Patent Application
20090082607
1. Field of the Invention
The present invention generally relates to a method for treating waste water and a system of treating waste water, and more particularly, to a method for treating fluoride-containing waste water and a system of treating waste water.
2. Description of Related Art
In the industry practices, for example, fabricating glass, plating process, refining aluminum and steel, and process of semiconductor device, fluoride is popularly and largely used, from which an issue of treating fluoride-containing waste water is derived. In order to avoid fluorine ions (F−) to contaminate our environment and to make the industrious water effluent meet the relevant emission standard for hazardous waste worked out by government, many efforts have been made intending to minimize the negative impact of industrious water effluent on the environment.
In general speaking, a technique for treating fluoride-containing waste water includes chemical coagulation method and fluidized bed crystallization (FBC) method. The chemical coagulation method is based on the fluorine ions (F−) concentration in fluoride-containing waste water where calcium compound solution with an appropriate concentration is added into to form insoluble calcium fluoride (CaF2) compound, following by adding coagulant and coagulant aid to coagulate, flocculate and precipitate the compound. Thereafter, the CaF2 compound can be separated. By using the FBC method, waste water and calcium compound are purred into a specifically-designed fluidized bed reaction tank, where under a strict and accurate program control the calcium fluoride would be crystallized on supports, the crystals would be gradually grown and finally be separated from the fluoride-containing waste water.
Since the component complexity of fluoride-containing waste water which contains also other kinds of chemicals except for waste fluoride acid, such as waste sulfuric acid and waste phosphonic acid, thus, the above-mentioned treating procedure is not perfected and some bottlenecks hard to be solved are remained. For example, the FBC method is quite sensitive to the interferences of sulfate (SO42−) and phosphate (PO43−). That is to say, the waste sulfuric acid and the waste phosphonic acid in the fluoride-containing waste water would suppress the removing efficiency of fluorine ion (F−) which makes the waste water after the treating fail to meet an expected standard.
In terms of chemical coagulation method, the encountered problem is, for example, the dirt of calcium fluoride (CaF2) is easily built up on the inner walls of a waste water reaction tank and the pipelines thereof. Thus, the waste water reaction tank must be aperiodically cleaned up while shutting down the machines, which affects the treating speed of fluoride-containing waste water. If the dirt-depositing problem is serious, the efficiency of treating the fluoride-containing waste water in a tank body would be deteriorated and the lifetime in years of the treating equipment would be shortened.
In addition, if the fluoride acid (HF) concentration is unknown, calcium compound in excess of quantities may be added to enhance the chance of producing fluorine ions (F−) and calcium salt. As a consequence, the residual amount of calcium in waste water must be high-deflected in the successive treating process of waste water.
Moreover, in order to enhance the collision chance between molecules, the usage amount of the coagulant and the coagulant aid must be increased in the successive coagulation and flocculation process. Accordingly, the yield of fluorine-family hazardous sludge would be largely increased, which makes the cost for cleaning up, transporting and processing the hazardous waste.
Accordingly, the present invention is directed to provide a method for treating fluoride-containing waste water, which can effectively lighten the dirt-depositing problem on the walls of a reaction tank, largely reduce the usage amounts of calcium compound, coagulant and coagulant aid, the yield of sludge, lower the cost of treating waste water and make the treated fluoride-containing waste water meet the relevant emission standard for hazardous waste regardless of whether the water quality of the incoming fluoride-containing waste water.
The present invention is directed also to provide a crystallizing tank of waste water, capable of effectively treating the waste water with unstable water quality, lowering the chemical dosages of coagulant and coagulant aid, producing less sludge, lowering the cost for treating waste water, lengthening the lifetime of an equipment of treating waste water and making the discharged waste water from the crystallizing tank of waste water pass the relevant emission standard for hazardous waste.
The present invention is directed further to provide a system of treating waste water, which requires less coagulant and coagulant aid to effectively precipitate the contaminant in waste water, produces less sludge and effectively lowers operation cost of treating waste water and sludge.
