A coal-fired boiler flue gas deoxidation and waste heat recovery system and method

Abstract

The invention discloses a coal-fired boiler flue gas de-whitening and waste heat recovery system, and also discloses a coal-fired boiler flue gas de-whitening and waste heat recovery method. The invention adopts a highly water-absorbing aqueous solution, such as a calcium chloride solution, a lithium bromide solution, etc., to absorb water vapor in the exhaust gas after desulfurization by spraying, so that not only the water vapor carried by the flue gas is reduced, but also because the saturation temperature of the solution is higher than the saturation temperature of pure water under the same water vapor partial pressure, the flue gas temperature is also improved, so that the relative humidity of the flue gas is greatly reduced, so that when mixed with the ambient cold air, the condensation of water vapor is reduced or even completely eliminated, so as to achieve de-whitening discharge, and at the same time, the quality of flue gas waste heat recovery is also improved.

Description

Technical Field

[0001] The invention belongs to the technical field of boiler energy conservation and environmental protection, and specifically relates to a system and method for smoke whitening and waste heat recovery of a coal-fired boiler. Background Art

[0002] Since coal contains sulfur, desulfurization is an indispensable part of flue gas treatment for coal-fired boilers. At present, whether calcium desulfurization or ammonia desulfurization, it is generally wet desulfurization, that is, after the flue gas induced draft fan, a desulfurization tower is installed to spray limestone slurry (calcium desulfurization) or ammonia water (ammonia desulfurization) in a cycle to make sulfur dioxide and calcium carbonate (or ammonia) in the flue gas react to produce sulfite or sulfate. The water vapor contained in the flue gas of the wet desulfurization tower is basically saturated (saturated wet flue gas), and the temperature is 45-60℃.

[0003] Because the exhaust gas temperature after desulfurization is much higher than the ambient temperature and is saturated, when it encounters cold air, it will form a large amount of fog plumes (also called white plumes, smoke plumes), and even form droplets that fall to the ground, especially in winter. Since there are still trace amounts of acidic gases such as sulfur dioxide in the flue gas, the droplets formed are also acidic, causing environmental pollution.

[0004] In addition, wet saturated flue gas at 45-60℃ contains a large amount of heat. Although its quality is not high enough for power generation and steam production, it is still valuable for residential heating and boiler combustion air heating.

[0005] There are three technologies or methods currently being used or tested to eliminate the smoke plume from flue gas desulfurization of coal-fired boilers. The first is cooling and condensation, which cools the flue gas to 40°C or even below 30°C, condenses the water vapor in the flue gas, reduces the water vapor in the flue gas, and thus reduces the smoke plume. This method can greatly reduce the water vapor carried by the flue gas, but because the exhaust flue is still saturated, there is still a plume. The second is heating, using 110-150°C flue gas or other heat sources (such as turbine extraction, etc.) in front of the desulfurization tower to heat the saturated flue gas to make it overheated. After the relative humidity of the flue gas is reduced, the smoke plume will also be reduced when it encounters cold air. Because the gas-to-gas heat transfer coefficient is small, this method requires a large wall-type heat exchange equipment, and the heat exchange equipment is often damaged due to corrosion and dust blockage. The third is to mix some dry hot air into the exhaust gas to reduce the relative humidity of the mixed gas. In terms of anti-corrosion and anti-clogging, this method is superior to the second heating method. However, if the high-temperature flue gas before desulfurization is still selected as the heat source for air heating, there are still problems such as large heat exchange equipment. If the heat source for air heating is steam, high-temperature hot water, high-temperature flue gas before the air preheater and other heat sources are selected, additional energy consumption is increased, reducing the economic benefits of the boiler. In addition, the injection of a large amount of hot air will not only increase the energy consumption of the fan, but also affect its normal smoke exhaust due to the increase in chimney ventilation, as well as the normal smoke exhaust of the desulfurization system.

[0006] For example: Application No. 201710600358.1 describes a technology that combines the first method with the third method, in which part of the heat source for air heating comes from the waste heat of flue gas cooling after desulfurization, and part comes from steam or high-temperature hot water.

[0007] Patent No. 201720680534.2 describes the use of the first method to achieve partial whitening of flue gas through cooling and condensation.

[0008] Application No. 201810992331.6 describes the use of the first and second methods, using the 110-150°C flue gas before the desulfurization entrance to heat the low-temperature flue gas after cooling and condensation to achieve desulfurization.

[0009] Application No. 201811601863.9 describes the use of the third method, which is to eliminate the exhaust plume after desulfurization by mixing hot air. The heat source for hot air heating comes from the high-temperature flue gas before the inlet of the boiler air preheater.

[0010] Application No. 201810580242.0 describes the use of the first method and the third method, in which the heat source for heating the air comes partly from the flue gas at the desulfurization outlet and partly from the high-temperature flue gas before the desulfurization inlet.

[0011] In addition, whether heating the flue gas at the desulfurization outlet or heating the air for mixed air desulfurization, if the 110-150℃ flue gas before partial desulfurization is used as the heat source, the enthalpy of the flue gas entering the desulfurization tower will be reduced, and the temperature inside the desulfurization tower will eventually be reduced. For the system using calcium desulfurization, too low a temperature will also affect the desulfurization effect.

[0012] In terms of exhaust heat recovery after desulfurization, the current basic methods are either circulating water spraying or shell-and-tube heat exchanger heat exchange. For example, patent No. 201720680534.2 uses spraying to obtain flue gas waste heat, and then uses the waste heat for boiler combustion air heating. Patent No. 201820043528.0 provides a corrosion-resistant heat exchanger made of polytetrafluoroethylene to recover desulfurization exhaust waste heat.

[0013] In summary, for the desulfurization of flue gas from coal-fired boilers, whether the flue gas is heated or mixed with hot air, the heat exchange equipment is either large and easy to damage, or it requires additional energy consumption, and even affects the desulfurization effect. In terms of flue gas waste heat recovery, for flue gas at the desulfurization outlet of about 55°C, no matter what kind of high-efficiency heat exchange equipment and spray equipment are used, the patent number is 201720680534.2, and the maximum external hot water supply temperature can only be about 50°C (hot water that can be heated by users), and the external hot water temperature is even lower for the patent number 201820043528.0. For most urban centralized heating systems with a return water temperature of 50-60°C, if there is no heat pump system involved, there is almost no use value.

[0014] Therefore, in order to fundamentally solve the problems of flue gas whitening and residual heat recovery in coal-fired boilers, new technologies and methods need to be developed. Summary of the invention

[0015] In view of the defects of the existing technology on smoke whitening and waste heat recovery of coal-fired boilers, the present invention provides a new smoke whitening and waste heat recovery system for coal-fired boilers.

[0016] To solve the above problems, the present invention adopts the following technical scheme: a coal-fired boiler flue gas deoxidation and waste heat recovery system, including a flue gas induced draft fan, a solution regeneration tower, a limestone powder mixing tank, a slaked lime mixing tank, a regeneration spray pump, a solution purification liquid supply pump, a desulfurization tower, an absorption spray pump, a purified solution reflux pump, a solution absorption tower, a booster fan, a chimney, a sedimentation tank washing water spray pump, a sedimentation washing tank, a solution purification concentration tank, an absorbent crystal dissolution tank, a sodium carbonate mixing tank, a calcium carbonate washing tank, a mother liquor concentration tank, a sodium chloride crystal washing tank, a mother liquor cooling tank, and a potassium nitrate crystal washing tank.

[0017] The following is a further optimization of the above technical solution by the present invention: an absorption tower water sprinkling area for energy exchange is arranged inside the solution absorption tower.

[0018] Further optimization: the water sprinkling area of ​​the absorption tower includes fillers and coils.

[0019] Further optimization: the coiled tube is a multi-layer tube.

[0020] Further optimization: a plurality of coils are arranged transversely.

