CN112390438A - Method and system for zero discharge of flue gas desulfurization wastewater - Google Patents
Method and system for zero discharge of flue gas desulfurization wastewater Download PDFInfo
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- CN112390438A CN112390438A CN201910749038.1A CN201910749038A CN112390438A CN 112390438 A CN112390438 A CN 112390438A CN 201910749038 A CN201910749038 A CN 201910749038A CN 112390438 A CN112390438 A CN 112390438A
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Abstract
The invention discloses a method and a system for zero discharge of flue gas desulfurization wastewater, wherein the method comprises the following steps: carrying out buffer sedimentation treatment on the flue gas desulfurization wastewater, and separating to obtain raw water; performing multi-effect circulating evaporation treatment on raw water to obtain a concentrated solution; extracting high-temperature flue gas to dry the concentrated solution to obtain mixed salt; and mixing the miscellaneous salt with the subsequent flue gas, then carrying out dust removal and collection, and finally mixing the miscellaneous salt into the fly ash. The system comprises a buffering and settling unit, a multi-effect circulating evaporation unit, a concentrated solution collecting unit and a drying unit which are sequentially connected through pipelines, wherein the multi-effect circulating evaporation unit at least comprises a circulating evaporation subunit with two effects connected in series. The invention is suitable for treating the flue gas desulfurization wastewater of the coal-fired power generating set, can realize zero liquid discharge of the flue gas desulfurization wastewater, has short system flow, does not need the traditional three-header treatment and the traditional chemical softening treatment, fully utilizes the waste heat of the coal-fired power plant, has low cost and can ensure the long-term stable operation of the system.
Description
Technical Field
The invention relates to the technical field of desulfurization wastewater treatment, in particular to a method and a system for zero discharge of flue gas desulfurization wastewater.
Background
At present, the environment protection situation is severe, and particularly, after the comprehensive control of the discharge of water pollution sources is emphasized by the action plan of water pollution prevention and control (ten items of water) issued by the state academy in 2015, the discharge standard of wastewater in various industries is more and more strict, the pollution to the environment needs to be reduced to the maximum extent, and high-salt concentrated water in various industries also needs to reach zero liquid discharge. Limestone gypsum wet desulphurization is adopted for most coal-fired power generating sets, and the terminal wastewater is high-salinity wastewater after flue gas desulphurization. Desulfurization waste water concentration is high and the composition is complicated, and the salinity of waste water can not be handled to traditional triplex case, if the triplex case goes out the direct discharge and will cause very big harm to the environment. With the continuous improvement of the water treatment requirement, the realization of zero discharge of the desulfurization wastewater of the coal-fired power plant is imperative.
The desulfurization wastewater is the terminal wastewater of a coal-fired power plant, has high salt concentration (TDS: 30000-60000 mg/L), contains various heavy metal ions and contains CaSO4Tends to be saturated, belongs to typical high-salt wastewater which is difficult to treat and is difficult to treat by the traditional water treatment technology.
The main treatment technology of desulfurization waste water treatment at present is triple box precipitation filtration treatment, can not satisfy new emission requirement, and traditional triple box complex operation, the running cost is high. The current zero discharge technology of desulfurization waste water after passing through a triple box is mainly divided into a membrane method technology and a thermal method technology.
The technical route adopted by the membrane method technology is as follows: softening>Salt separation>Membrane concentration>And (4) crystallizing. The technical route has long flow, high investment and operation cost (the investment cost is more than 200 ten thousand per ton of water according to the water amount per hour, the treatment cost per ton of water is more than 80 yuan), poor overall economy, difficult later maintenance of the membrane and finally prepared NaCl and Na2SO4The salt economy is poor. In addition, there is also a small amount of miscellaneous salts that ultimately need to be handled separately in this route. With the increasing environmental protection requirement, the part of miscellaneous salt needs to be treated according to the danger waste, and the treatment cost is high.
