A system for extracting sodium sulfate from wastewater by using dry residual heat of white carbon black

Abstract

The application provides a system for extracting sodium sulfate from wastewater by using white carbon black drying waste heat, comprising a raw material liquid preheater, a one-effect evaporation assembly, a two-effect evaporation assembly, a crystallization leg, a thickener, a centrifugal filter and a dryer; first, the wastewater containing sodium sulfate is preheated by using two-effect steam; then, the wastewater containing sodium sulfate is heated by using high-temperature drying tail gas, and then gas-liquid separation is carried out in a one-effect separator; then, the one-effect concentrated liquid is heated by using one-effect steam, and then gas-liquid separation is carried out in a two-effect separator; then, the liquid from the two-effect separator is sequentially subjected to the crystallization leg, the thickener, the centrifugal filter and the dryer, and sodium sulfate powder is obtained; the drying tail gas generated by white carbon black spray drying is combined with multi-effect evaporation technology to recover sodium sulfate products from wastewater, and the obtained water is reused for production, so that zero discharge of wastewater is realized, environmental protection benefits are obvious, the process is short and compact, the waste heat utilization rate is high, and the operation cost is low.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of silica production, specifically to a system for extracting sodium sulfate from wastewater by evaporating wastewater from silica drying. Background Technology

[0002] Silica is a white powder, mainly referring to precipitated silica, fumed silica, and ultrafine silica gel. As an environmentally friendly and high-performance additive, silica is mainly used in rubber products, textiles, papermaking, pesticides, and food additives.

[0003] Currently, the precipitated silica industry primarily uses sodium silicate (Na2SiO3) and sulfuric acid (H2SO4) as raw materials. The main product, silica (SiO2), is obtained through solid-liquid separation and subsequent drying in the form of precipitation. The byproduct is sodium sulfate (Na2SO4), present in the production wastewater at a concentration of approximately 3%. Due to its low concentration and high extraction cost, almost all companies in the industry, both internationally and domestically, discharge it into rivers, lakes, and seas. This not only results in the loss of byproducts but also negatively impacts the surrounding environment, particularly water systems. In recent years, with increasingly stringent domestic environmental policies, treating wastewater with high sodium sulfate content has become a top priority for the industry. Some companies have attempted membrane concentration combined with MVR evaporation technology, while others have directly used steam as a heat source for multi-effect evaporation crystallization. Although these methods ultimately yield anhydrous sodium sulfate, the high cost has prevented most from achieving large-scale industrial production, forcing them to abandon these approaches midway.

[0004] Currently, the drying process in precipitated silica production lines generally adopts spray drying. During the product drying process, a large amount of high-temperature drying exhaust gas is emitted. A single unit can emit 80,000 standard cubic meters of exhaust gas at 100°C. Enterprises generally perform simple waste heat recovery, and the exhaust gas is discharged after being cooled to about 75°C. Only a small portion of the heat is recovered, and most of the heat is lost through external discharge. Summary of the Invention

[0005] The purpose of this invention is to provide a system for extracting sodium sulfate by evaporating wastewater using the residual heat from drying silica.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A system for extracting sodium sulfate by evaporating wastewater using waste heat from drying silica includes a raw material preheater, a first-effect evaporation unit, a second-effect evaporation unit, a crystallization leg, a thickener, a centrifugal filter, and a dryer.

[0008] The feed liquid preheater is used to preheat the feed liquid. The inlet of the tube side of the feed liquid preheater is used to let in cold feed liquid containing sodium sulfate. The outlet of the tube side of the feed liquid preheater is connected to the feed liquid inlet of the first-effect separator. The inlet of the shell side of the feed liquid preheater is connected to the steam outlet of the second-effect separator. The outlet of the shell side of the feed liquid preheater is used to discharge the condensate generated after the second-effect steam heat exchange and cooling. The outlet of the shell side of the feed liquid preheater is connected to the inlet of the vacuum pump.

[0009] The single-effect evaporation unit includes a single-effect separator, a single-effect heater, a dry exhaust gas pressurizing fan, and a single-effect circulating pump;

[0010] The liquid outlet at the bottom of the first-effect separator is connected to the liquid inlet at the top of the tube side of the first-effect heater. The liquid outlet at the bottom of the tube side of the first-effect heater is connected to the liquid inlet of the first-effect circulating pump. The liquid outlet of the first-effect circulating pump is connected to the circulating liquid inlet of the first-effect separator.

[0011] The air inlet of the dry exhaust gas pressurizing blower is connected to the air outlet of the bag filter through a pipe. The air outlet of the dry exhaust gas pressurizing blower is connected to the air inlet of the shell side of the first-effect heater through a pipe. The air outlet of the shell side of the first-effect heater is used to discharge the low-temperature exhaust gas after heat exchange and cooling. The condensate outlet of the shell side of the first-effect heater is used to discharge the first-effect condensate generated during the heat exchange and cooling process of the dry exhaust gas.

