A limestone-gypsum flue gas desulfurization system and a limestone-gypsum flue gas desulfurization method

Abstract

The present invention belongs to the field of environmental protection, and in particular, relates to a limestone-gypsum flue gas desulfurization system and a limestone-gypsum flue gas desulfurization method. The desulfurization system provided by the present invention includes: a limestone pulping pool, a limestone-gypsum flue gas desulfurization tower, a gypsum slurry separation device, a gypsum dehydration device, a recovery pool, a wastewater separation device, a chemical precipitation device, a foam separator and an external drainage pipe. The system provided by the present invention can control the LAS concentration in the desulfurization tower at a low level by adding a foam separator and returning the desulfurization wastewater from which LAS is removed by foam separation to the desulfurization tower, thereby eliminating the root cause of foaming in the desulfurization tower, and then the desulfurization system can operate normally under high chloride ion concentration conditions, that is, realize the high concentration rate operation of the desulfurization system, and significantly reduce the discharge of desulfurization wastewater. Moreover, the foam separator has a simple structure, low investment and operation and maintenance costs, and has obvious economic advantages.

Description

Technical Field

[0001] The invention belongs to the field of environmental protection, and in particular relates to a limestone-gypsum flue gas desulfurization system and a limestone-gypsum flue gas desulfurization method. Background Art

[0002] As my country's environmental protection efforts continue to increase, flue gas desulfurization equipment has been widely installed in the thermal power generation industry. Limestone-gypsum wet flue gas desulfurization (WFGD) technology has become the leading technology for flue gas desulfurization at home and abroad because of its wide range of coal applications and high desulfurization efficiency. In the process of wet desulfurization flue gas washing, the flue gas fly ash is washed into the limestone-gypsum slurry, and the harmful substances such as chloride ions and heavy metal ions contained in it also enter the flue gas desulfurization system. In the gypsum treatment process, it enters the desulfurization wastewater link with the flushing water, forming desulfurization wastewater rich in heavy metals and chloride ions. In order to maintain the material balance of the desulfurization device slurry circulation system, prevent the corrosion of the desulfurization equipment and ensure the quality of gypsum, a certain amount of wastewater must be discharged from the system.

[0003] At present, most of the desulfurization wastewater from power plants is directly discharged after conventional treatment. Conventional desulfurization wastewater treatment mainly adopts the three-step treatment of neutralization, reaction and flocculation, or new processes such as electroflocculation, and finally discharges wastewater containing more salt substances. This wastewater contains more cations such as calcium, magnesium, copper, iron, manganese, and Cl - 、SO4 2- Although the anions can barely meet the discharge standards, this direct discharge often still causes serious pollution to the water body. Only a few power plants in China are forced to discharge zero desulfurization wastewater due to special reasons, and the deep treatment technology of desulfurization wastewater is still in the exploratory stage. It can be said that each plant has its own way. Since the energy consumption of the end evaporation heat method to achieve zero wastewater discharge is extremely high, in general, the method of first concentrating and reducing the amount and then evaporating is used to achieve zero wastewater discharge. It can be seen that the discharge volume of desulfurization wastewater directly affects the difficulty and investment cost of achieving zero discharge.

[0004] Cl in desulfurization wastewater - It comes from flue gas, limestone, and make-up water. The chlorine contained in the coal is converted into HCl after burning in the boiler furnace, and HCl is absorbed by the desulfurization slurry. Limestone is ground into very fine powder as an absorbent, and the chlorine and heavy metals contained in it will dissolve quickly in the slurry pool. - The chemical properties of Cl are very stable and will not cause changes in concentration due to chemical reactions. Therefore, in the process of slurry circulation and concentration, Cl is often used. - The concentration change of the slurry is used to determine the concentration degree of the slurry and decide whether it is necessary to discharge the sewage. Therefore, the Cl in the desulfurization wastewater is currently -Concentration is the main parameter that determines whether desulfurization wastewater should be discharged. When conditions permit, increasing the concentration multiple as much as possible can reduce the amount of wastewater discharged.

[0005] Since coal quality, limestone composition, make-up water quality, and the operation mode of the desulfurization absorber all have a direct impact on the quality of desulfurization wastewater, it is difficult to provide representative water quality data for desulfurization wastewater. The quality of desulfurization wastewater from different thermal power plants will vary greatly. Even the same wet desulfurization system will frequently change the water quality due to frequent changes in coal quality and make-up water, and even have different water quality at different times. The industry standard DL / T1477-2015 "Technical Supervision Guidelines for Desulfurization Devices in Thermal Power Plants" also clearly requires strict control of Cl in the absorber slurry - The content is less than 10000mg / L, and the water balance calculation basis generally recognized by design units is the Cl - The content is not higher than 20000mg / L. After actual investigation, the current domestic wet flue gas desulfurization wastewater Cl - The content is generally lower than 10000 mg / L, mainly because Cl is the nominal parameter of desulfurization wastewater. - Once the content is high, the desulfurization efficiency will decrease, and even affect the operating parameters of the desulfurization operation. Discharging wastewater in advance can reduce Cl - content, the desulfurization performance can be easily maintained, resulting in high discharge of most desulfurization wastewater, which adds a great burden to the subsequent zero emission.

[0006] From the above analysis, it can be seen that the prior art generally believes that the Cl - The content is the direct cause of the desulfurization operation. In order to reduce the discharge of desulfurization wastewater, a variety of methods have been developed to reduce or remove Cl in desulfurization wastewater. - The content of technology, such as reverse osmosis, forward osmosis, electrodialysis and other membrane desalination, or the use of ion exchange, extraction and other methods to reduce Cl - There are even some people who use NaOH powder to remove HCl from the flue gas to reduce the Cl content of desulfurization wastewater. - It is generally believed that as long as the desulfurization wastewater Cl - When the content is reduced, the wastewater can be returned to the tower for reuse. - The content is reduced, especially the membrane desalination method, which can indeed realize the return of desulfurization wastewater to the tower for reuse and achieve the reduction of desulfurization wastewater. - Its chemical properties are extremely stable. - It is very difficult to remove it from wastewater. Therefore, this method has high investment costs and brings great economic burden to enterprises. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a limestone-gypsum flue gas desulfurization system and a limestone-gypsum flue gas desulfurization method. The desulfurization system provided by the present invention can achieve high concentration rate operation, thereby effectively reducing the discharge of desulfurization wastewater. In addition, the investment and operation costs of the system are low, and it has good economic benefits.

