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Wastewater evaporation crystallization treatment

信息来源: | 发布日期: 2017-01-18 | 浏览量:
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First, change the concept of ideas, turning waste into treasure

Wastewater is also a resource. Chemical resources such as cellulose, sugar, protein, nitrogen acid, inorganic salt and other useful resources in industrial waste water, such as biochemical, inorganic salt chemical, food industry, meat processing, paper industry, alcohol and so on, , The management of waste water to extract useful resources in the waste water, waste water through the steam condensate into the water, waste water is not waste, to achieve clean production and the real sense of the beautiful environment.

 

Whether the past or the current business is to obtain the maximum economic efficiency for the purpose. If only in the wastewater treatment investment, no output, the enterprise is not a positive. Since the promulgation of national national environmental protection law, some companies would rather fine, do not seriously carry out waste water treatment, so the effluent efflux phenomenon occurs, more driven by the benefits that waste is to throw money, the more thorough governance, money Throw the more, so whether it is environmental management, or the person in charge of business, must change the concept of ideas, waste is the resources. Governance wastewater should be an investment, there is output, social benefits, but also economic benefits of an industry, especially with high concentrations of waste water business, waste water is Po, the higher the concentration of wastewater, the use of evaporator concentration, continuous crystallization of the input The less (because of the less water). For enterprises with low concentrations of waste water, to change the original product production process, so that the concentration of waste water in order to reduce waste water treatment. Such as glutamic acid industry, glutamic acid products, large amount of waste water, low concentration (including ammonium sulfate concentration of 3-4%), most enterprises in order to compete, in order to obtain large profits, governance is not complete, often secretly discharged, usually stored Where the waste water quickly became a reservoir, and even occupied a river. Wastewater in the ammonium sulfate, sugar, protein, cellulose are all useful substances. Foreign glutamic acid enterprises do not have waste water production process, the production process and China's glutamic acid extraction process is very different from the fermentation of glutamic acid solution, after membrane filtration, cut off sugar, protein, cellulose as feed, and then 9% Of ammonium glutamate solution, evaporated to 28% concentrated, the use of four effect film + heat pump evaporation process, the maximum evaporation temperature below 75 ℃, evaporation of 1 ton of water, only consumption of 0.20 tons of steam.

 

And then the isoelectric point continuous crystallization, glutamic acid crystallization once, it becomes γ-shaped crystal, particle size greater than 0.15mm, and containing ammonium sulfate (some ammonium chloride) wastewater concentration of 13-14%, and then evaporate the crystallization of ammonium sulfate fertilizer. This production process completely solve the ammonia nitrogen industrial wastewater difficult to manage the problem, and the output part of the cost of governance to offset, as well as the balance, this is the enterprise welcomed the wastewater treatment program. 

 

Second, the use of vacuum evaporation crystallization process of industrial wastewater treatment.

This process is very mature, is currently used in industrial wastewater extraction of ammonium chloride (agricultural grade), ammonium sulfate, sodium chloride, sodium sulfate and other inorganic salts, has decades of history. Especially in recent years, more and more advanced technology, energy consumption is getting lower and lower, the degree of automation is getting higher and higher, the material is getting better and better, longer life. Here I introduce the vacuum evaporation and vacuum continuous crystallization of the production process.


  1,Vacuum evaporation process: that is, under the vacuum state of the lower boiling point of the physical properties of low temperature (100 ℃ -40 ℃) evaporation and concentration, the higher the vacuum, the lower the boiling point of the liquid. (Check the water vapor technical characteristics table) How is the vacuum formed? Is the instantaneous condensation of steam suddenly formed, and then supplemented by a vacuum pump to take non-condensable gas to ensure the stability of the vacuum, the most economical way is to use normal temperature cooling water or low temperature cooling water condensing steam. How do we control the level of vacuum? Control the temperature and water cooling water on it.