[0012] The double-effect evaporation unit includes a first-effect concentrate transfer pump, a second-effect separator, a second-effect heater, and a second-effect circulation pump;

[0013] The inlet of the first-effect concentrate transfer pump is connected to the outlet at the bottom of the first-effect separator; the outlet of the first-effect concentrate transfer pump is connected to the inlet of the first-effect concentrate of the second-effect separator; the outlet at the bottom of the second-effect separator is connected to the inlet at the top of the tube side of the second-effect heater; the outlet at the bottom of the tube side of the second-effect heater is connected to the inlet of the second-effect circulation pump; and the outlet of the second-effect circulation pump is connected to the inlet of the circulating liquid of the second-effect separator.

[0014] The inlet of the shell side of the double-effect heater is connected to the steam outlet of the first-effect separator. The condensate outlet of the shell side of the double-effect heater is used to discharge the double-effect condensate generated during the heat exchange and cooling process of the first-effect steam.

[0015] The liquid outlet at the bottom of the double-effect separator is connected to the liquid inlet of the crystallizing leg. The liquid outlet of the crystallizing leg is connected to the liquid inlet of the thickener. The thickener is used for sedimentation separation. The bottom slurry outlet of the thickener is connected to the slurry inlet of the centrifugal filter. The centrifugal filter is used for centrifugal separation. The wet filter residue outlet of the centrifugal filter is connected to the feed inlet of the dryer through a material conveyor. The dryer is used for drying and dehydrating the wet material. The discharge outlet of the dryer is used to discharge the finished sodium sulfate powder.

[0016] Preferably, the supernatant outlet of the thickener is connected to the inlet of the first-effect separator via a pipe.

[0017] Preferably, the filtrate outlet of the centrifugal filter is connected to the inlet of the first-effect separator via a pipe.

[0018] This application has achieved the following beneficial technical effects:

[0019] (1). This application performs deep waste heat recovery on the high-temperature drying tail gas generated in the drying process. Using the recovered waste heat, multi-effect evaporation technology is used to evaporate the sodium sulfate-containing wastewater to obtain anhydrous sodium sulfate and high-purity recycled water.

[0020] (2). The key point of this application is to use the waste heat of the exhaust gas emitted during the production of the main product to recover and sell the by-product from the solution, while obtaining high-purity water which can be reused in the production of the main product. This saves the cost of preparing high-purity water for the production line, achieves zero wastewater discharge, and generates certain economic benefits.

[0021] (3) This invention first uses double-effect steam to preheat sodium sulfate-containing wastewater; then uses high-temperature dry tail gas to heat the sodium sulfate-containing wastewater in a first-effect process, followed by gas-liquid separation in a first-effect separator; then uses first-effect steam to heat the first-effect concentrate in a second-effect process, followed by gas-liquid separation in a second-effect separator; then the liquid effluent from the second-effect separator passes sequentially through a crystallizer, a thickener, a centrifugal filter, and a dryer to obtain sodium sulfate powder; by utilizing the waste heat from the main product production process combined with multi-effect evaporation technology, sodium sulfate product is successfully recovered from sodium sulfate-containing wastewater, while maintaining low operating costs and generating considerable economic benefits. The high-purity water obtained from evaporation is reused in production, achieving zero wastewater discharge in the process, resulting in significant environmental benefits. The process is short and compact, with high waste heat utilization rate, and is worthy of promotion and implementation in the same or similar industries. Attached Figure Description

[0022] Figure 1 A schematic diagram of a system for extracting sodium sulfate from wastewater by evaporating wastewater using the residual heat from drying silica is provided in the embodiments of this invention;

[0023] In the diagram: 101 Raw material liquid preheater;

[0024] 201 First-effect separator, 202 First-effect heater, 203 Drying exhaust gas pressurizing fan, 204 First-effect circulating pump;

[0025] 301 Single-effect concentrate transfer pump, 302 Double-effect separator, 303 Double-effect heater, 304 Double-effect circulating pump;

[0026] 401 Crystallizer leg, 402 Thickener, 403 Centrifugal filter, 404 Dryer;

[0027] 5. Spray drying tower, 6. Bag filter, 7. Vacuum pump. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, and not all of them. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown in the figure: raw material liquid preheater 101; first-effect separator 201, first-effect heater 202, dry exhaust gas pressurizing fan 203, first-effect circulating pump 204; first-effect concentrate transfer pump 301, second-effect separator 302, second-effect heater 303, second-effect circulating pump 304; crystallizer leg 401, thickener 402, centrifugal filter 403, dryer 404; spray drying tower 5, bag filter 6, vacuum pump 7.

