CN105461104A - Treatment process of concentrated salt wastewater produced by coal chemical industry - Google Patents

Abstract

A treatment process for the concentrated salt wastewater produced by the coal chemical industry is that the concentrated salt wastewater produced by the coal chemical industry passes through the first security filter, and then enters the nanofiltration device after pressurization, and the water produced by the nanofiltration device is sent to the hydrogen ion exchanger device at the back end for treatment , so that the zero hardness of the wastewater is lower than 0.1ppm; and then enter the decarbonization tower through negative pressure operation to decompose the carbon dioxide in the wastewater; add sodium hydroxide to the effluent of the decarbonization tower to adjust the pH value to be alkaline, and then enter the second security filter. The effluent enters the concentrated water reverse osmosis membrane device, and the fresh water generated is used for rehydration of circulating water, and the generated high-concentration brine is used for coal blending or evaporation and crystallization to ensure zero discharge of waste water. The invention has the advantages of low investment, low operating cost and high recovery rate.

Description

A treatment process for concentrated salt wastewater produced by coal chemical industry

technical field

The invention belongs to a technical method for reprocessing concentrated brine, in particular to a technical method for reprocessing concentrated brine produced after advanced treatment and reuse of coal chemical industry wastewater.

Background technique

The coal chemical process is an industry that converts coal into gas, liquid and solid products or semi-products, and then further processes them into chemical and energy products. Including coking, coal gasification, coal liquefaction, etc.

my country's coal chemical industry is currently mainly distributed in areas with relatively rich coal resources such as Northwest China. The scale and water consumption of new coal chemical enterprises are huge. The water consumption per ton of products is more than ten tons, and the annual water consumption is usually as high as tens of millions of cubic meters. However, the distribution of water resources in these areas is very small, or they are located in areas with relatively sensitive environments. Depending on the location, the capacity of the water environment is very limited. Environmental protection requires enterprises to maximize the use of production and domestic wastewater or zero discharge. Water resources and water environment issues have become constraints. One of the main problems in the development of the chemical industry.

Coal chemical industry wastewater often has a large amount of water and complex water quality, containing a large amount of phenols, polycyclic aromatic hydrocarbons, heterocycles, cyanides, oil, and ammonia nitrogen, etc. Water pretreatment + membrane system desalination, usually the recovery rate does not exceed 70%, and the treatment of concentrated brine that produces more than 30% becomes the key to zero discharge of wastewater. COD≥200mg/l), the main problem of using conventional concentrated water reverse osmosis for further treatment is serious membrane fouling and low recovery rate (less than 40%), resulting in a total recovery rate of about 80%, and a high recovery rate of about 20%. Concentrated brine needs to be equipped with an evaporation and crystallization device to achieve zero discharge of wastewater. Due to the large processing capacity and high energy consumption of this device, it leads to large investment and high operating costs. It can be said that the economic cost of achieving zero discharge of wastewater is huge. The scale of evaporation and crystallization can effectively reduce the investment and operating costs of wastewater treatment in enterprises. Therefore, the reprocessing and efficient recovery of concentrated brine has become one of the keys to improve the total recovery rate of the system and reduce the scale investment and operation treatment cost of the terminal evaporation crystallization device.

Based on the above processes, for large-scale coal chemical projects, the discharge of wastewater is large, and the scale of advanced treatment and reuse is often thousands of tons per hour. From the perspective of zero discharge of wastewater, it is necessary to minimize the high investment and high cost of the terminal evaporation crystallization device. Only by further improving the recovery rate of the front stage and reducing the design scale of evaporation and crystallization; and solving the environmental protection and economic pressure of the enterprise as a whole.

Contents of the invention

The object of the present invention is to provide a process for treating concentrated salt wastewater produced in coal chemical industry with low investment, low operating cost and high recovery rate for the advanced treatment of coal chemical industry wastewater.

