A desulfurization wastewater zero discharge process and system coupled with a flue gas desulfurization and denitrification process

Abstract

This invention relates to a zero-discharge process and system for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes. The zero-discharge system for desulfurization wastewater consists of a spray drying tower, a desulfurization ash addition device, a desulfurization ash mixer, a bag filter, an induced draft fan, and a salt bin. The flue gas desulfurization and denitrification process system is coupled with a bypass flue drying system. The hot flue gas from the end of the limestone-gypsum wet denitrification process is mixed with the neutralized desulfurization wastewater. Soluble salts and suspended solids in the desulfurization wastewater evaporate under the hot flue gas. The evaporated solids are collected by the bag filter and disposed of uniformly. This invention achieves "waste-to-waste treatment," eliminating the need for additional chemical agents and increasing steam consumption, resulting in low system operating costs. Each process step is unaffected by fluctuations in the composition of the desulfurization wastewater, the composition of the added desulfurization ash, or the flue gas composition. The process flow is short, with high operational stability, low equipment operation and maintenance costs, and unattended operation is possible.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater purification technology, and in particular to a zero-discharge process and system for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes. Background Technology

[0002] Currently, the mainstream technologies for flue gas purification in the steel industry for sintering and pelletizing are limestone-gypsum wet desulfurization and denitrification processes and semi-dry desulfurization and denitrification processes. Among them, the limestone-gypsum wet desulfurization and denitrification process generates desulfurization wastewater, which contains suspended solids, chloride ions, sulfate ions, heavy metals, etc. In order to meet the emission standards, it needs to be purified. Most steel companies use wet flushing after treating the desulfurization wastewater through a three-compartment tank (neutralization tank + settling tank + clarification tank), or use long-process evaporation crystallization to separate crystalline salts.

[0003] However, the above methods for treating desulfurization wastewater have obvious defects and shortcomings: the triple-tank treatment + wet slag flushing method uses the desulfurization wastewater for slag cooling and transportation, and the pollutants in the wastewater are "solidified" in the slag-water system or slag. This only achieves pollutant transfer and still poses environmental risks, easily causing secondary pollution from heavy metals and high salt ions, and does not truly achieve wastewater discharge compliance. While the long-process evaporation crystallization process can achieve zero discharge, its process flow is long, its operational stability is poor, and its investment and operating costs are high, as detailed below: (1) The chloride ions, sulfate ions, heavy metals and other substances in the desulfurization wastewater of steel enterprises exceed the standard. Using it for wet slag flushing can easily cause environmental problems such as groundwater pollution and odorous gas overflow. Usually, the chloride ion content in the desulfurization wastewater is ≥20000mg / L and the salt content is ≥35000mg / L. It is highly corrosive and poses a safety hazard to the stable operation of the blast furnace slag flushing production process equipment.

[0004] (2) The long-process evaporation crystallization process has a long process flow and introduces a variety of chemical agents, which increases energy consumption such as steam and electricity, resulting in high operating and investment costs.

[0005] (3) The long-process evaporation crystallization process is affected by factors such as high salt and calcium scale in desulfurization wastewater, water quality fluctuations, and inadequate equipment operation and maintenance. The system has poor operational stability and requires high operational skills from operators.

[0006] Therefore, how steel companies can achieve short-process, stable, efficient, and low-cost resource utilization of desulfurization wastewater remains an urgent problem to be solved. Summary of the Invention

