CN109704920B

CN109704920B - Energy-saving process and device for producing fuel ethanol from low-concentration fermentation liquor

Info

Publication number: CN109704920B
Application number: CN201910137368.5A
Authority: CN
Inventors: 蓝仁水; 黄贵明
Original assignee: New Tianjin T & D Co ltd
Current assignee: New Tianjin T & D Co ltd
Priority date: 2019-02-25
Filing date: 2019-02-25
Publication date: 2024-01-30
Anticipated expiration: 2039-02-25
Also published as: CN109704920A

Abstract

The invention relates to an energy-saving process method and device for producing fuel ethanol from low-concentration fermentation broth, in particular to an energy-saving process method and device for producing fuel ethanol from industrial tail gas fermentation broth through a rectification process. The whole alcohol rectifying system at least comprises a first rectifying tower, a second rectifying tower, a third rectifying tower, a fourth rectifying tower and other four towers, a dehydration unit and other matched equipment. The heat integration among the first rectifying tower, the second rectifying tower, the third rectifying tower and the fourth rectifying tower and the application of other heat exchange and energy saving technologies in the system greatly reduce the operation energy consumption. The optimized heat exchange system organically unifies the dehydration unit and the rectification system, and improves the stability and flexibility of the whole rectification system. The invention overcomes the defects of the prior art, reduces the operation energy consumption by more than 30 percent compared with the current advanced fuel ethanol rectification process method, has obvious practicality and economic benefit and has wide application prospect.

Description

Energy-saving process and device for producing fuel ethanol from low-concentration fermentation liquor

Technical Field

The invention relates to an energy-saving process method and device for producing fuel ethanol from low-concentration fermentation broth, in particular to an energy-saving process method and device for producing fuel ethanol from industrial tail gas fermentation broth through a rectification process.

Background

With the increasing shortage of energy resources such as petroleum and coal, environmental pollution, greenhouse effect and the like, fuel ethanol is used as a renewable energy source and is increasingly paid attention to in various aspects. The traditional fuel ethanol is mainly prepared from grain crops such as sorghum, corn, sweet potato, cassava and the like serving as raw materials through a biological fermentation way. The fuel ethanol is prepared from grains as raw materials, and has the phenomena of 'competing with people for grains and competing with grains for land'.

The industrial tail gas microbial fermentation technology is adopted to convert the steel industrial tail gas into fuel ethanol, and meanwhile, the byproduct high-protein feed and compressed natural gas have the characteristics of sufficient raw materials, high concentration and easy collection.

Because industrial tail gas fermentation belongs to a gas fermentation process, the concentration of ethanol in fermentation liquor is very low (generally the ethanol content is only 2-4%), and the content of ethanol in fermentation liquor is far lower than that of ethanol in fermentation liquor of traditional grain crops (10-16%) except for special description. At present, a three-tower distillation method is mostly adopted in the process of producing fuel ethanol from fermentation mash, and the method has the defect of higher energy consumption in production. If the rectification process of preparing fuel ethanol by fermenting industrial tail gas still adopts the conventional process method, the energy consumption in the rectification process is necessarily high, and the economy of the process for producing fuel ethanol by fermenting industrial tail gas is severely restricted.

Chinese patent CN200410094085.0 discloses a "fuel ethanol production method", which essentially adopts the original process of adding molecular sieve in single beer column and single rectifying column, and has high operation energy consumption although the process flow is simple.

CN200710057523.X discloses a process for ethanol rectification by adopting a three-tower heat integration device: the whole ethanol rectification system comprises three towers such as a crude distillation tower, a low-pressure azeotropic distillation tower, a high-pressure azeotropic distillation tower and the like, heat integration is carried out among the three towers of the crude distillation tower, the low-pressure azeotropic distillation tower and the high-pressure azeotropic distillation tower, a lateral line gas phase of the crude distillation tower provides partial energy for the low-pressure azeotropic distillation tower, a top gas phase of the high-pressure azeotropic distillation tower provides energy for a tower kettle of the crude distillation tower, an alcohol product is respectively extracted from the low-pressure azeotropic distillation tower and the high-pressure azeotropic distillation tower, and the alcohol product is still a double-effect rectification process of a single-mash tower and a double-rectification tower in practice, and the operation energy consumption is high.

CN200710058736.4 discloses a "fuel ethanol production equipment and method", which essentially adopts a three-tower rectification process method of adding molecular sieve into a double-mash tower (a coarse tower and a rectifying tower, and a recovering tower, and the three towers are subjected to heat integration operation, thereby realizing a three-effect process and having lower operation energy consumption.

CN201010545523.6 discloses a "distillation dehydration device and process for co-production of fuel ethanol and common grade edible alcohol", similar to the process method provided by CN200710058736.4, the heat integration operation among three towers of a crude distillation tower, a combined tower and a rectification tower is realized, and the improvement part is that: the gas phase at the top of the combined tower is boosted by an ethanol gas compressor and then is divided into three strands, one strand is removed from a reboiler of the crude distillation tower, one strand is removed from a reboiler of the methanol tower, the other strand is removed from a molecular sieve adsorption tower for dehydration, and dehydrated absolute ethanol gas returns to a rectifying unit to heat the reboiler of the crude distillation tower kettle, so that the operation energy consumption is further reduced compared with the process method provided by CN 200710058736.4. The methanol tower arranged in CN201010545523.6 belongs to the necessary equipment for co-producing common grade edible ethanol, but belongs to redundant equipment for a fuel ethanol device. The concentration of methanol in the fermentation liquor is far lower than that of ethanol, and the azeotropic alcohol obtained by rectification can meet the GB 18350-2013 standard of modified fuel ethanol without removing methanol after dehydration. The provision of the compressor greatly increases the electricity consumption of the CN201010545523.6 providing process and increases the investment and maintenance costs of the moving equipment (compressor).

CN201710542687.5 discloses an "energy-saving clean production method of fuel ethanol", the rectification process of fuel ethanol is substantially identical to CN200710058736.4, and is a three-tower rectification process method adopting a double-mash tower (coarse tower, rectification tower lower portion), a double-rectification tower (rectification tower upper portion, recovery tower upper portion) and molecular sieve, except that dehydrated absolute ethanol gas is used for preheating fermented mash, and the process is identical to CN 201010545523.6. The difference between CN201710542687.5 and CN201010545523.6 is that in the process method provided by CN201710542687.5, the heating steam of the reboiler of the first rectifying tower of the rectifying dehydration unit is fresh steam, the discharged steam condensate is collected and then is sent to the kettle of the first rectifying tower to directly heat the kettle liquid of the tower, and according to the process method, the reboiler of the kettle of the first rectifying tower can be completely omitted, the steam can be directly introduced into the kettle of the first rectifying tower, and the same effect can be achieved by adopting direct steam heating. The process method provided by CN201710542687.5 has no substantial breakthrough compared with CN201010545523.6, and the direct mixing of the steam condensate into the wastewater at the bottom of the first rectifying tower is a very uneconomical method.

Disclosure of Invention

The invention aims to provide an energy-saving process method and device for producing fuel ethanol from low-concentration fermentation broth, in particular to an energy-saving process method and device for producing fuel ethanol from industrial tail gas fermentation broth through a rectification process, which can overcome the defects of the prior art. The invention adopts four-tower rectification and four-effect heat integration process based on the process of the three-tower alcohol rectification system commonly used at present, thereby greatly reducing the operation energy consumption. The process method provided by the invention has remarkable practicability and economic benefit.

