Energy-saving method and system for deep utilization of low-temperature waste heat in the whole system of cogeneration device

Abstract

The present invention provides an energy-saving method and system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device, including a cogeneration device, a C4 aromatics combined device, and an ethylene cracking device. The desalted water heated by the slag cooler of the CFB boiler is sequentially heat-exchanged with the top gas phase of the extraction tower in the boundary area of ​​the aromatics extraction device, the desalted water after heat exchange from the low-temperature economizer of the CFB boiler, and the exhaust gas of the CFB boiler, and then sent to the high-pressure deaerator of the cogeneration device for deoxidation; the quenching water supplied by the ethylene cracking device is heat-exchanged with the low-temperature air preheater of the CFB boiler in the boundary area of ​​the cogeneration device, so that the air in the intake port is heated and enters the large public air duct of the CFB boiler; then it is divided into two routes to enter the primary air heating system and secondary air heating system of the CFB boiler respectively, and heat-exchanges with the exhaust steam of the deaerator, the boiler water, etc., and the heated hot primary air and hot secondary air are introduced into the furnace for fluidization and combustion. The deep utilization of low-temperature waste heat of the whole system is realized, the exhaust temperature, the internal consumption of system steam, and the coal consumption are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of deep utilization of waste heat and energy saving in the whole system of a cogeneration device of a chemical enterprise, and specifically provides an energy-saving method and system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device. Background Art

[0002] At present, the chemical enterprise has built 3×360t / h ultra-high pressure circulating fluidized bed boilers (12.5MPa), 2×65MW double-extraction condensing steam turbine generator sets, and 1×160t / h medium-pressure gas boiler (2.45MPa 310℃), which are equipped with environmental protection facilities such as desulfurization, denitrification, and dust removal. Among them, 1#, 2# and 3# boilers are 360t / h ultra-high pressure circulating fluidized bed boilers, and 4# boiler is a 300t / h medium-pressure gas auxiliary boiler.

[0003] The cogeneration unit has an ultra-high pressure circulating fluidized bed boiler, steam turbine and chemical water system. The desalted water provided by the chemical water in the steam-water system passes through a low-pressure heater, a deaerator and a high-pressure heater respectively. The desalted water heated to a qualified temperature enters the economizer, a steam drum and a superheater to produce qualified ultra-high pressure steam. The overall energy level has a large room for development. The smoke and air system draws cold air in through the primary and secondary fans, and after being gradually heated by the heater and the air preheater at the tail end of the flue, it enters the furnace of the ultra-high pressure circulating fluidized bed boiler for fluidization and combustion. The smoke exhaust loss after combustion is relatively large.

[0004] The heat of the top gas phase of the stripping tower (C-630) in the aromatics extraction unit of the C4 aromatics complex is removed by the method of "air cooling + circulating water cooler". The air cooling consumes electricity, and the circulating water cooler consumes circulating water, and the heat at the top of the tower is not effectively utilized.

[0005] At present, ethylene cracking circulates about 4,500 tons of quench water per hour, and some condensed quench water and cracking gasoline enter the quench water settling tank. After the quench water is separated, it passes through the process stripping tower. The hydrocarbon gas is stripped out from the top of the tower to exchange heat with the quench oil to produce dilution steam. The heat is not effectively utilized.

[0006] Based on the current status of energy level utilization in thermal power and chemical plant systems, there is an urgent need to provide an energy-saving method and system for realizing deep utilization of low-temperature waste heat in the entire system of cogeneration equipment, so as to maximize energy recovery, reduce coal consumption, and achieve the goal of energy conservation and emission reduction. Summary of the invention

[0007] The present invention proposes an energy-saving method and system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device. On the one hand, waste heat such as sewage and exhaust steam in the quenching water system of an ethylene device and the steam-water system of a cogeneration device is used to heat the inlet air temperature of a primary fan and a secondary fan of a boiler, and the "exergy value conversion" is cleverly solved at the air preheater of the flue at the rear of the boiler, so that a low-quality heat source is converted into a high-quality heat source; on the other hand, the desalted water after heating in a slag cooler is heat-exchanged with steam at the top of an aromatic stripping tower to recover low-quality thermal energy that cannot be effectively utilized by a chemical device, and heat energy is recovered and steam consumption and coal consumption are reduced at the low-temperature economizer of the boiler, thereby achieving the technical problem of energy saving and emission reduction.

[0008] The present invention is achieved by the following technical solutions:

[0009] The present invention provides an energy-saving method for deep utilization of low-temperature waste heat in the whole system of a cogeneration device, comprising an ultra-high pressure circulating fluidized bed boiler of the cogeneration device, hereinafter referred to as a CFB boiler, a steam turbine generator unit and a chemical water system, an extraction tower of an aromatics extraction device C-603 of a C4 aromatics combined device in a chemical device, hereinafter referred to as an extraction tower, and an ethylene cracking device, characterized in that desalted water 29 heated by a slag cooler from the CFB boiler is transported to a desalted water heat exchanger 31 of the extraction tower within a boundary 30 of the aromatics extraction device to exchange heat with an incoming heat medium 32, the heat medium 32 coming from the gas phase at the top of the extraction tower, the heat medium 32 being cooled to become a cold medium 33 after heat exchange and discharged back to the extraction tower, the desalted water 29 heated by the slag cooler of the CFB boiler, The heated desalted water 35 is heated to about 70°C by heat exchange at 50°C; then it is transported to the boundary area 34 of the cogeneration device, mixed with the drain tank drain 36 from the cogeneration device to form the desalted water 37 before the feed water heater heat exchange, enters the feed water heater 38 of the cogeneration device, continues to exchange heat with the entering secondary non-adjustable extraction steam 40 from the steam turbine, and the desalted water 39 after heat exchange with the feed water heater is heated to 70-90°C, and then it is sent to the low-temperature economizer 27 of the CFB boiler for further heat exchange and heating, and the desalted water 42 after heat exchange with the low-temperature economizer is heated from 70-90°C to about 120°C, and then sent to the high-pressure deaerator 43 of the cogeneration device to reduce the steam consumption of the high-pressure deaerator 43, and the exhaust steam 13 discharged from the high-pressure deaerator 43 is returned to the drain tank 14 for reuse after the waste heat is utilized;

