Three-tower rectification device for refining ethanol and process for refining ethanol

Abstract

The invention discloses a three-tower rectification device for refining ethanol. The three-tower rectification device comprises a primary preheater, a secondary preheater, a crude distillation tower, a crude distillation tower top condenser, a water washing tower, a first rectification tower feeding pump, a first rectification tower, a second rectification tower feeding pump, a second rectification tower and a purification device, the first-stage preheater, the second-stage preheater and the coarse distillation tower are connected in sequence; the top of the coarse distillation tower is circularly connected with the coarse distillation tower top condenser, and the water scrubbing tower is connected with the coarse distillation tower and the coarse distillation tower top condenser respectively; one end of the first rectifying tower feeding pump is connected with the first rectifying tower, and the other end is connected with the coarse distillation tower; one end of the second rectifying tower feeding pump is connected with the second rectifying tower, and the other end is connected with the coarse distillation tower; the purification device is respectively connected with the first rectifying tower and the second rectifying tower. According to the process, separation and purification are carried out through a three-tower rectification and purification device, the process production device is simple, the production route is short, the energy utilization rate is high, environmental protection and energy conservation are achieved, and the safety coefficient is high.

Description

Technical Field

[0001] The present invention relates to the technical field of ethanol production, and more particularly to a three-column rectification device for refining ethanol and a process for refining ethanol. Background Art

[0002] With the development and progress of human society, the consumption of traditional fossil energy by humans has gradually increased, and at the same time, it will also cause serious environmental pollution. Therefore, it is particularly important to discover a new green, low-carbon and renewable energy source, and fuel ethanol has emerged as the times require.

[0003] Fuel ethanol is a fuel produced by fermenting biomass (such as crops like corn, cassava, sugarcane, beet, etc., as well as lignocellulose, seaweed, etc.). Fuel ethanol not only has the characteristics of being clean and renewable, but can also be used as a fuel improver to improve the octane number and oxygen content of gasoline, improve the quality of vehicle exhaust, and reduce pollution. In recent years, with the continuous progress of technology, the second-generation fuel ethanol technology using lignocellulose as the raw material has gradually become the focus of research and development. With the fluctuation of oil prices in the international market and the improvement of environmental protection requirements, the demand for fuel ethanol has been increasing year by year; at the same time, China has also started to encourage the production of fuel ethanol from non-grain crops and put forward new requirements for various consumptions in the production process and the quality of fuel ethanol products. Under this background, it is necessary to adjust and upgrade the original device to meet the requirements of new production raw materials, new energy consumption, and new product standards.

[0004] At present, relatively mature dehydration methods include azeotropic rectification, extractive rectification with salt addition, adsorption dehydration, etc., but these methods have high energy consumption and are not conducive to the refining of high-concentration ethanol. At present, a production method and device for biomass anhydrous ethanol are publicly disclosed in China, which mentions that the steam permeation membrane separation and purification technology has the advantages of simple operation, high separation efficiency, high degree of automation, low requirements for equipment operating conditions, and no introduction of a third component, and has obvious advantages compared with other technologies. By adopting the steam permeation membrane separation and purification process, the energy consumption of the whole system can be reduced by more than 50% compared with the traditional process.

[0005] Therefore, developing a three-column rectification device for refining ethanol and a process for refining ethanol, optimizing the heat exchange process, achieving the purpose of reducing energy consumption, improving the energy utilization rate, and improving the product quality is the key problem that needs to be solved urgently in ethanol production at present. Summary of the Invention

[0006] In view of this, the present invention provides a three-column rectification device for refined ethanol and a process for refined ethanol, which solves the problems of high energy consumption and low separation efficiency in the process of ethanol production in China. On the basis of meeting the purity of ethanol products, the present invention couples three-column rectification with molecular sieve adsorption or membrane separation technology, makes full use of the heat of materials, achieves the purpose of reducing production energy consumption, thereby greatly reducing production costs; improves the ethanol separation efficiency, increases product quality and output, and increases economic benefits.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A three-column rectification device for refined ethanol, comprising: a primary preheater, a secondary preheater, a rough distillation column, a rough distillation column top condenser, a water washing column, a first rectification column feed pump, a first rectification column, a second rectification column feed pump, a second rectification column and a purification device;

[0009] Wherein, the primary preheater, the secondary preheater and the rough distillation column are connected in sequence;

[0010] The top of the rough distillation column is connected in a cycle with the rough distillation column top condenser, and the water washing column is respectively connected with the rough distillation column and the rough distillation column top condenser;

[0011] One end of the first rectification column feed pump is connected to the first rectification column, and the other end is connected to the rough distillation column;

[0012] One end of the second rectification column feed pump is connected to the second rectification column, and the other end is connected to the rough distillation column;

[0013] The purification device is respectively connected to the first rectification column and the second rectification column.

