Flue gas water extraction lime mineralization method tempering process

Abstract

The invention relates to the technical field of flue gas treatment, in particular to a flue gas water extraction lime mineralization method tempering process. Comprising the following steps that S1, flue gas lifting water generated on a production line is introduced into a first water tank through a pipeline to be stored; s2, inputting the flue gas lift water stored in the first water tank into softening, crystallizing and granulating equipment through a water pump, and adding limestone into the softening, crystallizing and granulating equipment to adjust the pH value of the flue gas lift water; s3, the flue gas extracted water with the pH adjusted to 6 in the softening crystallization granulation equipment is input into solid-liquid separation equipment; and S4, carrying out solid-liquid separation on the input flue gas lifting water by the solid-liquid separation equipment, conveying the separated water into a second water tank for storage and recycling, discharging the separated sludge, and carrying out unified collection treatment. According to the conditioning process, a limestone conditioning process route is provided, the problem that the conventional conditioning cost of flue gas water extraction is high is solved, and the feasibility, the safety and the economical efficiency of the flue gas water extraction conditioning technology are realized.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas treatment, and in particular to a flue gas water extraction lime mineralization conditioning process. Background Art

[0002] Water resources are basic natural resources and strategic economic resources, and are an important foundation for sustainable social and economic development, ecological balance and a harmonious environment. Thermal power generation, as a high-water-consuming industry, accounts for 20% of all industrial water consumption. The water problem has become a constraint on the construction and development of the power industry in northern China, and flue gas water extraction is one of the key directions for water conservation in coal-fired power plants in water-scarce areas.

[0003] At present, more than 90% of the flue gas desulfurization of coal-fired boilers in thermal power generation enterprises and other chemical enterprises adopts the wet desulfurization process of limestone gypsum method. The wet desulfurization process consumes a lot of water. Taking coal-fired power plants as an example, the water consumption of the wet desulfurization process accounts for more than 60% of the total water consumption of air-cooled units in the whole plant. Therefore, reducing the water consumption of the desulfurization system is an important task for power plants to save water and reduce consumption. The flue gas water extraction technology can recover the moisture carried by the flue gas after desulfurization. It is the only way for thermal power plants to reduce the water consumption per unit of power generation, and it is also the main promotion technology for solving water shortages in water-scarce areas in the future.

[0004] At present, most of the domestic wet flue gas desulfurization devices have cancelled the gas-gas heat exchanger (GGH). The clean flue gas at the outlet of the desulfurization is saturated wet flue gas with a temperature of about 45℃-60℃. A large amount of water vapor and low-temperature waste heat in the flue gas are discharged into the environment, resulting in a waste of resources. Flue gas water extraction technology is a new process technology for extracting condensed water from desulfurized saturated clean flue gas. Its principle is based on the principle of phase change condensation of wet saturated water vapor under different partial pressures. It uses the wet saturation or supersaturation conditions of the flue gas after desulfurization, adopts cooling means, condenses and collects water, and realizes efficient water extraction and large-scale recycling of flue gas.

[0005] There are three main technical routes for flue gas water extraction: condensation technology, liquid absorption technology, and membrane separation technology. Among them, the condensation method is the mainstream technology currently used on an industrial scale. The condensation method flue gas water extraction technology cools the clean flue gas after desulfurization in the water extraction device, causing the water vapor in the flue gas to undergo a phase change, from gas to liquid and condense and precipitate.

[0006] Since the flue gas at the outlet of the wet flue gas desulfurization process contains a small amount of acidic gases such as SO3 and SO2 and droplets carrying dissolved corrosive ions such as sulfate and chloride ions, the recovered water from the flue gas extraction generally has a low pH (2.0-3.0), SO4 2- Due to its high content, it cannot be used directly in production and life. In this regard, the dual alkali method (adding sodium hydroxide and sodium carbonate to flue gas water) is currently used to condition the water, and there are few studies on other flue gas water conditioning processes at home and abroad.

