WO2006094437A1

WO2006094437A1 - A method and an multi-effect evaporation for waste water of alkylene oxides

Info

Publication number: WO2006094437A1
Application number: PCT/CN2005/001427
Authority: WO
Inventors: Depei Liu
Original assignee: Depei Liu
Priority date: 2005-02-03
Filing date: 2005-09-08
Publication date: 2006-09-14
Also published as: CN1321070C; CN1673104A

Abstract

The present invention relates to a treatment method of industrial waste water for producing alkylene oxides and a multi-effect evaporation equipment. The method comprises the following steps: firstly, treating the waste water by multi-effect evaporation treatment and resulting in the waste water solution with different concentration of calcium chloride. Secondly, said waste solution is evaporated and condensed to result in the calcium chloride concentrated solution. The concentrated solution is subjected to crystalizing and being dried to result in the calcium chloride solid, and then the waste vapor is condensed and reclaimed. The multi-effect evaporation equipment comprises some sections, concentration part and solid separation equipment. The sections and between the sections, the concentration part and the solid separation equipment are connected with pipes each other. The method and the equipment of the invention are simple, economic and high efficiency.

Description

Process for treating alkylene oxide production wastewater and multi-effect evaporation device thereof

The present invention relates to a method and apparatus for treating industrial wastewater, and more particularly to a method for treating wastewater generated in an alkylene oxide production process and a device for use thereof. . Background technique

The present invention is generally referred to as an alkylene oxide such as propylene oxide, epichlorohydrin, hexamethylene oxide, epoxycyclohexane, and ethylene oxide. The background art will be described below by taking propylene oxide as an example.

With the development of China's fine chemical and polyurethane industries, epoxy propylene products are in an ascending channel. Because the production of alkylene oxide by the chlorohydrin method is low in investment and simple in technology, it is widely used in China. However, the calcium chloride-containing wastewater produced by the acrylochlorohydrin production process adopted in China's epoxy propylene production equipment seriously pollutes the environment.

The main reason for the domestic chlorohydrin propylene oxide production capacity is that there is no breakthrough. The key is that the wastewater and waste residue generated by the process are not easy to handle, and it is not suitable for the increasingly strict requirements of environmental protection.

The wastewater produced by the chlorohydrin method is highly difficult to treat due to its high temperature, high alkalinity and high chemical oxygen demand. The calcium chloride content of the wastewater is 40~60g/L, resulting in biochemistry. The treated strain is difficult to survive. At present, many domestic manufacturers of epoxy propylene sulphide are built along the river along the Yangtze River. The large amount of the above-mentioned wastewater is generally diluted with fresh water, and after biochemical treatment is required, biochemical treatment is carried out.

However, the above-mentioned method of first diluting and then performing biochemical treatment requires a running cost of at least several yuan to several tens of yuan/ton of wastewater, and the investment cost is large, and the domestic propylene oxide wastewater is basically untreated, resulting in a production cycle of the chlorohydrin method. The process of oxypropane is facing elimination; in addition, the treatment method is low in automation, such as full automation control, not only the investment is large, but also the quality of the instrument is not very good, which makes the automation difficult to achieve; Generally no The law is used back.

Therefore, the above treatment method greatly increases the production cost, and the enterprise is generally unbearable. At the same time, the contradiction in wastewater treatment leads to high chemical oxygen demand in the wastewater, which increases the sewage pressure and causes serious pollution to the surrounding environment. Therefore, the industrial wastewater generated by the chlorohydrin process, especially the chlorohydrin process. Governance has always been the bottleneck of enterprise development.

In order to reduce or eradicate the pollution of waste water and waste slag production, a relatively mature light pollution propylene oxide production technology has been developed internationally. This technology is mostly an indirect oxidation method, namely, the epoxy propylene/ethylbenzene method (PO). /SM) and propylene oxide/isobutane method (PO/MTBE). However, the indirect oxidation method PO/SM, PO MTBE route has the disadvantage of high investment cost, and the market supply and demand balance of its by-products directly affects the normal production of propylene oxide. The process of producing propylene oxide by the chlorohydrin process has been widely used in the industry due to its low cost, simple process and equipment, especially in China. Therefore, it is urgent to solve the problem of wastewater treatment generated in the chlorohydrin process.

In addition, although calcium chloride is a "toxic" substance in wastewater, calcium chloride itself is an important chemical product and can be widely used in industries such as agriculture, mining, oil drilling, environmental protection, food, and medicine. Traditional wastewater treatment methods waste a large amount of calcium chloride.

Therefore, it is necessary to provide a wastewater treatment method and apparatus produced in an alkylene oxide production process, particularly a chlorohydrin process, to overcome the disadvantages of the prior art and to rescue the chlorohydrin propylene oxide process. Summary of the invention

The technical problem to be solved by the present invention is to provide a process for treating an alkylene oxide production wastewater which is simple in process, low in cost and high in efficiency.

Another technical problem to be solved by the present invention is to provide a multi-effect evaporation apparatus which processes wastewater generated in an alkylene oxide production process and can recycle waste water.

