CN110452092B - Method for refining fuel ethanol by material and heat integration through tower-membrane coupling - Google Patents
Method for refining fuel ethanol by material and heat integration through tower-membrane coupling Download PDFInfo
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Abstract
The invention discloses a method for refining fuel ethanol by material and heat integration through tower-membrane coupling, which is a rectification-purification process system consisting of a three-tower rectification section and a purification section, wherein the three-tower rectification section consists of a pressure-reducing crude distillation tower connected with a pressure-increasing crude distillation tower in parallel and then connected with the pressure-increasing crude distillation tower in series, and the purification section consists of a membrane separation device. 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 refining fuel ethanol by material and heat integration through tower-membrane coupling.
Technical Field
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. In the embodiment about expansion of production of biofuel ethanol and popularization and use of ethanol gasoline for vehicles, which is issued by the minister of national ministry of 15.9.2017, the national ministry of 9.7 requires that the ethanol for vehicles is basically covered all over the country in 2020. 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 energy-saving and emission-reducing requirements and reducing subsidies of fuel ethanol, one 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. For this process route, the optimization process mainly focuses on the heat recovery and utilization process design of the rectification section [ document 1: li Penghui, fuel ethanol three-tower differential pressure distillation process simulation optimization and tower process design [ D ]. Western Ann, university of northwest, 2017; document 2: shelfer JR, bennett H, shelfer Grant T, et al, process and apparatus for commercial producing motor fuel-grade ethanol WO2008024109A1[ P ].2008-02-28 ], or a more energy-efficient new technology is 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, gu Xuegong, beautiful silk in the interior, etc.. CN104262090B P, 2016-06-29).
CN102126920B (document 4, korea flight, ding Weijun, lin Changjun, and the like) patent three-tower three-effect differential pressure heat integration method for preparing azeotropic ethanol, CN102126920B [ P ].2013-09-25, and the like describe a three-tower three-effect differential pressure heat integration method for rectifying ethanol, and the three-tower three-effect differential pressure heat integration method has obvious energy-saving advantages compared with the traditional two-tower rectification and purification process (document 5, zhang Minhua, dong Xiuqin, lv Huisheng, and the like, and a 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 from the material flow at the top of the distillation tower I on one hand and from 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 rectifying section adopts three towers connected in parallel with an integrated device, and the conditions of pressurization, normal pressure and decompression are respectively adopted, and the purification section adopts a pervaporation membrane process. In the heat unit, steam at the top of a pressurized rectifying tower I is heated by a reboiler at a tower bottom of an atmospheric rectifying tower II, steam at the top of the atmospheric rectifying tower II is heated by a reboiler at a tower bottom of a reduced pressure rectifying tower III, steam required by the system is accessed by the reboiler at the top of the pressurized rectifying tower I, and product steam generated by a pervaporation membrane is used for preheating fermented mash. In the material unit, the top discharge 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 towers and a membrane separation device, improving the material and heat integrating degree of the rectifying section and the purifying section, and further reducing system energy consumption.
In order to achieve the purpose, the invention adopts the technical scheme that:
the invention relates to a method for refining fuel ethanol by material and heat integration through tower-membrane coupling, which comprises the following steps:
the fermented mash is divided into two paths of mash after three-stage preheating: mash F1 and mash F2; wherein, the mash F1 is directly fed into a decompression coarse distillation tower 1; directly feeding mash F2 into a pressurizing rough distillation tower 2, connecting a pressure-reducing rough distillation tower 1 and the pressurizing rough distillation tower 2 in parallel in the material flow direction, feeding the mash F1 into the pressure-reducing rough distillation tower 1 for rough distillation under reduced pressure to obtain tower top ethanol steam a1, performing primary heat exchange on the fermented mash, and then feeding into a pressurizing rectification tower 3 for pressure rectification; the wastewater obtained from the tower bottom of the reduced pressure rough distillation tower 1 is discharged out of the system after tertiary heat exchange of the fermented liquor;
the mash F2 enters a pressurizing rough distillation tower 2 for pressurizing rough distillation to obtain tower top ethanol steam, the tower top ethanol steam is subjected to heat exchange in a reboiler h11 of a depressurizing rough distillation tower 1, a part of ethanol steam b1 flows back to the pressurizing rough distillation tower 2, a part of ethanol steam b2 enters a steam permeable membrane component 4 after being preheated by external steam, a tower bottom ethanol solution b3 of the pressurizing rough distillation tower 2 enters a pressurizing rectification tower 3 after heat exchange, and tower bottom wastewater is discharged out of the system after three-stage heat exchange of fermented mash;