[0030] This application provides a system for extracting sodium sulfate by evaporating wastewater using the residual heat from drying silica, including a raw material liquid preheater 101, a first-effect evaporation assembly, a second-effect evaporation assembly, a crystallization leg 401, a thickener 402, a centrifugal filter 403, and a dryer 404.

[0031] The raw material liquid preheater 101 is used to preheat the raw material liquid (containing sodium sulfate wastewater). The inlet of the tube side of the raw material liquid preheater 101 is used to allow the cold raw material liquid (containing sodium sulfate wastewater) to flow in. The outlet of the tube side of the raw material liquid preheater 101 is connected to the raw material liquid inlet of the first-effect separator 201. The air inlet of the shell side of the raw material liquid preheater 101 is connected to the second-effect steam outlet of the second-effect separator 302. The outlet of the shell side of the raw material liquid preheater 101 is used to discharge the condensate generated after the second-effect steam heat exchange and cooling. The air outlet of the shell side of the raw material liquid preheater 101 is connected to the air inlet of the vacuum pump 7.

[0032] The single-effect evaporation assembly includes a single-effect separator (i.e., a single-effect gas-liquid separator) 201, a single-effect heater 202, a dry exhaust gas pressurizing fan 203, and a single-effect circulating pump 204.

[0033] The liquid outlet at the bottom of the first-effect separator 201 is connected to the liquid inlet at the top of the tube side of the first-effect heater 202, the liquid outlet at the bottom of the tube side of the first-effect heater 202 is connected to the liquid inlet of the first-effect circulating pump 204, and the liquid outlet of the first-effect circulating pump 204 is connected to the circulating liquid inlet of the first-effect separator 201.

[0034] The air inlet of the dry exhaust gas pressurizing fan 203 is connected to the air outlet of the bag filter 6 through a pipe. The air outlet of the dry exhaust gas pressurizing fan 203 is connected to the air inlet of the shell side of the first-effect heater 202 through a pipe. The air outlet of the shell side of the first-effect heater 202 is used to discharge the low-temperature exhaust gas after heat exchange and cooling. The condensate outlet of the shell side of the first-effect heater 202 is used to discharge the first-effect condensate generated during the heat exchange and cooling process of the dry exhaust gas.

[0035] The double-effect evaporation assembly includes a first-effect concentrate transfer pump 301, a second-effect separator (i.e., a second-effect gas-liquid separator) 302, a second-effect heater 303, and a second-effect circulation pump 304.

[0036] The inlet of the first-effect concentrate transfer pump 301 is connected to the outlet at the bottom of the first-effect separator 201. The outlet of the first-effect concentrate transfer pump 301 is connected to the inlet of the first-effect concentrate of the second-effect separator 302. The outlet at the bottom of the second-effect separator 302 is connected to the inlet at the top of the tube side of the second-effect heater 303. The outlet at the bottom of the tube side of the second-effect heater 303 is connected to the inlet of the second-effect circulating pump 304. The outlet of the second-effect circulating pump 304 is connected to the circulating liquid inlet of the second-effect separator 302.

[0037] The inlet of the shell side of the double-effect heater 303 is connected to the steam outlet of the first-effect separator 201. The condensate outlet of the shell side of the double-effect heater 303 is used to discharge the double-effect condensate generated during the heat exchange and cooling process of the first-effect steam.

[0038] The liquid outlet at the bottom of the double-effect separator 302 is also connected to the liquid inlet of the crystallization leg 401. The liquid outlet of the crystallization leg 401 is connected to the liquid inlet of the thickener 402. The thickener 402 is used for sedimentation separation. The slurry outlet at the bottom of the thickener 402 is connected to the slurry inlet of the centrifugal filter 403. The centrifugal filter 403 is used for centrifugal separation. The wet filter residue outlet of the centrifugal filter 403 is connected to the feed inlet of the dryer 404 through a material conveyor. The dryer 404 is used for drying and dehydrating the wet material. The discharge outlet of the dryer 404 is used to discharge the finished sodium sulfate powder.

[0039] In one embodiment of this application, the supernatant outlet of the thickener 402 is connected to the inlet of the first-effect separator 201 via a pipe.

[0040] In one embodiment of this application, the filtrate outlet of the centrifugal filter 403 is connected to the inlet of the first-effect separator 201 via a pipe.

[0041] In this application, hot air generated by burning natural gas in a hot blast furnace enters the spray drying tower from the top. Silica slurry is sprayed from atomizing nozzles on the inner top wall of the spray drying tower. The hot air collides with the silica slurry to achieve heat exchange and drying. Then, the mixed airflow of the dried material and the high-temperature drying exhaust gas enters a bag filter. After filtration by the bag filter, silica powder is produced. The drying exhaust gas generated after filtration by the bag filter is drawn into a drying exhaust gas pressurizing fan and then sent to a single-effect heater to heat the wastewater containing sodium sulfate.