[0014] Preferably, the above device further includes: a rough distillation column bottom reboiler, an auxiliary reboiler, a rough distillation column bottom gas-liquid separator, an auxiliary condenser I, a first rectification column bottom reboiler, a first rectification column bottom gas-liquid separator, an auxiliary condenser II, a second rectification column bottom reboiler;

[0015] Wherein, the purification device includes a molecular sieve adsorption bed;

[0016] One end of the rough distillation column bottom reboiler is connected to the bottom of the rough distillation column, and the other end is sequentially connected to the auxiliary reboiler and the rough distillation column bottom gas-liquid separator. The rough distillation column bottom reboiler is also connected to the top of the first rectification column;

[0017] One end of the rough distillation column bottom gas-liquid separator is connected to the rough distillation column, and the other end is connected to the primary preheater;

[0018] One end of the auxiliary condenser is connected to the reboiler at the bottom of the rough distillation column, and the other end is respectively connected to the first distillation column, the molecular sieve adsorption bed, and the second distillation column;

[0019] One end of the reboiler at the bottom of the first distillation column is connected to the bottom of the first distillation column, and the other end is respectively connected to the gas-liquid separator at the bottom of the first distillation column, the second auxiliary condenser, and the second distillation column;

[0020] One end of the gas-liquid separator at the bottom of the first distillation column is connected to the first distillation column, and the other end is connected to the secondary preheater;

[0021] The second auxiliary condenser is also respectively connected to the pipeline between the first auxiliary condenser and the molecular sieve adsorption bed and the pipeline between the first auxiliary condenser and the second distillation column;

[0022] The reboiler at the bottom of the second distillation column is connected in a cycle with the second distillation column.

[0023] Preferably, the above device further includes: a reboiler at the bottom of the rough distillation column, a compressor for the first distillation column, a reboiler at the bottom of the first distillation column, a first auxiliary condenser, a valve 1, an auxiliary reboiler, a gas-liquid separator at the bottom of the first distillation column, a compressor for the second distillation column, a reboiler at the bottom of the second distillation column, a second auxiliary condenser, a valve 2, and a gas-liquid separator at the bottom of the second distillation column;

[0024] Among them, the purification device includes a membrane separation preheater, a membrane separation feed pump, a membrane separation device, a membrane separation turbine, and a product condenser;

[0025] The reboiler at the bottom of the rough distillation column is connected in a cycle with the rough distillation column and is also connected to the primary preheater;

[0026] One end of the compressor for the first distillation column is connected to the top of the first distillation column, and the other end is connected to the reboiler at the bottom of the first distillation column;

[0027] One end of the reboiler at the bottom of the first distillation column is connected to the bottom of the first distillation column, and the other end is respectively connected to the first auxiliary condenser and the auxiliary reboiler;

[0028] One end of the valve 1 is connected to the first auxiliary condenser, and the other end is respectively connected to the first distillation column, the valve 2, and the membrane separation preheater;

[0029] The auxiliary reboiler is also connected to the gas-liquid separator at the bottom of the first distillation column. One end of the gas-liquid separator at the bottom of the first distillation column is connected to the first distillation column, and the other end is connected to the secondary preheater;

[0030] One end of the compressor for the second distillation column is connected to the top of the second distillation column, and the other end is connected to the reboiler at the bottom of the second distillation column;

[0031] The bottom reboiler of the second rectification column is also respectively connected to the bottom of the second rectification column, the gas-liquid separator at the bottom of the second rectification column, and the second auxiliary condenser;

[0032] The gas-liquid separator at the bottom of the second rectification column is also connected to the second rectification column; the second auxiliary condenser is also connected to the second valve; the second valve is also connected to the second rectification column;

[0033] One end of the membrane separation feed pump is connected to the membrane separation preheater, and the other end is connected to the membrane separation device; the membrane separation device is also respectively connected to the membrane separation turbine and the product condenser.

[0034] Preferably, the molecular sieve used in the molecular sieve adsorption bed is 3A molecular sieve.

[0035] Preferably, the steam permeation membrane of the membrane separation device is an inorganic molecular sieve or an imide fiber membrane.

[0036] Preferably, the rough distillation column, the first rectification column, and the second rectification column are all plate columns or packed columns.

[0037] Another object of the present invention is to provide a process for refining ethanol. Using the above-mentioned three-column rectification device for refining ethanol, it includes the following steps:

[0038] S1. The used post-fermentation raw material liquid is first heated in the primary preheater and the secondary preheater. After reaching the feed temperature and pressure of the rough distillation column, the raw material liquid enters the feed port of the rough distillation column to complete the feeding;

[0039] S2. After the system runs stably, the non-condensable gas formed at the top of the rough distillation column enters the water washing tower. After removing carbon dioxide by water washing, it returns to the top of the rough distillation column to participate in rectification again. The top product is sent to the second rectification column for refining. The bottom liquid of the column is reboiled and then, after gas-liquid separation, the gas phase is used as gas reflux, and the liquid phase is used as a heat source to preheat the raw material liquid at the first stage. The side-line product of the rough distillation column enters the first rectification column for refining;

[0040] S3. The top products of the first rectification column and the second rectification column are combined and then enter the molecular sieve adsorption bed or the membrane separation device for purification to obtain ethanol products.

