CN107686204B - Method for comprehensively utilizing heat energy in viscose fiber acid wastewater treatment process - Google Patents
Method for comprehensively utilizing heat energy in viscose fiber acid wastewater treatment process Download PDFInfo
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Abstract
The invention relates to a method for comprehensively utilizing heat energy in the process of treating viscose fiber acid wastewater, which comprises the following steps of: cooling the acid wastewater to a temperature required by a membrane filtration concentration system for treatment; filtering and concentrating the cooled acidic wastewater by using a membrane filtering and concentrating system to obtain an acidic wastewater concentrated solution; preheating the acid wastewater concentrated solution, and then feeding the acid wastewater concentrated solution into an evaporation system for further evaporation and concentration; and (3) exchanging heat between the acidic wastewater in the step (1) and the acidic wastewater concentrated solution in the step (3) as cold and heat sources, and simultaneously cooling the acidic wastewater and preheating the acidic wastewater concentrated solution. The invention fully realizes the comprehensive utilization of heat energy in the viscose high-temperature acidic wastewater treatment process, and reduces energy consumption and operation cost.
Description
Technical Field
The invention relates to a method for comprehensively utilizing heat energy in the process of treating viscose acid wastewater, belongs to the field of viscose production, and particularly relates to the field of treatment of viscose acid wastewater.
Background
The acidic wastewater discharged from the spinning and practicing workshop of the viscose fiber factory contains sulfuric acid, sodium sulfate and zinc sulfate, and the current treatment mode is as follows: acid wastewater is discharged to a sewage treatment plant and is uniformly treated after being mixed with other sewage, and the discharge of a large amount of salt-containing wastewater not only influences the biochemical treatment effect of subsequent wastewater, but also wastes energy. The research changes the treatment process of the acid water, and the sulfuric acid, the sodium sulfate and the zinc sulfate in the acid water are recovered, so that the acid and salt content in the external drainage water can be reduced, the biochemical treatment difficulty is reduced, the sewage treatment cost is reduced, and the development trend of environmental protection, energy saving and cost reduction is better met. With the increasingly stricter industry competition and environmental protection policy, viscose enterprises begin to pay attention to the recycling treatment of acidic wastewater. The existing viscose enterprises adopt an evaporation mode to concentrate and recycle the acidic wastewater, and an evaporation system has the defects of high investment and high operating cost, and the high cost and energy consumption become the biggest restriction on the development of the acidic water concentration and recycling process. At present, the membrane filtration concentration technology is widely applied to the field of treating the salt-containing wastewater due to the advantages of low energy consumption and high efficiency, but the technology is not suitable for treating the high-concentration salt-containing wastewater. Meanwhile, the membrane filtration device requires that the temperature of the filter medium is reduced to below 40 ℃, and the higher the temperature of the medium entering the evaporation system is, the lower the energy consumption of the system is.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for comprehensively utilizing heat energy in the viscose fiber acid wastewater treatment process, which is feasible, stable and effective in process, can fully and effectively utilize the heat energy of high-temperature acid wastewater, and reduces the steam consumption for treating the acid wastewater by using an evaporation system. The invention adopts the production process combining membrane filtration and evaporation to carry out concentration treatment on the acidic water, fully exerts the technical advantages of membrane filtration and evaporation on the treatment of high-concentration and low-concentration acidic wastewater, can save equipment investment and operation cost, and improves operation efficiency. The invention comprehensively utilizes the heat energy of the high-temperature acidic wastewater membrane filtration and evaporation treatment, fully utilizes the heat energy of the high-temperature acidic wastewater and saves the overall energy consumption of the system.
The technical scheme for solving the technical problems is as follows: a method for comprehensively utilizing heat energy in the process of treating viscose acid wastewater comprises the following steps:
(1) cooling the acid wastewater to a temperature required by a membrane filtration concentration system for treatment;
(2) filtering and concentrating the cooled acidic wastewater by using a membrane filtering and concentrating system to obtain an acidic wastewater concentrated solution;
(3) preheating the acid wastewater concentrated solution, and then feeding the acid wastewater concentrated solution into an evaporation system for further evaporation and concentration;
And (3) exchanging heat between the acidic wastewater in the step (1) and the acidic wastewater concentrated solution in the step (3) as cold and heat sources, and simultaneously cooling the acidic wastewater and preheating the acidic wastewater concentrated solution.
On the basis of the technical scheme, the invention can be further improved as follows.
Furthermore, the viscose acid wastewater is fiber washing water which is discharged in the viscose production process and carries acid bath, and the discharge position is before fiber cutting or after the fiber cutting.