[0021] Further optimization: the solution regeneration tower is made of one of glass fiber reinforced plastics or plastic-lined steel plate materials.

[0022] Further optimization: the solution absorption tower is made of one of glass fiber reinforced plastics or plastic-lined steel plate materials.

[0023] Further optimization: the filler in the water sprinkling area of ​​the absorption tower is made of PVC material.

[0024] Further optimization: the coil is made of an outer lining plastic pipe, and the material of the outer lining plastic pipe is one of titanium, titanium alloy, Hastelloy, copper, carbon steel, and stainless steel.

[0025] In addition to carbon, hydrogen, oxygen, nitrogen and sulfur, coal also contains a small amount of chlorides, fluorides, and minerals such as aluminosilicates, carbonates and sulfates formed by sodium ions, potassium ions, iron or ferrous ions, copper ions, etc. Some of them form gases during the combustion process. For example, chlorides generally form hydrogen chloride gas, sulfides and sulfates generate sulfur dioxide and sulfur trioxide, which are mixed into the flue gas, and some of them generate high-melting point silicates and oxides, which are melted into fly ash and discharged with the flue gas. Therefore, in the regeneration tower and absorption tower, the spray solution will inevitably absorb and dissolve them when exchanging heat and mass with the flue gas. Sulfurous acid and sulfuric acid will aggravate the corrosion of the system and must be removed. Ions like sodium ions, potassium ions and nitrates have poor water absorption. Excessive accumulation of these ions in the spray solution will affect the water vapor partial pressure of the solution absorbent and even affect the solubility of the absorbent. Therefore, if you want to achieve a stable cycle of solution spraying, you must purify these undesirable ions.

[0026] In order to make this method process sustainable, the solution needs to be regenerated after absorbing water vapor. At the same time, it is necessary to remove impurity ions mixed in when in contact with flue gas, such as sulfite, sulfate, chloride, nitrate, sodium, magnesium, potassium, etc., to maintain the purity of the solution and prevent the impurity ions from affecting the water absorption performance of the solution.

[0027] In order to solve the above problems, the present invention also provides a method for removing white smoke from coal-fired boiler and recovering waste heat, comprising the following steps:

[0028] 1) Use lithium bromide solution to pre-treat flue gas

[0029] 2) Desulfurize the flue gas discharged from step 1

[0030] 3) Remove iron ions, ferrous ions, aluminum ions, copper ions, and fluoride ions from lithium bromide solution

[0031] 4) Reuse of lithium bromide in the output liquid of the slaked lime mixing tank

[0032] 5) Eliminate the sodium ions, potassium ions, chloride ions, and nitrate ions in the output solution of step 4

[0033] 6) Energy recovery and utilization.

[0034] The following is a further optimization of the above scheme by the present invention: in the above step 3), the solution in step 1 first enters the limestone powder mixing tank, and the pH value of the solution in the limestone powder mixing tank reaches above 5.5 by adding limestone powder, and then the solution in the limestone powder mixing tank enters the slaked lime mixing tank, and slaked lime is added to make the pH value of the solution in the slaked lime mixing tank reach above 9, and a precipitate is formed. At the same time, by increasing the pH value of the solution, the acidified solution is prevented from excessively corroding subsequent equipment. The precipitate in the slaked lime mixing tank enters the precipitation washing tank, and then deionized water is added to the precipitation washing tank for washing, and the ratio of the volume of deionized water to the volume of the precipitate in the precipitation washing tank is 1:1. The washing water in the precipitation washing tank enters the solution regeneration tower and is sprayed toward the flue gas in a mist form, and the solution in the slaked lime mixing tank enters the solution absorption tower.

[0035] Further optimization: in step 4), the solution purification supply pump extracts 1-5% of the total solution circulation volume from the slaked lime mixing tank for purification, a part of which enters the solution purification concentration tank, and a part of which enters the absorbent crystal dissolution tank. In the solution purification concentration tank, it is heated by 0.2-0.4MPa steam to produce most of the lithium bromide crystals after concentration. Then the lithium bromide crystals enter the absorbent crystal dissolution tank and are dissolved by the clarified liquid delivered by the solution purification supply pump. The chloride ions, sodium ions, potassium ions, nitrate ions and calcium ions in the mother liquor produced by the solution purification concentration tank will be greatly enriched, and the lithium bromide solution can be purified.

[0036] Further optimization: In step 5), the solution in the solution purification concentration tank enters the sodium carbonate mixing tank, and the pH value of the mother liquor is adjusted to 10 by adding some sodium carbonate into the sodium carbonate mixing tank to balance the sodium ions in the mother liquor, and at the same time remove some calcium ions to facilitate the subsequent crystallization of sodium chloride and potassium nitrate;

[0037] The precipitate in the sodium carbonate mixing tank enters the calcium carbonate washing tank, and deionized water is added to the calcium carbonate washing tank for washing. The mass ratio of the deionized water to the precipitate in the calcium carbonate washing tank is 1:1;

[0038] The mother liquor in the sodium carbonate mixing tank enters the mother liquor concentration tank, and is heated by 0.2-0.4MPa steam to precipitate sodium chloride crystals, and some lithium bromide crystals are also mixed in it. 90-100℃ deionized water is introduced into the sodium chloride crystal washing tank to wash the crystals produced in the mother liquor concentration tank. The mass ratio of deionized water to the crystals in the mother liquor concentration tank is 0.2:1;

[0039] The mother liquor in the mother liquor concentration tank is sent to the mother liquor cooling tank, and the mother liquor temperature is reduced to below 20°C with 10-15°C cold water. At the same time, potassium sulfate is added to the mother liquor cooling tank, and the mass ratio of potassium sulfate to the mother liquor in the mother liquor cooling tank is 0.5:1. Crystals are precipitated and enter the potassium nitrate crystal washing tank. Cold water at 10-15°C is passed into the potassium nitrate crystal washing tank for washing, and the mass ratio of cold water to the crystals in the potassium nitrate crystal washing tank is 0.2:1. Potassium nitrate crystals are separated in the potassium nitrate crystal washing tank.

[0040] This scheme adopts a highly water-absorbing aqueous solution, such as calcium chloride solution, lithium bromide solution, etc., to absorb water vapor in the exhaust gas after desulfurization through spraying. Since the saturation temperature of the solution is higher than the saturation temperature of pure water under the same water vapor partial pressure, the solution will also release absorption heat in the process of absorbing water vapor carried by the flue gas, thereby increasing the flue gas temperature. After spraying absorption, not only the water vapor carried by the flue gas is reduced, but also the temperature is increased, so that the relative humidity of the flue gas is greatly reduced, thereby reducing or even completely eliminating water vapor condensation when mixed with the ambient cold air, and achieving white emission. At the same time, because the saturation temperature of the solution is higher than the saturation temperature of pure water under the same water vapor partial pressure, the solution can obtain an absorption temperature higher than the flue gas temperature when absorbing water vapor, thereby improving the quality of flue gas waste heat.

[0041] The beneficial effects of the present invention are as follows: 1. The flue gas temperature is increased by more than 20°C on the existing basis without consuming additional steam and hot water through solution spraying; 2. The water vapor content carried by the discharged flue gas can be reduced by more than 20% without cooling and condensing; 3. The flue gas waste heat recovery temperature can be more than 20°C higher than the flue gas temperature at the desulfurization outlet, which basically meets the requirement of direct heating of 50-60°C heat network return water; 4. While achieving flue gas desulfurization and flue gas waste heat recovery, the temperature in the desulfurization tower is not reduced to ensure that the desulfurization effect is not affected; 5. The spraying solution can use the flue gas's own thermal energy resources to achieve regeneration; 6. To ensure the sustainability of the system cycle, the solution purification process consumes only a small amount of high-grade steam or hot water resources.

