A raw flue gas dechlorination device for wet desulfurization system

Abstract

The invention discloses a raw flue gas dechlorination device for a wet flue gas desulfurization system, including a fan, the fan is connected to a desulfurization absorption tower through an original flue, an HCl absorption device is arranged in the original flue, the HCl absorption device includes a packing layer and an absorption layer, the absorption layer includes a horizontally arranged demister pipe, a liquid holding tank is correspondingly installed at the lower part of the demister pipe, a circulating water branch pipe is arranged at the bottom of the liquid holding tank, a guide groove is arranged between the demister pipe and the liquid holding tank, the liquid outlet of the liquid holding tank is connected to a first graphite cooler, the first graphite cooler is connected to a dual-medium filter, the dual-medium filter is connected to a high-pressure pump, the high-pressure pump is connected to a DTRO membrane device, the concentrated water outlet of the DTRO membrane device is connected to a decomposition tower, and the top of the decomposition tower is connected to an industrial hydrochloric acid storage tank. The dechlorination device has opened up a new way for a zero-emission project of limestone-gypsum wet desulfurization wastewater, and has the characteristics of low operating cost, resource utilization of industrial hydrochloric acid, no influence on fly ash resource utilization, and optimization of desulfurization system operation.

Description

Technical Field

[0001] The invention belongs to the technical field of zero-discharge of wastewater from limestone-gypsum wet desulfurization in coal-fired power plants, and in particular relates to a raw flue gas dechlorination device for a wet desulfurization system. Background Art

[0002] As a major industrial water user and wastewater discharger, coal-fired enterprises have focused on saving and protecting water resources, and have gradually implemented water-saving optimization and transformation throughout the plant, following the principle of "quality-based recycling and cascade utilization" to achieve no wastewater discharge. With the country's increasing speed in water pollution control, major power efficiency and power environmental protection companies have invested in the exploration of zero-emission technology and process research and development of desulfurization wastewater in recent years.

[0003] The limestone-gypsum wet desulfurization chemical reaction process determines that the slurry in the absorber is in a liquid-solid mixture environment with high hardness for a long time; therefore, the desulfurization wastewater is the terminal wastewater of coal-fired enterprises, and its most typical water quality characteristics are high Cl - , high Ca 2+ 、High Mg 2+ , high suspended solids, high dissolved salts, high and medium metals, etc. The limestone-gypsum wet flue gas desulfurization process design takes into account the factors of equipment corrosion and gypsum slurry crystallization, and generally requires that the Cl in the absorption tower slurry - The concentration is controlled within 20000mg / L. Therefore, the discharge of desulfurization wastewater depends first on the Cl in the desulfurization absorption tower slurry. - The equilibrium concentration of Cl - The lower the equilibrium concentration is, the greater the wastewater discharge will be; secondly, it depends on Cl - Balance of total amount in and out of the desulfurization system, Cl - The main sources are coal-fired flue gas and process water. The Cl carried by coal-fired flue gas per unit time is - The total amount is more than twice that of process water; in addition to flue gas and gypsum dehydration, it can carry a small amount of Cl - In addition, the main control Cl - The equilibrium concentration depends on the reasonable desulfurization wastewater discharge.

[0004] Combined with the characteristics of desulfurization wastewater and Cl - The total balance control shows that the zero discharge process of desulfurization wastewater can be started from two major ideas. One is to reduce the Cl - The second is to directly dispose of the discharged desulfurization wastewater. The current common desulfurization wastewater zero discharge technology is limited to the latter, and its technical route mainly consists of three process units: pretreatment softening, chemical or physical concentration, and transfer or direct solidification. Yang Jianguo, Geng Ziwen and others from Zhejiang University studied the use of NaOH, Na 2 CO 3、NaHCO 3 Three common alkaline substances, the alkaline solution prepared with desulfurization wastewater is atomized and sprayed into the flue between the air preheater and the dust collector through a gas-liquid two-phase flow nozzle. This process includes reducing the Cl - However, the ultimate goal of the current zero-emission desulfurization wastewater process in the industry is to either produce solid crystalline salt or transfer the crystalline salt to boiler fly ash under the premise of achieving solid-liquid separation.

