CN215049255U - Resourceful pretreatment system of coal fired power plant desulfurization waste water - Google Patents
Resourceful pretreatment system of coal fired power plant desulfurization waste water Download PDFInfo
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Abstract
The utility model relates to a coal fired power plant desulfurization waste water's resourceful pretreatment system, this resourceful pretreatment system include along desulfurization waste water advancing direction connected gradually sink the pond in advance, remove the magnesium pond, remove sulphur pond, degree of depth sulphur removal pond and calcium removal pond in advance, wherein, the bottom that removes the magnesium pond and degree of depth sulphur removal pond deposits the export and still connects fire retardant preparation mechanism, the bottom that removes the calcium pond deposits the export and still connects outside desulfurizing tower. Compared with the prior art, the utility model discloses carry out resource utilization with the produced mud of each unit of desulfurization waste water zero release preliminary treatment technology, and the use of magnesium hydroxide and ettringite as fire retardant in coordination is surveyd to the heavy point, when guaranteeing follow-up embrane method zero release technology steady operation, realizes the abundant resource utilization of mud, has apparent economy and environmental benefit.
Description
Technical Field
The utility model belongs to the technical field of environmental protection and solid useless resourceization, a coal fired power plant desulfurization waste water's resourceization pretreatment systems is related to.
Background
The desulfurization wastewater is used as the tail end wastewater of a power plant, the source of water is complex, the water quality and water quantity characteristics are influenced by multiple factors such as coal, limestone and the operation of a desulfurization system, and the treatment difficulty is high. At present, with the research and development and improvement of membrane materials, the cost of a membrane device is reduced, and the membrane separation technology is more and more widely applied in the field of wastewater treatment and is based on the membrane integration technology and evaporative crystallizationThe desulfurization wastewater zero-discharge process is mature day by day. However, desulfurized wastewater has a strong tendency to scale, and Ca is used for zero-emission processes employing membrane concentration and evaporative crystallization2+、Mg2+And SO4 2-Is easy to cause membrane pollution and leads to the reduction of water production flux. For Ca2+、Mg2+Is less difficult to remove, but SO4 2-The existence of the calcium sulfate can easily cause the permanent calcium sulfate scale formation of a membrane system (such as forward osmosis) or an evaporation system in the concentration process, and the service life of the membrane material is reduced. Therefore, the desulfurization waste water needs to be subjected to softening pretreatment before concentration.
At present, the chemical precipitation method is most commonly applied in the desulfurization wastewater softening pretreatment process. The method converts the soluble substances to be removed in the water into insoluble substances to be precipitated by adding chemical agents, but the method has the defects of less applicable insoluble compounds, large chemical agent usage amount and large solid waste generation amount, and limits the practical application of the technology. Chinese patent CN108117224B discloses a desulfurization wastewater pretreatment method, which removes heavy metal ions, organic pollutants and nitrogen-containing pollutants in wastewater by combining a chemical precipitation method and a biological method, wherein the total nitrogen concentration in the treated wastewater is lower than 15mg/L, and the COD concentration is lower than 60 mg/L. Firstly, when the desulfurization wastewater is pretreated by adopting a chemical precipitation method, only the removal of heavy metals is considered, and a large amount of hardness ions still exist in the wastewater, so the method is not suitable for a downstream membrane method zero-discharge process; secondly, no reasonable way and method are provided for the treatment and disposal of the chemical sludge generated in the treatment process, and the common problems of large medicament usage amount and solid waste generation amount caused by the chemical precipitation method are still solved.
SUMMERY OF THE UTILITY MODEL
The utility model aims at providing a coal fired power plant desulfurization waste water's resourceful pretreatment systems, when carrying out degree of depth softening treatment to desulfurization waste water, realize the utilization of system's mud to compensation pretreatment systems running cost.
The purpose of the utility model can be realized through the following technical scheme:
one of the technical scheme of the utility model provides a coal fired power plant desulfurization waste water's resourceful pretreatment systems, include along desulfurization waste water advancing direction connected gradually sink the pond in advance, remove the magnesium pond, remove sulphur pond, degree of depth sulphur removal pond and calcium removal pond in advance, wherein, the bottom that removes the magnesium pond and degree of depth sulphur removal pond deposits the export and still connects fire retardant preparation mechanism, the bottom that removes the calcium pond deposits the export and still connects outside desulfurizing tower.
Furthermore, the bottom precipitation outlet of the pre-precipitation tank and the pre-desulfurization tank is also connected with an external gypsum cyclone.
Furthermore, the bottom precipitation outlet of the deep sulfur removal tank is also connected with the inlet of the pre-precipitation tank in a return mode.
Further, the fire retardant preparation mechanism is also connected with the pre-desulfurizing tank in a returning way.
Furthermore, the fire retardant preparation mechanism comprises a dehydrator, a washing machine and a dryer which are sequentially connected along the precipitate treatment direction.
Further, the preliminary sedimentation tank is also connected with a calcium oxide doser and a first flocculant doser.
Further, the magnesium removal pool is also connected with a magnesium removal agent doser and a dispersing agent doser.
Furthermore, the pre-desulfurizing pool is also connected with a pre-desulfurizing agent doser.
Furthermore, the deep desulfurization pool is also connected with a dispersing agent doser, a deep desulfurization agent doser and a second flocculating agent doser.
Further, the calcium removal pool is also connected with a calcium removal agent doser.
Further, a first sedimentation tank is arranged between the preliminary sedimentation tank and the magnesium removal tank.
Further, a second sedimentation tank is arranged between the magnesium removal tank and the pre-desulfurization tank.
Furthermore, a third sedimentation tank is arranged between the pre-desulfurization tank and the deep desulfurization tank.