Thermal methods are divided into multiple-effect evaporation and flue gas evaporation. The multi-effect evaporation is that the wastewater is softened and then the desulfurized wastewater is concentrated or evaporated into mixed salt by adopting steam. Flue gas steamThe method is characterized in that high-temperature (flue gas above 300 ℃ in front of an air preheater) or low-temperature (flue gas about 150 ℃ at the inlet of a dust remover) flue gas is adopted to directly dry the desulfurization waste water into mixed salt. The subsequent treatment of the miscellaneous salt finally obtained by multi-effect evaporation is difficult, and the CaSO4The heat exchange tube is easy to be blocked due to scaling in the evaporation process, and generally needs to be cleaned once in 2-3 months. The flue gas evaporation has certain influence on a flue gas system, and if the extracted flue gas amount is too large, a series of problems of unit heat efficiency reduction, unstable combustion, aggravation of cold end corrosion of an air preheater and the like can be caused. Multiple effect evaporation to avoid CaSO4Scaling, requiring a perfect softening pretreatment, the overall operating cost will be higher than 60 yuan/ton water. The heat efficiency of the unit is reduced by the evaporation of the flue gas, if the heat efficiency of the unit is kept unchanged, the coal consumption needs to be increased properly, and the overall operation cost is about 40 yuan/ton of water on the basis of considering the coal consumption.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an optimized flue gas desulfurization wastewater zero-discharge method and system, which are suitable for flue gas desulfurization wastewater treatment of a coal-fired power generating set, can realize zero liquid discharge of flue gas desulfurization wastewater and have short system flow.
One aspect of the invention provides a method for zero discharge of flue gas desulfurization wastewater, comprising the following steps:
A. carrying out buffer sedimentation treatment on the flue gas desulfurization wastewater, and separating to obtain raw water;
B. performing multi-effect circulating evaporation treatment on raw water to obtain a concentrated solution;
C. extracting high-temperature flue gas to dry the concentrated solution to obtain mixed salt;
D. and mixing the miscellaneous salt with the subsequent flue gas, then performing dust removal and collection, and mixing the miscellaneous salt into the fly ash.
According to one embodiment of the method for zero emission of flue gas desulfurization wastewater, in the step A, suspended matters in raw water are controlled to be below 1000 mg/L; in the step B, the raw water concentration multiplying power is controlled to be 5-10 times, and the flow speed of the multi-effect circulating evaporation treatment is controlled to be more than 2.8 m/s.
According to an embodiment of the method for zero emission of flue gas desulfurization wastewater, in the step C, the extracted high-temperature flue gas is flue gas from before an air preheater and at a temperature of 300-350 ℃, and the amount of the extracted high-temperature flue gas is controlled to be not higher than 2% of the total amount of the flue gas.
According to an embodiment of the method for zero emission of flue gas desulfurization wastewater, in the step B, each effect of concentrated water obtained by multiple-effect cyclic evaporation treatment is subjected to cyclone separation treatment to obtain top concentrated water and bottom solid-liquid mixture, wherein the top concentrated water is subjected to next effect continuous evaporation, the last effect of concentrated water is taken as concentrated solution to be subjected to drying treatment, and the bottom solid-liquid mixture is taken as seed crystal or is mixed with pre-seed crystal and then is refluxed to continue multiple-effect cyclic evaporation treatment, wherein the pre-seed crystal is anhydrous calcium sulfate powder.
The invention also provides a system for zero discharge of flue gas desulfurization wastewater, which comprises a buffer settling unit, a multi-effect circulating evaporation unit, a concentrated solution collecting unit and a drying unit which are sequentially connected through pipelines, wherein the multi-effect circulating evaporation unit at least comprises two circulating evaporation sub-units which are serially connected, wherein,
the water inlet of the buffering sedimentation unit is connected with a flue gas desulfurization waste water pipeline, the water outlet of the buffering sedimentation unit is connected with the water inlet of the multi-effect circulating evaporation unit, and the concentrated water outlet of the multi-effect circulating evaporation unit is connected with the water inlet of the concentrated solution collection unit;
the water outlet of the concentrated solution collecting unit is connected with the water inlet of the drying unit, the drying unit is also connected with an upstream pipeline of the high-temperature flue gas supply flue through an inlet flue and is connected with a downstream pipeline of the high-temperature flue gas supply flue through an outlet flue, and the downstream pipeline of the high-temperature flue gas supply flue is connected with the dust removal unit.
