator to further capture the acid mist entrained in the pyrolysis gas and send it to the benzene elution process.

[0076] The mother liquor in the upper part of the lower section of the saturator is continuously pumped out by a large mother liquor circulation pump and sent to the annular spraying chamber in the upper section of the saturator for circulation spraying. The circulating mother liquor after spraying flows to the lower section of the saturator through the central downcomer. In the lower section of the saturator, the crystal nuclei move upward through the saturated medium, causing the crystals to grow and causing grain classification. When the crystal ratio in the ammonium sulfate mother liquor in the lower section of the saturator reaches 25%-40% (v%), the slurry at the bottom is pumped to the indoor crystallization tank by a crystallization pump. The mother liquor overflowing from the full flow port of the saturator flows to the full flow tank by gravity, and then is continuously pumped to the back chamber of the saturator for circulation spraying by a small mother liquor circulation pump to further remove ammonia from the pyrolysis gas.

[0077] When the ammonium sulfate crystals in the indoor crystallization tank accumulate to a certain extent, the ammonium sulfate slurry at the bottom of the crystallization tank is discharged to the ammonium sulfate centrifuge through the sight glass control. After centrifugal separation in the centrifuge, the ammonium sulfate crystals are separated from the ammonium sulfate mother liquor. The ammonium sulfate crystals separated from the centrifuge are first discharged to the screw conveyor through the chute, and then conveyed to the vibrating fluidized bed dryer by the screw conveyor. After drying and cooling, they enter the ammonium sulfate storage hopper. The ammonium sulfate crystals coming out of the ammonium sulfate storage hopper are automatically weighed and packaged and then sent to the finished product warehouse.

[0078] The mother liquor filtered out of the centrifuge and the mother liquor flowing out of the crystallization tank flow back to the lower section of the saturator.

[0079] The dry tail gas from the vibrating fluidized bed dryer is equipped with two-stage dust removal before being discharged into the atmosphere. First, most of the dust entrained in the tail gas is removed by two sets of dry cyclone dust collectors, and then the tail gas is pumped to the tail gas cleaning tower by the tail gas induced draft fan. The tail gas cleaning tower pump circulates liquid to continuously spray the tail gas to further remove the residual dust entrained in the tail gas. Finally, the mist collector removes the droplets entrained in the tail gas before it is discharged into the atmosphere.

[0080] The 92.5% concentrated sulfuric acid required for the saturator of the ammonium sulfate process is regularly transferred from the sulfuric acid storage tank to the sulfuric acid high-level tank, and then added to the saturator system through flow control.

[0081] Benzene elution process: The pyrolysis gas from the ammonium sulfate process is cooled from 55°C to about 25°C after heat exchange with the circulating water in the upper section and the cooling water in the lower section in the final cooling tower. It enters the benzene washing tower from the bottom and contacts with the circulating washing oil sprayed on the top of the tower in countercurrent from bottom to top. The benzene in the pyrolysis gas is absorbed by the circulating washing oil, and then leaves the benzene washing tower to be sent to the desulfurization and sulfur recovery process after the mist droplets are removed by the mist collection section of the tower.

[0082] The rich oil at the bottom of the benzene washing tower is pressurized by the rich oil pump and sent to the lean-rich oil heat exchanger to exchange heat with the hot lean oil coming out of the bottom of the debenzene tower. The rich oil is heated to 160°C and enters the debenzene tower. The crude benzene vapor evaporated from the top of the debenzene tower enters the crude benzene condenser cooler and is cooled to about 30°C by 32°C circulating water and 16°C cooling water, and then enters the crude benzene oil-water separator for separation. The separated crude benzene enters the crude benzene reflux tank, and part of the crude benzene is pumped to the top of the debenzene tower for reflux by the crude benzene reflux pump, and the rest flows into the crude benzene intermediate tank and is pumped to the crude benzene storage tank in the comprehensive tank area by the crude benzene delivery pump. The separated crude benzene separation water is sent to the water seal storage tank of the final cooler.

