CN104262089B - Method and device for dehydrating and refining biofuel - Google Patents

Abstract

The invention relates to a method for dehydration and refining of biofuels. The fermentation liquid used for preparing biofuel alcohol is rectified under normal pressure, the temperature of the tower bottom is 95-105°C, and the temperature of the tower top is 70-95°C; from the bottom of the rectification tower The waste water is separated, and the gas output from the top of the rectification tower is partially condensed by the partial condenser, and the condensate is returned to the rectification tower with a reflux ratio of 1~3.5; the uncondensed gas is pressurized to >0.3Mpa and then enters the steam permeation membrane for separation The permeate side is pumped by a vacuum pump, and the water vapor is extracted from the permeate side of the steam permeable membrane separator to cool down and then collected; at the same time, anhydrous alcohol gas is output from the retentate side, and after condensation, anhydrous water with a water content of <0.1wt% is obtained. Alcoholic liquid products. The invention also provides a special device for the method. The method and its device combine atmospheric distillation, compressor and new high-efficiency steam permeation membrane separator for the dehydration treatment of biofuel alcohol, and have the advantages of energy saving and high efficiency, small footprint of the device, environmental friendliness and simple operation, etc. .

Description

Method and device for dehydration and refining of biofuel

technical field

The present invention relates to a method and device for dehydration and purification of biofuels, in particular to a method and device for dehydration and purification of biofuels that integrate a rectification tower, a compressor, a new type of high-efficiency steam permeation membrane separation device, and thermal energy secondary utilization technology , belonging to the separation domain.

Background technique

With the rapid development of industry, the consumption of energy is increasing day by day, and fuel resources such as oil and coal, which are natural energy sources, are bound to be exhausted day by day. In order to cope with the energy crisis, new energy sources must be opened up. The research on the preparation of fuel alcohol by biomass fermentation began in the late last century. The fuel is obtained from the fermentation liquid of corn and other food crops through dehydration. It is not limited by natural resources and is a sustainable energy source. Biofuels are fermented according to different grain varieties and methods to obtain different alcohols, mainly methanol, ethanol or butanol. Since the fermentation liquid contains about 90wt.% water, dehydration refining is an important link in the biofuel production process. Since ethanol and water will form an ethanol-water azeotrope, it is difficult to achieve complete dehydration with a single rectification method, and most of them need to be further dehydrated through steps such as azeotropic rectification, extractive rectification and molecular sieve adsorption, thus making the entire process bloated Complicated and energy-intensive. Among them, the introduction of entrainer or extractant not only increases the economic cost but also brings great harm to the environment, while the molecular sieve adsorption method has the problems of low primary recovery and high energy consumption. Chinese patent CN102260140A proposes to condense all the gas near the azeotropic composition at the top of the rectification tower into liquid, then heat it to 80-90°C and send it into the pervaporation membrane module. This process causes a huge waste of energy consumption. The phenomenon of serious concentration polarization and temperature difference polarization occurs during the vaporization process. Chinese patent CN103071307A adopts pressurized rectification, and the gas at the outlet of the partial condenser directly enters the steam permeation separation device for dehydration; the disadvantage is that pressurized rectification will reduce the relative volatility of alcohol and water, reduce the efficiency of rectification separation, and increase energy consumption. The steam permeation separation device is a low-pressure separation device of <0.2Mpa (gauge pressure). The operating pressure is low, resulting in low flux and a large membrane area required. The pressure is easy to fluctuate, and the corresponding equipment investment cost is relatively high.

Contents of the invention

The invention provides a method and device for dehydration and refining of biofuels. The process of dehydration and purification of biofuels has simple process, low energy consumption, no need to add a third component, and achieves the goals of cost reduction and environmental friendliness.

