CN110511115B - Method for coupling and strengthening separation of fuel ethanol by rectifying tower and membrane - Google Patents
Method for coupling and strengthening separation of fuel ethanol by rectifying tower and membrane Download PDFInfo
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Abstract
The invention discloses a method for strengthening separation of fuel ethanol by coupling a rectifying tower and a membrane, which is a rectifying-purifying process system consisting of a vacuum rectifying tower and three pressurized rectifying towers, wherein feed mash is fed in parallel to form a four-tower rectifying section, and a purifying section consisting of three membrane separation devices. The method has the advantages of greatly saving steam consumption, high quality of primary discharging, high system automation degree, small occupied area of the device, convenient equipment maintenance, reliable and durable membrane material consumption, high resource utilization rate and the like.
Description
Technical Field
The invention relates to a method for coupling and strengthening separation of fuel ethanol by a rectifying tower and a membrane.
Background
The development and utilization of fossil energy face serious problems of environmental pollution and resource exhaustion. The ethanol has the advantages of moderate carbon-oxygen composition, high octane number, no overload of greenhouse gases and pollutants after combustion and the like during combustion, is used as a gasoline additive, and has a huge market. The fuel ethanol is absolute ethanol with the volume concentration of more than 99.5 percent, and has the functions of oxygenation and combustion supporting when being used as a fuel oil improver, thereby achieving the purposes of energy conservation and environmental protection. Meanwhile, the biofuel ethanol has the regenerability, so the process for preparing the fuel ethanol by the biological route is widely used by the ethanol industry at home and abroad. Under the background of improving the national requirements on energy conservation and emission reduction and reducing subsidies of fuel ethanol, a main way is to achieve the purpose of reducing cost and making profit for enterprises by continuously optimizing the process for refining the biofuel ethanol. The volume concentration of ethanol in fermentation mash of biomass such as starch, fructosyl polysaccharide, cellulose and the like is 2-20%, and when the biomass such as starch is fermented, the volume concentration of ethanol can reach 8-20%. The process of rectifying and extracting the fuel ethanol needs to be realized by means of salting, extracting and rectifying or molecular sieve adsorption and dehydration. Aiming at the process route, the optimization process mainly focuses on the heat recycling process design of the rectification section [ document 1: Lepenghui, three-tower differential pressure distillation process simulation optimization of fuel ethanol and tower process design [ D ]. Western Ann: northwest university, 2017; document 2 Shelfer JR, Bennett H, Shelfer Grant T, et al, process and apparatus for a commercial production motor fuel-grade ethanol WO2008024109a1[ P ]. 2008-02-28 ], or a more energy efficient new technology employed in the purification section of the fuel ethanol production process.
The vapor permeable membrane separation and purification technology has the advantages of high separation efficiency, high automation degree, simple operation, low requirement on equipment use conditions, no introduction of a third component, difficulty in environmental pollution and the like, and has obvious advantages in the organic solvent refining process. Compared with the traditional process, the steam unit consumption of the whole system can be saved by more than 30-50% by adopting a steam permeable membrane separation and purification process [ document 3, study on red, beautiful and stand-by, etc. ] A production method and a device of biomass absolute ethyl alcohol are CN104262090B [ P ] 2016-06-29 ].
The patent CN102126920B [ document 4, Hanfei, Dingwei military, Linchang Jun, etc. ] the technology of rectifying ethanol by three-tower three-effect differential pressure heat integration described in CN102126920B [ P ].2013-09-25 ] has obvious energy saving advantage compared with the traditional two-tower rectifying and purifying technology (document 5, Zhang Mianhua, Xiuqin, Luhui, etc. ] of fuel ethanol production method, CN1298859C [ P ].2007-02-07 ]. The rectification section adopts a crude distillation tower, a rectification tower I and a rectification tower II integrated device to rectify the ethanol, and the purification section adopts molecular sieve to absorb and dehydrate. In a heat main flow, external primary steam firstly provides a heat source for a reboiler of a rectifying tower II, and tower top steam heats a tower kettle of a rectifying tower I. The crude distillation tower is provided with two reboilers, and the heat source is derived from the material flow at the top of the rectifying tower I on the one hand and the anhydrous ethanol product steam of the molecular sieve adsorption unit on the other hand. In the main material flow, fermented liquor enters the upper part of the crude distillation tower after being preheated by two sections, and after the crude distillation, part of crude wine gas at the top of the tower forms crude wine condensate after heat exchange and is fed into the rectifying tower I. After rectification, part of azeotropic ethanol gas at the top of the tower reflows to the upper part of the rectifying tower I, and the other part of azeotropic ethanol gas enters a molecular sieve adsorption unit. And (4) feeding the tower bottom material after rectification into the lower part of a rectification tower II for further rectification, refluxing a part of distillate, and feeding the rest of distillate into a rectification tower I. The technological process is only optimized and described for the rectifying section, and in the actual molecular sieve adsorption technological process, the molecular sieve-fed ethanol solution has high required concentration (the volume concentration of ethanol is more than or equal to 93.5 percent), so that the problem of high requirement on the number of the tower plates of the rectifying tower I exists. The molecular sieve adsorption process produces a low ethanol concentration of about 25%, which reduces feedstock utilization if not recycled, and otherwise results in additional steam consumption. In addition, a plurality of flash tanks are used in the rectification process, so that the equipment investment is increased.