In order to solve the above technical problems, the technical solution of the present invention is: an epoxy hydrazine production waste The water treatment method comprises the step (1), and the wastewater is subjected to multi-effect evaporation treatment, thereby obtaining a solution containing different concentrations of calcium chloride in each effect.

The method further comprises the step (2) of further concentrating the solution after the multi-effect evaporation treatment in the step (1) to obtain a calcium chloride concentrate.

The wastewater treatment method further comprises the step (3) of crystallizing or drying the calcium chloride concentrate of the step (2) to obtain a calcium chloride solid.

The wastewater treatment method further includes the step (4) condensing and recovering wastewater steam.

The step of pretreating the wastewater is further included before the step (1): adjusting the temperature of the wastewater to be 75 ° C to 85 ° C, adding the pH of the wastewater to the acid to adjust the pH of the wastewater to 6.0-8.0, thereby making the calcium carbonate and the high boiling point The insoluble organic matter is precipitated, the precipitate is removed, and the pretreated wastewater is finally stored in an insulated conditioning tank.

The multi-effect evaporation treatment of the step (1) may be a cross flow or a reverse flow, and the effects of the multi-effect device include a heating evaporation device and a separation device, and the heating evaporation device and the separation device are connected to each other or connected by a pipeline. The step (2) is evaporating to form a concentrated liquid in an external heating forced circulation evaporating crystallizing tank or a heat transfer oil heated forced circulation evaporator, and the step (3) is crystallization in a crystal separator or a sheeting machine, and is baked. Dry in a dryer or drying tower.

The multi-effect evaporation device of the step (1) is a five-effect evaporation device. When the cross-flow is taken, the wastewater liquid is sequentially evaporated by the first, fourth, and fifth effects to enter the second effect and the third effect evaporation, and the step (2) Is further evaporated in a third-effect crystallization tank to form a concentrate; step (3) is crystallization and separation in a crystal separator connected to the crystallization tank and the third effect; when countercurrent is taken, the step ( 1) The wastewater liquid is heated by the fifth, fourth, third, second and first effects in turn, and the step (2) is to further vaporize the five-effect treated wastewater into the forced circulation evaporator heated by the heat transfer oil. Concentration to form a calcium chloride concentrate, step (3) is to introduce the concentrate into the tableting machine for crystallization and separation; step (4) is to use a condenser, a condensate storage tank or a cooling pool, a water gas separator and The water ring vacuum pump performs condensation to recover wastewater vapor. Another technical solution of the present invention is: a multi-effect evaporation device for an alkylene oxide production wastewater treatment method, which mainly comprises a plurality of effect, concentration unit and solid separation device, and each effect, efficiency and concentration unit It is connected to the solid separation device through a pipe.

The effects of the multi-effect device include a heating evaporation device and a separation device, and the heating evaporation device and the separation device communicate with each other or with a pipeline; the concentration unit is an external heating forced circulation evaporation crystallizing tank or a heat transfer oil heating Forced circulation evaporator; the solid separation device refers to a crystal separator, a sheeting machine or a drying device.

The multi-effect evaporation device comprises 5 effects, which can be applied to a cross-flow or counter-current treatment process. When the cross-flow is adopted, the first, fourth, and fifth effects are used, and the falling film evaporator is used, and the first effect is to generate steam. Heating, the second effect adopts an external heating natural circulation evaporator, the third effect adopts an external heating forced circulation evaporator and the external heating forced circulation evaporation crystallization tank; when the reverse flow is adopted, the multi-effect evaporation device further includes the heat conduction The oil-heated forced circulation evaporator, the first effect uses a forced circulation evaporator, and the other four uses a falling film evaporator, and the first effect uses raw steam as a heating source.

The multi-effect evaporation device further comprises a condenser, a cooling pool, a water gas separator and a water ring vacuum pump; the condenser condenses the last-effect steam, generates condensed water, and recovers it by the cooling pool, and separates the water and gas. And the water ring vacuum pump is connected to the condenser, and the steam discharged from the condenser is directly discharged or sent to the cooling pool after being treated by the water gas separator and the water ring vacuum pump; the multi-effect evaporation device further includes A preheater that heats to adjust the temperature of the stream before it enters the effect, and a condensate tank for collecting the condensed water discharged from each effect.

The beneficial effects of the invention are as follows: the method for treating the alkylene oxide production wastewater of the invention, the multi-effect evaporation treatment of the wastewater, thereby obtaining the calcium chloride solution with different concentrations in each effect, the process is simple, the cost is low, and the wastewater can be not only Treatment, reducing the toxicity of wastewater, meeting emission standards, and the resulting different concentrations of calcium chloride solution can be directly packaged into products for sale or use. In the circular economy of waste recycling, calcium chloride is regarded as an important resource for recycling. It has only successfully solved the problem of sewage treatment for enterprises that have been plagued by the production of alkylene oxide products, and has also created new profit growth points for enterprises, and wins in one fell swoop. In particular, it is possible to solve the problem of effective treatment of wastewater generated in the process of producing propylene oxide by the chlorohydrin process, so that the process of producing epoxidized propylene by the chlorohydrin process can be preserved and the production scale can be expanded.