The energy-saving process method for producing fuel ethanol from low-concentration fermentation broth provided by the invention comprises the following steps:

1) At least comprises a first rectifying tower, a second rectifying tower, a third rectifying tower and a fourth rectifying tower;

2) The first rectifying tower is a composite tower, the upper part of the first rectifying tower is a first rectifying section, the middle part of the first rectifying tower is a light component removing section, and the lower part of the first rectifying tower is a first coarse tower;

3) The second rectifying tower is a stripping tower, and the feeding part is a second coarse tower;

4) The third rectifying tower is a stripping tower, and the feeding part is a third crude tower;

5) The fourth rectifying tower is a composite tower, the upper part of the fourth rectifying tower is a second rectifying section, the middle part of the fourth rectifying tower is a fusel oil extraction section, and the lower part of the fourth rectifying tower is a dehydration section;

6) The first rectifying tower, the second rectifying tower, the third rectifying tower and the fourth rectifying tower are heat integrated, and the gas phase at the top of the fourth rectifying tower is used as a heating source of the tower kettle of the third rectifying tower to provide the required heat for the third rectifying tower; the gas phase at the top of the third rectifying tower is used as a heating source of the tower kettle of the second rectifying tower to provide the required heat for the second rectifying tower; the gas phase at the top of the second rectifying tower is used as a heating source at the bottom of the first rectifying tower to provide the required heat for the first rectifying tower;

7) The gas phase of the dehydration unit is preferably from the gas phase at the top of a fourth rectifying tower, can be the evaporated gas phase of azeotropic alcohol liquid phase, and can be the gas phase at the top of other rectifying towers in the rectifying system;

8) The anhydrous ethanol gas phase produced by the dehydration unit is preferably used as a heating source of a third rectifying tower kettle, can be used as a heating source of a second rectifying tower kettle, can be used as a heating source of a first rectifying tower kettle, can be used for preheating fermented mash, can be used for preheating a first rectifying tower feed, can be used for preheating a second rectifying tower feed, can be used for preheating a third rectifying tower feed, and can be used for preheating a fourth rectifying tower feed; the absolute ethanol gas phase condensate is the fuel ethanol product (or alcohol product).

According to the technical method provided by the invention, the dehydration unit is a molecular sieve dehydration tower or a pervaporation membrane. The light wine discharged by the dehydration unit firstly enters the first rectifying tower or is fed into the fourth rectifying tower, the second rectifying tower or the third rectifying tower.

According to the process method provided by the invention, when fuel ethanol is not required to be produced, the dehydration unit can be stopped, partial azeotropic alcohol is extracted from the top or side line of the first rectifying tower, and partial azeotropic alcohol is extracted from the top or upper liquid phase side line of the fourth rectifying tower; or the azeotropic alcohol extracted from the first rectifying tower enters a reflux tank or a tower top of a fourth rectifying tower, and all alcohol products are extracted from the tower top or the upper liquid phase side line of the fourth rectifying tower; or the azeotropic alcohol extracted from the fourth rectifying tower enters a reflux tank or a tower top of the first rectifying tower, and all alcohol products are extracted from the tower top or the upper liquid phase side line of the first rectifying tower. Realize the co-production operation of fuel ethanol and azeotropic alcohol products.

According to the process method provided by the invention, fermentation mash firstly enters the first rectifying tower; the feed of the second rectifying tower is from the lower liquid phase side stream discharge of the feed of the first rectifying tower; the feed of the third rectifying tower is from the liquid phase side discharge below the feed of the first rectifying tower or from the liquid phase side discharge below the feed of the second rectifying tower; the fermented mash can also be divided into three strands, and the three strands are respectively sent to a first rectifying tower, a second rectifying tower and a third rectifying tower; the fermented mash can also enter a second rectifying tower, the feed of the first rectifying tower comes from the liquid phase side discharge below the feed of the second rectifying tower, and the feed of the third rectifying tower comes from the liquid phase side discharge below the feed of the first rectifying tower or comes from the liquid phase side discharge below the feed of the second rectifying tower; the fermented mash can also enter a third rectifying tower, the feed of the second rectifying tower comes from the liquid phase side discharge below the feed of the third rectifying tower, and the feed of the first rectifying tower comes from the liquid phase side discharge below the feed of the third rectifying tower or comes from the liquid phase side discharge below the feed of the second rectifying tower; the feed of the fourth rectifying tower is a mixed material from the liquid phase side stream discharge above the feed of the first rectifying tower, the liquid phase side stream discharge above the feed of the second rectifying tower, the third rectifying tower overhead or the liquid phase side stream discharge above the feed of the third rectifying tower. The second rectification column overhead or liquid phase side offtake above its feed and the third rectification column overhead or liquid phase side offtake above its feed may be separately or both introduced into a location above the feed to the first rectification column in accordance with the foregoing method.

According to the technical method provided by the invention, the whole rectifying device system is internally provided with three mash-containing sections, namely the lower part of a first rectifying tower, the lower part of a second rectifying tower and the lower part of a third rectifying tower; the bottoms of the first rectifying tower, the second rectifying tower and the third rectifying tower are respectively discharged with mash-containing wastewater; the fourth rectifying tower kettle discharges the waste water without mash; the first rectifying tower can be a stripping tower and a top-free rectifying section; the second rectifying tower can be a composite tower, and the top of the second rectifying tower is provided with a rectifying section; the third rectifying tower can be a composite tower, and the top of the third rectifying tower is provided with a rectifying section.

According to the technical method provided by the invention, the third rectifying tower can be stopped, and the gas phase at the top of the fourth rectifying tower is used as a heating source of the tower kettle of the second rectifying tower to provide the required heat for the second rectifying tower.

According to the process method provided by the invention, a fifth rectifying tower can be additionally arranged between the third rectifying tower and the fourth rectifying tower, and the fifth rectifying tower, the first rectifying tower, the second rectifying tower, the third rectifying tower and the fourth rectifying tower form five-effect heat integration operation, so that the operation energy consumption is further reduced. The gas phase at the top of the fourth rectifying tower is used as a heating source of the tower kettle of the fifth rectifying tower to provide the required heat for the fifth rectifying tower; the gas phase at the top of the fifth rectifying tower is used as a heating source of the third rectifying tower kettle to provide the third rectifying tower with required heat; the gas phase at the top of the third rectifying tower is used as a heating source of the tower kettle of the second rectifying tower to provide the required heat for the second rectifying tower; the gas phase at the top of the second rectifying tower is used as a heating source at the bottom of the first rectifying tower to provide the required heat for the first rectifying tower. The anhydrous ethanol gas phase produced by the dehydration unit is preferably used as a heating source of the tower kettle of the fifth rectification tower, can be used as a heating source of the tower kettle of the third rectification tower, can be used as a heating source of the tower kettle of the second rectification tower, and can be used as a heating source of the tower kettle of the first rectification tower. The second rectification column overhead or its feed upper liquid phase side offtake, the third rectification column overhead or its feed upper liquid phase side offtake, and the fifth rectification column overhead or its feed upper liquid phase side offtake may be separately or all introduced into the first rectification column feed upper location as described above.

According to the process method provided by the invention, azeotropic alcohol products are preferably obtained from the top of the first rectifying tower or the upper side line thereof and the top of the fourth rectifying tower or the upper side line thereof respectively; the fusel oil is extracted from the liquid phase side line in the middle part of the fourth rectifying tower; the first rectifying tower, the second rectifying tower, the third rectifying tower, the fifth rectifying tower and the fourth rectifying tower are all of composite tower structures, and rectifying sections are arranged at the upper parts of the towers.

According to the technical method provided by the invention, a plurality of fusel oil extraction ports are arranged near the feeding position (above or below the feeding position) of the fourth rectifying tower, and the fusel oil is discharged through the proper fusel oil extraction ports according to the feeding concentration and the operation condition of the fourth rectifying tower.

According to the process method provided by the invention, the fuel ethanol product (or the alcohol product or the steam condensate) can preheat azeotropic alcohol extracted by the first rectifying tower, can preheat light alcohol discharged by the dehydration unit, can preheat fermented mash, can preheat the feed of the first rectifying tower, can preheat the feed of the second rectifying tower, can preheat the feed of the third rectifying tower and can preheat the feed of the fourth rectifying tower, so that heat is recovered, and cooling water consumption is reduced.

