A coke oven flue gas semi-dry process flue gas waste heat comprehensive utilization system

Abstract

The application discloses a coke oven flue gas semi-dry process flue gas waste heat comprehensive utilization system, which comprises an ammonia wastewater heat exchange unit, wherein the waste heat of the coking flue gas after desulfurization and denitrification is used for ammonia evaporation of ammonia wastewater; the ammonia wastewater heat exchange unit comprises an ammonia water heat exchange assembly, which is used for heat exchange between the coking flue gas and the ammonia wastewater; the flue gas waste heat comprehensive utilization system further comprises an MGGH heat exchange unit, wherein the MGGH heat exchange unit comprises a flue gas cooler and a flue gas heater; the flue gas cooler is used for reducing the inlet temperature of the coking flue gas in the desulfurization and dust removal process; and the flue gas heater is used for increasing the inlet temperature of the coking flue gas in the denitrification process. The application fully combines the ammonia evaporation section of the coking plant, and makes the chemical production workshop and the desulfurization and denitrification unit organically combined, so that they are mutually beneficial, and the coking plant achieves the purpose of cost reduction and benefit increase.

Description

Technical Field

[0001] This invention belongs to the field of flue gas treatment technology, and specifically relates to a comprehensive utilization system for waste heat from coke oven flue gas in a semi-dry process. Background Technology

[0002] Currently, most coking plants have adopted various semi-dry processes to treat coke oven flue gas in order to meet the latest emission standards and to estimate project costs, ultimately achieving environmental compliance. The main process routes of these semi-dry processes are generally relatively fixed, following a sequence of desulfurization, dust removal, and denitrification. Some projects may not be able to implement more detailed or complex configurations due to site limitations. However, in terms of treating coke oven flue gas itself, the aforementioned semi-dry processes are somewhat insufficient in terms of waste heat utilization. Therefore, to address the issue of fully and rationally utilizing system heat, adjustments and optimizations are made to the existing semi-dry process routes. Summary of the Invention

[0003] In view of the shortcomings and defects of the existing technology, the present invention aims to provide a comprehensive utilization system for waste heat of coke oven flue gas in a semi-dry process.

[0004] The technical solution adopted by this invention to solve the technical problem is as follows:

[0005] A comprehensive waste heat utilization system for a semi-dry coke oven flue gas process includes an ammonia wastewater heat exchange unit, which uses the waste heat from the desulfurization and denitrification coking flue gas to strip ammonia from the wastewater.

[0006] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the ammonia wastewater heat exchange unit includes an ammonia water heat exchange component, which is used to exchange heat between the coking flue gas and the ammonia wastewater.

[0007] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the ammonia water heat exchange component includes a first steam-water heat exchanger and a second steam-water heat exchanger connected together; the first steam-water heat exchanger is used to exchange heat between the coking flue gas and softened water, so that the softened water forms softened water vapor; the second steam-water heat exchanger is used to exchange heat between the softened water vapor and the ammonia wastewater, so that the temperature of the ammonia wastewater increases.

[0008] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, a heat exchange medium circulation loop is formed between the first steam-water heat exchanger and the second steam-water heat exchanger. The heat exchange medium enters the second steam-water heat exchanger after being heated by coking flue gas in the first steam-water heat exchanger, and returns to the first steam-water heat exchanger as a cold source medium after being cooled in the second steam-water heat exchanger.

[0009] Preferably, a downcomer and a riser are provided between the first steam-water heat exchanger and the second steam-water heat exchanger. The downcomer is used to transport the softened water entering the shell side of the second steam-water heat exchanger from the shell side of the second steam-water heat exchanger to the first steam-water heat exchanger, and the riser is used to transport the softened water steam from the first steam-water heat exchanger to the shell side of the second steam-water heat exchanger.

[0010] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the first steam-water heat exchanger is a heat pipe steam generator.

[0011] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the second steam-water heat exchanger is a steam-collecting heat exchanger.

[0012] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the flue gas inlet of the first steam-water heat exchanger is connected to the flue gas outlet of the denitrification reactor in the desulfurization and denitrification process.

[0013] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the ammonia wastewater heat exchange unit further includes an ammonia stripping tower. The ammonia wastewater flows from the ammonia stripping tower into the ammonia water heat exchange component. After heat exchange, the ammonia wastewater flows back to the ammonia stripping tower for flash evaporation.

[0014] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the ammonia stripping tower and the tube side of the second steam-water heat exchanger form a circulation path for ammonia wastewater; preferably, the ammonia wastewater outlet of the ammonia stripping tower is connected to the tube side inlet of the second steam-water heat exchanger, and the tube side outlet of the second steam-water heat exchanger is connected to the ammonia wastewater inlet of the ammonia stripping tower.