The present invention provides a method for treating fluoride-containing waste water. First, fluoride-containing waste water and calcium compound are poured into a crystallization reaction tank having multiple crystallizing webs for a reaction between the fluoride-containing waste water and calcium compound so as to form calcium fluoride (CaF2) crystals on the crystallizing webs. The fluoride-containing waste water and the calcium compound are stirred. Then, the fluoride-containing waste water is drained out of the crystallization reaction tank to conduct the successive process steps.
In an embodiment of the present invention, the material of the above-mentioned crystallizing web is, for example, stainless steel 316 or nickel chromium molybdenum steel.
In an embodiment of the present invention, the above-mentioned crystallizing webs in the crystallization reaction tank are, for example, arranged in parallel to each other.
In an embodiment of the present invention, the surfaces of the above-mentioned crystallizing webs are, for example, arranged in perpendicular to or parallel to the bottom of the crystallization reaction tank.
In an embodiment of the present invention, the above-mentioned calcium compound is, for example, calcium hydroxide (Ca(OH)2) or calcium chloride (CaCl2).
In an embodiment of the present invention, the above-mentioned process steps include following steps, for example. First, the fluoride-containing waste water and the calcium compound are poured into a reaction tank to create calcium fluoride (CaF2) by a reaction between the fluoride-containing waste water and the calcium compound. Next, the fluoride-containing waste water and coagulant are poured into a coagulating tank to coagulate the calcium fluoride (CaF2). Then, the fluoride-containing waste water and coagulant aid are poured into a flocculating tank, and the fluoride-containing waste water is stirred for forming calcium fluoride flocs in the waste water. Further, the fluoride-containing waste water is poured into a sludge-precipitating tank.
In an embodiment of the present invention, the above-mentioned coagulant is, for example, aluminum salt or iron salt.
In an embodiment of the present invention, the above-mentioned coagulant aid is, for example, macromolecule polymer.
In an embodiment of the present invention, the above-mentioned method further includes a step of removing the calcium fluoride (CaF2) crystals on the crystallizing webs by shaking the crystallizing webs to drop the calcium fluoride (CaF2) crystals off from the crystallizing webs.
By using the method for treating fluoride-containing waste water of the present invention, the calcium fluoride (CaF2) crystals formed after a reaction between the fluorine ions and calcium compound dwell on the crystallizing webs in the crystallization reaction tank, which is able to effectively reduce the dirt-depositing on the inner walls of a waste water reaction tank and the pipelines thereof.
In addition, since most of the fluorine ions (F−) have been reacted with the calcium compound on the crystallizing webs to form the calcium fluoride (CaF2) crystals, thus, the chemical dosages of coagulant and coagulant aid can be reduced in the successive treating steps and the yield of sludge is lowered, which contribute to effectively lower the cost of treating fluoride-containing waste water.
The present invention also provides a crystallizing tank of waste water suitable for a system of treating waste water. The crystallizing tank includes a tank body, a crystallizing device, an agitator, an inlet pipeline of waste water, an outlet pipeline of waste water, and an agent-feeding line. The crystallizing device is disposed in the tank body and includes a shaking part, a supporting part and multiple crystallizing webs. The supporting part connects the shaking part. The crystallizing webs are disposed on the supporting part. The agitator is disposed in the tank body. The inlet pipeline of waste water is connected between the tank body and a tank of raw waste water. The outlet pipeline of waste water is connected between the tank body and a reaction tank of waste water of the system of treating waste water. The agent-feeding line is disposed on the tank body.
In an embodiment of the present invention, the material of the above-mentioned crystallizing web is, for example, stainless steel 316 or nickel chromium molybdenum steel.
In an embodiment of the present invention, the above-mentioned crystallizing webs in the tank body are, for example, arranged in parallel to each other.
In an embodiment of the present invention, the surfaces of the above-mentioned crystallizing webs are, for example, arranged in perpendicular to or parallel to the bottom of the tank body.