Processing method of the present invention comprises the following steps:

(1) After the concentrated salt wastewater produced by the coal chemical industry is pressurized by the lift pump, scale inhibitors are added to the outlet pipe. After passing through the first security filter, it is pressurized by the nanofiltration booster pump and then enters the nanofiltration device. The water produced by the filter device is sent to the hydrogen ion exchanger device at the back end, and the concentrated water is sent to the softening and clarifying tank at the front end of the advanced treatment for further treatment and reuse;

Nanofiltration (NF) is a molecular-level separation technology whose separation membrane has a nanoscale pore size, which is between reverse osmosis and microfiltration. Like reverse osmosis, nanofiltration membrane is a pressure-driven membrane separation technology, but its mass transfer mechanism is different. Generally, nanofiltration membranes are charged (mostly negative charges), and the separation behavior of inorganic salts is not only affected by chemical potential. control, and is also affected by the potential gradient. When the flux is constant, the applied pressure required by the nanofiltration process is much lower than that of reverse osmosis, and it has a retention capacity of 90% for organic substances with a relative molecular mass greater than 300; since the nanofiltration membrane is charged, through electrostatic interaction, It can hinder the penetration of multivalent ions (especially multivalent cations), and can remove most of the hardness in wastewater; especially the salt rejection rate of multivalent anions is very high, reaching more than 95%; the recovery rate of nanofiltration system About 80% or more;

(2) The nanofiltration water is treated by a hydrogen ion exchanger (weak acid cation exchange resin is used), so that the zero hardness of the wastewater is lower than 0.1ppm;

(3) The effluent from the hydrogen ion exchanger enters the decarbonization tower, and the carbon dioxide in the wastewater is decomposed through negative pressure operation;

(4) The effluent from the decarbonization tower enters the intermediate pool, and the pH value is adjusted to be alkaline by adding sodium hydroxide. It first passes through the lifting pump to increase the pressure and then enters the second security filter. The effluent is then boosted by the reverse osmosis booster pump and then enters the concentrated Water reverse osmosis membrane device, the fresh water generated is reused for circulating water replenishment, and the amount of high-concentration brine produced is very small, which can be blended with coal or evaporated and crystallized to ensure zero discharge of waste water.

The coal chemical industry wastewater of the present invention is the concentrated brine produced by the biochemical tail water after advanced treatment and membrane desalination system treatment. Sexual solids (TDS) are between 10000-15000mg/L.

For example, the first security filter in step (1) and the second security filter in step (4) usually use a large flux, internal pressure filter, the design requires an inlet pressure of 0.3-0.6MPa, and a filtration accuracy of 5um; the form is a vertical circle The cylinder is composed of a cylinder body and a filter element. The material of the cylinder body is SUS304, and the material of the filter element is PP folding. There are many domestic manufacturers, such as the JSP-DJMF series model produced by Jinsanyang Water Treatment Company, Shanghai Weixiu Filtration Equipment Co., Ltd. The WX-L series produced by Jiangsu Mingrui Filtration, the MRBA series filter produced by Jiangsu Mingrui Filtration, etc.;

The nanofiltration device as described in step (1) (the membrane element is produced by GE in the United States, anti-pollution type, model DURASLJCKNF8040,), the inlet water pressure is 0.8-1.0Mpa, the designed membrane flux is 14-20LMH, and the system recovery rate is about 80%, the total desalination rate of the system is 50-70%; the rejection rate of polyvalent anion salts reaches more than 90%; it can remove most of the hardness in wastewater.

The hydrogen ion exchanger as described in step (2) uses a weak acid cation exchange resin (usually a weaker reactive group such as a carboxyl group (-COOH group), etc., this ion exchange resin can only exchange Ca ²⁺ , Mg in a weak base ²⁺ , etc., but the Na ⁺ and K ⁺ ions in the strong base cannot be exchanged. The specific operation requires the inlet water to be at room temperature and the inlet water pressure to be 0.2-0.4MPa. Alkalinity-related hardness, effluent hardness is less than 0.1ppm. Hydrochloric acid regeneration is used for regeneration, which has a wide range of sources and low cost.

As described in step (3), the negative pressure is maintained at -0.1~-0.15MPa, and the carbon dioxide in the effluent is less than 10ppm.

As described in step (4), the concentrated water reverse osmosis membrane device adopts HERO operation technical requirements, adding sodium hydroxide to the feed water to adjust the pH value to 9-11, the feed water pressure is 2.0-2.4Mpa, and the membrane flux is 25-28L/m ² .h, the recovery rate of the device can reach more than 90%.

As described above, the HERO operation technique is as follows:

HERO is the abbreviation of High Efficiency Reverse Osmosis. At present, it has been widely used in foreign countries, and is widely used in high-purity water manufacturing in the semiconductor industry, seawater desalination, power plant circulating water replenishment system, oil refinery sewage and other industrial fields. However, it is not widely used in China at present.