[0042] In this application, the initial temperature of the dried exhaust gas is 100±25℃, and the final emission temperature of the exhaust gas is <50℃.

[0043] Relative humidity of dry exhaust gas: 80–120%;

[0044] Initial concentration of sodium sulfate-containing wastewater: >3%;

[0045] Initial temperature of sodium sulfate-containing wastewater: 50±10℃;

[0046] Initial pH value of sodium sulfate-containing wastewater: >6.5;

[0047] Initial turbidity of sodium sulfate solution: <5.0 NTU.

[0048] In this application, multi-effect evaporation is a series evaporation operation in which the secondary steam of the previous effect is used as the heating steam of the next effect. In multi-effect evaporation, the operating pressure of each effect, the temperature of the corresponding heating steam, and the boiling point of the solution decrease sequentially.

[0049] In this application, the condensate generated in various places, including the first-effect condensate, the second-effect condensate, the steam condensate generated by the raw material liquid preheater 101, etc., can all be reused in production.

[0050] The methods and apparatus not described in detail in this invention are all prior art and will not be elaborated further.

[0051] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for extracting sodium sulfate from wastewater by evaporating wastewater from the drying process of precipitated silica, characterized in that, The system includes a raw material preheater, a first-effect evaporator, a second-effect evaporator, a crystallizer, a thickener, a centrifugal filter, and a dryer. The raw material preheater is used to preheat the raw material. The inlet of the tube side of the raw material preheater is used to allow the cold raw material containing sodium sulfate to flow in. The outlet of the tube side of the raw material preheater is connected to the raw material inlet of the first-effect separator. The inlet of the shell side of the raw material preheater is connected to the steam outlet of the second-effect separator. The outlet of the shell side of the raw material preheater is used to discharge the condensate generated after the second-effect steam heat exchange and cooling. The outlet of the shell side of the raw material preheater is connected to the inlet of the vacuum pump. The single-effect evaporation unit includes a single-effect separator, a single-effect heater, a dry exhaust gas pressurizing fan, and a single-effect circulating pump; The liquid outlet at the bottom of the first-effect separator is connected to the liquid inlet at the top of the tube side of the first-effect heater. The liquid outlet at the bottom of the tube side of the first-effect heater is connected to the liquid inlet of the first-effect circulating pump. The liquid outlet of the first-effect circulating pump is connected to the circulating liquid inlet of the first-effect separator. The air inlet of the dry exhaust gas pressurizing blower is connected to the air outlet of the bag filter through a pipe. The air outlet of the dry exhaust gas pressurizing blower is connected to the air inlet of the shell side of the first-effect heater through a pipe. The air outlet of the shell side of the first-effect heater is used to discharge the low-temperature exhaust gas after heat exchange and cooling. The condensate outlet of the shell side of the first-effect heater is used to discharge the first-effect condensate generated during the heat exchange and cooling process of the dry exhaust gas. The double-effect evaporation unit includes a first-effect concentrate transfer pump, a second-effect separator, a second-effect heater, and a second-effect circulation pump; The inlet of the first-effect concentrate transfer pump is connected to the outlet at the bottom of the first-effect separator; the outlet of the first-effect concentrate transfer pump is connected to the inlet of the first-effect concentrate of the second-effect separator; the outlet at the bottom of the second-effect separator is connected to the inlet at the top of the tube side of the second-effect heater; the outlet at the bottom of the tube side of the second-effect heater is connected to the inlet of the second-effect circulation pump; and the outlet of the second-effect circulation pump is connected to the inlet of the circulating liquid of the second-effect separator. The inlet of the shell side of the double-effect heater is connected to the steam outlet of the first-effect separator. The condensate outlet of the shell side of the double-effect heater is used to discharge the double-effect condensate generated during the heat exchange and cooling process of the first-effect steam. The liquid outlet at the bottom of the double-effect separator is also connected to the liquid inlet of the crystallization leg. The liquid outlet of the crystallization leg is connected to the liquid inlet of the thickener. The thickener is used for sedimentation separation. The bottom slurry outlet of the thickener is connected to the slurry inlet of the centrifugal filter. The centrifugal filter is used for centrifugal separation. The wet filter residue outlet of the centrifugal filter is connected to the feed inlet of the dryer through a material conveyor. The dryer is used for drying and dehydrating the wet material. The discharge outlet of the dryer is used to discharge the finished sodium sulfate powder. The supernatant outlet of the thickener is connected to the inlet of the first-effect separator via a pipeline; The filtrate outlet of the centrifugal filter is connected to the inlet of the first-effect separator via a pipe.

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