[0042] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flow chart of the present invention when a lithium bromide solution is used in an embodiment;

[0044] Figure 2 Schematic diagram of the structure of the solution absorption tower in the embodiment of the present invention;

[0045] Figure 3 2. It is a top view of the water sprinkling area of ​​the solution absorption tower in the embodiment of the present invention;

[0046] Figure 4It is a side sectional view of the water sprinkling area of ​​the absorption tower of the present invention.

[0047] In the figure, 1, flue gas induced draft fan, 2, solution regeneration tower, 3, limestone powder mixing tank, 4, slaked lime mixing tank, 5, regeneration spray pump, 6, solution purification liquid supply pump, 7, desulfurization tower, 8, absorption spray pump, 9, purification solution reflux pump, 10, solution absorption tower, 11, booster fan, 12, chimney, 13, sedimentation tank washing water spray pump, 14, sedimentation washing tank, 15, solution purification concentration tank, 16, absorbent crystal dissolution tank, 17. Sodium carbonate mixing tank, 18. Calcium carbonate washing tank, 19. Mother liquor concentration tank, 20. Sodium chloride crystal washing tank, 21. Mother liquor cooling tank, 22. Potassium nitrate crystal washing tank, 10-1. Absorption tower sprayer, 10-2. Absorption tower water sprinkling area, 10-3. Absorption tower water tray, 10-4. Heat carrier medium inlet pipe, 10-5. Coil, 10-6. Packing, 10-7. Heat carrier medium outlet pipe, 10-8. Sprinkling area tube sheet. DETAILED DESCRIPTION

[0048] Embodiment 1, as Figure 1-4 As shown, a coal-fired boiler flue gas deoxidation and waste heat recovery system includes a flue gas induced draft fan 1, a solution regeneration tower 2, a limestone powder mixing tank 3, a slaked lime mixing tank 4, a regeneration spray pump 5, a solution purification liquid supply pump 6, a desulfurization tower 7, an absorption spray pump 8, a purified solution reflux pump 9, a solution absorption tower 10, a booster fan 11, a chimney 12, a sedimentation tank washing water spray pump 13, a sedimentation washing tank 14, a solution purification concentration tank 15, an absorbent crystal dissolving tank 16, a sodium carbonate mixing tank 17, a calcium carbonate washing tank 18, a mother liquor concentration tank 19, a sodium chloride crystal washing tank 20, a mother liquor cooling tank 21, and a potassium nitrate crystal washing tank 22.

[0049] The solution absorption tower 10 includes a shell with a cavity arranged inside, an absorption tower water sprinkling area 10-2 is arranged near the middle of the shell, an absorption tower water storage tray 10-3 for storing a certain amount of liquid is arranged near the bottom of the absorption tower water sprinkling area 10-2 in the shell, and an absorption tower sprayer 10-1 for spraying water mist into the shell is arranged near the top of the absorption tower water sprinkling area 10-2 in the shell.

[0050] The water sprinkling area 10-2 of the absorption tower is provided with coils 10-5 and fillers 10-6. A plurality of coils 10-5 are arranged transversely (horizontally), and one end of the plurality of coils 10-5 is connected to a heat carrier inlet pipe 10-4, and the other end is connected to a heat carrier outlet pipe 10-7. The coils 10-5 and fillers 10-6 (water sprinkling fillers in the high-temperature section) are arranged in multiple layers, and the multiple layers of coils 10-5 and fillers 10-6 are alternately arranged. The coils 10-5 adopt a multi-layer tube design.

[0051] The heat medium inlet pipe 10 - 4 and the heat medium outlet pipe 10 - 7 are connected to a heat exchanger or a heat sink through a circulation pump.

[0052] The flue gas induced draft fan 1 is connected to the lower smoke inlet of the solution regeneration tower 2, the upper smoke outlet of the solution regeneration tower 2 is connected to the smoke inlet of the desulfurization tower 7, and the bottom liquid outlet of the solution regeneration tower 2 is connected to the limestone powder mixing tank 3.

[0053] The smoke outlet at the top of the desulfurization tower 7 is connected to the smoke inlet near the lower end of one side of the solution absorption tower 10. The smoke outlet near the upper end of one side of the solution absorption tower 10 is transported to the chimney 12 through a booster fan 11. The liquid outlet at the bottom of the solution absorption tower 10 is connected to the top spray in the solution regeneration tower 2 through a regeneration spray pump 5.

[0054] One side of the limestone powder mixing tank 3 is connected to a slaked lime mixing tank 4, which is connected to the absorption tower sprayer 10-1 through an absorption spray pump 8. The slaked lime mixing tank 4 is also connected to a precipitation washing tank 14, which is connected to the top spray in the solution regeneration tower 2 through a precipitation tank washing water spray pump 13. There are two top sprays in the solution regeneration tower 2, one of which is connected to the precipitation tank washing water spray pump 13, and the other is connected to the regeneration spray pump 5.

[0055] The slaked lime mixing tank 4 is connected to a solution purification concentration tank 15 and an absorbent crystal dissolving tank 16 via a solution purification liquid supply pump 6 , and the solution purification concentration tank 15 and the absorbent crystal dissolving tank 16 are connected.

[0056] The solution purification and concentration tank 15 is connected to the sodium carbonate mixing tank 17, the sodium carbonate mixing tank 17 is connected to the calcium carbonate washing tank 18, the sodium carbonate mixing tank 17 is connected to the mother liquor concentration tank 19, the mother liquor concentration tank 19 is connected to the sodium chloride crystal washing tank 20, the mother liquor concentration tank 19 is connected to the mother liquor cooling tank 21, and the mother liquor cooling tank 21 is connected to the potassium nitrate crystal washing tank 22.

[0057] The absorbent crystal dissolving tank 16 , the calcium carbonate washing tank 18 , the sodium chloride crystal washing tank 20 , the potassium nitrate crystal washing tank 22 and the mother liquor cooling tank 21 are connected to the slaked lime mixing tank 4 through the purified solution reflux pump 9 .

[0058] The filler 10-6 is surrounded by a water sprinkling area tube sheet 10-8, on which holes are provided for the coil 10-5 to pass through, and the water sprinkling area tube sheet 10-8 is sealed and connected to the coil 10-5.

[0059] The present application also provides a method for decolorizing and recovering waste heat from flue gas of a coal-fired boiler using the above-mentioned system. The following will use the flue gas of a 130t / h high-pressure fluidized bed boiler in a certain factory and lithium bromide solution as examples to illustrate the best embodiment of the present invention.

[0060] A certain factory has a 130t / h high-pressure fluidized bed boiler, with a flue gas temperature of 120℃ at the desulfurization inlet, an inlet pressure of 101kPa, a flue gas volume flow rate of about 178,000 Nm³ / h, a flue gas mass flow rate of about 244t / h, of which the water vapor content is about 15.53t / h, and a flue gas temperature of 54℃ at the desulfurization outlet. The desulfurization is carried out by the limestone calcium method. Through calculation, the water vapor partial pressure of the flue gas at the desulfurization inlet is 10.21kPa, and the water vapor partial pressure of the flue gas at the desulfurization outlet is 14.94kPa.

[0061] The steps of this method are as follows:

[0062] 1. Flue gas pretreatment

[0063] The flue gas (120°C) first enters the solution regeneration tower 2 from the bottom of the tower (a flue gas inlet is provided on one side of the solution regeneration tower 2 near the bottom) under the action of the flue gas induced draft fan 1, and a lithium bromide solution with a concentration of 45% and a temperature of 68°C is sprayed into the solution regeneration tower 2 from the top of the tower at a rate of about 22.77 t / h (a top spray is provided near the upper end of the solution regeneration tower 2, and the spray extends to the outside of the solution regeneration tower 2 and is connected to the regeneration spray pump 5). The solution and the flue gas transfer heat and mass inside the solution regeneration tower 2, and finally the flue gas temperature drops to 80°C, the water vapor partial pressure in the solution regeneration tower 2 rises to 13.4 kPa, and is discharged from the solution regeneration tower 2; the concentration of the lithium bromide solution increases from 45% to 55%, the temperature is 80°C, and the solution regeneration tower 2 is discharged from the bottom drain port of the tower, with a flow rate of about 18.63 t / h, and the lithium bromide solution is initially stored at the bottom of the solution regeneration tower 2 and the solution absorption tower 10.