[0005] First, the desulfurization wastewater zero discharge project generally has practical problems such as complex process routes, high investment costs, tight construction sites, and high operation and maintenance costs. Secondly, although the method of producing solid mixed salt is not affected by the later policy orientation, its resource utilization is a serious problem currently faced, and will eventually involve solidification and landfill. 2 SO 4 The method of separating salt with NaCl is more suitable for areas with developed economy, concentrated chemical enterprises and abundant snow resources, but it cannot ensure long-term resource utilization. The method of solidifying in fly ash does not belong to resource utilization. It just avoids the disposal of terminal solid waste while implementing existing policy standards. At present, this method can be accepted by most coal-fired enterprises. Once the policy standards are refined, the definition of terminal solid waste of desulfurization wastewater is upgraded or the downstream industry standards for fly ash resource utilization are improved, this method will face the situation of upgrading and transformation again. Summary of the invention

[0006] The purpose of the present invention is to provide a raw flue gas dechlorination device for a wet flue gas desulfurization system, which uses water as a circulating absorbent to directly and efficiently capture HCl gas in the flue gas and reduce the Cl - Total amount.

[0007] The technical scheme adopted by the present invention is a raw flue gas dechlorination device for a wet flue gas desulfurization system, comprising a fan, the fan is connected to the inlet of a desulfurization absorption tower through an L-shaped raw flue, an HCl absorption device is horizontally arranged in the vertical flue section of the raw flue, the HCl absorption device comprises a packing layer and an absorption layer arranged up and down, the absorption layer comprises a defogger pipe arranged horizontally in sequence, a V-shaped liquid holding tank is correspondingly installed at the lower part of each defogger pipe, a circulating water branch pipe is arranged at the bottom of each liquid holding tank, an inverted V-shaped guide groove is arranged between each defogger pipe and each liquid holding tank, wherein on the outer side of the flue at the other end of the liquid holding tank, after the absorption liquid converges, it is connected to a first graphite cooler through a pipeline, the first graphite cooler is connected to a dual-medium filter, the dual-medium filter is connected to a high-pressure pump, the high-pressure pump is connected to a DTRO membrane device, the concentrated water outlet of the DTRO membrane device is connected to a desorption tower, and the top of the desorption tower is connected to an industrial hydrochloric acid storage tank.

[0008] The present invention is also characterized in that:

[0009] The fresh water outlet of the DTRO membrane device is connected to the circulating water tank, the circulating water tank is connected to the circulating water pump, and the circulating water pump is connected to the water inlet of the circulating water branch pipe located outside the flue.

[0010] The precipitate outlet of the analytical tower is connected to the second graphite cooler, and the second graphite cooler is connected to the circulating water tank.

[0011] The circulating water branches are all porous drip pipes.

[0012] The guide grooves and the liquid holding grooves are distributed in a staggered manner.

[0013] The beneficial effects of the present invention are:

[0014] The washed acid solution is subjected to membrane concentration, thermal analysis and other processes to finally produce industrial hydrochloric acid with a concentration of 30%. The acid solution discharged by the dechlorination device is characterized by high chlorine, low hardness and low suspended solids. It avoids the softening link in the conventional desulfurization wastewater zero discharge process and improves the stability of the membrane concentration process, thereby saving a lot of operating agent costs. Before and after the membrane concentration device, the acid solution can also be directly generated into chloride salts by adding alkaline neutralizing agents (such as sodium carbonate, sodium hydroxide, etc.), and then the thermal concentration and solidification process is used to achieve zero wastewater discharge, which can also significantly reduce the risks of scaling and clogging of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of a raw flue gas dechlorination device for a wet desulfurization system of the present invention;

[0016] Figure 2 It is a schematic structural diagram of an HCl absorption device in a raw flue gas dechlorination device for a wet flue gas desulfurization system of the present invention;

[0017] In the figure, 1. fan, 2. original flue, 3. desulfurization absorption tower, 4. liquid holding tank, 5. guide groove, 6. demister pipe, 7. packing layer, 8. absorption layer, 9. first graphite cooler, 10. dual-media filter, 11. high-pressure pump, 12. DTRO membrane device, 13. circulating water tank, 14. circulating water pump, 15. analytical tower, 16. second graphite cooler, 17. industrial hydrochloric acid storage tank, 18. circulating water branch pipe. DETAILED DESCRIPTION