[0010] The quench water 300t / h1 with a temperature of 80℃ supplied from the outlet main pipe of the quench water pump of the ethylene cracking unit is led to the total water inlet of the low-temperature air preheater 4 of the CFB boiler in the boundary area 3 of the cogeneration unit, and is heated by heat exchange with the air 5 at the inlet of the main air inlet pipeline of the low-temperature air preheater 4 to return to the ethylene cracking unit as the return quench water 2. The temperature of the air 5 at the inlet is increased from the normal temperature of 25℃ to the first-level hot air 6 of 55℃, and then enters the large public air duct 7 of the CFB boiler through the exhaust main pipeline; after that, it is divided into two routes to output the first-level hot primary air 8 and the first-level hot secondary air 15, of which After the first-level hot primary air 8 enters the primary air heating system M of the CFB boiler connected to the large common air duct 7 of the CFB boiler, and the first-level hot secondary air 15 enters the secondary air heating system N of the CFB boiler connected to the large common air duct 7 of the CFB boiler, first, the first-level hot primary air 8 is compressed and heated by the primary fan 9 of the CFB boiler, and the output temperature reaches 10-20°C. The first-level hot secondary air 15 is compressed and heated by the secondary fan 16 of the CFB boiler, and the temperature rise reaches 10-20°C. 7, the secondary hot primary air 10 enters the heater 11 of the primary fan for heat exchange and heating, and then outputs the tertiary hot primary air 12 at 75-90°C, and the secondary hot secondary air 17 enters the heater 18 of the secondary fan for heat exchange and heating, and then outputs the tertiary hot secondary air 19 at 75-90°C, and the tertiary hot primary air 12 and the tertiary hot secondary air 19 are then introduced into the air preheater 23 of the tail flue of the CFB boiler for heat exchange and heating with the high-temperature flue gas 25 of the tail flue, and energy conversion is realized in the air preheater, and the temperature of the flue gas 26 after heat exchange in the air preheater reaches 160-170°C, and the air The flue gas 26 discharged from the air preheater 23 after heat exchange enters the low-temperature economizer 27, and after heat exchange, the flue gas temperature is reduced to the low-temperature flue gas 28 of about 95°C, and the desalted water 39 after heat exchange by the make-up water heater is heated by the waste heat of the flue gas temperature to output the desalted water 42 after heat exchange by the low-temperature economizer. The low-temperature economizer 27 is set in the flue between the air preheater and the electric bag integrated dust collector; finally, the hot primary air and hot secondary air after heat exchange are introduced into the furnace 24 for fluidization and combustion; the air preheater 23 is located in the tail flue 22 of the CFB boiler;

[0011] The deaerator exhaust steam 13 discharged from the high-pressure deaerator 43 of the cogeneration unit or the boiler continuous drainage 20 of the CFB boiler are respectively introduced into the heater 11 of the primary fan and the heater 18 of the secondary fan for heat exchange, so as to increase the wind temperature of the hot primary air and the hot secondary air by 10-20°C, and realize secondary heating in series with the front-end low-temperature air preheater 4; the deaerator exhaust steam 13 after heat exchange condenses into the drain tank 14; the boiler continuous drainage 20 is discharged to the fixed discharge 21.

[0012] The present invention discloses an energy-saving system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device, comprising an ultra-high pressure circulating fluidized bed boiler of the cogeneration device, hereinafter referred to as a CFB boiler, a steam turbine generator unit and a chemical water system, an extraction tower of an aromatics extraction device C-603 of a carbon four aromatics combined device in a chemical device, hereinafter referred to as an extraction tower, and an ethylene cracking device, characterized in that desalted water 29 heated by a slag cooler of the CFB boiler is transported to a desalted water heat exchanger 31 of the extraction tower in a boundary area 30 of the aromatics extraction device through a transport pipeline, and exchanges heat with an incoming heat medium 32, the heat medium 32 comes from the gas phase at the top of the extraction tower, the heat medium 32 is cooled to a cold medium 33 after heat exchange, and is discharged back to the extraction tower, the desalted water 29 heated by the slag cooler of the CFB boiler is heat exchanged at 50°C The heated desalted water 35 is heated to about 70°C; then it is transported to the boundary area 34 of the cogeneration device through the transmission pipeline, connected to the transmission pipeline of the drain tank drain 36 of the cogeneration device, mixed into the desalted water 37 before the feed water heater heat exchange, and then enters the feed water heater 38 of the cogeneration device, and continues to exchange heat with the entering non-adjustable extraction steam 40 from the second stage of the steam turbine, and the desalted water 39 after the feed water heater heat exchange is heated to 70-90°C, and then sent to the low-temperature economizer 27 of the CFB boiler for further heat exchange and heating, and the desalted water 42 after the low-temperature economizer heat exchange is increased from 70-90°C to about 120°C, and is sent to the high-pressure deaerator 43 of the cogeneration device to reduce the steam consumption of the high-pressure deaerator 43, and the exhaust steam 13 discharged from the high-pressure deaerator 43 is returned to the drain tank 14 for reuse after the waste heat is utilized;

[0013] The quench water 1 supplied from the outlet main pipe of the quench water pump of the ethylene cracking unit has a temperature of about 80°C, and is led to the total water inlet of the low-temperature air preheater 4 of the CFB boiler in the boundary area 3 of the cogeneration unit through the transmission pipeline. The quench water 2 after heat exchange with the air 5 at the inlet of the low-temperature air preheater 4 is returned to the ethylene cracking unit. The temperature of the inlet air 5 is increased from the normal temperature of 25°C to the first-level hot air 6 of 55°C, and then enters the large public air duct 7 of the CFB boiler through the exhaust main pipeline; then, the first-level hot primary air 8 and the first-level hot secondary air 1 are output in two ways. 5, after the first-level hot primary air 8 enters the primary air heating system M of the CFB boiler connected to the large common air duct 7 of the CFB boiler, and the first-level hot secondary air 15 enters the secondary air heating system N of the CFB boiler connected to the large common air duct 7 of the CFB boiler, firstly, the first-level hot primary air 8 is compressed and heated by the primary fan 9 of the CFB boiler, and then the output temperature rise reaches 10-20°C. The second-level hot secondary air 15 is compressed and heated by the secondary fan 16 of the CFB boiler, and then the output temperature rise reaches 10-20°C. The secondary hot secondary air 17, the secondary hot primary air 10 enters the heater 11 of the primary fan for heat exchange and heating, and then outputs the third-level hot primary air 12 at 75-90°C, the secondary hot secondary air 17 enters the heater 18 of the secondary fan for heat exchange and heating, and then outputs the third-level hot secondary air 19 at 75-90°C, and then enters the air preheater 23 of the tail flue of the CFB boiler through the conveying pipeline to heat and heat with the high-temperature flue gas 25 of the tail flue, and realizes energy conversion at the air preheater. The temperature of the flue gas 26 after heat exchange in the air preheater reaches 160-170°C, and the air The flue gas 26 discharged from the air preheater 23 after heat exchange enters the low-temperature economizer 27, and the flue gas temperature is reduced to about 95°C after heat exchange to the low-temperature flue gas 28. The desalted water 39 after heat exchange with the water heater is heated by the flue gas waste heat and outputs the desalted water 42 after heat exchange with the low-temperature economizer. The low-temperature economizer is set in the flue between the air preheater and the electric bag integrated dust collector; finally, the hot primary air and hot secondary air after heat exchange are introduced into the furnace 24 for fluidization and combustion; the air preheater 23 is located in the tail flue 22 of the CFB boiler;

[0014] The deaerator exhaust steam 13 discharged from the high-pressure deaerator 43 of the cogeneration unit is introduced into the heater 11 of the primary fan through a transmission pipeline, or the boiler waste water 20 of the CFB boiler is introduced into the heater 18 of the secondary fan through a transmission pipeline for heat exchange, so as to increase the wind temperature of the hot primary air and the hot secondary air by 10-20°C, and realize secondary heating in cascade with the front-end low-temperature air preheater 4; the deaerator exhaust steam condensate after heat exchange with the deaerator exhaust steam 13 is transported to the drain tank 14 through a transmission pipeline; the boiler waste water 20 is transported to the fixed discharge 21 through a transmission pipeline.