Vacuum evaporation can be divided into single-effect production, can also be divided into multi-effect production, the more effective the lower the energy consumption, but the greater the investment industry. The determination of the effect is based on the amount of material evaporation and concentration, investment and energy consumption to determine the comparison. Material evaporation of water per hour, now can do a single set of evaporation per hour 250 tons -50 kg. In order to save energy, in front of the first effect plus a steam jet compression pump (referred to as heat pump), the energy consumption is lower, the evaporation of 1 ton of water How much steam is required for the boiler, for the steam consumption ratio. That is often said that the evaporation of 1 ton of water consumed how much steam, which is a measure of advanced evaporation or not an important parameter, the world's advanced level is:
    Single-effect + heat pump steam consumption ratio 0.55 ~ 0.65
    Double-effect + heat pump steam consumption ratio of 0.38 ~ 0.42
    Three-effect + heat pump steam consumption ratio of 0.28 ~ 0.33
    Four-effect + heat pump steam consumption ratio of 0.20 ~ 0.22
    Five-effect + heat pump steam consumption ratio of 0.16 ~ 0.18

China's vacuum evaporation energy consumption in some industries is close to the world's advanced level, but most of the industry level is still low, mainly in the different boiling point of the feed, the second flash and condensate heat reuse, vacuum is not high , The material boiling point temperature is not low enough, as well as automatic adjustment of the instrument material difference and so on. More important is the theoretical level and the actual level of work innovation ability, still far behind the developed countries.


2,vacuum crystallization process
Vacuum crystallization is divided into: vacuum evaporation continuous crystallization and vacuum flashing cooling continuous crystallization, are in a vacuum state, the crystallization temperature of the boiling point of the physical characteristics of the decline, continuous crystallization.
Vacuum evaporation crystallization process is in the vacuum state of the evaporation side of the crystallization, such as sodium glutamate is the use of this process, according to scale that with an annual output of 2-4 million tons of monosodium glutamate, a set of vacuum evaporation equipment can be. Industrial waste water extraction of inorganic salts, such as ammonium chloride, ammonium sulfate, sodium chloride, sodium sulfate, sodium bicarbonate, also used vacuum continuous crystallization. This process can be single effect, can also be multi-effect, according to the number of evaporation, the crystallization temperature according to the crystallization of the process characteristics and saturation solubility curve to determine. Practical application, the crystallization temperature as low as possible, to facilitate the crystallization of equipment to choose cheaper materials, reduce investment costs, the temperature is too low is not desirable. Because the second-rate steam is not too large capacity, equipment to do large and increase investment. Vacuum evaporation crystallization process is characterized by large grain size, uniform particles, low energy consumption, low operating costs, high technical content.

Vacuum flash crystal crystallization process is vacuum, while flashing side of the flash, while crystallization. Crystallization temperature can be done very low, in order to improve the yield, even before 0 ℃ can be done. Glutamic acid isoelectric point continuous crystallization, that is, flash crystallization process, he asked 2-3 ℃ crystallization, flashing steam almost 0 ℃. The flashing process is to cool the temperature too. For example, from 30 ° C to 10 ° C, the specific heat of the crystalline solution × the weight of the crystalline solution / hour × (30 ° C to 10 ° C) divided by 10 ° C The latent heat of vaporization of the solution is equal to the amount of flash steam / So that the evaporation of so much steam, crystallization solution can be reduced from 30 ℃ to 10 ℃, while the vacuum requires the same low-temperature cooling water, or even frozen brine to condense flash steam, also need a vacuum pump to extract non-condensable gas to keep the vacuum stable. Vacuum fading crystallization process is also widely used, glutamic acid, iso-dimensional C satisfied, xylitol, vitamin C, inorganic salts, magnesium sulfate heptahydrate, industrial potassium nitrate, copper sulfate pentahydrate are used. Compared with the intermittent cooling crystallization process, the biggest advantage is the low energy consumption, the size of the crystal grain can be controlled, the uniformity of the particle size garden, high technical content, small footprint, the total investment cost is not high.