[0007] This invention provides a zero-discharge process and system for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes. The flue gas desulfurization and denitrification process system is coupled with a bypass flue drying system. The hot flue gas from the end of the limestone-gypsum wet denitrification process is mixed with the neutralized desulfurization wastewater. Soluble salts and suspended solids in the wastewater evaporate under the hot flue gas, and the evaporated solids are collected by a bag filter and disposed of centrally. This invention achieves "waste-to-waste treatment," eliminating the need for additional chemical reagents and increasing steam consumption, resulting in low operating costs. It also reduces the amount of ammonia injected in the denitrification section, improving denitrification efficiency. Each process step is unaffected by fluctuations in the composition of the desulfurization wastewater, the composition of the chemically added desulfurization ash, or the composition of the flue gas. The process flow is short, with high operational stability, low equipment operation and maintenance costs, and can be performed unattended.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A zero-discharge process for desulfurization wastewater coupled with flue gas desulfurization and denitrification is disclosed. In the flue gas desulfurization and denitrification process, the flue gas from the steel industry undergoes a series of purification processes, including electrostatic dust removal, heat exchange and cooling, wet desulfurization, wet electrostatic dust removal, heating, SCR denitrification, and heat exchange and cooling, before being discharged in compliance with emission standards. Desulfurization wastewater is generated during the wet desulfurization process. The zero-discharge process for desulfurization wastewater includes the following steps: 1) Under the action of the induced draft fan, a portion of the hot flue gas with a temperature of 250-300℃ after wet desulfurization and heating is introduced tangentially into the top of the spray drying tower as a heat source for the evaporation of desulfurization wastewater. 2) The desulfurization wastewater is drawn out by the wastewater pump, and desulfurization ash is added into the desulfurization wastewater pipeline. The desulfurization ash and desulfurization wastewater are mixed in the desulfurization ash mixer and neutralized. The solid content in the neutralized desulfurization wastewater is ≤200000mg / L and the pH value is 7~9. 3) In the spray drying tower, the neutralized desulfurization wastewater is atomized and sprayed out by the atomizer, and comes into direct contact with the hot flue gas and mixes thoroughly. The desulfurization wastewater evaporates under the action of high temperature flue gas, and the generated crystalline salt is collected at the bottom of the spray drying tower and sent into the salt bin by the bin pump. 4) Under the action of the induced draft fan, the flue gas after evaporation and cooling in the spray drying tower carries the crystalline salt particles into the bag filter. The temperature of the flue gas exiting the spray drying tower is ≥130℃. The intercepted crystalline salt particles are collected by the ash hopper at the bottom of the bag filter and then sent to the salt silo through the second silo pump. 5) The flue gas purified by the bag filter is reintroduced into the flue gas desulfurization and denitrification process system and merged into the flue gas pipeline after desulfurization and before heating; the crystallized salt in the salt tank is periodically discharged and centrally treated.

[0009] Both the induced draft fan and the wastewater pump are controlled by frequency conversion. The flow rate of the hot flue gas entering the spray drying tower is adjusted according to the real-time monitored temperature of the hot flue gas and the pressure difference between the inlet and outlet of the spray drying tower. The flow rate of the desulfurization wastewater entering the spray drying tower is also adjusted through the interlocking control system.

[0010] The desulfurization wastewater generated during the wet desulfurization process is replaced by other high-salt wastewater, which includes activated coke acid desulfurization wastewater, coal gas condensate, dust removal ash washing water, and reverse osmosis ultra-concentrated solution. The other high-salt wastewater is directly introduced into the desulfurization ash mixer and mixed with the desulfurization ash.

[0011] The heating process is completed by a heating furnace. A hot flue gas shut-off valve and a hot flue gas flow regulating valve are installed on the hot flue gas pipeline between the heating furnace and the spray drying tower. The flue gas purified by the bag filter re-enters the flue gas desulfurization and denitrification process system through the flue gas bypass pipeline, which is equipped with a flue gas shut-off valve.

[0012] The flue gas from the steel industry is sintering flue gas and / or pelletizing flue gas. The flue gas from the steel industry exchanges heat with the flue gas after wet electrostatic precipitator in the flue gas reheater to cool down. After the flue gas from the steel industry is cooled down, it enters the wet desulfurization reaction tower for wet desulfurization. After the flue gas after wet electrostatic precipitator is heated up, it enters the flue gas heat exchanger to exchange heat with the clean flue gas after SCR denitrification reaction. After further heat exchange and heating, the flue gas enters the heating furnace for heating. After the clean flue gas is cooled down, it is discharged through the chimney.

[0013] A zero-discharge system for desulfurization wastewater coupled with a flue gas desulfurization and denitrification process is proposed. The flue gas desulfurization and denitrification process system comprises an electrostatic precipitator, a flue gas reheater, a wet desulfurization reaction tower, a wet electrostatic precipitator, a flue gas heat exchanger, a heating furnace, an SCR denitrification reactor, and a chimney, all connected sequentially via flue gas ducts. The zero-discharge system for desulfurization wastewater comprises a spray drying tower, a desulfurization ash addition device, a desulfurization ash mixer, a bag filter, an induced draft fan, and a salt bin. The hot flue gas outlet of the heating furnace is connected to the tangential flue gas inlet at the top of the spray drying tower via a hot flue gas duct. The wet desulfurization process... The desulfurization wastewater outlet of the reaction tower is connected to the atomizer at the top of the spray drying tower via a desulfurization wastewater pipeline; a wastewater pump and a desulfurization ash mixer are installed on the desulfurization wastewater pipeline, and the desulfurization ash mixer is equipped with a desulfurization ash inlet connected to the desulfurization ash addition device; the crystallization salt outlet at the bottom of the spray drying tower is connected to the salt bin via crystallization salt pipeline one, and a bin pump one is installed on crystallization salt pipeline one; the flue gas outlet of the spray drying tower is connected to the bag filter and induced draft fan via an outlet flue gas pipeline, and the crystallization salt outlet of the ash hopper at the bottom of the bag filter is connected to the salt bin via crystallization salt pipeline two, and a bin pump two is installed on crystallization salt pipeline two.