after the ethanol steam at the top of the pressurized rectifying tower 3 exchanges heat with a reboiler h21 of the pressurized coarse distillation tower 2, a part of ethanol steam c1 refluxes, a part of ethanol steam c2 exchanges heat with ethanol solution b3 at the bottom of the pressurized coarse distillation tower 2 and then enters the pressurized coarse distillation tower 2 for pressurized coarse distillation, and the wastewater at the bottom of the tower is discharged out of the system after three-stage heat exchange of fermented liquor;
purifying by a vapor permeable membrane component 4 to obtain product vapor d1, sequentially performing secondary heat exchange on the pressurized coarse distillation tower 2 reboiler h22 and fermented mash to obtain a fuel ethanol product, and condensing outlet wastewater obtained by purification and then discharging the condensed outlet wastewater out of the system;
the whole system related by the method comprises a rectification section and a purification section, wherein the rectification section comprises a decompression rough distillation tower 1, a pressurization rough distillation tower 2, a pressurization rectification tower 3 and four reboilers h11, h21, h22 and h31, wherein the decompression rough distillation tower 1 and the pressurization rough distillation tower 2 are connected in parallel; the purification section comprises a vapour permeable membrane module 4, wherein the vapour permeable membrane module 4 is provided with a preheater and a condenser; the rectifying section and the purifying section are in material connection with an inlet of the vapor permeable membrane component 4 through a preheater and the top of the pressurized coarse distillation tower 2; the product outlet of the vapor permeable membrane component 4 is in heat exchange connection with a reboiler h22 of the pressurized coarse distillation tower 2;
wherein the reflux ratio of the ethanol steam at the top of the pressurizing coarse distillation tower 2 and the pressurizing rectification tower 3 is 0.5-3.5; the volume concentration range of the ethanol vapor entering the vapor permeable membrane component 4 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 operation temperature, the pressure, the reflux ratio and the like of the pressurized coarse distillation tower 2; preferably, the ethanol vapor b2 is preheated to a concentration in the range of 75% by volume or more, entering the vapor permeable membrane module 4.
In the scheme, the tower plate numbers of the reduced pressure rough distillation tower 1, the pressurized rough distillation tower 2 and the pressurized rectification tower 3 are respectively more than or equal to 35, more than or equal to 40 and more than or equal to 55, the absolute pressure range of the reduced pressure rough distillation tower 1 is 25-55 kPa, the absolute pressure range of the pressurized rough distillation tower 2 is 100-500 kPa, the absolute pressure range of the pressurized rectification tower 3 is 400-600 kPa, the tower top temperature ranges of the reduced pressure rough distillation tower 1, the pressurized rough distillation tower 2 and the pressurized rectification tower 3 are respectively 57-68 ℃, 82-110 ℃, 120-130 ℃, the tower bottom temperature ranges of the reduced pressure rough distillation tower 1, the pressurized rough distillation tower 2 and the pressurized rectification tower 3 are respectively 72-86 ℃, 100-130 ℃ and 125-135 ℃.
In the scheme, the tower plate numbers of the decompression coarse distillation tower 1, the pressurization coarse distillation tower 2 and the pressurization rectification tower 3 are respectively 35-40, more than or equal to 44 and 55-65, the absolute pressure range of the pressurization coarse distillation tower 2 is 140-485 KPa, the tower top temperature range of the pressurization coarse distillation tower 2 is 85-100 ℃, and the tower kettle temperature range of the pressurization coarse distillation tower 2 is 110-130 ℃.
The reflux ratio of the ethanol steam at the top of the pressurizing rough distillation tower 2 and the pressurizing rectification tower 3 is 1.5-2.5 and 1.5-3.5 respectively.
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 h31 of the pressurized rectifying tower 3 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 does not contain 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 a system;
(5) Compared with the traditional rectification mode, the combined tower rectification and membrane separation integrated process can save steam by about 60 percent; compared with the traditional molecular sieve adsorption purification process, the combined tower rectification and membrane separation integrated process can save about 25% of steam. The steam unit consumption of the whole system can be reduced to 1.1 ton Steam generating device Ton of Fuel ethanol Left and right.
In a word, the method realizes the aim of preparing the fuel ethanol from the biological fermentation mash with high efficiency and low energy consumption. Compared with the existing rectification and purification processes, 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 processes, high fuel ethanol atom economy and the like.
Drawings
FIG. 1 is a schematic process flow diagram of a method for refining fuel ethanol by material and heat integration through tower-membrane coupling.