The preparation method of viscose fiber usually includes three steps of viscose preparation, spinning formation and post-treatment, generally, pure alpha-cellulose (called pulp) is extracted from cellulose raw material, and is treated by caustic soda and carbon disulfide to obtain orange-yellow sodium cellulose xanthate, and then the orange-yellow sodium cellulose xanthate is dissolved in dilute sodium hydroxide solution to become viscous spinning stock solution called viscose. Filtering, curing (standing at a certain temperature for about 18-30 h to reduce the esterification degree of cellulose xanthate), defoaming, and performing wet spinning, wherein a coagulating bath (acid bath) consists of sulfuric acid, sodium sulfate and zinc sulfate. The cellulose sodium xanthate in the viscose is decomposed by the action of sulfuric acid in the coagulating bath, the cellulose is regenerated and precipitated, and the obtained cellulose fiber is washed by water, desulfurized, bleached and dried to form the viscose fiber. The wastewater treated by the invention is fiber washing water with acid bath generated in wet spinning between spinning and refining cars in a production line for producing viscose fibers in a viscose fiber factory, and the position of the wastewater discharged from the spinning and refining cars is before or after the fibers in the wet spinning are cut.
Furthermore, the temperature of the viscose acid wastewater is 85-98 ℃, the concentration of each component is 5-13g/L of sulfuric acid, 15-40g/L of sodium sulfate and 0.3-1.1g/L of zinc sulfate, and the turbidity is 30-50 ntu.
Since the coagulation bath consists of sulfuric acid, sodium sulfate and zinc sulfate, its rinsing water naturally also contains these substances. Turbidity refers to the degree of obstruction that occurs when suspended matter in water passes through to light. The suspended substances in water are generally mud, sand, fine organic and inorganic substances, plankton, microorganism, colloidal substances and the like. The turbidity of water is related not only to the content of suspended substances in the water, but also to their size, shape, refractive index, etc. Therefore, the viscose acid wastewater obviously contains a certain amount of suspended matters.
Further, before the temperature reduction in the step (1), the acidic wastewater can be pretreated: after the acid wastewater is collected, the acid wastewater is stirred at constant temperature and naturally settled, and then suspended matters in the water are removed by filtration.
More specifically, the viscose acid wastewater is conveyed to a collecting tank by a pump for centralized collection, and after the viscose acid wastewater is stirred at a constant temperature for a preset time, the stirring is stopped, and the viscose acid wastewater naturally settles under the action of gravity.
Furthermore, the collecting tank is a carbon steel lining high-temperature glue device and is provided with a stirrer.
The collecting tank can be formed by transforming a high-temperature-resistant carbon steel rubber-lined storage tank, the temperature resistance range of the collecting tank is 110 ℃, a stirrer is additionally arranged on the collecting tank, and the collecting tank can be matched with some existing detection systems and control systems to carry out the step (1) of the invention. Specifically, the stirrer is a frame type or paddle type stirrer, and the rotating speed of the stirrer is 50-100 rpm.
Further, the constant-temperature stirring temperature of the acidic wastewater is 85-95 ℃, and the time is 1.5-3 h; the natural settling time is 1-2h, and the temperature of the acidic wastewater is reduced to 30-38 ℃ after the natural settling; the filtration adopts micro-filtration equipment with the aperture of 0.1um-10 um.
Microfiltration refers to a technique for separating particles from a fluid (gas or liquid), and belongs to one of filtration techniques, which is different from other separation methods and applicable ranges, and is between conventional filtration and ultrafiltration.
The pretreatment of the acidic wastewater before the step (1) of the invention comprises the following specific steps: the viscose fiber acid wastewater is collected to a stirring device and then stirred, then dissolved colloidal substances and other impurities in the water are separated out and settled down through natural settling, and the separated sediment and suspended substances are filtered and removed by a filtering device. The principle is as follows: colloidal substances and other impurities dissolved in the acidic wastewater can be continuously collided and agglomerated into large particles along with stirring, the stirring is stopped, the large particles are naturally settled for 1 to 2 hours, the formed large particles can be separated out and deposited at the bottom of the collecting tank, then the separated sediments and suspended matters are removed by filtering equipment, and the turbidity of the water is reduced to 8 to 15 ntu.
The invention removes colloidal substances and other suspended matters in the viscose fiber acid wastewater by adopting stirring, settling and filtering modes, reduces the turbidity of the wastewater, improves the operation efficiency of further treatment by using a membrane filtration concentration system in the next step, reduces the operation cost, prolongs the membrane use period, shortens the membrane cleaning time, and has promotion and guiding significance for applying the membrane filtration concentration technology to viscose fiber acid wastewater treatment.
Further, the acid wastewater in the step (1) is cooled to 30-38 ℃ by adopting a heat exchange cooling and vacuum flash cooling mode.
The temperature reduction can be carried out in the pretreatment specifically, after natural sedimentation, or after the pretreatment is finished completely. The purpose of cooling makes acid waste water reach the required temperature through membrane filtration concentration system, and too high temperature can produce the destruction to membrane filtration concentration system, is unfavorable for going on of filtration concentration moreover. Further, a heat exchanger is adopted for heat exchange and cooling, a cold source is provided for the heat exchanger, the acidic wastewater concentrated solution is obtained after being treated by the membrane filtration concentration system in the step (2), the vacuum flash evaporation cooling adopts multi-stage vacuum flash evaporation, and generated secondary steam is used for the evaporation system in the step (3).