[0015] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the ammonia stripping tower is equipped with a flash tank for flash evaporation of the ammonia wastewater.

[0016] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the flue gas waste heat comprehensive utilization system further includes an MGGH heat exchange unit, which includes a flue gas cooler and a flue gas heater. The flue gas cooler is used to reduce the inlet temperature of coking flue gas in the desulfurization and dust removal process, and the flue gas heater is used to increase the inlet temperature of coking flue gas in the denitrification process.

[0017] Preferably, a circulating loop of heat exchange medium is formed between the flue gas cooler and the flue gas heater; the heat exchange medium enters the flue gas heater after being heated by coking flue gas in the flue gas cooler, and then, after being cooled in the flue gas heater, part of the heat exchange medium flows into the flue gas cooler and part flows back into the flue gas heater; the heat exchange medium is preferably softened water.

[0018] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the flue gas outlet of the flue gas cooler is connected to the flue gas inlet of the desulfurization reactor.

[0019] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the flue gas inlet of the flue gas heater is connected to the flue gas outlet of the dust collector, and the flue gas outlet of the flue gas heater is connected to the flue gas inlet of the denitrification reactor.

[0020] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the dust collector is a bag filter dust collector.

[0021] In the above-mentioned flue gas waste heat comprehensive utilization system, as a preferred embodiment, the flue gas waste heat comprehensive utilization system further includes a desulfurization and denitrification unit, which includes the desulfurization reactor, the dust collector and the denitrification reactor connected in sequence along the flue gas flow direction.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The ultra-low temperature retrofit coking project using the semi-dry process, by embedding the MGGH unit, not only ensures that the desulfurization reaction takes place at the optimal reaction temperature, but also reduces the size of the desulfurization reactor and bag filter by about 30%, while still meeting the temperature requirements of the subsequent denitrification reaction. This invention optimizes the project's initial investment cost and subsequent operation and maintenance cost.

[0024] (2) This invention fully integrates the coking plant’s own ammonia stripping section, so that the chemical production workshop and the desulfurization and denitrification unit are organically combined, which are mutually beneficial and enable the coking plant to achieve the goal of reducing costs and increasing efficiency. Attached Figure Description

[0025] Figure 1 This is a structural diagram of a waste heat utilization system for a semi-dry process of coke oven flue gas.

[0026] Among them, 1 is the flue gas cooler, 2 is the flue gas heater, 3 is the desulfurization reactor, 4 is the bag filter, 5 is the denitrification reactor, 6 is the heat pipe steam generator, 7 is the steam heat exchanger, 8 is the soft water pump, 9 is the downcomer, 10 is the riser, 11 is the ammonia stripping tower, 12 is the flash tank, 13 is the induced draft fan, 14 is the owner's softened water unit, 15 is the coking raw flue gas inlet, 16 is the flow meter, 17 is the water supply valve, 18 is the softened water tank, 19 is the level gauge, 20 is the overflow pipe, 21 is the softened water return pipe, 22 is the softened water circulation main pipe, 23 is the softened water circulation pump, 24 is the pressure gauge, 25 is the pressure transmitter, 26 is the thermometer, 27 is the waste ammonia water frequency conversion circulation pump, and 28 is the water supply pipe for the steam heat exchanger. Detailed Implementation

[0027] To highlight the objectives, technical solutions, and advantages of this invention, the following embodiments further illustrate the invention. These examples are provided to explain the invention and not to limit it. The technical solutions of this invention are not limited to the specific embodiments listed below, but also include any combination of the various specific embodiments.

[0028] See Figure 1 This invention provides a comprehensive waste heat utilization system for a semi-dry coke oven gas process. The system includes an MGGH heat exchange unit, which comprises a flue gas cooler 1 and a flue gas heater 2. The flue gas cooler 1 is located before the desulfurization reactor 3 in the semi-dry coking process and is used to reduce the temperature of the coking flue gas entering the desulfurization reactor 3. Specifically, the flue gas outlet of the flue gas cooler 1 is connected to the flue gas inlet of the desulfurization reactor 3. The raw coke oven gas drawn from the coke oven machine side and the coke side flows into the flue gas cooler 1 through the raw coke oven gas inlet 15. After being cooled by the flue gas cooler 1, the temperature of the coke oven gas drops from, for example, about 250°C to, for example, about 120°C, keeping the temperature of the cooled coke oven gas above the acid dew point to prevent acid corrosion of the desulfurization reactor 3. Furthermore, the reduced temperature of the coke oven gas reduces the amount of flue gas entering the desulfurization reactor 3, optimizing the desulfurization reactor design (e.g., reducing the size of the desulfurization reactor). After the temperature of the coke oven flue gas decreases, the evaporation of water in the quicklime desulfurization agent slows down during the desulfurization reaction in desulfurization reactor 3, which can enhance the adsorption and mass transfer efficiency of the neutralization reaction.