[0014] The wastewater pump is a variable frequency pump, and the induced draft fan is a variable frequency fan. At least three layers of temperature transmitters are installed inside the spray drying tower. An inlet flue gas temperature transmitter and an inlet flue gas pressure transmitter are installed on the upstream hot flue gas duct of the spray drying tower, and an outlet flue gas temperature transmitter and an outlet flue gas pressure transmitter are installed on the downstream outlet flue gas duct of the spray drying tower. The inlet flue gas temperature transmitter, inlet flue gas pressure transmitter, outlet flue gas temperature transmitter, and outlet flue gas pressure transmitter are connected to the induced draft fan and wastewater pump via a control system. The silo pump is interlocked with the control system; the flue gas inlet pipe of the bag filter is equipped with an inlet flue gas pressure transmitter II, and the flue gas outlet pipe is equipped with an outlet flue gas pressure transmitter II. The flue gas pressure transmitter II and the outlet flue gas pressure transmitter II are interlocked with the control system and the silo pump II; the desulfurization ash addition device is equipped with a dosing control valve, and the desulfurization wastewater pipe downstream of the mixer is equipped with a solid particulate matter detection device and a pH value detection device. The solid particulate matter detection device and the pH value detection device are interlocked with the dosing control valve and the control system.

[0015] The flue gas reheater is an MGGH flue gas reheater or a WGGH flue gas reheater; an industrial fresh water inlet is provided on the desulfurization wastewater pipeline near the wet desulfurization reaction tower.

[0016] The flue gas outlet of the induced draft fan is connected to the flue gas pipeline upstream of the flue gas heat exchanger via a flue gas bypass pipeline, and a flue gas shut-off valve is installed on the flue gas bypass pipeline.

[0017] The hot flue gas pipeline between the heating furnace and the spray drying tower is equipped with a hot flue gas shut-off valve and a hot flue gas flow regulating valve.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1) In this invention, the neutralized desulfurization wastewater and the hot flue gas after limestone-gypsum wet flue gas denitrification enter the spray drying tower at the same time. The heat of the hot flue gas is used to spray dry the desulfurization wastewater, and the alkaline desulfurization ash is used to neutralize the desulfurization wastewater. The suspended solids and crystalline salts in the spray drying tower are collected by a bag filter and sent to the salt bin for unified disposal. This achieves low-cost, zero-discharge treatment of desulfurization wastewater with high salt content, and the process flow is short. 2) This invention achieves "waste treatment with waste", the system does not require the introduction of other chemical agents, does not increase steam consumption, and has low operating costs; 3) The ammonia nitrogen in the sintering / pelletizing desulfurization wastewater is used to convert the spray-dried flue gas into ammonia-containing flue gas. The ammonia-containing flue gas after passing through the bag filter is re-entered into the flue gas desulfurization and denitrification process system, which can reduce the amount of ammonia injected into the denitrification unit and improve the denitrification effect.

[0019] 4) Each process step is not affected by fluctuations in the composition of desulfurization wastewater, the composition of chemical desulfurization ash, or the composition of flue gas, resulting in high operational stability and low equipment operation and maintenance costs. 5) The flow rate of hot flue gas entering the spray drying tower and the flow rate of desulfurization wastewater can be automatically adjusted according to specific process parameters such as flue gas temperature and evaporation mixing effect. The degree of automation is high and it can achieve unattended operation. Attached Figure Description

[0020] Figure 1 This is a flowchart of the zero-discharge process for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes as described in this invention.