[0008] The present invention provides a limestone-gypsum flue gas desulfurization system, comprising:

[0009] limestone pulping pond;

[0010] A limestone-gypsum flue gas desulfurization tower connected to the slurry outlet of the limestone slurry tank;

[0011] A gypsum slurry separation device connected to the gypsum slurry outlet of the limestone-gypsum flue gas desulfurization tower;

[0012] A gypsum dehydration device connected to the bottom flow outlet of the gypsum slurry separation device;

[0013] A recovery water tank connected to the overflow port of the gypsum slurry separation device and the drain port of the gypsum dehydration device respectively; the recovery water tank is provided with a first water outlet and a second water outlet, and the first water outlet is connected to the limestone slurry making tank;

[0014] A wastewater separation device connected to the second water outlet of the recovery pool; the underflow outlet of the wastewater separation device is connected back to the recovery pool;

[0015] A chemical precipitation device connected to the overflow port of the wastewater separation device;

[0016] A foam separator and an external drainage pipe are connected to the clear liquid outlet of the chemical precipitation equipment; the clean water outlet of the foam separator is connected to the limestone pulping tank or the limestone-gypsum flue gas desulfurization tower, and the foam water outlet of the foam separator is connected to the external drainage pipe.

[0017] Preferably, the foam separator is a protein skimmer.

[0018] Preferably, the foam separator is a secondary protein skimmer;

[0019] The secondary protein separator includes a first protein separator and a second protein separator, wherein the water inlet of the first protein separator is connected to the clear liquid outlet of the chemical precipitation equipment, the clean water outlet of the first protein separator is connected to the limestone pulping tank or the limestone-gypsum flue gas desulfurization tower, the foam water outlet of the first protein separator is connected to the water inlet of the second protein separator, the clean water outlet of the second protein separator is connected to the limestone pulping tank or the limestone-gypsum flue gas desulfurization tower, and the foam water outlet of the second protein separator is connected to the external drainage pipe.

[0020] Preferably, the gypsum slurry separation equipment is a gypsum cyclone.

[0021] Preferably, the gypsum dehydration equipment is a vacuum belt conveyor.

[0022] Preferably, the wastewater separation equipment is a wastewater cyclone.

[0023] Preferably, the chemical precipitation equipment includes a wastewater treatment triple tank and a sedimentation tank;

[0024] The wastewater treatment triple tank comprises a neutralization tank, a reaction tank and a flocculation tank arranged in series, and the water inlet of the neutralization tank is connected to the overflow port of the wastewater separation equipment;

[0025] The water inlet of the sedimentation tank is connected to the water outlet of the flocculation tank, and the clear liquid outlet of the sedimentation tank is connected to the water inlet of the foam separator and the external drainage pipe respectively.

[0026] Preferably, it also includes a process water delivery pipeline;

[0027] The water outlet end of the process water delivery pipeline is connected to the desulfurization absorption tower and the gypsum dehydration equipment respectively.

[0028] Preferably, it also includes a wastewater collection tank;

[0029] The wastewater collection tank is arranged between the overflow of the wastewater separation equipment and the water inlet of the chemical precipitation equipment. The water inlet of the wastewater collection tank is connected to the overflow of the wastewater separation equipment, and the water outlet of the wastewater collection tank is connected to the water inlet of the chemical precipitation equipment.

[0030] The present invention provides a limestone-gypsum flue gas desulfurization method, which is carried out in the limestone-gypsum flue gas desulfurization system described in the above technical solution, and comprises the following steps:

[0031] The limestone powder is made into limestone slurry in a limestone slurry making tank, and then the limestone slurry is transported to a limestone-gypsum flue gas desulfurization tower as a desulfurization absorbent;

[0032] The raw flue gas enters the limestone-gypsum flue gas desulfurization tower from the raw flue gas inlet and contacts the slurry sprayed on the top of the tower in countercurrent. During the countercurrent contact, the slurry absorbs sulfur dioxide in the raw flue gas and then falls to the bottom of the tower. The clean flue gas after desulfurization is discharged from the clean flue gas outlet on the top of the tower. The slurry falling to the bottom of the tower reacts with the air blown into the tower through the air inlet, so that the calcium sulfite in the slurry is oxidized into gypsum. A part of the slurry at the bottom of the tower is sent to the top of the tower through the slurry circulation pipeline and sprayed again, and the other part of the slurry at the bottom of the tower is discharged through the gypsum slurry outlet set at the bottom of the tower.

[0033] The discharged bottom slurry enters the gypsum slurry separation equipment for separation to obtain wet gypsum and gypsum slurry separation wastewater respectively;

[0034] The wet gypsum is discharged through the bottom flow outlet of the gypsum slurry separation device and enters the gypsum dehydration device for dehydration to obtain dry gypsum and dehydrated water respectively;

[0035] The gypsum slurry separation wastewater is discharged through the overflow port of the gypsum slurry separation equipment, and merges with the dewatering water discharged from the gypsum dehydration equipment into the recovery pool. A part of the water in the recovery pool is returned to the limestone pulping pool as recycled water to participate in pulping; the other part is transported to the wastewater separation equipment for separation, and the separated underflow is returned to the recovery pool, and the separated overflow enters the chemical precipitation equipment;

[0036] The overflow from the wastewater separation device is chemically precipitated in a chemical precipitation device to obtain a clear liquid;

[0037] The clear liquid is discharged through the clear liquid outlet of the chemical precipitation device, and a part of the clear liquid enters the foam separator for foam separation to obtain foam separation clean water and foam water respectively;

[0038] The foam separation purified water is returned to the limestone pulping tank to participate in pulping, or returned to the limestone-gypsum flue gas desulfurization tower to participate in desulfurization;

[0039] The foam water is combined with another part of the clear liquid discharged from the chemical precipitation equipment and enters the external drainage pipe as external wastewater;

[0040] During this period, process water is regularly added to the limestone-gypsum flue gas desulfurization system to maintain the material balance of the slurry in the limestone-gypsum flue gas desulfurization tower.

[0041] Preferably, the concentration of sodium linear alkylbenzene sulfonate in the foam separation water purification is ≤4 mg / L.

[0042] Preferably, the chloride ion concentration of the discharged wastewater is ≥30000 mg / L.