[0041] In the present invention, when the molecular sieve adsorption process is selected for purification, the refining process steps are as follows:

[0042] (1) The used post-fermentation raw material liquid is first heated in the primary preheater and the secondary preheater. After reaching the feed temperature and pressure of the rough distillation column, the raw material liquid enters the feed port of the rough distillation column to complete the feeding;

[0043] (2) After the system operates stably, the non-condensable gas formed at the top of the rough distillation column enters the water scrubbing column. After removing carbon dioxide through water scrubbing, it returns to the top of the rough distillation column to participate in the rectification process again. The distillate at the top is sent to the second rectification column for refining. The bottom liquid of the column is reboiled and then, after gas-liquid separation, the gas phase is used as the gas reflux, and the liquid phase is used as the heat source to preheat the raw material liquid at the first stage. The side-line product of the rough distillation column enters the first rectification column for refining;

[0044] (3) After the first rectification column refines the crude product, the gas phase at the top is used as the heat source to enter the reboiler at the bottom of the rough distillation column for heat exchange. The bottom liquid of the column is reboiled and then, after gas-liquid separation, the gas phase is used as the gas reflux, and the liquid phase is used as the heat source to preheat the raw material liquid at the second stage;

[0045] (4) After the second rectification column refines the distillate from the top of the rough distillation column, the gas phase at the top is used as the heat source to enter the reboiler at the bottom of the first rectification column for heat exchange. Part of the bottom liquid of the column is reboiled and used as the gas reflux of the rough distillation column, and part is used as the distillate;

[0046] (5) After the distillates at the tops of the first rectification column and the second rectification column are heat-exchanged multiple times, part of them is used as the respective liquid reflux to participate in the rectification process again, and the remaining part is combined and enters the molecular sieve adsorption bed. After adsorption, ethanol products are obtained, and the waste liquid is discharged from the system.

[0047] In the present invention, when the membrane separation technology is selected for purification, the refining process steps are as follows:

[0048] 1) The fermented raw material liquid used first enters the first-stage preheater and the second-stage preheater for heating. After reaching the feeding temperature and pressure of the rough distillation column, the raw material liquid enters the feeding port of the rough distillation column to complete the feeding;

[0049] 2) After the feeding liquid enters the rough distillation column, the mixed liquid enters the rectification column at a fixed flow rate. After the system operates stably, the non-condensable gas formed at the top of the rough distillation column enters the water scrubbing column. After removing carbon dioxide through water scrubbing, it returns to the top of the rough distillation column to participate in the rectification process again. The distillate at the top is sent to the second rectification column for refining. The bottom liquid of the column is reboiled and then, after gas-liquid separation, the gas phase is used as the gas reflux, and the liquid phase is used as the heat source to preheat the raw material liquid at the first stage. The side-line product of the rough distillation column enters the first rectification column for refining;

[0050] 3) The high-quality ethanol water vapor formed at the top of the first rectification column enters the compressor. The compressor further increases the temperature and pressure of the top steam, and then transports it to the reboiler of the rectification column as the heat fluid to exchange heat with the bottom medium of the column, providing heat source for the first rectification column. After heat exchange, part of the top product returns to the rectification column, and part enters the membrane separation device for further purification. After heat exchange, the bottom medium is separated by the first gas-liquid separator, and the separated gas is returned to the rectification column as the reboiling gas, and the liquid is discharged from the system after heat exchange with the second heat exchanger;

[0051] 4) After the top product of the rough distillation column enters the second rectification column for further purification, the high-quality ethanol steam formed at the top of the second rectification column enters the compressor. The compressor further increases the temperature and pressure of the top steam, and then transports it to the reboiler of the rectification column as a heat fluid to exchange heat with the bottom medium, providing heat source for the second rectification column. The top product flows back into the rectification column, and part of it enters the membrane separation device for further purification. After the bottom medium exchanges heat, it passes through the second gas-liquid separator to separate the gas as reboiler gas and return it to the rectification column, while the liquid is discharged from the system.

[0052] 5) After multiple heat exchanges, the combined and preheated top products of the first and second rectification columns enter the membrane separation device through the membrane separation feed pump. After separation and condensation, ethanol products meeting the requirements are obtained, and the waste gas is discharged from the system after vacuum extraction by the turbine.

[0053] Preferably, the absolute pressure range of the rough distillation column is 0.04 - 0.06 MPa, the top temperature range of the rough distillation column is 60 - 65 °C, and the bottom temperature range is 75 - 85 °C; the absolute pressure range of the first rectification column is 0.10 - 0.30 MPa, the top temperature range of the first rectification column is 100 - 110 °C, and the bottom temperature range is 120 - 125 °C; the absolute pressure range of the second rectification column is 0.40 - 0.60 MPa, the top temperature range of the second rectification column is 120 - 125 °C, and the bottom temperature range is 145 - 150 °C.

[0054] Preferably, the reflux ratio of the ethanol vapor at the top of the rough distillation column is 2 - 4, the reflux ratio of the ethanol vapor at the top of the first rectification column is 4 - 6, and the reflux ratio of the ethanol vapor at the top of the second rectification column is 0.5 - 1.

[0055] Preferably, the fermented raw material liquid is a fermentation broth obtained from lignocellulose, rich in starch, sugar, etc. through processes such as pulverization, saccharification, and cooking, and its ethanol concentration is 1.5 - 10%.