Patent CN104262090B [ document 3] describes a method for refining biofuel ethanol, which adopts a technique combining a thermally driven distillation method and membrane separation. The rectification section adopts three towers connected in parallel with an integrated device, and adopts the conditions of pressurization, normal pressure and decompression respectively, and the purification section adopts the pervaporation membrane process. In the heat unit, the steam at the top of the pressurized rectifying tower I is used for heating a reboiler at the bottom of the atmospheric rectifying tower II, the steam at the top of the atmospheric rectifying tower II is used for heating a reboiler at the bottom of the reduced pressure rectifying tower III, the steam required by the system is accessed by the reboiler at the top of the pressurized rectifying tower I, and the product steam generated by the pervaporation membrane is used for preheating fermentation mash. In the material unit, the top material of each rectifying tower is directly connected to the pervaporation membrane device after mixing and heat exchange. The process adopts a three-tower parallel design, so the discharge temperature difference is relatively large, the temperature difference between the pressure rectifying tower and the vacuum rectifying tower reaches 50 ℃, the utilization rate of the generated heat is low under the condition, and the problem of overhigh energy consumption still exists.
In summary, at present, although the processes of biofuel ethanol are improved by optimizing and improving from the rectification section and the purification section, the steam permeable membrane technology has the operation characteristics of low requirement on feed concentration, high separation efficiency, no need of reflux and the like, a great improvement space is still left in the process of matching and combining with the rectification section, and the aim of reducing the energy consumption of the whole process can be further achieved by strengthening the separation by combining the rectification process and the membrane separation characteristic of the fuel ethanol.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method has the advantages of reasonably distributing material flow, fully utilizing material heat, further reducing temperature difference between rectifying towers and between the rectifying tower and a membrane separation device, improving the degree of fit between the material and heat of the rectifying section and the purifying section, and further reducing system energy consumption.
In order to realize the purpose, the invention adopts the technical scheme that:
the invention relates to a method for coupling and strengthening separation of fuel ethanol by a rectifying tower and a membrane, which comprises the following steps:
the fermented mash is divided into four paths of mash after being preheated by two stages: mash F1, mash F2, mash F3, and mash F4; wherein mash F1 is directly fed into the vacuum rectification tower 1; the mash F2 is fed into a pressurized rectifying tower 2 after being preheated for the first stage; the mash F3 is fed into a pressurized rectifying tower 3 after being preheated for one stage, the mash F4 is fed into a pressurized rectifying tower 4 after being preheated for two stages, the reduced pressure rectifying tower 1, the pressurized rectifying tower 2, the pressurized rectifying tower 3 and the pressurized rectifying tower 4 are connected in parallel in the material flow direction, the mash F1 enters the reduced pressure rectifying tower 1 for reduced pressure rectification to obtain tower top ethanol steam, a part of ethanol steam a1 after the first-stage heat exchange of the fermented mash flows back to the reduced pressure rectifying tower 1, and the other part of ethanol steam a2 enters the pressurized rectifying tower 4 for pressurized rectification after the two-stage heat exchange; waste water obtained from the tower bottom of the reduced pressure distillation tower 1 is discharged out of the system after heat exchange in a tower 1 reboiler h12 in sequence;
after the mash F2 enters a pressurized rectifying tower 2 for pressurized rectification, a part of tower top ethanol steam b1 is obtained and exchanges heat with a reboiler h11 of a reduced pressure rectifying tower 1 and then flows back to the pressurized rectifying tower 2, a part of ethanol steam b2 enters a steam permeation membrane component 5 after being preheated by external steam, and the tower bottom wastewater of the pressurized rectifying tower 2 is discharged out of the system after three-stage heat exchange for the fermented mash;
after the mash F3 enters a pressurized rectifying tower 3 for pressurized rectification, a part of obtained overhead ethanol steam c1 exchanges heat with a reboiler h21 of the pressurized rectifying tower 2 and then flows back to the pressurized rectifying tower 3, a part of overhead ethanol steam c2 enters a steam permeable membrane component 6 after being preheated by external steam, and the tower bottom wastewater of the pressurized rectifying tower 3 is discharged out of the system after being subjected to three-stage heat exchange with the fermented mash;
after the mash F4 enters a pressurized rectifying tower 4 for pressurized rectification, a part of obtained tower top ethanol steam d1 exchanges heat with a reboiler h31 of the pressurized rectifying tower 3, then the obtained tower top ethanol steam flows back to the pressurized rectifying tower 4, a part of ethanol steam d2 at the tower top enters a steam permeable membrane component 7 after being preheated by external steam, and tower bottom wastewater of the pressurized rectifying tower 4 exchanges heat with a fourth stage of fermented mash and ethanol steam a2 and then is discharged out of the system;
purifying by a vapor permeable membrane component 5 to obtain product vapor e1, sequentially performing secondary heat exchange on the reduced pressure rectifying tower 1 reboiler h12 and fermented mash to obtain a fuel ethanol product P1, and condensing outlet wastewater obtained by purification and then discharging the condensed outlet wastewater out of the system;