[0043] Compared with the prior art, the present invention provides a limestone-gypsum flue gas desulfurization system and a limestone-gypsum flue gas desulfurization method. The desulfurization system provided by the present invention comprises: a limestone pulping tank; a limestone-gypsum flue gas desulfurization tower connected to the slurry outlet of the limestone pulping tank; a gypsum slurry separation device connected to the gypsum slurry outlet of the limestone-gypsum flue gas desulfurization tower; a gypsum dehydration device connected to the underflow outlet of the gypsum slurry separation device; a recovery water tank connected to the overflow outlet of the gypsum slurry separation device and the drainage outlet of the gypsum dehydration device respectively; the recovery water tank is provided with a first water outlet and a second water outlet, the first water outlet is connected to the limestone pulping tank; a wastewater separation device connected to the second water outlet of the recovery water tank; the underflow outlet of the wastewater separation device is connected back to the recovery water tank; a chemical precipitation device connected to the overflow outlet of the wastewater separation device; a foam separator and an external drainage pipe connected to the clear liquid outlet of the chemical precipitation device; the clean water outlet of the foam separator is connected to the limestone pulping tank or the limestone-gypsum flue gas desulfurization tower, and the foam water outlet of the foam separator is connected to the external drainage pipe. The present invention overcomes the technical prejudice commonly believed in the art that excessive chloride ion concentration will cause foaming of the desulfurization slurry, resulting in an artificially high slurry level, thereby affecting the operation of the desulfurization system, reducing the desulfurization efficiency, and increasing power consumption. It is found that the linear alkylbenzene sulfonate (LAS) inevitably present in the process water for desulfurization is the root cause of the bubbles in the slurry, and the chloride ion concentration only reflects the level of the LAS concentration. Based on this, the present invention no longer focuses on the reduction of the chloride ion concentration of the desulfurization slurry. The chloride ion concentration is only a nominal parameter of the concentration ratio of the desulfurization absorption tower. The system provided by the present invention starts from reducing the LAS concentration of the slurry. By adding a foam separator, the LAS in the desulfurization wastewater can be non-destructively separated, and then the desulfurization wastewater with LAS removed is directly or indirectly returned to the tower for circulation. The system provided by the present invention can control the LAS concentration in the desulfurization tower at a low level by returning the desulfurization wastewater from which LAS is removed by foam separation to the desulfurization tower, thereby eliminating the root cause of foaming in the desulfurization tower, and then the desulfurization system can operate normally under high chloride ion concentration conditions, that is, the high concentration rate operation of the desulfurization system is achieved, and the discharge of desulfurization wastewater is significantly reduced. In addition, the foam separator has a simple structure, low investment and operation and maintenance costs, and has obvious economic advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0045] Figure 1 is a process flow chart of a limestone-gypsum flue gas desulfurization system provided by an embodiment of the present invention;

[0046] Figure 2 It is a process flow chart of a limestone-gypsum flue gas desulfurization system provided in a comparative example of the present invention. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The present invention provides a limestone-gypsum flue gas desulfurization system, comprising:

[0049] limestone pulping pond;

[0050] A limestone-gypsum flue gas desulfurization tower connected to the slurry outlet of the limestone slurry tank;

[0051] A gypsum slurry separation device connected to the gypsum slurry outlet of the limestone-gypsum flue gas desulfurization tower;

[0052] A gypsum dehydration device connected to the bottom flow outlet of the gypsum slurry separation device;

[0053] A recovery water tank connected to the overflow port of the gypsum slurry separation device and the drain port of the gypsum dehydration device respectively; the recovery water tank is provided with a first water outlet and a second water outlet, and the first water outlet is connected to the limestone slurry making tank;

[0054] A wastewater separation device connected to the second water outlet of the recovery pool; the underflow outlet of the wastewater separation device is connected back to the recovery pool;

[0055] A chemical precipitation device connected to the overflow port of the wastewater separation device;

[0056] A foam separator and an external drainage pipe are connected to the clear liquid outlet of the chemical precipitation equipment; the clean water outlet of the foam separator is connected to the limestone pulping tank or the limestone-gypsum flue gas desulfurization tower, and the foam water outlet of the foam separator is connected to the external drainage pipe.

[0057] See also Figure 1 , Figure 1 It is a process flow chart of a limestone-gypsum flue gas desulfurization system provided in an embodiment of the present invention. Figure 1Among them, 1 is a limestone pulping tank, 2 is a limestone-gypsum flue gas desulfurization tower, 2-1 is a raw flue gas inlet, 2-2 is a clean flue gas outlet, 2-3 is a slurry circulation pipeline, 2-4 is a gypsum slurry outlet, 2-5 is an air inlet, 2-6 is an oxidation fan, 3 is a gypsum slurry separation equipment, 4 is a gypsum dehydration equipment, 5 is a recovery water tank, 6 is a wastewater separation equipment, 7 is a wastewater collection tank, 8 is a wastewater treatment triple box, 8-1 is a neutralization tank, 8-2 is a reaction tank, 8-3 is a flocculation tank, 9 is a sedimentation tank, 10 is a foam separator, 10-1 is a first foam separator, 10-2 is a second foam separator, and 11 is an external drainage pipe.

[0058] The limestone-gypsum flue gas desulfurization system provided by the present invention comprises: a limestone pulping tank 1, a limestone-gypsum flue gas desulfurization tower 2, a gypsum slurry separation device 3, a gypsum dehydration device 4, a recovery water tank 5, a wastewater separation device 6, a chemical precipitation device, a foam separator 10 and an external drainage pipe 11.

[0059] In the desulfurization system provided by the present invention, the limestone slurry making tank 1 is used to prepare limestone slurry, and is provided with a limestone powder feed inlet, a water inlet and a slurry outlet, and a stirring device is preferably also provided in the tank.

[0060] In the desulfurization system provided by the present invention, the limestone-gypsum flue gas desulfurization tower 2 is a reaction device for desulfurizing flue gas and generating gypsum, a raw flue gas inlet 2-1 is arranged on the side wall of the tower kettle, a clean flue gas outlet 2-2 is arranged on the tower top, a circulating slurry outlet, a gypsum slurry outlet 2-4 and an air inlet 2-5 are arranged at the tower bottom, the circulating slurry outlet is connected to the liquid inlet end of the slurry circulation pipeline 2-3 of the desulfurization tower, the liquid outlet end of the slurry circulation pipeline 2-3 is connected to the slurry spraying device arranged at the top of the inner cavity of the desulfurization tower, and the air inlet 2-5 is connected to an oxidation fan 2-6 matched therewith.

[0061] In the desulfurization system provided by the present invention, the gypsum slurry separation device 3 is used to perform solid-liquid separation on the gypsum slurry discharged from the limestone-gypsum flue gas desulfurization tower 2, and is provided with a feed port, an overflow port and an underflow port, and the feed port of the gypsum slurry separation device 3 is connected to the gypsum slurry outlet of the limestone-gypsum flue gas desulfurization tower 2. In one embodiment provided by the present invention, the gypsum slurry separation device 3 is specifically selected from a gypsum cyclone.

[0062] In the desulfurization system provided by the present invention, the gypsum dehydration device 4 is used to dehydrate the wet gypsum discharged from the bottom flow outlet of the gypsum slurry separation device 3, and is provided with a feed inlet, a dry material outlet and a drain outlet, and the feed inlet of the gypsum dehydration device 4 is connected to the bottom flow outlet of the gypsum slurry separation device 3. In one embodiment provided by the present invention, the gypsum dehydration device 4 is specifically a vacuum belt conveyor.