[0083] The hot lean oil after debenzenization flows out from the bottom of the debenzenization tower and enters the storage tank at the bottom of the debenzenization tower. The hot lean oil flowing out from the bottom of the debenzenization tower is divided into two parts. One part of the hot lean oil enters the lean-rich oil heat exchanger through the lean oil pump to exchange heat with the rich oil, so that its temperature drops to about 80°C, and then enters the lean oil cooler, where it is cooled to about 30°C by 32°C circulating water and 16°C cooling water respectively, and is sent to the benzene washing tower to spray and wash the pyrolysis gas; the other part enters the lean oil circulation pump, and is sent to the lean oil tubular heating furnace for heating after pressurization. The heated lean oil is sent to the debenzenization tower kettle as a heat source.

[0084] The non-condensable gas from the crude benzene condensation cooler is recycled through the crude benzene second-stage cooler. Finally, the non-condensable gas enters the vacuum pump. The non-condensable gas discharged from the vacuum pump is sent to the pyrolysis gas pipeline in front of the benzene washing tower and is not discharged externally.

[0085] The washing oil from the new washing oil tank enters the new washing oil tank to supplement the circulating washing oil.

[0086] The fuel required by the lean oil tubular heating furnace is supplied by the pyrolysis gas after benzene washing and filtering through a filter.

[0087] During the operation of benzene washing and debenzening, the quality of the circulating wash oil gradually deteriorates. In order to ensure the quality of the wash oil, the wash oil section in the middle of the debenzening tower regenerates part of the wash oil. The lean oil in the regeneration section is pressurized by the regeneration circulation pump and heated by the electric heating furnace as the heat source of the regeneration section to regenerate the wash oil. The residual oil residue is transported by the regeneration circulation pump to the outside of the boundary area for unified treatment.

[0088] In order to reduce the naphthalene content in the wash oil, side-line naphthalene is collected at the top of the debenzene tower, and the naphthalene oil flows into the naphthalene extraction liquid tank and is pressed out by steam to the tar tank.

[0089] The final cooling tower is designed with condensate and water spray. During normal production, the condensate is circulated and sprayed to remove naphthalene through the condensate delivery pump. The obtained condensate flows into the final cooler water seal tank, and then into the condensate storage tank. The excess condensate is delivered to the boiler for combustion by the condensate delivery pump.

[0090] Desulfurization and sulfur recovery process: The pyrolysis gas from the benzene stripping process passes through the lower part of four series-connected air-spray desulfurization towers and countercurrently contacts with the desulfurization liquid sprayed from the top. After removing part of the hydrogen sulfide, the pyrolysis gas enters the lower part of the turbulent ball tower and countercurrently contacts with the desulfurization liquid sprayed from the top of the tower for washing. The polypropylene balls in the washing tower are constantly turbulent, thereby increasing the contact area and improving the desulfurization efficiency. Then, the pyrolysis gas enters the lower part of the packed desulfurization tower in series and countercurrently contacts with the desulfurization liquid sprayed from the top of the tower for washing (the desulfurization liquid and the coal gas are completely countercurrent). The H2S content in the coal gas is ≤0.2g / Nm 3 After the mist droplets are removed in the mist collection section, all of them are sent to the fine degassing process.

[0091] The main reactions of pyrolysis gas in the desulfurization tower are as follows:

[0092] H2S(g)→H2S

[0093] H2S+Na2CO3→NaHS+NaHCO3

[0094] NaHS+NaHCO3+(X-1)S→Na2S x +CO2+H2O

[0095] The desulfurized liquid that has absorbed H2S from the air-spray desulfurization tower passes through the desulfurization tower liquid seal tank I to the solution circulation tank I, and is sent to the regeneration tower I through the solution circulation pump I for co-flow regeneration with the compressed air sent from the air compression station. The regenerated desulfurized liquid enters the lean liquid tank I, and the alkali solution from the alkali solution preparation tank and the catalyst supplemented by the catalyst storage tank are added to the lean liquid tank I. The lean liquid is sent to the air-spray desulfurization tower by the lean liquid pump I for recycling.