[0007] The double alkali method is to add sodium hydroxide and sodium carbonate to the flue gas water to adjust the pH of the water. The main disadvantages of this process are as follows: (1) The operating cost of water conditioning is high: the annual cost of flue gas water conditioning is more than 5 million yuan, and it cannot be conditioned in a timely and accurate manner. (2) The purified water reuse pipeline is seriously corroded: the purified water contains a large amount of corrosive ions, which causes serious corrosion and leakage of the carbon steel pipeline of the fire water system, and the fire water system is frequently shut down; among them, there are two main reasons for corrosion: ① After the double alkali method is conditioned, the pH is increased from 2.0-3.0 to 5.0-5.5, which is still acidic and therefore still corrosive (if the pH is further increased to neutral, the cost is too high); ② The double alkali method is used for conditioning to react and generate sodium salt, resulting in an increase in the salt content in the water, an increase in the conductivity of the water, and an increase in corrosiveness. (3) The operating pressure of boiler feed water treatment is high: the current double alkali method conditioning process causes an increase in the salt content of the purified water, and the ED I effluent conductivity in the chemical water treatment process is too high.

[0008] Based on this, it is urgent to design a new method of conditioning by lime mineralization of flue gas water extraction. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a flue gas water extraction lime mineralization tempering process, which not only carries out research on flue gas water extraction water quality control and proposes a limestone tempering process route, but also solves the problem of high cost of conventional flue gas water extraction tempering, and realizes the feasibility, safety and economy of flue gas water extraction tempering technology.

[0010] To achieve the above object, the technical solution of the present invention is implemented as follows: a flue gas water extraction lime mineralization method conditioning process, comprising the following steps:

[0011] S1. The smoke water generated on the production line is introduced into the first water tank through a pipeline for storage;

[0012] S2, inputting the flue gas water stored in the first water tank into the softening, crystallizing and granulating equipment through a water pump, and adding limestone into the softening, crystallizing and granulating equipment to adjust the pH of the flue gas water;

[0013] S3, extracting water from the flue gas adjusted to pH 6 in the softening crystallization granulation equipment and inputting it into the solid-liquid separation equipment;

[0014] S4, solid-liquid separation equipment performs solid-liquid separation on the input flue gas water extraction, and transports the separated water to the second water tank for storage and reuse, and discharges the separated sludge and collects it for unified treatment.

[0015] Preferably, the process of adding limestone to the softening, crystallizing and granulating equipment to adjust the pH of the flue gas water extraction in step S2 includes:

[0016] S21, introducing flue gas water extraction from the bottom of the softening crystallization granulation equipment, and discharging the flue gas water extraction adjusted to pH 6 from the top of the softening crystallization granulation equipment;

[0017] S22, in the process of flue gas water extraction and limestone reaction in the softening crystallization granulation equipment, limestone is automatically supplemented through the feeding equipment;

[0018] S23, open the exhaust port at the top of the softening crystallization granulation equipment to discharge the carbon dioxide produced by the reaction of flue gas water extraction and limestone.

[0019] Preferably, the solid-liquid separation process of the input flue gas water extraction by the solid-liquid separation equipment in step S4 includes:

[0020] S41, introducing the flue gas water after pH adjustment from the bottom of the solid-liquid separation equipment, and adding a coagulant and a coagulant aid to the introduced flue gas water to reduce the turbidity of the flue gas water;

[0021] S42. When the online turbidity meter detects that the turbidity of the flue gas water extraction in the solid-liquid separation equipment is less than 5, the crystal water is output from the top of the solid-liquid separation equipment, and the sludge in the solid-liquid separation equipment is discharged from the outlet at the bottom of the solid-liquid separation equipment.

[0022] Preferably, the order of adding the coagulant and the coagulant-boosting agent to the flue gas water extraction in S42 is to first add the coagulant to the flue gas water extraction, and then add the coagulant-boosting agent.