In fig. 1, 1 is a reduced pressure rough distillation tower, 2 is a pressurized rough distillation tower, 3 is a pressurized rectification tower, 4 is a steam permeation membrane module, h11 is a reboiler of the reduced pressure rough distillation tower 1, h21 and h22 are reboilers of the pressurized rough distillation tower 2, h31 is a reboiler of the pressurized rectification tower 3, F1 and F2 are respectively mash entering the reduced pressure rough distillation tower 1 and the pressurized rough distillation tower 2, a1 is ethanol steam which is discharged from the top of the reduced pressure rough distillation tower 1 and enters the pressurized rectification tower 3, b1 and b2 are respectively ethanol steam which flows back from the pressurized rough distillation tower 2 and enters the steam permeation membrane 4, c1 and c2 are respectively ethanol steam which flows back from the pressurized rectification tower 3 and enters the pressurized rough distillation tower 2, and d1 is product steam of the steam permeation membrane module 4.
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 steam savings when feed mash ethanol concentration is varied, the number of three column trays and reflux ratio are varied. But it is not excluded that the effect of further reducing the amount of steam consumed by unit product can be achieved by optimizing other operating conditions based on the process diagram on the premise of ensuring that the concentration of the product ethanol meets the requirement of using the product ethanol as fuel ethanol.
As shown in fig. 1, a schematic process flow diagram of a method for refining fuel ethanol by material and heat integration through tower-membrane coupling is shown, wherein the material flow and the heat flow of the process are as follows:
material flow: the fermented mash is divided into two paths of mash F1 and mash F2 after three-stage preheating, wherein the mash F1 enters a decompression coarse distillation tower 1, and the mash F2 enters a pressurization coarse distillation tower 2. After passing through the pressure reduction rough distillation tower 1, tower bottom liquid is subjected to three-stage heat exchange for mash to obtain wastewater, and tower top ethanol steam a1 is subjected to primary preheating for fermented mash and then enters a pressurization rectification tower 3. After the mash F2 enters the pressurizing coarse distillation tower 2, tower bottom liquid is subjected to tertiary heat exchange for mash to obtain a wastewater discharge system, tower top ethanol steam is subjected to heat exchange for a tower 1 reboiler h11 and then is divided into two parts, ethanol steam b1 flows back, the ethanol steam b2 enters the steam permeable membrane separation component 4, product steam d1 and wastewater are obtained after membrane separation, and the product steam d1 is sequentially subjected to secondary heat exchange for the pressurizing coarse distillation tower 2 reboiler h22 and the fed fermented mash to obtain a fuel ethanol product. Before entering the pressurized rectifying tower 3, the ethanol steam a1 is mixed with ethanol solution b3 at the bottom of the pressurized crude distillation tower 2. The ethanol steam at the top of the pressurized rectifying tower 3 exchanges heat with a reboiler h21 of the pressurized coarse distillation tower 2, then a part of ethanol steam c1 refluxes, and a part of ethanol steam c2 exchanges heat with the ethanol solution at the bottom of the pressurized coarse distillation tower 2 and then enters the pressurized coarse distillation tower 2. The residue in the 3-tower of the pressurized rectifying tower is subjected to three-stage heat exchange with mash to obtain waste water and then discharged out of the system;
and (3) heat flow: the heat is supplied to the reboiler h31 of the pressurized rectifying tower 3 by primary steam from the outside. The heat of the reboiler h21 of the pressurized coarse distillation tower 2 is derived from the ethanol steam at the top of the pressurized rectifying tower 3, and the reboiler h22 is supplied with heat by the fuel ethanol steam d1 purified by a steam permeable membrane. The heat of the reboiler h11 of the decompression coarse distillation tower 1 comes from the ethanol steam at the top of the pressurization coarse distillation tower 2. The fermented mash passes through the steam a1 at the top of the tower 1 and the ethanol steam d1 in sequence and exchanges heat with the bottoms of the towers 1, 2 and 3, a small amount of steam is needed in the separation process of the steam permeable membrane component 4 and is provided by the outside, but the heat consumption of the whole system can be ignored;
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 system heat loss; (3) The advantages of high purification and low-concentration feed separation 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) Two sets of vapor permeable membrane separation devices are matched based on the characteristic that the concentration and the temperature of the wine gas at the tower top meet the membrane separation requirement, so that the excessive heat consumption caused by the overload of the temperature of the feed liquid is avoided;