According to one embodiment of the system for zero emission of flue gas desulfurization wastewater of the present invention, each effect circulation evaporation sub-unit of the multi-effect circulation evaporation unit comprises a separation chamber, a heater, a concentrated water pump and a circulation pump;
the circulation concentration part at the lower part of the separation chamber is connected with a water inlet of the heater through a circulation pump, the circulation concentration part at the lower part of the separation chamber is also connected with a water inlet of the heater in the next effective circulation evaporation subunit or a water inlet of the concentrated solution collection unit through a concentrated water pump, a steam outlet of the heater is connected with a steam-water separation part at the upper part of the separation chamber, and a steam inlet is connected with a heat source pipeline or the steam-water separation part at the upper part of the separation chamber in the previous effective circulation evaporation subunit;
and the water outlet of the buffer sedimentation unit is connected with a circulating concentration part at the lower part of a separation chamber in a primary circulating evaporation subunit of the multi-effect circulating evaporation unit.
According to an embodiment of the system for zero emission of flue gas desulfurization wastewater of the present invention, each of the multiple-effect circulating evaporation sub-units further includes a cyclone disposed between the concentrate pump and the heater or the concentrated solution collection unit in the next-effect circulating evaporation sub-unit, the top of the cyclone is connected to the water inlet of the heater or the water inlet of the concentrated solution collection unit in the next-effect circulating evaporation sub-unit, and the bottom of the cyclone is connected to the seed crystal tank, and the seed crystal tank is connected to the circulating concentration portion at the lower portion of the separation chamber in each of the multiple-effect circulating evaporation sub-units through the seed crystal pump.
According to one embodiment of the system for zero emission of flue gas desulfurization wastewater, the lower part of the heater in each effect circulating evaporation subunit of the multiple-effect circulating evaporation unit is further provided with a distilled water outlet, wherein a steam-water separation part at the upper part of a separation chamber in the last effect circulating evaporation subunit is connected with a condenser provided with a vacuum pump.
According to one embodiment of the system for zero emission of flue gas desulfurization wastewater, the drying unit comprises dryers and atomizers which are arranged in a plurality of units, a main pipe between the concentrated solution collecting unit and each dryer is in a high-flow and large-pipe-diameter backflow arrangement, redundant concentrated solution flows back into the concentrated solution collecting unit, and the concentrated solution from the concentrated solution collecting unit is atomized and sprayed into each dryer.
According to one embodiment of the system for zero emission of flue gas desulfurization wastewater, the buffer settling unit comprises a buffer settling tank, a sludge pump and a water inlet pump, the sludge pump and the water inlet pump are connected with the buffer settling tank, and the concentrated solution collecting unit comprises a concentrated solution tank and a concentrated solution pump; the upstream pipeline of the high-temperature flue gas supply flue is connected with a flue gas inlet of the air preheater, and the downstream pipeline of the high-temperature flue gas supply flue is connected with a flue gas outlet of the air preheater.
Compared with the prior art, the invention provides an optimized flue gas desulfurization wastewater zero-discharge method and system technology, which are suitable for flue gas desulfurization wastewater treatment of a coal-fired power generating set, can realize zero liquid discharge of flue gas desulfurization wastewater, and have short system flow. The flue gas desulfurization wastewater does not need the traditional triple box treatment and the traditional chemical softening treatment, simultaneously makes full use of the waste heat (low-parameter steam, flue gas waste heat and the like) of the coal-fired power plant, has low overall investment and operation cost, and can ensure the long-term stable operation of the system.
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Fig. 1 shows a schematic configuration diagram of a system for zero emission of flue gas desulfurization wastewater according to an exemplary embodiment of the present invention.
Description of reference numerals:
1-buffer settling tank, 2-water inlet pump, 3-sludge pump, 41-first effect separation chamber, 51-first effect heater, 61-first effect circulating pump, 71-first effect cyclone, 81-first effect concentrated water pump, 42-last effect separation chamber, 52-last effect heater, 62-last effect circulating pump, 72-last effect cyclone, 82-last effect concentrated water pump, 9-crystal seed tank, 91-crystal seed, 10-crystal seed pump, 11-concentrated liquid tank, 12-concentrated liquid pump, 13-condenser, 14-vacuum pump, 15-dryer, 16-SCR denitration device, 17-air preheater, 18-dust remover, 19-inlet flue of dryer, 20-outlet flue of dryer.