[0056] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0057] In the process of the present invention, separation and purification are carried out through a three-column rectification and purification device. The process production device is simple, the production route is short, the process flow is shortened by about 30%, the equipment floor area is reduced, the operation parameters are easier to control, the energy utilization rate is high, the energy saving reaches 40% - 50%, and the safety factor is relatively high, fully ensuring the safety of personnel, thus significantly improving the economic benefits of the enterprise.

[0058] The membrane separation device of the process of the present invention uses a reverse osmosis membrane. This technology breaks through the azeotropic limit, has high separation efficiency, and saves 90% energy compared with the traditional distillation method. The molecular sieve adsorption bed uses 3A molecular sieve, which has high adsorption performance and selectivity, good stability. After adsorption, the water content of ethanol can be reduced to less than 0.03%. Through vacuum backwashing (-0.08 MPa) + high-temperature ethanol steam (150 °C) regeneration, the service life of the molecular sieve can be extended to more than 10 years. The process of the present invention has the advantages of simple operation, low operating cost, high degree of equipment automation, small environmental pollution to the outside world, wide application, etc. It has obvious technical advantages compared with other ethanol separation devices, reduces the external energy consumption, improves the economic benefits of production enterprises, and has broad application prospects.

[0059] The process of the present invention has low energy consumption to the outside world. The reboiler distillate of the rectification column exchanges heat with the feed of the column, integrates and utilizes the heat of the rectification unit operation, optimizes the heat exchange network, improves the energy utilization rate, reduces the subsequent heating steam consumption by 30%, and further improves the yield of ethanol products. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0061] Figure 1 It is the device structure diagram when the purification device of the present invention is a molecular sieve;

[0062] Figure 2 It is the device structure diagram when the purification device of the present invention is a membrane separation device;

[0063] Among them, in the figure:

[0064] 1 - primary preheater, 2 - secondary preheater, 3 - rough distillation column, 4 - rough distillation column top condenser, 5 - rough distillation column bottom reboiler, 6 - auxiliary reboiler, 7 - rough distillation column bottom gas-liquid separator, 8 - water washing column, 9 - first rectification column feed pump, 10 - first rectification column, 11 - auxiliary condenser I, 12 - first rectification column bottom reboiler, 13 - first rectification column bottom gas-liquid separator, 14 - second rectification column feed pump, 15 - second rectification column, 16 - auxiliary condenser II, 17 - second rectification column bottom reboiler, 18 - molecular sieve adsorption bed, 19 - first rectification column compressor, 20 - valve I, 21 - second rectification column compressor, 22 - valve II, 23 - second rectification column bottom gas-liquid separator, 24 - membrane separation preheater, 25 - membrane separation feed pump, 26 - membrane separation device, 27 - membrane separation turbine, 28 - product condenser. Detailed Embodiments

[0065] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0066] Embodiment 1

[0067] For the project of producing 30,000 tons of cellulose fuel ethanol per year, see Figure 1 , in this embodiment, the purification device adopts a molecular sieve adsorption bed, which specifically includes: a primary preheater 1, a secondary preheater 2, a crude distillation column 3, a crude distillation column top condenser 4, a water washing column 8, a first distillation column feed pump 9, a first distillation column 10, a second distillation column feed pump 14, a second distillation column 15, a crude distillation column bottom reboiler 5, an auxiliary reboiler 6, a crude distillation column bottom gas-liquid separator 7, an auxiliary condenser I 11, a first distillation column bottom reboiler 12, a first distillation column bottom gas-liquid separator 13, an auxiliary condenser II 16, a second distillation column bottom reboiler 17, and a molecular sieve adsorption bed 18;

[0068] Among them, the primary preheater 1, the secondary preheater 2, and the crude distillation column 3 are connected in sequence;

[0069] The top of the crude distillation column 3 is connected in a cycle with the crude distillation column top condenser 4, and the water washing column 8 is respectively connected with the crude distillation column 3 and the crude distillation column top condenser 4;

[0070] One end of the first distillation column feed pump 9 is connected to the first distillation column 10, and the other end is connected to the crude distillation column 3;

[0071] One end of the second distillation column feed pump 14 is connected to the second distillation column 15, and the other end is connected to the crude distillation column 3;

[0072] One end of the crude distillation column bottom reboiler 5 is connected to the bottom of the crude distillation column 3, and the other end is sequentially connected to the auxiliary reboiler 6 and the crude distillation column bottom gas-liquid separator 7. The crude distillation column bottom reboiler 5 is also connected to the top of the first distillation column 10;

[0073] One end of the crude distillation column bottom gas-liquid separator 7 is connected to the crude distillation column 3, and the other end is connected to the primary preheater 1;

[0074] One end of the auxiliary condenser I 11 is connected to the crude distillation column bottom reboiler 5, and the other end is respectively connected to the first distillation column 10, the molecular sieve adsorption bed 18, and the second distillation column 15;

[0075] One end of the reboiler 12 at the bottom of the first rectification column is connected to the bottom of the first rectification column 10, and the other end is respectively connected to the gas-liquid separator 13 at the bottom of the first rectification column, the auxiliary condenser II 16, and the second rectification column 15;

[0076] One end of the gas-liquid separator 13 at the bottom of the first rectification column is connected to the first rectification column 10, and the other end is connected to the secondary preheater 2;

[0077] The auxiliary condenser II 16 is also respectively connected to the pipeline between the auxiliary condenser I 11 and the molecular sieve adsorption bed 18 and the pipeline between the auxiliary condenser I 11 and the second rectification column 15;

[0078] The reboiler 17 at the bottom of the second rectification column is connected in a cycle with the second rectification column 15.