Usually the operating pH of the RO process is low. The primary purpose of reducing the pH of the feed water by adding acid is to reduce the tendency of calcium carbonate scaling in RO concentrated water, that is, to reduce the Langelier index [LSI]. When LSIc=pHc-pHs<0, Carbonate does not scale; HERO technology is the opposite. It is a reverse osmosis process that operates under zero hardness, low alkalinity, and high PH value conditions. It is a special case of RO technology. Under high PH conditions: organic matter remains dissolved state, it will not be adsorbed on the membrane wall, and few organisms can survive under high pH conditions, and it is impossible to reproduce. Under high pH conditions, the solubility of silicon will increase significantly. The above characteristics solve the membrane system very well. The problems of organic pollution, biological pollution, and silicon scaling increase the recovery rate of the RO system. In order to prevent the pollution of brackish water at high pH (such as hardness, alkalinity, iron, manganese, etc.), pretreatment usually uses Weak acid cation resin system and degasser to remove these pollutants.

The concentrated water reverse osmosis device used in the present invention adopts the HERO operation mechanism, and the reverse osmosis feedwater operates under the conditions of zero hardness, low alkalinity and high pH value. Compared with conventional reverse osmosis technology, it has no organic matter and biological fouling, no knot The recovery rate of wastewater can reach more than 90%, and the recovery rate of the entire wastewater treatment system can be increased to more than 95%, which greatly reduces the scale and operation cost of subsequent evaporation and crystallization treatment of high-concentration brine. Compared with the traditional RO process, the HERO system is only limited by the osmotic pressure of the membrane, and the recovery rate reaches over 90%. There is no fouling of silicon, organic matter and organisms, and there is very little cleaning. The effluent can be used for circulating water replenishment or desalinated water supply. The amount of water discharge is very small, and it is easy to reuse all of it or carry out further evaporation and crystallization.

Compared with the prior art, the present invention has the following characteristics:

1. The concentrated water produced by the biochemical tail water after pretreatment and membrane desalination system (usually using ultrafiltration + reverse osmosis process), suspended solids, colloids, macromolecular organic matter, etc. in the wastewater have been removed in the previous stage, and the turbidity Low, mainly organic matter and salts, nanofiltration devices can be used directly, using its membrane characteristics to remove some salts and most of the hardness, remove some organic matter, COD removal rate can reach 50%, improve the follow-up device for concentrated brine treatment operating conditions.

2. The nanofiltration produced water passes through the weak acid cation exchange resin to remove the wastewater to zero hardness. By adjusting the pH value and adopting the HERO operating condition, the recovery rate of the system is greatly improved, and the scale investment and operation cost of the subsequent evaporation and crystallization device system are reduced.

3. Compared with the conventional concentrated water reverse osmosis process, the recovery rate of the process of the present invention is greatly improved, from 40% to 90%, and the recovery rate of the entire wastewater treatment system can be increased to 95%, and the resulting high-concentration brine is very little , the scale and operating cost of the subsequent evaporation and crystallization device will be greatly reduced.

4. The process of the present invention has the advantages of simplicity, low investment, high recovery rate, less land occupation, and low operating cost, and has a good effect on enterprises implementing "zero discharge" of production wastewater.

Description of drawings

Fig. 1 schematic flow chart of the present invention.

detailed description

Example 1

(1) Nanofiltration device

Concentrated water (COD: 150mg/L, TDS: 10000mg/L, total hardness: 500mg/L) after advanced treatment and membrane desalination of biochemical tail water enters the concentrated brine pool, and the pressure is raised to 0.3MPa by the lift pump, and passes through the first The security filter is then pressurized to 0.8MPa by the nanofiltration booster pump. The nanofiltration device is arranged in a one-stage and two-stage form. Each container has 6 membrane elements connected in series. The membrane element is DURASLJCKNF8040, and the designed membrane flux is 18L/m ^2.h , the water produced by the nanofiltration device (COD is 80mg/L, hardness is 50mg/L, and the yield is 80%) is sent to the hydrogen ion exchanger device at the back end, and the concentrated water is sent to the softening and clarifying tank at the front end of the advanced treatment for further treatment Reuse;

(2) Resin hard removal unit

The nanofiltration product water then enters the resin hard removal unit, using a hydrogen ion exchanger (weak acid cation exchange resin), the product water is at room temperature and the pressure is 0.2MPa, so that the total hardness in the wastewater is 0.084mg/L, and at the same time, part of the alkali is removed Spend;