Detailed Description
All of the features disclosed in this specification, or all of the steps in any method or process so disclosed, may be combined in any combination, except combinations of features and/or steps that are mutually exclusive.
Any feature disclosed in this specification may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.
The method and system for zero discharge of flue gas desulfurization wastewater of the present invention will be specifically described below.
The invention firstly provides a method for zero discharge of flue gas desulfurization wastewater, and specifically relates to a method for realizing zero discharge of flue gas desulfurization wastewater, which comprises the steps of carrying out simple gravity settling on wastewater generated by a flue gas desulfurization system (without a triple box), carrying out multi-effect circulating evaporation treatment to obtain concentrated solution after concentration, completely evaporating the concentrated solution after concentration by using high-temperature flue gas, returning miscellaneous salts evaporated to dryness in the wastewater to a dust remover along with the flue gas, and finally uniformly mixing the miscellaneous salts into fly ash to realize zero discharge.
According to an exemplary embodiment of the present invention, the method for zero emission of flue gas desulfurization wastewater comprises the following steps.
Step A:
and carrying out buffer sedimentation treatment on the flue gas desulfurization wastewater, and separating to obtain raw water. Preferably, the suspended matter in the raw water is controlled below 1000 mg/L.
This step has saved the triplex case, adopts simple settlement preliminary control suspended solid in the flue gas desulfurization waste water, and the system is simpler.
And B:
and carrying out multi-effect circulating evaporation treatment on the raw water to at least obtain a concentrated solution. Preferably, the raw water concentration multiplying power is controlled to be 5-10 times, and the flow rate of the multi-effect circulating evaporation treatment is controlled to be more than 2.8 m/s.
The energy consumption of an evaporation system can be reduced by adopting multi-effect circulating evaporation treatment, at least two-effect circulating evaporation treatment is recommended to be adopted according to the water quality characteristics of the flue gas desulfurization wastewater, and 2-3-effect circulating evaporation treatment is preferred.
To prevent fouling, it is preferred to employ a cyclonic separation process to reflux the seeds during the effective cyclic evaporation process, whereby fresh seed addition is not required during normal operation.
Specifically, each effect concentrated water obtained by the multi-effect cyclic evaporation treatment is subjected to cyclone separation treatment to obtain top concentrated water and bottom solid-liquid mixture, wherein the top concentrated water is subjected to next effect cyclic evaporation, the last effect concentrated water is used as a concentrated solution to be subjected to subsequent drying treatment, and the bottom solid-liquid mixture is used as a seed crystal or is mixed with a pre-seed crystal and then flows back to continue the multi-effect cyclic evaporation treatment.
Wherein, the newly added crystal seeds adopt anhydrous calcium sulfate powder, and then the newly generated crystals in the concentration process of the raw water can be attached to the surface of the crystal seeds with the same crystal form to grow, thereby avoiding the scaling on the inner wall of the pipeline.
And C:
and extracting high-temperature flue gas to dry the concentrated solution to obtain the miscellaneous salt.
The high-temperature flue gas extracted in the step is preferably flue gas which comes from the front of an air preheater and has the temperature of 300-350 ℃, the amount of the extracted high-temperature flue gas is controlled to be not higher than 2% of the total amount of the flue gas so as to avoid adverse effects on an original flue gas system, and the high-temperature flue gas can ensure that a concentrated solution is completely evaporated to dryness to obtain miscellaneous salts.
Moreover, the drying treatment preferably adopts a bypass mode of being connected with the flue gas pipeline in parallel to lead out high-temperature flue gas, so that the required flue gas amount is small, and the influence on an original flue gas system can be avoided.
Step D:
and mixing the miscellaneous salt with the subsequent flue gas, then performing dust removal and collection, and mixing the miscellaneous salt into the fly ash.
The miscellaneous salt evaporated to dryness in the concentrated solution returns to an inlet flue of a dust remover along with the flue gas, and is finally uniformly mixed into the fly ash after being subjected to dust removal and collection in the dust remover.
According to the above control method concept, the invention also provides a system for zero discharge of flue gas desulfurization wastewater.
Fig. 1 shows a schematic configuration diagram of a system for zero emission of flue gas desulfurization wastewater according to an exemplary embodiment of the present invention.