Further, a heat exchanger is adopted for heat exchange and cooling, a cold source is provided for the heat exchanger, the acidic wastewater concentrated solution is obtained after being treated by the membrane filtration concentration system in the step (2), the vacuum flash evaporation cooling adopts multi-stage vacuum flash evaporation, and generated secondary steam is used for the evaporation system in the step (3).
When the method is specifically implemented in the step 1), the cooling process of the acidic wastewater with higher temperature is to adopt a heat exchange cooling and vacuum flash cooling mode to divide the pretreated high-temperature acidic wastewater into two parts, the first part of the high-temperature acidic wastewater is cooled by adopting a multi-stage vacuum flash process, secondary steam generated after flash evaporation enters an evaporation system for use, the second part of the high-temperature acidic wastewater is cooled by adopting a heat exchanger, and what provides a cold source for the heat exchange of the high-temperature acidic wastewater is the acidic wastewater concentrated solution after filtration and concentration treatment by a membrane filtration and concentration system. The proportion of the treatment capacity of the two specific modes can be adjusted according to the requirements of actual production and heat exchange. Therefore, no additional cold source is introduced in the process of cooling the acidic wastewater, and the heat energy generated during cooling is fully collected and utilized to the evaporation system.
Further, the membrane filtration concentration system in the step (2) adopts a membrane combination treatment mode of ultrafiltration, reverse osmosis or ultrafiltration and electrodialysis, or adopts a membrane combination treatment mode of ceramic membrane, reverse osmosis or ceramic membrane and electrodialysis.
The membrane filtration and concentration system can adopt a membrane filtration and concentration mode mainly comprising ultrafiltration, namely a membrane combined treatment mode comprising ultrafiltration, reverse osmosis or ultrafiltration and electrodialysis, and also can adopt a membrane filtration and concentration mode mainly comprising ceramic membranes, namely a membrane combined treatment mode comprising ceramic membranes, reverse osmosis or ceramic membranes and electrodialysis.
Further, the temperature of the acid wastewater concentrated solution treated by the membrane filtration concentration system is 33-38 ℃; the concentration of each component is 25-30g/L of sulfuric acid, 75-90g/L of sodium sulfate and 2-2.5/L of zinc sulfate. And the filtrate separated by the membrane filtration concentration system is reused as the production water to the viscose fiber production system.
Further, the acidic wastewater concentrated solution in the step (3) is preheated by adopting a heat exchange and temperature rise mode, and the temperature after preheating is 82-90 ℃.
Further, a heat exchanger is adopted for heat exchange and temperature rise, and the acidic wastewater in the step (1) is used for providing a heat source for the heat exchanger.
The initial temperature of the acid wastewater concentrated solution obtained in the step (2) is not high, preheating is needed for better subsequent evaporation and concentration, and a heat source used for preheating is the acid wastewater with higher temperature in the previous step (1), that is, the acid wastewater with higher temperature in the step (1) and the acid wastewater concentrated solution with lower temperature treated by the membrane filtration and concentration system are cold and heat sources for each other, heat exchange is carried out on the two solutions through a heat exchanger, comprehensive utilization of heat energy is provided, and energy consumption and operation cost are reduced.
Further, the evaporation system adopts a multi-effect evaporation device, a multi-stage flash evaporation device or an MVR evaporator, and the concentration of each component in the final concentrated solution obtained after the treatment of the evaporation system is 120g/L of sulfuric acid 115-. And recycling the final concentrated solution obtained after the treatment of the evaporation system to an acid bath step in a viscose production system, and recycling the condensed water generated by the evaporation system as production water to the viscose production system.
The membrane filtration concentration system is suitable for treating low-concentration acidic wastewater, and firstly carries out membrane filtration concentration on fiber flushing water which is discharged in the production process of the pretreated viscose and contains an acid bath, so that the acid and salt concentrations are primarily improved. The evaporation system is suitable for treating high-concentration acidic wastewater, and can further improve the concentration of acidity and salt in the wastewater, so that the concentrated acidic wastewater can be used for an acid bath system in a viscose production workshop. The filtrate and the condensed water generated in the two systems can also be used as the production water to be recycled to the viscose fiber production system.
The production process combining the membrane filtration concentration system and the evaporation system is adopted to carry out concentration treatment on the acidic wastewater, so that the technical advantages of the evaporation system and the membrane filtration concentration system for respectively treating high-concentration wastewater and low-concentration wastewater are fully exerted, the equipment investment and the operating cost can be saved, and the operating efficiency is improved. The invention can reduce the salt content of the discharged water, realize the recycling of resources, reduce the sewage treatment cost and the production cost, and has promotion and guidance significance for the benign development of the whole viscose industry.