[0063] In the desulfurization system provided by the present invention, the recovery water pool 5 is used to recover the overflow separated by the gypsum slurry separation equipment 3 and the dewatered water of the gypsum dehydration equipment 4, and to indirectly return part of the recovered water to the tower for reuse. A water inlet, a first water outlet and a second water outlet are arranged on the recovery water pool 5. A stirring device is preferably also arranged in the pool. The water inlet of the recovery water pool 5 is respectively connected to the overflow port of the gypsum slurry separation equipment 3 and the drain port of the gypsum dehydration equipment 4, and the first water outlet of the recovery water pool 5 is connected to the water inlet of the limestone pulping pool 1.

[0064] In the desulfurization system provided by the present invention, the wastewater separation device 6 is used to circulate the recycled water in the recycling pool 5, and the bottom flow obtained by the treatment is returned to the pool. The wastewater separation device 6 is provided with a water inlet, an overflow port and a bottom flow port, and the water inlet of the wastewater separation device 6 is connected to the second water outlet of the recycling pool 5. In an embodiment provided by the present invention, the wastewater separation device 6 is specifically selected as a wastewater cyclone.

[0065] In the desulfurization system provided by the present invention, the chemical precipitation device is used to chemically precipitate the overflow of the wastewater separation device 6, and is provided with a water inlet and a clear liquid outlet, and the water inlet of the chemical precipitation device is connected to the overflow of the wastewater separation device 6. In one embodiment provided by the present invention, the chemical precipitation device includes a wastewater treatment triple tank 8 and a sedimentation tank 9; the wastewater treatment triple tank 8 specifically includes a neutralization tank 8-1, a reaction tank 8-2 and a flocculation tank 8-3 arranged in series, the water inlet of the neutralization tank 8-1 is connected to the overflow of the wastewater separation device 6; the water inlet of the sedimentation tank 9 is connected to the water outlet of the flocculation tank 8-3. In the present invention, the neutralization tank 8-1 is used to add alkali solution to adjust the pH value of the wastewater, preferably adjusting the pH value to above 8.5, more preferably 8.5-9.5; the reaction tank 8-2 is used for a mixed reaction of wastewater and organic sulfide, the organic sulfide includes but is not limited to TMT-15, and the addition concentration of the organic sulfide is preferably controlled at 1-5wt%; the flocculation tank 8-3 is used for a mixed reaction of wastewater and flocculant, and the addition amount of the flocculant is preferably controlled at 0.1-0.3wt%.

[0066] In the desulfurization system provided by the present invention, a wastewater collection tank 7 is preferably provided between the overflow port of the wastewater separation device 6 and the water inlet of the chemical precipitation device, for buffering the overflow of the wastewater separation device 6, and a water inlet and a water outlet are provided thereon, and a stirring device is preferably provided in the tank, the water inlet of the wastewater collection tank 7 is connected to the overflow port of the wastewater separation device 6, and the water outlet of the wastewater collection tank 7 is connected to the water inlet of the chemical precipitation device. In the embodiment in which the chemical precipitation device provided by the present invention includes a wastewater treatment triple tank 8 and a sedimentation tank 9, the water outlet of the wastewater collection tank 7 is connected to the water inlet of the neutralization tank 8-1.

[0067] In the desulfurization system provided by the present invention, the foam separator 10 is used to perform foam separation on part of the effluent after the chemical precipitation treatment, non-destructively remove the linear alkylbenzene sulfonate (LAS) in the water body, and directly or indirectly return the defoamed clean water obtained after the treatment to the tower for reuse. A water inlet, a clean water outlet and a foam water outlet are arranged on the foam separator 10. The water inlet of the foam separator 10 is connected to the clear liquid outlet of the chemical precipitation equipment, and the clean water outlet of the foam separator 10 is connected to the water inlet of the limestone pulping tank 1 or the limestone-gypsum flue gas desulfurization tower 2. In the embodiment of the chemical precipitation equipment provided by the present invention including the wastewater treatment triple box 8 and the sedimentation tank 9, the water inlet of the foam separator 10 is connected to the clear liquid outlet of the sedimentation tank 9. In one embodiment provided by the present invention, the foam separator 10 is specifically selected as a protein separator, and the protein separator includes but is not limited to a primary protein separator, a secondary protein separator or a tertiary and above protein separator. In an embodiment of the present invention, the foam separator 10 is selected as a secondary protein separator, and the secondary protein separator includes a first protein separator 10-1 and a second protein separator 10-2, the water inlet of the first protein separator 10-1 is connected to the clear liquid outlet of the chemical precipitation equipment, the clean water outlet of the first protein separator 10-1 is connected to the limestone pulping tank 1 or the limestone-gypsum flue gas desulfurization tower 2, the foam water outlet of the first protein separator 10-1 is connected to the water inlet of the second protein separator 10-2, and the clean water outlet of the second protein separator 10-2 is connected to the limestone pulping tank 1 or the limestone-gypsum flue gas desulfurization tower 2.

[0068] In the desulfurization system provided by the present invention, the external drainage pipe 11 is a channel for wastewater to be discharged from the desulfurization system. Part of the effluent after the chemical precipitation treatment (i.e., the effluent that does not enter the foam separator 10) and the externally discharged foam water produced by the foam separator 10 are discharged from the desulfurization system through the external drainage pipe 11. The water inlet end of the external drainage pipe 11 is respectively connected to the clear liquid outlet of the chemical precipitation equipment and the foam water outlet of the foam separator 10. In the embodiment in which the chemical precipitation equipment provided by the present invention includes a wastewater treatment triple box 8 and a sedimentation tank 9, the water inlet end of the external drainage pipe 11 is connected to the clear liquid outlet of the sedimentation tank 9. In the embodiment in which the foam separator 10 provided by the present invention is selected as a secondary protein separator, the water inlet end of the external drainage pipe 11 is connected to the foam water outlet of the second protein separator 10-2.

[0069] In the desulfurization system provided by the present invention, the system also includes a process water delivery pipeline for regularly adding process water to the desulfurization system to maintain the material balance of the slurry in the limestone-gypsum flue gas desulfurization tower; the water outlet end of the process water delivery pipeline is preferably connected to the desulfurization absorption tower 2 and the gypsum dehydration equipment 4 respectively.