As shown in fig. 1, according to an exemplary embodiment of the present invention, the system for zero emission of flue gas desulfurization wastewater comprises a buffer settling unit, a multi-effect circulation evaporation unit, a concentrated solution collection unit and a drying unit which are connected in sequence through a pipeline, wherein the multi-effect circulation evaporation unit comprises at least two circulation evaporation sub-units which are arranged in series.
The following describes each part separately.
The water inlet of the buffering sedimentation unit is connected with the flue gas desulfurization waste water pipeline, and the water outlet of the buffering sedimentation unit is connected with the water inlet of the multi-effect circulating evaporation unit. Wherein, the buffering settlement unit mainly realizes simple gravity buffering settlement of the flue gas desulfurization waste water which is not treated by the triple box, and removes part of suspended matters. Preferably, the buffering and settling unit comprises a buffering and settling tank 1, and a sludge pump 3 and a water inlet pump 2 which are connected with the buffering and settling tank 1, sludge settled at the bottom is intermittently discharged through the sludge pump 3, and raw water at the upper part is pumped out through the water inlet pump 2 and pumped into the multi-effect circulating evaporation unit.
The multi-effect circulation evaporation unit carries out multi-effect circulation evaporation concentration treatment on raw water, and a concentrated water outlet of the multi-effect circulation evaporation unit is connected with a water inlet of the concentrated solution collection unit. The effect number of the multi-effect circulating evaporation unit is determined according to the specific water quantity and the water quality, and two to three effects are generally set in the flue gas desulfurization wastewater zero discharge system.
Specifically, each effect circulating evaporation sub-unit of the multi-effect circulating evaporation unit of the invention comprises a separation chamber, a heater, a concentrated water pump and a circulating pump, for example, one effect circulating evaporation sub-unit comprises a one effect separation chamber 41, a one effect heater 51, a one effect circulating pump 61 and a one effect concentrated water pump 81, and the last effect circulating evaporation sub-unit comprises a last effect separation chamber 42, a last effect heater 52, a last effect circulating pump 62 and a last effect concentrated water pump 82.
Wherein, the flash evaporation of the concentrated water and/or the raw water is realized after the separation chamber is heated, part of water forms secondary steam, and the concentrated water and/or the raw water are concentrated. The separating chamber comprises a lower circulating concentration part and an upper steam-water separation part. The heater heats the concentrated water and/or the raw water, the concentrated water pump is used for outputting the concentrated water, and the circulating pump is used for circulating the concentrated water and/or the raw water.
The water outlet of the buffer sedimentation unit is connected with the circulating concentration part at the lower part of the separation chamber in the one-effect circulating evaporation subunit of the multi-effect circulating evaporation unit so as to supply the raw water to the multi-effect circulating evaporation unit for multi-effect circulating evaporation concentration.
The circulation concentration part at the lower part of the separation chamber is connected with a water inlet of the heater through a circulation pump, the circulation concentration part at the lower part of the separation chamber is also connected with a water inlet of the heater in the next effective circulation evaporation subunit or a water inlet of the concentrated solution collection unit through a concentrated water pump, a steam outlet of the heater is connected with a steam-water separation part at the upper part of the separation chamber, and a steam inlet is connected with a heat source pipeline or the steam-water separation part at the upper part of the separation chamber in the last effective circulation evaporation subunit.
In order to avoid scaling, each effect circulating evaporation sub-unit of the multi-effect circulating evaporation unit further comprises a cyclone arranged between the concentrated water pump and a heater or a concentrated solution collecting unit in the next effect circulating evaporation sub-unit, for example, one effect circulating evaporation sub-unit comprises a first effect cyclone 71, and the last effect circulating evaporation sub-unit comprises a last effect cyclone 72. The top of the cyclone is connected with the water inlet of a heater in the next-effect circulating evaporation system or the water inlet of the concentrated solution collecting unit, the bottom of the cyclone is connected with the seed crystal tank 9, and the seed crystal tank 9 is connected with the circulating and concentrating part at the lower part of the separation chamber in each effect circulating evaporation subunit through the seed crystal pump 10, so that the liquid flows back to each effect circulating evaporation subunit. At system start-up, a small amount of seed crystal 91 may be artificially added directly to the seed tank 9.