[0023] Preferably, the coagulant is polyaluminium chloride, the coagulant booster is polyacrylamide, and the addition ratio of PAC to PAM is 500:1.

[0024] Preferably, the amount of PAM added per liter in the flue gas water extraction is 10-15 mg, and the amount of PAC added is 0.02-0.03 mg.

[0025] Preferably, the calcium carbonate purity of the limestone supplemented by the feeding equipment is not less than 90%, and the supplemented limestone is granular with a particle size of 0.5-3 mm.

[0026] Preferably, the time for adjusting the pH of the flue gas water extraction in step S2 is 2-3 minutes.

[0027] Preferably, the height of limestone in the softening, crystallization and granulation equipment is 2-3 m.

[0028] Preferably, the flow rate of the softening crystallization granulation equipment is 50 m / h-80 m / h.

[0029] The beneficial effects of the present invention are embodied in:

[0030] (1) The conditioning process provided by the present invention does not use the hazardous chemicals used in the traditional double alkali method, such as hydrochloric acid, sodium hydroxide and sodium hypochlorite. This is not only easy to manage, but also has a short process flow using limestone, a simple process, and is easy to promote. In addition, the entire process uses less equipment, occupies less space, requires less investment, and reduces the cost of flue gas water extraction.

[0031] (2) The cost of the tempering process reagent provided by the present invention is low, not more than 1.0 yuan / t, thereby reducing the cost of flue gas water extraction.

[0032] (3) The tempering process provided by the present invention has high water utilization rate and less wastewater discharge, which is beneficial to environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a process flow chart of the present invention;

[0034] Figure 2 This is a flow chart of the process of extracting water from flue gas in a softening, crystallizing and granulating device according to the present invention;

[0035] Figure 3 This is a flow chart of the process of extracting water from flue gas in a solid-liquid separation device according to the present invention;

[0036] Figure 4 This is a curve diagram showing the relationship between pH and time in the flue gas water extraction process of the present invention. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] like Figure 1-4 As shown:

[0040] The present invention provides a flue gas water extraction lime mineralization method conditioning process, comprising the following steps:

[0041] S1. The smoke generated on the production line is lifted and introduced into the water tank through a pipeline for storage, waiting for subsequent centralized treatment.

[0042] S2. The flue gas water stored in the water tank is input into the softening, crystallizing and granulating equipment through a water pump, and limestone is added into the softening, crystallizing and granulating equipment to adjust the pH value of the flue gas water.

[0043] The process of adding limestone to the softening, crystallizing and granulating equipment to adjust the pH of the flue gas water extraction in step S2 includes:

[0044] S21, introducing flue gas water extraction from the bottom of the softening crystallization granulation equipment, and discharging the flue gas water extraction adjusted to pH 6 from the top of the softening crystallization granulation equipment;

[0045] S22, in the process of flue gas water extraction and limestone reaction in the softening crystallization granulation equipment, limestone is automatically supplemented through the feeding equipment;

[0046] S23, open the exhaust port at the top of the softening crystallization granulation equipment to discharge the carbon dioxide produced by the reaction of flue gas water extraction and limestone.

[0047] Since the purer the acid calcium, the better the reaction effect and the lower the suspended solids in the effluent, the calcium carbonate purity of the limestone added by the feeding equipment is not less than 90%, and the added limestone is granular with a particle size of 0.5mm-3mm.

[0048] Working principle of automatic addition of limestone to solid-liquid separation equipment: The limestone mineralization device adopts "softening crystallization granulation equipment + solid-liquid separation and filtration" equipment. The diameter of the softening crystallization granulation equipment is DN200mm, the operating flow rate is controlled at 50m / h-55m / h, and the limestone filling height is 3m. As the flue gas water extraction reacts with the limestone, the limestone gradually decreases. When the limestone height drops to about 1.5m, the limestone automatic addition device is started to replenish the limestone.