(3) Decarbonization unit

The effluent of the hydrogen ion exchanger enters the decarbonization tower, and the carbon dioxide in the water is removed through negative pressure operation of -0.1Mpa, so that the residual amount of CO ₂ in the water is 10ppm;

(4) concentrated water reverse osmosis device

The concentrated water after decarburization enters the intermediate pool, adjusts the pH value to 9 by adding sodium hydroxide, raises the pressure to 0.3MPa through the water pump, enters the second security filter, and then pressurizes the effluent to 2.0Mpa through the reverse osmosis booster pump , into the concentrated water reverse osmosis device, the design membrane flux is 28L/m ² .h, the control recovery rate is 90%, and the water quality of the produced water reaches the "Code for Design of Industrial Circulating Cooling Water Treatment" (GB50050-2007) for recycling recycled water for recycled water Replenish water quality requirements, and the main indicators COD: 10mg/l, TDS: 100mg/l, better than (GB50050-2007) water quality standards (COD≤30mg/l, TDS≤1000mg/l) control requirements, as circulating water replenishment Reuse, the produced high-concentration brine is sent to the evaporation and crystallization device.

Example 2

(1) Nanofiltration device

Concentrated water (COD: 200mg/L, TDS: 12000mg/L, total hardness: 750mg/L) after advanced treatment and membrane desalination of biochemical tail water enters the brine pool, and the pressure is raised to 0.4MPa by the lift pump, and passes through the first The security filter is then pressurized to 0.9MPa by the nanofiltration booster pump, the designed membrane flux is 16L/m ² .h, the water produced by the nanofiltration device (COD is 100mg/L, total hardness is 75mg/L, the yield 80%) to the hydrogen ion exchanger device at the back end, and the concentrated water is sent to the softening and clarifying tank at the front end of the advanced treatment for further treatment and reuse;

(2) Resin hard removal unit

The nanofiltration product water enters the resin hard removal unit, using a hydrogen ion exchanger (weak acid cation exchange resin), the product water is at room temperature and the pressure is 0.3MPa, so that the total hardness in the wastewater is lower than 0.092mg/L, and the removal part is attached Alkalinity;

(3) Decarbonization unit

The effluent from the hydrogen ion exchanger enters the decarburizer, and the carbon dioxide in the water is removed through negative pressure operation below -0.12Mpa, so that the residual CO ₂ in the water is 9.55ppm;

(4) concentrated water reverse osmosis device

The concentrated water after decarbonization enters the intermediate pool, adjusts the pH value to 10 by adding sodium hydroxide, raises the pressure to 0.4MPa through the water pump, enters the security filter, and then pressurizes to 2.2Mpa through the reverse osmosis booster pump, and enters the concentrated water. Water reverse osmosis device, the design membrane flux is 26.5L/m ² .h, the control recovery rate is 90%, and the water quality of the produced water reaches the water quality of the reclaimed water reused in the "Code for Design of Industrial Circulating Cooling Water Treatment" (GB50050-2007). Requirements, and the main indicators COD: 15mg/l, TDS: 120mg/l, better than (GB50050-2007) water quality standards (COD≤30mg/l, TDS≤1000mg/l) control requirements, as circulating water replenishment and reuse , the high-concentration brine produced is sent to the evaporation and crystallization device.

Example 3

(1) Nanofiltration device

Concentrated water (COD: 250mg/L, TDS: 15000mg/L, total hardness: 1000mg/L) after advanced treatment and membrane desalination of biochemical tail water enters the concentrated brine pool, and the pressure is raised to 0.6MPa by the lift pump, and passes through the first The security filter is then pressurized to 1.0MPa by the nanofiltration booster pump, the designed membrane flux is 14L/m2.h, and the nanofiltration device produces water (the effluent COD is 120mg/L, the total hardness is 100mg/L, the yield 80%) to the hydrogen ion exchanger device at the back end, and the concentrated water is sent to the softening and clarifying tank at the front end of the advanced treatment for further treatment and reuse;

(2) Resin hard removal unit

The nanofiltration product water enters the resin hard removal unit, passes through the hydrogen ion exchanger (weak acid cation exchange resin is used), the product water is at room temperature, and the pressure is 0.4MPa, so that the total hardness in the wastewater is 0.095mg/L, and at the same time, part of the alkali is removed Spend;

(3) Decarbonization unit

The water from the hydrogen ion exchanger enters the decarburizer, and the carbon dioxide in the water is removed through negative pressure operation below -0.15Mpa, so that the residual CO ₂ in the water is less than 9.0ppm;