According to the process method provided by the invention, the heat-integrated heat exchanger between the fourth rectifying tower and the third rectifying tower, the heat-integrated heat exchanger between the fourth rectifying tower and the fifth rectifying tower, the heat-integrated heat exchanger between the third rectifying tower and the second rectifying tower, the heat-integrated heat exchanger between the second rectifying tower and the first rectifying tower and the anhydrous ethanol gas-phase condenser produced by the dehydration unit can adopt a falling film reboiler, a pump forced circulation heat exchanger, an indirect heat exchange steam generator, a plate heat exchanger and a thermosiphon reboiler. According to the process method provided by the invention, only the reboiler at the bottom of the fourth rectifying tower in the fermentation broth rectifying device needs to be heated by introducing an external heat source, and the heat required by other reboilers and heat exchangers can be utilized by the heat in the system. The heating medium of the reboiler of the fourth rectifying tower kettle can be steam, heat conducting oil or a heating furnace. The type of heat-integrated heat exchanger, which heating medium is used, is merely an implementation detail of the process provided by the present invention, and does not constitute any limitation on the spirit of the present invention, and it is fully possible for a person skilled in the art to freely combine or use other types of heat exchangers to implement the present technology.

The invention provides an energy-saving process method and a device for producing fuel ethanol from low-concentration fermentation liquor, in particular to an energy-saving process method and a device for producing fuel ethanol from industrial tail gas fermentation liquor through a rectification process, which can also be used for rectification and dehydration processes of other aqueous solutions capable of forming low-boiling-point azeotropes with water. Typical materials that can form low boiling azeotropes with water include, but are not limited to, isopropanol, n-propanol, sec-butanol, tert-butanol, tetrahydrofuran, methyl acetate, ethyl acetate, pyridine, acetonitrile, and the like.

According to the process provided by the invention, typical operating conditions of each tower are as follows:

the operating pressure range of the top of the first rectifying tower is 8-90 kpa;

the operating pressure range of the top of the second rectifying tower is 20-280 kpa;

the operating pressure range of the top of the third rectifying tower is 70-500 kpa;

the operating pressure range of the top of the fourth rectifying tower is 100-1280 kpa;

the operating pressure of the dehydration unit is 100-1280 kpa.

All pressures in this invention are absolute unless specifically indicated.

According to the process provided by the invention, the preferred operating conditions of each column are:

the operation pressure at the top of the first rectifying tower is 30kpa, the temperature at the top of the tower is 50 ℃ and the temperature at the bottom of the tower is 78 ℃;

The operation pressure at the top of the second rectifying tower is 100kpa, the temperature at the top of the tower is 97 ℃, and the temperature at the bottom of the tower is 103 ℃;

the operation pressure of the top of the third rectifying tower is 180kpa, the temperature of the top of the tower is 114 ℃ and the temperature of the bottom of the tower is 119 ℃;

the operating pressure of the top of the fourth rectifying tower is 590kpa, the temperature of the top of the tower is 130 ℃ and the temperature of the bottom of the tower is 159 ℃;

the dehydration unit (vapor phase dehydration membrane module) was operated at a pressure of 590kpa.

Industrial tail gas fermentation belongs to a gas fermentation process, the concentration of ethanol in fermentation liquid is very low (generally only 2-4%), and the energy consumption control of the rectification process of the low-concentration industrial tail gas fermentation liquid belongs to a typical mash alcohol stripping control separation process. The three-tower rectification process method of the double-mash tower and the double-rectifying tower plus the molecular sieve provided by CN201710542687.5 is a rectification process method commonly adopted in the industry of producing fuel ethanol by fermenting grain crops at present, for example, the rectification process method is used in the rectification process of industrial tail gas fermentation liquor, and the operation energy consumption is very high. Taking the industrial tail gas fermentation liquor ethanol concentration of 3% as an example, according to the three-tower rectification process method provided by CN201710542687.5, the steam consumption of each ton of fuel ethanol is as high as 3.0 tons of steam.

According to the process method provided by the invention, the first crude tower at the lower part of the first rectifying tower, the second crude tower at the lower part of the second rectifying tower and the third crude tower at the lower part of the third rectifying tower form three-effect and heat integration stripping operation of low-concentration fermented mash; the first coarse tower at the lower part of the first rectifying tower, the second coarse tower at the lower part of the second rectifying tower, the third coarse tower at the lower part of the third rectifying tower and the fifth coarse tower at the lower part of the fifth rectifying tower form four-effect and heat integration steam stripping operation of low-concentration fermented mash; effectively overcomes the defects of the prior art (double-mash tower and mash double-effect steam stripping operation), and greatly reduces the operation energy consumption of producing fuel ethanol by industrial tail gas fermentation liquid.

By adopting the process method provided by the invention, as shown in the accompanying drawings 1-6, the conventional double-mash tower (double-mash tower and mash double-effect stripping operation) is improved into three mash towers, so that triple-effect and heat integrated stripping operation of mash is realized, the operation energy consumption is only 2.0 tons of steam/ton of fuel ethanol product, and the operation energy consumption is greatly reduced.

By adopting the process method provided by the invention, as shown in figure 8, the conventional double-mash tower (double-mash tower and mash double-effect stripping operation) is improved into four mash towers, the four-effect and heat integrated stripping operation of mash is realized, the operation energy consumption is only 1.8 tons of steam/ton of fuel ethanol product, and the operation energy consumption is greatly reduced.

The invention relates to an energy-saving process method and device for producing fuel ethanol from low-concentration fermentation broth, in particular to an energy-saving process method and device for producing fuel ethanol from industrial tail gas fermentation broth through a rectification process. The whole alcohol rectifying system at least comprises a first rectifying tower, a second rectifying tower, a third rectifying tower, a fourth rectifying tower and other four towers, a dehydration unit and other matched equipment. The heat integration among the first rectifying tower, the second rectifying tower, the third rectifying tower and the fourth rectifying tower and the application of other heat exchange and energy saving technologies in the system greatly reduce the operation energy consumption. The optimized heat exchange system organically unifies the dehydration unit and the rectification system, and improves the stability and flexibility of the whole rectification system. The invention overcomes the defects of the prior art, reduces the operation energy consumption by more than 30 percent compared with the current advanced fuel ethanol rectification process method, has extremely obvious practicality and economic benefit and has wide application prospect.

Drawings

FIG. 1 is a flow chart of an exemplary energy-efficient process for producing fuel ethanol from a low-concentration fermentation broth in accordance with the present invention; the dehydration unit adopts a gas phase dehydration membrane component.

FIG. 2 is an evolution process method of FIG. 1, wherein the top of the fourth rectifying tower shown in FIG. 1 does not produce an azeotropic alcohol gas phase dehydration unit; the liquid phase azeotropic alcohol extracted from the top of the first rectifying tower and the liquid phase azeotropic alcohol extracted from the top of the fourth rectifying tower enter an evaporator E144 together, and the vaporized alcohol gas phase is dehydrated into a unit.

FIG. 3 shows an evolution process of FIG. 2, wherein a part of liquid phase azeotropic alcohol is extracted from the upper side line of the first rectifying tower shown in FIG. 2 to the top of the fourth rectifying tower, and finally all azeotropic alcohol is extracted from the upper liquid phase side line of the fourth rectifying tower, and then enters an evaporator E144, and the vaporized alcohol gas phase is dehydrated.

FIG. 4 is a schematic diagram showing an evolution process of FIG. 1, wherein the vapor phase of the absolute ethanol produced by the dehydration unit shown in FIG. 1 is changed to be heated by a second reboiler E123 of the second rectifying tower; the dehydration unit adopts molecular sieve adsorption/regeneration switching operation for dehydration.

Fig. 5 is an evolution process of fig. 1, wherein the dehydration unit is deactivated when the production of azeotropic alcohol is switched, and the liquid phase withdrawn from the top of the first rectifying tower and the liquid phase withdrawn from the top of the fourth rectifying tower are used together as azeotropic alcohol products.

FIG. 6 shows an evolution process of FIG. 5, wherein when the azeotropic alcohol production is switched, a part of azeotropic alcohol is taken out from the upper side line of the first rectifying tower to the top of the fourth rectifying tower, and finally all azeotropic alcohol is taken out from the upper liquid phase side line of the fourth rectifying tower.