The multiple-effect circulating evaporation unit is in a forced circulating evaporation mode, raw water is heated by the heater in the circulating process and then enters the separation chamber for flash evaporation, secondary steam obtained by flash evaporation enters the next-effect heater for continuous heating, and therefore heat of the secondary steam is recycled. And continuously circulating, evaporating and concentrating part of the flash evaporated concentrated water by a circulating pump, allowing part of the concentrated water to enter a cyclone by a concentrated water pump for cyclone separation, allowing the concentrated water at the top of the cyclone to enter a next effect for continuous evaporation, and collecting a solid-liquid mixture at the bottom of the cyclone in a seed crystal tank 9.
In addition, the lower part of the heater in each effect circulating evaporation subunit of the multi-effect circulating evaporation unit is also provided with a distilled water outlet, and the steam-water separation part at the upper part of the separation chamber in the last effect circulating evaporation subunit is connected with a condenser 13 provided with a vacuum pump. That is, the secondary steam discharged from the last-effect separation chamber 42 is condensed into distilled water by the condenser 13. The multi-effect circulating evaporation unit operates in a micro-negative pressure state, and the vacuum degree is maintained through the vacuum pump 14.
The concentrated solution collecting unit is used for collecting concentrated water concentrated by the multi-effect circulation evaporation unit, and preferably comprises a concentrated solution tank 11 and a concentrated solution pump 12. The water outlet of the concentrated solution collecting unit is connected with the water inlet of the drying unit, and the concentrated solution pump 12 sends the concentrated solution in the concentrated solution tank 11 to the drying unit for evaporation.
The drying unit is connected via an inlet flue 19 to the upstream pipe of the high temperature flue gas supply flue and via an outlet flue 20 to the downstream pipe of the high temperature flue gas supply flue, which is connected to the dust removal unit. That is, the drying unit of the invention adopts a bypass form to be connected with the high-temperature flue gas supply flue in parallel, the extracted flue gas amount is small, and the influence on the original flue gas system is avoided.
Preferably, the drying unit comprises dryers 15 and atomizers (not shown) arranged in several trains, and the main pipe between the concentrate collecting unit and each dryer 15 is provided with a high-flow, large-pipe-diameter backflow arrangement and the excess concentrate flows back into the concentrate collecting unit, wherein the concentrate from the concentrate collecting unit is atomized and sprayed into each dryer.
An upstream pipe of the high-temperature flue gas supply flue is connected with a flue gas inlet of the air preheater 17 and a downstream pipe of the high-temperature flue gas supply flue is connected with a flue gas outlet of the air preheater 17 and is located downstream of the SCR denitration device 16.
In the dryer 15, the concentrated solution is atomized and then fully mixed with the high-temperature flue gas from the inlet flue 19 of the dryer, and then is quickly evaporated to dryness, and the dried mixed salt and the flue gas return to the inlet of the dust remover 18 through the outlet flue 20 of the dryer. The high-temperature flue gas adopts flue gas between an SCR denitration device 16 and an air preheater 17, and miscellaneous salts are uniformly mixed with the flue gas in a flue, collected by a dust remover 18 and then uniformly mixed into fly ash.
Therefore, the invention reduces the traditional triple box, chemical softening and other equipment, has simple system and effectively solves the problems of high investment and operation cost, incapability of treating miscellaneous salt, easiness in scaling, great influence on boilers and flues and the like commonly existing in other existing desulfurization wastewater treatment technologies.
The present invention will be described with reference to specific examples.
As shown in FIG. 1, in the embodiment, after the flue gas desulfurization wastewater before the triple box is precipitated by the buffer settling tank 1, suspended matters are below 1000mg/L, and then the raw water enters the multi-effect circulating evaporation unit.
The multi-effect circulating evaporation unit adopts a forced circulation evaporation mode, the wastewater is heated by the first-effect heater 51 and enters the first-effect separation chamber 41 for flash evaporation, part of the flash-evaporated concentrated water returns to the first-effect heater 51 for circulating evaporation by the first-effect circulating pump 61, and the flash-evaporated secondary steam is used as an evaporation heat source of the next effect to continuously evaporate the next-effect concentrated water. The flow rate of the pipeline is controlled to be more than 2.8m/s, and raw water is concentrated by 5-10 times in the multi-effect circulating evaporation unit.