[0018] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] The present invention provides a raw flue gas dechlorination device for a wet desulfurization system, such as Figure 1As shown, it includes a fan 1, which is connected to the inlet of a desulfurization absorption tower 3 through an original flue 2. The original flue 2 is an L-shaped flue. The vertical flue section of the original flue 2 is connected to the outlet of the fan 2, and an HCl absorption device is horizontally arranged in the vertical flue section of the original flue 2. The HCl absorption device includes a packing layer 7 and an absorption layer 8 arranged up and down. The absorption layer 8 includes a demister pipe 6 arranged horizontally in sequence. Both ends of each demister pipe 6 are fixed to the inner wall of the original flue 2. The cross section of the demister pipe 6 is an egg-shaped structure, and the side facing the flue gas has four protruding droplet barriers. The outer surface of the side facing away from the flue gas is smooth; a V-shaped liquid holding tank 4 is installed at the lower part of each demister pipe 6, and the liquid holding tank 4 is fixed on the inner wall of the original flue 2. A circulating water branch pipe 18 is arranged at the bottom of each liquid holding tank 4, and the circulating water branch pipe 18 is fixed on the inner wall of the original flue 2. The circulating water branch pipe 18 is a porous drip pipe. An inverted V-shaped guide groove 5 is arranged between each demister pipe 6 and each liquid holding tank 4. The guide groove 5 is fixed on the inner wall of the original flue 2, and the guide groove 5 and the liquid holding tank 4 are staggered. The flue gas washing is strengthened by changing the direction of the flue gas flow;

[0020] A confluent liquid outlet is provided on the outside of the flue at the other end of the liquid holding tank 4, and the liquid outlet is connected to the first graphite cooler 9 through a pipeline, the first graphite cooler 9 is connected to the dual-medium filter 10, the dual-medium filter 10 is connected to the high-pressure pump 11, the high-pressure pump 11 is connected to the DTRO membrane device 12, the fresh water outlet of the DTRO membrane device 12 is connected to the circulating water tank 13, the circulating water tank 13 is connected to the circulating water pump 14, the liquid inlet of the circulating water pump 14 is connected to the liquid inlet of the circulating water branch pipe 18 on the outside of the flue, and the liquid inlet of the circulating water branch pipe 18 and the liquid outlet of the liquid holding tank 4 are respectively located on the corresponding two sides of the flue;

[0021] The concentrated water outlet of the DTRO membrane device 12 is connected to the analytical tower 15, the top of the analytical tower 15 is connected to the industrial hydrochloric acid storage tank 17, the precipitate outlet of the analytical tower 15 is connected to the second graphite cooler 16, the second graphite cooler 16 is connected to the circulating water tank 13, or the sewage is discharged to the desulfurization process water tank. The desulfurization industrial water can be directly added to the circulating water tank.

[0022] The DTRO membrane device 12 is a hydrochloric acid selective concentration device. The first graphite cooler 9 and the second graphite cooler 16 are tubular heat exchange devices, with circulating water in the tube side and cooling water in the shell side.

[0023] The analytical tower 15 is a non-contact heat exchange packed tower, with high temperature steam passing through the tube side and concentrated acid liquid passing through the shell side.

[0024] The packing layer 7 is a particle with a certain geometric shape and size, which is generally randomly piled in the tower, also known as random packing or particle packing. Bulk packing is divided into annular packing layer, annular saddle packing layer, saddle packing layer and spherical packing layer according to different structural characteristics. The particle material can be selected from high temperature and corrosion resistant light ceramics. The main purpose is to intercept the droplets carried by the flue gas after passing through the absorption device. The packing layer 7 can be selectively configured;

[0025] The present invention provides a raw flue gas dechlorination device for a wet desulfurization system, and its specific working principle is:

