CN108383307B - Pretreatment method of molasses alcohol wastewater - Google Patents

Abstract

The invention belongs to the technical field of industrial sewage treatment, and discloses a pretreatment method of molasses alcohol wastewater. The pretreatment method comprises the steps of carrying out pretreatment of sedimentation, filtration and rectification on the molasses alcohol wastewater; the method specifically comprises the following steps: (1) and (3) settling: adding molasses alcohol wastewater into a gravity settling tank, adding a flocculating agent into the tank through a concentric distributor, filtering the wastewater after flocculation and gravity settling treatment through a filter, and performing microfiltration treatment through a membrane separation device; (2) and (3) rectification: the wastewater after the microfiltration treatment enters a rectifying tower for rectification to obtain a tower top product and a tower bottom product; and then respectively carrying out subsequent treatment. The pretreatment method has high separation efficiency, good stability and strong pertinence, can effectively remove colloids, flocculates and other solid particles in the wastewater, well separate and recover light components in the wastewater, can effectively reduce the load of the subsequent treatment process, ensures that the wastewater finally reaches the standard and is suitable for large-scale production.

Description

A kind of pretreatment method of molasses alcohol wastewater

technical field

The invention belongs to the technical field of industrial sewage treatment, and particularly relates to a pretreatment method for molasses alcohol wastewater.

Background technique

Molasses alcohol wastewater is an associated product of the molasses fermentation process to produce alcohol. Every ton of alcohol produced produces about 10 to 15 tons of wastewater. ～60000mg/L, pH is 3～4.5. Its large quantity, complex composition, strong acidity and deep chromaticity cause serious harm to the environment, and its treatment technology has become a bottleneck restricting the development of the alcohol industry. At present, the treatment methods of molasses alcohol wastewater mainly include biological method and physicochemical method. The concentrated combustion method in the physicochemical method evaporates and concentrates the molasses alcohol wastewater, sends the concentrated liquid to the boiler for combustion, and the heat generated is returned to the evaporation process.

The wastewater from the alcohol production process contains a large amount of carbohydrates, cellulose and hemicellulose, pigments, proteins, fats and gums and other substances. During the evaporation and concentration process, it will affect the fluid dynamics and heat transfer properties of the fluid, resulting in a decrease in flow rate. , scaling, local coking and other phenomena, reduce heat transfer efficiency and increase energy consumption. The waste water also contains low molecular compounds, such as n-propanol, isopropanol, formic acid, acetic acid, glycerol and lactic acid, etc. During the process of evaporation and concentration, some substances escape into the condensed water with the secondary steam, making it pure The CODCr value of the condensed water of water is higher than the national discharge standard, sometimes even close to 1000, so that the condensed water needs to be further treated before it can be discharged or reused. These problems directly affect the practical effect of the enrichment combustion method.

With the increasing promotion and application of fuel ethanol in the world, the process of producing fuel ethanol with molasses as raw material has been given more significance. The use of effective technical means to control the wastewater generated in the production process and reduce the energy consumption of the process is crucial to the survival and development of the molasses alcohol process, and is of great significance to environmental protection and sustainable economic development.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned shortcomings and deficiencies in the prior art that the solids in the molasses alcohol waste water affect the flow and heat transfer characteristics of the evaporation and concentration process, and the low molecular compounds escape during the evaporation and concentration process and enter the condensed water with the secondary steam. The purpose is to provide a pretreatment method for molasses alcohol wastewater with high efficiency, good stability, strong pertinence and obvious treatment effect.

The object of the present invention is realized through the following scheme:

A kind of pretreatment method of molasses alcohol waste water, carries out the pretreatment of sedimentation, filtration and rectification of molasses alcohol waste water, specifically comprises the following steps:

(1) Settling: add the molasses alcohol waste water into the gravity settling tank, the flocculant is put into the tank through the concentric circle distributor, the waste water after flocculation and gravity settling treatment is filtered by the filter, and then processed by the microfiltration of the membrane separation device;

(2) Rectification: after the microfiltration treatment, the waste water enters the rectification tower for rectification to obtain the top product and the tower bottom product; and then carry out subsequent treatment respectively.

In step (1), the flocculant may be a conventional flocculant in the art, preferably polyacrylamide.

The dosage of the flocculant is preferably 2-3 g/m ³ waste water.