[0079] Using the above device to refine ethanol, the process is as follows:

[0080] S1. The fermented raw material liquid used is first heated in the primary preheater 1 and the secondary preheater 2. After reaching the feeding temperature and pressure of the rough distillation column 3, the raw material liquid enters the feeding port of the rough distillation column 3 to complete the feeding;

[0081] In this step, the ethanol concentration of the fermented raw material liquid is 8%, the feeding temperature is 67 °C, and the pressure is 1 bar;

[0082] S2. After the system operates stably, the non-condensable gas formed at the top of the rough distillation column 3 enters the water washing tower 8. After the carbon dioxide is removed by water washing, it returns to the top of the rough distillation column 3 to participate in the rectification again. The overhead product is sent to the second rectification column 15 for refining. The bottom liquid of the tower is reboiled and then the gas phase after gas-liquid separation is used as the gas-phase reflux, and the liquid phase is used as the heat source to preheat the raw material liquid at the first stage. The side-line product of the rough distillation column 3 enters the first rectification column 10 for refining;

[0083] In this step, the absolute pressure range of the rough distillation column 3 is 0.04 - 0.06 MPa; the overhead temperature range of the rough distillation column 3 is 60 - 65 °C, the temperature range of the bottom of the tower is 75 - 85 °C, and the reflux ratio of the ethanol vapor at the top of the tower is 2 - 4;

[0084] In this step, the water washing tower 8 absorbs ethanol in the non-condensable gas through water, and at the same time discharges the non-condensable gas to the outside of the system;

[0085] S3. After the first rectification column 10 refines the crude product, the gas phase at the top of the tower is used as the heat source to enter the reboiler 5 at the bottom of the rough distillation column for heat exchange. The bottom liquid of the tower is reboiled and then the gas phase after gas-liquid separation is used as the gas-phase reflux, and the liquid phase is used as the heat source to preheat the raw material liquid at the second stage;

[0086] In this step, the absolute pressure range of the first rectification column is 0.10 - 0.3 MPa, the top temperature range of the first rectification column is 100 - 110 °C, the bottom temperature range is 120 - 125 °C, the reflux ratio of ethanol vapor at the top of the column is 4 - 6. After the vapor at the top of the column is used as a heat source for heat exchange, part of it is condensed as liquid reflux, and part of it goes to the molecular sieve adsorption bed 18 as the crude product;

[0087] S4. After the second rectification column 15 refines the distillate from the top of the crude distillation column, the vapor at the top of the column enters the reboiler 12 at the bottom of the first rectification column as a heat source for heat exchange. Part of the liquid in the bottom of the column is reboiled and used as the vapor reflux of the crude distillation column 3, and part is used as the distillate;

[0088] In this step, the absolute pressure range of the second rectification column 15 is 0.40 - 0.60 MPa, the top temperature range is 120 - 125 °C, the bottom temperature range is 145 - 150 °C, the reflux ratio of ethanol vapor at the top of the column is 0.5 - 1. After the vapor at the top of the column is used as a heat source for heat exchange, part of it is condensed as liquid reflux, and part of it goes to the molecular sieve adsorption bed 18 as the crude product;

[0089] S5. After the products taken from the tops of the first rectification column 10 and the second rectification column 15 are heat-exchanged multiple times, part of them is used as their respective liquid reflux to participate in the rectification process again, and the remaining part is combined and enters the molecular sieve adsorption bed 18. After adsorption, fuel ethanol products are obtained, and the waste liquid is discharged from the system;

[0090] In this step, the molecular sieve adsorption bed 18 is at atmospheric pressure. The molecular sieve belongs to 3A molecular sieve, the temperature is 170 °C, the operation time is 120 min, and 99.5% fuel ethanol products are obtained from the molecular sieve adsorption bed.

[0091] Compared with the traditional process, the energy consumption of this embodiment is significantly reduced. Only a small amount of external heat source is required to provide energy for the condensation of the vapor at the top of the crude distillation column. Other heat exchanges can be carried out through the heat exchange between the vapor and the liquid in the kettle, and the heat exchange between the waste liquid and the raw material, integrating and utilizing the waste heat of the rectification unit, reducing the energy consumption of the entire process flow, and increasing the yield of the target product.