the optimization criterion for the purification section is as follows: at present, 1/4 of low-concentration ethanol components can be generated in the advanced molecular sieve adsorption and purification process in the industry, in order to improve the utilization rate of the biomass raw material, the low-concentration ethanol needs to be recycled, and extra 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 pressure-reducing rough distillation tower 1 and the pressure rectification tower 3 is fixed, the number of the tower plates of the pressure-reducing rough distillation tower 2 is 46, the reflux ratio of the pressure-reducing rough distillation tower 2 is 1.2, and the reflux ratio of the pressure-rectifying tower 3 is 1.8. The volume concentration of ethanol in the fermented mash is 5.5%, 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 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 pressure-reducing rough distillation tower 1 and the pressure rectification tower 3 is fixed, the number of the tower plates of the pressure-reducing rough distillation tower 2 is 46, the reflux ratio of the pressure-reducing rough distillation tower 2 is 1.2, and the reflux ratio of the pressure-rectifying tower 3 is 1.8. The volume concentration of ethanol in the fermented mash is 11.9%, 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 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 pressure-reducing rough distillation tower 1 and the pressure rectification tower 3 is fixed, the number of the tower plates of the pressure-reducing rough distillation tower 2 is 46, the reflux ratio of the pressure-reducing rough distillation tower 2 is 1.2, and the reflux ratio of the pressure-rectifying tower 3 is 1.8. The volume concentration of the ethanol in the fermented mash is 13.9%, 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 pressure-reducing rough distillation tower 1 and the pressure rectification tower 3 is fixed, the number of the tower plates of the pressure-reducing rough distillation tower 2 is 46, the reflux ratio of the pressure-reducing rough distillation tower 2 is 1.2, and the reflux ratio of the pressure-rectifying tower 3 is 1.8. The volume concentration of the ethanol in the fermentation mash is 15.8%, 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 4 in the table 1.
TABLE 1 experimental comparison of ethanol concentrations in the fermentation broths with different feeds
In conclusion, under the operation of the process flow, the feed concentration of the fermented 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 tower plates of the fixed decompression rough distillation tower 1 and the pressure rectification tower 3 is 48, the number of the tower plates of the fixed pressure rough distillation tower 2 is 48, the reflux ratio of the fixed pressure rough distillation tower 2 is 1.2, and the reflux ratio of the fixed pressure rectification tower 3 is 1.8. The volume concentration of the ethanol in the fermentation mash is 11.9%, 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 5 in the table 2.
Example 6
The process flow chart is shown in figure 1, the raw material of the fermentation mash is corn, and the temperature is 29.9 ℃. The number of the tower plates of the pressure-reducing rough distillation tower 1 and the pressure-rectifying tower 3 is fixed, the number of the tower plates of the pressure-reducing rough distillation tower 2 is 46, the reflux ratio of the pressure-reducing rough distillation tower 2 is 1.0, and the reflux ratio of the pressure-rectifying tower 3 is 1.8. The volume concentration of the ethanol in the fermentation mash is 11.9%, 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 6 in the 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 pressure-reducing rough distillation tower 1 and the pressure-rectifying tower 3 is fixed, the number of the tower plates of the pressure-reducing rough distillation tower 2 is 46, the reflux ratio of the pressure-reducing rough distillation tower 2 is 1.2, and the reflux ratio of the pressure-rectifying tower 3 is reduced to 1.5. The volume concentration of ethanol in the fermented mash is 11.9%, 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.
TABLE 2 Experimental comparison results with varying reflux ratio
In conclusion, under the operation of the process flow, when the number of the tower plates of the pressurized rough distillation tower 2 is increased, the concentration of the product ethanol meets the use requirement of fuel ethanol (the concentration is more than or equal to 99.5 percent), and the steam consumption is slightly reduced. When the reflux ratio of the pressurizing rough distillation tower 2 is reduced, the concentration of the fuel ethanol product meets the use requirement of the fuel ethanol (the concentration is more than or equal to 99.5 percent), and the steam consumption is increased. When the reflux ratio of the pressurized rectifying tower 3 is reduced, the concentration of the fuel ethanol product meets the use requirement of the fuel ethanol (the concentration is more than or equal to 99.5 percent), and the steam consumption is increased. Compared with the traditional process or the combined tower molecular sieve integrated process, the steam consumption of the three examples 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 further 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 the invention 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 product separation degree, 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 refining fuel ethanol by material and heat integration through tower membrane coupling is characterized by comprising the following steps:
the fermented mash is divided into two paths of mash after three-stage preheating: mash (F1) and mash (F2); wherein mash (F1) is directly fed into a decompression coarse distillation tower (1); the mash (F2) is directly fed into a pressurizing coarse distillation tower (2), and the depressurizing coarse distillation tower (1) and the pressurizing coarse distillation tower (2) are connected in parallel in the material flow direction;
