A process system for coupling lignite-to-liquid oil to large coal-fired boiler power generation

Abstract

The present application relates to a kind of lignite oil coupling large coal-fired boiler power generation process system, belong to coal energy technical field.The present application is to solve the problem of low overall economic benefit in the process of lignite dry distillation for increasing the yield of coal gas and tar, the energy consumption of required pressurization and heating makes.The present application includes lignite oil sub-system and lignite boiler power generation subsystem;Lignite oil sub-system uses lignite as raw material to prepare kerosene and coal gas, lignite boiler power generation subsystem uses lignite, semi-coke generated by lignite oil sub-system and limestone as raw material for combustion power generation;Lignite oil sub-system and lignite boiler power generation subsystem produce coupling effect through double-helix pyrolysis furnace, screw feeder, back material valve, combustion chamber, cyclone separator and boiler back material pipe, lignite oil sub-system provides semi-coke for lignite boiler power generation subsystem, and lignite boiler power generation subsystem provides high-temperature circulating ash for lignite oil sub-system.The present application is mainly used for preparing kerosene, coal gas and power generation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal energy, and particularly relates to a process system for coupling lignite oil production and large-scale coal-fired boiler power generation. BACKGROUND

[0002] China is rich in coal, poor in oil and gas, and the foreign dependence of oil rose to 73% in 2020. Therefore, it is urgent to save energy, protect the environment, develop new energy and improve the comprehensive utilization rate of energy. Due to the low degree of coalification of lignite, it has high moisture, large pores, high volatile matter, low calorific value and large combustion difficulty. Low-temperature carbonization of lignite at 500-600 DEG C can produce low-temperature tar and produce liquid fuel. Lignite carbonization is the first step of the gasification process. After carbonization, a series of continuous and parallel reactions occur, including the reaction of residual coke and the reaction of gas products in the carbonization stage. During the carbonization stage, the organic matter in the coal changes with the increase of temperature, and the volatile matter escapes from the coal, and the residual coke or semi-coke is left. When lignite with low degree of coalification is carbonized, the yield of coal gas, tar and pyrolysis water is high, the amount of CO and CH4 in the coal gas is large, and the residual carbon has no cohesiveness. The heating conditions such as the final temperature of carbonization, the heating rate and the pressure have an effect on the carbonization process of the coal. Increasing the pressure and the heating rate can increase the yield of coal gas and tar. However, additional pressure and heating consume a certain amount of energy, and the economic benefit is low. SUMMARY

[0003] The technical problem to be solved by the present application is that in the lignite carbonization process, in order to increase the yield of coal gas and tar, the energy consumed by the required pressure and heating makes the overall economic benefit low, and a process system for coupling lignite oil production and large-scale coal-fired boiler power generation is further provided.

[0004] The technical scheme adopted by the present application to solve the above technical problem is:

[0005] A process system for coupling lignite oil production and large-scale coal-fired boiler power generation, comprising a lignite oil production subsystem and a lignite boiler power generation subsystem.

[0006] The lignite oil production subsystem comprises a lignite feeding mechanism, a double-spiral pyrolysis furnace, a raw coal gas separator, an oil residue separator, a kerosene storage chamber, a coal gas storage chamber, a sewage pool and a burner. The discharge port of the lignite feeding mechanism is connected with the feed port of the double-spiral pyrolysis furnace, the exhaust port of the double-spiral pyrolysis furnace is connected with the gas inlet port of the raw coal gas separator, and the gas outlet port of the raw coal gas separator is connected with the gas inlet port of the coal gas storage chamber. The oil residue separator is arranged at the bottom of the raw coal gas separator, and the liquid outlet port of the oil residue separator is connected with the liquid inlet port of the kerosene storage chamber. The burner is installed on the side wall of the double-spiral pyrolysis furnace, and one gas outlet port of the coal gas storage chamber is connected with the gas inlet port of the burner.