[0049] The technical principle of using limestone to treat flue gas and extract water is:

[0050] Since the pH of flue gas water is 2.0-3.0, the main components are acidic substances such as sulfuric acid. The principle of limestone mineralization is as follows:

[0051] H2SO4+CaCO3→CaSO4+H2O+CO2, CaCO3+H2O+CO2→Ca(HCO3)2

[0052] After merging, the reaction formula is: H2SO4+2CaCO3→CaSO4+Ca(HCO3)2, which means that 1 mol of calcium carbonate is consumed to generate 1 mol of alkalinity. + +CaCO3→Ca 2+ +HCO3 - .

[0053] Limestone consumption: Adjust pH from 2.2 to 6, the reaction H + The content is 10 -2.2 -10 -6 =3.15mmol / L (according to Ca 2+ calculate).

[0054] The pH adjustment time for extracting water from flue gas in step S2 is 2-3 minutes, the height of limestone in the softening crystallization granulation equipment is 2-3 meters, the softening crystallization granulation equipment adopts a fluidized bed form, water enters from the bottom and exits from the top, and the overall flow rate of the equipment is controlled at 50 meters / hour to 80 meters / hour.

[0055] Through such a setting, the calcium carbonate in the equipment can flow and generate shear force to prevent the reaction of limestone and sulfuric acid to form slightly soluble calcium sulfate, which is wrapped around the limestone and affects the reaction process. The outlet water pH can reach 5.5-6.0. The relationship curve between the pH and time of the flue gas water extraction in the softening crystallization granulation equipment is shown in Table 1.

[0056] Table 1 Relationship between flue gas conditioning pH and time

[0057] pH(25℃) 2.53 3.00 3.50 4.00 4.50 5.00 5.50 6.00 Time(S) 0.00 8.70 19.30 32.80 53.10 82.30 121.60 181.30

[0058] In addition, when performing step S2, the ED I effluent conductivity in the chemical water treatment process is ≤0.12μS / cm; and the surfaces of the softening, crystallization and granulation equipment and the water pump in contact with the flue gas water extraction are all made of stainless steel, and the average corrosion rate of carbon steel of the stainless steel material is ≤0.1mm / y, and the average corrosion rate of stainless steel is ≤0.05mm / y.

[0059] S3, the flue gas adjusted to pH 6 in the softening crystallization granulation equipment is extracted and input into the solid-liquid separation equipment.

[0060] This is because after the flue gas water is discharged from the crystallization granulation circulation softener equipment, the pH rises from 2-3 to 5-6, but due to the purity of the limestone, the turbidity of the outlet water is high, about 10NTU, and it needs to enter the intelligent integrated high-efficiency agglomeration solid-liquid separation equipment to remove the turbidity.

[0061] S4, solid-liquid separation equipment performs solid-liquid separation on the input flue gas water extraction, and transports the separated water to the water tank for storage and reuse, and discharges the separated sludge and collects it for unified treatment.

[0062] In step S4, the solid-liquid separation process of the input flue gas water extraction by the solid-liquid separation equipment includes:

[0063] S41. The flue gas water after pH adjustment is introduced from the bottom of the solid-liquid separation equipment, and a coagulant and a coagulant-assisting agent are added to the introduced flue gas water to reduce the turbidity of the flue gas water.

[0064] The order of adding coagulant and coagulant booster to the flue gas water is to first add coagulant polyaluminium chloride and then add coagulant booster polyacrylamide, and the addition ratio of PAC and PAM is 500:1; 10-15 mg of PAM and 0.02-0.03 mg of PAC are added per liter of flue gas water.

[0065] S42. When the turbidity of the flue gas water extraction in the solid-liquid separation equipment is less than 5, the crystal water is output from the top of the solid-liquid separation equipment, and the sludge in the solid-liquid separation equipment is discharged from the outlet at the bottom of the solid-liquid separation equipment.