A method for dehydration and refining of biofuels. The fermentation liquid used to prepare biofuel alcohol is sent to a rectification tower for atmospheric rectification. The temperature of the bottom of the tower is controlled at 95-105°C, and the temperature at the top of the rectification tower is 70-95°C. ℃; the waste water is separated from the bottom of the rectification tower, and collected in the waste water tank after heat exchange and cooling; the gas output from the top of the rectification tower is passed into the decondenser, and the cold water at 5 ~ 30 ℃ is used as the refrigerant to partially condense and condense The liquid is returned to the rectification tower for further rectification. The reflux ratio is 1-3.5. The uncondensed gas is pressurized to >0.3Mpa through the compressor, and the temperature rises naturally to >100°C. The permeation side of the membrane separator is pumped by a vacuum pump, so that alcohol and water are separated by steam permeation on the molecular sieve membrane, and the water vapor is extracted from the permeation side of the steam permeation membrane separator and collected after being cooled by a low-temperature coolant; The retentate side of the separator outputs gaseous anhydrous alcohol, which is condensed and stored in the product tank. The water content of the product anhydrous alcohol is <0.1 wt.%.

The waste water separated from the bottom of the rectification tower exchanges heat with the fermentation liquid before entering the rectification tower, and the fermentation liquid is preheated to 78-90°C.

The gaseous anhydrous alcohol output from the retentate side of the steam permeable membrane separator first exchanges heat with the still liquid of the rectifying tower, and then is further cooled by cold water and stored in the product tank.

The coolant used in the process of condensing and lowering the temperature of the water vapor extracted from the permeation side of the steam permeable membrane separator is -25°C-20°C ethylene glycol aqueous solution or calcium chloride aqueous solution from the refrigerant machine. The vacuum degree of the permeation side of the steam permeation membrane separator is 5-2000Pa.

The vapor permeable membrane is NaA molecular sieve membrane, T-type molecular sieve membrane, MOR molecular sieve membrane, ZSM-5 molecular sieve membrane, DDR molecular sieve membrane or silicon dioxide membrane.

The present invention also provides a device for the above biofuel dehydration and refining method, including a raw material tank (1), a preheater (3), a rectification tower (4), a partial condenser (5), and a compressor connected by pipelines (9) and a vapor permeable membrane separator (10), the raw material tank (1) is connected to the inlet of the preheater (3) through the raw material pump (2), and the outlet of the preheater (3) is connected to the rectifying tower (4) The raw material inlets of the reboiler (8) are connected to the bottom liquid outlet of the reboiler (8) in order to connect the drain pump (16), the preheater (3) and the waste water tank (17); the column of the rectification column (4) The top gas output pipe leads to the decondenser (5), the condensate outlet of the decondenser (5) leads to the reflux liquid tank (6), and the reflux liquid tank (6) is connected to the rectification tower (4) through the reflux pump (7) ) is connected to the reflux liquid inlet; the gas outlet of the decondenser (5) is connected to the inlet of the steam permeable membrane separator (10) through the compressor (9), and the retentate of the steam permeable membrane separator (10) The side of the vapor permeation membrane separator (10) is connected to the permeate side through the permeate output pipe to the permeate The liquid condenser (13) is finally connected to the permeate tank (14); the permeate condenser (13) is provided with coolant inlet and outlet pipes; the permeate tank (14) is connected with a vacuum pump (15).

The decondenser (5) and the product condenser (11) are respectively connected with the cooling water system (19) to form a refrigerant circulation pipeline.

The coolant inlet pipe and outlet pipe of the permeate condenser (13) are connected to the refrigerant machine (20) to form a cycle.

The steam permeation membrane separator (10) is composed of a plurality of tubular steam permeation membrane modules connected in series, parallel or in combination. The steam permeation membrane is NaA molecular sieve membrane, T-type molecular sieve membrane, MOR molecular sieve membrane, ZSM-5 molecular sieve membrane, DDR molecular sieve membrane or silica membrane.

The invention integrates atmospheric rectification and pressurized steam permeation membrane separation technology to dehydrate and refine biofuel to obtain high-purity ethanol with a water content of <0.1wt.%. The dehydration process can overcome the limitation of azeotropic equilibrium without introducing a third component, and at the same time avoid the bloated and complicated defects of the traditional process. Atmospheric rectification has low energy consumption and high relative volatility of alcohol and water, which improves the separation efficiency of alcohol and water in the rectification tower; the atmospheric pressure gas output from the top of the rectification tower is pressurized by the compressor and enters the steam permeation membrane separator It can increase the dehydration rate of the membrane separator. Since the gas will naturally heat up when it is pressurized, there is no need to install a superheater in the membrane unit, which is conducive to the stability of the process pressure. In addition, the present invention enables the waste water at the bottom of the rectification separation and the gas-phase dehydration alcohol product obtained by membrane separation to recover and utilize heat before leaving the system, reducing the boiler load for heating the reboiler. The entire technological process has the advantages of energy saving and high efficiency, small footprint, zero pollution, simple operation, high resource utilization rate, etc., and has huge market application prospects.