[0007] The brown coal boiler electronic system comprises a boiler coal feeding mechanism, a cyclone separator, a boiler back feeding pipe, a combustion chamber, a tail flue, a two-stage superheater, an economizer, a chimney, a limestone bin and a high-pressure fan; the discharge outlet of the limestone bin and the discharge outlet of the double-spiral pyrolysis furnace are connected to the boiler coal feeding mechanism, and the exhaust outlet of the high-pressure fan is connected to the air inlet of the boiler coal feeding mechanism; the discharge outlet of the boiler coal feeding mechanism is in communication with the hearth of the combustion chamber; the exhaust outlet of the combustion chamber is in communication with the air inlet of the cyclone separator, the exhaust outlet of the cyclone separator is in communication with the air inlet of the tail flue, and the exhaust outlet of the tail flue is in communication with the air inlet of the chimney; the two-stage superheater and the economizer are arranged in the tail flue in sequence along the flow direction of the flue gas; the ash discharge outlet of the cyclone separator is in communication with the ash inlet of the boiler coal feeding mechanism, one end of the boiler back feeding pipe is connected to the ash discharge outlet of the cyclone separator, and the other end of the boiler back feeding pipe is connected to the double-spiral pyrolysis furnace.

[0008] Further, the brown coal feeding mechanism comprises a crusher, a screw feeder and a spreader, the discharge outlet of the crusher is in communication with the material inlet of the screw feeder, the discharge outlet of the screw feeder is in communication with the material inlet of the spreader, and the discharge outlet of the spreader is in communication with the material inlet of the double-spiral pyrolysis furnace.

[0009] Further, the brown coal oil production subsystem further comprises a return ash screw feeder, the discharge outlet of the oil residue separator is in communication with the material inlet of the return ash screw feeder, and the discharge outlet of the return ash screw feeder is connected to the side wall of the double-spiral pyrolysis furnace.

[0010] Further, the brown coal oil production subsystem further comprises a coal gas purifier, the gas discharge outlet of the raw coal gas separator is in communication with the gas inlet of the coal gas purifier, and the gas discharge outlet of the coal gas purifier is in communication with the gas inlet of the coal gas storage chamber.

[0011] Further, the brown coal oil production subsystem further comprises a pressurized fan, the gas discharge outlet of the coal gas purifier is in communication with the gas inlet of the pressurized fan, and the gas discharge outlet of the pressurized fan is in communication with the gas inlet of the coal gas storage chamber.

[0012] Further, the boiler coal feeding mechanism comprises a screw feeder, a raw material bin, a belt metering coal feeder and a back feeding valve; the discharge outlet of the raw material bin is in communication with the material inlet of the belt metering coal feeder, the discharge outlet of the belt metering coal feeder is in communication with one material inlet of the back feeding valve; the discharge outlet of the double-spiral pyrolysis furnace is in communication with the material inlet of the screw feeder, the discharge outlet of the screw feeder is in communication with the other material inlet of the back feeding valve; the discharge outlet of the limestone bin is in communication with the other material inlet of the back feeding valve; the discharge outlet of the back feeding valve is in communication with the hearth of the combustion chamber, the exhaust outlet of the high-pressure fan is connected to the air inlet of the back feeding valve; and the ash discharge outlet of the cyclone separator is in communication with the ash inlet of the back feeding valve.

[0013] Further, the lignite boiler power generation system further comprises an air preheater, and the exhaust port of the tail flue is communicated with the smoke inlet of the air preheater.

[0014] Further, the lignite boiler power generation system further comprises a dust collector, the smoke outlet of the air preheater is communicated with the smoke inlet of the dust collector, and the smoke outlet of the dust collector is communicated with the smoke inlet of the chimney.

[0015] Further, the lignite accounted for 5% to 40% of the total amount is input into the lignite oil production subsystem, and the lignite accounted for 60% to 95% of the total amount is input into the lignite boiler power generation system.

[0016] Compared with the prior art, the lignite oil production system has the following beneficial effects:

[0017] 1. The heat required by the double-spiral pyrolysis furnace in the lignite oil production subsystem is partly provided by the fly ash of the lignite boiler power generation system and partly provided by the combustion of the coal gas generated by the double-spiral pyrolysis furnace, so that the heat is not required to be provided from outside, and the energy consumption is reduced.

[0018] 2. The semi-coke generated in the lignite oil production subsystem is used as part of the fuel of the lignite boiler power generation system, so that the waste of energy is avoided.

[0019] 3. The lignite oil production coupled with the coal boiler power generation process realizes the cogeneration of lignite oil production, gas production and power generation, develops the source of supplementary oil resources and improves the comprehensive utilization rate of energy, effectively realizes the comprehensive utilization of lignite, and has a good development prospect. DETAILED DESCRIPTION

[0020] The accompanying drawings are part of the present application and serve to provide a further understanding of the present application, the schematic embodiments of the present application and the description thereof serve to explain the present application, but do not constitute an improper limitation on the present application.