And after the concentrated water in each effect in the multi-effect circulating evaporation unit passes through the cyclones 71-72 respectively, collecting the solid-liquid mixture at the bottom in the seed crystal tank 9, and then returning the solid-liquid mixture to each effect circulating evaporation subunit through the seed crystal pump 10. And enabling concentrated water at the tops of the cyclones 71-72 to enter the next effect for continuous circulating evaporation. The system is started up by manually adding a small amount of seed crystal 91 to maintain the proper amount of seed crystal for the system.
The concentrated solution after evaporation concentration is collected in a concentrated solution tank 11, and then is conveyed to a dryer 15 through a concentrated solution pump 12, wherein a conveying pipeline between the concentrated solution tank 11 and the dryer 15 is of a main pipe type, the flow is 2-4 times of the actually required flow, and the flow speed of the pipeline is controlled to be more than 2.5 m/s.
The dryer 15 adopts the high temperature flue gas of about 350 ℃ before the air heater 17 to evaporate the concentrate, and the dense water volume that the dryer 15 was handled is designed according to the demand of high temperature flue gas, in order to reduce a series of influences such as boiler efficiency, combustor stability and air preheater cold junction corruption, the high temperature flue gas volume that the dryer 15 extracted is not higher than the total amount of flue gas 2%.
The concentrated water is atomized and then sprayed into the dryer 15, a double-fluid spray gun or a high-speed rotary atomizer can be adopted as the atomization form, the particle size of the atomized concentrated solution is 50-100 um, and the pressure drop of the dryer 15 is within the range of 400-800 Pa.
The concentrated solution is dried to obtain miscellaneous salt, and finally enters a dust remover 18 through a flue. The miscellaneous salt and the smoke dust are mixed evenly in the dust remover 18 and then mixed into the fly ash.
The flue gas desulfurization wastewater zero-discharge treatment technical route provided by the invention really realizes wastewater zero discharge, the system is simple, the investment cost is saved by more than 20%, the operation cost is below 20 yuan/ton of water, the system can be effectively prevented from scaling, the system can stably operate for a long time, and the cleaning period of the heat exchange tube is more than 6 months.
The invention is not limited to the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification and any novel method or process steps or any novel combination of features disclosed.
Claims (10)
1. A method for zero emission of flue gas desulfurization wastewater, which is characterized by comprising the following steps:
A. carrying out buffer sedimentation treatment on the flue gas desulfurization wastewater, and separating to obtain raw water;
B. performing multi-effect circulating evaporation treatment on raw water to obtain a concentrated solution;
C. extracting high-temperature flue gas to dry the concentrated solution to obtain mixed salt;
D. and mixing the miscellaneous salt with the subsequent flue gas, then performing dust removal and collection, and mixing the miscellaneous salt into the fly ash.
2. The method for zero discharge of flue gas desulfurization wastewater as claimed in claim 1, wherein in step a, suspended matters in raw water are controlled to be below 1000 mg/L; in the step B, the raw water concentration multiplying power is controlled to be 5-10 times, and the flow speed of the multi-effect circulating evaporation treatment is controlled to be more than 2.8 m/s.
3. The method for zero emission of flue gas desulfurization wastewater according to claim 1, wherein in the step C, the extracted high-temperature flue gas is flue gas from the front of an air preheater and at the temperature of 300-350 ℃, and the amount of the extracted high-temperature flue gas is controlled to be not more than 2% of the total amount of the flue gas.
4. The method for zero discharge of flue gas desulfurization wastewater as claimed in claim 1, wherein in step B, the concentrated water obtained from each effect is subjected to cyclone separation treatment to obtain concentrated water at the top and solid-liquid mixture at the bottom, wherein the concentrated water at the top is subjected to the next effect of continuous evaporation and the concentrated water at the last effect is subjected to drying treatment, and the solid-liquid mixture at the bottom is used as seed crystal or mixed with pre-seed crystal and then refluxed to continue the multi-effect cyclic evaporation treatment, wherein the pre-seed crystal is anhydrous calcium sulfate powder.