purifying by a vapor permeable membrane component 6 to obtain product vapor f1, sequentially performing secondary heat exchange on the reduced pressure rectifying tower 1 reboiler h12 and fermented mash to obtain a fuel ethanol product P1, and condensing outlet wastewater obtained by purification and then discharging the outlet wastewater out of the system;
purifying by a vapor permeable membrane component 7 to obtain product vapor g1, sequentially performing primary heat exchange on a pressurized rectifying tower 2 reboiler h22, a pressurized rectifying tower 3 reboiler h32 and ethanol vapor a2 to obtain a fuel ethanol product P2, and condensing outlet wastewater obtained by purification and discharging the outlet wastewater out of the system;
the whole set of system related to the method comprises a rectification section and a purification section, wherein the rectification section comprises a decompression rectification tower 1, a pressurization rectification tower 2, a pressurization rectification tower 3, a pressurization rectification tower 4 and seven reboilers, namely h11, h12, h21, h22, h31, h32 and h41, which are connected in parallel with feed mash; the purification section comprises vapor permeable membrane modules 5, 6 and 7, wherein each vapor permeable membrane module is provided with a preheater and a condenser respectively; the rectifying section and the purifying section are respectively in material connection with an inlet of a steam permeation membrane component 5 through a preheater at the top of the pressurized rectifying tower 2, in material connection with an inlet of a steam permeation membrane component 6 through a preheater at the top of the pressurized rectifying tower 3, and in material connection with an inlet of a steam permeation membrane component 7 through a preheater at the top of the pressurized rectifying tower 4; the product outlets of the vapor permeable membrane components 5 and 6 are in heat exchange connection with a reboiler h12 of the reduced pressure rectifying tower 1, and the product outlet of the vapor permeable membrane component 7 is in heat exchange connection with a reboiler h22 of the pressurized rectifying tower 2;
wherein the reflux ratios of the ethanol steam at the top of the pressurized coarse distillation tower 2, the pressurized rectifying tower 3 and the pressurized rectifying tower 4 are all 0.5-3.5; the volume concentration range of the ethanol steam entering the steam permeation membrane assemblies 5, 6 and 7 after preheating is more than 55 percent;
in the scheme, the requirement of the fuel ethanol purification section on the concentration of ethanol steam entering a membrane separation system can influence the design of tower plate number parameters, the operating temperature, the pressure, the reflux ratio and the like of the pressurized rectifying towers 2, 3 and 4; preferably, the ethanol vapor b2, c2, d2 preheated to enter the vapor permeation membrane module 5, 6, 7 has a concentration range of 75% by volume or more.
In the scheme, the number of the tower plates of the vacuum rectifying tower 1, the pressure rectifying tower 2, the pressure rectifying tower 3 and the pressure rectifying tower 4 is more than or equal to 45, the absolute pressure range of the vacuum rectifying tower 1 is 10-100 kPa, the pressure ranges of the pressure rectifying towers 2, 3 and 4 are 100-400 kPa, 400-800 kPa and 1200-1800 kPa respectively, the tower top temperature ranges of the vacuum rectifying tower 1, the pressure rectifying tower 2, the pressure rectifying tower 3 and the pressure rectifying tower 4 are 40-80 ℃, 80-120 ℃, 110-160 ℃ and 150-190 ℃, and the tower kettle temperature ranges of the vacuum rectifying tower 1, the pressure rectifying tower 2, the pressure rectifying tower 3 and the pressure rectifying tower 4 are 60-100 ℃, 100-140 ℃, 140-180 ℃ and 180-220 ℃ respectively.
More preferably, the number of the tower plates of the vacuum rectification tower 1, the pressure rectification tower 2, the pressure rectification tower 3 and the pressure rectification tower 4 is more than or equal to 52, the absolute pressure range of the vacuum rectification tower 1 is 20-80 kPa, the pressure ranges of the pressure rectification towers 2, 3 and 4 are 140-220 kPa, 490-670 kPa and 1360-1500 kPa respectively, the tower top temperature ranges of the vacuum rectification tower 1, the pressure rectification tower 2, the pressure rectification tower 3 and the pressure rectification tower 4 are 50-75 ℃, 85-110 ℃, 110-155 ℃ and 155-180 ℃, and the tower kettle temperature ranges of the vacuum rectification tower 1, the pressure rectification tower 2, the pressure rectification tower 3 and the pressure rectification tower 4 are 70-95 ℃, 105-130 ℃, 145-180 ℃ and 180-215 ℃ respectively.
The reflux ratios of the ethanol steam at the top of the decompression rectifying tower 1, the pressurization rectifying tower 2, the pressurization rectifying tower 3 and the pressurization rectifying tower 4 are respectively 1.0-2.5, 1.2-3.0 and 1.2-3.0.
In the above scheme, the vapor permeable membrane is an inorganic molecular sieve membrane or a polyimide fiber membrane.
The biomass raw material source of the fermentation mash fed by the process comprises one or more of cellulose, starch, corn, cassava, jerusalem artichoke roots, plant straws and other biomass, and the volume concentration of the ethanol in the fermentation mash is more than or equal to 2%.
The method has the innovation points that the problems of low material and heat integrating degree of a rectifying section and a purifying section and high energy consumption of the whole process existing in the conventional process for the biofuel ethanol are solved, the equipment requirement of the rectifying section and the steam use amount can be further reduced by combining the influence of the process conditions of the purifying section on the rectifying section, the characteristic of no low-concentration ethanol by-product in vapor permeable membrane separation is combined, the ethanol reflux of the purifying section is cancelled, and the steam use amount of the rectifying section can be further reduced. Provides a new low-energy-consumption route for preparing fuel ethanol from the biological mash.