[0064] 2. Flue gas desulfurization

[0065] The flue gas enters the desulfurization tower 7 through the smoke outlet on the solution regeneration tower 2, undergoes desulfurization treatment, and then outputs saturated wet flue gas at 54°C.

[0066] 3. Remove the iron ions, ferrous ions, aluminum ions, copper ions, and fluoride ions in the lithium bromide solution output from step 1

[0067] Because the lithium bromide solution is in contact with the flue gas, a large amount of sulfurous acid, sulfuric acid, dust, and a large amount of impurity ions are dissolved in the solution. Therefore, after the solution is discharged from the solution regeneration tower 2, it first enters the limestone powder mixing tank 3, and the pH value of the solution in the limestone powder mixing tank 3 reaches above 5.5 by adding limestone powder, and most of the sulfurous acid and sulfuric acid react to generate calcium sulfite and calcium sulfate. Then the solution in the limestone powder mixing tank 3 enters the slaked lime mixing tank 4, and slaked lime is added to make the pH value of the solution in the slaked lime mixing tank 4 reach above 9, and iron ions, ferrous ions, aluminum ions, copper ions, and fluoride ions are precipitated by calcium hydroxide to generate calcium carbonate, copper hydroxide, and calcium hydroxide. Ferrous iron, ferric hydroxide, aluminum hydroxide, calcium fluoride and other precipitates, and at the same time, by increasing the pH value of the solution, the acidified solution is prevented from excessively corroding the subsequent equipment. The precipitates in the limestone powder mixing tank 3 and the slaked lime mixing tank 4 are sent to the precipitation washing tank 14 through the conveying equipment (auger), and then deionized water is added to the precipitation washing tank 14 for washing. The ratio of the volume of deionized water to the volume of the precipitates in the precipitation washing tank 14 is 1:1. The washing water in the precipitation washing tank 14 enters the top of the solution regeneration tower 2 through the precipitation tank washing water spray pump 13 and is sprayed to the flue gas in a mist form. The clarified liquid after the slaked lime mixing tank 4 is sent to the solution absorption tower 10 by the absorption spray pump 8.

[0068] 4. Purification of lithium bromide solution in the output liquid of slaked lime mixing tank 4

[0069] The solution purification supply pump 6 extracts 1% of the total solution circulation volume (the total solution volume of the entire system) of the clarified solution from the slaked lime mixing tank 4 for purification treatment, a part of which enters the solution purification concentration tank 15, and a part of which enters the absorbent crystal dissolving tank 16. In the solution purification concentration tank 15, it is heated by 0.2MPa steam to produce most of the lithium bromide crystals after concentration, and then the lithium bromide crystals are transported into the absorbent crystal dissolving tank 16 through the conveying equipment (auger), and are dissolved by the clarified liquid conveyed by the solution purification supply pump 6. The chloride ions, sodium ions, potassium ions, nitrate ions and calcium ions in the mother liquor produced by the solution purification concentration tank 15 will be greatly enriched, so that the lithium bromide solution can be purified.

[0070] 5. Eliminate sodium ions, potassium ions, chloride ions, and nitrate ions in the output mother liquor of step 4

[0071] Usually, the sodium ions and potassium ions in the flue gas come from fly ash, while the chloride ions and nitrate ions come from the flue gas components. Therefore, in general, the chloride ions and nitrate ions in the solution are higher than the sodium ions and potassium ions. In order to eliminate these four ions, the ion concentration needs to be balanced. The solution (mother liquor) in the solution purification concentration tank 15 enters the sodium carbonate mixing tank 17, and part of the sodium carbonate is added through the sodium carbonate mixing tank 17 to adjust the pH value of the mother liquor to about 10, balance the sodium ions in the mother liquor, and remove part of the calcium ions at the same time, so as to facilitate the subsequent crystallization of sodium chloride and potassium nitrate;

[0072] The precipitate in the sodium carbonate mixing tank 17 is transported to the calcium carbonate washing tank 18 via a conveying device (auger), and deionized water is added to the calcium carbonate washing tank 18 for washing. The mass ratio of the deionized water to the precipitate in the calcium carbonate washing tank 18 is 1:1.

[0073] The mother liquor from the sodium carbonate mixing tank 17 enters the mother liquor concentration tank 19, and is heated by 0.2MPa steam to precipitate sodium chloride crystals. At the same time, some lithium bromide crystals are mixed in it. Because the solubility of sodium chloride does not change significantly with the solution temperature, while the solubility of lithium bromide increases significantly with the increase of solution temperature, 90°C hot water (deionized water) is introduced into the sodium chloride crystal washing tank 20 to wash the crystals produced in the mother liquor concentration tank 19. The mass ratio of hot water (deionized water) to the crystals in the mother liquor concentration tank 19 is 0.2:1, so as to achieve the separation of sodium chloride and lithium bromide.

[0074] The mother liquor from the mother liquor concentration tank 19 is enriched with nitrate and potassium ions. At this time, the mother liquor in the mother liquor concentration tank 19 is sent to the mother liquor cooling tank 21, and the mother liquor temperature is reduced to below 20°C by using 10°C cold water. At the same time, potassium sulfate is added to the mother liquor cooling tank 21, and the mass ratio of potassium sulfate to the mother liquor in the mother liquor cooling tank 21 is 0.5:1. The nitrate will be precipitated as potassium nitrate crystals and mixed with some lithium bromide crystals. The potassium nitrate crystals are transported to the potassium nitrate crystal washing tank 22 by using a conveying device. Similarly, according to the sensitivity of the solubility of potassium nitrate and lithium bromide crystals to temperature, 10°C cold water is introduced into the potassium nitrate crystal washing tank 22 for washing, and the ratio of cold water to the mass of the crystals in the potassium nitrate crystal washing tank 22 is 0.2:1. The potassium nitrate crystals are separated in the potassium nitrate crystal washing tank 22;

[0075] In summary, the separation of undesirable ions such as chloride ions, sodium ions, potassium ions, and nitrate ions in the solution is achieved, and then the washing liquid (dissolving liquid) in the potassium nitrate crystal washing tank 22, the sodium chloride crystal washing tank 20, the calcium carbonate washing tank 18, and the absorbent crystal dissolving tank 16 are all sent back to the solution spray circulation (solution absorption tower 10) by the purified solution reflux pump 9 to achieve the recovery of the absorption medium.

[0076] 6. Energy recovery

[0077] After being treated by the desulfurization tower 7, the saturated wet flue gas with a temperature of 54°C is output and enters the smoke inlet at the lower end of one side of the solution absorption tower 10. At the same time, the absorption spray pump 8 sprays the lithium bromide solution with a concentration of 55%, a temperature of about 80°C, and a flow rate of 18.63 t / h from the top of the solution absorption tower 10 (absorption tower sprayer 10-1). The solution and the flue gas are heat and mass transferred in the absorption tower water spraying area 10-2 in the solution absorption tower 10. Finally, the flue gas temperature rises to 75°C, and the water vapor partial pressure drops to 12.5 kPa, and the flue gas is discharged from the solution absorption tower 10. The flue gas is then transported to the chimney 12 by the booster fan 11; the lithium bromide solution concentration drops from 55% to 45%, the temperature is 68°C, and the solution absorption tower 10 is discharged from the bottom of the tower and sent to the top of the solution regeneration tower 2 through the regeneration spray pump 5. The flow rate is about 22.77 t / h.