The concentric circle distributor is located above the gravity settling tank.

The wall of the gravity sedimentation tank is a cylinder, and the bottom of the tank is preferably a cone; it is convenient for the sediment to gather and discharge.

The water outlet of the gravity settling tank is located on the upper part of the tank wall.

The waste water after flocculation and gravity settling treatment is discharged through the water outlet of the gravity settling tank, and passes through the filter installed in the water outlet pipeline.

The filter is preferably a synthetic fiber fabric or a porous filter medium with a pore size of less than 0.1 mm. The filtration can be used to remove colloids, flocs and other solid particles with a particle size greater than 0.1 mm in wastewater. The filtered wastewater is sent to the membrane separation device by a pressurized pump.

In step (1), the microfiltration treatment is to remove particles with a particle size larger than 0.1 μm.

The membrane separation device adopts the principle of microfiltration and hollow fiber membrane components to remove particles with a particle size greater than 0.1 μm in wastewater. Preferably, a pulsed compressed air membrane purge regeneration system is used to regenerate the membrane module.

The rectifying tower described in step (2) adopts the stripping mode of the overhead feed. The rectifying tower is preferably a tray tower or a packed tower, with 18 to 20 trays; it is preferably operated under negative pressure. The rectification preferably uses preheating in alcohol production as a heat source.

The column top product described in step (2) is a substance with a volatility greater than that of water, such as ethanol, n-propanol and isopropanol, etc., and is subsequently added to an alcohol by-product treatment system for unified treatment.

The tower kettle product described in the step (2) is the main body of the pretreated wastewater, and the subsequent treatment can be carried out according to the conventional treatment process.

The invention provides a pretreatment method for molasses alcohol wastewater. The specific steps of the method are as follows: the molasses alcohol wastewater enters a circular gravity sedimentation tank for pretreatment, and the flocculant is put into the tank by a metering pump through a concentric distributor, and the flocculation and The wastewater after gravity sedimentation is filtered to remove colloids, flocs and other solid particles with a particle size greater than 0.1mm; it is pumped to a membrane separation device to remove particles with a particle size greater than 0.1μm; the wastewater is treated by rectification. Homogeneous separation, the top product of the tower is the substances with higher volatility than water in the waste water, such as ethanol, n-propanol and isopropanol, etc. After condensation, it is added to the alcohol by-product treatment system for unified treatment, and the waste water from the tower kettle is transported to the subsequent treatment section. The rectification tower adopts negative pressure operation and the stripping method of the feed at the top of the tower. Depending on the content of low boilers in the wastewater, 18 to 20 theoretical trays are used. Engineering dosage in order to achieve the purpose of energy saving and emission reduction.

The pretreatment method of the invention has high separation efficiency, good stability and strong pertinence, can effectively remove colloids, flocs and other solid particles in wastewater, can well separate and recover light components in wastewater, and can effectively reduce subsequent The load of the treatment process ensures that the final discharge of wastewater meets the standard, which is suitable for large-scale production.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. the present invention adopts flocculant to carry out flocculation on molasses alcohol waste water, and gravity sedimentation is used to enrich the flocs, and filter to remove colloids, flocs and other solid particles whose particle diameter is greater than 0.1 mm; Particles with a particle size greater than 0.1 μm. Through the above technical means, the fluid mechanics and heat transfer characteristics of wastewater can be improved, the flow resistance can be reduced, the heat transfer coefficient of the evaporation and concentration process can be improved, and the phenomena such as scaling and local coking can be reduced, so as to achieve the purpose of energy saving and consumption reduction.

2. The light components in the wastewater are separated, which effectively solves the problem that the COD of the condensed water in the subsequent evaporation and concentration process exceeds the standard, and ensures the discharge of the wastewater up to the standard.

3. Partially remove COD from wastewater, and the removal rate is about 30%.

4. Recycle ethanol, n-propanol, isopropanol and other substances in wastewater to realize the reuse of resources.

5. The distillation tower is operated under negative pressure, which provides a technical guarantee for the use of low-grade waste heat in alcohol production as a heat source, realizes the cascade utilization of energy, effectively reduces the consumption of thermal utilities, and achieves the purpose of energy saving and emission reduction.

6. Suitable for mass production.

Description of drawings

Fig. 1 is the process flow schematic diagram of the pretreatment method of molasses alcohol waste water of the present invention.