The invention has the beneficial effects that: the cold source is not additionally introduced in the process of cooling the high-temperature acidic wastewater, the heat energy in the processes of cooling and heating the high-temperature acidic wastewater is fully balanced, the energy consumption of treating the high-temperature acidic wastewater by adopting a technology combining membrane filtration concentration and evaporation is reduced, the comprehensive utilization of the heat energy is fully realized, and the energy consumption and the running cost are reduced.
Detailed Description
The principles and features of this invention are described below in conjunction with examples which are set forth to illustrate, but are not to be construed to limit the scope of the invention.
The invention aims at fiber washing water which is discharged from a spinning and practicing workshop of a viscose fiber factory and is provided with an acid bath, wherein the discharge position is before or after fiber cutting, the water temperature is 85-98 ℃, the sulfuric acid is 5-13g/L, the sodium sulfate is 15-40g/L, the zinc sulfate is 0.3-1.1g/L, and the turbidity is 30-50 ntu. Cooling the acid wastewater to a temperature required by a membrane filtration concentration system for treatment, wherein the temperature can be reduced to 30-38 ℃ by utilizing heat exchange cooling and vacuum flash cooling; filtering and concentrating the cooled acidic wastewater by using a membrane filtration and concentration system to obtain an acidic wastewater concentrated solution, wherein the temperature of the acidic wastewater concentrated solution is 33-40 ℃, and the concentration of each component is 25-30g/L of sulfuric acid, 75-90g/L of sodium sulfate and 2-2.5g/L of zinc sulfate; preheating the acid wastewater concentrated solution in a heat exchange and temperature rise mode, and then entering an evaporation system for further evaporation and concentration, wherein the temperature after preheating is 82-90 ℃.
And (3) recycling the filtrate separated by the membrane filtration concentration system as the production water to the viscose fiber production system, recycling the final concentrated solution obtained by the treatment of the evaporation system to the acid bath of the viscose fiber production system, and recycling the condensed water generated by the evaporation system as the production water to the viscose fiber production system.
The heat exchange cooling and the heat exchange heating are realized by a heat exchanger, the acid wastewater with higher temperature and the acid wastewater concentrated solution with lower temperature treated by the membrane filtration concentration system are mutually cold and heat sources, and the heat exchange is carried out on the two solutions by the heat exchanger; the vacuum flash cooling adopts multi-stage vacuum flash, and the generated secondary steam is used for an evaporation system.
The following examples and comparative examples are given to illustrate the above problems.
Example 1
The temperature is 85 ℃, the water quantity is 200m3The acidic wastewater (detected by the detection, after colloid and suspended matters are removed by a pretreatment process, the turbidity is 10ntu, the acidic wastewater is divided into two parts according to a proportion, the temperature of the acidic wastewater is reduced to 30 ℃ by a multistage vacuum flash evaporation mode, 5.6t of secondary steam with the temperature of more than 60 ℃ generated by the vacuum flash evaporation enters a multi-effect evaporation system for use, and the high-temperature acidic wastewater with the total discharge of 25 percent and 33 ℃ concentrated solution separated by a membrane filtration concentration system are subjected to heat exchange by a heat exchanger to reduce the temperature to 35 ℃.
The two parts of cooled acid wastewater enter a membrane filtration concentration system together for further treatment to obtain 40m3The temperature of the acid wastewater concentrated solution is 33 ℃; the concentration of each component is 25g/L sulfuric acid, 75g/L sodium sulfate and 2g/L zinc sulfate, 160m is separated by a membrane filtration concentration system3And the filtrate is reused as the production water to the viscose fiber production system.
The acid wastewater concentrated solution is preheated and then enters an evaporation systemPreheating by heat exchange, heating to 82 deg.C with high-temperature acidic wastewater accounting for 25% of total discharge amount by heat exchange with heat exchanger, and evaporating to obtain 8.5m3The final concentrated solution containing 115g/L sulfuric acid, 345g/L sodium sulfate and 9.5g/L zinc sulfate is recycled to the acid bath step in the viscose fiber production system, 31.5m is generated by the evaporation system3And recycling the/h condensed water as production water to a viscose fiber production system.
Example 2
The temperature is 85 ℃, the water quantity is 200m3The acidic wastewater (detected by the detection, the turbidity is 10ntu after colloid and suspended matters are removed from the acidic wastewater (5 g/L, 15g/L, 0.3g/L, and 50ntu) by a pretreatment process, the acidic wastewater is divided into two parts according to a proportion and is subjected to cooling treatment, the high-temperature acidic wastewater accounting for 80 percent of the total discharge amount is cooled to 30 ℃ by a multi-stage vacuum flash evaporation mode, 5.6t of secondary steam with the temperature of more than 60 ℃ generated by the vacuum flash evaporation enters a multi-effect evaporation system for use, and the high-temperature acidic wastewater accounting for 20 percent of the total discharge amount and 33 ℃ concentrated solution separated by a membrane filtration concentration system are cooled to 35 ℃ by heat exchange of a heat exchanger.