[0078] In the solution absorption tower 10, the heating pipe network supplies 60°C heating return water to the coil 10-5 in the absorption tower water spraying area 10-2, about 94t / h, which enters from the bottom of the absorption tower water spraying area 10-2, is heated by the solution in the absorption tower water spraying area 10-2, and is heated to about 70°C, and is supplied from the upper part of the absorption tower water spraying area 10-2;

[0079] Since the flue gas in the solution absorption tower 10 is relatively clean, both sulfur dioxide and impurities are greatly reduced compared with before desulfurization, the solution discharged from the bottom of the absorption tower is directly pumped out by the regeneration spray pump 5 and sent to the solution regeneration tower 2;

[0080] The flue gas discharged from the solution absorption tower 10 has a temperature of 75°C and a water vapor partial pressure of 12.5 kPa, which is equivalent to an air moisture content of about 83 g / kg (dry air). For air at 75°C and a moisture content of 83 g / kg (dry air), when it is mixed with ambient air at a temperature above 11°C and a moisture content of 4.9 g / kg (dry air) (relative humidity 60%), it can be ensured that water vapor condensation will not occur, thereby achieving flue gas de-whitening.

[0081] Embodiment 2, in the above embodiment 1, the above-mentioned method for removing white smoke from coal-fired boiler and recovering waste heat has the following steps:

[0082] 1. Flue gas pretreatment

[0083] The flue gas (120°C) first enters the solution regeneration tower 2 from the bottom of the tower (a flue gas inlet is provided on one side of the solution regeneration tower 2 near the bottom) under the action of the flue gas induced draft fan 1, and a lithium bromide solution with a concentration of 45% and a temperature of 68°C is sprayed into the solution regeneration tower 2 from the top of the tower at a rate of about 22.77 t / h (a top spray is provided near the upper end of the solution regeneration tower 2, and the spray extends to the outside of the solution regeneration tower 2 and is connected to the regeneration spray pump 5). The solution and the flue gas transfer heat and mass inside the solution regeneration tower 2, and finally the flue gas temperature drops to 80°C, the water vapor partial pressure in the solution regeneration tower 2 rises to 13.4 kPa, and is discharged from the solution regeneration tower 2; the concentration of the lithium bromide solution increases from 45% to 55%, the temperature is 80°C, and the solution regeneration tower 2 is discharged from the bottom drain port of the tower, with a flow rate of about 18.63 t / h, and the lithium bromide solution is initially stored at the bottom of the solution regeneration tower 2 and the solution absorption tower 10.

[0084] 2. Flue gas desulfurization

[0085] The flue gas enters the desulfurization tower 7 through the smoke outlet on the solution regeneration tower 2, undergoes desulfurization treatment, and then outputs saturated wet flue gas at 54°C.

[0086] 3. Remove the iron ions, ferrous ions, aluminum ions, copper ions, and fluoride ions in the lithium bromide solution output from step 1

[0087] Because the lithium bromide solution is in contact with the flue gas, a large amount of sulfurous acid, sulfuric acid, dust, and a large amount of impurity ions are dissolved in the solution. Therefore, after the solution is discharged from the solution regeneration tower 2, it first enters the limestone powder mixing tank 3, and the pH value of the solution in the limestone powder mixing tank 3 reaches above 5.5 by adding limestone powder, and most of the sulfurous acid and sulfuric acid react to generate calcium sulfite and calcium sulfate. Then the solution in the limestone powder mixing tank 3 enters the slaked lime mixing tank 4, and slaked lime is added to make the pH value of the solution in the slaked lime mixing tank 4 reach above 9, and iron ions, ferrous ions, aluminum ions, copper ions, and fluoride ions are precipitated by calcium hydroxide to generate calcium carbonate, copper hydroxide, and calcium hydroxide. Ferrous iron, ferric hydroxide, aluminum hydroxide, calcium fluoride and other precipitates, and at the same time, by increasing the pH value of the solution, the acidified solution is prevented from excessively corroding the subsequent equipment. The precipitates in the limestone powder mixing tank 3 and the slaked lime mixing tank 4 are sent to the precipitation washing tank 14 through the conveying equipment (auger), and then deionized water is added to the precipitation washing tank 14 for washing. The ratio of the volume of deionized water to the volume of the precipitates in the precipitation washing tank 14 is 1:1. The washing water in the precipitation washing tank 14 enters the top of the solution regeneration tower 2 through the precipitation tank washing water spray pump 13 and is sprayed to the flue gas in a mist form. The clarified liquid after the slaked lime mixing tank 4 is sent to the solution absorption tower 10 by the absorption spray pump 8.

[0088] 4. Purification of lithium bromide solution in the output liquid of slaked lime mixing tank 4

[0089] The solution purification supply pump 6 extracts 2.5% of the total solution circulation volume (the total solution volume of the entire system) of the clarified solution from the slaked lime mixing tank 4 for purification treatment, a part of which enters the solution purification concentration tank 15, and a part of which enters the absorbent crystal dissolving tank 16. In the solution purification concentration tank 15, it is heated by 0.3MPa steam to produce most of the lithium bromide crystals after concentration, and then the lithium bromide crystals are transported into the absorbent crystal dissolving tank 16 through the conveying equipment (auger), and are dissolved by the clarified liquid conveyed by the solution purification supply pump 6. The chloride ions, sodium ions, potassium ions, nitrate ions and calcium ions in the mother liquor produced by the solution purification concentration tank 15 will be greatly enriched, so that the lithium bromide solution can be purified.

[0090] 5. Eliminate sodium ions, potassium ions, chloride ions, and nitrate ions in the output mother liquor of step 4

[0091] Usually, the sodium ions and potassium ions in the flue gas come from fly ash, while the chloride ions and nitrate ions come from the flue gas components. Therefore, in general, the chloride ions and nitrate ions in the solution are higher than the sodium ions and potassium ions. In order to eliminate these four ions, the ion concentration needs to be balanced. The solution (mother liquor) in the solution purification concentration tank 15 enters the sodium carbonate mixing tank 17, and part of the sodium carbonate is added through the sodium carbonate mixing tank 17 to adjust the pH value of the mother liquor to about 10, balance the sodium ions in the mother liquor, and remove part of the calcium ions at the same time, so as to facilitate the subsequent crystallization of sodium chloride and potassium nitrate;

[0092] The precipitate in the sodium carbonate mixing tank 17 is transported to the calcium carbonate washing tank 18 via a conveying device (auger), and deionized water is added to the calcium carbonate washing tank 18 for washing. The mass ratio of the deionized water to the precipitate in the calcium carbonate washing tank 18 is 1:1.

[0093] The mother liquor from the sodium carbonate mixing tank 17 enters the mother liquor concentration tank 19, and is heated by 0.3MPa steam to precipitate sodium chloride crystals. At the same time, some lithium bromide crystals are mixed in it. Because the solubility of sodium chloride does not change significantly with the solution temperature, while the solubility of lithium bromide increases significantly with the increase of solution temperature, 95°C hot water (deionized water) is introduced into the sodium chloride crystal washing tank 20 to wash the crystals produced in the mother liquor concentration tank 19. The mass ratio of hot water (deionized water) to the crystals in the mother liquor concentration tank 19 is 0.2:1, so as to achieve the separation of sodium chloride and lithium bromide.

[0094] The mother liquor, nitrate and potassium ions are enriched in the mother liquor from the mother liquor concentration tank 19. At this time, the mother liquor in the mother liquor concentration tank 19 is sent to the mother liquor cooling tank 21, and the mother liquor temperature is reduced to below 20°C by using 12.5°C cold water. At the same time, potassium sulfate is added to the mother liquor cooling tank 21, and the mass ratio of potassium sulfate to the mother liquor in the mother liquor cooling tank 21 is 0.5:1. The nitrate will be precipitated as potassium nitrate crystals and mixed with some lithium bromide crystals. The potassium nitrate crystals are transported to the potassium nitrate crystal washing tank 22 by using a conveying device. Similarly, according to the sensitivity of the solubility of potassium nitrate and lithium bromide crystals to temperature, 12.5°C cold water is introduced into the potassium nitrate crystal washing tank 22 for washing, and the ratio of cold water to the mass of the crystals in the potassium nitrate crystal washing tank 22 is 0.2:1. The potassium nitrate crystals are separated in the potassium nitrate crystal washing tank 22;

[0095] In summary, the separation of undesirable ions such as chloride ions, sodium ions, potassium ions, and nitrate ions in the solution is achieved, and then the washing liquid (dissolving liquid) in the potassium nitrate crystal washing tank 22, the sodium chloride crystal washing tank 20, the calcium carbonate washing tank 18, and the absorbent crystal dissolving tank 16 are all sent back to the solution spray circulation (solution absorption tower 10) by the purified solution reflux pump 9 to achieve the recovery of the absorption medium.