Moreover, after the steps (2) and (3), a higher concentration of calcium chloride solution or a solid form thereof can be obtained to meet various industrial application needs.

The multi-effect evaporation device for treating an alkylene oxide production wastewater has a simple structure, can be effectively used for treating an alkylene oxide production wastewater, and can effectively recover calcium chloride. The device technology is mature and reliable, and can realize full automatic control. Although the one-time investment cost of the device is relatively high, the investment can be recovered in one to three years. According to the calculation, the method for treating waste water of the invention can generate about 20 yuan per ton of wastewater (excluding the profit of condensed water returning water). DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of one embodiment of a multi-effect evaporation apparatus of the present invention.

Fig. 2 is a flow chart of wastewater treatment corresponding to the multi-effect evaporation device of Fig. 1.

Fig. 3 is a schematic view showing another embodiment of the multi-effect evaporation device of the present invention.

Figure 4 is a partial enlarged view of the left half of the ΠΙ-ΠΙ along the line of Figure 3.

Figure 5 is a partial enlarged view of the right half of the ΠΙ-ΠΙ along the line of Figure 3.

Fig. 6 is a flow chart of wastewater treatment corresponding to the multi-effect evaporation device of Fig. 3. detailed description

The invention relates to a method for treating an alkylene oxide production wastewater, which comprises the following steps: (1) First, multi-effect evaporation treatment of the wastewater liquid to obtain different concentrations of calcium chloride solution;

(2) Then, continue to steam the wastewater solution after the multi-effect evaporation treatment in step (1) Concentrated to obtain a calcium chloride concentrate having a high concentration such as 70% or more;

(3) The concentrated liquid of the step (2) is crystallized or dried and separated to obtain a calcium chloride solid such as calcium chloride powder or calcium chloride dihydrate; wherein the separation method of calcium chloride may be centrifugal separation or a cooling method or a flashing method or a direct drying method, the solid separation device used may be a crystal separator or a sheeting machine, and the drying device may be a dryer or a drying tower;

(4) Condensation recovery of wastewater steam.

In the present invention, the alkylene oxide production wastewater may be, for example, propylene oxide production wastewater, epichlorohydrin production, epoxy hexanone, epoxy cyclohexane production wastewater, and ethylene oxide production wastewater, especially The chlorohydrin process produces wastewater from the process of producing propylene oxide and epichlorohydrin.

The treatment of the epoxy hydrazine production wastewater of the present invention is carried out in a multi-effect evaporation apparatus, wherein the effect refers to the area of the multi-effect evaporation apparatus heated by steam (generally water vapor), and also releases the steam to the subsequent In the zone, the zone is used to supply some of the required heat of vaporization, ie the residual liquid (bottom) from one effect is the next (more concentrated) liquid feedstock. Each effect includes a steam outlet and a liquid outlet, as well as equipment that provides evaporative heating. Wherein, the heat supply of the heating device is provided by steam from the former effect, and for the first effect of the multi-effect evaporation device, the heat supply is generally provided by fresh steam (raw steam) or by Another stream that provides the proper temperature heat is provided. Such a heating device may be arranged in the form of a reboiler in the liquid (i.e., bottom) portion of the effect, and the heating device may also be in the form of a heated surface similar to a tube or plate.

In the foregoing step (1), the multi-effect evaporation treatment of the wastewater may be carried out by means of countercurrent or cross-flow (the countercurrent and cross-flow are defined for the flow direction of the wastewater liquid between the respective effects), and the following example is The cross-flow processing device and the process are specifically described. The second example is a detailed description of the counter-current processing device and the process. Please refer to FIG. 1 and FIG. 2 in detail. In this embodiment, each effect includes at least one evaporator and a separator, and the evaporator and the separator are in communication with each other, and the evaporator can transport the gas or liquid stream to the separator or another effect evaporator through the pipeline, and the separator is also The gas or liquid stream can be transported through the pipeline to the next evaporator or separator, allowing the stream to circulate in multiple effective evaporators and separators, continuously reducing the boiling temperature. Wherein, the evaporator may be any one or more of a forced circulation evaporator, a short tube vertical evaporator, a long tube vertical evaporator, a horizontal tube evaporator, and a wiped film evaporator.

Referring to Fig. 1, in one embodiment of the present invention, the multi-effect evaporation device may be a five-effect evaporator, and the five-effect evaporator mainly includes five effective and connecting pipes. The third effect comprises two heating evaporators 8, 9, an external heating forced circulation evaporation crystallization tank 10, a crystal separator 11, the two heating evaporators 8, 9 are connected to each other, the crystallization tank 10 is connected to the two heating evaporators, and the crystal separation is 11 It is connected to the crystallizing tank 10. In the present embodiment, the treated stream of the three-effect evaporators 8, 9 is introduced into the crystallizing tank 10, further heated and evaporated to concentrate to form a concentrate, and finally crystals are obtained in the crystal separator 11. Crystal separator 11 is used to separate calcium chloride solids.

