Mining, steel wastewater treatment technology
The rapid development of modern industry, the problems that come with it are more prominent than one. Treatment of industrial steel plant wastewater in what ways? For the current production process analysis of China's steel industry. There are steel materials to choose from, including sintering, iron making, steel making and other production processes. The resulting steel waste water comes from the production process water and some set water, cooling water, washing water and so on. The indirect cooling water is only contaminated by heat during use, and can be reused after being cooled; the direct cooling water is directly contacted with the product materials, and contains pollutants, which can be reused or cascaded after being treated.
Mining wastewater treatment:
The characteristics of mine wastewater are large changes in water quantity and water quality, and the wastewater is acidic. It is necessary to reasonably determine the treatment scale of the mine wastewater, and the fluctuation of the water quality of the treated water should not be too large. It is often necessary to set up a regulating pool and regulate the reservoir, first collecting the water and then processing it. The mine wastewater is a sulfuric acid type wastewater, generally having a pH of 1.5 to 6. Such a low sulfuric acid content obviously has no recovery value, and therefore a neutralization treatment method is often used. For the treatment of mine acid waste water, the lime neutralization method is generally adopted.
The use of lime to neutralize the change of water quality of mine acid waste water, the use of lime to neutralize the water quality change of acidic wastewater, the original water quality treatment, the appearance of yellow turbid clarified colorless lime is too high, and the pH value is 2~3 9~12, which is appropriately reduced. Control pH arsenic / (mg / L) 1.6 0.003 ~ 0.2 value of 8 ~ 9 fluorine / (mg / L) 10 0.8 ~ 1.0 total iron / (mg / L) 926 0.03 ~ 0.22 lime dosage / (g / L) 5~6 In view of the fact that Fe(OH)3 is much better than Fe(OH)2 in precipitation and dewatering performance, in order to reduce the ability to treat structures and equipment, it is aerated or catalyzed by nitric oxide, and then neutralized with lime. It can improve the sedimentation effect and the effluent quality. The treatment of acid waste water in mines is inseparable from the neutralization method. The commonly used neutralizers are limestone and lime. Because other neutralizers are not expensive, the Ca2+ in the treated water is often high or saturated. Special attention should be paid to the problem of water quality stabilization, otherwise it will cause blockage of pipes and equipment and bring more losses to production. The second section of the sinter plant wastewater treatment and reuse sintering process is to mix the mineral powder, fuel and solvent in a certain proportion, mix, and then ignite and burn at high temperature, using the high temperature generated by the combustion of the fuel, so that the mixture Local melting, the bulk particles are bonded into a massive sintered ore, as a raw material for iron making, while removing harmful impurities such as sulfur, arsenic, zinc , lead , etc. during the combustion process. The sintered ore is cooled, crushed and sieved to form 5~50mm granular material and sent to the blast furnace for smelting.
Sources of wastewater and water quality, water volume Sintering plant wastewater mainly comes from wet dust removal drainage, flushing floor water and equipment cooling drainage. Wet dewatering contains a large amount of suspended solids, which can be used in cascade or recycled after treatment. If discharged, it must be treated to meet discharge standards; flushing floor water is intermittent drainage, high suspended matter content, and contains large particulate materials. After purification, it can be recycled; equipment cooling water, water quality is not contaminated by dirt, only the water temperature rises (called heat pollution), after cooling treatment, generally can be recycled and reused. Therefore, the wastewater pollution of the sinter plant mainly refers to the wastewater containing high suspended matter. If it is directly discharged without treatment, it will be more harmful, and waste water resources and a large amount of useful materials that can be recycled. After the sedimentation and concentration of the sinter plant wastewater, the sludge has a high iron content and has a good recovery value.
Wastewater treatment method:
The main goal of the sinter plant wastewater treatment is to remove suspended solids, in other words, the treatment of dust removal and washing wastewater. The main technical difficulty in the treatment of such wastewater is sludge dewatering. After the sedimentation of the sinter plant wastewater, the sludge contains high iron grade and precipitates quickly, but it is difficult to dewater due to certain viscosity. The advanced degree of process equipment in China's sinter plants is very different, and the wastewater treatment process also coexists. There are five kinds of wastewater treatment processes commonly used in China: the advection sedimentation tank dispersion treatment process, the concentrated concentration sludge treatment process, the centralized concentration zipper treatment process, the concentrated concentration vacuum filter (or filter press) treatment process, and concentration. Concentrated integrated treatment process.