Furthermore, a fourth sedimentation tank is arranged between the deep desulfurization tank and the calcium removal tank.
Furthermore, a fifth sedimentation tank is arranged behind the calcium removal tank.
The second technical scheme of the utility model provides a coal fired power plant desulfurization waste water's resourceful pretreatment method, its adoption is as above-mentioned resourceful pretreatment system implementation, this resourceful pretreatment method includes following step:
(1) feeding the desulfurization wastewater to be treated into a pre-settling tank, adding calcium oxide and a first flocculating agent, settling and separating, discharging the obtained effluent into a magnesium removal tank, and discharging the obtained precipitate to a gypsum cyclone;
(2) adding a magnesium removing agent and a dispersing agent into the magnesium removing pool, continuously settling and separating after the magnesium removing treatment is finished, discharging the obtained precipitate to a flame retardant preparation mechanism, and enabling the obtained effluent to flow into a pre-desulfurization pool;
(3) adding a pre-desulfurizing agent into the pre-desulfurizing tank for pre-desulfurizing treatment to obtain a mud-water mixed solution, continuously settling and separating, sending the obtained precipitate into a gypsum cyclone, and enabling the obtained effluent to flow into a deep desulfurizing tank;
(4) adding a deep desulfurization agent into the deep desulfurization pool, simultaneously adding a second flocculating agent and a dispersing agent, carrying out deep desulfurization treatment, then, continuously settling and separating, sending the obtained precipitate part into a flame retardant preparation mechanism, and enabling the obtained effluent to flow into a calcium removal pool;
(5) adding a calcium removing agent into the calcium removing pool for calcium removing treatment, then, carrying out precipitation separation, sending the obtained precipitate serving as a desulfurizing agent into a desulfurizing tower, and carrying out subsequent treatment on the obtained effluent serving as inlet water of a downstream membrane method zero-emission process.
Further, in the step (1), the retention time of the desulfurization wastewater in the preliminary sedimentation tank is 0.5-48h, the addition amount of the calcium oxide is 50-10000mg/L, and the first flocculating agent is one or more of aluminum salt, iron salt or polyacrylamide, and the addition amount is 0.01-200 mg/L.
Further, in the step (2), the hydraulic retention time of the magnesium removing pool is 0.5-49h, the magnesium removing agent is one or more of potassium hydroxide, sodium carbonate, sodium bicarbonate, calcium oxide or calcium hydroxide, the adding amount of the magnesium removing agent is 0.5-100g/L, the dispersant is one or more of sodium dodecyl benzene sulfonate, sodium pyrophosphate or polyisobutylene succinimide ashless additives, and the adding amount of the dispersant is 0.01-100mg/g DS (namely the dry solid content of the sludge).
Further, in the step (3), the hydraulic retention time of the pre-desulfurizing tank is 0.5-48h, the pre-desulfurizing agent is one or more of calcium oxide, calcium hydroxide, calcium chloride, calcium chlorate, calcium bicarbonate, calcium gluconate, calcium dihydrogen phosphate, calcium nitrate, calcium hydrogen sulfate, calcium hydrogen sulfite, calcium bromide or calcium iodide, and the adding amount of the pre-desulfurizing agent is 0.05-50 g/L.
Further, in the step (4), the hydraulic retention time of the deep sulfur removal tank is 0.5-48h, the deep sulfur removal agent is one or more of alumina, aluminum hydroxide, aluminum chloride or sodium aluminate, the adding amount of the deep sulfur removal agent meets the condition that the molar ratio of the residual calcium ions after the reaction in the sulfur removal tank is finished to the sulfur in the deep sulfur removal tank is 1-6, the molar ratio of the added aluminum ions to the sulfur element contained in the deep sulfur removal tank is 1-4, and the second flocculating agent is one or more of cationic, anionic or nonionic PAM, quaternary ammonium flocculating agent and polyamine-low molecular weight organic flocculating agent.
Further, in the step (5), the hydraulic retention time in the calcium removal tank is 0.5-24h, the calcium removal agent is one or more of sodium carbonate, sodium bicarbonate, potassium carbonate or ammonium bicarbonate, and the adding amount of the calcium removal agent is 0.05-100 g/L.
Further, the precipitates obtained in the step (2) and the step (4) are sequentially dehydrated, washed, extracted and dried in a flame retardant preparation mechanism to obtain a raw material of the flame retardant or the synergistic flame retardant, and a dehydrating solution, a cleaning waste solution and a condensing solution generated in the preparation process flow back to the pre-desulfurization tank for continuous treatment.
The utility model discloses carry out resource utilization with the produced mud of each unit of desulfurization waste water zero release preliminary treatment technology, and the use of magnesium hydroxide and ettringite as fire retardant in coordination is surveyd to the heavy point, when guaranteeing follow-up embrane method zero release technology steady operation, realizes the abundant resource utilization of mud, has apparent economy and environmental benefit.
Compared with the prior art, the utility model has the advantages of it is following:
(1) hardness ion and SO4 2-The operation pressure of the subsequent membrane method zero emission process can be reduced through efficient removal, and the dehydration liquid and the condensate liquid generated in the fire retardant purification step flow back to ensure that the whole system has no wastewater and sludge emission, so that the zero emission in the real sense is realized.
(2) Through sewage fractional precipitation and sludge classification resource, the sludge reduction effect is maximized, the sludge treatment pressure of the power plant is reduced, and the complete resource utilization of the sludge is realized.
(3) The addition of the sediments in the deep desulfurization tank of the reflux part and the lime slurry avoids the influence of heavy metal ions and the like on the purity of subsequent sediments, the deep graded salt separation target is completed on the premise of efficiently removing the hardness ions in the desulfurization wastewater, and the purity of the sludge in each unit can reach more than 98%.