[0066] Table 2 Comparison of water quality data before and after the limestone adjustment method for flue gas water extraction

[0067] Serial number index Water quality before flue gas water conditioning Water quality after flue gas water conditioning 1 pH 3 6.0 2 Total alkalinity (mmol / L) 0 0 3 Total hardness (mmol / L) 0.183 3.15 4 <![CDATA[1 / 2SO4 2- (mg / L)]]> 525 525 5 <![CDATA[Cl - (mg / L)]]> 345 345 6 <![CDATA[F - (mg / L)]]> 0.908 0.819 7 Turbidity (NTU) 6.8 2.6

[0068] The double alkali method (sodium hydroxide and sodium carbonate) is used to simultaneously compare the flue gas water extraction and conditioning. The double alkali method produces the following chemical reactions:

[0069] Na2CO3+SO2→Na2SO3+CO2(1)

[0070] 2NaOH+SO2→Na2SO3+H2O(2)

[0071] NA2SO3+SO2+H20→2NaHSO3(3)

[0072] The reaction after merging is: 2Na0H+2SO2→2NAHSO3; NaCO3+SO2→NA2S03+CO2,

[0073] By comparing the above and below, it can be seen that after using the double alkali method for water quality adjustment, 1 mol of NaOH is consumed to generate 1 mol of alkalinity, and 1 mol of NaCO3 is consumed to generate 1 mol of NaSO3. The soluble ion concentration in water should be greater than the ion concentration using the limestone method, and the annual reagent cost is about 5 million yuan.

[0074] Table 3 Comparison of water quality before and after using double alkali method and limestone conditioning method for flue gas water extraction

[0075]

[0076] By comparing the water quality data before and after the flue gas water conditioning, we can see that the pH value increased from 3.0 to 6.0, and other total hardness, total alkalinity, 1 / 2SO4 2- , C l - 、F -Indicators such as temperature, turbidity (NTU) and so on have not increased or decreased significantly. The water after flue gas water conditioning can be used for unit production. The cost of flue gas water conditioning per ton of water is not higher than 1 yuan, and the annual chemical cost is not higher than 3 million yuan, and the chemical cost is reduced by 60%.

[0077] In addition, the present invention has found that in the traditional flue gas water extraction process, by installing 2×660MW lignite-fired units, the whole plant production water adopts mixed flue gas water extraction, and the water extraction pH is about 3.0. Through experiments, the optimal ratio of sodium carbonate and sodium hydroxide 2:1 is currently used for flue gas water extraction conditioning, and the pH value of flue gas water extraction is raised from about 3.0 to 5.5-6.0. The annual flue gas water extraction is about 1 million tons, and the annual reagent cost is about 5 million yuan. The reagent cost is relatively high, and there is a serious corrosion of the whole plant water system, especially the fire water carbon steel system. The conductivity of the EDI outlet water of the boiler feed water treatment system is close to 0.15μS / cm, which exceeds the expected value of the "Water and Steam Quality Standard for Thermal Power Generators and Steam Power Equipment" (GB / T 12145-2016), and the unit thermal system has the risk of salt accumulation and scaling.

[0078] In order to reduce the operation cost and prevent the corrosion of the water system of the whole plant and the high conductivity of the EDI outlet water of the boiler feed water, the present invention adopts limestone to adjust the flue gas water, and the pH of the flue gas water is raised from about 3 to about 6. The annual consumption of limestone is 13,300 tons, the cost is 1.95 million yuan (the unit price of limestone is 150 yuan / t), and the cost of reagents is saved by 61%.