[0021] In the diagram: 1. Electrostatic precipitator 2. Flue gas reheater 3. Wet desulfurization reaction tower 4. Wet electrostatic precipitator 5. Flue gas heat exchanger 6. Heating furnace 7. SCR denitrification reactor 8. Chimney 9. Spray drying tower 10. Bag filter 11. Exhaust fan 12. Silo pump 1 13. Silo pump 2 14. Salt silo 15. Desulfurization ash addition device 16. Desulfurization ash mixer 17. Hot flue gas shut-off valve 18. Hot flue gas flow regulating valve 19. Flue gas shut-off valve Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings: like Figure 1 As shown, the present invention discloses a zero-discharge process for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes. In the flue gas desulfurization and denitrification process, the flue gas from the steel industry undergoes a series of purification processes, including electrostatic dust removal, heat exchange and cooling, wet desulfurization, wet electrostatic dust removal, heating, SCR denitrification, and heat exchange and cooling, before being discharged in compliance with standards. Desulfurization wastewater is generated during the wet desulfurization process. The zero-discharge process for desulfurization wastewater includes the following steps: 1) Under the action of the induced draft fan 11, a portion of the hot flue gas with a temperature of 250-300℃ after wet desulfurization and heating is introduced tangentially into the top of the spray drying tower 9 as a heat source for the evaporation of desulfurization wastewater. 2) The desulfurization wastewater is drawn out by the wastewater pump and desulfurization ash is added into the desulfurization wastewater pipeline. The desulfurization ash and desulfurization wastewater are mixed in the desulfurization ash mixer 16 and neutralized. The solid content in the neutralized desulfurization wastewater is ≤200000mg / L and the pH value is 7~9. 3) In the spray drying tower 9, the neutralized desulfurization wastewater is atomized and sprayed out by the atomizer, and comes into direct contact with the hot flue gas and mixes thoroughly. The desulfurization wastewater evaporates under the action of the high temperature flue gas, and the generated crystalline salt is collected at the bottom of the spray drying tower 9 and sent into the salt bin 14 through the bin pump 12. 4) Under the action of the induced draft fan 11, the flue gas after evaporation and cooling in the spray drying tower 9 carries the crystalline salt particles into the bag filter 10. The flue gas temperature exiting the spray drying tower 9 is ≥130℃. The intercepted crystalline salt particles are collected by the ash hopper at the bottom of the bag filter 10 and then sent to the salt silo 14 by the second silo pump 13. 5) The flue gas purified by the bag filter 10 re-enters the flue gas desulfurization and denitrification process system and flows into the flue gas pipeline after desulfurization and before heating; the crystallized salt in the salt bin 14 is periodically discharged and centrally treated.

[0023] The induced draft fan 11 and the wastewater pump are both controlled by frequency conversion. The flow rate of the hot flue gas entering the spray drying tower 9 is adjusted according to the real-time monitored temperature of the hot flue gas and the pressure difference between the inlet and outlet of the flue gas in the spray drying tower 9. The flow rate of the desulfurization wastewater entering the spray drying tower 9 is also adjusted by interlocking the control system.

[0024] This invention can not only treat desulfurization wastewater generated during wet desulfurization (such as limestone-gypsum wet desulfurization), but also treat other high-salt wastewater including activated coke acid desulfurization wastewater, coal gas condensate, dust removal ash washing water and reverse osmosis ultra-concentrated liquid. Other high-salt wastewater can be directly introduced into the desulfurization ash mixer to mix with the desulfurization ash.

[0025] The heating process is completed by the heating furnace 6. A hot flue gas shut-off valve 17 and a hot flue gas flow regulating valve 18 are installed on the hot flue gas pipeline between the heating furnace 6 and the spray drying tower 9. The flue gas purified by the bag filter 10 re-enters the flue gas desulfurization and denitrification process system through the flue gas bypass pipeline. A flue gas shut-off valve 19 is installed on the flue gas bypass pipeline.

[0026] The flue gas from the steel industry is sintering flue gas and / or pelletizing flue gas. The flue gas from the steel industry exchanges heat with the flue gas after wet electrostatic precipitator in the flue gas reheater 2 to cool down. After the flue gas from the steel industry is cooled down, it enters the wet desulfurization reaction tower 3 for wet desulfurization. After the flue gas after wet electrostatic precipitator is heated up, it enters the flue gas heat exchanger 2 to exchange heat with the clean flue gas after SCR denitrification reaction. After further heat exchange and heating, the flue gas enters the heating furnace 6 for heating. After the clean flue gas is cooled down, it is discharged through the chimney 8.

[0027] like Figure 1As shown, the present invention discloses a zero-discharge system for desulfurization wastewater coupled with a flue gas desulfurization and denitrification process. The flue gas desulfurization and denitrification process system consists of an electrostatic precipitator 1, a flue gas reheater 2, a wet desulfurization reaction tower 3, a wet electrostatic precipitator 4, a flue gas heat exchanger 5, a heating furnace 6, an SCR denitrification reactor 7, and a chimney 8, which are connected sequentially through a flue gas pipeline. The zero-discharge system for desulfurization wastewater consists of a spray drying tower 9, a desulfurization ash addition device 15, a desulfurization ash mixer 16, a bag filter 10, an induced draft fan 11, and a salt bin 14. The hot flue gas outlet of the heating furnace 6 is connected to the tangential flue gas inlet at the top of the spray drying tower 9 through a hot flue gas pipeline. The desulfurization wastewater outlet of the wet desulfurization reaction tower 3 is connected to the atomizer at the top of the spray drying tower 9 through a desulfurization wastewater pipeline; a wastewater pump and a desulfurization ash mixer are installed on the desulfurization wastewater pipeline, and the desulfurization ash mixer is equipped with a desulfurization ash inlet connected to the desulfurization ash addition device 15; the crystallization salt outlet at the bottom of the spray drying tower 9 is connected to the salt bin 14 through a crystallization salt pipeline, and a bin pump 12 is installed on the crystallization salt pipeline; the flue gas outlet of the spray drying tower 9 is connected to the bag filter 10 and the induced draft fan 11 through an outlet flue gas pipeline, and the crystallization salt outlet of the ash hopper at the bottom of the bag filter 10 is connected to the salt bin 14 through a crystallization salt pipeline, and a bin pump 13 is installed on the crystallization salt pipeline.