In an embodiment of the present invention, the above-mentioned agitator is, for example, propeller type agitator, paddle type agitator or turbine type agitator.
The present invention makes the portion to be removed (for example, fluorine ions) in waste water react with a specific chemical (for example, calcium compound) to create crystals (for example, calcium fluoride (CaF2) crystals) on the crystallizing webs, thus, the dirt-depositing on the inner walls of the reaction tank and in the pipelines thereof can be improved. Besides, the crystallizing tank of waste water of the present invention has removed most of hazardous substance in the waste water, thus, the dosages of the chemicals in the successive process, such as coagulant and coagulant aid, can be saved, and the sludge yield is reduced, which effectively save the cost of treating waste water.
The present invention further provides a system of treating waste water, which includes a tank of raw waste water, a crystallizing tank of waste water; a reaction tank of waste water, a coagulating tank, a flocculating tank and a sludge-precipitating tank. The crystallizing tank of waste water connects the tank of raw waste water and includes a tank body, a shaking part, a supporting part, multiple crystallizing webs, an agitator and an agent-feeding line. The crystallizing webs are disposed on the supporting part. The agitator is disposed in the tank body. The reaction tank of waste water connects the crystallizing tank of waste water. The coagulating tank connects the reaction tank of waste water. The flocculating tank connects the coagulating tank. The sludge-precipitating tank connects the flocculating tank.
In an embodiment of the present invention, the material of the above-mentioned crystallizing web is, for example, stainless steel 316 or nickel chromium molybdenum steel.
In an embodiment of the present invention, the above-mentioned crystallizing webs in the tank body are, for example, arranged in parallel to each other.
In an embodiment of the present invention, the surfaces of the above-mentioned crystallizing webs are, for example, arranged in perpendicular to or parallel to the bottom of the tank body.
In an embodiment of the present invention, the above-mentioned coagulating tank further includes a first pipeline for pouring coagulant into the coagulating tank.
In an embodiment of the present invention, the above-mentioned coagulant is, for example, aluminum salt or iron salt.
In an embodiment of the present invention, the above-mentioned flocculating tank further includes a second pipeline for pouring coagulant aid into the flocculating tank.
In an embodiment of the present invention, the above-mentioned coagulant aid is, for example, macromolecule polymer.
The system of treating waste water of the present invention uses the crystallizing tank of waste water to remove most of the hazardous substance in the waste water and make the hazardous substance crystallized in solid form, then conducts successive chemical coagulating, flocculating and precipitating processes. Since after the treating by the crystallizing tank of waste water, the concentration of suspended solid particles is largely diluted, thus, the usage amounts of the coagulant and the coagulant aid are saved and the sludge yield is significantly reduced. On the whole, the present invention is advantageous in significantly lowering the operation cost for treating waste water and agent-saving, time-saving and advancing chemical reaction efficiency.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
Referring to
Continuing to
The material of the above-mentioned crystallizing web 144 is, for example, stainless steel 316 or nickel chromium molybdenum steel. The number of the disposed crystallizing webs 144 depends on a real need. The crystallizing webs 144 are arranged in parallel to each other in the tank body 120, while the surfaces of the crystallizing webs 144 are arranged, for example, either in perpendicular to the bottom of the tank body 120 or parallel to the bottom thereof.