[0096] The desulfurization liquid that has absorbed H2S from the turbulent spherical tower passes through the liquid seal tank of the turbulent spherical desulfurization tower to the solution circulation tank, and is supplemented with the alkali solution from the alkali solution preparation tank and the catalyst solution supplemented from the catalyst storage tank, and then is pumped to the regeneration tower II by the solution circulation pump II. After the solution and the compressed air sent from the air compressor station are regenerated in parallel, it returns from the upper part of the regeneration tower to the top of the turbulent spherical tower to be sprayed for desulfurization, and is recycled in this way; the desulfurization lean liquid from the regeneration tower II first enters the packed desulfurization tower II, and the desulfurization liquid that has absorbed H2S flows through the liquid seal tank II of the desulfurization tower to the semi-lean liquid tank, and is also supplemented with the alkali solution from the alkali solution preparation tank and the catalyst solution supplemented from the catalyst storage tank, and then is pressurized by the semi-lean liquid pump and enters the packed desulfurization tower I. The desulfurization liquid that has absorbed H2S flows through the liquid seal tank of the desulfurization tower to the rich liquid tank, and is pumped to the regeneration tower II by the rich liquid pump, and the lean liquid regenerated in parallel with the compressed air sent from the air compressor station is returned from the upper part of the tower to the top of the desulfurization tower to be sprayed for desulfurization, and is recycled in this way.

[0097] The main reactions occurring in the regeneration tower are as follows:

[0098] NaHS+0.5O2→S↓+NaOH

[0099] Na2S x +0.5O2+H2O→2NaOH+xS↓

[0100] The sulfur foam produced in the regeneration tower flows into the sulfur foam tank from the expanded part at the top of the regeneration tower, and is sent to the sulfur melting kettle after stirring and settling to produce sulfur for sale. The clear liquid discharged from the sulfur melting kettle enters the solution buffer tank and is pressurized by the buffer tank submersible pump and sent to the solution circulation tank.

[0101] Fine removal process: The content of naphthalene, tar, ammonia, etc. in the pyrolysis gas from the desulfurization and sulfur recovery process cannot meet the intake requirements of the subsequent low-temperature liquefaction and separation of natural gas technology. In order to avoid the condensation of naphthalene, tar and other impurities under low temperature conditions and blockage of the treatment system, it is necessary to finely remove naphthalene, tar, ammonia, etc., and the impurity content is less than 1mg / Nm 3The present invention adopts the mature TSA (temperature swing adsorption) technology, namely dry adsorption to remove impurities. Specifically:

[0102] The pyrolysis gas from the desulfurization and sulfur recovery process contains a small amount of benzene, naphthalene and tar, which can easily cause compressor blockage, and impurities and hydrogen sulfide, hydrocyanic acid, ammonia, organic sulfur, etc. can easily cause subsequent equipment corrosion, so the pyrolysis gas needs to be refined and purified. It is first pressurized to 0.5MPa (G) by a reciprocating compressor, and TSA is used to temperature-swing adsorb naphthalene and tar. A multi-tower process is used to remove tar and naphthalene, and then enters the PSA section to remove benzene.

[0103] The working process of the adsorption tower is roughly as follows:

[0104] a) Adsorption process

[0105] Naphthalene, tar, NH3, H2S and other heavy hydrocarbon impurities in the pyrolysis gas are adsorbed at room temperature, and the purified gas is sent to the pyrolysis gas production LNG device. When the TSA pretreatment tower is saturated with tar and naphthalene, it enters the regeneration process.

[0106] b) Depressurization process

[0107] The pretreatment tower unloads pressure in the opposite direction of adsorption, that is, toward the inlet end, and the gas is discharged to the pipeline network and sent to the boiler system.

[0108] c) Heating to desorb impurities

[0109] The regenerated gas of TSA is heated to 140℃ and then blown through the adsorption layer in the opposite direction of adsorption, so that naphthalene, tar, NH3, H2S and other aromatic compounds can be completely desorbed under heating. The regenerated analytical gas is sent back to the pipeline network and sent to the boiler system.

[0110] d) Cooling the desorbent

[0111] After desorption is completed, stop heating the regeneration gas, and continue to use room temperature regeneration gas to purge the adsorption bed in the opposite direction of the air inlet to cool it to the adsorption temperature. The cooled desorption gas is also sent back to the pipeline network to the boiler system.

[0112] e) Boosting process

[0113] The treated pyrolysis gas is used to pressurize the pretreatment tower to the adsorption pressure in the opposite direction of the adsorption, and the pretreatment tower can now carry out the next round of adsorption.

[0114] Fine desulfurization process: wet desulfurization cannot remove organic sulfur, and the concentration of sulfide after removal is 200mg / Nm 3 Therefore, it is necessary to remove sulfides to meet the sulfur content requirements in LNG raw gas.