[0029] Preferably, after the coke oven flue gas undergoes desulfurization in the desulfurization reactor 3, it flows into the bag filter 4 for dust removal. Since the temperature of the coke oven flue gas entering the desulfurization reactor 3 has already been reduced by the flue gas cooler 1, the temperature of the coke oven flue gas entering the bag filter 4 is also reduced accordingly. To ensure that the semi-dry process requires the bag filter to be designed with a filtration velocity of less than 0.7 m / min, the cost of the filter bags accounts for about 30% of the total cost of the bag filter. Therefore, reducing the operating temperature of the filter bags can significantly reduce the specifications, materials, and quantity of the filter bags (for example, after the temperature of the coke oven flue gas decreases, the amount of coke oven flue gas entering the bag filter is reduced, and the filter bag area will decrease when the filtration velocity of the bag filter is constant, thus reducing the number of filter bags required). This optimizes the one-time investment cost of the bag filter components and the corresponding maintenance costs in the later stages.

[0030] After the cooling, desulfurization, and dust removal meet the standards, in order to make full use of the heat of the original coke oven flue gas, the coke oven flue gas then flows from the bag filter 4 into the flue gas heater 2 of the MGGH heat exchange unit. The flue gas heater 2 heats the coke oven flue gas, and then the coke oven flue gas enters the denitrification reactor 5 for denitrification reaction. The setting of the flue gas heater 2 increases the temperature of the coke oven flue gas entering the denitrification reactor, which can reduce the load and synchronization rate of the supplementary heating system, and achieve the effect of energy saving and consumption reduction. The flue gas cooler 1 and the flue gas heater 2 constitute a closed-loop MGGH circulating heat exchange system. A circulating loop of heat exchange medium is formed between the flue gas cooler 1 and the flue gas heater 2, and the heat exchange medium is preferably softened water. After being heated by coking flue gas in the flue gas cooler 1, the heat exchange medium enters the flue gas heater 2 as the heat source medium for the flue gas heater 2. After being cooled in the flue gas heater 2, part of the heat exchange medium flows back into the flue gas cooler 1 through the softened water circulation main pipe 22, and part flows back into the flue gas heater 2 through the softened water return pipe 21. If necessary, the softened water heat exchange medium cooled by the flue gas heater 2 can also be completely returned to the flue gas cooler 1 for cooling the original coking flue gas. The softened water return pipe 21 is an auxiliary... Figure 1 The pipe indicated by the upward arrow in the middle is the main softened water circulation pipe 22. Figure 1 The pipeline indicated by the downward arrow in the middle, the softened water return pipeline 21 controls the actual amount of softened water entering the flue gas heater 2 through the valve, thereby controlling the heat exchange of the circulation system and the flue gas temperature at the outlet of the flue gas cooler, so as to meet the temperature requirements of the desulfurization reaction; the softened water circulation main pipeline 22 is for transferring heat from the flue gas cooler and the reheater through water medium.

[0031] Preferably, the softened water flowing out of the flue gas heater 2 enters the softened water return pipeline 21 and the softened water circulation main pipeline 22 respectively through the softened water circulation pump 23, wherein the softened water circulation pump 23 includes one working and one standby softened water circulation pump, which is used to provide power for the heat transfer medium of the flue gas cooler and heater.

[0032] Preferably, the flue gas waste heat comprehensive utilization system further includes a desulfurization and denitrification unit, which includes a desulfurization reactor 3 (preferably using sodium bicarbonate process for desulfurization, with NaHCO3 as the desulfurizing agent), a bag filter 4, and a denitrification reactor 5 (preferably using medium-low temperature SCR process for denitrification, with 20% concentration ammonia water as the denitrification agent).

[0033] As a preferred embodiment, the flue gas waste heat utilization system also includes an ammonia wastewater heat exchange unit. The coking flue gas flowing out from the desulfurization and denitrification process enters the ammonia wastewater heat exchange unit, and the waste heat of the coking flue gas is used in the ammonia stripping process of the ammonia stripping wastewater. The ammonia wastewater can be the ammonia stripping wastewater from the coking plant's own ammonia stripping section. This setup allows the chemical production workshop to be organically combined with desulfurization and denitrification, so that they can benefit each other and enable the coking plant to achieve the goal of cost reduction and efficiency improvement.