(4) The solid precipitate has high purity, and is substantially free of impurities, desulfurized gypsum (CaSO)4) And desulfurizing agent (CaCO)3) The purification is carried out without extra treatment means, and the resource utilization is facilitated.
(5) The magnesium hydroxide and the ettringite are recycled, the flame retardant can be prepared independently or in proportion by doping, the particle size of the dispersing agent is lower than 5 mu m by adding, and the requirements of national standards HG/T4531-containing 2013 and HG/T4496-containing 2013 can be met. The ettringite serving as a framework is beneficial to uniform dispersion of magnesium hydroxide in the flame retardant material, and the effect of the ettringite serving as a synergistic flame retardant is better.
(6) The utility model relates to a zero release preliminary treatment technology ton water treatment cost is lower (24-30 yuan), through the utilization of the resource of mud, under the prerequisite of sparingly handling the processing cost, but the resource recovery cost of desulfurization gypsum, desulfurizer and fire retardant 45-50%, have apparent social, economic and environmental benefit.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a Scanning Electron Microscope (SEM) morphology of precipitates generated in the magnesium removal tank, the pre-sulfur removal tank, the deep sulfur removal tank and the calcium removal tank in example 2;
FIG. 3 is an FT-IR spectrum of ettringite precipitate from the fourth settling tank of example 2;
FIG. 4 is a graph showing the particle size and thermogravimetric analysis of the magnesium hydroxide and ettringite precipitates of example 2;
FIG. 5 is a comparison of Limiting Oxygen Index (LOI) and actual flame retardant effectiveness (for ethylene-vinyl acetate copolymer, EVA) for synergistic flame retardants prepared by precipitation and compounding of magnesium hydroxide and ettringite at different blending ratios in example 4;
the notation in the figure is:
1-a preliminary sedimentation tank, 2-a first sedimentation tank, 3-a magnesium removal tank, 4-a second sedimentation tank, 5-a preliminary sulfur removal tank, 6-a third sedimentation tank, 7-a deep sulfur removal tank, 8-a fourth sedimentation tank, 9-a calcium removal tank, 10-a fifth sedimentation tank, 11-a dehydrator, 12-a washing machine, 13-a dryer, 14-a calcium oxide doser, 15-a first flocculant doser, 16-a magnesium removal agent doser, 17-a dispersant doser, 18-a preliminary sulfur removal agent doser, 19-a deep sulfur removal agent doser, 20-a second flocculant doser, 21-a calcium removal agent doser.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
The following will explain the recycling pretreatment system of the present invention in detail.
For when carrying out degree of depth softening treatment to desulfurization waste water, realize the utilization as resources of system's mud, the utility model provides a coal fired power plant desulfurization waste water's resourceful pretreatment system, as shown in fig. 1, include along the preliminary sedimentation tank 1 that desulfurization waste water advancing direction connected gradually, remove magnesium pond 3, remove sulphur pond 5, degree of depth sulphur pond 7 and remove calcium pond 9 in advance, wherein, remove magnesium pond 3 and degree of depth sulphur pond 7's bottom and deposit the export and still connect fire retardant preparation mechanism, the bottom that removes calcium pond 9 deposits the export and still connects outside desulfurizing tower.
In some embodiments, the sedimentation outlet at the bottom of the pre-sedimentation tank 1 and the pre-desulfurization tank 5 is also connected with an external gypsum cyclone.
In some embodiments, the bottom sedimentation outlet of the deep sulfur removal tank 7 is also connected back to the inlet of the pre-sedimentation tank 1.
In some embodiments, the flame retardant preparation mechanism is also connected back to the pre-desulfurization tank 5.
In some embodiments, the flame retardant preparation mechanism includes a dehydrator 11, a washing machine 12, and a dryer 13 connected in sequence along a precipitate treatment direction.
In some embodiments, the pre-settling tank 1 is further connected to a calcium oxide doser 14 and a first flocculant doser 15 for adding a first flocculant.
In some embodiments, the magnesium removal tank 3 is further connected to a magnesium removal agent doser 16 and a dispersant doser 17 for adding a magnesium removal agent and a dispersant, respectively.
In some embodiments, the pre-desulfurization tank 5 is further connected to a pre-desulfurization agent doser 18 for adding a desulfurization agent.
In some embodiments, the deep desulfurization tank 7 is further connected to a dispersant doser 17, a deep desulfurization agent doser 19, and a second flocculant doser 20 for adding a dispersant, a deep desulfurization agent, and a second flocculant, respectively.
In some embodiments, the decalcifying pond 9 is further connected to a decalcifying agent adder 21 for adding a decalcifying agent.
In some embodiments, a first sedimentation tank 2 is further provided between the preliminary sedimentation tank 1 and the magnesium removal tank 3.
In some embodiments, a second sedimentation tank 4 is also provided between the magnesium removal tank 3 and the pre-sulphur removal tank 5.
In some embodiments, a third settling pond 6 is also provided between the pre-sulphur removal pond 5 and the deep sulphur removal pond 7.
In some embodiments, a fourth sedimentation tank 8 is further provided between the deep sulphur removal tank 7 and the calcium removal tank 9.
In some embodiments, a fifth sedimentation tank 10 is further provided behind the delime tank 9.
Next, the method of the present invention for the resource pretreatment will be described in detail.