[0015] The energy-saving system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device is characterized in that there are three CFB boilers, and the low-temperature economizers of the CFB boilers are connected in parallel to form a low-temperature economizer system, and an economizer total water inlet and an economizer total water outlet are provided, the economizer total water inlet is respectively connected to the low-temperature economizer water inlets, and the economizer total water outlet is respectively connected to the low-temperature economizer water outlets.

[0016] The energy-saving system for realizing deep utilization of low-temperature waste heat of the whole system of a cogeneration device is characterized in that the low-temperature air preheater 4 includes a heat exchanger, a water distribution header, a water collection header, a water pipeline, and an air pipeline. A plurality of heat exchangers 402 are provided, and the heat exchanger 402 includes a shell and a built-in heat exchanger module 403; a plurality of heat exchanger modules 403 are provided in each heat exchanger 402; the heat exchanger module is a fin tube heat exchanger including a shell, an H-type fin tube bundle 4035, a water inlet 4031, a water outlet 4032, an air inlet 4033, and an air outlet 4034; the water inlet 4031 of each heat exchanger module is connected to the unit water outlet 4042 of the water distribution header 404, The water outlet 4032 of each heat exchanger module is connected to the unit water inlet 4052 of the water assembly manifold 405; the heat exchanger is provided with an air inlet pipe 4021 and an air outlet pipe 4022, the air inlet 4033 of each heat exchanger module in the heat exchanger is connected to the air inlet pipe 4021, and the air outlet 4034 of each heat exchanger module is connected to the air outlet pipe 4022; the water distribution manifold 404 is provided with a total water inlet 4041 of a low-temperature air preheater, and the water assembly manifold 405 is provided with a total water outlet 4051 of a low-temperature air preheater; each air inlet pipe 4021 is connected to the main air inlet pipeline of the low-temperature air preheater, and each air outlet pipe 4022 is connected to the main exhaust pipeline of the low-temperature air preheater.

[0017] The technical features of the present invention are: 1. Low-temperature air preheating deep utilization technology. A set of low-temperature air preheater is added in the area of ​​the cogeneration device, and then a public air inlet duct is added to connect with the original inlet ducts of the primary and secondary fans of the three ultra-high pressure circulating fluidized bed boilers in the cogeneration device. A pipe with a diameter of DN300 is added from the outlet main pipe of the ethylene device quenching water pump to lead a stream of quenching water. The quenching water is cooled to below 60°C and then returned to the E-130 quenching water outlet. The quenching water heats the fan inlet air, and the fan inlet air temperature is increased from about 25°C to about 55°C, and then the fan, heater (heating of exhaust steam, condensate, etc.) and other steps are heated to about 90°C before entering the tail flue air preheater, and the boiler exhaust gas temperature will be increased to about 165°C.

[0018] 2. Technology for synergistic deep utilization of chemical low-temperature heat sources and boiler flue gas waste heat. The cooling water return desalted water of the ultra-high pressure circulating fluidized bed boiler slag cooler of the cogeneration unit is sent to the aromatics extraction unit through a pipeline to recover the process waste heat of the stripping tower C-603, so that the temperature of the desalted water is heated from 50°C to about 70°C, and then sent to the boundary area of ​​the cogeneration unit through a pipeline, mixed with the drain water in the drain tank, and heated by the make-up water heater before being sent to the newly added CFB boiler low-temperature economizer. The waste heat of the CFB boiler exhaust temperature is used by the newly added low-temperature economizer to heat the desalted water, so that the temperature of the desalted water is increased from 70-90°C to about 120°C.

[0019] The above technical solutions of the present invention realize:

[0020] 1. Raise the initial temperature of desalted water entering the low-temperature economizer: Use the low-temperature waste heat from the aromatics extraction unit to heat the desalted water from 50°C to about 70°C, then send it to the boundary area of ​​the cogeneration unit through a pipeline, mix it with the drain water from the drain tank, and send it to the newly added CFB boiler low-temperature economizer.

[0021] 2. The quench water (design value is 300t / h, 80℃) of the ethylene cracking unit is led to the thermal power boundary area through the pipeline, and enters a newly added low-temperature air preheater system. The quench water is used to exchange heat with the inlet air to increase the inlet air temperature (from normal temperature 25℃ to 55℃), and enters the newly added public air duct at the inlet of the primary and secondary fans of the CFB boiler. After being pressurized by the primary and secondary fans and cascade heated by the heater, energy conversion is achieved at the air preheater at the rear flue of the boiler, and the tail exhaust temperature of the CFB boiler is increased, realizing the innovative design of "exergy value conversion, low quality and high use".

[0022] 3. Utilize the low-temperature waste heat of sewage, exhaust steam and steam condensate from the cogeneration device: introduce the continuous sewage from the ultra-high pressure circulating fluidized bed boiler and the exhaust steam from the deaerator into the heater of the boiler's primary fan and secondary fan, increase the wind temperature by more than 10°C, realize cascade heating with the low-temperature air preheater, realize energy conversion at the air preheater at the rear flue of the boiler, and increase the tail flue gas temperature of the CFB boiler.

[0023] 4. Using the waste heat of the exhaust gas temperature at the tail of the CFB boiler, a low-temperature economizer is added to the flue between the air preheater and the electric bag integrated dust collector to reduce the flue gas temperature from about 165°C to about 95°C. The recovered flue gas heat heats the hot desalted water of the cogeneration unit, raising the temperature of the desalted water from 70-90°C to about 120°C and returns to the deaerator.

[0024] Effects of the Invention

[0025] After the implementation of the present invention, on the one hand, quench water is used to heat the CFB boiler inlet air, and the low-grade thermal energy of the quench water is recovered, and the heat is recovered by heat exchange between the desalted water of the slag cooler and the steam at the top of the aromatics stripping tower; on the other hand, the low-temperature waste heat of the whole system such as the flue gas waste heat of the cogeneration device, the unit heat recovery, the waste heat of the sewage, the waste heat of the exhaust steam, etc. is recovered to cascade and synergistically heat the desalted water, while ensuring that the lowest wall temperature of the low-temperature economizer is far away from the acid dew point, thereby avoiding the risk of low-temperature corrosion of the wall surface, and achieving stable and reliable comprehensive recovery of the low-temperature waste heat of the whole system such as the flue gas waste heat, reducing the internal consumption of the cogeneration device system. Steam, thereby greatly reducing fuel consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the system and workflow of the present invention.