The invention has the following advantages
(1) The vapor permeable membrane purification technology has the advantages of high one-time discharging quality, high automation degree, simple operation, low requirement on equipment using conditions, no introduction of a third component, difficulty in environmental pollution and the like, and has obvious advantages in the organic solvent refining process;
(2) the invention has the advantages of high matching degree of materials and heat of the rectifying section and the purifying section, moderate temperature difference between equipment, sufficient heat exchange, high heat utilization rate and the like, the main heat source of the system is provided by a reboiler h41 of the pressurized rectifying tower 4 through the outside, and the preheating process before the purifying section enters the steam permeable membrane needs a very small amount of external heat source;
(3) the steam permeable membrane is adopted for purification, so that the requirements on the number of tower plates of a rectifying tower of a rectifying section, operating conditions and the like can be reduced, and the energy consumption of the rectifying section is further reduced;
(4) compared with the traditional molecular sieve adsorption purification process, the product produced in the steam permeable membrane purification process has no low-concentration ethanol, does not need to be refluxed and rectified, can improve the utilization rate of raw materials at one time, and reduces the energy consumption of the system;
(5) compared with the traditional rectification mode, the combined tower rectification and membrane separation integrated process can save steam by about 67 percent; compared with the traditional molecular sieve adsorption purification process, the combined tower rectification and membrane separation integrated process can save steam by about 43 percent. The steam unit consumption of the whole system can be reduced to 0.9 ton Steam generating device Per ton of Fuel ethanol Left and right.
In conclusion, the method of the invention realizes the purpose of preparing the fuel ethanol from the biological fermentation mash with high efficiency and low energy consumption. Compared with the existing rectification and purification process, the combined process provided by the invention has the advantages of high utilization rate of raw materials, high product one-time extraction purity (the volume concentration of the fuel ethanol product separated and purified by a vapor permeable membrane can reach more than 99.5%), high product quality, low equipment cost, high system automation rate, simplicity in operation, low product unit consumption, environmental friendliness, renewability, high material and heat matching degree of the rectification and purification process, high fuel ethanol atom economy and the like.
Drawings
FIG. 1 is a schematic process flow diagram of the method for enhanced separation of fuel ethanol by coupling a rectifying tower and a membrane.
In fig. 1, 1 is a reduced pressure rectifying tower, 2 is a pressurized rectifying tower, 3 is a pressurized rectifying tower, 4 is a pressurized rectifying tower, 5, 6 and 7 are steam permeation membrane modules, h11 and h12 are reboilers of the reduced pressure rectifying tower 1, h21 and h22 are reboilers of the pressurized rectifying tower 2, h31 and h32 are reboilers of the pressurized rectifying tower 3, h41 is a reboiler of the pressurized rectifying tower 4, F1, F2, F3 and F4 are respectively mash entering the reduced pressure rectifying tower 1, the pressurized rectifying tower 2, the pressurized rectifying tower 3 and the pressurized rectifying tower 4, a1 and a2 are respectively reflux of the reduced pressure rectifying tower 1 and ethanol steam entering the pressurized rectifying tower 4, b1 and b2 are respectively reflux of the pressurized rectifying tower 2 and ethanol steam entering the steam rectifying tower 5, c permeable membranes 8 and c2 are respectively reflux of the pressurized rectifying tower 3 and ethanol steam entering the steam module 6, d 92 and d2 are respectively entering the pressurized rectifying tower reflux module of the pressurized rectifying tower 4, e1, f1, g1 are the product vapors from the vapor permeable membrane modules 5, 6, 7, respectively, P1 is the fuel ethanol produced by the vapor permeable membrane modules 5, 6, and P2 is the fuel ethanol produced by the vapor permeable membrane module 7.
Detailed Description
The present invention will be described in detail with reference to specific examples, which are not intended to limit the scope of the present invention. Examples include the effect of the system on the degree of steam savings when the feed mash ethanol concentration, number of distillation column trays and reflux ratio are varied. But not excluding that the effect of further reducing the consumption of steam by unit product can be achieved on the premise of ensuring that the concentration of the product ethanol meets the requirement of using the product ethanol as fuel ethanol by optimizing other operation conditions based on a process diagram.
As shown in fig. 1, a schematic process flow diagram of the method for the enhanced separation of fuel ethanol by coupling a rectifying tower and a membrane is shown, and the material flow and the heat flow of the process are as follows:
material flow: the fermented mash is subjected to two-stage preheating and then divided into four paths of mash F1, F2, F3 and F4, wherein the mash F1 enters a reduced pressure rectifying tower 1, the mash F2 enters a pressurized rectifying tower 2 after being subjected to one-stage preheating, the mash F3 enters a pressurized rectifying tower 3 after being subjected to one-stage preheating, and the mash F4 enters a pressurized rectifying tower 4 after being subjected to two-stage preheating. After passing through a reduced pressure rectifying tower 1, tower bottom liquid exchanges heat with a reboiler h12 of the tower 1 to obtain wastewater, the ethanol steam at the tower top preheats the fermented mash for the first stage and then is divided into two parts of ethanol steam a1 and a2, wherein the ethanol steam a1 directly flows back, and the ethanol steam a2 is fed into a pressurized rectifying tower 4 after two-stage heat exchange. After mash F2 enters a pressurized rectifying tower 2, tower bottom liquid exchanges heat with mash F2 to obtain waste water, ethanol steam at the tower top is divided into two parts, namely ethanol steam b1 and b2, the ethanol steam b1 exchanges heat with a tower 1 reboiler h11 and then flows back, the ethanol steam b2 enters a steam permeable membrane component 5, membrane separation is carried out to obtain product steam e1 and waste water, and the product steam e1 sequentially exchanges heat with feed mash in a decompression rectifying tower 1 reboiler h12 for the second time to obtain a fuel ethanol product P1. After mash F3 enters a pressurized rectifying tower 3, tower bottom liquid exchanges heat with mash F3 to obtain waste water, ethanol steam at the tower top is divided into two parts, namely ethanol steam c1 and c2, the ethanol steam c1 exchanges heat with a tower 2 reboiler h21 and then flows back, the ethanol steam c2 enters a steam permeable membrane component 6, membrane separation is carried out to obtain product steam F1 and waste water, and the product steam F1 sequentially exchanges heat with feed mash in a decompression rectifying tower 1 reboiler h12 for the second time to obtain a fuel ethanol product P1. After mash F4 enters a pressurized rectifying tower 4, tower bottom liquid of the tower 4 exchanges heat with mash F4 and ethanol steam a2 to obtain waste water, the ethanol steam at the tower top is divided into two parts of ethanol steam d1 and d2, ethanol steam d1 exchanges heat with a reboiler h31 of a tower 3 and then flows back, the ethanol steam d2 enters a steam permeable membrane component 7 and is subjected to membrane separation to obtain product steam g1 and waste water, and the product steam g1 sequentially exchanges heat with ethanol steam a2 for the reboiler h22 of the pressurized rectifying tower 2, the reboiler h32 of the pressurized rectifying tower 3 and the mash F4 of the mash to obtain a fuel ethanol product P2.