The two parts of cooled acid wastewater enter a membrane filtration concentration system together for further treatment to obtain 33m3The temperature of the acid wastewater concentrated solution is 33 ℃; the concentration of each component is 30g/L sulfuric acid, 90g/L sodium sulfate and 2.5g/L zinc sulfate, 167m separated by a membrane filtration concentration system3And the filtrate is reused as the production water to the viscose fiber production system.
The acid wastewater concentrated solution is preheated and then enters an evaporation system, the preheating adopts a heat exchange and temperature rise mode, the acid wastewater concentrated solution and high-temperature acid wastewater accounting for 20 percent of the total discharge amount are subjected to heat exchange by a heat exchanger and temperature rise to 82 ℃, and the acid wastewater concentrated solution is treated by the evaporation system to obtain 8.4m3The final concentrated solution containing 118g/L sulfuric acid, 354g/L sodium sulfate and 9.5g/L zinc sulfate is recycled to the acid bath step in the viscose fiber production system, and 24.6m is generated by an evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Example 3
The temperature is 90 ℃ and the water quantity is 200m3The acidic wastewater (detected by 10g/L of sulfuric acid, 30g/L of sodium sulfate, 0.8g/L of zinc sulfate and 40ntu of turbidity) is pretreated to remove colloids and suspended matters, the turbidity is 10ntu, the acidic wastewater is divided into two parts according to a proportion and is subjected to cooling treatment, the high-temperature acidic wastewater accounting for 52 percent of the total discharge amount is cooled to 30 ℃ in a multi-stage vacuum flash evaporation mode, 4.6t of secondary steam with the temperature higher than 60 ℃ generated by the vacuum flash evaporation enters a multi-effect evaporation system for use, and the high-temperature acidic wastewater accounting for 48 percent of the total discharge amount and a 35 ℃ concentrated solution separated by a membrane filtration concentration system are subjected to heat exchange by a heat exchanger to be cooled to 38 ℃.
The two parts of cooled acid wastewater enter a membrane filtration concentration system together for further treatment to obtain 80m3The temperature of the acid wastewater concentrated solution is 33 ℃; the concentration of each component is 25g/L sulfuric acid, 75g/L sodium sulfate and 2g/L zinc sulfate, 120m separated by a membrane filtration concentration system3And the filtrate is reused as the production water to the viscose fiber production system.
The acid wastewater concentrated solution is preheated and then enters an evaporation system, the preheating adopts a heat exchange and temperature rise mode, the acid wastewater concentrated solution and high-temperature acid wastewater accounting for 48 percent of the total discharge amount are subjected to heat exchange by a heat exchanger and temperature rise to 85 ℃, and the acid wastewater concentrated solution is treated by the evaporation system to obtain 17.4m3The final concentrated solution containing 117g/L of sulfuric acid, 351g/L of sodium sulfate and 10g/L of zinc sulfate is recycled to the acid bath step in the viscose fiber production system, and 62.6m of the final concentrated solution is produced by an evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Example 4
The temperature is 90 ℃ and the water quantity is 200m3The acidic wastewater (detected by 10g/L of sulfuric acid, 30g/L of sodium sulfate, 0.8g/L of zinc sulfate and 40ntu of turbidity) is pretreated to remove colloids and suspended matters, the turbidity is 10ntu, the acidic wastewater is divided into two parts according to a proportion to be subjected to cooling treatment, the high-temperature acidic wastewater accounting for 60 percent of the total discharge amount is cooled to 30 ℃ in a multi-stage vacuum flash evaporation mode, 5.4t of secondary steam with the temperature higher than 60 ℃ generated by the vacuum flash evaporation enters a multi-effect evaporation system for use, and the high-temperature acidic wastewater accounting for 40 percent of the total discharge amount is separated from a membrane filtration concentration system And the obtained 35 ℃ concentrated solution is subjected to heat exchange by a heat exchanger and is cooled to 38 ℃.
The two parts of cooled acid wastewater enter a membrane filtration concentration system together for further treatment to obtain 66.5m3The temperature of the acid wastewater concentrated solution is 35 ℃; the concentration of each component is 30g/L sulfuric acid, 90g/L sodium sulfate and 2.5g/L zinc sulfate, and 133.5m is separated by a membrane filtration concentration system3And the filtrate is reused as the production water to the viscose fiber production system.