[0027] Figure 2 This is a schematic diagram of the structure of the low-temperature air preheater, water and air flow of the present invention.

[0028] Figure 3 This is a front schematic diagram of the heat exchanger module of the low-temperature air preheater of the present invention.

[0029] Figure 4 This is a side view of the heat exchanger module of the low-temperature air preheater of the present invention.

[0030] Figure 5 This is a schematic diagram of the internal connections of the low-temperature air preheater of the present invention.

[0031] Description of the accompanying drawings:

[0032] System number: 1 (supplied by the outlet main pipe of the quench water pump of the ethylene cracking unit) quench water; 2 (after heat exchange in the low-temperature air preheater of the cogeneration unit) return quench water; 3 cogeneration unit boundary; 4 (low-temperature air preheater of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit); 5 inlet air; 6 first-stage hot air; 7 large public air duct of the ultra-high pressure circulating fluidized bed boiler; 8 first-stage hot primary air; 9 (the primary fan of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit); 10 (the second-stage hot primary air after compression and heating by the primary fan of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit); 11 the heater of the primary fan; 12 the third-stage hot primary air (after heating by the heater of the primary fan of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit); 13 deaerator exhaust steam ; 14 (deaerator exhaust condensate after heat exchange in the heater of the primary fan of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit) to the drain tank; 15 first-level hot secondary air; 16 (secondary fan of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit); 17 (secondary hot secondary air after compression and heating by the secondary fan of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit); 18 heater of the secondary fan; 19 (third-level hot secondary air after heating by the heater of the secondary fan of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit); 20 (boiler drainage of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit); 21 (boiler drainage after heat exchange in the heater of the primary fan of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit) to the fixed row; 22 (ultra-high pressure circulating fluidized bed boiler of the cogeneration unit) 1. Rear flue of circulating fluidized bed boiler; 2. Air preheater of the rear flue of ultra-high pressure circulating fluidized bed boiler of cogeneration unit; 2. Hot primary air and hot secondary air are introduced into the furnace after heating by air preheater of ultra-high pressure circulating fluidized bed boiler of cogeneration unit; 2. High temperature flue gas of the rear flue of ultra-high pressure circulating fluidized bed boiler of cogeneration unit; 2. Flue gas after heat exchange by air preheater of ultra-high pressure circulating fluidized bed boiler of cogeneration unit; 2. Low temperature economizer of ultra-high pressure circulating fluidized bed boiler; 2. Low temperature flue gas after heat exchange by low temperature economizer of ultra-high pressure circulating fluidized bed boiler of cogeneration unit; 2. Desalted water after heating by slag cooler of ultra-high pressure circulating fluidized bed boiler; 3. Boundary of aromatics extraction unit; 3. Low temperature economizer of ultra-high pressure circulating fluidized bed boiler; 3. Low temperature economizer of ultra-high pressure circulating fluidized bed boiler; 3. Low temperature economizer of ultra-high pressure circulating fluidized bed boiler; 3. Low temperature economizer of ultra-high pressure circulating fluidized bed boiler; 3. Low temperature economizer of ultra-high pressure circulating fluidized bed boiler; 3. Low temperature economizer of ultra-high pressure circulating fluidized bed boiler; 3. Low temperature economizer of ultra-high pressure circulating fluidized bed boiler; 3. Desalted water after heating by slag cooler of ultra-high pressure circulating fluidized bed boiler; 3. Boundary of aromatics extraction unit; 3. (Aromatics extraction unit C-603) Extraction tower desalted water heat exchanger; 32 Hot medium; 33 Cold medium; 34 Cogeneration unit boundary; 35 Desalted water after heating; 36 (Cogeneration unit) Drain box drain; 37 (Cogeneration unit) Desalted water before heat exchange by feed water heater; 38 (Cogeneration unit) Feed water heater; 39 Desalted water after heat exchange by feed water heater; 40 (Cogeneration unit) Secondary non-adjustable steam extraction of steam turbine; 41 (Cogeneration unit) Secondary non-adjustable steam extraction of steam turbine after heat exchange condensate; 42 (Cogeneration unit ultra-high pressure circulating fluidized bed boiler) Desalted water after heat exchange by low temperature economizer; 43 (Cogeneration unit) High pressure deaerator; 44 The equipment and pipelines in the virtual frame involve the old system;Primary air heating system M, secondary air heating system N. ;

[0033] Low-temperature air preheater number description: Low-temperature air preheater 4, heat exchanger 402, air inlet 4021, air outlet 4022, heat exchanger module 403 (9 modules W1-W9), water inlet 4031, water outlet 4032, air inlet 4033, air outlet 4034, H-type fin tube bundle 4035, water distribution header 404, total water inlet 4041, unit water outlet 4042, water collection header 405, total water outlet 4051, unit water inlet 4052, DETAILED DESCRIPTION

[0034] See also Figure 1-5 As shown, an energy-saving method for deep utilization of low-temperature waste heat in the whole system of a cogeneration device of the present invention comprises an ultra-high pressure circulating fluidized bed boiler of the cogeneration device, hereinafter referred to as the CFB boiler, a steam turbine generator unit and a chemical water system, an extraction tower of an aromatics extraction device C-603 of a carbon four aromatics combined device in a chemical device, hereinafter referred to as the extraction tower, and an ethylene cracking device. Desalted water 29 heated by a slag cooler of the CFB boiler is transported to a desalted water heat exchanger 31 of the extraction tower in a boundary area 30 of the aromatics extraction device to exchange heat with an incoming heat medium 32, the heat medium 32 coming from the gas phase at the top of the extraction tower, the heat medium 32 is cooled to a cold medium 33 after heat exchange and discharged back to the extraction tower, the desalted water 29 heated by the slag cooler of the CFB boiler is transported to a boundary area 30 of the aromatics extraction device by a heat exchanger 31 of the extraction tower, and the heat medium 32 is exchanged with the incoming heat medium 32, the heat medium 32 comes from the gas phase at the top of the extraction tower, the heat medium 32 is cooled to a cold medium 33 after heat exchange and discharged back to the extraction tower, the desalted water 29 heated by the slag cooler of the CFB boiler is transported to a boundary area 30 of the aromatics extraction device by a heat exchanger 31 of the extraction tower, and the desalted water 29 ... The desalted water 35 is heated at 0℃ by heat exchange to about 70℃; it is then transported to the boundary area 34 of the cogeneration device, mixed with the drain tank drain 36 from the cogeneration device to form the desalted water 37 before the feed water heater heat exchange, enters the feed water heater 38 of the cogeneration device, continues to exchange heat with the entering secondary non-adjustable extraction steam 40 from the steam turbine, and is heated to 70-90℃. The desalted water 39 after heat exchange with the feed water heater is then sent to the low-temperature economizer 27 of the CFB boiler for further heat exchange and heating, and the desalted water 42 after heat exchange with the low-temperature economizer is heated from 70-90℃ to about 120℃, and is sent to the high-pressure deaerator 43 of the cogeneration device to reduce the steam consumption of the high-pressure deaerator 43, and the exhaust steam 13 discharged from the high-pressure deaerator 43 is returned to the drain tank 14 for reuse after the waste heat is utilized;