A heat flow: heat is supplied to a reboiler h41 of the pressurized rectifying tower 4 by primary steam from the outside. The heat of the reboiler h31 of the pressurized rectifying tower 3 comes from the ethanol steam d1 at the top of the pressurized rectifying tower 4, and the reboiler h32 supplies heat by the fuel ethanol steam g1 purified by the vapor permeable membrane 7. The heat of the reboiler h21 of the pressurized rectifying tower 2 is derived from the ethanol steam c1 at the top of the pressurized rectifying tower 3, and the reboiler h22 supplies heat by the fuel ethanol steam g1 purified by the vapor permeable membrane 7. The heat of the reboiler h11 of the reduced pressure rectifying tower 1 comes from the ethanol steam b1 at the top of the pressurized rectifying tower 2, and the reboiler h12 exchanges heat with the bottom liquid of the reduced pressure rectifying tower 1 through the fuel ethanol steam e1 purified by a vapor permeable membrane. The fermented mash passes through tower top steam of a tower 1 and ethanol steam e1 and F1 for heat exchange, mash F2 passes through tower bottom liquid of a tower 2 for preheating before entering a pressurized rectifying tower 2, mash F3 passes through tower bottom liquid of a tower 3 for preheating before entering a pressurized rectifying tower 3, and mash F4 and ethanol steam a2 pass through ethanol steam g1 and tower bottom liquid of a tower 4 for preheating in sequence before entering a pressurized rectifying tower 4. The separation process of the vapour permeable membrane modules 5, 6 and 7 requires a small amount of vapour, supplied from the outside, but with a negligible heat consumption relative to the whole system.
The technical scheme of the invention is further explained as follows:
the optimization criterion aiming at the rectifying section is as follows: (1) fully preheating mash before entering each tower according to the operating temperature condition of each tower; (2) the mash entering tower quantity and reflux ratio distribution follow the principle of minimum heat loss of the system; (3) the separation advantages of high purification and low concentration feed of the vapor permeable membrane are fully exerted; (4) the feeding mode is matched with the selection of design parameters and operation conditions of each tower; (5) matching two groups of vapor permeable membrane separation devices based on the characteristic that the concentration and the temperature of the wine gas at the tower top meet the membrane separation requirement, and avoiding the overload of the temperature of the feed liquid and the additional consumption of heat;
the optimization criterion for the purification section is as follows: the low-concentration ethanol component of about 1/4 can be generated in the advanced molecular sieve adsorption and purification process in the industry at present, in order to improve the utilization rate of the biomass raw material, the low-concentration ethanol needs to be recycled, and additional steam is needed for purification. And the adoption of the steam permeable membrane purification process has no generation and backflow reuse of low-concentration ethanol, so that the steam consumption can be greatly reduced.
The effect of the process of the present invention is further illustrated by the following specific examples.
Example 1
The process flow diagram is shown in figure 1, the fermentation mash raw material is corn, and the temperature is 29.9 ℃. The number of the tower plates of the vacuum distillation tower 1 is fixed to 55, the number of the tower plates of the pressure distillation towers 2, 3 and 4 is fixed to 61, and the feeding positions of the vacuum distillation tower 1, the pressure distillation towers 2, 3 and 4 are respectively at 35, 45 and 45 tower plates (counted from the tower bottom). The reflux ratio of the vacuum distillation tower 1 is fixed to 1.6, and the reflux ratios of the pressurized distillation towers 2, 3 and 4 are fixed to 1.8. The volume concentration of ethanol in the fermented mash is 5.3%, and after feeding, the operation conditions of each tower in the combined tower, the steam amount consumed by the ethanol as a unit fuel of the system, the energy-saving condition relative to the traditional process and the energy-saving condition relative to the molecular sieve integrated process of the combined tower are shown in example 1 in table 1.
Example 2
The process flow diagram is shown in figure 1, the fermentation mash raw material is corn, and the temperature is 29.9 ℃. The number of the tower plates of the vacuum distillation tower 1 is fixed to 55, the number of the tower plates of the pressure distillation towers 2, 3 and 4 is fixed to 61, and the feeding positions of the vacuum distillation tower 1, the pressure distillation towers 2, 3 and 4 are respectively at 35, 45 and 45 tower plates (counted from the tower bottom). The reflux ratio of the vacuum distillation tower 1 is fixed to 1.6, and the reflux ratios of the pressurized distillation towers 2, 3 and 4 are fixed to 1.8. The volume concentration of the ethanol in the fermented mash is 12.0%, and after feeding, the operation conditions of each tower in the combined tower, the steam amount consumed by the ethanol in unit fuel of the system, the energy-saving condition relative to the traditional process and the energy-saving condition relative to the molecular sieve integrated process of the combined tower are shown in example 2 in table 1.