[0021] Figure 1 It is a schematic diagram of the whole structure of the present application.

[0022] The reference signs are explained as follows: 1, crusher; 2, screw feeder; 3, spreader; 4, double-spiral pyrolysis furnace; 5, raw coal gas separator; 6, oil residue separator; 7, kerosene storage room; 8, coal gas purifier; 9, pressure fan; 10, coal gas storage room; 11, sewage pool; 12, screw feeder; 13, cyclone separator; 14, boiler return pipe; 15, return valve; 17, combustion chamber; 18, tail flue; 19, superheater; 20, limestone bin; 21, coal economizer; 22, air preheater; 23, dust collector; 24, chimney; 25, high-pressure fan; 26, burner; 27, fly ash screw feeder; 28, raw material bin; and 29, belt metering coal feeder. DETAILED DESCRIPTION

[0023] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments will be described clearly and completely below with reference to the drawings in the embodiments of the present application. The following embodiments are used to explain the present application but not to limit the scope of the present application.

[0024] Referring to Figure 1 The present application provides a process system for coupling lignite oil production and large coal-fired boiler power generation, which comprises a lignite oil production subsystem and a lignite boiler power generation subsystem.

[0025] The lignite oil production subsystem comprises a crusher 1, a screw feeder 2, a spreader 3, a double-screw pyrolysis furnace 4, a raw coal gas separator 5, an oil residue separator 6, a kerosene storage chamber 7, a coal gas purifier 8, a pressurizing fan 9, a coal gas storage chamber 10, a sewage pool 11, a burner 26 and a fly ash return screw feeder 27. The discharge port of the crusher 1 is communicated with the feed port of the screw feeder 2, the discharge port of the screw feeder 2 is communicated with the feed port of the spreader 3, and the discharge port of the spreader 3 is communicated with the feed port of the double-screw pyrolysis furnace 4. The exhaust port of the double-screw pyrolysis furnace 4 is communicated with the gas inlet of the raw coal gas separator 5, the gas outlet of the raw coal gas separator 5 is communicated with the gas inlet of the coal gas purifier 8, the gas outlet of the coal gas purifier 8 is communicated with the gas inlet of the pressurizing fan 9, and the gas outlet of the pressurizing fan 9 is communicated with the gas inlet of the coal gas storage chamber 10. The oil residue separator 6 is arranged at the bottom of the raw coal gas separator 5, the liquid outlet of the oil residue separator 6 is communicated with the liquid inlet of the kerosene storage chamber 7, the discharge port of the oil residue separator 6 is communicated with the feed port of the fly ash return screw feeder 27, and the discharge port of the fly ash return screw feeder 27 is connected to the side wall of the double-screw pyrolysis furnace 4. The burner 26 is installed on the side wall of the double-screw pyrolysis furnace 4, one gas outlet of the coal gas storage chamber 10 is communicated with the gas inlet of the burner 26, and the coal gas storage chamber 10 also supplies gas to the gas user.

[0026] The lignite boiler power generation system comprises a screw feeder 12, a cyclone separator 13, a boiler return pipe 14, a return valve 15, a combustion chamber 17, a tail flue 18, a two-stage superheater 19, a limestone bin 20, an economizer 21, an air preheater 22, a dust collector 23, a chimney 24, a high-pressure fan 25, a raw material bin 28 and a belt metering coal feeder 29; the discharge port of the raw material bin 28 is connected with the feeding port of the belt metering coal feeder 29, the discharge port of the belt metering coal feeder 29 is connected with one feeding port of the return valve 15; the discharge port of the double-screw pyrolysis furnace 4 is connected with another feeding port of the return valve 15 through the screw feeder 12; the discharge port of the limestone bin 20 is connected with another feeding port of the return valve 15; the discharge port of the return valve 15 is connected with the furnace of the combustion chamber 17; the smoke outlet of the combustion chamber 17 is connected with the smoke inlet of the cyclone separator 13, the smoke outlet of the cyclone separator 13 is connected with the smoke inlet of the tail flue 18, the smoke outlet of the tail flue 18 is connected with the smoke inlet of the air preheater 22, the smoke outlet of the air preheater 22 is connected with the smoke inlet of the dust collector 23, and the smoke outlet of the dust collector 23 is connected with the smoke inlet of the chimney 24; the two-stage superheater 19 and the economizer 21 are arranged in the tail flue 18 in sequence along the flow direction of the flue gas; the ash outlet of the cyclone separator 13 is connected with the ash inlet of the return valve 15, and the exhaust port of the high-pressure fan 25 is connected with the air inlet of the return valve 15; one end of the boiler return pipe 14 is connected with the ash outlet of the cyclone separator 13, and the other end of the boiler return pipe 14 is connected with the double-screw pyrolysis furnace 4.