The multi-effect evaporation device of the present invention further comprises a preheater 3, 2, 21, a condensate storage tank 16, a direct condenser 17, a cooling water tank 18, a water gas separator 19 (water ring vacuum pump 20 is provided), and a water ring vacuum pump. 20. Among them, the preheater is used to preheat the stream to adjust the temperature before the stream enters the effect. Both the condensate storage tank 16 and the direct condenser 17 are in communication with the last effect, and the condensate storage tank 16 is used to collect a portion of the steam discharged from the last effect. The direct condenser 17 condenses the last-discharged steam to form condensed water, which is recovered by the cooling water tank 18. The water gas separator 19 and the water ring vacuum pump 20 are in communication with the direct condenser 17, and the steam discharged from the direct condenser 17 is treated by the water gas separator 19 and the water ring vacuum pump 20 to be discharged.

The wastewater treatment method of the present invention will be further described below.

In the above step of wastewater treatment, more preferably, the epoxy may be added before the step (1) The wastewater generated in the production of alkane, for example, the step of pretreating the wastewater generated in the chlorohydrin propylene oxide production process, is mainly used to adjust the temperature and pH of the wastewater. In this embodiment, the pretreatment can be carried out as follows: First, the waste water is filtered through a sieve, the pore size of the sieve is about 60 mesh, and the impurities in the waste water are removed; then, the temperature of the waste water is adjusted to 75°. At C-85 °C, the wastewater is passed through the ORP automatic acid addition system, and the pH of the wastewater is adjusted to 6.0-7.0 with hydrochloric acid, so that the calcium carbonate and the high-boiling insoluble organic matter are precipitated, and then the sediment is removed by the sludge discharging system; The pretreated wastewater is stored in an insulated conditioning tank and the water quality is adjusted.

In the step (1), the multi-effect evaporation treatment causes the stream to be treated to perform a series of evaporation treatments in a manner of gradually decreasing the pressure in each effect, and the boiling point temperature in the continuous effect is gradually lowered due to the pressure gradient between the effects. The condensed steam which has been used as one effect can be used as the next effective heating medium, and provides the evaporation heat of the next effective liquid material treatment, so as to gradually separate the substances having different boiling points.

Referring to Figures 1 and 2, in this example, a five-effect evaporator is used to carry out a cross-flow evaporation treatment of the wastewater. The pretreated wastewater liquid is sent to the five-effect evaporator through the feed pump P01. First, the wastewater liquid (the initial concentration of calcium chloride is about 5%) is introduced into the preheater 3, and the partial condensed water generated by the second effect evaporator 6 and the third effect evaporators 8, 9 is heated, and the temperature is 80. °C is raised to 100-110 ° C; then introduced into the preheater 2, heated by the condensed water produced by the first effect evaporator 4, the temperature is raised from 100-110 ° C to 130-140 ° C, and then entered One-effect, four-effect, five-effect, preheater 21 (heated by condensed water produced by two-effect, three-effect), two-effect, three-effect, and finally the waste liquid produces a concentrate in the third-effect crystallization tank 10.

The steam passes through the first effect in turn, into the second effect, the third effect, the four effect, the fifth effect, and finally the condensation treatment. Specifically, the steam generated by the first effect separator 5 is directly sent to the second effect evaporator 6 as a heat source, and so on, and the steam generated by the second effect separator 7 is directly sent to the third effect evaporator 8 9, as a heat source.

A part of the condensed water produced by each effect evaporator is sent to the liquid pool, and a part is used as a preheater. The heat source of 3, 21 is sent to the condensate storage tank 16. The first-effect evaporator 4 uses raw steam as a heating source, and is non-polluting, and the condensed water is directly returned to the boiler as a heat source of the preheater 2.