[0096] 6. Energy recovery

[0097] After being treated by the desulfurization tower 7, the saturated wet flue gas with a temperature of 54°C is output and enters the smoke inlet at the lower end of one side of the solution absorption tower 10. At the same time, the absorption spray pump 8 sprays the lithium bromide solution with a concentration of 55%, a temperature of about 80°C, and a flow rate of 18.63 t / h from the top of the solution absorption tower 10 (absorption tower sprayer 10-1). The solution and the flue gas are heat and mass transferred in the absorption tower water spraying area 10-2 in the solution absorption tower 10. Finally, the flue gas temperature rises to 75°C, and the water vapor partial pressure drops to 12.5 kPa, and the flue gas is discharged from the solution absorption tower 10. The flue gas is then transported to the chimney 12 by the booster fan 11; the lithium bromide solution concentration drops from 55% to 45%, the temperature is 68°C, and the solution absorption tower 10 is discharged from the bottom of the tower and sent to the top of the solution regeneration tower 2 through the regeneration spray pump 5. The flow rate is about 22.77 t / h.

[0098] In the solution absorption tower 10, the heating pipe network supplies 60°C heating return water to the coil 10-5 in the absorption tower water spraying area 10-2, about 94t / h, which enters from the bottom of the absorption tower water spraying area 10-2, is heated by the solution in the absorption tower water spraying area 10-2, and is heated to about 70°C, and is supplied from the upper part of the absorption tower water spraying area 10-2;

[0099] Since the flue gas in the solution absorption tower 10 is relatively clean, both sulfur dioxide and impurities are greatly reduced compared with before desulfurization, the solution discharged from the bottom of the absorption tower is directly pumped out by the regeneration spray pump 5 and sent to the solution regeneration tower 2;

[0100] The flue gas discharged from the solution absorption tower 10 has a temperature of 75°C and a water vapor partial pressure of 12.5 kPa, which is equivalent to an air moisture content of about 83 g / kg (dry air). For air at 75°C and a moisture content of 83 g / kg (dry air), when it is mixed with ambient air at a temperature above 11°C and a moisture content of 4.9 g / kg (dry air) (relative humidity 60%), it can be ensured that water vapor condensation will not occur, thereby achieving flue gas de-whitening.

[0101] Embodiment 3, in the above embodiment 1, the above-mentioned method for removing white smoke from coal-fired boiler and recovering waste heat has the following steps:

[0102] 1. Flue gas pretreatment

[0103] The flue gas (120°C) first enters the solution regeneration tower 2 from the bottom of the tower (a flue gas inlet is provided on one side of the solution regeneration tower 2 near the bottom) under the action of the flue gas induced draft fan 1, and a lithium bromide solution with a concentration of 45% and a temperature of 68°C is sprayed into the solution regeneration tower 2 from the top of the tower at a rate of about 22.77 t / h (a top spray is provided near the upper end of the solution regeneration tower 2, and the spray extends to the outside of the solution regeneration tower 2 and is connected to the regeneration spray pump 5). The solution and the flue gas transfer heat and mass inside the solution regeneration tower 2, and finally the flue gas temperature drops to 80°C, the water vapor partial pressure in the solution regeneration tower 2 rises to 13.4 kPa, and is discharged from the solution regeneration tower 2; the concentration of the lithium bromide solution increases from 45% to 55%, the temperature is 80°C, and the solution regeneration tower 2 is discharged from the bottom drain port of the tower, with a flow rate of about 18.63 t / h, and the lithium bromide solution is initially stored at the bottom of the solution regeneration tower 2 and the solution absorption tower 10.

[0104] 2. Flue gas desulfurization

[0105] The flue gas enters the desulfurization tower 7 through the smoke outlet on the solution regeneration tower 2, undergoes desulfurization treatment, and then outputs saturated wet flue gas at 54°C.

[0106] 3. Remove the iron ions, ferrous ions, aluminum ions, copper ions, and fluoride ions in the lithium bromide solution output from step 1

[0107] Because the lithium bromide solution is in contact with the flue gas, a large amount of sulfurous acid, sulfuric acid, dust, and a large amount of impurity ions are dissolved in the solution. Therefore, after the solution is discharged from the solution regeneration tower 2, it first enters the limestone powder mixing tank 3, and the pH value of the solution in the limestone powder mixing tank 3 reaches above 5.5 by adding limestone powder, and most of the sulfurous acid and sulfuric acid react to generate calcium sulfite and calcium sulfate. Then the solution in the limestone powder mixing tank 3 enters the slaked lime mixing tank 4, and slaked lime is added to make the pH value of the solution in the slaked lime mixing tank 4 reach above 9, and iron ions, ferrous ions, aluminum ions, copper ions, and fluoride ions are precipitated by calcium hydroxide to generate calcium carbonate, copper hydroxide, and calcium hydroxide. Ferrous iron, ferric hydroxide, aluminum hydroxide, calcium fluoride and other precipitates, and at the same time, by increasing the pH value of the solution, the acidified solution is prevented from excessively corroding the subsequent equipment. The precipitates in the limestone powder mixing tank 3 and the slaked lime mixing tank 4 are sent to the precipitation washing tank 14 through the conveying equipment (auger), and then deionized water is added to the precipitation washing tank 14 for washing. The ratio of the volume of deionized water to the volume of the precipitates in the precipitation washing tank 14 is 1:1. The washing water in the precipitation washing tank 14 enters the top of the solution regeneration tower 2 through the precipitation tank washing water spray pump 13 and is sprayed to the flue gas in a mist form. The clarified liquid after the slaked lime mixing tank 4 is sent to the solution absorption tower 10 by the absorption spray pump 8.

[0108] 4. Purification of lithium bromide solution in the output liquid of slaked lime mixing tank 4

[0109] The solution purification supply pump 6 extracts 5% of the total solution circulation volume (the total solution volume of the entire system) of the clarified solution from the slaked lime mixing tank 4 for purification treatment, a part of which enters the solution purification concentration tank 15, and a part of which enters the absorbent crystal dissolving tank 16. In the solution purification concentration tank 15, it is heated by 0.4MPa steam to produce most of the lithium bromide crystals after concentration, and then the lithium bromide crystals are transported into the absorbent crystal dissolving tank 16 through the conveying equipment (auger), and are dissolved by the clarified liquid conveyed by the solution purification supply pump 6. The chloride ions, sodium ions, potassium ions, nitrate ions and calcium ions in the mother liquor produced by the solution purification concentration tank 15 will be greatly enriched, so that the lithium bromide solution can be purified.

[0110] 5. Eliminate sodium ions, potassium ions, chloride ions, and nitrate ions in the output mother liquor of step 4

[0111] Usually, the sodium ions and potassium ions in the flue gas come from fly ash, while the chloride ions and nitrate ions come from the flue gas components. Therefore, in general, the chloride ions and nitrate ions in the solution are higher than the sodium ions and potassium ions. In order to eliminate these four ions, the ion concentration needs to be balanced. The solution (mother liquor) in the solution purification concentration tank 15 enters the sodium carbonate mixing tank 17, and part of the sodium carbonate is added through the sodium carbonate mixing tank 17 to adjust the pH value of the mother liquor to about 10, balance the sodium ions in the mother liquor, and remove part of the calcium ions at the same time, so as to facilitate the subsequent crystallization of sodium chloride and potassium nitrate;

[0112] The precipitate in the sodium carbonate mixing tank 17 is transported to the calcium carbonate washing tank 18 via a conveying device (auger), and deionized water is added to the calcium carbonate washing tank 18 for washing. The mass ratio of the deionized water to the precipitate in the calcium carbonate washing tank 18 is 1:1.