The utility model provides a pair of coal fired power plant desulfurization waste water's resourceful pretreatment method, it adopts as above-mentioned resourceful pretreatment system to implement, can specifically see as shown in figure 1, this resourceful pretreatment method includes following step:
(1) feeding the desulfurization wastewater to be treated into a pre-settling tank 1, adding calcium oxide and a first flocculating agent, settling and separating, discharging the obtained effluent into a magnesium removal tank 3, and discharging the obtained precipitate to a gypsum cyclone;
(2) adding a magnesium removing agent and a dispersing agent into the magnesium removing pool 3, continuously settling and separating after the magnesium removing treatment is finished, discharging the obtained precipitate to a flame retardant preparation mechanism, and enabling the obtained effluent to flow into a pre-desulfurization pool 5;
(3) adding a pre-desulfurizing agent into the pre-desulfurizing tank 5 for pre-desulfurizing treatment to obtain a mud-water mixed solution, continuously settling and separating, sending the obtained precipitate into a gypsum cyclone, and enabling the obtained effluent to flow into a deep desulfurizing tank 7;
(4) adding a deep desulfurization agent into the deep desulfurization tank 7, simultaneously adding a second flocculating agent and a dispersing agent, performing deep desulfurization treatment, continuously settling and separating, feeding the obtained precipitate into a flame retardant preparation mechanism, and allowing the obtained effluent to flow into a calcium removal tank 9;
(5) adding a calcium removing agent into the calcium removing pool 9 for calcium removing treatment, then, carrying out precipitation separation, sending the obtained precipitate serving as a desulfurizer into a desulfurizing tower, and carrying out subsequent treatment on the obtained effluent serving as inlet water of a downstream membrane method zero-emission process.
In some embodiments, in the step (1), the retention time of the desulfurization waste water in the pre-settling tank 1 is 0.5-48h, preferably, the addition amount of the calcium oxide (which can be added in the form of lime slurry) is 50-10000mg/L, and the first flocculating agent is preferably one or more of aluminum salt, iron salt or polyacrylamide, and the addition amount is preferably 0.01-200 mg/L.
In some embodiments, in the step (2), the hydraulic retention time of the magnesium removing pool 3 is 0.5-49h, the precipitation treatment time is 0.5-48h, preferably, the magnesium removing agent is one or more of potassium hydroxide, sodium carbonate, sodium bicarbonate, calcium oxide or calcium hydroxide, the adding amount is preferably 0.5-100g/L, the dispersant is preferably one or more of sodium dodecyl benzene sulfonate, sodium pyrophosphate, polyisobutylene succinimide ashless additive or stearic acid dispersant, and the adding amount is preferably 0.01-100mg/g DS (namely sludge dry solid content).
In some embodiments, in the step (3), the hydraulic retention time of the pre-sulfur removal tank 5 is preferably 0.5 to 48 hours, and preferably, the pre-sulfur removal agent is one or more of calcium oxide, calcium hydroxide, calcium chloride, calcium chlorate, calcium bicarbonate, calcium gluconate, calcium dihydrogen phosphate, calcium nitrate, calcium hydrogen sulfate, calcium hydrogen sulfite, calcium bromide or calcium iodide, and the adding amount is preferably 0.05 to 50 g/L.
In some embodiments, in the step (4), the hydraulic retention time of the deep sulfur removal tank 7 is 0.5 to 48 hours, preferably, the deep sulfur removal agent is one or more of alumina, aluminum hydroxide, aluminum chloride or sodium aluminate, the deep sulfur removal agent is preferably added in an amount such that the molar ratio of calcium ions remaining after the reaction in the deep sulfur removal tank is 1 to 6 to sulfur in the deep sulfur removal tank 7, the molar ratio of the added aluminum ions to sulfur contained in the deep sulfur removal tank 7 is preferably 1 to 4, the second flocculant is preferably one or more of cationic, anionic or nonionic PAM, quaternary ammonium flocculant, polyamine-low molecular weight organic flocculant, and the used dispersant is the same as that in the step (2).
In some embodiments, in step (5), the hydraulic retention time in the calcium removal tank 9 is 0.5-24h, and the calcium removal agent is preferably one or more of sodium carbonate, sodium bicarbonate, potassium carbonate or ammonium bicarbonate, and the dosage of the calcium removal agent is preferably 0.05-100 g/L.
In some embodiments, the precipitates obtained in the steps (2) and (4) are dehydrated, washed, extracted and dried in the fire retardant preparation mechanism in sequence to obtain the fire retardant or the raw material of the synergistic fire retardant, and the dehydrated liquid, the cleaning waste liquid and the condensed liquid generated in the preparation process flow back to the pre-desulfurization tank 5 for continuous treatment. Preferably, the precipitate is subjected to dispersion treatment to obtain a precipitate mixed solution, the precipitate mixed solution enters a dehydrator 11, the dehydrated precipitate is washed by deionized water and then soaked at a liquid-solid ratio of 5-30, the soaked precipitate particles are dried at 30-100 ℃ for 1-48h, and the operation is repeated for 1-5 times to obtain the nano-particles. The powder of the precipitate obtained in the step (2) and the precipitate obtained in the step (4) and obtained by a flame retardant preparation mechanism can be independently used as a flame retardant, and the two can also be uniformly mixed according to the mass ratio of 0.1-100:1, and the mixture is compounded and synergistically used to improve the flame retardant effect.
The reaction principle of each part on the system of the utility model is as follows:
1) a pre-settling stage: firstly, removing suspended solid in the desulfurization wastewater, adding a small amount of lime and a coagulant aid to perform flocculation and pH adjustment, so that part of heavy metal ions form hydroxide precipitates to be removed and flow back to a cyclone, the purity of solid precipitates obtained subsequently is ensured, the recycling requirement is met, and the reaction formula is shown in (1).
Am++m(OH)-→A(OH)m↓ (1)
Wherein A ism+Is the heavy metal ions in the desulfurization waste water.