Fig. 2 is the process flow diagram of the pretreatment method of molasses alcohol waste water of the present invention. In the figure: 1-1 is the first pressurizing pump; 1-2 is the second pressurizing pump; 1-3 is the third pressurizing pump; 2 is a concentric distributor; 3 is a circular gravity sedimentation tank; 4 is a filter; 5 is a membrane separation device; 6 is a rectifying tower; 7 is a reboiler.

Detailed ways

The present invention will be described in further detail below with reference to the examples, but the embodiments of the present invention are not limited thereto. The materials involved in the following examples can be obtained from commercial sources.

Fig. 1 is the technological process of the pretreatment method of molasses alcohol waste water of the present invention, comprising:

(1) Sedimentation: The molasses alcohol wastewater enters the gravity sedimentation tank for pretreatment, the flocculant polyacrylamide is put into the tank by the metering pump through the concentric circle distributor, and the wastewater after flocculation and gravity sedimentation is removed by the filter. Colloids, flocs and other solid particles are pumped into the membrane separation unit.

(2) Membrane separation: The wastewater enters the membrane separation device for microfiltration treatment, removes particles with a particle size larger than 0.1 μm in the wastewater, and sends it to the rectification tower.

(3) Rectification: The rectification tower separates the waste water into two products at the top of the tower and the tower. The product at the top of the tower is a substance with greater volatility than water in the waste water, which is added to the alcohol by-product treatment system for unified treatment after condensation;

Example 1

In this embodiment, a pretreatment method of molasses alcohol wastewater is provided. The pretreatment object in the present embodiment is the molasses alcohol waste water obtained from domestic alcohol production plants with molasses as raw material to produce alcohol, and the main water quality indicators are: pH4.2, COD _Cr 110416mg/L, total sugar content 21068mg/L, The ethanol content is 0.1%, the n-propanol content is 0.045%, the isopropanol content is 0.015%, and the solid suspended matter content is 12640 mg/L.

Including the following process steps:

(1) The molasses alcohol wastewater enters the gravity sedimentation tank for flocculation and sedimentation treatment with the flocculant input by the metering pump. The amount of the flocculant polyacrylamide added by the metering pump is 2g/ ^m3 of waste water, and the flocculant is put into the circular gravity sedimentation tank through the concentric circle distributor. The bottom of the gravity sedimentation tank is a cone, which is convenient for the accumulation and discharge of sediments. The wastewater after flocculation and sedimentation passes through the filter installed on the outlet pipe of the sedimentation tank. The filter medium adopts synthetic fiber fabric with a pore size of 0.07-0.1mm to remove colloids, flocs and other solid particles with a particle size larger than 0.1mm in the wastewater.

(2) The filtered wastewater is sent to the membrane separation device by a pressurized pump. The membrane separation device adopts the principle of microfiltration, and the hollow fiber microporous membrane module has a pore size distribution range of 0.08 to 0.1 μm to remove particles with a particle size larger than 0.1 μm in the wastewater; the membrane module is regenerated by a pulse compressed air membrane purging regeneration system. . The wastewater treated by the membrane separation device is sent to the rectification tower by a pressurized pump.

(3) The rectifying tower is a tray tower with 19 theoretical trays and 25 F1 type float valve trays. It adopts negative pressure operation and the stripping method of the feed at the top of the tower, and the vacuum degree at the top of the tower is controlled at -55～-58kPa , the corresponding top temperature is 78-81℃. The light components obtained at the top of the rectification tower are mainly ethanol, n-propanol and isopropanol, etc. After condensation, they are added to the alcohol by-product treatment system for unified treatment, and the waste water from the tower reactor is transported to the subsequent treatment section. The distillation column uses the waste heat from alcohol production as a heat source. The pretreatment effects are shown in Table 1.

