Preparation method of fuel ethanol

Abstract

The invention relates to the field of fuel preparation, and discloses a preparation method of fuel ethanol. The preparation method comprises the following steps: pretreating a cellulose raw material, and then carrying out neutral gas explosion, enzymolysis, fermentation and rectification; the pretreatment method comprises the following steps: S1, performing primary crushing on a cellulose raw material to obtain a material subjected to primary crushing; s2, drying the material subjected to primary crushing to obtain a dried material; s3, screening the dried material to obtain a screened first material of which the particle size is less than or equal to 5cm and a screened second material of which the particle size is greater than 5cm; s4, performing secondary crushing on the screened second material, and mixing the obtained material subjected to secondary crushing with the screened first material; and S5, tabletting the mixed material. An independent feeder does not need to be arranged, stable, uniform and continuous feeding is guaranteed, and the dosage of an enzyme preparation can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the field of fuel preparation, and particularly to a method for preparing fuel ethanol. Background Art

[0002] Fuel ethanol is an emerging green industry arising from the oil crisis and air pollution control. It is mainly made from grains (such as corn and wheat), tubers (such as sweet potatoes, cassava, and potatoes), sugars (such as molasses), or cellulose (such as crop straws, waste wood, and paper pulp). Through fermentation and distillation, 95% (v / v) ethanol is obtained, dehydrated to get fuel ethanol, and then a denaturant is added to obtain denatured fuel ethanol. Cellulose fuel ethanol is a type of fuel ethanol.

[0003] Straw is a solid material with a relatively low bulk density, typical data being 45 - 50 kg / m3 (15 - 20% moisture). During transportation, it has a large volume, the raw material is prone to fluctuations, the material is easy to float, and the workshop environment is poor. Moreover, the water content of the straw raw material is also unstable. Throughout the year, the water content of the straw varies within the range of 10 - 45%, and the change in moisture also affects the bulk density. The proportion of straw leaves, stems, and straw pith in the raw material also varies with different round bales / square bales or batches, resulting in different bulk densities. The instability of the material bulk density directly affects the key design of the pretreatment for stability and load.

[0004] The core equipment in the pretreatment part is the feeder. Under normal pressure, the straw is pressurized in this equipment and then enters the explosion puffing equipment for explosion puffing. This feeder requires a stable, uniform, and continuous supply of straw. However, in practical operation, due to the low and unstable bulk density of the straw, the volume fluctuation of the straw material is relatively large, and the material transportation shows pulsating fluctuations, resulting in large fluctuations in the operation of the feeder, inability to feed evenly and stably, and easy blockage. The blockage of the feeder correspondingly affects the process stability of the cooking reactor, and the discharge port of the explosion puffing equipment is prone to coking and blockage. Subsequently, it affects the stable and efficient operation of subsequent enzymatic hydrolysis and other units and the start-up rate of the entire device.

[0005] Therefore, there is an urgent need for a fuel ethanol preparation process that can improve the bulk density and bulk density stability of the material, avoid blockage failures and wear of the feeder, ensure the stable, uniform, and continuous feeding, and thus ensure the long-term stable operation of the equipment. Summary of the Invention

[0006] The object of the present invention is to overcome the problems existing in the prior art, including that the bulk density of straw materials is low and unstable, the volume of straw materials fluctuates greatly, the material transportation is in a pulsating fluctuation, resulting in large fluctuations in the operation of the feeder, unable to feed evenly and stably, easy to block, the blockage of the feeder correspondingly affects the process stability of the cooking reactor, the discharge port of the air explosion equipment is easy to coke and block, and then affects the stable and efficient operation of subsequent units such as enzymatic hydrolysis and the start-up rate of the whole device. A method for preparing fuel ethanol is provided. After tabletting, the material of this preparation method reaches a relatively high and stable bulk density, enters the air explosion equipment through a regulating valve, and there is no need to set up a feeder anymore, avoiding the blockage failure and wear of the feeder, ensuring the stable, uniform and continuous feeding, ensuring the long-term stable operation of the equipment, realizing the efficient utilization of subsequent equipment, reducing the dosage of enzyme preparation, and improving the start-up rate.