In the step (1), the wastewater liquid produced in the process of producing propylene oxide by the chlorohydrin method is heated by the preheaters 3 and 2 and enters the first effect evaporator 4 in parallel with the raw steam flow, and is evaporated by one effect. The secondary steam and the feed liquid are both sent to the first effect separator 5, and the secondary steam is subjected to gas-liquid separation through the first effect separator 5, wherein the secondary steam enters the second effect evaporator 6 as a heat source, and the separator 5 The bottom liquid is sent to the fourth-effect evaporator 12 for heating and evaporation; after that, the liquid and vapor of the evaporator 12 are introduced into the fourth-effect separator 13 for vapor-liquid separation, wherein the liquid material and steam are re-introduced into the fifth effect. The condensate of the evaporator 14, the fourth effect evaporator 12 is sent back to the liquid pool, a part of which is introduced into the fifth effect evaporator 14, and another part is directly introduced into the condensate storage tank 16; the liquid and the steam are in the fifth effect evaporator 14 is further heated and evaporated, and then introduced into the fifth effect separator 15 for gas-liquid separation, and the separated liquid phase material is heated by the preheater 21 and then introduced into the second effect evaporator 6, and the vapor is directly introduced into the cold. The condensed water of the evaporator 14 is introduced into the condensate storage tank 16 and a part of the return liquid pool; the liquid material entering the second effect evaporator 6 is further heated and evaporated, and the heating heat source is introduced by the first effect. The steam and the liquid material generated in the evaporator 6 are introduced into the second effect separator 7 for gas-liquid separation, and then introduced into the third effect evaporators 8, 9 for evaporation concentration, and the evaporator 6 is condensed. Part of the water is sequentially introduced into the preheater 3, 21 as a heat source and a part of the return liquid pool; the liquid material is further evaporated and concentrated in the evaporators 8, 9 and the steam generated therefrom is sent to the third effect crystallizing tank 10 to obtain a concentration. The liquid, the steam generated in the crystallization tank 10 is sent to the fourth effect evaporator 12 as a heat source, the third effect evaporator 8 and the third effect evaporator 9 are in communication with each other, and the partial condensed water generated by the third effect evaporator 9 enters the first The three-effect evaporator 8 serves as a heat source, and a part of the condensed water generated by the three-effect evaporator is sequentially introduced as a heat source into the preheaters 3 and 21 to warm the liquid, and finally to the liquid. A portion of the condensate storage tank 16, is returned to the liquid pool.

The steam generated by the fifth effect separator 15 is introduced into the direct condenser 17, and the condensed water is returned to the cold. However, after the pool 18 is condensed by circulation, the steam is discharged through the water gas separator 19 and the water ring vacuum pump 20 and discharged.

In the step (2), the wastewater liquid is further evaporated and concentrated in the third effect crystallizing tank 10, and the concentration of the calcium chloride is concentrated to about 70 to 90%, and introduced into the crystal separator 11, and then the step (3) is separated in the crystal. The device 11 is cooled to form calcium chloride crystals (containing crystal water) and separated, and the calcium chloride crystals can be separated from the concentrate by any one of a centrifugal separation method, a cooling method or a flash method. Among them, the more preferred separation method is centrifugal separation method, the calcium chloride crystal is separated by a centrifugal separator, the granular calcium chloride is sent to the automatic packaging system for packaging and transported, and the saturated solution of calcium chloride is transported to the third effect. The evaporators 8, 9 are further evaporated and concentrated, and then returned to the third effect crystallizing tank 10 and the crystal separator 11 for re-evaporation concentration and recrystallization separation treatment.

The foregoing steps (4) can be directly discharged after the multi-effect evaporation can be obtained in the condensate storage tank 16 and the cooling water tank 18, or all the condensed water can be returned to the workshop for reuse. If the target is not met, it can be directly processed biologically. Biological treatment is well known in the art and typical design criteria can be found in the standard engineering manual for wastewater treatment.

This step uses five-effect evaporation, the first, fourth, and fifth effects. Because the concentration of the liquid is low, the falling film evaporator is used, and the second effect is the external heating natural circulation evaporator, because the third effect liquid The concentration is higher, and the external heating forced circulation evaporator and crystallizer are used to prevent the formation of dirt. In this way, the heat transfer efficiency is improved, the evaporation speed is fast, the heating time is short, the evaporation temperature is low, the coking is not easy, and the cleaning is easy. Using the wastewater treatment method and apparatus of this example, the industrial wastewater from the production of propylene oxide by the chlorohydrin process is treated, and the chemical oxygen demand (COD) of the condensed water in the condensate storage tank 16 and the cooling water tank 18 is treated. Less than 100 mg / l, meeting the wastewater treatment discharge requirements, wherein the chemical oxygen demand (COD) refers to the amount of oxidant required to oxidize the oxidized substance in the water sample under the specified conditions, The milligrams of oxygen consumed by the water is expressed. Case 2

Please refer to Figure 3 to Figure 6. The multi-effect evaporation device in this example includes five effects 23-27, enrichment 28, and further includes preheaters 30-33 connected to the first to fourth effects, and a water cooler 29 connected to the fifth effect, and The water ring vacuum pump 50 and the cooling water tank (not shown) connected to the water cooler 29 are connected to the primary, secondary and tertiary auto-evaporators 40-42 between the first effect 23 and the enrichment effect 28, and store the condensed water. The condensate tanks 53, 54, a thickener 22 for pretreating the wastewater liquid, and a tableting machine (not shown) for forming calcium chloride crystals and separating the crystals. Each equipment unit is connected to each other by pipes to realize the transmission of steam, liquid and solid materials. The multi-effect evaporation apparatus of this example is used for counter-current treatment of wastewater generated from an alkylene oxide production process.

Among the various effect evaporators, one of the most prone to fouling is 23, the heat transfer oil effect evaporator (enhanced effect) 28 uses a forced circulation evaporator, and the remaining four effects use a falling film evaporator. The first effect 23 uses raw steam (new steam) as a heating source.