[0113] The mother liquor from the sodium carbonate mixing tank 17 enters the mother liquor concentration tank 19, and is heated by 0.4MPa steam to precipitate sodium chloride crystals. At the same time, some lithium bromide crystals are mixed in it. Because the solubility of sodium chloride does not change significantly with the solution temperature, while the solubility of lithium bromide increases significantly with the increase of solution temperature, 100°C hot water (deionized water) is introduced into the sodium chloride crystal washing tank 20 to wash the crystals produced in the mother liquor concentration tank 19. The mass ratio of hot water (deionized water) to the crystals in the mother liquor concentration tank 19 is 0.2:1, so as to achieve the separation of sodium chloride and lithium bromide.

[0114] The mother liquor from the mother liquor concentration tank 19 is enriched with nitrate and potassium ions. At this time, the mother liquor in the mother liquor concentration tank 19 is sent to the mother liquor cooling tank 21, and the mother liquor temperature is reduced to below 20°C by using 15°C cold water. At the same time, potassium sulfate is added to the mother liquor cooling tank 21, and the mass ratio of potassium sulfate to the mother liquor in the mother liquor cooling tank 21 is 0.5:1. The nitrate will be precipitated as potassium nitrate crystals and mixed with some lithium bromide crystals. The potassium nitrate crystals are transported to the potassium nitrate crystal washing tank 22 by using a conveying device. Similarly, according to the sensitivity of the solubility of potassium nitrate and lithium bromide crystals to temperature, 15°C cold water is introduced into the potassium nitrate crystal washing tank 22 for washing, and the ratio of cold water to the mass of the crystals in the potassium nitrate crystal washing tank 22 is 0.2:1. The potassium nitrate crystals are separated in the potassium nitrate crystal washing tank 22;

[0115] In summary, the separation of undesirable ions such as chloride ions, sodium ions, potassium ions, and nitrate ions in the solution is achieved, and then the washing liquid (dissolving liquid) in the potassium nitrate crystal washing tank 22, the sodium chloride crystal washing tank 20, the calcium carbonate washing tank 18, and the absorbent crystal dissolving tank 16 are all sent back to the solution spray circulation (solution absorption tower 10) by the purified solution reflux pump 9 to achieve the recovery of the absorption medium.

[0116] 6. Energy recovery

[0117] After being treated by the desulfurization tower 7, the saturated wet flue gas with a temperature of 54°C is output and enters the smoke inlet at the lower end of one side of the solution absorption tower 10. At the same time, the absorption spray pump 8 sprays the lithium bromide solution with a concentration of 55%, a temperature of about 80°C, and a flow rate of 18.63 t / h from the top of the solution absorption tower 10 (absorption tower sprayer 10-1). The solution and the flue gas are heat and mass transferred in the absorption tower water spraying area 10-2 in the solution absorption tower 10. Finally, the flue gas temperature rises to 75°C, and the water vapor partial pressure drops to 12.5 kPa, and the flue gas is discharged from the solution absorption tower 10. The flue gas is then transported to the chimney 12 by the booster fan 11; the lithium bromide solution concentration drops from 55% to 45%, the temperature is 68°C, and the solution absorption tower 10 is discharged from the bottom of the tower and sent to the top of the solution regeneration tower 2 through the regeneration spray pump 5. The flow rate is about 22.77 t / h.

[0118] In the solution absorption tower 10, the heating pipe network supplies 60°C heating return water to the coil 10-5 in the absorption tower water spraying area 10-2, about 94t / h, which enters from the bottom of the absorption tower water spraying area 10-2, is heated by the solution in the absorption tower water spraying area 10-2, and is heated to about 70°C, and is supplied from the upper part of the absorption tower water spraying area 10-2;

[0119] Since the flue gas in the solution absorption tower 10 is relatively clean, both sulfur dioxide and impurities are greatly reduced compared with before desulfurization, the solution discharged from the bottom of the absorption tower is directly pumped out by the regeneration spray pump 5 and sent to the solution regeneration tower 2;

[0120] The flue gas discharged from the solution absorption tower 10 has a temperature of 75°C and a water vapor partial pressure of 12.5 kPa, which is equivalent to an air moisture content of about 83 g / kg (dry air). For air at 75°C and a moisture content of 83 g / kg (dry air), when it is mixed with ambient air at a temperature above 11°C and a moisture content of 4.9 g / kg (dry air) (relative humidity 60%), it can be ensured that water vapor condensation will not occur, thereby achieving flue gas de-whitening.

[0121] The beneficial effects of the present invention are as follows: 1. The flue gas temperature is increased to above 70°C without consuming additional steam and hot water; 2. The water vapor content carried by the discharged flue gas can be reduced by more than 20% without cooling and condensing; 3. The flue gas waste heat recovery temperature can be increased by more than 20°C compared with the flue gas temperature at the desulfurization outlet, basically meeting the requirement of direct heating of 50-60°C heat network return water; 4. While achieving flue gas desulfurization and flue gas waste heat recovery, the temperature in the desulfurization tower is not reduced to ensure that the desulfurization effect is not affected; 5. The spray solution can use the flue gas's own thermal energy resources to achieve regeneration, and achieve purification by consuming a small amount of high-grade steam or hot water resources to ensure the sustainability of the system cycle.

[0122] The present invention is not limited to the above-mentioned embodiments. Anyone should know that any technical solution identical or similar to the present invention made under the inspiration of the present invention shall fall within the protection scope of the present invention.

[0123] The techniques, shapes, and structural parts not described in detail in the present invention are all well-known techniques.

Claims

1. A coal-fired boiler flue gas deoxidation and waste heat recovery system, characterized in that: It includes flue gas induced draft fan, solution regeneration tower, limestone powder mixing tank, slaked lime mixing tank, regeneration spray pump, solution purification liquid supply pump, desulfurization tower, absorption spray pump, purified solution reflux pump, solution absorption tower, booster fan, chimney, sedimentation tank washing water spray pump, sedimentation washing tank, solution purification concentration tank, absorbent crystal dissolving tank, sodium carbonate mixing tank, calcium carbonate washing tank, mother liquor concentration tank, sodium chloride crystal washing tank, mother liquor cooling tank, potassium nitrate crystal washing tank; The solution absorption tower comprises a shell with a cavity arranged inside, an absorption tower water spraying area is arranged near the middle of the shell, an absorption tower water storage tray is arranged near the bottom of the absorption tower water spraying area in the shell for storing a certain amount of liquid, and an absorption tower sprayer is arranged near the top of the absorption tower water spraying area in the shell for spraying water mist into the shell; The water sprinkling area of ​​the absorption tower is provided with a coil and a high-temperature section water sprinkling filler, a plurality of coils are provided and arranged in a transverse manner, one end of the plurality of coils is connected to a heat medium inlet pipe, and the other end is connected to a heat medium outlet pipe, the coils and the high-temperature section water sprinkling filler are provided with multiple layers, and the multiple layers of coils and fillers are alternately arranged, and the coils adopt a multi-layer tube design; The flue gas induced draft fan is connected to the lower smoke inlet of the solution regeneration tower, the upper smoke outlet of the solution regeneration tower is connected to the smoke inlet of the desulfurization tower, and the bottom liquid outlet of the solution regeneration tower is connected to the limestone powder mixing tank; The smoke outlet at the top of the desulfurization tower is connected to the smoke inlet near the lower end of one side of the solution absorption tower, the smoke outlet arranged near the upper end of one side of the solution absorption tower is connected to the chimney through a booster fan, and the liquid outlet at the bottom of the solution absorption tower is connected to the top spray in the solution regeneration tower through a regeneration spray pump; One side of the limestone powder mixing tank is connected to a slaked lime mixing tank, which is connected to an absorption tower sprayer through an absorption spray pump. The slaked lime mixing tank is also connected to a precipitation washing tank, which is connected to a tower top spray in a solution regeneration tower through a precipitation tank washing water spray pump. Two tower top sprays are provided in the solution regeneration tower, one of which is connected to the precipitation tank washing water spray pump, and the other is connected to the regeneration spray pump. The slaked lime mixing tank is connected to a solution purification concentration tank and an absorbent crystal dissolving tank through a solution purification liquid supply pump, and the solution purification concentration tank is connected to the absorbent crystal dissolving tank; The solution purification concentration tank is connected to the sodium carbonate mixing tank, the sodium carbonate mixing tank is connected to the calcium carbonate washing tank, the sodium carbonate mixing tank is connected to the mother liquor concentration tank, the mother liquor concentration tank is connected to the sodium chloride crystal washing tank, the mother liquor concentration tank is connected to the mother liquor cooling tank, and the mother liquor cooling tank is connected to the potassium nitrate crystal washing tank; The absorbent crystal dissolving tank, the calcium carbonate washing tank, the sodium chloride crystal washing tank, the potassium nitrate crystal washing tank and the mother liquor cooling tank are connected with the slaked lime mixing tank through a purified solution reflux pump.