The fluoride-containing waste water in the tank body 120 induced through the inlet pipeline of fluoride-containing waste water 126 contacts the calcium compound induced through the agent-feeding line 130 would at the contacting instant be reacted with each other to form calcium fluoride (CaF2) crystals 146 in solid form on the crystallizing webs 144. The newly formed calcium fluoride crystals 146 serve as supports and play a roll of seed crystal cores, which would catalyst the successive chemical reaction to create calcium fluoride attached on the crystallizing webs 144 and the calcium fluoride crystals 146. In other words, the crystallizing webs 144 and the calcium fluoride crystals 146 at the time are served as the major chemical reaction area between the fluorine ions and calcium ions. This is why the crystallizing device 122 is able to effectively remove the most of fluorine ions in the fluoride-containing waste water regardless of whether the water quality of the fluoride-containing waste water in the tank body 120 is stable or not, which is helpful to maintain the water quality of the fluoride-containing waste water output to the reaction tank of fluoride-containing waste water 106 stable and keep the concentration of the fluorine ions therein low. As a consequence, the embodiment is able to reduce the calcium compound and the dosages of the coagulant and the coagulant aid in the successive process and largely lighten the dirt-depositing problem on the tank walls and in the pipelines of the system of treating waste water 100.
Note that the crystallizing device 122 includes a mechanism for removing the calcium fluoride crystals 146 on the crystallizing webs 144. In an embodiment, a programmable logic controller (PLC) (not shown) is used to electrically connect the third control valve 138 and the shaking part 140. To remove the calcium fluoride crystals 146 on the crystallizing webs 144, the PLC starts up the shaking part 140 so as to make the shaking part 140 reciprocate for swaying the crystallizing webs 144 on the supporting part 142; thus, the calcium fluoride crystals 146 on the crystallizing webs 144 would be dropped off to the bottom of the tank body 120 due to the gravity effect and the swaying action of the shaking part 140. Whenever the system of treating waste water 100 is on standby, the PLC starts up the third control valve 138 to remove the calcium fluoride crystals 146 on the bottom of the tank body 120. The crystallizing device 122 certainly can have a moving device (not shown) to move out the multiple crystallizing webs 144 from the crystallizing tank of fluoride-containing waste water 104. After the multiple crystallizing webs 144 is moved out of the crystallizing tank of fluoride-containing waste water 104 by the moving device and placed in another collecting tank (not shown), the shaking part 140 is used again to make the calcium fluoride crystals 146 on the crystallizing webs 144 dropped off to the collecting tank, following by collecting the dropped calcium fluoride crystals.
Continuing to
After the pre-treating of the crystallizing tank of fluoride-containing waste water 104, the fluoride-containing waste water sequentially flows through the reaction tanks of fluoride-containing waste water 106 and 108. In an embodiment, the calcium compound would be poured into the reaction tanks of fluoride-containing waste water 106 and 108 respectively through the first agent-pouring pipeline 148 and the second agent-pouring pipeline 150 and would react with the fluorine ions in the fluoride-containing waste water to create calcium fluoride (CaF2) solids.
The fluoride-containing waste water induced into the coagulating tank 110 would conduct coagulating reaction with the coagulant added through the third agent-pouring pipeline 152 and 10% hydrochloric acid (HCL) or 10% sodium hydroxide (NaOH) added through the fourth agent-pouring pipeline 154 to form calcium fluoride flocs, wherein the coagulant is, for example, 10% aluminium salt or iron salt. The pH of the fluoride-containing waste water is kept at pH 6-8 by adding hydrochloric acid or the sodium hydroxide so as to enhance the coagulating effect.
The fluoride-containing waste water in the flocculating tank 112 would react with the coagulant aid poured from the fifth agent-pouring pipeline 156 to make the calcium fluoride flocs grown to facilitate further depositing. In an embodiment, the coagulant aid is, for example, macromolecule polymer with a percent of weight, for example, 33%. The sludge-precipitating tank 114 is for settling the calcium fluoride sludge. The sludge-concentrating tank 115 is for lowering the water content of the calcium fluoride sludge and shrinking the sludge. In an embodiment, the sludge-concentrating tank 115 is a gravity concentrating tank. The calcium fluoride sludge after dewatering is delivered to the machine for making sludge cake 116, where sludge cakes are made to make transporting and processing the sludge in the successive procedure more convenient.