(4) concentrated water reverse osmosis device

The concentrated water after decarbonization enters the intermediate pool, adjusts the pH value to 10.5 by adding sodium hydroxide, raises the pressure to 0.6MPa through the water pump, enters the second security filter, and then pressurizes to 2.4Mpa through the reverse osmosis booster pump. Enter the concentrated water reverse osmosis device, the design membrane flux is 25L/m ² .h, the control recovery rate is 90%, and the water quality of the product reaches the "Code for Design of Industrial Circulating Cooling Water Treatment" (GB50050-2007). Water quality requirements, and the main indicators COD below 20mg/l, TDS below 150mg/l, better than (GB50050-2007) water quality standards (COD below 30mg/l, TDS below 1000mg/l), as circulating water replenishment Reuse, the produced high-concentration brine is sent to the evaporation and crystallization device.

Claims (10)

1., to the dense salt waste water treatment process that Coal Chemical Industry produces, it is characterized in that comprising the steps:

(1) the dense salt waste water of Coal Chemical Industry generation is after lift pump supercharging, outlet conduit adds Scale inhibitors, after the first cartridge filter, again by entering nanofiltration device after the supercharging of nanofiltration topping-up pump, nanofiltration device produces the H-ion exchanger device that water send rear end, and dense water delivers to the softening settling pond reprocessing reuse of advanced treatment front end;

(2) nanofiltration produces water through H-ion exchanger process, makes waste water zero hardness lower than 0.1ppm;

(3) H-ion exchanger water outlet enters decarbonizing tower, by negative-pressure operation, the carbonic acid gas in waste water is parsed;

(4) decarbonizing tower water outlet enters intermediate pool, through hydro-oxidation sodium adjust ph be alkalescence, first after lift pump adherence pressure, enter the second cartridge filter, water outlet enters dense water reverse osmosis membrane apparatus again after reverse osmosis booster pump supercharging, the fresh water produced is back to circulating cooling make-up water, the high strong brine produced carries out coal blending or evaporative crystallization, guarantees wastewater zero discharge.

2. as claimed in claim 1 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, it is characterized in that the dense salt waste water that Coal Chemical Industry produces is the strong brine that biochemical tail water produces after advanced treatment and the process of film desalination system, in dense water, chemical oxygen demand (COD) is between 150-250mg/L, and total dissolved solid is between 10000-15000mg/L.

3. as claimed in claim 1 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, it is characterized in that step (1) first cartridge filter and step (4) second cartridge filter adopt large flux, inner pressed strainer, design requirements intake pressure 0.3-0.6MPa, filtering accuracy 5um; Form is vertical cylinder, is made up of cylindrical shell and filter core, and cylindrical shell material is SUS304, and filter core material is that PP folds.

4. as claimed in claim 3 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, it is characterized in that step (1) first cartridge filter and step (4) second cartridge filter be golden three yang edema process companies produce JSP-DJMF serial model No., Shanghai Wei Xiu filter plant company limited produce WX-L series, Jiangsu bright auspicious filter produce MRBA Series Filter.

5. as claimed in claim 1 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, it is characterized in that the intake pressure 0.8-1.0Mpa of the nanofiltration device described in step (1), design membrane flux is 14-20LMH.

6. as claimed in claim 5 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, it is characterized in that the membrane element in the nanofiltration device described in step (1) is that U.S. GE produces, pollution-resistant, model is DURASLJCKNF8040.

7. as claimed in claim 1 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, it is characterized in that the H-ion exchanger described in step (2) adopts weakly acidic cationic exchanger resin, concrete operations require water inlet normal temperature, intake pressure 0.2 ~ 0.4MPa, following current or counter-current regeneration.

8. as claimed in claim 1 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, what it is characterized in that the H-ion exchanger described in step (2) goes out the water hardness lower than 0.1ppm.

9. as claimed in claim 1 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, it is characterized in that the negative pressure described in step (3) maintains-0.1 ~-0.15MPa, water outlet carbonic acid gas is less than 10ppm.

10. as claimed in claim 1 a kind of to Coal Chemical Industry produce dense salt waste water treatment process, it is characterized in that the described dense water reverse osmosis membrane apparatus of described step (4) adopts HERO running technology, water inlet hydro-oxidation sodium adjust ph 9-11, intake pressure 2.0 ~ 2.4Mpa, membrane flux is 25 ~ 28L/m ².h.