[0092] Example 2

[0093] For the project of an annual output of 30,000 tons of cellulosic fuel ethanol, see Figure 2, in this embodiment, the purification device is selected as a membrane separation device, which specifically includes: a primary preheater 1, a secondary preheater 2, a crude distillation column 3, a crude distillation column top condenser 4, a water washing column 8, a first distillation column feed pump 9, a first distillation column 10, a second distillation column feed pump 14, a second distillation column 15, a crude distillation column bottom reboiler 5, a first distillation column compressor 19, a first distillation column bottom reboiler 12, an auxiliary condenser 1 11, a valve 1 20, an auxiliary reboiler 6, a first distillation column bottom gas-liquid separator 13, a second distillation column compressor 21, a second distillation column bottom reboiler 17, an auxiliary condenser 2 16, a valve 2 22, a second distillation column bottom gas-liquid separator 23, a membrane separation preheater 24, a membrane separation feed pump 25, a membrane separation device 26, a membrane separation turbine 27, and a product condenser 28;

[0094] Among them, the primary preheater 1, the secondary preheater 2, and the crude distillation column 3 are connected in sequence;

[0095] The top of the crude distillation column 3 is connected in a cycle with the crude distillation column top condenser 4, and the water washing column 8 is respectively connected to the crude distillation column 3 and the crude distillation column top condenser 4;

[0096] One end of the first distillation column feed pump 9 is connected to the first distillation column 10, and the other end is connected to the crude distillation column 3;

[0097] One end of the second distillation column feed pump 14 is connected to the second distillation column 15, and the other end is connected to the crude distillation column 3;

[0098] One end of the crude distillation column bottom reboiler 5 is connected to the bottom of the crude distillation column 3, and the other end is sequentially connected to the auxiliary reboiler 6 and the crude distillation column bottom gas-liquid separator 7. The crude distillation column bottom reboiler 5 is also connected to the top of the first distillation column 10;

[0099] One end of the crude distillation column bottom gas-liquid separator 7 is connected to the crude distillation column 3, and the other end is connected to the primary preheater 1;

[0100] One end of the auxiliary condenser 1 11 is connected to the crude distillation column bottom reboiler 5, and the other end is respectively connected to the first distillation column 10, the molecular sieve adsorption bed 18, and the second distillation column 15;

[0101] The crude distillation column bottom reboiler 5 is connected in a cycle with the crude distillation column 3 and is also connected to the primary preheater 1;

[0102] One end of the first distillation column compressor 19 is connected to the top of the first distillation column 10, and the other end is connected to the first distillation column bottom reboiler 12;

[0103] One end of the first distillation column bottom reboiler 12 is connected to the bottom of the first distillation column 10, and the other end is respectively connected to the auxiliary condenser 1 11 and the auxiliary reboiler 6;

[0104] One end of valve 1 20 is connected to auxiliary condenser 1 11, and the other end is respectively connected to the first distillation column 10, valve 2 22, and membrane separation preheater 24;

[0105] Auxiliary reboiler 6 is also connected to the bottom gas-liquid separator 13 of the first distillation column. One end of the bottom gas-liquid separator 13 of the first distillation column is connected to the first distillation column 10, and the other end is connected to the secondary preheater 2;

[0106] One end of the second distillation column compressor 19 is connected to the top of the second distillation column 15, and the other end is connected to the bottom reboiler 17 of the second distillation column;

[0107] The bottom reboiler 17 of the second distillation column is also respectively connected to the bottom of the second distillation column 15, the bottom gas-liquid separator 23 of the second distillation column, and auxiliary condenser 2 16;

[0108] The bottom gas-liquid separator 23 of the second distillation column is also connected to the second distillation column 15; Auxiliary condenser 2 16 is also connected to valve 2 22; Valve 2 22 is also connected to the second distillation column 15;

[0109] One end of the membrane separation feed pump 25 is connected to the membrane separation preheater 24, and the other end is connected to the membrane separation device 26; The membrane separation device 26 is also respectively connected to the membrane separation turbine 27 and the product condenser 28.

[0110] Using the above device to refine ethanol, the process is as follows:

[0111] S1. After the used biomass raw material is fermented, the fermented mash enters the primary preheater 1 for heating, and the heated material flow enters the secondary preheater 2 for further heating to reach the feeding temperature and pressure of the distillation column. Then the material flow enters the feed port of the rough distillation column 3 to complete the feeding;

[0112] In this step, the biomass raw material is cellulose, the ethanol concentration in the raw material liquid after fermentation is 8%, the feeding temperature is 67 °C, and the pressure is 1 bar;

[0113] S2. After the feed liquid enters the rough distillation column 3, the mixed liquid enters the column at a fixed flow rate. After the system operates stably, the non-condensable gas formed at the top of the rough distillation column 3 enters the water wash tower 8, and after removing carbon dioxide by water washing, it returns to the top of the rough distillation column 3 to participate in rectification again. The top product is taken out and enters the second distillation column 15 for refining. The bottom liquid of the column is reboiled and after gas-liquid separation, the gas phase is used as gas reflux, and the liquid phase is used as a heat source to preheat the raw material liquid at the primary level. The side-line product of the rough distillation column 3 enters the first distillation column 10 for refining;

[0114] In this step, the absolute pressure range of the rough distillation column 3 is 0.04 - 0.06 MPa; the top temperature range of the rough distillation column 3 is 60 - 65 °C, the bottom temperature range of the column is 75 - 85 °C, and the reflux ratio of the ethanol vapor at the top of the column is 1 - 2;

[0115] In S3, the high-quality ethanol steam formed at the top of the first rectification column 10 enters the first rectification column compressor 19. The first rectification column compressor 19 further increases the temperature and pressure of the top steam, and then transports it to the first rectification column bottom reboiler 17 as a heat fluid to exchange heat with the column bottom medium, providing a heat source for the first rectification column 10. After heat exchange, part of the top product flows back into the first rectification column 10, and part enters the membrane separation device 26 for further purification. After heat exchange, the column bottom medium is separated by the first rectification column gas-liquid separator 13, and the separated gas returns to the first rectification column 10 as reboiler gas. The liquid is discharged from the system after heat exchange with the secondary preheater 2;