[0034] Preferably, the ammonia wastewater heat exchange unit includes an ammonia water heat exchange component, which includes a first steam-water heat exchanger and a second steam-water heat exchanger connected together. The first steam-water heat exchanger is preferably a heat pipe steam generator 6, and the second steam-water heat exchanger is preferably a steam collecting heat exchanger 7. The heat pipe steam generator 6 is used to exchange heat between coking flue gas and softened water, so that the softened water is vaporized to form softened water vapor. The steam collecting heat exchanger 7 is used to exchange heat between the softened water vapor and the ammonia wastewater, so that the temperature of the ammonia wastewater increases. Preferably, a downcomer 9 and an upcomer 10 are provided between the heat pipe steam generator 6 and the steam collector heat exchanger 7. The downcomer 9 is used to transport softened water from the shell side of the steam collector heat exchanger 7 to the steam generator 6. The upcomer 10 is used to transport softened water steam formed in the heat pipe steam generator 6 from the heat pipe steam generator 6 to the shell side of the steam collector heat exchanger 7. The cooling water (softened water) is initially introduced into the steam collector heat exchanger 7 and then undergoes a phase change cycle without frequent water replenishment. However, if the liquid level in the downcomer 9 drops due to leakage, water will be replenished in a chain reaction.

[0035] Preferably, the ammonia wastewater heat exchange unit further includes an ammonia stripping tower 11, and the tube side of the ammonia stripping tower 11 and the second steam-water heat exchanger, i.e., the steam-collecting heat exchanger 7, forms a circulation path for the ammonia wastewater. Preferably, the ammonia wastewater outlet of the ammonia stripping tower 11 is connected to the tube side inlet of the steam-collecting heat exchanger 7, and the tube side outlet of the steam-collecting heat exchanger 7 is connected to the ammonia wastewater inlet of the ammonia stripping tower 11. Preferably, a flash evaporator 12 is provided inside the ammonia stripping tower 11 for flash evaporation of the ammonia wastewater entering the ammonia stripping tower 11.

[0036] Preferably, a pressure transmitter 25 for judging the resistance of the heat exchanger, a waste ammonia water variable frequency circulation pump 27 for adjusting the flow rate of waste ammonia water, and a pressure gauge 24 are provided on the pipeline between the steam heat exchangers 7 and 11.

[0037] Specifically, firstly, softened water (preferably industrial softened water, which can cause scaling in the system's pipes, etc.) enters the softened water tank 18 from the owner's softened water unit 14 (wherein, a flow meter 16 for media consumption statistics and a water supply valve 17 for low-level interlocking water supply to the softened water tank 18 are installed on the pipeline between the owner's softened water unit 14 and the softened water tank 18; a level gauge 19 for softened water tank level display and interlocking alarm and an overflow pipe 20 are installed on the softened water tank 18), then enters the shell side of the steam collector heat exchanger 7 (steam collector shell and tube heat exchanger) through the water supply pipe 28 of the steam collector heat exchanger and the softened water pump 8. Afterwards, the softened water enters the heat pipe steam generator 6 from the shell side of the steam collector shell and tube heat exchanger 7 through the downcomer 9. In heat exchanger 6, softened water and coking flue gas (approximately 200°C) entering the heat pipe steam generator 6 from the denitrification reactor 5 exchange heat. The softened water absorbs heat to become saturated water, then absorbs more heat to become saturated steam. The saturated steam then enters the shell side of the steam collector heat exchanger 7 via riser 10. Ammonia wastewater flows from the wastewater outlet of the ammonia stripping tower 11 into the tube side of the steam collector heat exchanger 7. The ammonia wastewater and saturated steam exchange heat in the steam collector heat exchanger 7 (the ammonia wastewater exchanges heat with the shell-side steam in the tube side). After the ammonia wastewater temperature rises by approximately 15-20°C, it is pumped back to the ammonia stripping tower 11 in the chemical production section for flash evaporation. The cooling saturated water then re-enters the heat pipe steam generator 6 through downcomer 9 to generate, for example, 0.3 MPa. 140℃ steam circulates back and forth between the heat pipe steam generator 6 and the steam collection heat exchanger 7 in a closed-loop steam-water cycle, thereby completing the flash evaporation of ammonia wastewater in the ammonia stripping tower 11. Finally, the coking flue gas is discharged through the induced draft fan 13.