[0028] The wastewater pump is a variable frequency pump, and the induced draft fan 11 is a variable frequency fan; at least three layers of temperature transmitters are installed inside the spray drying tower; an inlet flue gas temperature transmitter and an inlet flue gas pressure transmitter are installed on the hot flue gas duct upstream of the spray drying tower 9, and an outlet flue gas temperature transmitter and an outlet flue gas pressure transmitter are installed on the outlet flue gas duct downstream of the spray drying tower 9. The inlet flue gas temperature transmitter, inlet flue gas pressure transmitter, outlet flue gas temperature transmitter, and outlet flue gas pressure transmitter are interlocked with the induced draft fan 11, wastewater pump, and silo pump 12 through a control system (to regulate the flow rate of hot flue gas and desulfurization wastewater). (And ash is fed in a timed manner according to the inlet and outlet pressure difference); the flue gas inlet pipe of the bag filter 10 is equipped with an inlet flue gas pressure transmitter 2, and the flue gas outlet pipe is equipped with an outlet flue gas pressure transmitter 2. The flue gas pressure transmitter 2 and the outlet flue gas pressure transmitter 2 are interlocked with the silo pump 2 13 through the control system (and ash is fed in a timed manner according to the inlet and outlet pressure difference); the desulfurization ash addition device 15 is equipped with a dosing control valve, and the desulfurization wastewater pipe downstream of the desulfurization ash mixer is equipped with a solid particulate matter detection device and a pH value detection device. The solid particulate matter detection device and the pH value detection device are interlocked with the dosing control valve through the control system.

[0029] The flue gas reheater 2 is an MGGH flue gas reheater or a WGGH flue gas reheater; an industrial fresh water inlet is provided on the desulfurization wastewater pipeline near the wet desulfurization reaction tower 3.

[0030] The flue gas outlet of the induced draft fan 11 is connected to the flue gas pipeline upstream of the flue gas heat exchanger 5 through a flue gas bypass pipeline, and a flue gas shut-off valve 19 is installed on the flue gas bypass pipeline.

[0031] A hot flue gas shut-off valve 17 and a hot flue gas flow regulating valve 18 are installed on the hot flue gas pipeline between the heating furnace 6 and the spray drying tower 9.

[0032] This invention provides a zero-discharge process and system for desulfurization wastewater in the steel industry. Coupled with a flue gas desulfurization and denitrification process and system, the neutralized desulfurization wastewater is mixed with hot flue gas from the end of a limestone-gypsum wet flue gas denitrification process. A special flow field is formed within a spray drying tower 9, where the desulfurization wastewater containing soluble salts and suspended solids evaporates under the hot flue gas. The evaporated solid crystalline salt is collected in a salt tank 14 for centralized treatment, thereby achieving zero discharge of desulfurization wastewater. The main process and effects are as follows: (1) The hot flue gas from the downstream heating furnace 6 of limestone-gypsum wet denitrification is used as the heat source. The temperature of the hot flue gas in this section is 250-300℃. The hot flue gas is introduced tangentially into the spray drying tower 9. The desulfurization wastewater after neutralization is sprayed through an atomizer at the top of the spray drying tower 9 and fully mixed with the hot flue gas. The desulfurization wastewater containing soluble and suspended solid particles is evaporated under the high temperature flue gas. Most of the solid entrainment (crystallized salt) after evaporation enters the bag filter 10 with the cooled flue gas. After being collected by the bag filter 10, it is sent to the salt bin 14. A small portion of the crystallized salt collected at the bottom of the spray drying tower 9 also enters the salt bin 14.

[0033] (2) The present invention adds a zero-discharge system for desulfurization wastewater to the existing flue gas desulfurization and denitrification system. It consists of an induced draft fan 11, a bag filter 10, a spray drying tower 9, a desulfurization ash addition device 15, a first silo pump 12, a second silo pump 13 and a salt silo 14. The desulfurization wastewater is dried and evaporated by hot flue gas, thereby achieving zero-discharge treatment of desulfurization flue gas and desulfurization wastewater, i.e., "treating waste with waste".