Advection sedimentation tank dispersion treatment process:
This is a simple, “old†treatment process, mostly for the extension of the legacy facilities. It is currently used in some workshops of small and medium-sized sintering plants or large-scale sintering plants. The mud cleaning method also introduces mechanical equipment, such as Chain scraper or mechanical grab crane. Concentrated concentrated sludge treatment process This process is a common process in small and medium sized sintering plants. The sinter plant wastewater enters the concentration tank first, and the bottom sediment sludge after concentration and sedimentation is sent to the thick mud bucket for treatment by the sand pump. The thick mud bucket is a structure built on the backing belt. In the thick mud bucket, the sludge is generally allowed to stand for 3 to 6 days. If the time is too long, the sludge will be compacted, which will make the sludge difficult to drain. If the time is too short, the sludge will contain too much aluminum . The mud discharge is done by a screw propeller. The concentrated concentrated sludge treatment process is an effective way to treat the wastewater of the sinter plant. At present, many small and medium-sized plants in China have adopted not only improved drainage water quality, but also recovered useful materials; but it is not suitable for large-scale sintering plants. Other processes. Concentrated concentrated zipper processing technology This method is characterized by the water quality after treatment can reach the water quality requirements of circulating water, and the sludge zipper ensures the continuity of sludge discharge.
The overflow water of the concentration tank is for recycling. The concentrated bottom sludge is discharged into the zipper and re-precipitated in the zipper. The precipitated sludge is transferred from the zipper to the returning belt and sent to the mixing ingredients. The water content can reach 20% to 30%, and the overflow water of the zipper machine is returned to the concentration tank. Concentrated concentrated vacuum filtration (or pressure filtration) process The concentrated concentration treatment in the front part of the method is basically the same as the above, and the latter part of the sludge treatment uses a vacuum filter (or a filter press). In recent years, through industrial tests, the belt filter press has a good effect in sludge dewatering in the sinter plant, providing a new choice for design. Centralized concentration and comprehensive treatment Centralized concentration and comprehensive treatment is a more advanced process for wastewater treatment in sinter plants. It is characterized by different measures according to the water quality, in order to achieve the most effective reuse and reduce the effluent discharge.
Sintering plant wastewater treatment technology and development trend With the development of steel industry technology, the sintering plant process tends to increase the size of the belt sintering machine. For the dust removal equipment of large factories, electric precipitators are often used, thus replacing the wet dedusting, and the main wastewater of the sintering plant is fundamentally solved. From the actual situation in China, the wet dust removal equipment should be used in a long period of time and in a large range. Therefore, it is necessary to study new methods and new processes for wastewater treatment. According to the analysis of the development situation at home and abroad, the development trend of the wastewater treatment technology of the sinter plant can be summarized as follows.
Strengthening the treatment and implementing the wastewater generated by the re-use water technology sintering plant, generally do not contain toxic and harmful pollutants, and can be recycled or cascaded by cooling and precipitation. Strengthening the treatment of sinter plant wastewater can save water and recover useful materials, and its economic benefits are very objective. As long as the treatment process is selected, the production wastewater can reach or approach the goal of zero emissions.
Sludge dewatering is a key technology:
As mentioned above, the difficulty in the treatment of dusty wastewater in the sinter plant is the dewatering technology of the mud. The sintering process requires the addition of mixed ingredients to the sludge moisture content of not more than 12%, which is difficult to achieve in the current sludge dewatering process. Such measures have obviously not promoted the use value in the economy. Therefore, in the filtration and pressure filtration processes, it is necessary to strengthen the effect, such as selecting a suitable flocculant, improving the dehydration effect, or making a pellet, which is directly used for smelting.
Application of flocculant:
Foreign countries have added flocculants in the treatment of sintering wastewater in order to improve the quality of the effluent. China has gradually promoted the use of various types of flocculants. However, no matter which flocculant is used, it should be tested beforehand to determine the preferred agent and its optimal dosage. Section III Treatment and Utilization of Ironmaking Wastewater I. Overview The ironmaking process is to feed raw materials (ores and fluxes) and fuel ( coke ) into the blast furnace, and to pass hot air to smelt the raw materials into molten iron at high temperatures, and at the same time produce slag and blast furnace coal gas. The blast furnace slag produced by iron making is water quenched into water slag and used to produce cement and other products. It is a good building material. The ironworks includes blast furnaces, hot blast stoves, blast furnace gas washing facilities, blowers, cast iron machines, slag pools, etc., as well as auxiliary facilities.