 

3, vacuum multi-effect evaporation + spray drying process.

Wastewater in the use of useful substances such as protein, colloid and other materials are not suitable for crystallization of solid-liquid separation of the material, and the concentration of waste water is not high, the use of vacuum multi-effect evaporation + spray drying process, the wastewater can be steam condensate, Can be useful in the waste water into feed additives, such as meat combined with the processing plant in the bloody, washing water in the past are discarded as waste water, that is, pollution of the environment and the loss of resources, foreign countries have adopted this process Will all the blood protein recovery, sold to the feed mill, very popular, and Roulian plant has made economic benefits, do both. Starch industry in the corn, wheat, potatoes, washing water, soaking water containing starch, protein, lactic acid and so on. There are a lot of domestic starch plant it as waste water thrown away, which can be concentrated to 50% evaporation, and then spray dried into a protein feed additives, and soaked into water into a steam condensate, can be used as a process of water recycling, The stench of starch plant environment gone forever.

 

4, the technology is mature and reliable

The above techniques are physical processes, no chemical reactions, technically mature and reliable. People in the control of these technologies, there are new developments and innovations, but the completion of an engineering design, must be material and heat balance, which requires business cooperation, to provide the basic physical and chemical parameters of the wastewater, such as specific heat, crystallization Heat, severe, viscosity. (KG / hour), initial concentration, initial temperature, then to provide, the termination of the amount (KG / hour), the termination of concentration, the termination of the temperature (at different temperatures, different concentrations of the conditions), such as evaporation concentration, , If the need for vacuum crystallization, but also proposed crystal grain size requirements, to provide other substances in the wastewater content, to be accurate. Special waste water also provides steam partial pressure (higher boiling point) at different concentrations because the vapor partial pressure of the general salt solution can be found in the manual. Only with the enterprise in close cooperation to complete a perfect design and precision manufacturing.


Third, the waste water evaporation, crystallization of equipment and materials

1, vacuum evaporation equipment

(1) Falling film evaporator, falling film evaporator is widely used, low energy consumption (steam, electricity) thermal contact time is short, the initial material from the evaporator to the evaporator, often only tens of seconds, even if the four effects , No more than two minutes, especially adapted to heat-sensitive substances. Heat conduction temperature difference can also be produced, so the evaporation temperature can be designed very low. As mentioned above, glutamic acid concentration, is the choice of falling film evaporator, four-effect + heat pump. The first effect temperature is only 74 ℃ ~ 75 ℃. Falling film evaporator sub-DC and recirculating, DC from the energy saving and secondary evaporation and reuse are better than the recycling type, especially for heat-sensitive solution evaporation and concentration.
(2) external heating forced circulation evaporator, he consists of heating chamber and evaporation chamber, by the circulation pipe, circulating pump connected into a whole, it is suitable for the crystallization of particles or powder solution evaporation and concentration. Simple structure, easy to operate, the only problem is the circulating pump, power consumption is relatively high. At present, the domestic commonly used circulating pump is a single cantilever, double-end mechanical seal of the axial flow pump, flow, Yang Cheng small, low speed, mechanical seal with cooling water and sealed water, as long as the water clean and supply, The seal is generally not damaged, the evaporator after more than 30 years of operation to improve the domestic has mastered the non-blocking, no scaling and other technical points, has been able to design and foreign the same, high heat transfer coefficient evaporator.

 

2, vacuum evaporation mold and vacuum flash mold
Vacuum evaporation mold and vacuum flash mold continuous crystallization, it is completely different from the concept of intermittent crystallization intermittent crystallization of atmospheric pressure, vacuum evaporator and vacuum flash mold is continuous crystallization in a vacuum state, continuous feeding, continuous Discharge. The production is balanced continuously, the vacuum evaporator crystallizer is produced at the same pressure temperature while evaporating, while crystallizing the crystal, so it has a heating chamber and evaporates the crystallization chamber. Vacuum flashing crystallization is cooling crystallization. It needs to flash part of the heat (the heat into the steam flashing out) so it does not need heating room, only the sparkling crystallization chamber, and the crystallization chamber is divided into flash zone, nucleation growth zone, subsidence area, mother liquor separation The central circulation pipe area, especially the D, T, B type crystal tank, also has a vertical axial flow pump, to carry out their own cycle, so that the new material cooling, in the central circulation tube, not broken ring crystal in the metastable zone The normal growth, so this mold, crystal particles large, uniform size, garden slip, is intermittent crystallization can not be compared.