[0070] The present invention also provides a limestone-gypsum flue gas desulfurization method, which is carried out in the limestone-gypsum flue gas desulfurization system described in the above technical solution, and comprises the following steps:

[0071] Limestone powder is made into limestone slurry in a limestone slurry making tank 1, and then the limestone slurry is transported to a limestone-gypsum flue gas desulfurization tower 2 as a desulfurization absorbent;

[0072] The raw flue gas enters the limestone-gypsum flue gas desulfurization tower 2 from the raw flue gas inlet 2-1, and contacts with the slurry sprayed on the top of the tower in countercurrent; during the countercurrent contact, the slurry absorbs sulfur dioxide in the raw flue gas, and then falls to the bottom of the tower, and the clean flue gas after desulfurization is discharged from the clean flue gas outlet 2-2 on the top of the tower; the slurry falling into the bottom of the tower reacts with the air blown into the tower through the air inlet 2-5, so that the calcium sulfite in the slurry is oxidized into gypsum; a part of the slurry at the bottom of the tower is sent to the top of the tower through the slurry circulation pipeline 2-3 to be sprayed again, and the other part of the slurry at the bottom of the tower is discharged through the gypsum slurry outlet 2-4 set at the bottom of the tower;

[0073] The discharged bottom slurry enters the gypsum slurry separation device 3 for separation to obtain wet gypsum and gypsum slurry separation wastewater respectively;

[0074] The wet gypsum is discharged through the bottom flow outlet of the gypsum slurry separation device 3 and enters the gypsum dehydration device 4 for dehydration to obtain dry gypsum and dehydrated water respectively;

[0075] The gypsum slurry separation wastewater is discharged through the overflow port of the gypsum slurry separation device 3, and merges with the dewatering water discharged from the gypsum dehydration device 4 to the recovery pool 5. A part of the water in the recovery pool is returned to the limestone pulping pool 1 as recycled water to participate in pulping; the other part is transported to the wastewater separation device 6 for separation, and the separated underflow is returned to the recovery pool 5, and the separated overflow enters the chemical precipitation device;

[0076] The overflow from the wastewater separation device 6 is chemically precipitated in a chemical precipitation device to obtain a clear liquid;

[0077] The clear liquid is discharged through the clear liquid outlet of the chemical precipitation device, and a part of the clear liquid enters the foam separator 10 for foam separation to obtain foam separation clean water and foam water respectively;

[0078] The foam separation purified water is returned to the limestone pulping tank 1 to participate in pulping, or returned to the limestone-gypsum flue gas desulfurization tower 2 to participate in desulfurization;

[0079] The foam water is combined with another part of the clear liquid discharged from the chemical precipitation device and enters the external drainage pipe 11 as external wastewater;

[0080] During this period, process water is regularly added to the limestone-gypsum flue gas desulfurization system to maintain the material balance of the slurry in the limestone-gypsum flue gas desulfurization tower.

[0081] In the limestone-gypsum flue gas desulfurization method provided by the present invention, the linear alkylbenzene sulfonate (LAS) inevitably exists in the process water, and the concentration of the linear alkylbenzene sulfonate in the process water may be ≥1 mg / L. In one embodiment provided by the present invention, the concentration of the linear alkylbenzene sulfonate in the process water is 1.5-2 mg / L. In one embodiment provided by the present invention, the chloride ion concentration in the process water is 100-500 mg / L, more specifically 300 mg / L. In one embodiment provided by the present invention, the COD value of the process water is 50-300 mg / L, more specifically 100-200 mg / L.

[0082] In the limestone-gypsum flue gas desulfurization method provided by the present invention, the total recovery rate of the foam separator 10 is preferably ≥60%, more preferably ≥70%, most preferably ≥80%, and most preferably ≥90%; when the foam separator 10 selects a multi-stage foam separator (secondary and above), the recovery rate of each stage of the separator is preferably ≥60%, more preferably ≥70%. In the present invention, the LAS concentration of the influent of the foam separator 10 is preferably ≥10 mg / L; the linear alkylbenzene sulfonate concentration of the purified water produced by the foam separator 10 is preferably ≤4 mg / L. When the foam separator 10 selects a multi-stage foam separator, the concentration refers to the total concentration of linear alkylbenzene sulfonate after the purified water produced by each stage of the separator is combined; the LAS concentration of the foam water discharged from the foam separator 10 is preferably ≥60 mg / L, specifically 71 mg / L. When the foam separator 10 selects a multi-stage foam separator, the concentration refers to the linear alkylbenzene sulfonate concentration of the foam water discharged by the last stage of the separator.

[0083] In the limestone-gypsum flue gas desulfurization method provided by the present invention, the maximum value of the linear alkylbenzene sulfonate concentration in the slurry in the limestone-gypsum flue gas desulfurization tower 2 is preferably controlled to be 5-10 mg / L, specifically 5 mg / L, 5.5 mg / L, 6 mg / L, 6.5 mg / L, 7 mg / L, 7.5 mg / L, 8 mg / L, 8.5 mg / L, 9 mg / L, 9.5 mg / L or 10 mg / L. In one embodiment provided by the present invention, the linear alkylbenzene sulfonate concentration in the slurry in the limestone-gypsum flue gas desulfurization tower 2 is preferably controlled to be 5-7 mg / L, specifically 6 mg / L.

[0084] In the limestone-gypsum flue gas desulfurization method provided by the present invention, the chloride ion concentration of the discharged wastewater is preferably controlled at ≥30,000 mg / L, more preferably 30,000 mg / L to the highest concentration that the equipment of the desulfurization system can withstand chloride ion corrosion, most preferably 30,000 to 50,000 mg / L.

[0085] In the limestone-gypsum flue gas desulfurization method provided by the present invention, the COD value of the discharged wastewater can be controlled at 3000-8000 mg / L, and more specifically can be controlled at 5000 mg / L.

[0086] The technical solution provided by the present invention starts from reducing the LAS concentration of the slurry. By adding a foam separator, the LAS in the desulfurization wastewater can be non-destructively separated, and then the desulfurization wastewater with LAS removed is directly or indirectly returned to the tower for circulation. The technical solution provided by the present invention can control the LAS concentration in the desulfurization tower at a low level by returning the desulfurization wastewater with LAS removed by foam separation to the desulfurization tower, thereby eliminating the root cause of foaming in the desulfurization tower, and then the desulfurization system can operate normally under high chloride ion concentration conditions, that is, realize the high concentration ratio operation of the desulfurization system, and significantly reduce the discharge of desulfurization wastewater. Moreover, the foam separator has a simple structure, low investment and operation and maintenance costs, and has obvious economic advantages.

[0087] In addition, in the preferred technical scheme provided by the present invention, the foam separator specifically selects a protein separator, and more preferably selects a two-stage protein separator; the protein separator not only has the technical advantages of simple structure, stable performance, low energy consumption, low cost, and high recovery rate, but also the inlet LAS concentration has little effect on the recovery rate and produced water quality of the protein separator within a certain range, and is highly compatible with the desulfurization system of the present invention; and compared with a one-stage protein separator or a three-stage or above protein separator, a two-stage protein separator can balance and take into account good recovery rate, produced water quality and economy, and is therefore more suitable for the desulfurization system of the present invention.

[0088] For the purpose of greater clarity, the invention is described in detail through the following examples.