[0027] In the embodiment, the lignite oil production subsystem uses lignite as raw material to produce kerosene and gas, and the lignite boiler power generation system uses lignite, semi-coke produced by the lignite oil production subsystem and limestone as raw material to generate electricity; the lignite oil production subsystem and the lignite boiler power generation system are coupled through the double-screw pyrolysis furnace 4, the screw feeder 12, the return valve 15, the combustion chamber 17, the cyclone separator 13 and the boiler return pipe 14 to form a large cycle, the lignite oil production subsystem provides semi-coke and heat solid carrier for the lignite boiler power generation system, and the lignite boiler power generation system provides high-temperature circulating ash for the lignite oil production subsystem.

[0028] In the embodiment, the raw material bin 28, the belt metering coal feeder 29 and the return valve 15 constitute the boiler coal feeding mechanism of the lignite boiler power generation system.

[0029] The working processes of the lignite oil production subsystem and the lignite boiler power generation system will be described in detail below to express the advantages of the present application.

[0030] The working process of the lignite oil production subsystem is as follows:

[0031] Step 1, according to the lignite power unit coal consumption and lignite oil subsystem output, 5% to 40% of lignite is sent to the crusher 1 for crushing, the crushed lignite enters the coal hopper, and then is sent to the double screw pyrolysis furnace 4 through the screw feeder 2 and the spreader 3 in turn for pyrolysis;

[0032] Step 2, hot solid carrier is added to the double screw pyrolysis furnace 4, the temperature in the double screw pyrolysis furnace 4 is controlled in the range of 470℃ to 590℃ to realize the pyrolysis of lignite, the lignite is mixed and heated with the hot solid carrier in the double screw pyrolysis furnace 4, and is pyrolyzed by low-temperature dry distillation to produce raw coal gas and semi-coke;

[0033] Step 3, the raw coal gas produced by the double screw pyrolysis furnace 4 enters the raw coal gas separator 5 for gas and oil separation; the semi-coke and part of the hot solid carrier produced by the double screw pyrolysis furnace 4 pass through the screw feeder 12 and the return valve 15 in turn and are sent to the hearth of the combustion chamber 17 for combustion and heat release;

[0034] Step 4, cooling water is introduced into the raw coal gas separator 5, and the raw coal gas is cooled by the cooling water to produce coal gas, kerosene and ash residue in the raw coal gas separator 5;

[0035] Step 5, the coal gas produced by the raw coal gas separator 5 is sent to the coal gas purifier 8 for purification, the purified coal gas is stored in the coal gas storage room 10 under the action of the pressure fan 9, and the sewage produced by the coal gas purifier 8 is sent to the sewage pool 11; part of the coal gas in the coal gas storage room 10 is sent to the burner 26 for combustion to provide heat for the double screw pyrolysis furnace 4, and the other part of the coal gas is used by the coal gas user;

[0036] Step 6, the kerosene and ash residue produced by the raw coal gas separator 5 enter the oil residue separator 6 at the bottom, after the separation of the oil residue separator 6, the separated kerosene is sent to the kerosene storage room 7 for user use; the separated ash residue is sent back to the double screw pyrolysis furnace 4 through the ash lock and the ash return screw feeder 27, and then is sent to the hearth of the combustion chamber 17 through the screw feeder 12 and the return valve 15 for combustion and heat release, and the double screw pyrolysis furnace 4, the raw coal gas separator 5 and the oil residue separator 6 form a small cycle.