The acid wastewater concentrated solution is preheated and then enters an evaporation system, the preheating adopts a heat exchange and temperature rise mode, the acid wastewater concentrated solution and high-temperature acid wastewater accounting for 40 percent of the total discharge amount are subjected to heat exchange by a heat exchanger and temperature rise to 85 ℃, and the acid wastewater concentrated solution is treated by the evaporation system to obtain 16.5m3The final concentrated solution containing 120g/L sulfuric acid, 351g/L sodium sulfate and 10g/L zinc sulfate is recycled to the acid bath step in the viscose fiber production system, 50m generated by the evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Example 5
The temperature is 98 ℃ and the water quantity is 200m3The acidic wastewater (detected by the detection, the turbidity is 8ntu after colloid and suspended matters are removed by a pretreatment process, the acidic wastewater with the turbidity of 30ntu and the acidic wastewater with the turbidity of 13g/L, 40g/L, 1.1g/L and 30 g/L) is divided into two parts according to a proportion to be subjected to cooling treatment, the high-temperature acidic wastewater accounting for 40 percent of the total discharge amount is cooled to 30 ℃ by a multi-stage vacuum flash evaporation mode, 4.7t of secondary steam with the temperature higher than 60 ℃ generated by the vacuum flash evaporation enters a multi-effect evaporation system for use, and the high-temperature acidic wastewater accounting for 60 percent of the total discharge amount and a 35 ℃ concentrated solution separated by a membrane filtration concentration system are cooled to 38 ℃ by heat exchange of a.
The two parts of cooled acidic wastewater enter a membrane filtration concentration system together for further treatment to obtain 104m3The temperature of the acid wastewater concentrated solution is 35 ℃; the concentration of each component is 25g/L sulfuric acid, 75g/L sodium sulfate and 2g/L zinc sulfate, 96m separated by a membrane filtration concentration system3And the filtrate is reused as the production water to the viscose fiber production system.
The acid wastewater concentrated solution is preheated and then enters an evaporation system, the preheating adopts a heat exchange and temperature rise mode, the acid wastewater concentrated solution and high-temperature acid wastewater accounting for 60 percent of the total discharge amount are subjected to heat exchange by a heat exchanger and temperature rise to 90 ℃, and the acid wastewater concentrated solution is treated by the evaporation system to obtain 22.5m3The final concentrated solution containing 115g/L sulfuric acid, 345g/L sodium sulfate and 9.5g/L zinc sulfate is recycled to the acid bath step in the viscose fiber production system, 73.5m is generated by the evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Example 6
The temperature is 98 ℃ and the water quantity is 200m3The acidic wastewater (detected by the detection, the turbidity is 8ntu after colloid and suspended matters are removed by a pretreatment process, the acidic wastewater with the turbidity of 30ntu and the acidic wastewater with the turbidity of 13g/L, 39g/L, 1.1g/L and 30 g/L) is divided into two parts according to a proportion to be subjected to cooling treatment, the high-temperature acidic wastewater accounting for 50 percent of the total discharge amount is cooled to 30 ℃ in a multi-stage vacuum flash evaporation mode, 5.9t of secondary steam with the temperature of more than 60 ℃ generated by the vacuum flash evaporation enters a multi-effect evaporation system for use, and the high-temperature acidic wastewater accounting for 50 percent of the total discharge amount and a 35 ℃ concentrated solution separated by a membrane filtration concentration system are subjected to heat exchange by a heat exchanger.
The two parts of cooled acid wastewater enter a membrane filtration concentration system together for further treatment, and the treated acid wastewater is 86.5m3The temperature of the acid wastewater concentrated solution is 35 ℃; the concentration of each component is 30g/L sulfuric acid, 90g/L sodium sulfate and 2.5g/L zinc sulfate, 113.5m is separated by a membrane filtration concentration system3And the filtrate is reused as the production water to the viscose fiber production system.
The acid wastewater concentrated solution is preheated and then enters an evaporation system, the preheating adopts a heat exchange and temperature rise mode, the acid wastewater concentrated solution and high-temperature acid wastewater accounting for 50 percent of the total discharge amount are subjected to heat exchange by a heat exchanger and temperature rise to 90 ℃, and the acid wastewater concentrated solution is treated by the evaporation system to obtain 21.5m3The final concentrated solution containing 120g/L sulfuric acid, 360g/L sodium sulfate and 10g/L zinc sulfate is recycled to the acid bath step in the viscose fiber production system, 65m is generated by the evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Comparative example 1
The temperature is 85 ℃, the water quantity is 200m3The acid wastewater (detected as 5g/L of sulfuric acid, 15g/L of sodium sulfate, 0.3g/L of zinc sulfate and 50ntu of turbidity) is pretreated to remove colloids and suspended matters, the turbidity is 10ntu, the temperature is reduced to 30 ℃ by utilizing a multi-stage vacuum flash evaporation mode, and 7t of secondary steam with the temperature higher than 60 ℃ generated by the vacuum flash evaporation enters a multi-effect evaporation system for use.