Table 1 Pretreatment effect of molasses alcohol wastewater

Example 2

In this embodiment, a pretreatment method for molasses alcohol wastewater is provided. The pretreatment object in the present embodiment is the molasses alcohol waste water that is obtained from domestic alcohol production plants with molasses as raw material to produce alcohol. The wastewater is brown-black liquid, and the water quality indicators are: pH4.2, COD _Cr 111024mg/L, total sugar content 21214mg/L, ethanol content 0.11%, n-propanol content 0.043%, isopropanol content 0.015%, solid suspended solids Content 12742mg/L. Including the following process steps:

(1) The molasses alcohol wastewater enters the gravity sedimentation tank for flocculation and sedimentation treatment with the flocculant input by the metering pump. The amount of the flocculant polyacrylamide added by the metering pump is 2.3g/ ^m3 of waste water, and the flocculant is put into the circular gravity sedimentation tank through the concentric circle distributor. The bottom of the gravity sedimentation tank is a cone, which is convenient for the accumulation and discharge of sediments. The wastewater after flocculation and sedimentation passes through the filter installed on the outlet pipe of the sedimentation tank. The filter medium adopts synthetic fiber fabric with a pore size of 0.06-0.09mm to remove colloids, flocs and other solid particles with a particle size larger than 0.1mm in the wastewater.

(2) The filtered wastewater is sent to the membrane separation device by a pressurized pump. The membrane separation device adopts the principle of microfiltration, and the hollow fiber microporous membrane module has a pore size distribution range of 0.07 to 0.1 μm to remove particles with a particle size larger than 0.1 μm in the wastewater; the membrane module is regenerated by a pulse compressed air membrane purging regeneration system. . The wastewater treated by the membrane separation device is sent to the rectification tower by a pressurized pump.

(3) The rectifying column is a plate column with 18 theoretical trays and 26 sieve trays. It adopts negative pressure operation and the stripping method of the feed at the top of the column. The vacuum at the top of the column is controlled at -60～-62kPa. The temperature at the top of the tower is 77-80 °C. The light components obtained at the top of the rectification tower are mainly ethanol, n-propanol and isopropanol, etc. After condensation, they are added to the alcohol by-product treatment system for unified treatment, and the waste water from the tower reactor is transported to the subsequent treatment section. The distillation column uses the waste heat from alcohol production as a heat source. The preprocessing effect is shown in Table 2.

Table 2 Pretreatment effect of molasses alcohol wastewater

Example 3

In this embodiment, a pretreatment method of molasses alcohol wastewater is provided. The pretreatment object in the present embodiment is the molasses alcohol waste water obtained from domestic alcohol production plants with molasses as raw material to produce alcohol, and the main water quality indicators are: pH 4.1, COD _Cr 108962mg/L, total sugar content 20536mg/L, ethanol The content is 0.1%, the n-propanol content is 0.042%, the isopropanol content is 0.014%, and the solid suspended matter content is 11657 mg/L.

Including the following process steps:

(1) The molasses alcohol wastewater enters the gravity sedimentation tank for flocculation and sedimentation treatment with the flocculant input by the metering pump. The amount of the flocculant polyacrylamide added by the metering pump is 3g/ ^m3 of waste water, and the flocculant is put into the circular gravity sedimentation tank through the concentric circle distributor. The bottom of the gravity sedimentation tank is a cone, which is convenient for the accumulation and discharge of sediments. The wastewater after flocculation and sedimentation passes through the filter installed on the outlet pipe of the sedimentation tank. The filter medium adopts a porous filter medium with a pore size of 0.08-0.1mm to remove colloids, flocs and other solid particles with a particle size larger than 0.1mm in the wastewater. .

(2) The filtered wastewater is sent to the membrane separation device by a pressurized pump. The membrane separation device adopts the principle of microfiltration, and the hollow fiber microporous membrane module has a pore size distribution range of 0.07 to 0.09 μm to remove particles with a particle size larger than 0.1 μm in the wastewater; the membrane module is regenerated by a pulse compressed air membrane purging regeneration system. . The wastewater treated by the membrane separation device is sent to the rectification tower by a pressurized pump.

(3) The rectifying tower is a 19 theoretical plate, stainless steel rolling corrugated structured packing tower, adopts negative pressure operation and the stripping method of the top feed, the vacuum degree of the top of the tower is controlled at -58～-60kPa, and the corresponding top of the tower is The temperature is between 76 and 80°C. The light components obtained at the top of the rectification tower are mainly ethanol, n-propanol and isopropanol, etc. After condensation, they are added to the alcohol by-product treatment system for unified treatment, and the waste water from the tower reactor is transported to the subsequent treatment section. The distillation column uses the waste heat from alcohol production as a heat source. The preprocessing effects are shown in Table 3.