[0037] The working process of the lignite boiler power generation system is as follows:

[0038] Step 1, the remaining 60% to 95% of the lignite is crushed, and the crushed lignite is quantitatively conveyed to the chain coal feeder by the belt metering coal feeder 29, and then is conveyed to the return valve 15 by the chain coal feeder;

[0039] Step 2, the semi-coke and part of the hot solid carrier produced by the double screw pyrolysis furnace 4 are sent to the return valve 15 through the screw feeder 12;

[0040] Step 3, the limestone is sent into the return valve 15 from the limestone powder bin by pneumatic conveying;

[0041] Step 4, the lignite, semi-coke and limestone are mixed in the return valve 15 to achieve uniform distribution of the fuel; a large amount of circulating material is sent into the furnace of the combustion chamber 17 through the return leg of the return valve 15;

[0042] Step 5, the bed material is added to the boiler by the bed material adding system, and the ignition is started by the on-bed, under-bed or combined on-bed and under-bed starting mode;

[0043] Step 6, the lignite and the material are mixed and combusted in the furnace of the boiler to release heat, the high-temperature flue gas generated is cooled by the water-cooled wall, and the temperature of the flue gas is reduced; most of the fly ash carried by the flue gas enters the cyclone separator 13, and after the separation of the cyclone separator 13, part of the fly ash enters the double-spiral pyrolysis furnace 4 through the boiler return pipe 14, and the other part of the fly ash returns to the furnace of the combustion chamber 17 through the return valve 15;

[0044] Step 7, the flue gas enters the tail flue 18, and after the heat exchange of the two-stage superheater 19 and the economizer 21, the flue gas enters the air preheater 22; after the heat exchange between the flue gas and the cold air introduced into the air preheater 22, the temperature of the flue gas is further reduced, and after the dust removal of the dust remover 23, the flue gas enters the chimney 24 through the induced draft fan and is discharged into the atmosphere after meeting the emission conditions; the air preheated in the air preheater 22 enters the furnace of the combustion chamber 17 to provide oxygen;

[0045] Step 8, the cold slag device is arranged below the combustion chamber 17, and the low slag temperature is reduced to below 150℃ at the outlet of the cold slag device, and the discharged slag is collected by the conveying system.

[0046] In this embodiment, the semi-coke and part of the hot solid carrier generated by the double-spiral pyrolysis furnace 4 and the ash generated by the raw gas separator 5 are sent into the combustion chamber for combustion, the boiler burns the semi-coke, reduces the energy waste, and does not need to make substantial changes to the structure of the circulating fluidized bed boiler; only the furnace, various stages of the heating surface, the ignition burner, the air preheater and the economizer need to be designed or modified, thereby saving the equipment investment cost; and the lignite-to-oil subsystem does not set up a slag discharge part, and the lignite-to-oil subsystem discharges the slag through the lignite boiler subsystem, thereby reducing the investment and maintenance of part of the equipment and increasing the overall economic benefit.

[0047] In this embodiment, the lignite boiler subsystem provides high-temperature circulating ash for the lignite-to-oil subsystem, increases the temperature of the double-spiral pyrolysis furnace 4, and is beneficial to the pyrolysis of the lignite, and further beneficial to the generation of the coal gas and the kerosene.

[0048] While the application has been described with reference to particular embodiments thereof, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present application. It will be apparent to those skilled in the art that numerous modifications can be made within the scope of the present application as defined by the appended claims. It is intended that all such modification fall within the spirit and scope of the present application. It will be understood that the features described in connection with one embodiment can be used in connection with another embodiment.

Claims

1. A process system for lignite-to-oil conversion coupled with large-scale coal-fired boiler power generation, characterized in that: It includes lignite oil sub-system and lignite boiler sub-system; The lignite oil sub-system comprises a lignite feeding mechanism, a double-spiral pyrolysis furnace (4), a raw coal gas separator (5), an oil residue separator (6), a kerosene storage chamber (7), a coal gas storage chamber (10), a sewage pool (11) and a burner (26); the discharge port of the lignite feeding mechanism is connected with the feeding port of the double-spiral pyrolysis furnace (4), the exhaust port of the double-spiral pyrolysis furnace (4) is communicated with the gas inlet of the raw coal gas separator (5), and the gas outlet of the raw coal gas separator (5) is connected with the gas inlet of the coal gas storage chamber (10); the oil residue separator (6) is arranged at the bottom of the raw coal gas separator (5), and the liquid outlet of the oil residue separator (6) is connected with the liquid inlet of the kerosene storage chamber (7); the burner (26) is installed on the side wall of the double-spiral pyrolysis furnace (4), and one gas outlet of the coal gas storage chamber (10) is connected with the gas inlet of the burner (26). The lignite boiler sub-system comprises a boiler coal feeding mechanism, a cyclone separator (13), a boiler back feeding pipe (14), a combustion chamber (17), a tail flue (18), a two-stage superheater (19), an economizer (21), a chimney (24), a limestone bin (20) and a high-pressure fan (25); the discharge port of the limestone bin (20) and the discharge port of the double-spiral pyrolysis furnace (4) are connected with the boiler coal feeding mechanism, and the exhaust port of the high-pressure fan (25) is connected with the gas inlet of the boiler coal feeding mechanism; the discharge port of the boiler coal feeding mechanism is connected with the hearth of the combustion chamber (17); the exhaust port of the combustion chamber (17) is connected with the gas inlet of the cyclone separator (13), the exhaust port of the cyclone separator (13) is connected with the gas inlet of the tail flue (18), and the exhaust port of the tail flue (18) is connected with the gas inlet of the chimney (24); the two-stage superheater (19) and the economizer (21) are arranged in the tail flue (18) in sequence along the flow direction of the flue gas; the ash outlet of the cyclone separator (13) is connected with the ash inlet of the boiler coal feeding mechanism, one end of the boiler back feeding pipe (14) is connected with the ash outlet of the cyclone separator (13), and the other end of the boiler back feeding pipe (14) is connected with the double-spiral pyrolysis furnace (4); the lignite oil sub-system further comprises a dust returning spiral feeder (27), the discharge port of the oil residue separator (6) is connected with the feeding port of the dust returning spiral feeder (27), and the discharge port of the dust returning spiral feeder (27) is connected with the side wall of the double-spiral pyrolysis furnace (4).