2) Magnesium removal stage: the addition of the magnesium removing agent can remove magnesium hydroxide precipitate formed by magnesium ions in the desulfurization wastewater, and the addition of the dispersing agent or the use of other physical dispersing methods can enable magnesium hydroxide particles to meet the fire retardant standard. The reaction formula is shown in (2).
Mg2++2OH-→Mg(OH)2↓ (2)
3) A pre-sulfur removal stage: sulfate ions in the wastewater are removed as far as possible by adding a pre-desulfurizing agent with a lower price. The reaction formula is shown in (3).
4) And (3) a deep sulfur removal stage: the residual sulfate radicals in the wastewater are precipitated in an ettringite form by adding a deep desulfurizing agent, and the addition of the dispersing agent can enable ettringite particles to meet the fire retardant standard. The reaction formula is shown in (4).
5) A calcium removal stage: because the pre-sulfur removal agent contains calcium ions, the hardness of the wastewater is slightly improved, and the residual calcium ions can be efficiently removed by adding the calcium removal agent. The reaction formula is shown in (5).
Wherein the crystal water content in the ettringite changes with the change of reaction conditions.
In addition, if first flocculating agent input volume is less than in preliminary sedimentation tank 1 the utility model discloses the limited range can lead to the flocculation effect not obvious, makes settlement performance and dewatering performance relatively poor. If the first flocculating agent dosage is greater than in the preliminary sedimentation tank 1 the utility model discloses the limited scope can take place the colloid guard action, leads to precipitate granule flocculation effect also relatively poor, and the too high dewatering performance variation of mud mixed liquid viscosity. If the dosage of the magnesium removing agent is less than the limited range of the utility model, the magnesium ions can be removed incompletely, and the impurity content in the sediment of the rear section is high. If the adding amount of the pre-desulfurizing agent is less than the limited range of the utility model, the concentration of the residual sulfate radical is too high. If the adding amount of the deep sulfur removal agent is too large, the impurity content in the precipitate is too high, the purity is reduced, and the treatment cost is increased. If the adding amount of the deep desulfurizing agent is less than the limited range of the utility model, the sulfate radical can not be thoroughly removed.
The above embodiments may be implemented individually, or in any combination of two or more.
In order to illustrate the examples of the present invention or the implementation method in the prior art more clearly, the following is a brief description of the examples and the flame retardant property of the desulfurization waste water desulfurization precipitate, and the examples and the drawings in the following description are only some examples of the present invention, and for those skilled in the art, other examples or drawings can be obtained according to the drawings without any inventive labor.
Example 1:
a method for preparing a flame retardant by utilizing sludge of a desulfurization wastewater zero-discharge pretreatment system is shown in the attached drawing 1, and comprises a preliminary sedimentation tank 1, a first sedimentation tank 2, a magnesium removal tank 3, a second sedimentation tank 4, a preliminary desulfurization tank 5, a third sedimentation tank 6, a deep desulfurization tank 7, a fourth sedimentation tank 8, a calcium removal tank 9 and a fifth sedimentation tank 10 which are connected in sequence. The preliminary sedimentation tank 1 is also respectively connected with a calcium oxide doser 14 and a first flocculant doser 15, the magnesium removal tank 3 is also respectively connected with a magnesium remover doser 16 and a dispersant doser 17, the preliminary desulfurization tank 5 is also connected with a preliminary desulfurization agent doser 18, the deep desulfurization tank 7 is also respectively connected with a deep desulfurization agent doser 19, a second flocculant doser 20 and a dispersant doser 17, and the calcium removal tank 9 is also connected with a calcium remover doser 21.
The method comprises the following specific steps:
(1) the desulfurization wastewater to be treated enters the pre-settling tank 1, lime slurry (namely calcium oxide) and a first flocculating agent are respectively added into the pre-settling tank 1 through a calcium oxide doser 14 and a first flocculating agent doser 15, heavy metal ion adsorption and settlement are realized through the precipitate reflowed by the deep desulfurization tank 7 and the addition of the lime slurry, and suspended matters are removed. After the sedimentation and separation of the first sedimentation tank 2, the sediment flows back to the gypsum cyclone through the sludge delivery pump.
(2) The effluent of the first sedimentation tank 2 enters a magnesium removal tank 3, and magnesium ions in the desulfurization wastewater are removed by adding a magnesium removal agent through a magnesium removal agent adding device 16. Dispersing agent is added through a dispersing agent adding device 17, and after sedimentation separation is carried out in the second sedimentation tank 4, the generated high-purity magnesium hydroxide is taken as a fire retardant raw material for recovery through dehydration, purification and drying steps.
(3) The effluent of the second sedimentation tank 4 enters a pre-desulfurizing tank 5, and a pre-desulfurizing agent is added through a pre-desulfurizing agent adding device 18 to realize the primary removal of sulfate radicals. After the mud-water mixed liquid is settled and separated by the third sedimentation tank 6, the generated calcium sulfate is precipitated and dehydrated and then is recycled as the desulfurized gypsum.
(4) The effluent of the third sedimentation tank 6 enters a deep desulfurization tank 7, a deep desulfurization agent is added through a deep desulfurization agent adding device 19 to further remove sulfate radicals, a dispersing agent is added through a dispersing agent adding device 17, a second flocculating agent is added through a second flocculating agent adding device 20, after sedimentation separation is carried out in a fourth sedimentation tank 8, part of ettringite sediments flow back to the pre-sedimentation tank 1 to adsorb heavy metal ions, and the rest ettringite sediments are taken as flame retardant raw materials to be recovered through the steps of dehydration, purification and drying.