[0089] Example 1

[0090] (1) This embodiment provides a method such as Figure 1The limestone-gypsum flue gas desulfurization system shown comprises: a limestone pulping tank 1, a limestone-gypsum flue gas desulfurization tower 2, a gypsum slurry separation device 3, a gypsum dehydration device 4, a recovery water tank 5, a wastewater separation device 6, a wastewater collection tank 7, a wastewater treatment triple box 8, a sedimentation tank 9, a foam separator 10 and an external drainage pipe 11; wherein, a raw flue gas inlet 2-1 is arranged on the side wall of the tower kettle of the limestone-gypsum flue gas desulfurization tower 2, a clean flue gas outlet 2-2 is arranged on the top of the tower, a circulating slurry outlet, a gypsum slurry outlet 2-4 and an air inlet 2-5 are arranged at the bottom of the tower, and the circulating slurry outlet is connected to the liquid inlet of the slurry circulation pipe 2-3 of the desulfurization tower. The ends are connected, the liquid outlet end of the slurry circulation pipeline 2-3 is connected to the slurry spraying device arranged at the top of the inner cavity of the desulfurization tower, and the air inlet 2-5 is connected to the oxidation fan 2-6 matched therewith; the gypsum slurry separation equipment 3 specifically selects a gypsum cyclone; the gypsum dehydration equipment 4 specifically selects a vacuum belt conveyor; the wastewater separation equipment 6 specifically selects a wastewater cyclone; the wastewater treatment triple box 8 specifically includes a neutralization tank 8-1, a reaction tank 8-2 and a flocculation tank 8-3 arranged in series; the foam separator 10 specifically selects a secondary protein separator, specifically including a first protein separator 10-1 and a second protein separator 10-2; the specific connection relationship of each device and equipment is as follows Figure 1 As shown, no further details are given.

[0091] (2) This embodiment also provides a process for performing flue gas desulfurization in the above system, comprising the following steps:

[0092] Limestone powder is made into limestone slurry in a limestone slurry making tank 1, and then the limestone slurry is transported to a limestone-gypsum flue gas desulfurization tower 2 as a desulfurization absorbent;

[0093] The raw flue gas enters the limestone-gypsum flue gas desulfurization tower 2 from the raw flue gas inlet 2-1, and contacts with the slurry sprayed on the top of the tower in countercurrent; during the countercurrent contact, the slurry absorbs sulfur dioxide in the raw flue gas, and then falls to the bottom of the tower, and the clean flue gas after desulfurization is discharged from the clean flue gas outlet 2-2 on the top of the tower; the slurry falling into the bottom of the tower reacts with the air blown into the tower through the air inlet 2-5, so that the calcium sulfite in the slurry is oxidized into gypsum; a part of the slurry at the bottom of the tower is sent to the top of the tower through the slurry circulation pipeline 2-3 to be sprayed again, and the other part of the slurry at the bottom of the tower is discharged through the gypsum slurry outlet 2-4 set at the bottom of the tower;

[0094] The discharged bottom slurry enters the gypsum slurry separation device 3 for separation to obtain wet gypsum and gypsum slurry separation wastewater respectively;

[0095] The wet gypsum is discharged through the bottom flow outlet of the gypsum slurry separation device 3 and enters the gypsum dehydration device 4 for dehydration to obtain dry gypsum and dehydrated water respectively;

[0096] The gypsum slurry separation wastewater is discharged through the overflow port of the gypsum slurry separation device 3, and merges with the dewatering water discharged from the gypsum dehydration device 4 to the recovery pool 5. A part of the water in the recovery pool is returned to the limestone pulping pool 1 as recycled water to participate in pulping; the other part is transported to the wastewater separation device 6 for separation, and the separated underflow is returned to the recovery pool 5, and the separated overflow enters the chemical precipitation device;

[0097] The overflow from the wastewater separation device 6 is transported to the wastewater collection tank 7, and then enters the wastewater treatment triple tank 8 for neutralization, organic sulfide mixing reaction and flocculation, and then precipitates in the sedimentation tank 9 to obtain a clear liquid;

[0098] The clear liquid is discharged through the clear liquid outlet of the sedimentation tank 9, and a part of the clear liquid enters the first foam separator 10-1 for foam separation, and the foam water obtained after separation enters the second foam separator 10-2 to continue foam separation; the foam separation clean water produced by the first foam separator 10-1 and the second foam separator 10-2 is combined and returned to the limestone pulping tank 1 to participate in pulping;

[0099] The foam water produced by the second foam separator 10-2 is combined with another part of the clear liquid discharged from the sedimentation tank 9 and enters the external drainage pipe 11 as external wastewater;

[0100] During the operation of the system, process water is regularly added to the limestone-gypsum flue gas desulfurization tower 2 to maintain the material balance of the slurry in the limestone-gypsum flue gas desulfurization tower.

[0101] In the flue gas desulfurization process provided in this embodiment, the process water used is recycled water from urban sewage that does not meet the reuse standards, and the raw water has a chloride ion concentration of 300 mg / L, a LAS concentration of 1.5-2 mg / L, and a COD of 100-200 mg / L;

[0102] In the flue gas desulfurization process provided in this embodiment, during the operation of the system, the water inlet of the first foam separator 10-1 is 30 t / h, the net water output is 20 t / h, the water inlet of the second foam separator 10-2 is 10 t / h, the net water output is 7 t / h, and the amount of foam water discharged is 3 t / h; the LAS concentration of the water inlet of the first foam separator 10-1 is 10 mg / L, and the LAS concentration of the combined water produced by the first foam separator 10-1 and the second foam separator 10-2 is 4 mg / L; the LAS concentration of the water inlet of the second foam separator 10-2 is 24 mg / L, and the LAS concentration of the foam water discharged from the second foam separator 10-2 is 71 mg / L;

[0103] In the flue gas desulfurization process provided in this embodiment, during the operation of the system, the LAS concentration in the slurry in the limestone-gypsum flue gas desulfurization tower 2 is controlled at 5-7 mg / L;

[0104] In the above flue gas desulfurization process provided in this embodiment, during the operation of the system, the amount of wastewater discharged directly from the sedimentation tank 9 into the external drainage pipe 11 is 2 t / h;

[0105] In the flue gas desulfurization process provided in this embodiment, during the operation of the system, the external foam water from the second foam separator 10-2 and the external waste water from the sedimentation tank 9 converge in the external drainage pipe 11. After the confluence, the chloride ion concentration of the waste water is 30000 mg / L, the COD value is 5000 mg / L, and the total waste water discharge is 5 t / h;

[0106] In the flue gas desulfurization process provided in this embodiment, the foaming of the slurry in the limestone-gypsum flue gas desulfurization tower 2 was observed during system operation, and the results were: no obvious foaming was observed, the liquid level in the absorption tower was clear and accurate, the flow and current of the slurry circulation pump were stable, and the operation was smooth without cavitation.