[0035] The quench water 300t / h1 with a temperature of 80℃ supplied from the outlet main pipe of the quench water pump of the ethylene cracking unit is led to the total water inlet of the low-temperature air preheater 4 of the CFB boiler in the boundary area 3 of the cogeneration unit, and is heated by heat exchange with the air 5 at the inlet of the main air inlet pipeline of the low-temperature air preheater 4 to return to the ethylene cracking unit as the return quench water 2. The temperature of the air 5 at the inlet is increased from the normal temperature of 25℃ to the first-level hot air 6 of 55℃, and then enters the large public air duct 7 of the CFB boiler through the exhaust main pipeline; after that, it is divided into two routes to output the first-level hot primary air 8 and the first-level hot secondary air 15, of which After the first-level hot primary air 8 enters the primary air heating system M of the CFB boiler connected to the large common air duct 7 of the CFB boiler, and the first-level hot secondary air 15 enters the secondary air heating system N of the CFB boiler connected to the large common air duct 7 of the CFB boiler, first, the first-level hot primary air 8 is compressed and heated by the primary fan 9 of the CFB boiler, and the output temperature reaches 10-20°C. The first-level hot secondary air 15 is compressed and heated by the secondary fan 16 of the CFB boiler, and the temperature rise reaches 10-20°C. 7, the secondary hot primary air 10 enters the heater 11 of the primary fan for heat exchange and heating, and then outputs the tertiary hot primary air 12 at 75-90°C, and the secondary hot secondary air 17 enters the heater 18 of the secondary fan for heat exchange and heating, and then outputs the tertiary hot secondary air 19 at 75-90°C, and the tertiary hot primary air 12 and the tertiary hot secondary air 19 are then introduced into the air preheater 23 of the tail flue of the CFB boiler for heat exchange and heating with the high-temperature flue gas 25 of the tail flue, and energy conversion is realized in the air preheater, and the temperature of the flue gas 26 after heat exchange in the air preheater reaches 160-170°C, and the air The flue gas 26 discharged from the air preheater 23 after heat exchange enters the low-temperature economizer 27, and after heat exchange, the flue gas temperature is reduced to the low-temperature flue gas 28 of about 95°C, and the desalted water 39 after heat exchange by the make-up water heater is heated by the waste heat of the flue gas temperature to output the desalted water 42 after heat exchange by the low-temperature economizer. The low-temperature economizer 27 is set in the flue between the air preheater and the electric bag integrated dust collector; finally, the hot primary air and hot secondary air after heat exchange are introduced into the furnace 24 for fluidization and combustion; the air preheater 23 is located in the tail flue 22 of the CFB boiler;

[0036] The deaerator exhaust steam 13 discharged from the high-pressure deaerator 43 of the cogeneration unit or the boiler continuous drainage 20 of the CFB boiler are respectively introduced into the heater 11 of the primary fan and the heater 18 of the secondary fan for heat exchange, so as to increase the wind temperature of the hot primary air and the hot secondary air by 10-20°C, and realize secondary heating in series with the front-end low-temperature air preheater 4; the deaerator exhaust steam 13 after heat exchange condenses into the drain tank 14; the boiler continuous drainage 20 is discharged to the fixed discharge 21.

[0037] The present invention discloses an energy-saving system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device, comprising an ultra-high pressure circulating fluidized bed boiler of the cogeneration device, hereinafter referred to as a CFB boiler, a steam turbine generator unit and a chemical water system, an extraction tower of an aromatics extraction device C-603 of a carbon four aromatics combined device in a chemical device, hereinafter referred to as an extraction tower, and an ethylene cracking device. The desalted water 29 heated by the slag cooler of the CFB boiler is transported to the desalted water heat exchanger 31 of the extraction tower in the boundary area 30 of the aromatics extraction device through a transport pipeline, and exchanges heat with an incoming heat medium 32. The heat medium 32 comes from the gas phase at the top of the extraction tower. The heat medium 32 is cooled to become a cold medium 33 after heat exchange and is discharged back to the extraction tower. The desalted water 29 heated by the slag cooler of the CFB boiler is heated by heat exchange at 50°C to The heated desalted water 35 is about 70℃; it is then transported to the boundary area 34 of the cogeneration device through the transmission pipeline, connected to the transmission pipeline of the drain tank 36 of the cogeneration device, mixed with the desalted water 37 before the feed water heater heat exchange, and then enters the feed water heater 38 of the cogeneration device, and continues to exchange heat with the entering non-adjustable extraction steam 40 from the second stage of the steam turbine, and the desalted water 39 after the feed water heater heat exchange is heated to 70-90℃, and then sent to the low-temperature economizer 27 of the CFB boiler for further heat exchange and heating, and the desalted water 42 after the low-temperature economizer heat exchange is increased from 70-90℃ to about 120℃, and is sent to the high-pressure deaerator 43 of the cogeneration device to reduce the steam consumption of the high-pressure deaerator 43, and the exhaust steam 13 discharged from the high-pressure deaerator 43 is returned to the drain tank 14 for reuse after the waste heat is utilized;

[0038] The quench water 1 supplied from the outlet main pipe of the quench water pump of the ethylene cracking unit has a temperature of about 80°C, and is led to the total water inlet of the low-temperature air preheater 4 of the CFB boiler in the boundary area 3 of the cogeneration unit through the transmission pipeline. The quench water 2 after heat exchange with the air 5 at the inlet of the low-temperature air preheater 4 is returned to the ethylene cracking unit. The temperature of the inlet air 5 is increased from the normal temperature of 25°C to the first-level hot air 6 of 55°C, and then enters the large public air duct 7 of the CFB boiler through the exhaust main pipeline; then, the first-level hot primary air 8 and the first-level hot secondary air 1 are output in two ways. 5, after the first-level hot primary air 8 enters the primary air heating system M of the CFB boiler connected to the large common air duct 7 of the CFB boiler, and the first-level hot secondary air 15 enters the secondary air heating system N of the CFB boiler connected to the large common air duct 7 of the CFB boiler, firstly, the first-level hot primary air 8 is compressed and heated by the primary fan 9 of the CFB boiler, and then the output temperature rise reaches 10-20°C. The second-level hot secondary air 15 is compressed and heated by the secondary fan 16 of the CFB boiler, and then the output temperature rise reaches 10-20°C. The secondary hot secondary air 17, the secondary hot primary air 10 enters the heater 11 of the primary fan for heat exchange and heating, and then outputs the third-level hot primary air 12 at 75-90°C, the secondary hot secondary air 17 enters the heater 18 of the secondary fan for heat exchange and heating, and then outputs the third-level hot secondary air 19 at 75-90°C, and then enters the air preheater 23 of the tail flue of the CFB boiler through the conveying pipeline to heat and heat with the high-temperature flue gas 25 of the tail flue, and realizes energy conversion at the air preheater. The temperature of the flue gas 26 after heat exchange in the air preheater reaches 160-170°C, and the air The flue gas 26 discharged from the air preheater 23 after heat exchange enters the low-temperature economizer 27, and the flue gas temperature is reduced to about 95°C after heat exchange to the low-temperature flue gas 28. The desalted water 39 after heat exchange with the water heater is heated by the flue gas waste heat and outputs the desalted water 42 after heat exchange with the low-temperature economizer. The low-temperature economizer is set in the flue between the air preheater and the electric bag integrated dust collector; finally, the hot primary air and hot secondary air after heat exchange are introduced into the furnace 24 for fluidization and combustion; the air preheater 23 is located in the tail flue 22 of the CFB boiler;