Also included in the foregoing step (1) is a step of pretreating the wastewater. First, the wastewater containing about 5% & (12 ₎ enters the thickener 22 with a scraper, and the temperature of the mixed waste water is about 80 ° C. The wastewater having a pH of 11.5 to 12.0 is passed through the pH in the thickener 22. The automatic control system adds hydrochloric acid to adjust the pH to 7.0~8.0, so that (^ (30 ₃ and € (013⁄4 insoluble matter) precipitates, the precipitated sludge is sent to the lime calcination system in the plant through the sludge pump. At the same time, the waste water is kept warm. The water and water volume is adjusted in the thickener 22.

In the step (1), the pretreated wastewater is pumped to the five-effect evaporator, and the concentration of CaCl ₂ in the wastewater is concentrated to about 50% by evaporation and concentration. The step (2) is to send the wastewater of the step (1) to the wastewater. Concentrated evaporator 28 continues to concentrate to more than 70%, such as 75%, when the calcium chloride concentration reaches 75%, directly into the filming machine, step (3) to crystallize to produce calcium chloride dihydrate, the filming machine down Calcium chloride enters the packaging system and the finished product is packed into the warehouse.

In step (4), after a steam condensate is recovered by flash evaporation, return to the boiler. Ring use. The condensed water of the second, third, fourth and fifth effects reaches the target of COD _& 300mg/L, Cl^100mg/L, and can be returned to the epoxy propylene production workshop for production water according to the analysis.

As the boiling point of the solution increases with increasing concentration, in order to maintain the evaporation of the calcium chloride solution in a high concentration state, this example uses a high temperature resistant heat transfer oil as a hot fluid to heat the concentrated calcium chloride solution (concentration 50%) The heat transfer oil is converted into coal by coal, and the heat generated by the combustion is heated. This condensate also returns to the production floor. The steam generated by this effect is led to the fifth effect evaporator 27 for circulation processing.

In this example, each effect evaporation system includes an evaporation chamber and a separation chamber (shown icons) which are connected to each other, and the separation chamber is provided with a decanting device, which effectively avoids secondary vapor vapor entrainment and maintains condensed water COD. Qualified reuse, while avoiding corrosion of subsequent evaporators, pipes and fittings.

The flow route of steam, materials and condensate is shown in detail in Figure 3 to Figure 6. The details are as follows.

(1) Steam process

In order to minimize steam consumption, save energy, and reduce processing costs, this example uses a counter-current five-effect evaporator structure. The raw steam enters the first effect, and the second steam is separated from the liquid in the first effect separation chamber, and then enters the two-effect evaporator as a heat source, and the steam generated by the second-effect evaporation enters the three-effect, and the steam generated by the three-effect evaporation enters. The four-effect, four-effect evaporation of steam enters the five-effect evaporator as a heat source. The steam generated by the five-effect evaporation enters the water cooler 29 (condenser) and is condensed. The water cooler is connected to the water ring vacuum pump 50, and the resulting condensed water is stored in a cooling water tank and sent to the workshop for reuse. Enrichment 28 The secondary steam generated by evaporation is cooled by a spray cooler and returned to the production plant as liquid condensate. The steam generated by the primary, secondary, and tertiary evaporators 40, 41, and 42 is introduced into the second effect preheater 31, the third effect preheater 32, and the fourth effect preheater 33 for heat treatment.

(2) Material flow process

The raw material liquid is pressurized by the pump into the five-effect evaporator 27, and the five-effect 27 discharge is pumped into the four-effect preheater 33, and then pre-evaporated and then enters the four-effect evaporator 26. The four-effect evaporator 26 discharge is pumped to three effects After the preheater 32 enters the three-effect evaporator 25, the three-effect 25 discharge material is pumped into the second-effect preheater 31 to be pre-evaporated, and then enters the second-effect evaporator 24, and the second-effect 24 discharge is pumped to the first-effect preheater. After 30 pre-evaporation, the first-effect evaporator 23 is introduced, and the output of the first-effect 23 is successively passed through the first-stage, second-stage and third-stage self-evaporators 40, 41, 42 under pressure, and then enters the heat-conducting oil-efficiency evaporator (also called Concentration) 28 Continue to concentrate until the calcium chloride concentration reaches 75% and pump it through the discharge pump to the filming machine.

(3) Condensate flow

The condensed water produced by the first effect 23 is condensed by the raw steam, so that it is not contaminated, and the heat is recovered by the condensed water tanks 51, 52 and returned to the boiler for recycling. The second, third, and fourth effects 24, 25, and 26 condensate are discharged to the condensate tank. 53. 54, The condensate pool is divided into two, one is a qualified reuse pool, and the other is a substandard pool 54. According to the drainage water quality, the condensed water enters the qualified and unqualified pools respectively, the qualified water is reused in the production workshop, and the unqualified water enters the existing sewage treatment station.