Fig. 7 is an evolution process of fig. 1, the process of fig. 1 is simplified, the third rectifying tower is omitted, a part of the top gas phase of the fourth rectifying tower is heated by the second rectifying tower reboiler E122, and the other part is dehydrated. The dehydrated absolute ethanol gas phase is heated by a second reboiler E123 of the second rectifying tower.

Fig. 8 is an evolution process of fig. 1, further energy saving optimization of the process of fig. 1, with the addition of a fifth rectifying column between the third rectifying column and the fourth rectifying column. Heating one part of the gas phase at the top of the fourth rectifying tower to a fifth rectifying tower reboiler E162, and removing the other part of the gas phase from the top of the fourth rectifying tower to a dehydration unit; the dehydrated absolute ethanol gas phase is heated by a second reboiler E163 of the fifth rectifying tower; the fifth rectifying column top gas phase heats the third rectifying column reboiler E132.

Detailed Description

Specific embodiments of the invention are described in detail below with reference to the drawings, but are merely illustrative of the invention and not limiting.

Unless specifically indicated, the composition, structure, materials (connecting lines for connecting the respective columns, etc.), reagents, etc. of the process equipment such as the columns, etc. which are not specifically used in the examples, are commercially available or can be obtained by a method well known to those skilled in the art. The specific experimental methods, operating conditions involved are generally as set forth in conventional process conditions as well as in handbooks, or as recommended by the manufacturer.

As shown in fig. 1-8, the present invention provides an energy-saving device for producing fuel ethanol from a low concentration fermentation broth:

at least comprises four towers of a first rectifying tower T110, a second rectifying tower T120, a third rectifying tower T130 and a fourth rectifying tower T140 and connecting pipelines.

The feeding pipeline is connected with a tube side inlet of a condenser E111 of the first rectifying tower T110, an outlet of the tube side E111 is connected with a cold side inlet of a feeding preheater E113 of the first rectifying tower T110, and an outlet of the cold side E113 is connected to the middle part of the first rectifying tower T110. The top gas phase outlet of the first rectifying tower T110 is connected with the shell side gas phase inlet of the condenser E111 of the first rectifying tower T110, the shell side gas phase outlet of the condenser E111 of the first rectifying tower T110 is connected with the shell side gas phase inlet of the tail cooler E112 of the first rectifying tower T110, and the shell side gas phase outlet of the tail cooler E112 of the first rectifying tower T110 is connected to a vacuum system. The condenser E111 of the first rectifying tower T110 and the condensate outlet pipeline of the tail cooler E112 of the first rectifying tower T110 are divided into two, one is connected to the top reflux port of the first rectifying tower T110, and the other is connected to the top reflux port of the fourth rectifying tower T140. The E112 condensate outlet line is also connected to an industrial alcohol extraction line. The tower bottom of the first rectifying tower T110 is respectively connected with a tube side inlet of a reboiler E114 of the first rectifying tower T110 and a hot side inlet of a feed preheater E113 of the first rectifying tower T110. The hot side outlet of the feed preheater E113 of the first rectification column T110 is connected with a waste mash discharging pipeline. The reboiler tube side outlet of the first rectifying tower T110 is connected to the tower kettle of the first rectifying tower T110.

The liquid phase side line outlet above the feed of the first rectifying tower T110 is connected to the cold side inlet of the first feed preheater E141 of the fourth rectifying tower T140, and the liquid phase side line outlet below the feed of the first rectifying tower T110 is connected to the cold side inlet of the feed preheater E121 of the second rectifying tower T120.

The cold side outlet of the feeding preheater of the second rectifying tower T120 is divided into two parts, one part is connected to the feeding inlet of the second rectifying tower T120, and the other part is connected to the cold side inlet of the feeding preheater E131 of the third rectifying tower T130. The gas phase outlet at the top of the second rectifying tower T120 is connected with the gas phase inlet of the shell side of the reboiler E114 of the first rectifying tower T110, and the condensate outlet of the shell side of the reboiler E114 of the first rectifying tower T110 is connected with the cold side inlet of the first feeding preheater E141 of the fourth rectifying tower T140. And the tower bottom of the second rectifying tower T120 is respectively connected with a tube side inlet of a reboiler E122 of the second rectifying tower T120 and a hot side inlet of a feeding preheater E121 of the second rectifying tower T120. The hot side outlet of the feed preheater of the second rectifying tower T120 is connected to the hot side inlet of the feed preheater E113 of the first rectifying tower T110. And the tube side outlet of the reboiler of the second rectifying tower T120 is connected to the tower kettle of the second rectifying tower T120.

The outlet of the cold side of the feeding preheater E131 of the third rectifying tower T130 is connected to the feeding port of the third rectifying tower T130. The gas phase outlet at the top of the third rectifying tower T130 is connected with the gas phase inlet of the shell side of the reboiler E122 of the second rectifying tower T120, and the condensate outlet of the shell side of the reboiler E122 of the second rectifying tower T120 is connected with the cold side inlet of the first feeding preheater E141 of the fourth rectifying tower T140. The third rectifying tower T130 tower kettle is respectively connected with a first reboiler E132 tube side inlet of the third rectifying tower T130, a second reboiler E133 tube side inlet of the third rectifying tower T130 and a hot side inlet of a feeding preheater E131 of the third rectifying tower T130. The hot side outlet of the feed preheater of the third rectifying tower T130 is connected to the hot side inlet of the feed preheater E121 of the second rectifying tower T120. The outlet of the first reboiler E132 of the third rectifying tower T130 and the outlet of the second reboiler E133 of the third rectifying tower T130 are connected to the tower kettle of the third rectifying tower T130.

The cold side outlet of the first feeding preheater E141 of the fourth rectifying tower T140 is connected with the cold side inlet of the second feeding preheater E142 of the fourth rectifying tower T140, and the cold side outlet of the second feeding preheater E142 of the fourth rectifying tower T140 is connected with the feeding inlet of the fourth rectifying tower T140. The gas phase outlet at the top of the fourth rectifying tower T140 is respectively connected with the gas phase inlet of the first reboiler E132 shell side of the third rectifying tower T130 and the gas phase inlet of the dehydration unit. The third rectifying tower T130 is connected with a tower top reflux port of the fourth rectifying tower T140 through a shell side condensate outlet pipeline of the first reboiler E132.

The absolute ethyl alcohol gas phase pipeline produced by the dehydration unit is connected to the gas phase inlet of the second reboiler E133 shell side of the third rectifying tower T130, and the condensate outlet of the second reboiler E133 shell side of the third rectifying tower T130 is connected with the fuel ethanol product extraction pipeline. The light wine pipeline discharged from the dehydration unit is connected to the light wine feed inlet above the feed of the first rectifying tower T110.

And a plurality of fusel oil extraction outlets are respectively arranged above or below the feeding position of the fourth rectifying tower T140 and are respectively connected with a fusel oil extraction pipeline.

And the tower bottom of the fourth rectifying tower T140 is respectively connected with a tube side inlet of a reboiler E143 of the fourth rectifying tower and a hot side inlet of a first feeding preheater E141 of the fourth rectifying tower T140. The hot side outlet of the first feeding preheater E141 of the fourth rectifying tower T140 is connected with a wastewater discharge pipeline. And the tube side outlet of the reboiler E143 of the fourth rectifying tower T140 is connected to the tower kettle of the fourth rectifying tower. The heating steam pipeline is connected to the gas phase inlet of the E143 shell side of the reboiler E143 of the fourth rectifying tower T140, and the condensate outlet of the E143 shell side of the reboiler E143 of the fourth rectifying tower T140 is connected to the hot side inlet of the E142 second feeding preheater of the fourth rectifying tower T140. The hot side outlet of the second feed preheater E142 of the fourth rectifying tower T140 is connected with a heated steam condensate discharge pipeline.