[0034] This invention includes a hot flue gas shut-off valve 17 (such as a manual damper) and a hot flue gas flow regulating valve 18 (such as an electric regulating valve) installed on the hot flue gas pipeline, and a flue gas shut-off valve 19 (such as a manual damper) installed on the flue gas bypass pipeline. If the desulfurization wastewater zero-discharge system requires equipment maintenance, it can be isolated from the flue gas desulfurization and denitrification system through the hot flue gas shut-off valve 17 and the flue gas shut-off valve 19, without affecting the normal operation of the flue gas desulfurization and denitrification system.

[0035] (3) The present invention is equipped with a control system that adjusts the flow rate of desulfurization wastewater and hot flue gas entering the spray drying tower 9 at any time according to the operating status of the limestone-gypsum wet denitrification system and the zero-discharge system for desulfurization wastewater. Preferably, the flow rate of hot flue gas entering the zero-discharge system for desulfurization wastewater is 3% to 5% of the total hot flue gas at the end of the limestone-gypsum wet denitrification process, and the increase in moisture content of the flue gas flowing out of the spray drying tower 9 is ≤1.0% (approximately 0.5% to 1.0% during actual operation).

[0036] (4) In this invention, the agent used for the neutralization treatment of desulfurization wastewater is desulfurization ash produced by the steel enterprise itself, such as calcium-based desulfurization ash produced by CFB desulfurization (circulating fluidized bed flue gas desulfurization) or sodium-based desulfurization ash produced by SDS desulfurization (sodium bicarbonate dry desulfurization), so as to achieve "waste treatment with waste". The system does not need to introduce other chemical agents and does not increase steam consumption.

[0037] (5) The desulfurization wastewater zero discharge system described in this invention is not affected by fluctuations in the composition of desulfurization wastewater, chemical dosing (desulfurization ash) and flue gas composition. It has high operational stability, short process flow, low equipment operation and maintenance costs, and can achieve automatic control (unattended operation).

[0038] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0039]

Example

[0040] The zero-discharge system for desulfurization wastewater includes: 1 induced draft fan 11, 1 bag filter 10, 1 spray drying tower 9, 1 desulfurization ash addition device 15, 1 desulfurization ash mixer 16, 2 silo pumps (silo pump one 12 and silo pump two 13) and 1 salt silo 14. The hot flue gas inlet of spray drying tower 9 is connected to the hot flue gas pipeline after the heating furnace 6 in the limestone-gypsum wet flue gas denitrification system. The desulfurization wastewater pipeline from the limestone-gypsum wet flue gas denitrification system is connected to the desulfurization wastewater inlet of spray drying tower 9. A desulfurization ash mixer is installed on the desulfurization wastewater pipeline. The desulfurization ash inlet of the desulfurization ash mixer is connected to the desulfurization ash addition device 15. The flue gas outlet of spray drying tower 9 is connected to bag filter 10. The bottom of spray drying tower 9 is connected to salt bin 14 through crystallization salt pipeline 1 and bin pump 12. The flue gas outlet of bag filter 10 is connected to the flue gas inlet of induced draft fan 11. The ash hopper at the bottom of bag filter 10 is connected to salt bin 14 through crystallization salt pipeline 2 and bin pump 2 13. The flue gas outlet of induced draft fan 11 is connected to the flue gas pipeline upstream of flue gas heat exchanger 5 in the limestone-gypsum wet flue gas denitrification system through a flue gas bypass pipeline.

[0041] In this embodiment, manual dampers and electric regulating dampers are installed on the hot flue gas duct, and a manual damper is installed on the flue gas bypass duct. A frequency-controlled wastewater pump and a pH monitoring device are installed on the desulfurization wastewater duct, and an industrial fresh water flushing system is installed on the desulfurization wastewater duct near the wet desulfurization reaction tower 3. Temperature transmitters and pressure transmitters are installed at the hot flue gas inlet and outlet of the spray drying tower 9, respectively. The induced draft fan 11 is frequency-controlled. Three temperature transmitters are spaced at intervals along the height of the spray drying tower 9.

[0042] A portion of the hot flue gas (controlled at 3%–5% of the total flue gas volume) extracted from the heating furnace 6 in the limestone-gypsum wet flue gas denitrification system enters the spray drying tower 9. Desulfurization wastewater, neutralized by desulfurization ash, is pumped into the spray drying tower 9 and mixed with the hot flue gas. The amount of hot flue gas entering the spray drying tower 9 is controlled within a set range by frequency conversion adjustment of the induced draft fan 11, and the amount of desulfurization wastewater entering the spray drying tower 9 is also controlled within a set range by frequency conversion adjustment of the wastewater pump, thereby creating a specific flow field within the spray drying tower 9.