Table 3 Pretreatment effect of molasses alcohol wastewater

Example 4

In this embodiment, a pretreatment method of molasses alcohol wastewater is provided. The pretreatment object in the present embodiment is the molasses alcohol waste water obtained from domestic alcohol production plants with molasses as raw material to produce alcohol, and the main water quality indicators are: pH 4.2, COD _Cr 120123mg/L, total sugar content 21103mg/L, ethanol The content is 0.1%, the n-propanol content is 0.045%, the isopropanol content is 0.016%, and the solid suspended matter content is 12037 mg/L. Including the following process steps:

(1) The molasses alcohol wastewater enters the gravity sedimentation tank for flocculation and sedimentation treatment with the flocculant input by the metering pump. The amount of the flocculant polyacrylamide added by the metering pump is 2.7g/m3 of waste water, and the flocculant is put into the circular gravity sedimentation tank through the concentric circle distributor. The bottom of the gravity sedimentation tank is a cone, which is convenient for the accumulation and discharge of sediments. The wastewater after flocculation and sedimentation passes through the filter installed on the outlet pipe of the sedimentation tank. The filter medium adopts a porous filter medium with a pore size of 0.08-0.1mm to remove colloids, flocs and other solid particles with a particle size larger than 0.1mm in the wastewater. .

(2) The filtered wastewater is sent to the membrane separation device by a pressurized pump. The membrane separation device adopts the principle of microfiltration, and the hollow fiber microporous membrane module has a pore size distribution range of 0.07 to 0.1 μm to remove particles with a particle size larger than 0.1 μm in the wastewater; the membrane module is regenerated by a pulse compressed air membrane purging regeneration system. . The wastewater treated by the membrane separation device is sent to the rectification tower by a pressurized pump.

(3) The rectifying tower is a 20 theoretical plate, ceramic corrugated structured packing tower, adopts negative pressure operation and the stripping method of the top feed, the top vacuum is controlled at -60～-63kPa, and the corresponding top temperature At 76 ~ 78 ℃. The light components obtained at the top of the rectification tower are mainly ethanol, n-propanol and isopropanol, etc. After condensation, they are added to the alcohol by-product treatment system for unified treatment, and the waste water from the tower reactor is transported to the subsequent treatment section. The distillation column uses the waste heat from alcohol production as a heat source. The preprocessing effects are shown in Table 4.

The pretreatment effect of table 4 molasses alcohol wastewater

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (7)

1. The pretreatment method of the molasses alcohol wastewater is characterized in that the molasses alcohol wastewater is subjected to pretreatment of sedimentation, filtration and rectification, and specifically comprises the following steps:

(1) and (3) settling: adding molasses alcohol wastewater into a gravity settling tank, adding a flocculating agent into the tank through a concentric distributor, filtering the wastewater after flocculation and gravity settling treatment through a filter, and performing microfiltration treatment through a membrane separation device;

(2) and (3) rectification: the wastewater after the microfiltration treatment enters a rectifying tower for rectification to obtain a tower top product and a tower bottom product; respectively carrying out subsequent treatment;

the filter in the step (1) is a synthetic fiber fabric or a porous filter medium with the pore canal size of less than 0.1 mm;

the rectifying tower in the step (2) adopts a stripping mode of feeding from the top of the tower; the rectifying tower is provided with 18-20 tower plates; the rectifying tower adopts negative pressure operation; the rectification takes preheating in alcohol production as a heat source.

2. The pretreatment method of molasses alcohol wastewater according to claim 1, characterized in that: in the step (1), the flocculating agent is polyacrylamide.

3. The pretreatment method of molasses alcohol wastewater according to claim 1, characterized in that: in the step (1), the dosage of the flocculating agent is 2-3 g/m³And (4) waste water.

4. The pretreatment method of molasses alcohol wastewater according to claim 1, characterized in that: the rectifying tower in the step (2) is a plate tower or a packed tower.

5. The pretreatment method of molasses alcohol wastewater according to claim 1, characterized in that: and (3) the tower top product in the step (2) is a substance with volatility greater than that of water.

6. The pretreatment method of molasses alcohol wastewater according to claim 1, characterized in that: and (3) subsequently adding the tower top product in the step (2) into an alcohol byproduct treatment system for uniform treatment.

7. The pretreatment method of molasses alcohol wastewater according to claim 1, characterized in that: and (3) taking the tower bottom product in the step (2) as a main body of the pretreated wastewater.

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