[0007] To achieve the above object, the present invention provides a method for preparing fuel ethanol, wherein the preparation method includes the following steps: pretreating the cellulose raw material, then performing neutral air explosion, enzymatic hydrolysis, fermentation and rectification; wherein,

[0008] The pretreatment method includes:

[0009] S1. Crushing the cellulose raw material for the first time to obtain the material after the first crushing;

[0010] S2. Drying the material after the first crushing to obtain the dried material;

[0011] S3. Screening the dried material to obtain the first screened material with a particle size less than or equal to 5 cm and the second screened material with a particle size greater than 5 cm;

[0012] S4. Crushing the second screened material for the second time, and mixing the obtained material after the second crushing with the first screened material to obtain a mixed material;

[0013] S5. Tabletting the mixed material.

[0014] Through the above technical solutions, the beneficial effects of the present invention at least include:

[0015] The method provided by the present invention sets up a drying unit, ensuring the uniformity and stability of the moisture content of the cellulose raw material, and providing a stable raw material basis for subsequent steps such as tabletting. The present invention adopts two-stage crushing, with uniform crushing particle size, which can improve the explosion effect. After the cellulose raw material is crushed and tableted, it is directly subjected to explosion. Since the material after tabletting reaches a relatively high and stable bulk density, it enters the explosion equipment through a regulating valve. The explosion equipment does not set up a separate feeder, avoiding the blockage and wear faults of the industrial large-scale feeder, ensuring the stable, uniform and continuous feeding, ensuring the long-term stable operation of the equipment, significantly improving the operating rate of the equipment. In the preferred case, the operating rate is increased from 60 - 70% to over 90%. Due to the stable and continuous operation of the explosion equipment, the efficient utilization of subsequent equipment is realized, and the dosage of enzyme preparation is reduced. In the preferred case, the dosage of enzyme preparation is reduced by more than 20%. The bulk density of the material after tabletting increases, and the corresponding conveying and equipment are correspondingly reduced, saving equipment investment. In addition, through the regulating valve, the connection between the atmospheric pressure material in the extrusion process and the pressurized equipment is realized, and the process is simple. In addition, the cooking reactor adopts neutral explosion without adding acid, reducing the corrosion of the equipment and facilitating the long-term maintenance and continuous operation of the factory. The preparation method of the present invention has no sewage discharge process and is environmentally friendly.

[0016] In a preferred embodiment of the present invention, the method provided by the present invention makes full use of heat. The wet distillers grains and evaporated syrup are separated and enter the biomass boiler. The biomass boiler provides steam for the whole device, and the whole device does not need to provide steam separately, reducing energy consumption and saving costs. Description of the Drawings

[0017] Figure 1 It is a flow chart of the preparation method of fuel ethanol in a preferred embodiment of the present invention.

[0018] Description of the Reference Numerals

[0019] T1 Coarse Crushing Unit T2 Drying Unit T3 Screening Unit

[0020] T4 Fine Crushing Unit T5 Extrusion Unit T6 Explosion Unit

[0021] T7 Enzymolysis Unit T8 Fermentation Unit T9 Rectification Unit T10 Separation Unit

[0022] T11 Evaporation Unit T12 Biomass Boiler Detailed Embodiments

[0023] The endpoints and any values within the ranges disclosed in this document are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in this document.

[0024] The present invention provides a method for preparing fuel ethanol. Among them, the preparation method includes the following steps: pretreating the cellulose raw material, and then performing neutral explosion, enzymatic hydrolysis, fermentation, and rectification; among them,

[0025] The pretreatment method includes:

[0026] S1. First pulverize the cellulose raw material to obtain the material after the first pulverization;

[0027] S2. Dry the material after the first pulverization to obtain the dried material;

[0028] S3. Screen the dried material to obtain the first screened material with a particle size less than or equal to 5 cm and the second screened material with a particle size greater than 5 cm;

[0029] S4. Second pulverize the second screened material, and mix the obtained material after the second pulverization with the first screened material to obtain a mixed material;

[0030] S5. Tablet the mixed material.