Example 3
The process flow diagram is shown in figure 1, the fermentation mash raw material is corn, and the temperature is 29.9 ℃. The number of the tower plates of the vacuum distillation tower 1 is fixed to 55, the number of the tower plates of the pressure distillation towers 2, 3 and 4 is fixed to 61, and the feeding positions of the vacuum distillation tower 1, the pressure distillation towers 2, 3 and 4 are respectively at 35, 45 and 45 tower plates (counted from the tower bottom). The reflux ratio of the vacuum distillation tower 1 is fixed to 1.6, and the reflux ratios of the pressurized distillation towers 2, 3 and 4 are fixed to 1.8. The volume concentration of the ethanol in the fermented mash is 13.5%, and after feeding, the operation conditions of each tower in the combined tower, the steam amount consumed by the ethanol as a unit fuel of the system, the energy-saving condition relative to the traditional process and the energy-saving condition relative to the molecular sieve integrated process of the combined tower are shown in example 3 in table 1.
Example 4
The process flow diagram is shown in figure 1, the fermentation mash raw material is corn, and the temperature is 29.9 ℃. The number of the tower plates of the decompression rectifying tower 1 is fixed to be 55, the number of the tower plates of the pressurization rectifying tower 2, 3 and 4 is fixed to be 61, and the feeding positions of the rectifying towers 1, 2, 3 and 4 are respectively at the tower plates of 35, 45 and 45 (counted from the tower bottom). The reflux ratio of the vacuum distillation tower 1 is fixed to 1.6, and the reflux ratios of the pressurized distillation towers 2, 3 and 4 are fixed to 1.8. The volume concentration of ethanol in the fermented mash is 15.4%, and after feeding, the operation conditions of each tower in the combined tower, the steam amount consumed by the ethanol as a unit fuel of the system, the energy-saving condition relative to the traditional process and the energy-saving condition relative to the molecular sieve integrated process of the combined tower are shown in example 4 in table 1.
TABLE 1 experimental comparison of ethanol concentrations in fermentation broths with different feeds
In conclusion, under the operation of the process flow, the feed concentration of the fermentation mash is increased, and when the concentration of the fuel ethanol product is similar, the steam consumption is reduced, so that the steam quantity is obviously saved compared with the traditional process and the molecular sieve integrated process of the combined tower. In the existing fermentation process, when starch biomass such as corn and the like is used as a raw material for fermentation, the volume concentration of ethanol in fermentation mash is about 12%, the concentration of a product after the process flow is fed completely meets the use requirement of fuel ethanol (the concentration of the ethanol is more than or equal to 99.5%), and the steam saving effect of the process is obvious.
Example 5
The process flow diagram is shown in figure 1, the fermentation mash raw material is corn, and the temperature is 29.9 ℃. The number of the plate a of the vacuum distillation tower is fixed to 55, the number of the plate 2, 3 and 4 of the pressurization distillation tower is fixed to 61, and the feeding positions of the distillation towers 1, 2, 3 and 4 are respectively at the plate 35, 45 and 45 (counted from the tower bottom). The reflux ratio of the reduced pressure distillation tower 1 is reduced to 1.2, and the reflux ratios of the pressurized distillation towers 2, 3 and 4 are fixed to 1.8. The volume concentration of ethanol in the fermented mash is 13.0%, and after feeding, the operation conditions of each tower in the combined tower, the steam amount consumed by the ethanol as a unit fuel of the system, the energy-saving condition relative to the traditional process, and the energy-saving condition relative to the molecular sieve integrated process of the combined tower are shown as example 5 in table 2.
Example 6
The process flow diagram is shown in figure 1, the fermentation mash raw material is corn, and the temperature is 29.9 ℃. The number of the tower plates of the decompression rectifying tower 1 is fixed to be 55, the number of the tower plates of the pressurization rectifying towers 2, 3 and 4 is fixed to be 61, and the feeding positions of the rectifying towers 1, 2, 3 and 4 are respectively at the tower plates of 35, 45 and 45 (counted from the tower bottom). The reflux ratio of the pressurizing rectifying tower 2 is reduced to 1.5, the reflux ratio of the depressurizing rectifying tower 1 is 1.6, and the reflux ratios of the pressurizing rectifying tower 3 and the pressurizing rectifying tower 4 are fixed to 1.8. The volume concentration of ethanol in the fermented mash is 13.2%, and after feeding, the operation conditions of each tower in the combined tower, the steam amount consumed by the ethanol as a unit fuel of the system, the energy-saving condition relative to the traditional process, and the energy-saving condition relative to the molecular sieve integrated process of the combined tower are shown as example 6 in table 2.
Example 7
The process flow diagram is shown in figure 1, the fermentation mash raw material is corn, and the temperature is 29.9 ℃. The number of the tower plates of the decompression rectifying tower 1 is fixed to be 55, the number of the tower plates of the pressurization rectifying towers 2, 3 and 4 is fixed to be 61, and the feeding positions of the rectifying towers 1, 2, 3 and 4 are respectively at the tower plates of 35, 45 and 45 (counted from the tower bottom). The reflux ratio of the pressurized rectifying tower 3 is reduced to 1.5, the reflux ratio of the depressurized rectifying tower 1 is 1.6, and the reflux ratios of the pressurized rectifying towers 1 and 4 are fixed to 1.8. The volume concentration of ethanol in the fermented mash is 13.1%, and after feeding, the operation conditions of each tower in the combined tower, the steam amount consumed by the ethanol as a unit fuel of the system, the energy-saving condition relative to the traditional process, and the energy-saving condition relative to the molecular sieve integrated process of the combined tower are shown as example 7 in table 2.