The invention provides an energy-saving process method for producing fuel ethanol from low-concentration fermentation broth, which comprises the following steps:

1) At least comprises a first rectifying tower T110, a second rectifying tower T120, a third rectifying tower T130 and a fourth rectifying tower T140;

2) The first rectifying tower T110 is a composite tower, the upper part of the first rectifying tower is a first rectifying section S1101, the middle part of the first rectifying tower is a light component removing section S1102), and the lower part of the first rectifying tower is a first coarse tower S1103;

3) The second rectifying tower T120 is a stripping tower, and the feeding of the second rectifying tower T120 is a second coarse tower S1203;

4) The third rectifying tower T130) is a stripping tower, and the feeding of the stripping tower is a third coarse tower S1303;

5) The fourth rectifying tower T140 is a composite tower, the upper part of the fourth rectifying tower is provided with a second rectifying section S1401, the middle part of the fourth rectifying tower is provided with a fusel oil extraction section S1402, and the lower part of the fourth rectifying tower is provided with a dehydration section S1403;

6) The first rectifying tower T110, the second rectifying tower T120, the third rectifying tower T130 and the fourth rectifying tower T140 are in heat integration, and a gas phase at the top of the fourth rectifying tower T140 is used as a heating source of a tower kettle of the third rectifying tower T130 to provide required heat for the third rectifying tower T130; the gas phase at the top of the third rectifying tower T130 is used as a heating source of the tower kettle of the second rectifying tower T120 to provide the required heat for the second rectifying tower T120; the gas phase at the top of the second rectifying tower T120 is used as a heating source of the tower kettle of the first rectifying tower T110 to provide the required heat for the first rectifying tower T110;

7) The whole rectifying device system is internally provided with three mash-containing sections, namely a first rectifying tower lower part S1103, a second rectifying tower lower part S1203 and a third rectifying tower lower part S1303; the bottoms of the first rectifying tower T110, the second rectifying tower T120 and the third rectifying tower T130 are respectively discharged with mash-containing wastewater; and the fourth rectifying tower T140 is used for discharging the wastewater without mash.

8) The azeotropic alcohol product is respectively obtained from the top of the first rectifying tower T110 or the upper side line thereof and the top of the fourth rectifying tower T140 or the upper side line thereof; the fusel oil is extracted from the liquid phase side line in the middle part of the fourth rectifying tower T140;

9) A vapor phase dehydration unit for vapor phase at the top of the fourth rectifying tower T140 or for vapor phase of azeotropic alcohol liquid phase;

10 The anhydrous ethanol gas phase produced by the dehydration unit is preferably used as a heating source of a third rectifying tower T130 tower kettle, can be used as a heating source of a second rectifying tower T120 tower kettle, can be used as a heating source of a first rectifying tower T110 tower kettle, can be used for preheating fermented mash, can be used for preheating a first rectifying tower T110 feed, can be used for preheating a second rectifying tower T120 feed, can be used for preheating a third rectifying tower T130 feed, and can be used for preheating a fourth rectifying tower T140 feed.

The absolute ethanol gas phase condensate is the fuel ethanol product.

The process method provided by the invention comprises the following specific steps:

the industrial tail gas fermented liquor 101 is advanced in the tube pass of a first rectifying tower condenser E111, a material flow 102 preheated by a gas phase 104 at the top of a first rectifying tower T110 enters a cold side inlet of a feeding preheater E113 of the first rectifying tower T110, and a material flow 103 preheated by a waste fermented liquor 111 discharged from the tower bottom of the first rectifying tower T110 enters the upper part of a light component removal section S1102 at the middle part of the first rectifying tower T110. The gas phase 104 at the top of the first rectifying tower T110 enters the shell pass of a condenser E111 of the first rectifying tower T110, the non-condensable gas phase 105 of E111 enters the shell pass of a tail cooler E112 of the first rectifying tower T110, and the non-condensable gas 106 at the outlet of the shell pass of E112 is discharged to a vacuum system. The material flow 108 obtained by mixing the shell side condensate of the condenser E111 of the first rectifying tower T110 and the shell side condensate of the tail condenser E112 of the first rectifying tower T110 is divided into two parts, one part 109 flows back to the top of the first rectifying tower T110, and the other part 110 enters the top of the fourth rectifying tower T140. The shell side condensate of the tail cooler E112 of the first rectifying tower T110 is also extracted by a strand 107 as industrial alcohol. Waste mash 111 discharged from the tower bottom of the first rectifying tower T110 is discharged from the rectifying device through a stream 112 after heat exchange between a feed preheater E113 of the first rectifying tower T110 and the stream 102.

A liquid side stream 113 is led out from the first rectifying tower T110 between the first rectifying section S1101 and the light component removing section S1102. A liquid side stream 114 is drawn between the light ends section S1102 and the first crude column S1103 below the feed to the first rectification column T110. The material flow 114 is separated into two streams through a second rectifying tower feeding preheater E121 and a material flow 115 after heat exchange with waste mash 205 discharged from the tower kettle of a second rectifying tower T120, and a first material flow 201 enters the second rectifying tower T120; the second stream 202 enters a material preheater E131 of a third rectifying tower T130 to exchange heat with waste mash 304 discharged from the tower bottom of the third rectifying tower T130, and the stream 301 after heat exchange enters the third rectifying tower T130.

The second rectifying tower T120 and the first rectifying tower T110 are in heat integration operation, and the gas phase 203 at the top of the second rectifying tower T120 enters the shell pass of a reboiler E114 of the first rectifying tower T110 to provide heat required by separation for the first rectifying tower T110.

And the third rectifying tower T130 and the second rectifying tower T120 are subjected to heat integration operation, and the gas phase 302 at the top of the third rectifying tower T130 enters the shell pass of the second rectifying tower reboiler E122 to provide heat required by separation for the second rectifying tower T120.

The fourth rectifying tower T140 and the third rectifying tower T130 are subjected to heat integration operation, one gas phase 404 at the top of the fourth rectifying tower T140 enters the first reboiler E132 shell pass of the third rectifying tower T130, and partial heat required by separation is provided for the third rectifying tower T130; the other gas phase 405 at the top of the fourth rectifying tower T140 is fed into the gas phase dehydration film component M150, and the dehydrated absolute ethyl alcohol gas phase 407 is fed into the second reboiler E133 shell side of the third rectifying tower T130, so as to provide the other part of heat required by separation for the third rectifying tower T130. The heated steam 430 enters the fourth rectifying column T140 reboiler E143 shell side.

The liquid-phase side stream 113, the first rectifying tower reboiler E114 shell-side condensate 204 and the second rectifying tower T120 reboiler E122 shell-side condensate 303 are led out from the space between the first rectifying tower T110 and the light-removal section S1102, the mixed stream 401 is subjected to heat exchange with the wastewater 411 discharged from the tower kettle of the fourth rectifying tower T140 through the first feeding preheater E141 of the fourth rectifying tower T140, the heat exchanged stream 402 is subjected to heat exchange with the second feeding preheater E142 of the fourth rectifying tower T140 and the shell-side steam condensate 431 of the fourth rectifying tower T140, and the heat exchanged stream 403 enters the upper part of the dehydration section S1403 at the lower part of the fourth rectifying tower T140.

And a stream 413 obtained by mixing a condensate 110 obtained by mixing the shell-side condensate of the condenser E111 of the first rectifying tower T110 and the shell-side condensate of the tail condenser E112 of the first rectifying tower T110 and the shell-side condensate 406 of the first reboiler E132 of the third rectifying tower T130 enters the top of the fourth rectifying tower T140.

The waste mash 304 discharged from the third rectifying tower T130 tower kettle enters the hot side of the second rectifying tower T120 feeding preheater E121 after heat exchange of the third rectifying tower T130 feeding preheater E131, and the outlet stream 206 at the hot side of the second rectifying tower T120 feeding preheater E121 enters the hot side of the first rectifying tower T110 feeding preheater E113.

The light wine 409 generated by the gas phase dehydration membrane module M150 enters a first rectifying section S1101 of a first rectifying tower T110

The third rectifying column T130 second reboiler E133 shell side condensate 408 is a fuel ethanol product.

Fusel oil 410 is recovered from the fusel oil recovery section S1402 in the middle portion of the fourth rectifying column T140.

The fourth rectification column T140 discharges beer free wastewater 412 at the hot side outlet of the first feed preheater E141.

The fourth rectifying column T140 discharges steam condensate 432 from the hot side outlet of the second feed preheater E142.