[0031] In the present invention, the method for preparing fuel ethanol includes multiple core technologies such as cellulose raw material pretreatment technology, neutral explosion (steam explosion) technology, enzymatic hydrolysis, fermentation, and rectification. After the cellulose raw material of the cellulose ethanol device is first pulverized, it enters the drying unit for drying, and then is screened. The material with unqualified particle size is pulverized again (secondary fine pulverization) and mixed with the qualified material, and then enters the tablet pressing unit. After the material is extruded into tablets in the present invention, the material is directly subjected to explosion. The explosion equipment does not need to be provided with a separate feeder, which avoids the blockage and wear failures of large-scale industrial feeders, ensures the stable, uniform and continuous feeding, and ensures the long-term stable operation of the new equipment. Since the explosion equipment can operate stably and continuously, the subsequent equipment can also be efficiently utilized, and the dosage of enzyme preparation can be effectively reduced. In addition, the bulk density of the material after tableting increases, and the size of the corresponding conveying equipment decreases, saving equipment investment.

[0032] In order to obtain a more suitable particle size for the crushed material, thereby further improving the subsequent air explosion effect, preferably, in S1, the conditions of the first crushing are such that in the material after the first crushing, the content of the material with a particle size of 3 - 5 cm is greater than or equal to 85 wt%.

[0033] According to the present invention, preferably, the conditions of the first crushing are such that in the material after the first crushing, the content of the material with a particle size less than 3 cm is less than or equal to 5 wt%, and the content of the material with a particle size greater than 5 cm is less than or equal to 10 wt%.

[0034] The present invention has no particular limitation on the type of cellulose raw material, and conventional cellulose raw materials for preparing fuel ethanol can be selected. Preferably, the cellulose raw material is straw, and more preferably corn straw and / or wheat straw.

[0035] In order to further improve the uniformity and stability of the moisture in the cellulose raw material and provide a more stable raw material basis for subsequent tablet pressing, preferably, in S2, the conditions of the drying are such that the water content in the material after drying is 10 - 25 wt%.

[0036] The present invention has no particular limitation on the drying method, and conventional devices and methods in the art can be used for drying. For example, drying can be carried out in a drum dryer. Preferably, the conditions of the drying are such that the water content in the material at the outlet of the drum dryer is 15 - 20 wt%.

[0037] In the present invention, screening can be carried out using conventional equipment in the art for screening materials with different sizes. For example, a rotary screen equipment can be used for screening.

[0038] In order to make the particle size of the crushed material more uniform, thereby further improving the subsequent air explosion effect, preferably, in S4, the conditions of the second crushing are such that in the material after the second crushing, the content of the material with a particle size of 3 - 5 cm is greater than or equal to 85 wt%.

[0039] According to the present invention, preferably, the conditions of the second crushing are such that in the material after the second crushing, the content of the material with a particle size less than 3 cm is less than or equal to 5 wt%, and the content of the material with a particle size greater than 5 cm is less than or equal to 10 wt%.

[0040] In the present invention, crushing can be carried out using conventional crushing equipment in the art. For example, a crusher can be used for crushing.

[0041] In order to further increase the bulk density of the material after tableting and make the bulk density of the material after tableting more stable, thereby further improving the stability, uniformity, and continuity of the feeding, and enabling the equipment to operate stably for a long time. Preferably, in S5, the tableting conditions are such that the particle size of the material after tableting obtained by the tableting is 3 - 5 cm, and the thickness is 2 - 10 mm.

[0042] In the preferred case, the bulk density of the material after tableting obtained by the tableting is 500 - 700 kg / m 3 .

[0043] In the present invention, tableting can be performed using conventional tableting equipment in the art. For example, a straw tableting machine can be used for tableting.

[0044] In the present invention, the material after tableting directly enters the cooking reactor of the air explosion equipment through a regulating valve. There is no need to set a feeder in front of the cooking reactor, which avoids the blockage failure and wear of the feeder, ensures the stability, uniformity, and continuity of the feeding, ensures the long-term stable operation of the new equipment, realizes the efficient utilization of the subsequent equipment, reduces the dosage of enzyme preparations, and improves the operating rate.

[0045] According to the present invention, neutral air explosion is used in the cooking reactor without adding acid, which can reduce the corrosion of the equipment. Preferably, the method of neutral air explosion includes: cooking the material after tableting in the presence of medium-pressure steam.

[0046] According to the present invention, preferably, the pressure of the medium-pressure steam is 1.2 - 2 MPa, and the temperature of the medium-pressure steam is 180 - 250 °C.