the mash (F1) enters a reduced pressure rough distillation tower (1) for reduced pressure rough distillation to obtain tower top ethanol steam (a 1), and the fermented mash enters a pressurized rectifying tower (3) for pressurized rectification after primary heat exchange; the obtained tower kettle wastewater is discharged out of the system after tertiary heat exchange of the fermentation mash;
the mash (F2) enters a pressurizing rough distillation tower (2) for pressurizing rough distillation to obtain tower top ethanol steam, the tower top ethanol steam is subjected to heat exchange in a reboiler (h 11) of the depressurizing rough distillation tower (1), a part of ethanol steam (b 1) flows back to the pressurizing rough distillation tower (2), a part of ethanol steam (b 2) enters a steam permeation membrane component (4) after being preheated by external steam, the tower bottom ethanol solution (b 3) in the pressurizing rough distillation tower (2) is subjected to heat exchange and then enters a pressurizing rectification tower (3), and the tower bottom wastewater is discharged out of the system after being subjected to three-stage heat exchange;
after the ethanol steam at the top of the pressurized rectifying tower (3) exchanges heat with a reboiler (h 21) of the pressurized coarse distillation tower (2), part of the ethanol steam (c 1) flows back, part of the ethanol steam (c 2) exchanges heat with ethanol solution (b 3) at the bottom of the pressurized coarse distillation tower (2), enters the pressurized coarse distillation tower (2) for pressurized coarse distillation, and the wastewater at the bottom of the tower is discharged out of the system after three-stage heat exchange of fermented liquor;
purifying by a steam permeation membrane component (4) to obtain product steam (d 1), sequentially performing secondary heat exchange on a pressurized coarse distillation tower (2), a reboiler (h 22) and fermented mash to obtain a fuel ethanol product, and condensing outlet wastewater obtained by purification and discharging the condensed outlet wastewater out of the system;
the whole system related to the method comprises a rectification section and a purification section, wherein the rectification section comprises a reduced-pressure rough distillation tower (1) and a pressurized rough distillation tower (2) which are connected in parallel, a pressurized rectification tower (3) which is connected with the two towers in series, and four reboilers (h 11), (h 21), (h 22) and (h 31); the purification section comprises a steam permeation membrane component (4), wherein the steam permeation membrane component (4) is provided with a preheater and a condenser; the rectifying section and the purifying section are in material connection with an inlet of a vapor permeation membrane component (4) through a preheater at the top of the pressurized coarse distillation tower (2); the product outlet of the vapor permeation membrane component (4) is in heat exchange connection with a reboiler (h 22) of the pressurized rough distillation tower (2);
wherein the reflux ratios of the ethanol steam at the top of the pressurizing rough distillation tower (2) and the pressurizing rectification tower (3) are both 0.5-3.5; the volume concentration range of the ethanol steam entering the steam permeation membrane component (4) after preheating is more than 55 percent.
2. The method of claim 1, wherein: the ethanol steam volume concentration range entering the steam permeation membrane component (4) after preheating is more than 75 percent.
3. The method of claim 1, wherein: the tower plate numbers of the reduced pressure rough distillation tower (1), the pressurized rough distillation tower (2) and the pressurized rectification tower (3) are respectively more than or equal to 35, more than or equal to 40 and more than or equal to 55, the absolute pressure range of the reduced pressure rough distillation tower (1) is 25-55 kPa, the absolute pressure range of the pressurized rough distillation tower (2) is 100-500 kPa, the absolute pressure range of the pressurized rectification tower (3) is 400-600 kPa, the tower top temperature ranges of the reduced pressure rough distillation tower (1), the pressurized rough distillation tower (2) and the pressurized rectification tower (3) are 57-68 ℃, 82-110 ℃, 120-130 ℃, and the tower kettle temperature ranges of the reduced pressure rough distillation tower (1), the pressurized rough distillation tower (2) and the pressurized rectification tower (3) are 72-86 ℃, 100-130 ℃ and 125-135 ℃.
4. The method of claim 3, wherein: the tower plate numbers of the decompression rough distillation tower (1), the pressurization rough distillation tower (2) and the pressurization rectification tower (3) are respectively 35-40, more than or equal to 44 and 55-65, the absolute pressure range of the pressurization rough distillation tower (2) is 140-485 KPa, the tower top temperature range of the pressurization rough distillation tower (2) is 85-100 ℃, and the tower kettle temperature range of the pressurization rough distillation tower (2) is 110-130 ℃.
5. The method of claim 1, wherein: the reflux ratio of the ethanol steam at the top of the pressurizing rough distillation tower (2) and the pressurizing rectification tower (3) is 1.5-2.5 and 1.5-3.5 respectively.
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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