[0107] It can be seen that the chloride ion concentration of the discharged wastewater of the limestone-gypsum flue gas desulfurization system provided in this embodiment is as high as 30,000 mg / L during operation, and stable operation with a high concentration ratio can be achieved; but since the protein separator has no degradation ability for COD and LAS, the COD value of the discharged wastewater of the system is as high as 5,000 mg / L and cannot be discharged directly, but the total amount of desulfurization wastewater is very low, achieving effective reduction, which greatly reduces the cost burden for subsequent treatment or zero emission process.

[0108] Comparative Example 1

[0109] (1) This comparative example provides a Figure 2The limestone-gypsum flue gas desulfurization system shown in the figure comprises: a limestone pulping tank 1, a limestone-gypsum flue gas desulfurization tower 2, a gypsum slurry separation device 3, a gypsum dehydration device 4, a recovery water tank 5, a wastewater separation device 6, a wastewater collection tank 7, a wastewater treatment triple box 8, a sedimentation tank 9 and an external drainage pipe 11; wherein, the side wall of the tower kettle of the limestone-gypsum flue gas desulfurization tower 2 is provided with a raw flue gas inlet 2-1, a clean flue gas outlet 2-2 is provided at the top of the tower, and a circulating slurry outlet, a gypsum slurry outlet 2-4 and an air inlet 2-5 are provided at the bottom of the tower, and the circulating The slurry outlet is connected to the liquid inlet end of the slurry circulation pipeline 2-3 of the desulfurization tower, the liquid outlet end of the slurry circulation pipeline 2-3 is connected to the slurry spraying device arranged at the top of the inner cavity of the desulfurization tower, and the air inlet 2-5 is connected to the oxidation fan 2-6 matched therewith; the gypsum slurry separation equipment 3 specifically selects a gypsum cyclone; the gypsum dehydration equipment 4 specifically selects a vacuum belt conveyor; the wastewater separation equipment 6 specifically selects a wastewater cyclone; the wastewater treatment triple box 8 specifically includes a neutralization tank 8-1, a reaction tank 8-2 and a flocculation tank 8-3 arranged in series; the specific connection relationship of each device and equipment is as follows Figure 2 As shown, no further details are given.

[0110] (2) This comparative example also provides a process for flue gas desulfurization in the above system, comprising the following steps:

[0111] Limestone powder is made into limestone slurry in a limestone slurry making tank 1, and then the limestone slurry is transported to a limestone-gypsum flue gas desulfurization tower 2 as a desulfurization absorbent;

[0112] The raw flue gas enters the limestone-gypsum flue gas desulfurization tower 2 from the raw flue gas inlet 2-1, and contacts with the slurry sprayed on the top of the tower in countercurrent; during the countercurrent contact, the slurry absorbs sulfur dioxide in the raw flue gas, and then falls to the bottom of the tower, and the clean flue gas after desulfurization is discharged from the clean flue gas outlet 2-2 on the top of the tower; the slurry falling into the bottom of the tower reacts with the air blown into the tower through the air inlet 2-5, so that the calcium sulfite in the slurry is oxidized into gypsum; a part of the slurry at the bottom of the tower is sent to the top of the tower through the slurry circulation pipeline 2-3 to be sprayed again, and the other part of the slurry at the bottom of the tower is discharged through the gypsum slurry outlet 2-4 set at the bottom of the tower;

[0113] The discharged bottom slurry enters the gypsum slurry separation device 3 for separation to obtain wet gypsum and gypsum slurry separation wastewater respectively;

[0114] The wet gypsum is discharged through the bottom flow outlet of the gypsum slurry separation device 3 and enters the gypsum dehydration device 4 for dehydration to obtain dry gypsum and dehydrated water respectively;

[0115] The gypsum slurry separation wastewater is discharged through the overflow port of the gypsum slurry separation device 3, and merges with the dewatering water discharged from the gypsum dehydration device 4 to the recovery pool 5. A part of the water in the recovery pool is returned to the limestone pulping pool 1 as recycled water to participate in pulping; the other part is transported to the wastewater separation device 6 for separation, and the separated underflow is returned to the recovery pool 5, and the separated overflow enters the chemical precipitation device;

[0116] The overflow from the wastewater separation device 6 is transported to the wastewater collection tank 7, and then enters the wastewater treatment triple tank 8 for neutralization, organic sulfide mixing reaction and flocculation, and then precipitates in the sedimentation tank 9 to obtain a clear liquid;

[0117] The clear liquid is discharged through the clear liquid outlet of the sedimentation tank 9 and enters the external drainage pipe 11 as external wastewater;

[0118] During the operation of the system, process water is regularly added to the limestone-gypsum flue gas desulfurization tower 2 to maintain the material balance of the slurry in the limestone-gypsum flue gas desulfurization tower.

[0119] In the flue gas desulfurization process provided in this comparative example, the process water used is recycled water from urban sewage that does not meet the reuse standards, and the raw water chloride ion concentration is 300 mg / L, LAS is 1.5-2 mg / L, and COD is 100-200 mg / L;

[0120] In the above-mentioned flue gas desulfurization process method provided in this comparative example, during the operation of the system, the chloride ion concentration of the discharged wastewater is 5000 mg / L, LAS is 10 mg / L, COD is 1000 mg / L, and the wastewater discharge is 30 t / h. Due to the high COD, it needs subsequent treatment before discharge, but the high water volume increases the cost burden of subsequent treatment or zero emission process.

[0121] It can be seen that since the root cause of the slurry foaming has not been found, in order to avoid the desulfurization slurry foaming affecting the operating stability of the system, the comparative example desulfurization system can only control the slurry chloride ion concentration at a low level during operation, and the chlorine ion concentration of the discharged wastewater is only 5000 mg / L, which leads to a significant increase in its wastewater discharge, which is 6 times the discharge amount in Example 1.

[0122] Comparative Example 2

[0123] Referring to the limestone-gypsum flue gas desulfurization system and flue gas desulfurization process of comparative example 1, the only difference is that the concentration ratio of the system operation is gradually increased. It was found that when the chloride ion concentration of the external wastewater reached 4000 mg / L, obvious foam began to appear in the slurry of the limestone-gypsum flue gas desulfurization tower 2; when the chloride ion concentration of the external wastewater reached 6000 mg / L, a large amount of foam was generated in the slurry of the limestone-gypsum flue gas desulfurization tower 2, and it could not operate normally.

[0124] It can be seen that due to the failure to remove LAS in the slurry, the comparative limestone-gypsum flue gas desulfurization system can only operate normally when the chloride ion concentration of the discharged wastewater is lower than 5000 mg / L. Increasing the concentration ratio will cause the internal slurry of the limestone-gypsum flue gas desulfurization tower 2 to foam and fail to operate normally.