[0047] According to the present invention, preferably, the cooking time is 15 - 30 min.

[0048] In the preferred case, the solid content in the material obtained after neutral air explosion is 30 - 50 wt%.

[0049] In the preferred case, the yield of cellulose in the material obtained after neutral air explosion is greater than or equal to 90%, and the yield of hemicellulose is greater than or equal to 75%.

[0050] According to the present invention, after the cellulose raw material is pretreated and subjected to neutral air explosion, cellulose and hemicellulose have a high yield. Then, the cellulose and hemicellulose in the material obtained by neutral air explosion are enzymatically hydrolyzed to mainly decompose cellulose and hemicellulose into glucose and pentose.

[0051] According to the present invention, preferably, the enzyme used for enzymatic hydrolysis is cellulase.

[0052] In order to further improve the enzymatic hydrolysis efficiency, preferably, when performing the enzymatic hydrolysis, based on the production of 1 ton of fuel ethanol, the dosage of the cellulase preparation is 180 - 260 kg, preferably 200 - 240 kg.

[0053] According to a preferred embodiment of the present invention, the enzyme used for enzymatic hydrolysis is added in the form of an enzyme solution, and the content of the cellulase preparation in the enzyme solution is 10 - 20 wt%.

[0054] According to a preferred embodiment of the present invention, the product obtained after neutral steam explosion is diluted with water to obtain the material to be enzymatically hydrolyzed, and the dilution degree is such that the solid content in the material to be enzymatically hydrolyzed is 15 - 25 wt%, and then enzymatic hydrolysis is carried out.

[0055] According to the present invention, preferably, the temperature of the enzymatic hydrolysis is 50 - 55 °C, and the time is 60 - 80 h.

[0056] According to a preferred embodiment of the present invention, continuous enzymatic hydrolysis process is adopted for enzymatic hydrolysis.

[0057] According to the present invention, after enzymatic hydrolysis, an enzymatic hydrolysate is obtained, and then Saccharomyces cerevisiae is expanded in the enzymatic hydrolysate, and then the expanded material is introduced into a fermentation tank for batch fermentation; preferably, the inoculation amount for expansion is 10 - 20 V%.

[0058] Preferably, the temperature for expansion is 25 - 30 °C, and the time for expansion is such that the viable cell count in the expanded material is greater than or equal to 200 million cells / ml. More preferably, the time for expansion is 16 - 32 h. Under preferred conditions, the budding rate of Saccharomyces cerevisiae is above 20%, and the mortality rate is less than or equal to 10%.

[0059] According to the present invention, preferably, the temperature of the fermentation is 30 - 33 °C, and the time is 50 - 70 h.

[0060] According to a preferred embodiment of the present invention, batch C5 and C6 fermentation process is adopted for fermentation.

[0061] Under preferred conditions, based on the total volume of the fermentation broth, the content of the alcohol fraction obtained by fermentation is 6 - 8 V%.

[0062] According to the present invention, after fermentation, the mash is rectified to extract anhydrous alcohol. According to a preferred embodiment of the present invention, the rectification method includes: first, the mash is preheated through a mash preheater and then introduced into a rough distillation column for rough distillation, then the side-draw material from the rough distillation column is introduced into the first rectification column for the first rectification, and then the side-draw material from the first rectification column is introduced into the second rectification column for the second rectification; part of the top alcohol vapor of the first rectification column and part of the top alcohol vapor of the second rectification column enter a molecular sieve column for dehydration, and after dehydration, the ethanol gas is condensed and cooled through a cooler, and the condensate is used as finished alcohol and enters the ethanol product tank.

[0063] According to a specific embodiment of the present invention, the rough distillation column operates under negative pressure. The mature mash in the cellulose ethanol section is preheated by a mash preheater respectively and then enters the middle-upper part of the rough distillation column. The waste liquid at the bottom of the column is discharged from the bottom of the rough distillation column, and the rough liquor drawn from the side line of the rough distillation column enters the first rectification column.

[0064] Preferably, the top pressure of the rough distillation column is -0.078 to -0.058 MPaG, and the bottom pressure is -0.058 to -0.038 MPaG; the top temperature is 50 - 55 °C, and the bottom temperature is 80 - 85 °C; the ethanol content in the bottom of the column is less than or equal to 0.04 wt%; the reflux ratio of the rough distillation column is controlled to be 0.5 - 2, and the number of trays is 18 - 35.