2. The process system for lignite-to-liquid coupled with large coal-fired boiler power generation according to claim 1, characterized in that: The lignite feeding mechanism comprises a crusher (1), a screw feeder (2) and a spreader (3), the discharge port of the crusher (1) is communicated with the feeding port of the screw feeder (2), the discharge port of the screw feeder (2) is communicated with the feeding port of the spreader (3), and the discharge port of the spreader (3) is communicated with the feeding port of the double-spiral pyrolysis furnace (4).

3. The process system for lignite-to-liquid coupled with large coal-fired boiler power generation according to claim 1, characterized in that: The lignite-to-oil subsystem further comprises a coal gas purifier (8), the gas outlet of the coal gas separator (5) is connected with the gas inlet of the coal gas purifier (8), and the gas outlet of the coal gas purifier (8) is connected with the gas inlet of the coal gas storage chamber (10).

4. The process system for lignite-to-liquid coupled with large coal-fired boiler power generation according to claim 3, characterized in that: The lignite-to-oil subsystem further comprises a pressurized air blower (9), the gas outlet of the coal gas purifier (8) is connected with the gas inlet of the pressurized air blower (9), and the gas outlet of the pressurized air blower (9) is connected with the gas inlet of the coal gas storage chamber (10).

5. The process system for lignite-to-liquid coupled with large coal-fired boiler power generation according to claim 1, characterized in that: The coal feeding mechanism of the boiler comprises a screw feeder (12), a raw material bin (28), a belt metering coal feeder (29) and a return valve (15); the discharge port of the raw material bin (28) is connected with the feeding port of the belt metering coal feeder (29), and the discharge port of the belt metering coal feeder (29) is connected with one feeding port of the return valve (15); the discharge port of the double-screw pyrolysis furnace (4) is connected with the feeding port of the screw feeder (12), and the discharge port of the screw feeder (12) is connected with the other feeding port of the return valve (15); the discharge port of the limestone bin (20) is connected with the other feeding port of the return valve (15); the discharge port of the return valve (15) is connected with the furnace of the combustion chamber (17), and the exhaust port of the high-pressure air blower (25) is connected with the gas inlet of the return valve (15); the ash discharge port of the cyclone separator (13) is connected with the ash inlet of the return valve (15).

6. The process system for lignite-to-liquid coupled with large coal-fired boiler power generation according to claim 1, characterized in that: The lignite boiler subsystem further comprises an air preheater (22), and the exhaust port of the tail flue (18) is connected with the smoke inlet of the air preheater (22).

7. The process system for lignite-to-liquid coupled with large coal-fired boiler power generation according to claim 6, characterized in that: The lignite boiler subsystem further comprises a dust collector (23), and the exhaust port of the air preheater (22) is connected with the smoke inlet of the dust collector (23), and the exhaust port of the dust collector (23) is connected with the smoke inlet of the chimney (24).

8. The process system for lignite-to-liquid coupled with large coal-fired boiler power generation according to claim 1, characterized in that: The lignite input into the lignite-to-oil subsystem accounts for 5% to 40% of the total amount, and the lignite input into the lignite boiler subsystem accounts for 60% to 95% of the total amount.

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