The acid wastewater after being cooled enters a membrane filtration concentration system for further treatment, and 40m is obtained after the acid wastewater is treated by the membrane filtration concentration system3The temperature of the acid wastewater concentrated solution is 31 ℃; the concentration of each component is 25g/L sulfuric acid, 75g/L sodium sulfate and 2g/L zinc sulfate, and the components enter an evaporation system for further evaporation and concentration treatment. Treated by an evaporation system to obtain 8.5m3The final concentrated solution containing 118g/L sulfuric acid, 354g/L sodium sulfate and 9.5g/L zinc sulfate is recycled to the acid bath step of the viscose fiber production system, and 160m separated by the membrane filtration concentration system is treated331.5m from filtrate and evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Comparative example 2
The temperature is 85 ℃, the water quantity is 200m3The acid wastewater (detected as 5g/L of sulfuric acid, 15g/L of sodium sulfate, 0.5g/L of zinc sulfate and 50ntu of turbidity) directly enters an evaporation system for evaporation and concentration treatment. 8.5m obtained after treatment by an evaporation system3The final concentrated solution containing 118g/L sulfuric acid, 354g/L sodium sulfate and 9.5g/L zinc sulfate is recycled to the acid bath step of the viscose fiber production system, 191m is generated by the evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Comparative example 3
The temperature is 90 ℃ and the water quantity is 200m3The acid wastewater (detected as 10g/L of sulfuric acid, 30g/L of sodium sulfate, 0.8g/L of zinc sulfate and 40ntu of turbidity) is pretreated to remove colloids and suspended matters, the turbidity is 10ntu, the temperature is reduced to 30 ℃ by utilizing a multi-stage vacuum flash evaporation mode, and 8t of secondary steam generated by the vacuum flash evaporation and with the temperature higher than 60 ℃ enters a multi-effect evaporation system for use.
The acid wastewater after temperature reduction enters a membrane filtration concentration system together for further treatment to obtain 80m3The temperature of the acid wastewater concentrated solution is 31 ℃; the concentration of each component is 25g/L sulfuric acid, 75g/L sodium sulfate and 2g/L zinc sulfate, and the components enter an evaporation system for further evaporation and concentration treatment. Treated by an evaporation system to obtain 17m3The final concentrated solution containing 117g/L sulfuric acid, 351g/L sodium sulfate and 9.8g/L zinc sulfate is recycled to the acid bath step in the viscose fiber production system, and 120m separated by the membrane filtration concentration system is treated323m from filtrate and evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Comparative example 4
The temperature is 90 ℃ and the water quantity is 200m3The acid wastewater (detected as 10g/L of sulfuric acid, 30g/L of sodium sulfate, 0.8g/L of zinc sulfate and 40 g/L of turbidity 40ntu) directly enters an evaporation system for evaporation and concentration treatment. Treated by an evaporation system to obtain 17m 3The final concentrated solution containing 117g/L sulfuric acid, 351g/L sodium sulfate and 9.8g/L zinc sulfate is recycled to the acid bath step in the viscose fiber production system, 183m produced by the evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Comparative example 5
The temperature is 98 ℃ and the water quantity is 200m3The acid wastewater (detected to contain 13g/L of sulfuric acid, 40g/L of sodium sulfate, 1.1g/L of zinc sulfate and 30tu of turbidity) is pretreated to remove colloids and suspended matters, then the turbidity is 8ntu, the temperature is reduced to 30 ℃ by utilizing a multi-stage vacuum flash evaporation mode, and 10t of secondary steam with the temperature higher than 60 ℃ generated by the vacuum flash evaporation enters a multi-effect evaporation system for use.
The acid wastewater after temperature reduction enters a membrane filtration concentration system together for further treatment to obtain 104m3The temperature of the acid wastewater concentrated solution is 31 ℃; the concentration of each component is 25g/L sulfuric acid, 75g/L sodium sulfate and 2g/L zinc sulfate, and the components enter an evaporation system for further evaporation and concentration treatment. After the treatment of an evaporation system, 21.5m is obtained3120g/L sulfuric acid, 360g/L sodium sulfate, sulfuric acidRecycling the final concentrated solution of zinc 10g/L to the acid bath step in the viscose fiber production system, and treating and separating 96m by using a membrane filtration concentration system 382.5m from filtrate and evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Comparative example 6
The temperature is 90 ℃ and the water quantity is 200m3The acid wastewater (detected as 10g/L of sulfuric acid, 30g/L of sodium sulfate, 0.8g/L of zinc sulfate and 40-40 ntu turbidity) is subjected to a pretreatment process to remove colloids and suspended matters, then the turbidity is 10ntu, and the acid wastewater enters an evaporation system for evaporation and concentration treatment. After the treatment of an evaporation system, 16.5m is obtained3The final concentrated solution containing 120g/L sulfuric acid, 360g/L sodium sulfate and 10g/L zinc sulfate is recycled to the acid bath step in the viscose fiber production system, and 183.5m is produced by the evaporation system3And the/h condensed water is recycled to the viscose fiber production system as production water.