The typical raw materials of the process method provided by the invention comprise the following components:

the above-described ranges of raw material composition do not constitute any limitation to the present invention, and the present invention can be used for separation of fuel ethanol fermentation broths of various compositions.

Example 1:

as shown in FIG. 1, the industrial tail gas fermented mash 101 is advanced in the tube side of a condenser E111 of a first rectifying tower T110, a stream 102 preheated by a gas phase 104 at the top of the first rectifying tower T110 enters a cold side inlet of a feed preheater E113 of the first rectifying tower T110, and a stream 103 preheated by a waste fermented mash 111 discharged from the bottom of the first rectifying tower T110 enters the upper part of a middle light-removing section S1102 of the first rectifying tower T110. The gas phase 104 at the top of the first rectifying tower T110 enters the shell pass of a condenser E111 of the first rectifying tower T110, the non-condensable gas phase 105 of E111 enters the shell pass of a tail cooler E112 of the first rectifying tower T110, and the non-condensable gas 106 at the outlet of the shell pass of E112 is discharged to a vacuum system. The material flow 108 obtained by mixing the shell-side condensate of the condenser E111 of the first rectifying tower T110 and the shell-side condensate of the tail condenser E112 of the first rectifying tower T110 is divided into two parts, one part 109 is totally refluxed to the top of the first rectifying tower T110, and the other part 110 enters the top of the fourth rectifying tower T140. The shell side condensate of the tail cooler E112 of the first rectifying tower T110 is also extracted by a strand 107 as industrial alcohol. Waste mash 111 discharged from the tower bottom of the first rectifying tower T110 is discharged from the rectifying device through a stream 112 after heat exchange between a feed preheater E113 of the first rectifying tower T110 and the stream 102.

A liquid side stream 113 is led out from the first rectifying tower T110 between the first rectifying section S1101 and the light component removing section S1102. A liquid side stream 114 is drawn between the light ends section S1102 and the first crude column S1103 below the feed to the first rectification column T110. The material flow 114 is divided into two streams by a material flow 115 after heat exchange between a material flow entering the second rectifying tower T120 and a waste mash 205 discharged from the tower kettle of the second rectifying tower T120 through a material flow feeding preheater E121 of the second rectifying tower T120, a material flow entering the second rectifying tower T120 from a material flow 201 of the first stream, a material flow entering the third rectifying tower T130 from a material flow 202, a material flow entering the third rectifying tower T130 from a material flow feeding preheater E131 of the third rectifying tower T130, a waste mash 304 discharged from the tower kettle of the third rectifying tower T130, and a material flow 301 after heat exchange.

And the third rectifying tower T130 and the second rectifying tower T120 are subjected to heat integration operation, and the gas phase 302 at the top of the third rectifying tower T130 enters the shell pass of a reboiler E122 of the second rectifying tower T120 to provide heat required by separation for the second rectifying tower T12.

The liquid-phase side stream 113, the shell-side condensate 204 of the reboiler E114 of the first rectifying tower T110 and the shell-side condensate 303 of the second rectifying tower reboiler E122 are led out from the space between the first rectifying tower T110 and the light-removal section S1102, the mixed stream 401 is subjected to heat exchange with the wastewater 411 discharged from the tower kettle of the fourth rectifying tower T140 through the first feeding preheater E141 of the fourth rectifying tower T140, the stream 402 subjected to heat exchange is fed into the second feeding preheater E142 of the fourth rectifying tower T140 again, and subjected to heat exchange with the shell-side steam condensate 431 of the fourth rectifying tower T140, and the stream 403 subjected to heat exchange is fed into the upper part of the dehydration section S1403 at the lower part of the fourth rectifying tower T140.

The following gives a typical operating condition for each column in example 1, typical operating conditions and operating energy consumption are as follows:

the operation pressure at the top of the first rectifying tower T110 is 30kpa, the temperature at the top of the tower is 50 ℃ and the temperature at the bottom of the tower is 78 ℃;

The operation pressure at the top of the second rectifying tower T120 is 100kpa, the temperature at the top of the tower is 97 ℃, and the temperature at the bottom of the tower is 103 ℃;

the operating pressure at the top of the third rectifying tower T130 is 180kpa, the temperature at the top of the tower is 114 ℃ and the temperature at the bottom of the tower is 119 ℃;

the top operation pressure of the fourth rectifying tower T140 is 590kpa, the top temperature of the tower is 130 ℃, and the bottom temperature of the tower is 159 ℃;

According to the process method provided by the invention in FIG. 1, the conventional double-mash tower (double-mash tower and mash double-effect steam stripping operation) is improved into three mash towers, namely a first coarse tower S1103 at the lower part of a first rectifying tower T110, a second coarse tower S1203 at the lower part of a second rectifying tower T120 and a third coarse tower S1303 at the lower part of a third rectifying tower T130, so that triple-effect and heat integration steam stripping operation of mash is realized. The first rectifying tower T110, the second rectifying tower T120, the third rectifying tower T130 and the fourth rectifying tower T140 of the whole rectifying system form four-effect heat integration operation, the gas phase at the top of the fourth rectifying tower T140 is used as a heating source of a first reboiler E132 at the bottom of the third rectifying tower T130, a part of heat is provided for the third rectifying tower T130, the gas phase of absolute ethyl alcohol produced by a dehydration unit is used as a heating source of a second reboiler E133 at the bottom of the third rectifying tower T130, and another part of heat is provided for the third rectifying tower T130; the gas phase at the top of the third rectifying tower T130 is used as a heating source of the tower kettle of the second rectifying tower T120 to provide the required heat for the second rectifying tower T120; the gas phase at the top of the second rectifying tower T120 is used as a heating source of the tower kettle of the first rectifying tower T110 to provide the required heat for the first rectifying tower T110. The whole rectifying system only needs medium-pressure steam heating by a reboiler E143 at the bottom of the fourth rectifying tower T140, the operation energy consumption is only 2.0 tons of steam/ton of fuel ethanol product, and the operation energy consumption is greatly reduced.

The medium-pressure steam consumption is 50 tons/hour according to a 20 ten thousand tons/year fuel ethanol device and operation hours of 8000 hours/year. The heat required by other reboilers and heat exchangers can be utilized by the heat in the system.

According to the three-tower rectification process method of the double-mash tower and the double-rectifying tower plus molecular sieve provided by Chinese patent CN201710542687.5, the operation energy consumption of a rectification system is 3.0 tons of steam/ton of fuel ethanol. The medium-pressure steam consumption is 75 tons/hour according to a 20 ten thousand tons/year fuel ethanol device and operation hours of 8000 hours/year.

(3.0-2.0)/3.0≈33％

Compared with the three-tower rectification process method of double-mash tower, double-rectifying tower and molecular sieve provided by Chinese patent CN201710542687.5, the energy consumption of the process method provided by the invention shown in the figure 1 is reduced by about 33%.

Steam savings of 75-50=25 tons/hour can be achieved per hour.

Medium pressure steam can be saved by 25 tons/hour x 8000 hours/year = 200000 tons/year each year.

Steam cost can be saved every year by calculating 150 yuan per ton of steam:

200000 tons/year x 150 yuan/ton/10000 = 3000 tens of thousands yuan/year.

The energy-saving process method and the device for producing the fuel ethanol from the low-concentration fermentation liquid have extremely remarkable economic benefits.

Example 2:

as shown in fig. 2, it is an evolution process of fig. 1, and the differences with respect to the process shown in fig. 1 are as follows:

The top of the fourth rectifying tower T140 shown in FIG. 1 does not produce an azeotropic alcohol gas phase dehydration unit. The mixed material flow 415 of the liquid phase azeotropic alcohol 110 extracted from the top of the first rectifying tower T110 and the liquid phase azeotropic alcohol 414 extracted from the top of the fourth rectifying tower T140 enters an evaporator E144, and the vaporized alcohol gas phase 405 is dehydrated into a unit.