Source of wastewater:
Cooling of blast furnaces and hot blast stoves, washing of blast furnace gas, water quenching of slag and hydraulic conveying are the main water installations, and there are also some places where water consumption is small or intermittent. In terms of the role of water, the water used in ironworks can be divided into: indirect cooling water for equipment; direct cooling water for equipment and products; water for production process and other miscellaneous water. The resulting wastewater is also the indirect cooling of wastewater, direct cooling of equipment or products, and wastewater from the production process. The wastewater generated during the production process of the ironworks is mainly blast furnace gas washing water and slag wastewater.
Water quantity and quality of wastewater:
All the water supply in the ironworks is converted to waste water except for a very small amount of loss, so the water consumption is basically equivalent to the amount of wastewater. The blast furnace gas washing water is the main wastewater of the ironmaking plant. It is characterized by high water content, high suspended solid content, and contains harmful substances such as phenol and cyanide, which are harmful, so it is a representative wastewater of the iron making plant.
Technical route for wastewater treatment:
The main treatment technologies are: the removal of suspended solids; the control of temperature; the stability of water quality; the dehydration and utilization of sediment; and the repeated use of water.
1 Removal of suspended solids:
The pollution of ironmaking plant wastewater is mainly characterized by suspended solids pollution. The suspended solid content of blast furnace gas washing water reaches 1000-3000mg/L. After sedimentation, the suspended solid content of effluent should be less than 150mg/L. In view of the widespread application of coagulant in recent years, blast furnace gas washing water is mostly used in combination with polyacrylamide and iron salt, and has achieved good results.
2 temperature control:
After the water is used, the temperature of the water rises. It is called hot pollution, and it is recycled without water. Thermal pollution does not constitute damage to the environment. However, in order to ensure the cycle, cooling measures should be taken for different requirements of different systems. Several types of wastewater in ironworks produce temperature rise. Due to different production processes, some systems may not have cooling equipment, such as slag water. The temperature of the water has an effect on the effect of coagulation and sedimentation as well as the degree of scale and corrosion. The equipment indirect cooling water system shall be provided with a cooling tower, and the direct cooling water or process cooling system shall be determined on a case-by-case basis. Stable water quality The stability of water refers to whether the chemical composition of the water itself changes during the process of transporting water, causing corrosion or scaling. Water that is neither fouled nor corroded is called stabilized water. The method for controlling the scaling of carbonate is as follows: the acidification method is to use sulfuric acid or hydrochloric acid in water, and the solubility of CaSO4 and CaCl3 is much larger than that of CaCO3 to prevent scaling.
3 lime softening method:
The lime milk is put into the water, and the temporary hardness is removed by the dehardening action of the lime to soften the water. The mechanism of stabilizing water quality by adding the anti-scaling method is to add organophosphorus and polycarboxylic acid type scale inhibitors to the water, and to control the growth of the crystal and stabilize the water quality by utilizing their excellent dispersion and lattice distortion effects. . The most commonly used water stabilizers are sodium polyphosphate, NTMP (nitrophosphonate), EDP (ethanol diphosphonate), and polymaleic anhydride.
4 Dewatering and utilization of sediment:
The sediment of the ironworks is mainly blast furnace gas washing water sediment and blast furnace slag, which are used as treasure and discarded as sediment. The blast furnace water quenching slag is used to produce cement, which is in short supply and the technology is very mature. The main components of the blast furnace gas washing sediment are iron oxide and coke powder. The use of these sediments is very economical, and the environmental pollution is also reduced.
5 repeated water:
It should be pointed out that the removal of suspended solids, the control of temperature, the stability of water quality and the dehydration and utilization of sediment are the essential technologies to ensure the recycling of water. One loop is deducted, and which one is not solved well, circulating water is empty talk. They are not isolated, interconnected, and influence each other, so we must adhere to comprehensive treatment and form a virtuous circle.
Treatment of blast furnace gas washing water
Blast furnace gas washing process and wastewater properties:
The gas drawn from the blast furnace is called waste gas, which is first removed by gravity and then enters the washing equipment. The washing and cooling of the gas is achieved by convective contact of water and gas in the scrubber and venturi. Due to the direct contact between water and gas, fine solid impurities in the gas enter the water, and the water temperature rises. Some of the harmful substances such as phenol and cyanide in the minerals and gas are partially dissolved into the water to form blast furnace gas washing water. Representative washings include a scrubber, a venturi, and a washing process (see Figure 3-2) and a double venturi cascade process.