[0115] The method of removing hydrogen sulfide or organic sulfur by using solid absorbent or adsorbent is called dry desulfurization. The advantages of this method are that it can remove both hydrogen sulfide and organic sulfur, with high desulfurization efficiency, simple operation, simple equipment and convenient maintenance. However, the sulfur capacity of the desulfurizer used in dry desulfurization (the maximum amount of sulfur that can be removed by the desulfurizer per unit mass or volume) is limited, and regeneration is difficult. The desulfurizer needs to be replaced regularly, which is labor-intensive. Therefore, dry desulfurization is generally used in occasions with low sulfur content and high purification requirements. Therefore, it is generally connected after wet desulfurization as fine desulfurization or removal of organic sulfur in raw gas. At present, the commonly used dry desulfurization methods include cobalt-molybdenum hydrogenation conversion method, zinc oxide method, activated carbon method and iron oxide method.

[0116] Combined with the characteristics of the process parameters after the pyrolysis gas pretreatment of the present invention, the fine desulfurization of the present invention is intended to adopt a room temperature hydrolysis + activated carbon dry process for fine desulfurization to ensure the requirements of the subsequent process on the sulfur content.

[0117] The pyrolysis gas from the fine desulfurization process is heated to 90°C after heat exchange with the product gas in the gas heat exchanger, and first enters the hydrolysis desulfurization tank. Under the action of the catalyst, the COS remaining in the gas is hydrolyzed into H2S, and then adsorbed and removed together with the original residual H2S in the gas. After cooling in the hydrolysis gas cooler, it enters the fine desulfurization tank to remove trace COS and H2S and other organic sulfur and miscellaneous sulfur in the gas. After heat exchange with the product gas in the gas heat exchanger, it is preheated to 90°C, and then further heated to ~150°C by the steam heater. It enters the deoxygenation tank and the dechlorination tank to remove O2 and chlorides respectively to obtain refined gas. The refined gas recovers heat through the gas heat exchanger, and then is cooled by the water cooler, separated by the gas-liquid separator, and filtered by the gas filter. The total sulfur content is removed to less than 1mg / Nm 3 , sent to the decarburization process.

[0118] Decarbonization process: A purification process that uses active MDEA (N-methyldiethanolamine) chemical absorption to remove CO2.

[0119] Active MDEA decarbonization is a gas purification process that uses N-methyldiethanolamine (MDEA) aqueous solution as an absorbent to remove CO2 from industrial gas. This process is more economical than other CO2 removal methods in terms of investment, raw material consumption and utility costs, and is highly competitive and widely used. The characteristics of active MDEA are low absorption of hydrocarbons, no obvious foaming, MDEA resistance to degradation, and low annual solvent consumption.

[0120] The process principle is as follows:

[0121] Since H2S and MDEA can react directly, as shown in the following formula

[0122] H2S+2(R2NCH3)==2R2NCH3H++S2- (1)

[0123] Therefore, the absorption rate of H2S is only limited by the mass transfer rate in the gas phase (i.e., only controlled by the gas film), and the reaction speed is fast. The absorption reaction principle of CO2 and alcohol amine solution is shown in the following formula:

[0124] CO2+H2O==H + +HCO3- (2)

[0125] H + +R2NCH3==R2NCH3H + (3)

[0126] Pure MDEA solution does not react with CO2, but its aqueous solution can react with CO2 according to formula (2). This reaction is the transfer process of gas phase CO2 to liquid phase, which is mainly controlled by the liquid film effect and has a very slow rate. Formula (3) is an instantaneous reversible reaction. Therefore, formula (2) is the control step of MDEA absorbing CO2. In order to speed up the absorption rate, after adding 2-4% of activator R2NH to the MDEA solution, the reaction is carried out as follows:

[0127] R2NH+CO2==R2NCOOH (4)

[0128] R2NCOOH+R2NCH3+H2O==R2NH+R2CH3NH++HCO3- (5)

[0129] Combining equations (4) and (5), we get:

[0130] R2NCH3+CO2+H2O==R2CH3NH + +HCO3- (6)

[0131] From equations (4) to (6), it can be seen that the activator reacts directly with CO2, greatly accelerating the transfer rate of CO2 to the liquid phase, and MDEA is quickly activated and then circulates. The above equations are all reversible reactions, which proceed in reverse under low pressure and high temperature. The MDEA molecule contains a tertiary amine group, and the heat required for heating regeneration is much lower than that of the carbamate generated by primary and secondary amines.