Example 3:

as shown in fig. 3, it is an evolution process of fig. 2, and the differences with respect to the process shown in fig. 2 are as follows:

a part of liquid phase azeotropic alcohol 110 is extracted from the upper side line of the first rectifying tower T110 shown in FIG. 2 to the top of the fourth rectifying tower T140, and finally all azeotropic alcohol is extracted from the upper liquid phase side line 415 of the fourth rectifying tower T140, and then enters an evaporator E144, and the vaporized alcohol gas phase 405 is dehydrated.

Example 4:

as shown in fig. 4, it is an evolution process of fig. 1, and the differences with respect to the process shown in fig. 1 are as follows:

the dehydration unit shown in fig. 1 adopts molecular sieve T150A/B adsorption/regeneration switching operation to dehydrate, and the anhydrous ethanol gas phase 407 produced by the dehydration unit is heated by the second reboiler E123 of the second rectifying tower T120. The light wine 409 produced by the dewatering unit enters the first rectifying section S1101 of the first rectifying tower T110. The second reboiler E123 shell side condensate 408 of the second rectifying column T120 is a fuel ethanol product.

Example 5:

as shown in fig. 5, it is an evolution process of fig. 1, and the differences with respect to the process shown in fig. 1 are as follows:

when the production of azeotropic alcohol is switched, the dehydration unit is deactivated, and the liquid phase 110 withdrawn from the top of the first rectification column T110 and the liquid phase 414 withdrawn from the top of the fourth rectification column T140 are used together as an azeotropic alcohol product 415.

Example 6:

as shown in fig. 6, it is an evolution process of fig. 5, and the differences with respect to the process shown in fig. 5 are as follows:

when the production of azeotropic alcohol is switched, a part of azeotropic alcohol 110 is extracted from the upper side line of the first rectifying tower T110 to the top of the fourth rectifying tower T140, and finally all azeotropic alcohol is extracted from the upper liquid phase side line 415 of the fourth rectifying tower T140.

Example 7:

as shown in fig. 7, it is an evolution process of fig. 1, and the differences with respect to the process shown in fig. 1 are as follows:

the process of fig. 1 is simplified, the third rectifying tower T130 is omitted, a part 404 of the top gas phase of the fourth rectifying tower T140 heats the reboiler E122 of the second rectifying tower T120, and the other part 405 removes the water from the dehydration unit M150. The dehydrated ethanol gas phase 407 is heated by the second reboiler E123 of the second rectifying tower T120.

One typical operating condition and operating energy consumption for each column in example 7 is given below:

the operating pressure at the top of the second rectifying tower T120 is 170kpa, the temperature at the top of the tower is 92 ℃ and the temperature at the bottom of the tower is 118 ℃;

the top operation pressure of the fourth rectifying tower T140 is 570kpa, the top temperature is 129 ℃, and the bottom temperature is 158 ℃;

the dehydration unit (vapor phase dehydration membrane module) was operated at a pressure of 570kpa.

According to the process method provided by the invention in FIG. 7, only the reboiler E143 at the bottom of the fourth rectifying tower T140 needs medium-pressure steam heating in the whole rectifying system, and the operating energy consumption of the rectifying system is 2.7 tons of steam/ton of fuel ethanol.

Example 8:

as shown in fig. 8, it is an evolution process of fig. 1, and the differences with respect to the process shown in fig. 1 are as follows:

the process of fig. 1 is further energy-saving optimized, and a fifth rectifying tower T160 is added between the third rectifying tower T130 and the fourth rectifying tower T140. A portion 404 of the top gas phase of the fourth rectifying column T140 is heated by a reboiler E162 of the fifth rectifying column T160, and another portion 405 is taken to the dehydration unit M150. The dehydrated ethanol gas phase 407 is heated in the second reboiler E163 of the fifth rectifying column T160. The fifth rectifying column T160 overhead vapor phase 602 heats the third rectifying column T130 reboiler E132. The overhead of the second rectifying tower T120, namely the shell-side condensate 204 of the reboiler E114 of the first rectifying tower T110, is fed to the position above the feeding position of the first rectifying tower T110. The fourth rectifying column T140 is fed as a mixture of the liquid phase side draw 113 from the first rectifying column T110 feed, the third rectifying column T130 overhead 303, and the fifth rectifying column T160 overhead 603.

The following gives a typical operating conditions for each column in example 8, typical operating conditions and operating energy consumption are as follows:

the operation pressure at the top of the first rectifying tower T110 is 25kpa, the temperature at the top of the tower is 46 ℃, and the temperature at the bottom of the tower is 74 ℃;

the operating pressure at the top of the second rectifying tower T120 is 70kpa, the temperature at the top of the tower is 87 ℃ and the temperature at the bottom of the tower is 93 ℃;

the operating pressure at the top of the third rectifying tower T130 is 120kpa, the temperature at the top of the tower is 102 ℃ and the temperature at the bottom of the tower is 107 ℃;

the top operation pressure of the fifth rectifying tower T160 is 195kpa, the top temperature of the tower is 116 ℃ and the bottom temperature of the tower is 121 ℃;

the operating pressure at the top of the fourth rectifying tower T140 is 590kpa, the temperature at the top of the tower is 130 ℃ and the temperature at the bottom of the tower is 159 ℃;

According to the process method provided by the invention in FIG. 8, the conventional double-mash tower (double-mash double-effect stripping operation) is improved into four mash towers, namely, a first coarse tower S1103 at the lower part of a first rectifying tower T110, a second coarse tower S1203 at the lower part of a second rectifying tower T120, a third coarse tower S1303 at the lower part of a third rectifying tower T130 and a fifth coarse tower S1603 at the lower part of a fifth rectifying tower T160, so as to form a four-effect heat integration stripping operation of low-concentration fermented mash. The first rectifying tower T110, the second rectifying tower T120, the third rectifying tower T130, the fifth rectifying tower T160 and the fourth rectifying tower T140 of the whole rectifying system form five-effect heat integration operation, the gas phase at the top of the fourth rectifying tower T140 is used as a heating source of a first reboiler E162 at the bottom of the fifth rectifying tower, a part of heat is provided for the fifth rectifying tower T160, the gas phase of absolute ethyl alcohol produced by a dehydration unit is used as a heating source of a second reboiler E163 at the bottom of the fifth rectifying tower T160, and another part of heat is provided for the fifth rectifying tower T160; the gas phase at the top of the fifth rectifying tower T160 is used as a heating source of the tower kettle of the third rectifying tower to provide the required heat for the third rectifying tower T130; the gas phase at the top of the third rectifying tower T130 is used as a heating source of the tower kettle of the second rectifying tower T120 to provide the required heat for the second rectifying tower T120; the gas phase at the top of the second rectifying tower T120 is used as a heating source of the tower kettle of the first rectifying tower T110 to provide the required heat for the first rectifying tower T110. Only the reboiler E143 at the bottom of the fourth rectifying tower T140 needs medium-pressure steam heating, the operation energy consumption is only 1.8 tons of steam/ton of fuel ethanol product, and the operation energy consumption is greatly reduced.

According to the process provided in fig. 8 of the present invention, medium pressure steam consumption was 45 tons/hour in a 20 ten thousand ton/year fuel ethanol plant, operating hours 8000 hours/year. The heat required by other reboilers and heat exchangers can be utilized by the heat in the system.

Compared with the three-tower rectification process method of adding molecular sieve in the double-mash tower and the double-rectifying tower provided by CN201710542687.5, the operation energy consumption of a rectification system is 3.0 tons of steam per ton of fuel ethanol, and the medium-pressure steam consumption is 75 tons/hour:

(3.0-1.8)/3.0＝40％

compared with the three-tower rectification process method of adding molecular sieve in a double-mash tower and a double-rectifying tower provided by CN201710542687.5, the energy consumption of the process method provided by the invention is reduced by about 40 percent.

Steam savings of 75-45=30 tons/hour can be achieved per hour.

Medium pressure steam can be saved by 30 tons/hour x 8000 hours/year = 240000 tons/year each year.

Steam cost can be saved every year by calculating 150 yuan per ton of steam:

240000 ton/year×150 yuan/ton/10000=3600 ten thousand yuan/year.