[0079] In summary, the limestone mineralization technology used in the conditioning process provided by the present invention utilizes the reaction principle of H2SO4+2CaCO3→CaSO4+Ca(HCO3)2, and combines conventional water treatment equipment, such as floating bed, softening crystallization granulation equipment, intelligent integrated high-efficiency agglomeration solid-liquid separation and filtration equipment, etc., to achieve reliable and economic flue gas water conditioning. This not only has the advantages of energy saving, water saving, low operating cost, reliable equipment, stable operation, and high degree of automation, but also because limestone, that is, calcium carbonate, has the advantages of convenient material acquisition and low cost, compared with the conventional double alkali method for adjusting pH, the cost of the reagent can be reduced by more than 60%, and it has a wide range of market value.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A flue gas water extraction lime mineralization method conditioning process, characterized in that: The following steps are involved: S1. The smoke water generated on the production line is introduced into the first water tank through a pipeline for storage; S2, inputting the flue gas water stored in the first water tank into the softening, crystallizing and granulating equipment through a water pump, and adding limestone into the softening, crystallizing and granulating equipment to adjust the pH of the flue gas water; S3, extracting water from the flue gas adjusted to pH 6 in the softening crystallization granulation equipment and inputting it into the solid-liquid separation equipment; S4, solid-liquid separation equipment performs solid-liquid separation on the input flue gas water extraction, and transports the separated water to the second water tank for storage and reuse, and discharges the separated sludge and collects it for unified treatment.

2. A flue gas water extraction lime mineralization quenching and tempering process according to claim 1, characterized in that: The process of adding limestone to the softening, crystallizing and granulating equipment to adjust the pH of the flue gas water extraction in step S2 includes: S21, introducing flue gas water extraction from the bottom of the softening crystallization granulation equipment, and discharging the flue gas water extraction adjusted to pH 6 from the top of the softening crystallization granulation equipment; S22, in the process of flue gas water extraction and limestone reaction in the softening crystallization granulation equipment, limestone is automatically supplemented through the feeding equipment; S23, open the exhaust port at the top of the softening crystallization granulation equipment to discharge the carbon dioxide produced by the reaction of flue gas water extraction and limestone.

3. A flue gas water extraction lime mineralization quenching and tempering process according to claim 2, characterized in that: The solid-liquid separation process of the solid-liquid separation equipment for extracting water from the input flue gas in step S4 includes: S41, introducing the flue gas water after pH adjustment from the bottom of the solid-liquid separation equipment, and adding a coagulant and a coagulant-assisting agent to the introduced flue gas water to reduce the turbidity of the flue gas water; S42. When the turbidity of the flue gas water extraction in the solid-liquid separation equipment is less than 5, the crystal water is output from the top of the solid-liquid separation equipment, and the sludge in the solid-liquid separation equipment is discharged from the outlet at the bottom of the solid-liquid separation equipment.

4. A flue gas water extraction lime mineralization quenching and tempering process according to claim 3, characterized in that: The order of adding the coagulant and the coagulant-boosting agent to the flue gas water extraction in S42 is to first add the coagulant to the flue gas water extraction, and then add the coagulant-boosting agent.

5. A flue gas water extraction lime mineralization quenching and tempering process according to claim 4, characterized in that: The coagulant is polyaluminium chloride, the coagulant booster is polyacrylamide, and the addition ratio of PAC to PAM is 500:

1.

6. A flue gas water extraction lime mineralization quenching and tempering process according to claim 5, characterized in that: The amount of PAM added to the flue gas water extraction is 10-15 mg per liter, and the amount of PAC added is 0.02-0.03 mg per liter.

7. A flue gas water extraction lime mineralization quenching and tempering process according to claim 3 or 4, characterized in that: The calcium carbonate purity of the limestone supplemented by the feeding equipment is not less than 90%, and the supplemented limestone is in granular form with a particle size of 0.5-3 mm.

8. The flue gas water extraction lime mineralization tempering process according to claim 5, characterized in that: The time for adjusting the pH of the flue gas water extraction in step S2 is 2-3 minutes.

9. A flue gas water extraction lime mineralization quenching and tempering process according to claim 6, characterized in that: The height of the limestone in the softening, crystallization and granulation equipment is 2-3m.

10. A flue gas water extraction lime mineralization quenching and tempering process according to claim 7, characterized in that: The flow rate of the softening crystallization granulation equipment is 50 m / h-80 m / h.

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