Comparative analysis experiment
And (4) analyzing results:
through the energy consumption analysis of the membrane filtration concentration system and the evaporation system in the examples 1-6, the cost of 1 ton of filtrate separated by the membrane filtration concentration system is 5.8 yuan, and the cost of 1 ton of waste water evaporated by the evaporation system after the heat in the acid waste water is fully utilized is 25 yuan-30 yuan. Therefore, the membrane filtration concentration system can separate as much filtrate as possible in the wastewater treatment process, and the overall energy consumption is reduced.
In comparative examples 1, 3 and 5, the acidic wastewater is only cooled, the membrane concentrated solution is not preheated, the temperature of the liquid entering the evaporation system is 31 ℃, the operation cost of the membrane filtration concentration system is not changed, the low temperature of the liquid entering the evaporation system causes the large steam consumption of the evaporation system, 0.4t of steam is consumed for evaporating one ton of water, and the cost for evaporating one ton of water of the evaporation system is about 50 yuan.
In comparative examples 2, 4 and 6, the acidic wastewater is directly fed into the evaporation system for evaporation and concentration without passing through the membrane filtration and concentration system, the total amount of water is evaporated and separated in the evaporation system, and the cost of evaporating 1 ton of water in the evaporation system is about 4 times of the cost of separating 1 ton of water in the membrane filtration and concentration system. This results in 4 times the cost of water that could be separated by a membrane filtration concentration system in an evaporation system.
Therefore, in the examples 1 to 6, the cooling and preheating of the acidic wastewater are mutually used as cold and heat sources, the heat in the acidic wastewater is fully utilized, and compared with the comparative examples 1 to 6, the overall energy consumption can be reduced, so that the treatment cost of the acidic wastewater is reduced.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (6)
1. A method for comprehensively utilizing heat energy in the viscose acid wastewater treatment process is characterized by comprising the following steps:
(1) cooling the acid wastewater to a temperature required by a membrane filtration concentration system for treatment;
(2) filtering and concentrating the cooled acidic wastewater by using a membrane filtering and concentrating system to obtain an acidic wastewater concentrated solution;
(3) Preheating the acid wastewater concentrated solution, and then feeding the acid wastewater concentrated solution into an evaporation system for further evaporation and concentration;
the acidic wastewater in the step (1) and the acidic wastewater concentrated solution in the step (3) mutually serve as cold and heat sources to exchange heat, and meanwhile, the temperature of the acidic wastewater is reduced and the acidic wastewater concentrated solution is preheated;
cooling the acidic wastewater in the step (1) to 30-38 ℃ by adopting a heat exchange cooling and vacuum flash evaporation cooling mode; dividing the pretreated high-temperature acidic wastewater into two parts, cooling the first part of the high-temperature acidic wastewater by adopting a multi-stage vacuum flash vaporization process, introducing secondary steam generated after flash vaporization into the evaporation system in the step (3) for use, cooling the second part of the high-temperature acidic wastewater by adopting a heat exchanger for heat exchange, and providing a cold source for the second part of the high-temperature acidic wastewater, namely filtering and concentrating the acidic wastewater concentrated solution subjected to concentration treatment by the membrane filtering and concentrating system in the step (2).
2. The method for comprehensively utilizing the heat energy in the viscose acid wastewater treatment process according to claim 1, wherein the viscose acid wastewater is fiber washing water with acid bath discharged in a viscose production process, and the discharge position is before fiber cutting or after the fiber cutting.
3. The method for comprehensively utilizing heat energy in the process of treating viscose acid wastewater according to claim 2, wherein the temperature of the viscose acid wastewater is 85-98 ℃, the concentration of each component is 5-13g/L of sulfuric acid, 15-40g/L of sodium sulfate, 0.3-1.1g/L of zinc sulfate, and the turbidity is 30-50 NTU.
4. The method for comprehensively utilizing heat energy in the viscose acid wastewater treatment process according to any one of claims 1 to 3, wherein the temperature of the acid wastewater concentrated solution treated by the membrane filtration concentration system in the step (2) is 33-40 ℃, and the concentration of each component is 25-30g/L of sulfuric acid, 75-90g/L of sodium sulfate and 2-2.5g/L of zinc sulfate.
5. The method for comprehensively utilizing the heat energy generated in the viscose fiber acid wastewater treatment process according to any one of claims 1 to 3, wherein the acid wastewater concentrated solution in the step (3) is preheated by heat exchange at a temperature of 82-90 ℃.
6. The method for comprehensively utilizing the heat energy in the viscose acid wastewater treatment process according to claim 5, wherein a heat exchanger is used for heat exchange and temperature rise, and the acid wastewater in the step (1) is used for providing a heat source for the heat exchanger.
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