[0132] The pyrolysis gas from the fine desulfurization unit is sent to the absorption tower after dust is removed by the filter. The pyrolysis gas enters the absorption tower from the bottom, and the absorbent active MDEA solution is added from the top. The pyrolysis gas contacts the active MDEA solution at the top of the tower in the tower, and a large amount of CO2 is absorbed by the solution. The purified gas after CO2 removal is discharged from the top of the tower. The CO2 content in the purified gas is ≤20ppm. The discharged purified gas is cooled to 40°C by the top cooler of the absorption tower and then enters the top gas-liquid separator. The purified gas discharged from the upper part of the gas-liquid separator is sent to the secondary booster unit. The liquid collected at the bottom flows to the rich liquid flash tank for recycling. The rich liquid discharged from the bottom of the absorption tower first enters the rich liquid flash tank, and the flash gas flashed from the top returns to the inlet pipeline of the centrifugal compressor. The rich liquid discharged from the bottom is heat exchanged with the lean liquid at the bottom of the regeneration tower by the lean-rich liquid heat exchanger and then enters the regeneration tower for regeneration. The CO2 content in the decarbonized gas is less than 20PPm. The purified gas enters the LNG device after being compressed to 2.38MPa(G).

Claims

1. A process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal based on power generation, characterized in that: The following steps are involved: Step 1, transporting low calorific value coal for power generation to a circulating fluidized bed boiler and a fluidized bed coal pyrolysis furnace respectively, and the fluidized bed coal pyrolysis furnace produces semi-coke and pyrolysis gas; Step 2: The semi-coke produced by the fluidized bed coal pyrolysis furnace is transported to a circulating fluidized bed boiler. In the circulating fluidized bed boiler, the low calorific value coal, air and semi-coke for power generation are burned to produce high-temperature flue gas. The high-temperature flue gas is divided into two paths through a steam-water system. One path is purified and discharged to meet the emission standards, and the other path is used for power generation. The pyrolysis gas generated by the fluidized bed coal pyrolysis furnace is subjected to pyrolysis gas pretreatment and tar pretreatment to obtain tar and crude pyrolysis gas; Step 3, subjecting the crude pyrolysis gas to crude pyrolysis gas pretreatment, wherein the crude pyrolysis gas pretreatment mainly includes an ammonium sulfate process, a benzene elution process, a desulfurization and sulfur recovery process, a fine desulfurization process, a fine desulfurization process and a decarbonization process; Step 4, transporting the purified gas from the decarbonization process to the LNG device to prepare LNG and pipeline gas.

2. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 1 is characterized in that: The pyrolysis gas pretreatment is specifically as follows: After the pyrolysis gas comes out of the fluidized bed coal pyrolysis furnace, it passes through the first and second level cyclone dust collectors, the coal gas high temperature reheater, the coal gas electrostatic precipitator, and the coal gas waste heat recovery boiler for tar pretreatment.

3. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 2 is characterized in that: The pyrolysis gas pretreatment also includes a coal gas quenching tower, which is arranged before the coal gas waste heat recovery boiler. By spraying, the coal gas quenching tower removes the contained dust while cooling the pyrolysis gas. During the normal operation stage, the coal gas quenching tower is not put into operation and only serves as a high-temperature pyrolysis gas channel.

4. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 2 is characterized in that: The tar pretreatment is specifically as follows: The pyrolysis gas after the coal gas waste heat recovery boiler passes through the vertical intercooler and the electric tar collector in turn and then enters the coal gas exhauster, and then is divided into two paths, one is sent back to the fluidized bed coal pyrolysis furnace as a fluidized medium, and the other is directly sent through the coal gas buffer tank for crude pyrolysis gas pretreatment.

5. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 1 is characterized in that: The ammonium sulfate process adopts a PDS+baked rubber wet oxidation desulfurization process, with PDS+tannin extract as a composite catalyst and soda ash as an alkali source, specifically: The pyrolysis gas enters the spray-type ammonium sulfate saturator. In the upper section, the pyrolysis gas is divided into two streams and enters the annular chamber, where it contacts the circulating mother liquor in countercurrent. The ammonia in the gas is absorbed by the sulfuric acid in the mother liquor to generate ammonium sulfate. The pyrolysis gas after deammoniation is combined into one stream in the rear chamber of the spray-type ammonium sulfate saturator. After continuous spraying and washing by the small mother liquor circulation pump, it enters the first-stage cyclone acid remover in the spray-type ammonium sulfate saturator along the tangential direction to separate the acid mist entrained in the pyrolysis gas. Then it enters the second-stage acid mist collector outside the spray-type ammonium sulfate saturator to further capture the acid mist entrained in the pyrolysis gas and send it to the benzene elution process.

6. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 5 is characterized in that: The benzene elution process is specifically as follows: The pyrolysis gas from the ammonium sulfate process is cooled after heat exchange with the circulating water in the upper section and the cooling water in the lower section in the final cooling tower, and then enters the benzene washing tower from the bottom, and contacts with the circulating washing oil sprayed on the top of the tower from bottom to top in countercurrent. The benzene in the pyrolysis gas is absorbed by the circulating washing oil, and then leaves the benzene washing tower to be sent to the desulfurization and sulfur recovery process after the mist droplets are removed by the mist collection section of the tower.

7. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 6 is characterized in that: The desulfurization and sulfur recovery process is specifically as follows: The pyrolysis gas from the benzene elution process passes through the lower part of four series-connected air-spray desulfurization towers and is countercurrently contacted with the desulfurization liquid sprayed on the top to remove part of the hydrogen sulfide. Then, the pyrolysis gas enters the lower part of the turbulent spherical tower and is countercurrently contacted with the desulfurization liquid sprayed from the top of the tower for washing. Then, it enters the lower part of the packed desulfurization tower in series and is countercurrently contacted with the desulfurization liquid sprayed from the top of the tower for washing. After the droplets are removed by the mist capture section, all the gas is sent to the fine desulfurization process.

8. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 7 is characterized in that: The fine desorption process adopts TSA temperature swing adsorption, specifically: The pyrolysis gas from the desulfurization and sulfur recovery process is first pressurized by a reciprocating compressor, and then naphthalene and tar are adsorbed by TSA temperature swing adsorption. A multi-tower process is used to remove tar and naphthalene, and then enters the PSA section for benzene removal.

9. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 8, characterized in that: The fine desulfurization process adopts normal temperature hydrolysis + activated carbon dry process, specifically: The pyrolysis gas from the fine desulfurization process, after heat exchange with the product gas in the gas heat exchanger, first enters the hydrolysis desulfurization tank, then is cooled in the hydrolysis gas cooler, and then enters the fine desulfurization tank, and then exchanges heat with the product gas in the gas heat exchanger, and is further heated by the steam heater, and then enters the deoxygenation tank and the dechlorination tank to obtain refined gas. The refined gas recovers heat through the gas heat exchanger, and then is cooled by the water cooler, separated by the gas-liquid separator, and filtered by the gas filter before being sent to the decarbonization process.

10. The process for pyrolysis, combustion, graded conversion and quality-based utilization of low calorific value coal for power generation according to claim 9, characterized in that: The decarbonization process adopts the active MDEA chemical absorption method to remove CO2 purification process, specifically: The pyrolysis gas from the fine desulfurization process is sent to the absorption tower after dust is removed by the filter. The pyrolysis gas enters from the bottom of the absorption tower, and the absorbent active MDEA solution is added from the top of the tower. The pyrolysis gas contacts the active MDEA solution at the top of the tower in the tower, and the purified gas is discharged from the top of the tower. The discharged purified gas is cooled by the top cooler of the absorption tower and then enters the top gas-liquid separator. The purified gas discharged from the upper part of the gas-liquid separator is sent to the secondary booster unit, and the liquid collected at the bottom flows to the rich liquid flash tank for recycling. The rich liquid discharged from the bottom of the absorption tower first enters the rich liquid flash tank, and the flash gas flashed from the top returns to the inlet pipeline of the centrifugal compressor. The rich liquid discharged from the bottom enters the regeneration tower for regeneration after heat exchange with the lean liquid at the bottom of the regeneration tower through the lean-rich liquid heat exchanger. The purified gas enters the LNG device after compression.

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