[0038] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A comprehensive waste heat utilization system for coke oven flue gas in a semi-dry process, characterized in that, The flue gas waste heat utilization system includes an ammonia wastewater heat exchange unit, which uses the waste heat from the desulfurization and denitrification coking flue gas to strip ammonia from the wastewater. in, The ammonia wastewater heat exchange unit includes an ammonia water heat exchange component, which is used to exchange heat between the coking flue gas and the ammonia wastewater. The ammonia water heat exchange component includes a first steam-water heat exchanger and a second steam-water heat exchanger connected together. The first steam-water heat exchanger is used to exchange heat between the coking flue gas and softened water, so that the softened water forms softened water vapor. The second steam-water heat exchanger is used to exchange heat between the softened water vapor and the ammonia wastewater, so that the temperature of the ammonia wastewater increases. A circulation loop for the heat exchange medium is formed between the first and second steam-water heat exchangers. The heat exchange medium is heated by coking flue gas in the first steam-water heat exchanger, enters the second steam-water heat exchanger, and is cooled in the second steam-water heat exchanger before returning to the first steam-water heat exchanger as a cold source medium. A downcomer and a riser are provided between the first and second steam-water heat exchangers. The downcomer is used to transport the softened water entering the shell side of the second steam-water heat exchanger from the shell side to the first steam-water heat exchanger. The riser is used to transport the softened water steam from the first steam-water heat exchanger to the shell side of the second steam-water heat exchanger. The first steam-water heat exchanger is a heat pipe steam generator; the second steam-water heat exchanger is a steam collecting heat exchanger. The softened water enters the heat pipe steam generator through the downcomer to generate 0.3 MPa 140℃ steam, and the steam-water mixture circulates back and forth between the heat pipe steam generator and the steam collecting heat exchanger in a closed-loop steam-water cycle. The flue gas inlet of the first steam-water heat exchanger is connected to the flue gas outlet of the denitrification reactor in the desulfurization and denitrification process. The ammonia wastewater heat exchange unit also includes an ammonia stripping tower. The ammonia wastewater flows from the ammonia stripping tower into the ammonia water heat exchange component. After heat exchange, the temperature of the ammonia wastewater increases by 15-20°C and flows back to the ammonia stripping tower for flash evaporation. The ammonia stripping tower and the tube side of the second steam-water heat exchanger form a circulation path for ammonia wastewater; the ammonia wastewater outlet of the ammonia stripping tower is connected to the tube side inlet of the second steam-water heat exchanger, and the tube side outlet of the second steam-water heat exchanger is connected to the ammonia wastewater inlet of the ammonia stripping tower. The ammonia stripping tower is equipped with a flash tank for flash evaporation of the ammonia wastewater.

2. The flue gas waste heat comprehensive utilization system according to claim 1, characterized in that, The flue gas waste heat utilization system also includes an MGGH heat exchange unit, which includes a flue gas cooler and a flue gas heater. The flue gas cooler is used to reduce the inlet temperature of coking flue gas in the desulfurization and dust removal process, and the flue gas heater is used to increase the inlet temperature of coking flue gas in the denitrification process.

3. The flue gas waste heat comprehensive utilization system according to claim 2, characterized in that, A circulation loop of heat exchange medium is formed between the flue gas cooler and the flue gas heater; the heat exchange medium enters the flue gas heater after being heated by coking flue gas in the flue gas cooler, and then after being cooled in the flue gas heater, part of the heat exchange medium flows into the flue gas cooler and part flows back into the flue gas heater.

4. The flue gas waste heat comprehensive utilization system according to claim 3, characterized in that... The heat exchange medium is softened water.

5. The flue gas waste heat comprehensive utilization system according to claim 2, characterized in that, The flue gas outlet of the flue gas cooler is connected to the flue gas inlet of the desulfurization reactor.

6. The flue gas waste heat comprehensive utilization system according to claim 5, characterized in that, The flue gas inlet of the flue gas heater is connected to the flue gas outlet of the dust collector, and the flue gas outlet of the flue gas heater is connected to the flue gas inlet of the denitrification reactor.

7. The flue gas waste heat comprehensive utilization system according to claim 6, characterized in that, The dust collector is a bag filter.

8. The flue gas waste heat comprehensive utilization system according to claim 6, characterized in that, The flue gas waste heat comprehensive utilization system also includes a desulfurization and denitrification unit, which includes the desulfurization reactor, the dust collector and the denitrification reactor connected in sequence along the flue gas flow direction.

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