[0039] The deaerator exhaust steam 13 discharged from the high-pressure deaerator 43 of the cogeneration unit is introduced into the heater 11 of the primary fan through a transmission pipeline, or the boiler waste water 20 of the CFB boiler is introduced into the heater 18 of the secondary fan through a transmission pipeline for heat exchange, so as to increase the wind temperature of the hot primary air and the hot secondary air by 10-20°C, and realize secondary heating in cascade with the front-end low-temperature air preheater 4; the deaerator exhaust steam condensate after heat exchange with the deaerator exhaust steam 13 is transported to the drain tank 14 through a transmission pipeline; the boiler waste water 20 is transported to the fixed discharge 21 through a transmission pipeline.

[0040] The energy-saving system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device comprises three CFB boilers, the low-temperature economizers of the CFB boilers are connected in parallel to form a low-temperature economizer system, and an economizer total water inlet and an economizer total water outlet are provided, the economizer total water inlet is respectively connected to the low-temperature economizer water inlets, and the economizer total water outlet is respectively connected to the low-temperature economizer water outlets.

[0041] The energy-saving system for realizing deep utilization of low-temperature waste heat of the whole system of a cogeneration device, the low-temperature air preheater 4, includes a heat exchanger, a water distribution header, a water collection header, a water pipeline, and an air pipeline. The heat exchanger 402 is provided in multiple units, and the heat exchanger 402 includes a shell and a built-in heat exchanger module 403; each heat exchanger 402 is provided with multiple heat exchanger modules 403; the heat exchanger module is a fin tube heat exchanger including a shell, an H-shaped fin tube bundle 4035, a water inlet 4031, a water outlet 4032, an air inlet 4033, and an air outlet 4034; the water inlet 4031 of each heat exchanger module is connected to the unit water outlet 4042 of the water distribution header 404, and each The water outlet 4032 of the heat exchanger module is connected to the unit water inlet 4052 of the water collection tank 405; the heat exchanger is provided with an air inlet pipe 4021 and an air outlet pipe 4022, the air inlet 4033 of each heat exchanger module in the heat exchanger is connected to the air inlet pipe 4021, and the air outlet 4034 of each heat exchanger module is connected to the air outlet pipe 4022; the water distribution tank 404 is provided with a total water inlet 4041 of the low-temperature air preheater, and the water collection tank 405 is provided with a total water outlet 4051 of the low-temperature air preheater; each of the air inlet pipes 4021 is connected to the low-temperature air preheater air inlet main pipeline, and each of the air outlet pipes 4022 is connected to the low-temperature air preheater exhaust main pipeline.

[0042] See also Figure 3-5 The quenching water exchanges heat with the cold air 5 in reverse direction through the H-shaped fin tube bundle 4035. The cold air enters from the air inlet 4021 and is divided into 9 branches to enter the 9 heat exchanger modules 3 (W1-W9). In the module, the cold air exchanges heat with the cold air 5 introduced by the induced draft fan. The hot air passes through the shell of the low-temperature air preheater, and the flow direction is perpendicular to the fin tube. After the heat exchange, the hot air is collected at the outlet 4022 and enters the exhaust main pipeline to be discharged to the public air duct. The low-temperature air preheater is equipped with 3 heat exchangers, each of which has 3 heat exchanger modules. The heat exchanger module 3 has a total of 9 W1-W9. The quenching water flows in the heat exchanger module tube and the air flows outside the tube. After the reverse convection heat exchange, the heated hot air 6 enters the public air duct and is collected, and then enters the air inlet of the primary air heating system and the secondary air heating system of the CFB boiler.

[0043] The air flow direction is that the induced draft fan sucks cold air from the bottom of the low-temperature air preheater, and after heat exchange, it flows out from its side and is collected into the public air duct. The public air duct can provide hot air for multiple boilers at the same time.

[0044] The working process or working principle of the present invention is as follows:

[0045] The quench water 1 supplied from the outlet main pipe of the quench water pump of the ethylene cracking unit is transported to the boundary area 3 of the cogeneration unit, enters from the total water inlet of the low-temperature air preheater, and is discharged from the total water outlet of the low-temperature air preheater to heat the cold air 5 sucked in by the main air inlet pipeline of the low-temperature air preheater 4 of the ultra-high pressure circulating fluidized bed boiler in the boundary area of ​​the cogeneration unit, and heats the cold air at the intake of the unit at a normal temperature of 25°C to the primary hot air 6 at a temperature of 55°C, which is discharged from the main exhaust pipeline and merged into the large public air duct 7 of the ultra-high pressure circulating fluidized bed boiler; then the primary air and secondary air of the ultra-high pressure circulating fluidized bed boiler are respectively drawn out from the large public air duct, and are divided into two routes: one route is the primary hot primary air 8 sucked in from the large public air duct by the primary fan suction port of the ultra-high pressure circulating fluidized bed boiler, and is compressed and heated by the primary fan 9 to form the secondary hot primary air The wind 10 (temperature rise reaches 10-20°C) is then heated by the heater 11 of the primary fan with the exhaust steam 13 from the deaerator as the heating source to form the third-level hot primary air 12 with a temperature of 75-90°C, which is then merged into the air preheater 23 of the tail flue of the ultra-high pressure circulating fluidized bed boiler; the other way is that the first-level hot secondary air 15 is sucked from the large public air duct 7 by the suction port of the secondary fan 16 of the ultra-high pressure circulating fluidized bed boiler, and is compressed and heated by the secondary fan 16 to form the second-level hot secondary air 17 (temperature rise reaches 10-20°C), and then is heated by the heater 18 of the secondary fan with the boiler discharge water 20 or the medium-pressure steam condensate from the boiler as the heating source to form the third-level hot secondary air 19 with a temperature of 75-90°C, which is also merged into the air preheater 23 of the tail flue of the ultra-high pressure circulating fluidized bed boiler. Then, at the air preheater of the tail flue of the ultra-high pressure circulating fluidized bed boiler, the three-stage hot primary air, the three-stage hot secondary air and the high-temperature flue gas 25 of the tail flue are used to realize "exergy value conversion", and the exhaust flue gas after heat exchange in the air preheater of the ultra-high pressure circulating fluidized bed boiler (i.e., the flue gas after heat exchange in the air preheater 26) is heated to a temperature of 160-170°C and sent to the newly added low-temperature economizer.