[0125] Comparative Example 3

[0126] Referring to the limestone-gypsum flue gas desulfurization system and flue gas desulfurization process of comparative example 1, the only difference is that purified water without linear alkylbenzene sulfonate (LAS) is used as the supplementary water of the desulfurization system, and the concentration ratio of the system operation is gradually increased. It was found that when the chloride ion concentration of the discharged wastewater reached 40000 mg / L, there was still no obvious bubbling in the limestone-gypsum flue gas desulfurization tower 2. It can be seen that LAS is the root cause of the slurry bubbles. As long as the slurry does not contain LAS, the desulfurization system can be maintained at a high concentration ratio.

[0127] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A limestone-gypsum flue gas desulfurization system, characterized in that: include: limestone pulping pond; A limestone-gypsum flue gas desulfurization tower connected to the slurry outlet of the limestone slurry tank; A gypsum slurry separation device connected to the gypsum slurry outlet of the limestone-gypsum flue gas desulfurization tower; A gypsum dehydration device connected to the bottom flow outlet of the gypsum slurry separation device; A recovery water tank connected to the overflow port of the gypsum slurry separation device and the drain port of the gypsum dehydration device respectively; the recovery water tank is provided with a first water outlet and a second water outlet, and the first water outlet is connected to the limestone slurry making tank; A wastewater separation device connected to the second water outlet of the recovery pool; The underflow outlet of the wastewater separation equipment is connected back to the recovery pool; A chemical precipitation device connected to the overflow port of the wastewater separation device; A foam separator and an external drainage pipe are connected to the clear liquid outlet of the chemical precipitation equipment; the clean water outlet of the foam separator is connected to the limestone pulping tank or the limestone-gypsum flue gas desulfurization tower, and the foam water outlet of the foam separator is connected to the external drainage pipe.

2. The limestone-gypsum flue gas desulfurization system according to claim 1, characterized in that: The foam separator is a protein skimmer.

3. The limestone-gypsum flue gas desulfurization system according to claim 2, characterized in that: The foam separator is a secondary protein skimmer; The secondary protein separator includes a first protein separator and a second protein separator, wherein the water inlet of the first protein separator is connected to the clear liquid outlet of the chemical precipitation equipment, the clean water outlet of the first protein separator is connected to the limestone pulping tank or the limestone-gypsum flue gas desulfurization tower, the foam water outlet of the first protein separator is connected to the water inlet of the second protein separator, the clean water outlet of the second protein separator is connected to the limestone pulping tank or the limestone-gypsum flue gas desulfurization tower, and the foam water outlet of the second protein separator is connected to the external drainage pipe.

4. The limestone-gypsum flue gas desulfurization system according to claim 1, characterized in that: The gypsum slurry separation equipment is a gypsum cyclone; the gypsum dehydration equipment is a vacuum belt conveyor; and the wastewater separation equipment is a wastewater cyclone.

5. The limestone-gypsum flue gas desulfurization system according to claim 1, characterized in that: The chemical precipitation equipment includes a wastewater treatment triple tank and a sedimentation tank; The wastewater treatment triple tank comprises a neutralization tank, a reaction tank and a flocculation tank arranged in series, and the water inlet of the neutralization tank is connected to the overflow port of the wastewater separation equipment; The water inlet of the sedimentation tank is connected to the water outlet of the flocculation tank, and the clear liquid outlet of the sedimentation tank is connected to the water inlet of the foam separator and the external drainage pipe respectively.

6. The limestone-gypsum flue gas desulfurization system according to claim 1, characterized in that: It also includes process water delivery pipelines; The water outlet end of the process water delivery pipeline is connected to the limestone-gypsum flue gas desulfurization tower and the gypsum dehydration equipment respectively.

7. The limestone-gypsum flue gas desulfurization system according to claim 1, characterized in that: It also includes wastewater collection ponds; The wastewater collection tank is arranged between the overflow of the wastewater separation equipment and the water inlet of the chemical precipitation equipment. The water inlet of the wastewater collection tank is connected to the overflow of the wastewater separation equipment, and the water outlet of the wastewater collection tank is connected to the water inlet of the chemical precipitation equipment.

8. A limestone-gypsum flue gas desulfurization method, characterized in that: In the limestone-gypsum flue gas desulfurization system of claim 1, the method comprises the following steps: The limestone powder is made into limestone slurry in a limestone slurry making tank, and then the limestone slurry is transported to a limestone-gypsum flue gas desulfurization tower as a desulfurization absorbent; The raw flue gas enters the limestone-gypsum flue gas desulfurization tower from the raw flue gas inlet and contacts the slurry sprayed on the top of the tower in countercurrent. During the countercurrent contact, the slurry absorbs sulfur dioxide in the raw flue gas and then falls to the bottom of the tower. The clean flue gas after desulfurization is discharged from the clean flue gas outlet on the top of the tower. The slurry falling to the bottom of the tower reacts with the air blown into the tower through the air inlet, so that the calcium sulfite in the slurry is oxidized into gypsum. A part of the slurry at the bottom of the tower is sent to the top of the tower through the slurry circulation pipeline and sprayed again, and the other part of the slurry at the bottom of the tower is discharged through the gypsum slurry outlet set at the bottom of the tower. The discharged bottom slurry enters the gypsum slurry separation equipment for separation to obtain wet gypsum and gypsum slurry separation wastewater respectively; The wet gypsum is discharged through the bottom flow outlet of the gypsum slurry separation device and enters the gypsum dehydration device for dehydration to obtain dry gypsum and dehydrated water respectively; The gypsum slurry separation wastewater is discharged through the overflow port of the gypsum slurry separation equipment, and merges with the dewatering water discharged from the gypsum dehydration equipment into the recovery pool. A part of the water in the recovery pool is returned to the limestone pulping pool as recycled water to participate in pulping; the other part is transported to the wastewater separation equipment for separation, and the separated underflow is returned to the recovery pool, and the separated overflow enters the chemical precipitation equipment; The overflow from the wastewater separation device is chemically precipitated in a chemical precipitation device to obtain a clear liquid; The clear liquid is discharged through the clear liquid outlet of the chemical precipitation device, and a part of the clear liquid enters the foam separator for foam separation to obtain foam separation clean water and foam water respectively; The foam separation purified water is returned to the limestone pulping tank to participate in pulping, or returned to the limestone-gypsum flue gas desulfurization tower to participate in desulfurization; The foam water is combined with another part of the clear liquid discharged from the chemical precipitation equipment and enters the external drainage pipe as external wastewater; During this period, process water is regularly added to the limestone-gypsum flue gas desulfurization system to maintain the material balance of the slurry in the limestone-gypsum flue gas desulfurization tower.

9. The limestone-gypsum flue gas desulfurization method according to claim 8, characterized in that: The linear alkylbenzene sodium sulfonate concentration of the foam separation water purification is ≤4 mg / L.

10. The limestone-gypsum flue gas desulfurization method according to claim 8, characterized in that: The chloride ion concentration of the discharged wastewater is ≥30000 mg / L.

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