5. A system for zero discharge of flue gas desulfurization wastewater is characterized by comprising a buffer sedimentation unit, a multi-effect circulating evaporation unit, a concentrated solution collection unit and a drying unit which are sequentially connected through a pipeline, wherein the multi-effect circulating evaporation unit at least comprises a circulating evaporation subunit formed by connecting two effects in series, wherein,
the water inlet of the buffering sedimentation unit is connected with a flue gas desulfurization waste water pipeline, the water outlet of the buffering sedimentation unit is connected with the water inlet of the multi-effect circulating evaporation unit, and the concentrated water outlet of the multi-effect circulating evaporation unit is connected with the water inlet of the concentrated solution collection unit;
the water outlet of the concentrated solution collecting unit is connected with the water inlet of the drying unit, the drying unit is also connected with an upstream pipeline of the high-temperature flue gas supply flue through an inlet flue and is connected with a downstream pipeline of the high-temperature flue gas supply flue through an outlet flue, and the downstream pipeline of the high-temperature flue gas supply flue is connected with the dust removal unit.
6. The system for zero emission of flue gas desulfurization wastewater of claim 5, wherein each effect circulation evaporation sub-unit of the multi-effect circulation evaporation unit comprises a separation chamber, a heater, a concentrated water pump and a circulating pump;
the circulation concentration part at the lower part of the separation chamber is connected with a water inlet of the heater through a circulation pump, the circulation concentration part at the lower part of the separation chamber is also connected with a water inlet of the heater in the next effective circulation evaporation subunit or a water inlet of the concentrated solution collection unit through a concentrated water pump, a steam outlet of the heater is connected with a steam-water separation part at the upper part of the separation chamber, and a steam inlet is connected with a heat source pipeline or the steam-water separation part at the upper part of the separation chamber in the previous effective circulation evaporation subunit;
and the water outlet of the buffer sedimentation unit is connected with a circulating concentration part at the lower part of a separation chamber in a primary circulating evaporation subunit of the multi-effect circulating evaporation unit.
7. The system for zero emission of flue gas desulfurization wastewater of claim 6, wherein each effect circulation evaporation sub-unit of the multi-effect circulation evaporation unit further comprises a cyclone arranged between the concentrated water pump and the heater or the concentrated solution collection unit in the next effect circulation evaporation sub-unit, the top of the cyclone is connected with the water inlet of the heater or the water inlet of the concentrated solution collection unit in the next effect circulation evaporation system, the bottom of the cyclone is connected with the seed crystal tank, and the seed crystal tank is connected with the circulation concentration part at the lower part of the separation chamber in each effect circulation evaporation sub-unit through the seed crystal pump.
8. The system for zero discharge of flue gas desulfurization wastewater as recited in claim 6, wherein a distilled water outlet is further provided at a lower portion of the heater in each effect circulating evaporation subunit of the multiple effect circulating evaporation unit, wherein a steam-water separation portion at an upper portion of a separation chamber in the last effect circulating evaporation subunit is connected to a condenser provided with a vacuum pump.
9. The system for zero emission of wastewater generated by flue gas desulfurization according to claim 5, wherein the drying unit comprises dryers and atomizers arranged in a plurality of units, a main pipe between the concentrated solution collecting unit and each dryer is provided with a high-flow and large-pipe-diameter backflow device, and redundant concentrated solution flows back to the concentrated solution collecting unit, wherein the concentrated solution from the concentrated solution collecting unit is atomized and then sprayed into each dryer.
10. The system for zero emission of wastewater generated by flue gas desulfurization according to claim 5, wherein the buffer settling unit comprises a buffer settling tank/pond, a sludge pump and a water inlet pump which are connected with the buffer settling tank/pond, and the concentrated solution collecting unit comprises a concentrated solution tank and a concentrated solution pump; the upstream pipeline of the high-temperature flue gas supply flue is connected with a flue gas inlet of the air preheater, and the downstream pipeline of the high-temperature flue gas supply flue is connected with a flue gas outlet of the air preheater.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115124100A (en) * | 2022-06-27 | 2022-09-30 | 河北建投工程建设有限公司 | High-efficient high salt waste water evaporative crystallization system |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115124100A (en) * | 2022-06-27 | 2022-09-30 | 河北建投工程建设有限公司 | High-efficient high salt waste water evaporative crystallization system |
| CN115124100B (en) * | 2022-06-27 | 2023-12-22 | 河北建投工程建设有限公司 | High-efficient high salt waste water evaporation crystallization system |
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