[0046] The temperature of the desalted water 29 after being heated by the slag cooler of the ultra-high pressure circulating fluidized bed boiler of the cogeneration unit is 50°C. It is first sent to the aromatics extraction unit, and is heated to 70°C by the desalted water heat exchanger 31 of the C-603 extraction tower of the aromatics extraction unit. Then, it returns to the cogeneration unit and merges with the drain water of the drain tank of the cogeneration unit. After being heated by the make-up water heater 38 of the cogeneration unit, it forms desalted water with a temperature of 70-90°C (i.e., the desalted water 39 after heat exchange by the make-up water heater), and after being heated by the newly added low-temperature economizer, it forms desalted water with a temperature of 115-125°C (i.e., the desalted water 42 after heat exchange by the low-temperature economizer), and is sent to the high-pressure deaerator 43 of the cogeneration unit. According to the principle of energy conservation, the low-temperature waste heat of the chemical unit and the waste heat of the entire system in the cogeneration unit will eventually be utilized to greatly reduce the steam consumption of the high-pressure deaerator.

[0047] The deep utilization of low-temperature waste heat in the whole system of the cogeneration device can minimize the energy consumption of the whole system of the cogeneration device from the perspective of exergy conversion of the whole system and deep optimization of low-quality and high-use, reduce the exhaust temperature, reduce the internal consumption of steam in the system, and reduce the coal consumption. Under normal operation, the emission of flue gas pollutants can be reduced by a certain amount each year, achieving green, energy-saving and environmental protection effects, and having good economic and social benefits. In addition, the invention is suitable for energy-saving transformation of deep utilization of low-temperature waste heat in domestic cogeneration devices, self-contained power plants, thermal power plants, etc., and has broad promotion significance.

Claims

1. An energy-saving method for deep utilization of low-temperature waste heat in the whole system of a cogeneration device, comprising an ultra-high pressure circulating fluidized bed boiler of the cogeneration device, hereinafter referred to as a CFB boiler, a boiler steam turbine generator unit and a chemical water system, an extraction tower of an aromatics extraction device of a C4 aromatics complex in a chemical device, hereinafter referred to as an extraction tower, and an ethylene cracking device, characterized in that: The desalted water (29) heated by the slag cooler of the CFB boiler is transported to the desalted water heat exchanger (31) of the extraction tower in the boundary area (30) of the aromatics extraction device to exchange heat with the incoming hot medium (32). The hot medium (32) comes from the gas phase at the top of the extraction tower. The hot medium (32) is cooled to become a cold medium (33) after heat exchange and discharged back to the extraction tower. The desalted water (29) heated by the slag cooler of the CFB boiler is heated from 50°C to 70°C heated desalted water (35) and then transported to the boundary area (34) of the cogeneration device to be mixed with the drain water (36) from the drain tank of the cogeneration device to be used as the makeup water. The desalted water (37) before heat exchange in the heat exchanger enters the feed water heater (38) of the cogeneration device, and continues to exchange heat with the non-adjustable extraction steam (40) from the second stage of the steam turbine. The desalted water (39) after heat exchange with the feed water heater is heated to 70-90°C, and then sent to the low-temperature economizer (27) of the CFB boiler for further heat exchange and heating. The desalted water (42) after heat exchange with the low-temperature economizer, which is heated from 70-90°C to 120°C, is sent to the high-pressure deaerator (43) of the cogeneration device to reduce the steam consumption of the high-pressure deaerator (43), and the exhaust steam (13) discharged from the high-pressure deaerator (43) is returned to the drain tank (14) for reuse after the waste heat is utilized; A quench water (1) with a temperature of 80°C and 300 t / h is supplied from the outlet main pipe of the quench water pump of the ethylene cracking unit to the main water inlet of the low-temperature air preheater (4) of the CFB boiler in the boundary area (3) of the cogeneration unit. After heat exchange with the air (5) in the intake port of the low-temperature air preheater (4) and heating, the quench water (2) is returned to the ethylene cracking unit. The temperature of the intake port air (5) is increased from the normal temperature of 25°C to the primary hot air (6) of 55°C, and enters the large public air duct (7) of the CFB boiler through the exhaust main pipeline. After that, it is divided into two routes to output the primary hot air ( 8), first-level hot secondary air (15), wherein the first-level hot primary air (8) enters the primary air heating system of the CFB boiler connected to the large common air duct (7) of the CFB boiler, and the first-level hot secondary air (15) enters the secondary air heating system of the CFB boiler connected to the large common air duct (7) of the CFB boiler, specifically, the first-level hot primary air (8) is first compressed and heated by the primary fan (9) of the CFB boiler, and the output temperature reaches 10-20°C Secondary hot primary air (10), the first-level hot secondary air (15) is first compressed and heated by the secondary fan (1 6) After compression and heating, the temperature rise reaches 10-20°C for the secondary hot secondary air (17), the secondary hot primary air (10) enters the heater (11) of the primary fan for heat exchange and heating, and outputs the tertiary hot primary air (12) of 75-90°C, the secondary hot secondary air (17) enters the heater (18) of the secondary fan for heat exchange and heating, and outputs the tertiary hot secondary air (19) of 75-90°C, the tertiary hot primary air (12) and the tertiary hot secondary air (19) are then introduced into the air preheater (23) of the tail flue of the CFB boiler for heat exchange and heating with the high-temperature flue gas (25) of the tail flue, Energy conversion is achieved at the air preheater. The flue gas temperature after heat exchange in the air preheater reaches 160-170°C. The flue gas (26) after heat exchange in the air preheater discharged from the air preheater (23) enters the low-temperature economizer (27). After heat exchange, the flue gas temperature is reduced to low-temperature flue gas (28) of 95°C. The low-temperature economizer (27) is arranged in the flue between the air preheater and the electric bag integrated dust collector; finally, the hot primary air and hot secondary air after heat exchange are introduced into the furnace (24) for fluidization and combustion; the air preheater (23) is located in the tail flue (22) of the CFB boiler; The deaerator exhaust steam (13) discharged from the high-pressure deaerator (43) of the cogeneration device and the boiler continuous water (20) of the CFB boiler are respectively introduced into the heater (11) of the primary fan and the heater (18) of the secondary fan for heat exchange, so as to increase the air temperature of the hot primary air and the hot secondary air by 10 to 20° C., thereby realizing secondary heating in series with the front low-temperature air preheater (4); the deaerator exhaust steam (13) condenses after heat exchange to the drain tank (14); and the boiler continuous water (20) is discharged to the fixed discharge (21).