In order to adapt to the increasing boiling point of the concentrated solution of calcium chloride, the high-temperature heat-conducting oil is used to concentrate the calcium chloride solution with a concentration greater than 50%, and the heat-conducting oil is heated by the combustion gas, and the heat-conducting oil is returned to the gas furnace after heating. The inside is reheated, recycled, and the evaporator in the enhanced effect 28 is maintained under the push of the vacuum pump to maintain the negative pressure, thereby increasing the heating efficiency and increasing the effective temperature difference. Among them, the gas boiler part first converts the coal into a gas through a gas generating station, and then enters the gas boiler to burn and heat the heat conducting oil. The process flow is as follows: The gas is separated and returned to the gas through a gasoline separator, and the oil residue is filtered through the filter to enter the combustion furnace. After being heated, the gas is heated and then enters the heat transfer oil to evaporate and concentrate the calcium chloride solution. The auxiliary system of the heat transfer oil pumps the newly added heat transfer oil to the expansion tank through the oil. The expansion tank is provided with an exhaust pipe, and the lower part is connected to the gasoline separator and the return line. The expansion tank mainly prevents the volume change caused by the change of the cold and heat of the oil, and affects the normal operation of the system. At the same time, the exhaust gas generated during the operation is discharged, and the entire circulating heat transfer oil system is sealed to prevent oxidation. The system is equipped with a storage tank to store waste oil.

In the packaging part of the filming machine, a 75% calcium chloride solution is cooled and crystallized by a rotary drum machine to produce flaky calcium chloride dihydrate. The flaky calcium chloride enters the receiving hopper and is controlled by a spiral feeder. After the flow is processed, the finished packaging is carried out using a manual packaging system. The cooling system of the film forming machine uses condensed water to cool the high temperature calcium chloride through the heat exchanger built in the film forming machine to form crystals of calcium chloride dihydrate.

The multi-effect evaporation treatment wastewater process and equipment of the invention have mature and reliable technology and can realize full automatic control, and the one-time investment cost of the equipment is relatively high, but generally one to three years can recover the investment. After treatment, the condensed water can reach the discharge standard, and a large amount of calcium chloride solids are recovered, which solves the problem of effective treatment of the wastewater generated by the chlorohydrin process for producing the epoxidized propylene hydride process, so that the chlorohydrin process can produce the epoxidation process. It is possible to save and expand production scale. In particular, the countercurrent multi-effect evaporation treatment method and equipment of the second example can not only effectively recover the calcium chloride solids of the industrial product, but also all other treatment products, including condensed water, can be returned to the epoxy propylene production workshop for use as production water. It is calculated that the method for treating wastewater according to the present invention can generate a profit of about 20 yuan per ton of wastewater (and does not contain the profit of condensed water returning water).

In addition, calcium chloride is not only sold and applied as an industrial product in its solid form, but also a solution such as a solution having a concentration of 30 to 50% has been widely sold and applied as an industrial product, particularly in foreign markets. In the cross-flow and counter-current treatment processes of the first and second examples, the wastewater liquid is concentrated by evaporation from one effect to five effects, and the concentrated liquid formed by each effect can also be directly packaged into products for use as different concentrations of calcium chloride products or It can be sold without further concentrating by crystallization tank or thickening to form a concentrated solution of 70% or more (cooling crystals to form cesium chloride dihydrate or drying to form calcium chloride powder).

Taking the process and equipment of Example 2 as an example for specific analysis, the calcium chloride products of different concentrations are obtained by the process and apparatus of the present invention. Because the process is based on working temperature and pressure, in order to keep the process safe and stable, appropriate temperature and pressure conditions should be selected to control the evaporation of each effect according to the safety factor of the equipment. Because the liquid chamber pressure is increased, the boiling point of the solution can be lowered, and the temperature of the liquid chamber can be raised to facilitate evaporation. Therefore, the concentration of the calcium chloride solution can be obtained as needed to adjust the temperature and pressure of each effect. The following table shows a specific example parameter. According to the countercurrent process of Example 2, the initial concentration of calcium chloride in the wastewater solution is 5%, because the fifth effect 27 is lower. After the treatment, a part of the thickener 22 is introduced into the fifth effect 27, and a part is introduced into the fourth effect 26, so that the fifth effect concentration is higher than the fourth effect. According to the process flow described in the above second example, the processing parameters and results are as follows:

Table 1

It can be seen from the above table that the first to fifth effects and the first to third stages are processed by the evaporator to produce different concentrations of calcium chloride solution, which can be directly packaged into a solution product for use or sale, and the concentrated calcium chloride solution is cooled to form dihydrate. Calcium chloride. By adjusting various effects or heating area of the evaporator, steam (oil) temperature, liquid chamber (evaporation chamber) pressure, solution (waste water) temperature and other parameters, other concentrations of calcium chloride solution can be obtained to adapt to various Different requirements.

It can be understood that the different concentrations of the calcium chloride solution obtained by the respective effects of the multi-effect evaporation device of the foregoing embodiments are directly introduced into a drying device, or the crystal separator 11 or the tableting machine is replaced by a drying device directly. Different concentrations of the calcium chloride solution or the calcium chloride concentrate are dried to obtain a calcium chloride solid powder product. The drying device can be a dryer or a drying tower of the prior art.