[0043] After passing through the atomizing nozzle, the desulfurization wastewater is mixed with the hot flue gas in the form of fine liquid particles. The large surface area of ​​contact between the two ensures thorough evaporation of the desulfurization wastewater. The outlet flue gas temperature of the spray drying tower 9 should be controlled above 130℃ to ensure that it does not condense or carry unevaporated liquid before entering the bag filter. After the desulfurization wastewater containing soluble and suspended solid particles evaporates, the solid entrainment (crystalline salt) is collected at the bottom of the bag filter 10 and the spray drying tower 9, and then pumped to the salt bin 14 via the corresponding pump.

[0044] In this embodiment, the dissolved solids content in the desulfurization wastewater after neutralization treatment is controlled to be no higher than 200,000 mg / L, and the pH value is 7-9; the desulfurization wastewater pipeline and spray drying tower 9 are cleaned regularly by an industrial fresh water flushing system.

[0045] In this embodiment, the control logic of the control system is as follows: 1) The injection rate of desulfurization wastewater is set according to the conditions (temperature, pressure, etc.) of the hot flue gas after limestone-gypsum wet flue gas denitrification, and the injection rate of desulfurization wastewater is set according to the water quality of desulfurization wastewater. 2) Adjust the amount of desulfurization wastewater injected according to the value of the hot flue gas temperature transmitter at the inlet of spray drying tower 9; 3) Control the outlet flue gas temperature of spray drying tower 9 within the set range of 140-150℃, adjust the opening of induced draft fan 11 by frequency converter, and control the amount of hot flue gas injected into spray drying tower 9 to ensure the heat required for drying while preventing corrosion of downstream equipment. When the outlet flue gas temperature of spray drying tower 9 is below 130℃ for 3 minutes, stop introducing desulfurization wastewater into spray drying tower 9; 4) Determine the starting interval of silo pump 12 and silo pump 2 13 based on the pressure difference between the inlet and outlet of spray drying tower 9 and bag filter 10 to achieve timed ash conveying.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A desulfurization wastewater zero discharge process coupled with a flue gas desulfurization and denitrification process, in which the flue gas of the steel industry is sequentially subjected to purification treatment processes of electrostatic precipitation, heat exchange and cooling, wet desulfurization, wet electric precipitation, heating and temperature rise, SCR denitrification, heat exchange and cooling for standard emission, and desulfurization wastewater is generated in the wet desulfurization process; characterized in that, The zero-discharge process for desulfurization wastewater includes the following steps: 1) Under the action of the induced draft fan, a portion of the hot flue gas with a temperature of 250-300℃ after wet desulfurization and heating is introduced tangentially into the top of the spray drying tower as a heat source for the evaporation of desulfurization wastewater. 2) The desulfurization wastewater is drawn out by the wastewater pump, and desulfurization ash is added into the desulfurization wastewater pipeline. The desulfurization ash and desulfurization wastewater are mixed in the desulfurization ash mixer and neutralized. The solid content in the neutralized desulfurization wastewater is ≤200000mg / L and the pH value is 7~9. 3) In the spray drying tower, the neutralized desulfurization wastewater is atomized and sprayed out by the atomizer, and comes into direct contact with the hot flue gas and mixes thoroughly. The desulfurization wastewater evaporates under the action of high temperature flue gas, and the generated crystalline salt is collected at the bottom of the spray drying tower and sent into the salt bin by the bin pump. 4) Under the action of the induced draft fan, the flue gas after evaporation and cooling in the spray drying tower carries the crystalline salt particles into the bag filter. The temperature of the flue gas exiting the spray drying tower is ≥130℃. The intercepted crystalline salt particles are collected by the ash hopper at the bottom of the bag filter and then sent to the salt silo through the second silo pump. 5) The flue gas purified by the bag filter re-enters the flue gas desulfurization and denitrification process system and merges into the flue gas pipeline after desulfurization and before heating; the crystallized salt in the salt tank is periodically discharged and centrally treated.

2. The zero-discharge process for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes according to claim 1, characterized in that, Both the induced draft fan and the wastewater pump are controlled by frequency conversion. The flow rate of the hot flue gas entering the spray drying tower is adjusted according to the real-time monitored temperature of the hot flue gas and the pressure difference between the inlet and outlet of the spray drying tower. The flow rate of the desulfurization wastewater entering the spray drying tower is also adjusted through the interlocking control system.

3. The zero-discharge process for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes according to claim 1, characterized in that, The desulfurization wastewater generated during the wet desulfurization process is replaced by other high-salt wastewater, which includes activated coke acid desulfurization wastewater, coal gas condensate, dust removal ash washing water, and reverse osmosis ultra-concentrated solution. The other high-salt wastewater is directly introduced into the desulfurization ash mixer and mixed with the desulfurization ash.

4. The zero-discharge process for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes according to claim 1, characterized in that, The heating process is completed by a heating furnace. A hot flue gas shut-off valve and a hot flue gas flow regulating valve are installed on the hot flue gas pipeline between the heating furnace and the spray drying tower. The flue gas purified by the bag filter re-enters the flue gas desulfurization and denitrification process system through the flue gas bypass pipeline, which is equipped with a flue gas shut-off valve.