[0116] In this step, the absolute pressure range of the first rectification column 10 is 0.10 - 0.30 MPa, the top temperature range of the first rectification column 10 is 100 - 110 °C, the bottom temperature range is 120 - 125 °C, the reflux ratio of the top ethanol vapor is 4 - 6. After the top gas phase exchanges heat with the column bottom medium as a heat source, after condensation, part is used as liquid reflux, and part goes to the membrane separation device 26 as crude product;

[0117] In S4, the overhead product from the crude distillation column 3 enters the second rectification column 15 for further purification. The high-quality ethanol steam formed at the top of the second rectification column 15 enters the second rectification column compressor 21. The second rectification column compressor 21 further increases the temperature and pressure of the top steam, and then transports it to the second rectification column bottom reboiler 17 as a heat fluid to exchange heat with the column bottom medium, providing a heat source for the second rectification column 15. The top product flows back into the second rectification column 15, and part enters the membrane separation device 26 for further purification. After heat exchange, the column bottom medium is separated by the second rectification column gas-liquid separator 23, and the separated gas returns to the second rectification column 15 as reboiler gas. The liquid is discharged from the system;

[0118] In this step, the absolute pressure range of the second rectification column 15 is 0.40 - 0.60 MPa, the top temperature range of the second rectification column 15 is 120 - 125 °C, the bottom temperature range is 145 - 150 °C, the reflux ratio of the top ethanol vapor is 0.5 - 1. After the top gas phase exchanges heat with the column bottom medium as a heat source, after condensation, part is used as liquid reflux, and part goes to the membrane separation device as crude product;

[0119] In S5, after multiple heat exchanges, the overhead products from the first rectification column 10 and the second rectification column 15 are combined, preheated by the membrane separation preheater 24, and then enter the membrane separation device 26 through the membrane separation feed pump 25. After separation and condensation, ethanol products meeting the requirements are obtained, and the waste gas is discharged from the system after vacuum pumping by the membrane separation turbine 27.

[0120] In this step, the operating pressure of the membrane separation device 26 is negative pressure, the vapor permeation membrane is a polyimide fiber membrane, the temperature is 97 °C, the operating time is 120 min, and the ethanol product obtained from the membrane separation device 26 is 99.5% fuel ethanol vapor, which is condensed to obtain a 99.5% fuel ethanol product.

[0121] Compared with the traditional process, the energy consumption of this embodiment is significantly reduced. The outside only needs to provide partial steam heat for the membrane separation device. The product logistics of the membrane separation device exchanges heat with the feed logistics of the heat pump distillation column to integrate and utilize the operating heat of the distillation unit, optimize the heat exchange network, improve the energy utilization rate, and further increase the yield of ethanol products.

[0122] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts between the various embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method part.

[0123] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-tower distillation device for refining ethanol, characterized in that: include: A primary preheater, a secondary preheater, a crude distillation tower, a crude distillation tower top condenser, a water scrubber, a first distillation tower feed pump, a first distillation tower, a second distillation tower feed pump, a second distillation tower and a purification device; Wherein, the primary preheater, the secondary preheater, and the crude distillation tower are connected in sequence; The top of the crude distillation tower is cyclically connected to the crude distillation tower top condenser, and the water scrubber is respectively connected to the crude distillation tower and the crude distillation tower top condenser; One end of the first distillation tower feed pump is connected to the first distillation tower, and the other end is connected to the crude distillation tower; One end of the second distillation tower feed pump is connected to the second distillation tower, and the other end is connected to the crude distillation tower; The purification device is connected to the first distillation tower and the second distillation tower respectively.

2. A three-tower distillation device for refining ethanol according to claim 1, characterized in that: Also includes: A crude distillation tower bottom reboiler, an auxiliary reboiler, a crude distillation tower bottom gas-liquid separator, an auxiliary condenser 1, a first rectification tower bottom reboiler, a first rectification tower bottom gas-liquid separator, an auxiliary condenser 2, and a second rectification tower bottom reboiler; Wherein, the purification device comprises a molecular sieve adsorption bed; One end of the crude distillation tower bottom reboiler is connected to the bottom of the crude distillation tower, and the other end is connected to the auxiliary reboiler and the crude distillation tower bottom gas-liquid separator in sequence, and the crude distillation tower bottom reboiler is also connected to the top of the first distillation tower; One end of the crude distillation tower bottom gas-liquid separator is connected to the crude distillation tower, and the other end is connected to the primary preheater; The auxiliary condenser is connected to the reboiler at the bottom of the crude distillation tower at one end, and is respectively connected to the first distillation tower, the molecular sieve adsorption bed, and the second distillation tower at the other end; One end of the first distillation tower bottom reboiler is connected to the bottom of the first distillation tower, and the other end is respectively connected to the first distillation tower bottom gas-liquid separator, the second auxiliary condenser, and the second distillation tower; One end of the gas-liquid separator at the bottom of the first distillation tower is connected to the first distillation tower, and the other end is connected to the secondary preheater; The auxiliary condenser 2 is also connected to the pipeline between the auxiliary condenser 1 and the molecular sieve adsorption bed and the pipeline between the auxiliary condenser 1 and the second distillation tower respectively; The second distillation tower bottom reboiler is circularly connected to the second distillation tower.