2. A method for eliminating flue gas whitening and recovering waste heat from a coal-fired boiler using the system of claim 1, characterized in that: The following steps are involved: 1) Use lithium bromide solution to pre-treat flue gas 2) Desulfurize the flue gas discharged from step 1 3) Remove iron ions, ferrous ions, aluminum ions, copper ions, and fluoride ions from lithium bromide solution 4) Reuse of lithium bromide in the output liquid of the slaked lime mixing tank 5) Eliminate the sodium ions, potassium ions, chloride ions, and nitrate ions in the output solution of step 4 6) Energy recovery and utilization In step 1) flue gas pretreatment The 120℃ flue gas first enters the solution regeneration tower from the bottom of the tower under the action of the flue gas induced draft fan. At the same time, the lithium bromide solution with a concentration of 45% and a temperature of 68℃ is sprayed into the solution regeneration tower from the top of the tower at a rate of 22.77t / h. The lithium bromide solution and the flue gas conduct heat and mass transfer inside the solution regeneration tower. Finally, the flue gas temperature drops to 80℃, the water vapor partial pressure rises to 13.4kPa, and is discharged from the solution regeneration tower; the lithium bromide solution concentration increases from 45% to 55%, the temperature is 80℃, and it is discharged from the solution regeneration tower from the bottom drain port of the tower, with a flow rate of 18.63t / h, and the lithium bromide solution is initially stored at the bottom of the solution regeneration tower and the solution absorption tower; In step 2) flue gas desulfurization The flue gas enters the desulfurization tower through the smoke outlet on the solution regeneration tower, undergoes desulfurization treatment, and then outputs saturated wet flue gas at 54°C; In the above step 3), the solution in step 1 first enters the limestone powder mixing tank, and the pH value of the solution in the limestone powder mixing tank reaches above 5.5 by adding limestone powder. Then the solution in the limestone powder mixing tank enters the slaked lime mixing tank, and slaked lime is added to make the pH value of the solution in the slaked lime mixing tank reach above 9, and a precipitate is formed. At the same time, by increasing the pH value of the solution, the acidified solution is prevented from excessively corroding subsequent equipment. The precipitate in the slaked lime mixing tank enters the precipitation washing tank, and then deionized water is added to the precipitation washing tank for washing. The ratio of the volume of deionized water to the volume of the precipitate in the precipitation washing tank is 1:

1. The washing water in the precipitation washing tank enters the solution regeneration tower and is sprayed toward the flue gas in a mist form. The solution in the slaked lime mixing tank enters the solution absorption tower; In step 4), the solution purification supply pump extracts 1-5% of the total solution circulation volume from the slaked lime mixing tank for purification, a part of which enters the solution purification concentration tank, and a part of which enters the absorbent crystal dissolving tank. In the solution purification concentration tank, the solution is heated by 0.2-0.4MPa steam to produce most of the lithium bromide crystals after concentration. Then the lithium bromide crystals enter the absorbent crystal dissolving tank and are dissolved by the clarified liquid delivered by the solution purification supply pump. The chloride ions, sodium ions, potassium ions, nitrate ions and calcium ions in the mother liquor produced by the solution purification concentration tank will be greatly enriched, so that the lithium bromide solution can be purified; In step 5), the solution in the solution purification concentration tank enters the sodium carbonate mixing tank, and the pH value of the mother liquor is adjusted to 10 by adding some sodium carbonate into the sodium carbonate mixing tank to balance the sodium ions in the mother liquor, and at the same time remove some calcium ions to facilitate the subsequent crystallization of sodium chloride and potassium nitrate; The precipitate in the sodium carbonate mixing tank enters the calcium carbonate washing tank, and deionized water is added to the calcium carbonate washing tank for washing. The mass ratio of the deionized water to the precipitate in the calcium carbonate washing tank is 1:1; The mother liquor in the sodium carbonate mixing tank enters the mother liquor concentration tank, and is heated by 0.2-0.4MPa steam to precipitate sodium chloride crystals, and some lithium bromide crystals are also mixed in it. 90-100℃ deionized water is introduced into the sodium chloride crystal washing tank to wash the crystals produced in the mother liquor concentration tank. The mass ratio of deionized water to the crystals in the mother liquor concentration tank is 0.2:1; The mother liquor in the mother liquor concentration tank is sent to the mother liquor cooling tank, and the mother liquor temperature is reduced to below 20°C by using 10-15°C cold water. At the same time, potassium sulfate is added to the mother liquor cooling tank, and the mass ratio of potassium sulfate to the mother liquor in the mother liquor cooling tank is 0.5:

1. Crystals are precipitated and enter the potassium nitrate crystal washing tank. Cold water at 10-15°C is passed into the potassium nitrate crystal washing tank for washing, and the mass ratio of cold water to the crystals in the potassium nitrate crystal washing tank is 0.2:

1. Potassium nitrate crystals are separated in the potassium nitrate crystal washing tank; Energy recovery in step 6) After being treated in the desulfurization tower, the saturated wet flue gas with a temperature of 54°C enters the smoke inlet at the lower end of one side of the solution absorption tower. At the same time, the absorption spray pump sprays the lithium bromide solution with a concentration of 55%, a temperature of 80°C and a flow rate of 18.63t / h from the absorption tower sprayer at the top of the solution absorption tower. The lithium bromide solution and the flue gas conduct heat and mass transfer in the absorption tower water spraying area of ​​the solution absorption tower. Finally, the flue gas temperature rises to 75°C, and the water vapor partial pressure drops to 12.5kPa. It is discharged from the solution absorption tower and then transported to the chimney by the booster fan; the concentration of the lithium bromide solution drops from 55% to 45%, the temperature is 68°C, it is discharged from the solution absorption tower from the bottom of the tower and is pumped to the top of the solution regeneration tower for spraying through the regeneration spray pump, with a flow rate of 22.77t / h. In the solution absorption tower, the heating pipe network supplies 94t / h of 60℃ heating return water to the coils in the absorption tower water sprinkling area. The water enters from the bottom of the absorption tower water sprinkling area, is heated by lithium bromide solution in the absorption tower water sprinkling area, and is heated to 70℃, and is supplied from the upper part of the absorption tower water sprinkling area. The solution discharged from the bottom of the solution absorption tower is directly pumped out by the regeneration spray pump and sent to the solution regeneration tower.

Images