Description of drawings

Figure 1 is a schematic diagram of a biofuel dehydration refining system and device.

Among them, 1—raw material tank, 2—feed pump, 3—preheater, 4—atmospheric rectification tower, 5—decondenser, 6—reflux tank, 7—reflux pump, 8—reboiler, 9 —compressor, 10—steam permeation membrane separator, 11—retentate side condenser, 12—product tank, 13—permeation side condenser, 14—permeate tank, 15—vacuum pump, 16—bottom drain pump, 17—wastewater pool, 18—steam boiler, 19—cooling water system, 20—refrigerant machine.

detailed description

Example 1 Dehydration and refining of ethanol fermentation broth

The device shown in Figure 1 is used to dehydrate and refine the ethanol fermentation broth. The dehydration process is as follows:

Put the ethanol fermentation liquid with a water content of 92wt.% into the raw material tank 1, and under the promotion of the feed pump 2, preheat the fermented liquid in the raw material tank 1 through the preheater 3 to 78 ~ After 85°C, it is sent to the rectification tower 4. The total number of trays in the rectification tower is 12, and the feeding position is the 10th theoretical plate. The reboiler 8 maintains a tower bottom temperature of 95-105° C. under the heat supply conditions of the saturated water vapor from the steam boiler 18 and the anhydrous alcohol vapor on the retentate side of the steam permeation membrane separation unit 10; meanwhile, the rectification tower 4 The top of the tower is controlled to be 70-80°C by condensing the reflux liquid. Under normal pressure, ethanol and water are separated by rectification, the water in it falls to the bottom of the tower, and the ethanol gas entrains a small amount of water vapor to rise and discharge from the top of the tower. The tower kettle water is extracted from the reboiler 8 through the tower bottom drain pump 16, and then cooled to 30-50°C after heat exchange with the ethanol fermentation liquid in the preheater 3, and stored in the waste water pool 17, the ethanol content in the waste water is less than 0.1wt .%; The gas discharged from the top of the tower is partially condensed through the heat exchange between the partial condenser 5 and the water (5~30°C) from the cooling water system 19, and the condensate is passed into the reflux tank 6, and passes through the reflux according to the reflux ratio of 1~2.5 The pump 7 returns to the top of the rectification column 4 for controlling the temperature of the column top and enhancing the separation of the components in the column. The uncondensed gas (water content is 10-12wt.%) passed through the decondenser 5 is pressurized to 0.4Mpa (gauge pressure) by the compressor 9, and the gas is naturally raised to >100°C, and sent to the steam permeation membrane for separation 10 for further dehydration. The vapor permeation membrane separator 10 is composed of a plurality of tubular NaA molecular sieve membrane modules connected in series, with a total packing area of 160m ² . Turn on the vacuum pump 15 on the permeate side, and maintain the vacuum pressure at 800Pa. Ethanol and water in the gas phase are collected on both sides of the NaA molecular sieve membrane; that is, water vapor passes through the NaA molecular sieve membrane and accumulates on the permeate side, and ethanol gas accumulates on the retentate side because it does not pass through the NaA molecular sieve membrane. Under the action of vacuum suction, the water vapor on the permeation side is condensed by the low-temperature coolant from the refrigerant machine 20 through the permeation side condenser 13 and then enters the storage tank 14 (this water does not need to be discharged, and can be used as fermentation water in the system for recycling). The anhydrous ethanol gas output from the retentate side of the steam permeable membrane separator 10 passes through the reboiler 8, exchanges heat with the bottom liquid of the tower, and then cools down, then enters the condenser 11 and is condensed by normal temperature water from the cold water system 19 to form a high-purity ethanol product (moisture content<0.1wt.%), sent to the product tank 12 for storage.

Example 2 Dehydration and purification of ethanol fermentation broth with a water content of 95wt.%.