(5) The effluent of the fourth sedimentation tank 8 enters a calcium removal tank 9, and a calcium removal agent is added through a calcium removal agent adding device 21, so that the deep removal of residual calcium ions is realized. After the mud-water mixed liquid is settled and separated by the fifth sedimentation tank 10, the generated calcium carbonate is precipitated and dehydrated and then is reused as a desulfurizer in the desulfurizing tower. And taking the effluent of the fifth sedimentation tank 10 as the influent of the subsequent membrane method zero-emission process for subsequent treatment.
(6) The crude magnesium hydroxide generated by the magnesium removal tank 3 and the crude ettringite generated by the deep sulfur removal tank 7 are dehydrated by the sludge dehydrator 11 and then discharged into the washing machine 12, the two are efficiently purified by repeated washing and soaking, and finally dried by the dryer 13. And the sludge dewatering liquid, the cleaning waste liquid and the condensate liquid generated in the purification process flow back to the pre-desulfurization tank 5. The compound production or the independent production of the magnesium hydroxide flame retardant and the synthetic hydrotalcite flame retardant can be realized by controlling the mud discharge valve.
Example 2:
on the basis of the recycling treatment process in example 1, the operating process parameters in this example are as follows:
the concentration of suspended solid in the desulfurization wastewater to be treated is 5g/L, the concentration of sulfate radical is 5500mg/L, the concentration of magnesium ion is 2500mg/L, and the pH value is 6.88. Ca is required to be achieved after treatment2+<20mg/L，Mg2+<20mg/L， SO4 2-<50mg/L, and the magnesium hydroxide and the synthetic hydrotalcite fire retardant which are respectively and independently prepared need to respectively meet the requirements of HG/T4531-2013 and HG/T4496-2013.
In the embodiment, the dosage of the calcium oxide used in the preliminary sedimentation tank 1 is 0.25g/L, the hydraulic retention time is 24h, the first flocculating agent is anionic polyacrylamide with the molecular weight more than 106Da, the adding amount is 0.5mg/L, and the reflux ratio of the sediment in the deep sulfur removal tank 7 is 10 percent. After the sedimentation separation in the first sedimentation tank 2, suspended matters in the wastewater are efficiently removed, the turbidity of effluent is 86NTU, and supernatant is discharged intoAnd a magnesium removal tank 3. Heavy metal ions were measured on the sludge (HJ/T299-2007) in the first sedimentation tank 2 according to the sulfuric acid-nitric acid method for leaching toxicity of solid waste, and the results showed that only zinc and mercury ions were detected, which were 0.017mg/L and 0.00016mg/L, respectively, and no other heavy metal ions were detected (Table 1). Therefore, the sludge generated by the first sedimentation tank 2 belongs to common solid waste and can flow back to the gypsum cyclone.
TABLE 1 analysis of heavy metal content in sludge in the first sedimentation tank 2
| Index (I) | Sludge in the first sedimentation tank 2 | HJ/T 299-2007 |
| Cr(mg/L) | |
15 |
| Ni(mg/L) | ND | 5 |
| Zn(mg/L) | 0.017 | 100 |
| Hg(mg/L) | 0.00016 | 0.1 |
| Cd(mg/L) | ND | 1 |
| As(mg/L) | ND | 5 |
The effluent of the first sedimentation tank 2 enters a magnesium removal tank 3, the hydraulic retention time is 24h, the used magnesium removal agent is sodium hydroxide, and the adding amount is 8 g/L. Sodium dodecylbenzenesulfonate was used as a dispersant in an amount of 1mg/g DS. After sedimentation separation in a second sedimentation tank 4, Mg in the wastewater2+The concentration is only 2.8mmol/L, and the supernatant is discharged into a pre-desulfurizing tank 5. According to the X-ray fluorescence spectrum analysis (Table 3), the sludge produced by the second sedimentation tank 4 does not contain heavy metals, and the mass fraction of magnesium hydroxide in the sediment is 98.8%, so that the sludge can be recycled as a magnesium hydroxide flame retardant raw material.
The effluent of the second sedimentation tank 4 enters a pre-desulfurization tank 5, the hydraulic retention time is 24 hours, the used pre-desulfurization agent is calcium oxide, and the adding amount is 5.5 g/L. After settling and separating in a third settling pond 6, SO4 2-The concentration is 14mmol/L, and the supernatant is discharged into a deep sulfur removal tank 7. According to the chemical equilibrium calculation, the mass fractions of calcium sulfate, calcium hydroxide and magnesium hydroxide in the sludge generated by the third sedimentation tank 6 are 82.9%, 15.6% and 1.4%, respectively, which meet the requirements of limestone-gypsum wet flue gas desulfurization system design regulation (DL/T5196-2016) in a thermal power plant and can be used as desulfurization gypsum to flow back to the cyclone.
The third sedimentation tank 6 enters a deep desulfurization tank 7, the hydraulic retention time is 24 hours, the used deep desulfurization agent is sodium metaaluminate, the deep desulfurization agent is added according to the Al/S ratio of 2.5, the type and the adding amount of the dispersing agent are the same as those of the magnesium removal tank 3, the type and the adding amount of the flocculating agent are the same as those of the preliminary sedimentation tank 1, and the adding amount is 2.5mg/g DS. After sedimentation separation in a fourth sedimentation tank 8, SO4 2-The concentration is 0.4mmol/L, and the supernatant is discharged into a calcium removal tank 9. According to the X-ray fluorescence spectrum analysis (Table 3), the sludge produced by the fourth sedimentation tank 8 does not contain heavy metals, and the mass fraction of ettringite in the sediment is 88.1 percent, so the sludge can be used as a synthetic hydrotalcite fire retardant sourceAnd (5) recovering the material.