[0026] The absorption liquid in the circulating water tank 13 is pumped into the circulating water branch pipe 18 in the HCl absorption device through the circulating water pump 14. The flow rate of the circulating water pump 14 is adjusted to maintain a certain liquid level in the liquid holding tank 4. In the process of changing the direction of the flue gas, the flue gas is efficiently contacted with the absorption liquid in the liquid holding tank 4 with controllable flue gas temperature. The washed flue gas enters the desulfurization absorption tower 3 after the droplets are intercepted by the packing layer. The washed absorption liquid is then transported to the first graphite cooler 9 through a pipeline after converging at the other end of the liquid holding tank 4, and the temperature of the absorption liquid is reduced to a range of 30 to 40° C. The condensed absorption liquid is further removed from the suspended matter by the dual-media filter 10, and then transported to the DTRO membrane device 12 through the high-pressure pump 11 for acid concentration treatment. The produced fresh water returns to the circulating water tank 13, and the discharged concentrated water enters the analytical tower 15. The concentrated water in the analytical tower 15 volatilizes HCl gas after heat exchange with high-temperature steam, and is re-adsorbed to produce 30% concentration industrial hydrochloric acid. The precipitate discharged from the analysis tower 15 is cooled to a temperature within the range of 30 to 40° C. after passing through the second graphite cooler 16 and can be returned to the circulating water tank 13 or discharged to the desulfurization process water tank regularly.

[0027] During normal operation, if the circulating absorption liquid is insufficient, desulfurization industrial water can be directly added to the circulating water tank 13. The amount of industrial water added depends on the evaporation amount of the circulating absorption liquid during the gas-liquid contact process. This process itself has no wastewater discharge, but is only used to maintain a reasonable SO 4 2- and SO 3 2- In the concentration range, it is necessary to regularly discharge the precipitate from the analysis tower 15 to the desulfurization process water tank for secondary use in the desulfurization system, such as for flushing the demister of the absorption tower or the flushing of the desulfurization pipeline.

[0028] Hydrogen chloride is a colorless gas with a pungent odor. Its specific gravity is 1.268 times that of air. It is easily soluble in water. Its melting point is -114.6°C, its boiling point is -84.1°C, and its heat of formation is -92.340 kJ / mol. The high negative value of the heat of formation indicates that HCl gas is relatively stable. It only decomposes 0.014% at 1000°C. The solubility of hydrogen chloride in water is quite large. One volume of water can dissolve 450 volumes of hydrogen chloride. The heat released by water absorbing hydrogen chloride is 75.339 kJ / mol (HCl gas). Therefore, the temperature of hydrochloric acid will increase during the absorption process, and the partial pressure of hydrogen chloride above the hydrochloric acid aqueous solution will increase with the increase in temperature.

[0029] Combined with the chemical properties of hydrogen chloride, water is the most effective and cheapest absorbent for removing HCl pollutants from flue gas. When water is used to absorb hydrogen chloride in flue gas, not only does it generate heat of dissolution, but there is also heat transfer in the gas-liquid contact process. Therefore, the cooling of the circulating absorption liquid is particularly important. The lower the cooling temperature, the better it is for improving the absorption efficiency of HCl gas.

[0030] The key technology of the present invention is to control the temperature of the raw flue gas for desulfurization to not less than 90°C. If the flue gas temperature drops greatly, firstly, it will cause a large amount of evaporation of the circulating absorption liquid, and a larger amount of industrial water will need to be added to maintain the water balance of the circulating absorption liquid. Secondly, the water balance of the desulfurization system itself cannot be controlled, and the water consumption of normal water users of the desulfurization system cannot be met, which affects the stability of the operation of the desulfurization system. The HCl absorption device can achieve full contact with the flue gas through a limited amount of circulating absorption liquid, and control the temperature of the raw flue gas to drop within the range of 10 to 20°C. In addition, without the need to add alkaline agents, the pH value of the circulating absorption liquid is controlled at 2 to 4. The DTRO membrane device is a key device for controlling the pH value of the circulating absorption liquid. The normally added industrial water is neutral. During the contact process between the circulating absorption liquid and the raw flue gas, it not only absorbs HCl, but also absorbs SO 2 、SO 3 , HF and other acidic pollutants. Since the concentration of HF pollutants is relatively low, this process does not consider them separately. 2 After contacting with the circulating absorption liquid, H 2 SO 3 , due to H 2 SO 3 Dissolving in water is a reversible reaction, so maintaining the circulating absorption liquid in an acidic state can inhibit SO 2 The dissolution of H 2 SO 3 It will be naturally oxidized to H 2 SO 4 , or directly absorb SO 3 The generated H 2 SO 4Therefore, the circulating absorption liquid must be in an acidic state, that is, it can efficiently and selectively absorb HCl gas.