Present embodiment is that water content is its refining process with embodiment 1, and difference with embodiment 1 is:

The raw material is fermented liquid ethanol with a water content of 95wt.%.

The total number of trays in the rectification column is 12, and the feeding position is the fifth theoretical plate;

Fermentation broth preheating temperature 80 ~ 90 ℃;

The flow rate of feed pump 2 is 20000kg/h;

The top reflux ratio is 2.8~3.5;

The temperature at the top of the tower is controlled at 85-95°C;

The temperature of the tower kettle is controlled at 100-110°C;

The water content in the uncondensed gas through the partial condenser 5 is 20 wt.%;

Compressor pressure increased by 0.5Mpa (gauge pressure);

The vacuum pressure on the permeate side is 1500Pa;

The steam permeation membrane separator 10 is composed of multiple tubular T-type molecular sieve membrane modules connected in series, with a total packing area of 230m ² .

In this example, a high-purity ethanol product with a water content of <0.1wt.% was obtained by separation.

Example 3 Dehydration and purification of butanol fermentation broth

The refining process of this embodiment is the same as Example 1, and the difference from Example 1 is:

The raw material is a butanol fermentation broth with a water content of 98wt.%.

The total number of trays in the rectification tower is 20, and the feed position is the 10th theoretical tray;

The preheating temperature of the fermentation broth is 80-90°C;

The flow rate of feed pump 2 is 25000kg/h;

The top reflux ratio is 1~3.5;

The temperature at the top of the tower is controlled at 85-95°C;

The temperature of the tower kettle is controlled at 100-110°C;

The water content in the uncondensed gas through the partial condenser 5 is 30 wt.%;

Compressor pressure increased by 0.5Mpa (gauge pressure);

The vacuum pressure on the permeate side is 1300Pa;

The steam permeation membrane separator 10 is composed of multiple tubular T-type molecular sieve membrane modules connected in series, with a total packing area of 200m ² .

In this example, a high-purity butanol product with a water content of <0.1wt.% was obtained by separation.

The "wt.%" expressed above refers to the mass percentage.

Claims (2)

1. the special purpose device that bio-fuel dehydration is refined, it is characterised in that comprise the head tank (1), pre-connected by pipeline Hot device (3), rectifying column (4), fractional condenser (5), compressor (9) and water vapour penetration membrane separator (10), described head tank (1) passes through Raw material pump (2) is connected with preheater (3) import, and preheater (3) outlet is connected with the material inlet of rectifying column (4), and, then boil The tower bottoms outlet of device (8) is sequentially connected with positive displacement pump (16), preheater (3) and wastewater disposal basin (17)；The tower top of described rectifying column (4) Gas output tube is passed through fractional condenser (5), and the condensate outlet of fractional condenser (5) is passed through backflow flow container (6), and backflow flow container (6) is passed through Reflux pump (7) is connected with the backflow entrance of rectifying column (4)；The gas outlet of described fractional condenser (5) is by compressor (9) and steaming The import of vapour permeable membrane separator (10) is connected, and the retentate side of described water vapour penetration membrane separator (10) passes through output of products Guan Yi Secondary connection reboiler (8) and product condenser (11), be finally passed through products pot (12)；Described water vapour penetration membrane separator (10) Per-meate side connects penetrating fluid condenser (13) by penetrating fluid outlet tube, is finally passed through infiltration flow container (14)；Penetrating fluid condenser (13) input pipe and the outlet tube of coolant it are provided with；Described infiltration flow container (14) is connected with vacuum pump (15)；Described fractional condenser (5) and Product condenser (11) is linked to be medium circulation pipeline with cooling water system (19) respectively；The cooling of described penetrating fluid condenser (13) It is linked to be circulation between the input pipe of agent and outlet tube and coolant machine (20)；Described water vapour penetration membrane separator (10) is by multiple pipes Formula vapor permeation membrane component forms in the way of series, parallel or series-parallel connection.

Special purpose device the most according to claim 1, it is characterised in that described vapor permeable membrane be NaA molecular sieve membrane, T-shaped point Sub-sieve membrane, MOR molecular screen membrane, ZSM-5 molecular sieve film, DDR molecular screen membrane or silicon dioxide film.