Claims

Claim

A method for treating wastewater from an epoxy oxime production process, comprising the steps of: (1) subjecting the wastewater to a multi-effect evaporation treatment, thereby obtaining a solution containing different concentrations of calcium chloride in each effect.

2. The method for treating an alkylene oxide production wastewater according to claim 1, wherein the method further comprises the step (2) of further evaporating and concentrating the solution after the multi-effect evaporation treatment in the step (1) to obtain chlorine. Calcium concentrate.

The method for treating an alkylene oxide production wastewater according to claim 2, wherein the wastewater treatment method further comprises the step (3) of crystallizing or drying the calcium chloride concentrate of the step (2). Treatment, to obtain calcium chloride solids.

The method for treating an alkylene oxide production wastewater according to claim 3, wherein the wastewater treatment method further comprises the step of: (4) condensing and recovering wastewater steam.

The method for treating alkylene oxide production wastewater according to claim 1, characterized in that: before the step (1), the step of pretreating the wastewater is further included: adjusting the temperature of the wastewater to be 75 ° C - 85 ° C The pH of the wastewater is adjusted to 6.0-8.0, so that calcium carbonate and high-boiling insoluble organic matter are precipitated, the precipitate is removed, and the pretreated wastewater is finally stored in an insulated conditioning tank.

The method for treating an alkylene oxide production wastewater according to claim 4, wherein: the multi-effect evaporation treatment of the step (1) may be a cross flow or a reverse flow, and the effects of the multi-effect device include heating. An evaporation device and a separation device, wherein the heating evaporation device and the separation device are connected to each other or connected by a pipeline; and the step (2) is an external heating forced circulation evaporation crystallizing tank or a guide The hot oil heated forced circulation evaporator evaporates to form a concentrate, and the step (3) is crystallization in a crystal separator or a pelletizer, and dried in a dryer or a drying tower.

The method for treating an alkylene oxide production wastewater according to claim 6, wherein: the multi-effect evaporation device of the step (1) is a five-effect evaporation device, and when the cross-flow is taken, the wastewater liquid is sequentially passed through The first, fourth, and fifth effects are heated and evaporated to enter the second effect and the third effect evaporation, and the step (2) is further evaporated in the third effect crystallizing tank to form a concentrated liquid; the step (3) is in the same with the crystallizing tank and Crystallization and separation in the third-effect connected crystal separator; when the countercurrent is drawn, the wastewater liquid in the step (1) is sequentially heated and evaporated by the fifth, fourth, third, second, and first effects, and the step (2) is The five-effect treated wastewater liquid is introduced into the heat-conducting oil-heated forced circulation evaporator to be further evaporated and concentrated to form a calcium chloride concentrate, and the step (3) is to introduce the concentrated liquid into the tableting machine for crystallization and separation; (4) Condensation and recovery of wastewater vapor by condenser, condensate storage tank or cooling water tank, water gas separator and water ring vacuum pump.

8. A multi-effect evaporation device for an alkylene oxide production wastewater treatment method, characterized in that: the multi-effect evaporation device mainly comprises a plurality of effect, concentration units and solid separation devices, and each effect and effect The concentration unit and the solid separation device are connected by a pipe.

9. The multi-effect evaporation apparatus according to claim 8, wherein: each of the effects of the multi-effect device comprises a heating evaporation device and a separation device, and the heating evaporation device and the separation device are connected to each other or connected by a pipeline. The concentration unit is a forced circulation evaporator heated by an external heating forced circulation evaporation crystallization tank or a heat transfer oil; the solid separation device refers to a crystal separator, a sheeting machine or a drying device.

10. The multi-effect evaporation apparatus according to claim 9, wherein: said multi-effect steaming The hair-emitting device includes 5 effects, which can be applied to the cross-flow or counter-current treatment process. When the cross-flow is taken, the first, fourth, and fifth effects are adopted, and the falling film evaporator is used, and the first effect is heated by the steam, the second The external heating natural circulation evaporator is used, the third effect is an external heating forced circulation evaporator and the external heating forced circulation evaporation crystallization tank; when the reverse flow is adopted, the multi-effect evaporation device further includes the heat conduction oil heating forced The circulating evaporator, the first effect uses a forced circulation evaporator, and the other four uses a falling film evaporator, and the first effect uses raw steam as a heating source.

11. The multi-effect evaporation apparatus according to claim 10, wherein: said multi-effect evaporation apparatus further comprises a condenser, a cooling water tank, a water gas separator and a water ring vacuum pump; and the condenser discharges the steam from the last effect Condensation, condensed water is generated, and is recovered by a cooling pool. The water gas separator and the water ring vacuum pump are connected to the condenser, and the steam discharged from the condenser is directly discharged or sent through the water gas separator and the water ring vacuum pump. The multi-effect evaporation device further includes a preheater for preheating the stream to adjust the temperature before the stream enters the effect, and a condensate storage tank for collecting the condensed water discharged from each effect.