[0065] According to a specific embodiment of the present invention, the first rectification column operates under slightly positive pressure. The rough liquor drawn from the side line of the rough distillation column enters the first rectification column, where mass transfer occurs with the rising steam from the bottom of the column on the trays. The alcohol vapor overflows from the top of the column. A part of the overhead gas is condensed and cooled by the reboiler and aftercooler of the rough distillation column as the reflux of the column, and another part enters the molecular sieve dehydration and then goes to the ethanol product tank. The material drawn from the side line of the first rectification column enters the second rectification column.

[0066] Preferably, the top pressure of the first rectification column is 0.06 - 0.08 MPaG, and the bottom pressure is 0.08 - 0.1 MPaG; the top temperature is 90 - 95 °C, and the bottom temperature is 115 - 125 °C; the ethanol content in the bottom of the column is less than or equal to 0.04 wt%; the reflux ratio of the first rectification column is controlled to be 1.5 - 5, and the number of trays is 50 - 80.

[0067] According to a specific embodiment of the present invention, the second rectification column operates under pressure. The material drawn from the side line of the first rectification column enters the second rectification column. Under the action of steam, the alcohol vapor continuously overflows from the top of the second rectification column. A part of the alcohol vapor enters the first rectification column as the reflux through the reboiler of the first rectification column, and another part of the alcohol vapor is heated by the alcohol vapor superheater and then enters the molecular sieve column for dehydration and then goes to the ethanol product tank.

[0068] Preferably, the top pressure of the second rectification column is 0.4 - 0.45 MPaG, and the bottom pressure is 0.44 - 0.45 MPaG; the top temperature is 120 - 130 °C, and the bottom temperature is 150 - 160 °C; the ethanol content in the bottom of the column is less than or equal to 0.04 wt%; the reflux ratio of the second rectification column is controlled to be 3 - 8, and the number of trays is 50 - 85.

[0069] In a specific embodiment of the present invention, in the molecular sieve column, adsorption dehydration is carried out under the conditions of a temperature of 120 - 130 °C and a pressure of 0.04 - 0.05 MPaG.

[0070] After the molecular sieve is adsorbed and dehydrated, the molecular sieve can be regenerated. In a specific embodiment of the present invention, the molecular sieve regeneration is carried out under the condition that the pressure is -0.09 MPaG to -0.07 MPaG.

[0071] The finished alcohol vapor overflows from the upper part of the molecular sieve tower. After the finished alcohol vapor exchanges heat through the product cooler, it is sent to the ethanol product tank.

[0072] In a specific embodiment of the present invention, most of the finished alcohol vapor coming out from the top of the molecular sieve tower is taken out as a product after passing through the cooler, and a small part of the finished alcohol vapor enters another molecular sieve tower to be regenerated, which is used to regenerate the molecular sieve. The light wine formed by the molecular sieve regeneration enters the light wine tank. Two sets of molecular sieve towers are provided. One set of molecular sieve towers is used for dehydration, and the other set of molecular sieve towers is for regeneration. The two sets of molecular sieve towers are alternately used for dehydration.

[0073] According to the present invention, preferably, the finished alcohol vapor used for molecular sieve regeneration accounts for 20-40% of the total volume of the finished alcohol vapor.

[0074] According to the present invention, preferably, the preparation method of fuel ethanol further includes: subjecting the rectified waste mash to plate-and-frame separation to obtain a filter cake and a clear liquid; evaporating the clear liquid to obtain a syrup-containing feed liquid and evaporation condensate, and the evaporation condensate can be recycled as dilution water for the enzymatic hydrolysis unit; the filter cake and the syrup-containing feed liquid enter the biomass boiler. The steam generated in the biomass boiler can be used as a heat source for the rectification unit, the air explosion unit and the drying unit, and the device no longer needs to provide a separate steam heat source, thereby reducing energy consumption and saving costs.

[0075] Preferably, the solid content in the filter cake after plate-and-frame separation is 45-55 wt%, and the solid content in the clear liquid is 2-3 wt%.