2. An energy-saving system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device, comprising an ultra-high pressure circulating fluidized bed boiler of the cogeneration device, hereinafter referred to as a CFB boiler, a steam turbine generator unit and a chemical water system, an extraction tower of an aromatics extraction device of a C4 aromatics complex in a chemical device, hereinafter referred to as an extraction tower, and an ethylene cracking device, characterized in that: The desalted water (29) heated by the slag cooler of the CFB boiler is transported to the desalted water heat exchanger (31) of the extraction tower in the boundary area (30) of the aromatics extraction unit through a transport pipeline to exchange heat with the incoming heat medium (32). The heat medium (32) comes from the gas phase at the top of the extraction tower. The heat medium (32) is cooled to become a cold medium (33) after heat exchange and discharged back to the extraction tower. The desalted water (29) heated by the slag cooler of the CFB boiler is heated from 50°C to 70°C heated desalted water (35); then it is transported to the boundary area (34) of the cogeneration unit through a transport pipeline and connected to the transport pipeline of the drain tank (36) of the cogeneration unit for mixing. After being combined into the desalted water (37) before heat exchange with the feed water heater, it enters the feed water heater (38) of the cogeneration device, continues to exchange heat with the incoming non-adjustable extraction steam (40) from the second stage of the steam turbine, and the desalted water (39) after heat exchange with the feed water heater is heated to 70-90°C, and then sent to the low-temperature economizer (27) of the CFB boiler for further heat exchange and heating. The desalted water (42) after heat exchange with the low-temperature economizer is heated from 70-90°C to 120°C, and is sent to the high-pressure deaerator (43) of the cogeneration device to reduce the steam consumption of the high-pressure deaerator (43), and the exhaust steam (13) discharged from the high-pressure deaerator (43) is returned to the drain tank (14) for reuse after the waste heat is utilized; A channel of quench water (1) with a temperature of 80°C from the outlet main pipe of the quench water pump of the ethylene cracking unit is led to the main water inlet of the low-temperature air preheater (4) of the CFB boiler in the boundary area (3) of the cogeneration unit through a transmission pipeline, and the quench water (2) after heat exchange with the air (5) at the inlet of the low-temperature air preheater (4) is returned to the ethylene cracking unit. The temperature of the inlet air (5) is increased from the normal temperature of 25°C to the primary hot air (6) of 55°C, and enters the large public air duct (7) of the CFB boiler through the exhaust main pipeline; then, the primary hot air is output in two ways. (8), first-level hot secondary air (15), the first-level hot primary air (8) enters the primary air heating system of the CFB boiler connected to the large common air duct (7) of the CFB boiler, the first-level hot secondary air (15) enters the secondary air heating system of the CFB boiler connected to the large common air duct (7) of the CFB boiler, specifically, the first-level hot primary air (8) is first compressed and heated by the primary fan (9) of the CFB boiler, and then outputs the second-level hot primary air (10) with a temperature rise of 10 to 20°C, the first-level hot secondary air (15) is first compressed and heated by the secondary fan (9) of the CFB boiler, and then outputs the second-level hot primary air (10) with a temperature rise of 10 to 20°C, After compression and heating by the secondary fan (16), the secondary hot secondary air (17) with a temperature rise of 10 to 20°C is output. The secondary hot primary air (10) then enters the heater (11) of the primary fan for heat exchange and heating and outputs the tertiary hot primary air (12) with a temperature of 75 to 90°C. The secondary hot secondary air (17) then enters the heater (18) of the secondary fan for heat exchange and heating and outputs the tertiary hot secondary air (19) with a temperature of 75 to 90°C. The tertiary hot secondary air (19) is then transported to the air preheater (23) of the tail flue of the CFB boiler through a transmission pipeline and heat-exchanged with the high-temperature flue gas (25) of the tail flue for heating. Energy conversion is realized at the air preheater, and the flue gas temperature after heat exchange in the air preheater reaches 160-170°C. The flue gas (26) after heat exchange discharged from the air preheater (23) enters the low-temperature economizer (27), and the flue gas temperature is reduced to low-temperature flue gas (28) of 95°C after heat exchange. The low-temperature economizer is arranged in the flue between the air preheater and the electric bag integrated dust collector; finally, the hot primary air and hot secondary air after heat exchange are introduced into the furnace (24) for fluidization and combustion; the air preheater (23) is located in the tail flue (22) of the CFB boiler; The deaerator exhaust steam (13) discharged from the high-pressure deaerator (43) of the cogeneration device is introduced into the heater (11) of the primary fan through a conveying pipeline, and the boiler drainage (20) of the CFB boiler is introduced into the heater (18) of the secondary fan through a conveying pipeline for heat exchange, thereby increasing the air temperature of the hot primary air and the hot secondary air by 10 to 20° C., thereby realizing secondary heating in series with the front low-temperature air preheater (4); the deaerator exhaust steam condensate after heat exchange with the deaerator exhaust steam (13) is conveyed to the drain tank (14) through a conveying pipeline; and the boiler drainage (20) is conveyed to the fixed discharge (21) through a conveying pipeline.

3. The energy-saving system for deep utilization of low-temperature waste heat in the whole system of a cogeneration device as claimed in claim 2, characterized in that: There are three CFB boilers, and the low-temperature economizers of the CFB boilers are connected in parallel to form a low-temperature economizer system, and an economizer total water inlet and an economizer total water outlet are provided. The economizer total water inlet is respectively connected to the low-temperature economizer water inlets, and the economizer total water outlet is respectively connected to the low-temperature economizer water outlets.

4. The energy-saving system for realizing deep utilization of low-temperature waste heat of the whole system of cogeneration device according to claim 2, characterized in that: The low-temperature air preheater (4) comprises a heat exchanger, a water distribution header, a water collection header, a water pipeline, and an air pipeline. A plurality of heat exchangers (402) are provided, and the heat exchanger (402) comprises a shell and a built-in heat exchanger module (403); a plurality of heat exchanger modules (403) are provided in each heat exchanger (402); the heat exchanger module is a fin tube heat exchanger comprising a shell, an H-shaped fin tube bundle (4035), a water inlet (4031), a water outlet (4032), an air inlet (4033), and an air outlet (4034); the water inlet (4031) of each heat exchanger module is connected to a unit water outlet (4042) of the water distribution header (404), and the water outlet (4032) of each heat exchanger module is connected to a unit water outlet (4042) of the water distribution header (404). ) is connected to the unit water inlet (4052) of the water collection manifold (405); the heat exchanger is provided with an air inlet pipe (4021) and an air outlet pipe (4022); the air inlet (4033) of each heat exchanger module in the heat exchanger is connected to the air inlet pipe (4021), and the air outlet (4034) of each heat exchanger module is connected to the air outlet pipe (4022); the water distribution manifold (404) is provided with a low-temperature air preheater total water inlet (4041), and the water collection manifold (405) is provided with a low-temperature air preheater total water outlet (4051); each of the air inlet pipes (4021) is connected to the low-temperature air preheater air inlet main pipeline, and each of the air outlet pipes (4022) is connected to the low-temperature air preheater exhaust main pipeline.

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