[0031] By using the device of the present invention, the HCl concentration in the flue gas after washing is controlled within a relatively low range, and the Cl concentration in the slurry of the desulfurization absorption tower is maintained at the same level as that in the slurry of the desulfurization absorption tower. - concentration, which can significantly reduce the amount of desulfurization wastewater discharged, and even achieve no desulfurization wastewater discharge. After the coal-fired power plants generally implement water-saving transformation, the unit flue gas carries Cl - The total amount is about twice that of process water. If the unit burns high-chlorine coal, the ratio will increase to a certain extent. If the chloride ion concentration of the process water of the desulfurization system is controlled at a low level, the ratio will still increase to a certain extent. - The amount of desulfurization wastewater discharged accounts for 70% of the total amount entering the desulfurization system, and the amount of desulfurization wastewater discharged can be reduced by 70% accordingly. Among them, about 15% of the chloride ions can be carried out of the desulfurization system through gypsum and flue gas. Considering the removal efficiency of HCl in flue gas by this process, the normal amount of desulfurization wastewater discharged accounts for about 25% before the implementation of the project. Under normal circumstances, this proportion of water can be completely consumed by using it in the boiler slag machine or mixing dry slag with wet after simple treatment by the existing three-unit box wastewater treatment process. If the unit burns high-sulfur coal, the corresponding amount of gypsum produced will increase, and the normal amount of desulfurization wastewater discharged can be further reduced, and even the desulfurization system does not need to discharge wastewater.

[0032] The key to the gas-liquid contact process of the present invention is to avoid the use of nozzle spraying contact, and in the absence of a volume tank, the efficient circulation of the absorption liquid can be guaranteed. If there is a HCl absorption device with a similar liquid holding effect, it belongs to the protection scope of this patent.

Claims

1. A raw flue gas dechlorination device for a wet flue gas desulfurization system, characterized in that: The invention comprises a fan (1), wherein the fan (1) is connected to the inlet of a desulfurization absorption tower (3) through an L-shaped original flue (2), an HCl absorption device is horizontally arranged in the vertical flue section of the original flue (2), the HCl absorption device comprises a packing layer (7) and an absorption layer (8) arranged in an upper and lower manner, the absorption layer (8) comprises a demister pipe (6) arranged horizontally in sequence, a V-shaped liquid holding tank (4) is correspondingly installed at the lower part of each demister pipe (6), a circulating water branch pipe (18) is arranged at the bottom of each liquid holding tank (4), and an inverted V-shaped liquid holding tank (4) is arranged between each demister pipe (6) and each liquid holding tank (4). A flow guide groove (5) of a type, wherein the flow guide groove (5) and the liquid holding groove (4) are both arranged in a staggered manner; wherein the liquid outlet of the liquid holding groove (4) is connected to a first graphite cooler (9) via a pipeline, the first graphite cooler (9) is connected to a dual-medium filter (10), the dual-medium filter (10) is connected to a high-pressure pump (11), the high-pressure pump (11) is connected to a DTRO membrane device (12), the concentrated water outlet of the DTRO membrane device (12) is connected to a desorption tower (15), and the top of the desorption tower (15) is connected to an industrial hydrochloric acid storage tank (17); The fresh water outlet of the DTRO membrane device (12) is connected to a circulating water tank (13), the circulating water tank (13) is connected to a circulating water pump (14), and the liquid inlet of the circulating water pump (14) is connected to the water inlet of a circulating water branch pipe (18) located outside the flue; The precipitate outlet of the analytical tower (15) is connected to a second graphite cooler (16), and the second graphite cooler (16) is connected to a circulating water tank (13); Both ends of each demister pipe (6) are fixed to the inner wall of the original flue (2). The cross section of the demister pipe (6) is an egg-shaped structure, with four raised droplet barrier strips on the side facing the flue gas, and a smooth outer surface on the side facing away from the flue gas.

2. The raw flue gas dechlorination device for a wet flue gas desulfurization system according to claim 1, characterized in that: The circulating water branches (18) are all porous drip pipes.

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