Since the system of treating waste water 100 of the present invention employs the crystallizing tank of fluoride-containing waste water 104 and the crystallizing webs 144 in the crystallizing tank of fluoride-containing waste water 104, the dirt-depositing of the system of treating waste water 100 is improved. Besides, the fluoride-containing waste water after being treated by the crystallizing tank of fluoride-containing waste water 104 has a lower concentration of fluorine ions and a lower concentration of suspended solids, therefore, the dosages of the calcium compound, the coagulant and the coagulant aid are reduced along with a less yield of the sludge, which result in a less cost for treating the fluoride-containing waste water and a lighter burden for treating the sludge waste.
The method for treating fluoride-containing waste water would be depicted hereinafter based on an example of the system of treating waste water 100.
Continuing to
Note that the crystallizing web 144 can hold up the calcium fluoride crystals (CaF2) 146 and makes them attached on the crystallizing web 144. The initially formed calcium fluoride crystals (CaF2) 146 function like supports to attract incoming calcium fluoride crystals (CaF2) 146 produced in the successive reactions, so that the incoming calcium fluoride crystals (CaF2) 146 dwell on the crystallizing web 144 and the existed calcium fluoride crystals (CaF2) 146. Along with a time history and the growing of the calcium fluoride crystals (CaF2) 146, the fluorine ions (F−) would be effectively removed. Since most of the calcium fluoride crystals (CaF2) 146 are built up on the crystallizing web 144, thus, the dirt-depositing on the various reaction tank bodies and the pipeline thereof in the system of treating waste water 100 can be improved, which is further helpful to lengthen the lifetime years of the system of treating waste water 100. In addition, the major chemical reactions to remove the fluorine ions (F−) occur on the crystallizing web 144. In fact, the crystallizing web 144 and the calcium fluoride crystals (CaF2) 146 thereon are contributed to increase the chance of creating the calcium fluoride crystals (CaF2) 146 by reacting between the fluorine ions (F−) and the calcium compound. As a result, the dosages of the calcium compound in the reaction tanks of fluoride-containing waste water 106 and 108 are largely lowered.
While the fluoride-containing waste water and the calcium are pouring, the fluoride-containing waste water and the calcium compound are stirred and mixed up by the agitator 124, which enhances the collision chance between the fluorine ions (F−) (not on the crystallizing web 144 and still free from reacting with the calcium compound) and the calcium compound, so as to reduce the concentration of the fluorine ions (F−) in the crystallizing tank of fluoride-containing waste water 104 as much as possible.
The method for treating fluoride-containing waste water of the present invention also includes removing the calcium fluoride crystals (CaF2) 146 on the crystallizing web 144. In an embodiment, a programmable logic controller (PLC) (not shown) is used and electrically connected to the shaking part 140 and the third control valve 138. Whenever to clean up the calcium fluoride crystals (CaF2) 146 on the crystallizing web 144, the PLC starts up the shaking part 140 to vibrate the crystallizing web 144; meanwhile, the calcium fluoride crystals (CaF2) 146 would be dropped off from the crystallizing web 144 and fall to the bottom of the tank body 120 by means of gravity effect and the regular shake of the crystallizing web 144. When the system of treating waste water 100 is on standby, the PLC turns on the third control valve 138 at the bottom of the tank body 120, so as to move the calcium fluoride crystals (CaF2) out of the tank body 120 via the crystals-outputting pipeline 132.
After that referring to
In summary, the present invention has at least following advantages:
1. Most of calcium fluoride crystals are grown on the crystallizing web, thus, the present invention is able to improve the dirt-depositing of the reaction tank body and the pipelines and further lengthen the lifetime years of the equipment of treating fluoride-containing waste water.
2. The crystallizing web is able to enhance the chance of creating the calcium fluoride, which contributes to largely reduce the dosage of the calcium compound in the reaction tank of waste water.
3. When the fluoride-containing waste water flows through the crystallizing web, the concentration of the suspended solids in the water is reduced, this is helpful to lower the usage amounts of the coagulant and the coagulant aid required by the successive chemical coagulating process.
4. The present invention produces less sludge than the prior art.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