The embodiments are described in detail so that those skilled in the relevant art can make appropriate modifications, alterations and combinations of the methods according to the present invention to realize the technology. It is expressly intended that all such modifications and adaptations of the process flow provided by the present invention, as well as such modifications and adaptations, which would be apparent to those of ordinary skill in the art, are intended to be within the spirit, scope and content of the present invention.

Claims

1. An energy-saving process for producing fuel ethanol from low-concentration fermentation broth is characterized in that:

1) Comprises at least a first rectifying tower (T110), a second rectifying tower (T120), a third rectifying tower (T130) and a fourth rectifying tower (T140);

2) The first rectifying tower (T110) is a composite tower, the upper part of the first rectifying tower (T110) is a first rectifying section (S1101), the middle part is a light component removing section (S1102), and the lower part is a first coarse tower (S1103);

3) The second rectifying tower (T120) is a stripping tower, and the feeding of the second rectifying tower is a second coarse tower (S1203);

4) The third rectifying tower (T130) is a stripping tower, and the feeding part is a third coarse tower (S1303) below;

5) The fourth rectifying tower (T140) is a composite tower, the upper part of the fourth rectifying tower (T140) is a second rectifying section (S1401), the middle part is a fusel oil extraction section (S1402), and the lower part is a dehydration section (S1403);

6) The heat integration is realized among the first rectifying tower (T110), the second rectifying tower (T120), the third rectifying tower (T130) and the fourth rectifying tower (T140), and the gas phase at the top of the fourth rectifying tower (T140) is used as a heating source of the tower kettle of the third rectifying tower (T130) to provide the required heat for the third rectifying tower (T130); the gas phase at the top of the third rectifying tower (T130) is used as a heating source of the tower kettle of the second rectifying tower (T120) to provide the second rectifying tower (T120) with required heat; the gas phase at the top of the second rectifying tower (T120) is used as a heating source of the tower kettle of the first rectifying tower (T110) to provide the required heat for the first rectifying tower (T110);

7) Three mash-containing sections are arranged in the whole rectifying device system, namely a first crude tower at the lower part of a first rectifying tower (S1103), a second crude tower at the lower part of a second rectifying tower (S1203) and a third crude tower at the lower part of a third rectifying tower (S1303); the first rectifying tower (T110) tower kettle, the second rectifying tower (T120) tower kettle and the third rectifying tower (T130) tower kettle respectively discharge mash-containing wastewater; the fourth rectifying tower (T140) is used for discharging the wastewater without mash;

8) The azeotropic alcohol product is obtained from the top of the first rectifying tower (T110) or the upper side line thereof and the top of the fourth rectifying tower (T140) or the upper side line thereof respectively; the fusel oil is extracted from the middle liquid phase side line of the fourth rectifying tower (T140);

9) A fourth rectifying tower (T140) is provided with an evaporation gas phase dehydration unit of a top gas phase or an azeotropic alcohol liquid phase;

10 The absolute ethyl alcohol gas phase produced by the dehydration unit is used as a heating source of a third rectifying tower (T130) tower kettle, or is used as a heating source of a second rectifying tower (T120) tower kettle, or is used as a heating source of a first rectifying tower (T110) tower kettle, or is used for preheating fermentation mash; or for preheating the feed to the first rectification column (T110), or for preheating the feed to the second rectification column (T120), or for preheating the feed to the third rectification column (T130), or for preheating the feed to the fourth rectification column (T140); the absolute ethanol gas phase condensate is the fuel ethanol product.

2. The process according to claim 1, wherein the dehydration unit is a molecular sieve dehydration column or a pervaporation membrane; the light wine discharged from the dehydration unit enters a first rectifying tower (T110) or is fed into a fourth rectifying tower (T140), a second rectifying tower (T120) or a third rectifying tower (T130).

3. The process according to claim 1, wherein the dehydration unit is deactivated when fuel ethanol production is not required, part of the azeotropic alcohol is withdrawn from the top or side stream of the first rectification column (T110), and part of the azeotropic alcohol is withdrawn from the top or upper liquid phase side stream of the fourth rectification column (T140); or the azeotropic alcohol extracted from the first rectifying tower (T110) enters a reflux tank or a tower top of a fourth rectifying tower (T140), and all alcohol products are extracted from the tower top or the upper liquid phase side line of the fourth rectifying tower (T140); or the azeotropic alcohol extracted from the fourth rectifying tower (T140) enters a reflux tank or a tower top of the first rectifying tower (T110), and all alcohol products are extracted from the tower top or the upper liquid phase side line of the first rectifying tower (T110).

4. The process according to claim 1, wherein the fermentation broth is introduced in a manner selected from the group consisting of:

1) Feeding into a first rectifying tower (T110), feeding into a second rectifying tower (T120) from a liquid phase side line discharging below the feeding of the first rectifying tower (T110), and feeding into a third rectifying tower (T130) from a liquid phase side line discharging below the feeding of the first rectifying tower (T110) or from a liquid phase side line discharging below the feeding of the second rectifying tower (T120);

2) Dividing the fermented mash into three strands, and respectively removing a first rectifying tower (T110), a second rectifying tower (T120) and a third rectifying tower (T130);

3) The fermented mash enters a second rectifying tower (T120), the feed of a first rectifying tower (T110) is from the liquid phase side discharge below the feed of the second rectifying tower (T120), the feed of a third rectifying tower (T130) is from the liquid phase side discharge below the feed of the first rectifying tower (T110) or from the liquid phase side discharge below the feed of the second rectifying tower (T120);

4) The fermented mash enters a third rectifying tower (T130), the feed of a second rectifying tower (T120) is from the liquid phase side discharge below the feed of the third rectifying tower (T130), the feed of a first rectifying tower (T110) is from the liquid phase side discharge below the feed of the third rectifying tower (T130) or from the liquid phase side discharge below the feed of the second rectifying tower (T120); the feed of the fourth rectifying tower (T140) is a mixed material from the liquid phase side discharge above the feed of the first rectifying tower (T110), the overhead of the second rectifying tower (T120) or the liquid phase side discharge above the feed of the overhead of the third rectifying tower (T130) or the liquid phase side discharge above the feed of the overhead of the third rectifying tower.

5. The process according to claim 1, characterized in that the top operating pressure of the first rectification column (T110) is from 8 to 90kPa; the top operating pressure of the second rectifying tower (T120) is 20-280 kPa; the top operating pressure of the third rectifying column (T130) is 70-500 kPa; the top operation pressure of the fourth rectifying tower (T140) is 100-1280 kPa; the operating pressure of the dehydration unit is 100-1280 kpa.

6. The process according to claim 1, characterized in that the third rectifying column (T130) is deactivated and the top gas phase of the fourth rectifying column (T140) is used as a heating source for the bottom of the second rectifying column to provide the second rectifying column (T120) with the required heat; or a fifth rectifying tower (T160) is added between the third rectifying tower (T130) and the fourth rectifying tower (T140), the fifth rectifying tower (T160), the first rectifying tower (T110), the second rectifying tower (T120), the third rectifying tower (T130) and the fourth rectifying tower (T140) form five-effect heat integration operation, and a gas phase at the top of the fourth rectifying tower (T140) is used as a heating source of a tower kettle of the fifth rectifying tower (T160) to provide required heat for the fifth rectifying tower (T160); the gas phase at the top of the fifth rectifying tower (T160) is used as a heating source of the tower kettle of the third rectifying tower (T130) to provide the required heat for the third rectifying tower (T130); the gas phase at the top of the third rectifying tower (T130) is used as a heating source of the tower kettle of the second rectifying tower (T120) to provide the second rectifying tower (T120) with required heat; the gas phase at the top of the second rectifying tower (T120) is used as a heating source of the tower kettle of the first rectifying tower (T110) to provide the required heat for the first rectifying tower (T110); the anhydrous ethanol gas phase produced by the dehydration unit is used as a heating source of a tower kettle of a fifth rectifying tower, a heating source of a tower kettle of a third rectifying tower, a heating source of a tower kettle of a second rectifying tower (T120) and a heating source of a tower kettle of a first rectifying tower (T110).