3. A three-tower distillation device for refining ethanol according to claim 1, characterized in that: Also includes: Reboiler at the bottom of the crude distillation tower, compressor at the first distillation tower, reboiler at the bottom of the first distillation tower, auxiliary condenser 1, valve 1, auxiliary reboiler, gas-liquid separator at the bottom of the first distillation tower, compressor at the second distillation tower, reboiler at the bottom of the second distillation tower, auxiliary condenser 2, valve 2, gas-liquid separator at the bottom of the second distillation tower; Wherein, the purification device includes a membrane separation preheater, a membrane separation feed pump, a membrane separation device, a membrane separation turbine, and a product condenser; The crude distillation tower bottom reboiler is connected to the crude distillation tower in a circulation manner and is also connected to the primary preheater; One end of the first distillation tower compressor is connected to the top of the first distillation tower, and the other end is connected to the reboiler at the bottom of the first distillation tower; One end of the first distillation tower bottom reboiler is connected to the bottom of the first distillation tower, and the other end is respectively connected to the auxiliary condenser 1 and the auxiliary reboiler; One end of the valve 1 is connected to the auxiliary condenser 1, and the other end is respectively connected to the first distillation tower, the valve 2 and the membrane separation preheater; The auxiliary reboiler is also connected to the gas-liquid separator at the bottom of the first distillation tower, one end of the gas-liquid separator at the bottom of the first distillation tower is connected to the first distillation tower, and the other end is connected to the secondary preheater; One end of the second distillation tower compressor is connected to the top of the second distillation tower, and the other end is connected to the reboiler at the bottom of the second distillation tower; The second distillation tower bottom reboiler is also connected to the bottom of the second distillation tower, the second distillation tower bottom gas-liquid separator and the auxiliary condenser 2 respectively; The gas-liquid separator at the bottom of the second distillation tower is also connected to the second distillation tower; the auxiliary condenser 2 is also connected to the valve 2; the valve 2 is also connected to the second distillation tower; One end of the membrane separation feed pump is connected to the membrane separation preheater, and the other end is connected to the membrane separation device; the membrane separation device is also connected to the membrane separation turbine and the product condenser respectively.

4. A three-tower distillation device for refining ethanol according to claim 2, characterized in that: The molecular sieve used in the molecular sieve adsorption bed is 3A molecular sieve.

5. A three-tower distillation device for refining ethanol according to claim 3, characterized in that: The steam permeable membrane of the membrane separation device is an inorganic molecular sieve or an imide fiber membrane.

6. A three-tower distillation device for refining ethanol according to claim 4 or 5, characterized in that: The crude distillation tower, the first distillation tower and the second distillation tower are all plate towers or packed towers.

7. A process for refining ethanol, characterized in that: The three-tower distillation device for refining ethanol according to claim 6 comprises the following steps: S1, the fermented raw material liquid is heated in the primary preheater and the secondary preheater in turn. After reaching the feed temperature and pressure of the crude distillation tower, the raw material liquid enters the feed port of the crude distillation tower to complete the feeding; S2. After the system maintains stable operation, the non-condensable gas formed at the top of the crude distillation tower enters the water washing tower, and after being washed with water to remove carbon dioxide, it returns to the top of the crude distillation tower to participate in distillation again. The top of the tower is extracted and enters the second distillation tower for refining. After the bottom kettle liquid is reboiled and separated from the gas and liquid, the gas phase is refluxed as the gas phase, and the liquid phase is used as a heat source to preheat the raw liquid in the first stage. The side product of the crude distillation tower enters the first distillation tower for refining; S3, the tops of the first distillation tower and the second distillation tower are combined and then enter the purification device for purification to obtain ethanol product.

8. A process for refining ethanol according to claim 7, characterized in that: The absolute pressure range of the crude distillation tower is 0.04-0.06MPa, the top temperature range of the crude distillation tower is 60-65°C, and the temperature range of the bottom of the tower is 75-85°C; the absolute pressure range of the first distillation tower is 0.10-0.30MPa, the top temperature range of the first distillation tower is 100-110°C, and the temperature range of the bottom of the tower is 120-125°C; the absolute pressure range of the second distillation tower is 0.40-0.60MPa, the top temperature range of the second distillation tower is 120-125°C, and the temperature range of the bottom of the tower is 145-150°C.

9. A process for refining ethanol according to claim 7, characterized in that: The ethanol vapor reflux ratio of the top of the crude distillation tower is 2-4, the ethanol vapor reflux ratio of the top of the first distillation tower is 4-6, and the ethanol vapor reflux ratio of the top of the second distillation tower is 0.5-1.

10. A process for refining ethanol according to claim 7, characterized in that: The fermented raw material liquid is a fermented mash obtained after the wood cellulose, which is rich in starch and sugar, undergoes processes such as crushing, saccharification, and cooking, and the ethanol concentration thereof is 1.5-10%.

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