5. The zero-discharge process for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes according to claim 1, characterized in that, The flue gas from the steel industry is sintering flue gas and / or pelletizing flue gas. The flue gas from the steel industry exchanges heat with the flue gas after wet electrostatic precipitator in the flue gas reheater to cool down. After the flue gas from the steel industry is cooled down, it enters the wet desulfurization reaction tower for wet desulfurization. After the flue gas after wet electrostatic precipitator is heated up, it enters the flue gas heat exchanger to exchange heat with the clean flue gas after SCR denitrification reaction. After further heat exchange and heating, the flue gas enters the heating furnace for heating. After the clean flue gas is cooled down, it is discharged through the chimney.

6. A zero-discharge system for desulfurization wastewater coupled with a flue gas desulfurization and denitrification process, used to achieve the zero-discharge process for desulfurization wastewater coupled with the flue gas desulfurization and denitrification process as described in any one of claims 1 to 5; characterized in that, The flue gas desulfurization and denitrification process system consists of an electrostatic precipitator, a flue gas reheater, a wet desulfurization reaction tower, a wet electrostatic precipitator, a flue gas heat exchanger, a heating furnace, an SCR denitrification reactor, and a chimney, all connected sequentially via flue gas ducts. The zero-discharge system for desulfurization wastewater comprises a spray drying tower, a desulfurization ash addition device, a desulfurization ash mixer, a bag filter, an induced draft fan, and a salt bin. The hot flue gas outlet of the heating furnace is connected to the tangential flue gas inlet at the top of the spray drying tower via a hot flue gas duct, and the desulfurization wastewater outlet of the wet desulfurization reaction tower is connected via... The desulfurization wastewater pipeline is connected to the atomizer at the top of the spray drying tower; a wastewater pump and a desulfurization ash mixer are installed on the desulfurization wastewater pipeline, and the desulfurization ash mixer is equipped with a desulfurization ash inlet connected to the desulfurization ash addition device; the crystallization salt outlet at the bottom of the spray drying tower is connected to the salt silo through crystallization salt pipeline one, and silo pump one is installed on crystallization salt pipeline one; the flue gas outlet of the spray drying tower is connected to the bag filter and induced draft fan through the outlet flue gas pipeline, and the crystallization salt outlet of the ash hopper at the bottom of the bag filter is connected to the salt silo through crystallization salt pipeline two, and silo pump two is installed on crystallization salt pipeline two.

7. A zero-discharge system for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes according to claim 6, characterized in that, The wastewater pump is a variable frequency pump, and the induced draft fan is a variable frequency fan. At least three layers of temperature transmitters are installed inside the spray drying tower. An inlet flue gas temperature transmitter and an inlet flue gas pressure transmitter are installed on the upstream hot flue gas duct of the spray drying tower, and an outlet flue gas temperature transmitter and an outlet flue gas pressure transmitter are installed on the downstream outlet flue gas duct of the spray drying tower. The inlet flue gas temperature transmitter, inlet flue gas pressure transmitter, outlet flue gas temperature transmitter, and outlet flue gas pressure transmitter are connected to the induced draft fan and wastewater pump via a control system. The silo pump is interlocked with the control system; the flue gas inlet pipe of the bag filter is equipped with an inlet flue gas pressure transmitter II, and the flue gas outlet pipe is equipped with an outlet flue gas pressure transmitter II. The flue gas pressure transmitter II and the outlet flue gas pressure transmitter II are interlocked with the control system and the silo pump II; the desulfurization ash addition device is equipped with a dosing control valve, and the desulfurization wastewater pipe downstream of the mixer is equipped with a solid particulate matter detection device and a pH value detection device. The solid particulate matter detection device and the pH value detection device are interlocked with the dosing control valve and the control system.

8. A zero-discharge system for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes according to claim 6, characterized in that, The flue gas reheater is an MGGH flue gas reheater or a WGGH flue gas reheater; an industrial fresh water inlet is provided on the desulfurization wastewater pipeline near the wet desulfurization reaction tower.

9. A zero-discharge system for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes according to claim 6, characterized in that, The flue gas outlet of the induced draft fan is connected to the flue gas pipeline upstream of the flue gas heat exchanger via a flue gas bypass pipeline, and a flue gas shut-off valve is installed on the flue gas bypass pipeline.

10. A zero-discharge system for desulfurization wastewater coupled with flue gas desulfurization and denitrification processes according to claim 6, characterized in that, The hot flue gas pipeline between the heating furnace and the spray drying tower is equipped with a hot flue gas shut-off valve and a hot flue gas flow regulating valve.

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