Example 8
The process flow diagram is shown in figure 1, the fermentation mash raw material is corn, and the temperature is 29.9 ℃. The number of the tower plates of the decompression rectifying tower 1 is fixed to be 55, the number of the tower plates of the pressurization rectifying towers 2, 3 and 4 is fixed to be 61, and the feeding positions of the rectifying towers 1, 2, 3 and 4 are respectively at the tower plates of 35, 45 and 45 (counted from the tower bottom). The reflux ratio of the pressurizing rectifying tower 4 is reduced to 1.5, the reflux ratio of the depressurizing rectifying tower 1 is 1.6, and the reflux ratios of the pressurizing rectifying tower 1 and the pressurizing rectifying tower 3 are fixed to 1.8. The volume concentration of the ethanol in the fermentation mash is 13.3%, and after feeding, the operation conditions of each tower in the combined tower, the steam consumption of the ethanol fuel per unit of the system, the energy-saving condition relative to the traditional process and the energy-saving condition relative to the molecular sieve integrated process of the combined tower are shown in the example 8 in the table 2.
TABLE 2 Experimental comparison results with varying reflux ratio
In summary, under the operation of the process flow, when the reflux ratio of the vacuum distillation tower 1 or the pressure distillation towers 2, 3 or 4 is respectively reduced, and the concentration of the product ethanol meets the use requirement of the fuel ethanol (the ethanol concentration is more than or equal to 99.5%), the steam consumption is improved, but compared with the traditional process or the combined tower molecular sieve integrated process, the steam consumption of the four embodiments is obviously saved.
The invention relates to a method for preparing biofuel ethanol by using a combined tower rectification and membrane separation integrated device. Based on the advantages and the characteristics of membrane process purification, the invention has the advantage of further reducing the steam consumption of the system by highly matching the relationship between the materials and the heat of the rectification section and the purification section, namely, has the advantages of high-efficiency resource utilization and good environmental protection. The membrane device has mature process for efficiently purifying organic compounds such as ethanol and the like, and the process flow also has the advantages of high one-time discharging quality, high system automation degree, small system occupied area, convenient equipment maintenance, reliable and durable membrane consumable materials and the like. Therefore, the invention has the value of actually replacing the conventional rectification and purification combined process in the existing biofuel ethanol production.
Claims (8)
1. A method for coupling a rectifying tower and a membrane to enhance separation of fuel ethanol is characterized by comprising the following steps:
the fermented mash is divided into four paths of mash after being preheated by two stages: mash (F1), mash (F2), mash (F3) and mash (F4); wherein the mash (F1) is directly fed into the vacuum rectification tower (1); the mash (F2) is fed into a pressurized rectifying tower (2) after being preheated for the first stage; the mash (F3) is fed into a pressurized rectifying tower (3) after being preheated for the first stage, the mash (F4) is fed into the pressurized rectifying tower (4) after being preheated for the second stage, and the reduced pressure rectifying tower (1), the pressurized rectifying tower (2), the pressurized rectifying tower (3) and the pressurized rectifying tower (4) are connected in parallel in the material flow direction;
the mash (F1) enters a reduced pressure rectifying tower (1) for reduced pressure rectification to obtain tower top ethanol steam, a part of ethanol steam (a1) after the primary heat exchange of the fermented mash refluxes to the reduced pressure rectifying tower (1), and the other part of ethanol steam (a2) enters a pressurized rectifying tower (4) for pressurized rectification after two-stage heat exchange; waste water obtained at the tower bottom of the vacuum rectification tower (1) is discharged out of the system after heat exchange of a reboiler (h12) of the vacuum rectification tower (1) in sequence;
after the mash (F2) enters a pressurized rectifying tower (2) for pressurized rectification, a part of tower top ethanol steam (b1) obtained is subjected to heat exchange in a reboiler (h11) of a reduced pressure rectifying tower (1), then flows back to the pressurized rectifying tower (2), a part of ethanol steam (b2) enters a steam permeation membrane component (5) after being preheated by external steam, and the tower bottom wastewater of the pressurized rectifying tower (2) is discharged out of the system after being subjected to three-stage heat exchange on fermented mash;
after the mash (F3) enters a pressurized rectifying tower (3) for pressurized rectification, a part of tower top ethanol steam (c1) obtained is subjected to heat exchange in a reboiler (h21) of the pressurized rectifying tower (2), then flows back to the pressurized rectifying tower (3), a part of the tower top ethanol steam (c2) enters a steam permeation membrane component (6) after being preheated by external steam, and the tower bottom wastewater of the pressurized rectifying tower (3) is discharged out of the system after being subjected to three-stage heat exchange on the fermented mash;
after the mash (F4) enters a pressurized rectifying tower (4) for pressurized rectification, a part of tower top ethanol steam (d1) obtained is subjected to heat exchange in a reboiler (h31) of the pressurized rectifying tower (3), then flows back to the pressurized rectifying tower (4), a part of the tower top ethanol steam (d2) enters a steam permeation membrane component (7) after being preheated by external steam, and the tower bottom wastewater of the pressurized rectifying tower (4) is discharged out of the system after being subjected to heat exchange in a fermentation mash fourth stage and ethanol steam (a2) second stage;