Blast furnace gas washing water treatment process:
The blast furnace gas washing water treatment process mainly includes precipitation (or coagulation and sedimentation), stable water quality, cooling (there is no cooling of the top power generation facility), and sludge treatment. Precipitation and removal of suspended solids are more radiant precipitation tanks, and the effect is better. The process flow adopted in China is as follows. Lime softening-carbonization process The sewage after washing the gas is coagulated and precipitated by the radiant sedimentation tank. 80% of the effluent is sent to the cooling device (cooling tower), and the remaining 20% ​​of the pump is softened to the accelerated clarifier. The softened water and the cooling water are mixed with the flue gas, carbonized, and then pumped back to the gas washing equipment for recycling. The mud is discharged from the bottom of the sedimentation tank, sent to a concentration tank for secondary concentration, and then sent to a vacuum filter for dehydration. The overflow pool overflows into the sedimentation tank or directly goes to the water absorption well for recycling. The gas is sent to the mud storage bin for sintering.
Add pharmaceutical process:
The waste water after washing the gas is coagulated and precipitated through the sedimentation tank, and a scale inhibitor is added on the pipeline at the outlet of the sedimentation tank to prevent calcium carbonate from scaling, and at the same time prevent the formation of scale by the combination of iron oxide, silicon dioxide and zinc hydroxide. The pH should be adjusted when using the agent. In order to ensure that the water is circulated under a certain concentration factor, the sewage is discharged to the outside of the system regularly, and new water is continuously added to keep the water quality stable.
Acidizing process:
The waste water discharged from the gas washing tower is naturally precipitated (or coagulated and precipitated) through the radiant sedimentation tank, and the upper layer of clean water is sent to the cooling tower for cooling, and then sent to the circulation system by the lower collecting pool of the tower, and the acid port is set on the conveying pipeline, and waste The waste sulfuric acid in the acid pool is uniformly added to the water through a suitable amount of the hose. After the sludge is dehydrated, it is sent to the sintering. Lime softening - pharmaceutical process This treatment method uses lime softening (20% to 30% water) and combined with drug and scale inhibition. As a result of the combination of different water quality stabilizers, the synergistic effect is achieved and the water quality stabilization effect is enhanced.
Blast furnace slag wastewater treatment:
The blast furnace slag water quenching method is divided into slag pool water quenching and pre-furnace water quenching. The blast furnace slag slag wastewater generally refers to the wastewater generated by water quenching before the furnace. Because the circulating water quality requirements are low, the slag water can be circulated after separation, and the high temperature does not affect the slag. Therefore, in the slag water system, it can be designed as a circulation system with only supplementary water and no sewage. There are several methods for separating slag water.
Slag filtration method:
The slag water mixture is introduced into a set of filter tanks, and the slag itself is used as a filter material, so that the slag and water are passed through the filter tank to intercept the slag in the tank, and the water is filtered. The filtered water suspension has a small content, and during the slag filtration process, the temporary hardness of the water can be lowered, and the filter material does not have to be backwashed, and the recycling is better. However, the filter pool has a large area, and generally requires several filter tank rotation operations, and it is difficult to automatically control, so the slag filtration method is only suitable for the slag water separation of the small blast furnace.
Trough dewatering method (RASA Lhasa method). The slag water is pumped into a tank. The bottom of the tank and the wall of the tank are blocked by stainless steel wire mesh. It is like a filter tank, but the dewatering area is much larger than the filter tank. less. The dehydrated water slag is controlled by the valve at the lower part of the tank and is transported by the truck. The effluent from the dewatering tank entrains the scum and enters the sedimentation tank. The slag under the sediment is returned to the dewatering tank, and the overflow water is used for cooling cycle.
Drum dehydration method (INBA Inaba method) The slag water is introduced into a rotating cylindrical device, and the slag water mixture is introduced into the drum through uniform distribution, since the outer cylinder of the drum is woven by stainless steel wire. With the grid structure, the slag and water entering the drum are quickly separated. The water flows through the slag and the net from the lower part of the drum; the slag moves in a circular motion with the drum. When the slag is brought to the upper part of the circumference, the slag is transported out by the self-weight falling onto the output belt conveyor at the center of the drum to realize the separation of water and slag. Since all the slag is separated in the drum, there is no scum, and there is no need to set up a sedimentation facility, which greatly improves the efficiency. This is an advanced slag water separation equipment.
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