The type of mold is divided into FC type, Oslo type and DTB type, the world is in the three kinds of mold on the basis of continuous research and continuous improvement to form their own style, toward more energy efficient, more material, Crystallization effect is better in the direction of effort. China is also working hard, the designer developed monosodium glutamate vacuum evaporation mold, diameter φ5600, height 14m, volume 130m3, MSG particles 3-4mm long, 1 ~ 1.2mm in diameter, vertical axial pump only 15KW, Anhui, Bengbu, Fengyuan Biochemical Group company put into production, its technical level and foreign advanced level has been almost the same.

 

3, spray drying equipment

Spray drying is divided into pressure, airflow, centrifugal, these technologies are mature, China in the dye (pressure spray drying), white carbon black (centrifugal spray drying), the pharmaceutical industry (air spray drying) It is very common, the technology is also very mature, the main structure is divided into feeding system, atomization system, drying system, gas-solid separation system, at present, the maximum diameter of the drying tower can be done 12M, the maximum dry evaporation of water can be done 15000㎏ / Hour of their own development of the centrifugal atomizer has been foreign experts praise the peer.

 

4, material: material selection is correct or not, directly related to evaporation, crystallization, drying equipment life. Wastewater is acidic, alkaline, with chloride ions, sulfur ions, ammonium ions, different concentrations of salt, corrosive is not the same, so we must choose the appropriate material to ensure the normal operation of the equipment, the temperature is different, the material model also different.
 Such as: containing chlorine ions in the evaporation of water when the crystallization
    Temperature below 40 ℃, the material selection 2304 #, duplex stainless steel
    Temperature at 40 ℃ ~ 90 ℃, the material selection 2205 #, duplex stainless steel
    Temperature above 90 ℃, the material selection 2507 #, duplex stainless steel
 Such as: containing chloride ions, but also contains ammonium ions in the evaporation of waste water crystallization
    Temperature below 40 ℃, the material selection 2205 #, duplex stainless steel
    Temperature at 40 ℃ ~ 90 ℃, the material selection 2507 #, duplex stainless steel
    Temperature above 90 ℃, the material selection 254SMo or titanium.

For acidic or alkaline salt PH = 4 to 10 between the wastewater can choose austenitic 316L, 304L, the higher the temperature requirements of the better material. The chlorine, sulfur ions in the presence of water, you must use duplex stainless steel, because the two-phase stainless steel on the stress corrosion cracking, point corrosion and intergranular corrosion has excellent corrosion resistance.

 

Fourth, the direction of hard work
Clean production, industrial waste zero emissions, environmental protection departments at all levels of government has been pursuing the goal, but also enterprises, especially the direction of the old business efforts, the current problem is still troubled by the funds business, technological transformation funds difficult to implement, we hope that scientific and technological personnel See the government, banks and enterprises to join hands, for the common goal, and actively raise funds for the realization of cleaner production, to achieve social and economic benefits of the double harvest and work together.


  Our scientific and technical personnel on the basis of the existing technology, will continue to study the zero discharge of industrial waste in the new problems.


1, in order to reduce capital investment, the development of a set of equipment at the same time to extract two kinds of salt water, such as sodium chloride and sodium sulfate, sodium chloride and ammonium chloride and other new technology, the current technology has a breakthrough, construction design Completed, only to be put into operation and then vigorously promote.


2, in order to reduce the capital investment, with less expensive material instead of delicate

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