[0076] Preferably, the clear liquid after plate-and-frame separation is evaporated in the evaporation system. The evaporation system is a quadruple-effect evaporation. The temperature of the first-effect evaporation is 95-99 °C, and the pressure is 90-99 kPa. The temperature of the second-effect evaporation is 61-70 °C, and the pressure is 30-50 kPa. The temperature of the third-effect evaporation is 52-60 °C, and the pressure is 17-28 kPa; the temperature of the fourth-effect evaporation is 50-55 °C, and the pressure is 12-25 kPa. Under the preferred conditions, the concentration of the syrup in the syrup-containing feed liquid obtained after evaporation is 50-60 wt%.

[0077] According to a preferred embodiment of the present invention, in combination with Figure 1A method for preparing fuel ethanol is described. The preparation method includes the following steps: introducing biomass straw into a coarse crushing unit T1 for the first crushing to obtain the material after the first crushing; introducing the material after the first crushing into a drying unit T2 for drying to obtain the dried material; introducing the dried material into a screening unit T3 for screening to obtain the first screened material with a particle size less than or equal to 5 cm and the second screened material with a particle size greater than 5 cm; introducing the second screened material into a fine crushing unit T4 for the second crushing, mixing the obtained material after the second crushing with the first screened material, and then introducing the mixture into an extrusion unit T5 for tablet pressing to obtain the tableted material. The tableted material is introduced into a pneumatic explosion unit T6 through a screw conveyor for neutral pneumatic explosion. The material after neutral pneumatic explosion is introduced into an enzymatic hydrolysis unit T7 for enzymatic hydrolysis, and then Saccharomyces cerevisiae is inoculated into the enzymatic hydrolysate for amplification culture. The material after amplification culture is fermented in a fermentation unit T8, and then the mash obtained after fermentation is introduced into a rectification unit T9 for rectification to extract anhydrous alcohol. The waste mash after rectification is introduced into a separation unit T10 for separation to obtain a filter cake and a clear liquid; the clear liquid is introduced into an evaporation unit T11 for evaporation to obtain a syrup-containing feed liquid and evaporation condensate. The evaporation condensate is recycled as dilution water for the enzymatic hydrolysis unit T7, and the syrup-containing feed liquid and the filter cake are introduced into a biomass boiler T12. Part of the steam generated by the biomass boiler is used as a heat source for the rectification unit T9, part is used as a heat source for the pneumatic explosion unit T6, and part is used as a heat source for the drying unit T2. The pneumatic explosion waste gas of the pneumatic explosion unit T6 is used as a heat source for the evaporation equipment of the evaporation unit T11.

[0078] The pressures in the present invention are all gauge pressures.

[0079] The present invention will be described in detail below through examples and comparative examples. In the following examples, unless otherwise specified, all are conventional methods; the reagents and materials used, unless otherwise specified, can be obtained from commercial channels.

[0080] The following examples are used to illustrate the method for preparing fuel ethanol.

[0081] Example 1

[0082] A cellulose ethanol plant with a scale of 30,000 tons / year and an annual operating time of 8,000 hours

[0083] Raw material pretreatment:

[0084] In the coarse crushing unit, corn straw (with a moisture content of 15 wt%, an impurity content of about 10 wt%, and a bulk density of 25 kg / m 3)The first crushing is carried out in a crusher. After the first crushing, in the material, the content of the material with a particle size of 3 - 5 cm is 85 wt%, the content of the material with a particle size less than 3 cm is 5 wt%, and the content of the material with a particle size greater than 5 cm is 10 wt%. In the drying unit, the material after the first crushing is dried in a drum dryer, and the water content of the material at the outlet of the drum dryer is 20 wt%. In the screening unit, the dried material is screened by a rotary screen device to obtain the first screened material with a particle size less than or equal to 5 cm and the second screened material with a particle size greater than 5 cm. In the fine crushing unit, the second screened material with a particle size greater than 5 cm is crushed for the second time in a crusher. After the second crushing, in the material, the content of the material with a particle size of 3 - 5 cm is 88 wt%, the content of the material with a particle size less than 3 cm is 4 wt%, and the content of the material with a particle size greater than 5 cm is 8 wt%. The material after the second crushing and the first screened material with a particle size less than or equal to 5 cm are mixed. In the extrusion unit, the mixed material is tableted by a straw tablet press. The particle size of the tableted material is 4 cm, the thickness is 6 mm, and the bulk density of the tableted material is 650 kg / m 3 。

[0085] Neutral explosion puffing:

[0086] The tableted material enters the cooking reactor of the explosion puffing equipment through a regulating valve. In the presence of medium-pressure steam with a pressure of 1.5 MPa and a temperature of 220 °C, the tableted material is cooked for 20 min; the solid content in the material obtained after neutral explosion puffing is 45 wt%, the cellulose yield in the material obtained after neutral explosion puffing is 90%, and the hemicellulose yield is 75%.