The effluent of the fourth sedimentation tank 8 enters a calcium removal tank 9, the hydraulic retention time is 12h, the used calcium removal agent is sodium bicarbonate, and the adding amount is 0.28 g/L. After sedimentation separation in a fifth sedimentation tank 10, Ca2+The concentration is only 0.04mmol/L, and the supernatant can be used as the inlet water of the subsequent zero-emission process. As can be seen from the X-ray energy spectrum analysis (EDS) (Table 2), the precipitate does not contain heavy metals, and meets the requirements of DL/T5196-.
TABLE 2 sludge EDS of the fifth settling tank 10
| Element(s) | Mass ratio (%) | Element ratio (%) |
| O | 48.22 | 59.84 |
| C | 11.43 | 19.88 |
| Ca | 40.35 | 20.28 |
| In total (%) | 100.00 | 100.00 |
The crude magnesium hydroxide generated by the magnesium removal tank 3 and the crude ettringite generated by the deep sulfur removal tank 7 are respectively discharged to the sludge dewatering machine 11 to be dewatered at the rotating speed of 2000r/min, and the differential speed is respectively 1.8 percent and 2.3 percent. Then discharged into an industrial washing machine 12, washed repeatedly for 3 times and soaked for 30min to realize the high-efficiency purification of the two, and finally dried by a dryer 13 at 60 ℃ for 8h to obtain solid flame retardant particles. And (5) drying.
TABLE 3 XRF analysis of the precipitate (% by weight, calculated as element)
| Element(s) | Ca | Al | Mg | O | H | S |
| Crude Mg (OH)2 | 0.65 | 0 | 40.88 | 40.88 | 3.44 | 0 |
| Refined Mg (OH)2 | 0.37 | 0 | 41.10 | 41.10 | 3.44 | 0 |
| Coarse ettringite | 20.31 | 5.70 | 0 | 62.36 | 4.88 | 6.75 |
| Fine ettringite | 19.28 | 4.68 | 0 | 63.52 | 5.06 | 7.46 |
XRF analysis (Table 3) showed that the magnesium hydroxide and ettringite contents were elevated. And the sludge dewatering liquid, the cleaning waste liquid and the condensate liquid generated in the purification process flow back to the pre-desulfurization tank 5. The properties of the precipitate obtained in this example are shown in tables 4 and 5 in comparison with the national flame retardant standards.
TABLE 4 comparison of magnesium hydroxide flame retardant standards with HG/T4531-2013
| Magnesium hydroxide flame retardant standard | The obtained magnesium hydroxide precipitate | |
| Mass fraction/% of magnesium hydroxide | ≥97.5 | 99.8 |
| Calcium oxide mass fraction/%) | ≤0.10 | 0.084 |
| Water content/%) | ≤0.5 | 0.47 |
| Mass fraction of chloride/% | ≤0.10 | 0.09 |
| Laser particle size/mum | 0.5-1.5 | 1.28 |
| Loss on ignition/%) | ≥30.0 | 37.1 |
| Whiteness degree | ≥95 | 95.9 |
TABLE 5 comparison of synthetic hydrotalcite flame retardant standards with HG/T4496-containing 2013
| Ettringite fire retardant standard | The obtained ettringite precipitate | |
| Agglomeration index | ≤50 | 36 |
| Alumina mass fraction/%) | 14.6-18.9 | 18.6 |
| Heavy metals (in Pb)/%) | ≤0.001 | 0.00046 |
| Iron mass fraction/% | ≤0.05 | 0.008 |
| pH (20g/L) suspension | 7.0-9.0 | 8.9 |
| Whiteness degree | ≥90 | 92 |
| Dry weight loss (105 ℃ C.)/%) | ≤0.5 | 0.44 |
FIG. 3 is a FT-IR spectrum of the ettringite precipitate in the fourth settling pond 8 in example 2, the FT-IR spectrum showing that there are-OH, Ca-OH-Ca, Ca-OH-Al and Al-OH-Al bonds in the precipitate, which are broken when the material is burned, and thus the flame retardant effect is obtained;
FIG. 4 shows the particle size and thermogravimetric analysis of the magnesium hydroxide and ettringite precipitates of example 2, and it can be seen from FIG. 4(a) that both particle sizes are smaller than 5 μm. As shown in FIG. 4(b), the deep desulfurization unit precipitates show endothermic peaks above 80 ℃ during thermogravimetric analysis due to the change of the precipitates in conversion to calcium sulfoaluminate monosulfide; free water in the precipitate is gradually lost at 80 ℃; Ca-SO in the precipitate at 150 deg.C4Key position decomposition will occur; then the Al-OH-Al bond is broken at 250 ℃ and converted into Al2O3(ii) a The chemical changes at 300-500 ℃ are mainly the bond breakage of-OH, Ca-OH-Ca, Ca-OH-Al and the like in the precipitate, and the properties all indicate that the desulfurization waste water desulfurization precipitate has the condition of being used as a flame retardant.
Example 3:
compared to example 2, most of them are the same, except that in this example: the adding amount of calcium oxide in the preliminary sedimentation tank 1 is 300 mg/L; adding sodium hydroxide into the magnesium removing pool 3, wherein the adding amount is 10 g/L; 6g/L of calcium hydroxide is added into the pre-desulfurization tank 5; the deep desulfurization pool 7 adds aluminum hydroxide with a molar ratio Al/S of 0.8, and the reflux ratio is 15 percent; washing 10g of crude magnesium hydroxide or ettringite precipitate with deionized water for 4 times, and soaking in deionized water at a liquid-solid ratio of 4 for 10 min. Tables 6 and 7 prove that the precipitate generated by the desulfurization wastewater treatment can meet the fire retardant standard, and further illustrate that different reaction conditions have certain influence on the purity of the precipitate, and the reaction conditions of the process need to be strictly controlled, so that the obtained precipitate meets the national fire retardant standard.