purifying by a steam permeation membrane component (5) to obtain product steam (e1), sequentially performing secondary heat exchange on a reboiler (h12) of the reduced pressure rectifying tower (1) and fermented mash to obtain a fuel ethanol product (P1), and condensing outlet wastewater obtained by purification and discharging the condensed outlet wastewater out of the system;
purifying by a steam permeation membrane component (6) to obtain product steam (f1), sequentially performing secondary heat exchange on a reboiler (h12) of the reduced pressure rectifying tower (1) and fermented mash to obtain a fuel ethanol product (P1), and condensing outlet wastewater obtained by purification and discharging the condensed outlet wastewater out of the system;
purifying by a steam permeation membrane component (7) to obtain product steam (g1), sequentially performing primary heat exchange on a pressurized rectifying tower (2) reboiler (h22), a pressurized rectifying tower (3) reboiler (h32), ethanol steam (a2) and mash (F4) to obtain a fuel ethanol product (P2), and condensing outlet wastewater obtained by purification and then discharging the outlet wastewater out of the system;
the whole set of system related to the method comprises a rectification section and a purification section, wherein the rectification section comprises a reduced pressure rectification tower (1), a pressurized rectification tower (2), a pressurized rectification tower (3), a pressurized rectification tower (4) and seven reboilers (h11), (h12), (h21), (h22), (h31), (h32) and (h41) which are connected in parallel with feed mash; the purification section comprises steam permeation membrane modules (5), (6) and (7), wherein each steam permeation membrane module is provided with a preheater and a condenser respectively; the rectifying section and the purifying section are in material connection with an inlet of a steam permeation membrane component (5) through a preheater at the top of the pressurized rectifying tower (2), are in material connection with an inlet of a steam permeation membrane component (6) through a preheater at the top of the pressurized rectifying tower (3), and are in material connection with an inlet of a steam permeation membrane component (7) through a preheater at the top of the pressurized rectifying tower (4); the product outlets of the steam permeation membrane assemblies (5) and (6) are in heat exchange connection with a reboiler (h12) of the reduced pressure rectifying tower (1), and the product outlet of the steam permeation membrane assembly (7) is in heat exchange connection with a reboiler (h22) of the pressurized rectifying tower (2);
wherein the reflux ratios of the ethanol steam at the top of the pressurized coarse distillation tower (2), the pressurized rectifying tower (3) and the pressurized rectifying tower (4) are all 0.5-3.5; the volume concentration range of the ethanol steam entering the steam permeation membrane assemblies (5), (6) and (7) after preheating is more than 55 percent.
2. The method of claim 1, wherein: the ethanol steam b2, c2 and d2 entering the steam permeation membrane modules (5), (6) and (7) after preheating have a volume concentration range of more than 75 percent.
3. The method of claim 1, wherein: the tower plates of the pressure-reducing rectifying tower (1), the pressure-increasing rectifying tower (2), the pressure-increasing rectifying tower (3) and the pressure-increasing rectifying tower (4) are all more than or equal to 45, the absolute pressure range of the pressure-reducing rectifying tower (1) is 10-100 kPa, the pressure ranges of the pressure-increasing rectifying towers (2), (3) and (4) are 100-400 kPa, 400-800 kPa and 1200-1800 kPa respectively, the tower top temperature ranges of the pressure-reducing rectifying tower (1), the pressure-increasing rectifying tower (2), the pressure-increasing rectifying tower (3) and the pressure-increasing rectifying tower (4) are 40-80 ℃, 80-120 ℃, 110-160 ℃, 150-190 ℃, and the tower kettle temperature ranges of the pressure-reducing rectifying tower (1), the pressure-increasing rectifying tower (2), the pressure-increasing rectifying tower (3) and the pressure-increasing rectifying tower (4) are 60-100 ℃, 100-140 ℃, 140-180 ℃ and 180-220 ℃ respectively.
4. The method of claim 3, wherein: the tower plates of the reduced pressure rectifying tower (1), the pressure rectifying tower (2), the pressure rectifying tower (3) and the pressure rectifying tower (4) are all more than or equal to 52, the absolute pressure range of the reduced pressure rectifying tower (1) is 20-80 kPa, the pressure ranges of the pressure rectifying towers (2), (3) and (4) are 140-220 kPa, 490-670 kPa and 1360-1500 kPa respectively, the tower top temperature ranges of the reduced pressure rectifying tower (1), the pressure rectifying tower (2), the pressure rectifying tower (3) and the pressure rectifying tower (4) are 50-75 ℃, 85-110 ℃, 110-155 ℃ and 155-180 ℃, and the tower kettle temperature ranges of the reduced pressure rectifying tower (1), the pressure rectifying tower (2), the pressure rectifying tower (3) and the pressure rectifying tower (4) are 70-95 ℃, 105-130 ℃, 145-180 ℃ and 180-215 ℃ respectively.
5. The method of claim 1, wherein: the reflux ratios of the ethanol steam at the top of the vacuum distillation tower (1), the pressure distillation tower (2), the pressure distillation tower (3) and the pressure distillation tower (4) are respectively 1.0-2.5, 1.2-3.0 and 1.2-3.0.
6. The method of claim 1, wherein: the vapor permeable membrane is an inorganic molecular sieve membrane or a polyimide fiber membrane.
7. The method of claim 1, wherein: the ethanol volume concentration of the fermented mash is more than or equal to 2 percent.
8. The method of claim 1, wherein: the biomass raw material of the fermented mash is one or more of cellulose, starch, corn, cassava, jerusalem artichoke roots and stalks of plants.
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| CN102757308A (en) * | 2012-07-03 | 2012-10-31 | 张锋新 | Method of preparing high-purity ethanol |
| CN104341268A (en) * | 2013-08-09 | 2015-02-11 | 中国石油天然气股份有限公司 | Continuous dehydration method for fuel ethanol |
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