TABLE 6 comparison of magnesium hydroxide flame retardant standards with HG/T4531-2013
TABLE 7 comparison of synthetic hydrotalcite flame retardant standards with HG/T4496-containing 2013
| Ettringite fire retardant standard | The obtained ettringite precipitate | |
| Agglomeration index | ≤50 | 46 |
| Alumina mass fraction/%) | 14.6-18.9 | 14.8 |
| Heavy metals (in Pb)/%) | ≤0.001 | 0.0005 |
| Iron mass fraction/% | ≤0.05 | 0.012 |
| pH (20g/L) suspension | 7.0-9.0 | 8.5 |
| Whiteness degree | ≥90 | 92.6 |
| Dry weight loss (105 ℃ C.)/%) | ≤0.5 | 0.44 |
In the same way, if different reagents are adopted in the magnesium removal tank 3 in the embodiment, the desulfurization wastewater is adjusted to 11.0, the mass fraction of the obtained magnesium hydroxide is more than or equal to 97.5%, but impurities in the precipitate may increase, and the washing times need to be increased to meet the requirements of actual production. In the deep sulfur removal tank 7, other agents are adopted, and the precipitate can meet the flame retardant standard, but the purity is possibly low, the mass fraction of chloride ions is possibly increased, and the production requirement can be met only by increasing the adding amount and increasing the content of the precipitate.
Example 4:
compared with the embodiment 2, the fire retardant is mostly the same, except that the fire retardant produced in the embodiment is prepared by compounding magnesium hydroxide and ettringite according to the mass ratio of 1: 2. The LOI value of the magnesium hydroxide flame retardant prepared from the pretreatment system was slightly higher than that of the synthetic hydrotalcite flame retardant as determined by Limiting Oxygen Index (LOI) (FIG. 5) analysis. The LOI value of the synergistic flame retardant compounded by the two is higher, and the LOI value is continuously increased along with the increase of the mixing rate, and when the mixing rate reaches 60 percent, the LOI value is increased to 34 percent. The actual flame retardant effect of the EVA material is verified, and the phenomenon that the EVA material melts and drips disappears along with the increase of the doping ratio of the synergistic flame retardant material, so that the formed carbon layer is more compact, the flame retardant effect is better, and the analysis result is consistent with the LOI analysis result.
To sum up, the utility model provides an utilize method of desulfurization waste water zero release pretreatment systems mud preparation fire retardant, carry out resource utilization with the produced mud of each unit of desulfurization waste water zero release pretreatment technology, and magnesium hydroxide and ettringite are surveyd as the use of fire retardant in coordination to the repeated point, when guaranteeing follow-up embrane method zero release technology steady operation, realize the abundant resource utilization of mud, have apparent economy and environmental benefit.
The embodiments described above are intended to facilitate the understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention according to the disclosure of the present invention.
Claims (10)
1. The utility model provides a coal fired power plant desulfurization waste water's resourceful pretreatment system, its characterized in that includes along desulfurization waste water advancing direction the preliminary sedimentation pond that connects gradually, removes the magnesium pond, removes sulphur pond, degree of depth sulphur pond and removes the calcium pond in advance, wherein, the bottom that removes the magnesium pond and degree of depth sulphur pond deposits the export and still connects fire retardant preparation mechanism, the bottom that removes the calcium pond deposits the export and still connects outside desulfurizing tower.
2. The coal-fired power plant desulfurization wastewater resource pretreatment system as recited in claim 1, wherein the bottom precipitation outlet of the preliminary sedimentation tank and the preliminary desulfurization tank is further connected with an external gypsum cyclone.
3. The coal-fired power plant desulfurization wastewater resource pretreatment system as recited in claim 1, wherein the bottom precipitation outlet of the deep desulfurization tank is also connected back to the inlet of the pre-precipitation tank.
4. The coal-fired power plant desulfurization wastewater resource pretreatment system as recited in claim 1, wherein the fire retardant preparation mechanism is further connected back to the pre-desulfurization tank.
5. The resource pretreatment system for desulfurization wastewater of coal-fired power plant according to claim 1, characterized in that the fire retardant preparation mechanism comprises a dehydrator, a washing machine and a dryer which are sequentially connected along the direction of precipitate treatment.
6. The coal-fired power plant desulfurization wastewater resource pretreatment system of claim 1, characterized in that the preliminary sedimentation tank is further connected with a calcium oxide doser and a first flocculant doser;
the magnesium removal tank is also connected with a magnesium removal agent doser and a dispersing agent doser.
7. The coal-fired power plant desulfurization wastewater resource pretreatment system of claim 1, characterized in that the pre-desulfurization tank is further connected with a pre-desulfurization agent doser.
8. The resource pretreatment system for desulfurization wastewater of coal-fired power plant according to claim 1, characterized in that the deep desulfurization tank is further connected with a dispersant doser, a deep desulfurization agent doser and a second flocculant doser.
9. The resource pretreatment system for desulfurization wastewater of coal-fired power plant as recited in claim 1, wherein the calcium removal tank is further connected with a calcium remover doser.
10. The coal-fired power plant desulfurization wastewater resource pretreatment system as recited in claim 1, characterized in that a first sedimentation tank is further provided between the preliminary sedimentation tank and the magnesium removal tank, a second sedimentation tank is further provided between the magnesium removal tank and the preliminary desulfurization tank, a third sedimentation tank is further provided between the preliminary desulfurization tank and the deep desulfurization tank, a fourth sedimentation tank is further provided between the deep desulfurization tank and the calcium removal tank, and a fifth sedimentation tank is further provided behind the calcium removal tank.
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