[0087] Enzymatic hydrolysis:

[0088] The neutral explosion puffing product is diluted with water to obtain the material to be enzymatically hydrolyzed, and the dilution degree is such that the solid content in the material to be enzymatically hydrolyzed is 20 wt%. A continuous enzymatic hydrolysis process is adopted, and the material to be enzymatically hydrolyzed is enzymatically hydrolyzed using a cellulase solution (the content of cellulase preparation in the enzyme solution is 15 wt%) at a temperature of 50 °C for 70 h. An enzymatic hydrolysate is obtained.

[0089] Fermentation:

[0090] Saccharomyces cerevisiae (Angel yeast) is inoculated into the enzymatic hydrolysate (inoculation amount 15 V%), and expanded cultivation is carried out at a temperature of 25 °C for 18 h. The viable cell count in the material after expanded cultivation is 200 million cells / ml, the budding rate of Saccharomyces cerevisiae is 20%, and the mortality rate is 10%. Then the material after expanded cultivation is fermented by an intermittent C5 fermentation process at a temperature of 32 °C for 60 h. The ethanol content in the obtained fermentation broth is 6.5 V%.

[0091] Rectification to extract anhydrous alcohol:

[0092] After the fermented mature mash is preheated by a mash preheater respectively, it enters the middle-upper part of the rough distillation column for rough distillation, and the waste liquid at the bottom of the column is discharged from the bottom of the rough distillation column. The top pressure of the rough distillation column is -0.068 MPaG, and the bottom pressure is -0.048 MPaG; the top temperature is 52.4 °C, and the bottom temperature is 83 °C; the ethanol content in the bottom of the column is 0.04 wt%; the reflux ratio is 1; the number of trays is 26.

[0093] The rough liquor drawn from the side line of the rough distillation column enters the first rectification column for the first rectification. The top pressure of the first rectification column is 0.07 MPaG, and the bottom pressure is 0.0935 MPaG; the top temperature is 93 °C, and the bottom temperature is 119.5 °C; the ethanol content in the bottom of the column is 0.04 wt%; the reflux ratio is 2.6; the number of trays is 64. Under the action of steam, the alcohol vapor overflows from the top of the first rectification column. Part of it enters the first rectification column as reflux through the reboiler of the rough distillation column, and the other part of the alcohol vapor is heated by the alcohol vapor superheater and then enters the molecular sieve column for dehydration at a temperature of 125 °C and a pressure of 0.045 MPaG.

[0094] The material drawn from the side line of the first rectification column enters the second rectification column for the second rectification. The top pressure of the second rectification column is 0.42 MPaG, and the bottom pressure is 0.445 MPaG; the top temperature is 126.6 °C, and the bottom temperature is 155.4 °C; the ethanol content in the bottom of the column is 0.04 wt%; the reflux ratio is 3.8; the number of trays is 72. Mass transfer occurs with the rising steam at the bottom of the column on the trays, and the alcohol vapor overflows from the top of the column. The alcohol vapor at the top of the column is used as the heat source for the first rectification. The alcohol vapor at the top of the column serves as the heat source for the reboiler at the bottom of the first rectification column, and then enters the cooler. Part of the cooled material is used as the reflux of the first rectification column, and the other part is drawn out and enters the molecular sieve column for dehydration at a temperature of 125 °C and a pressure of 0.045 MPaG.

[0095] After the alcohol vapor overflowing from the tops of the first rectification column and the second rectification column is dehydrated in the molecular sieve column, finished wine gas with an alcohol content of 25 V% is obtained at the top of the molecular sieve column. Part of the finished wine gas is heat-exchanged through a product cooler and then enters the ethanol product tank for storage. The other part of the finished wine gas enters another molecular sieve column to be regenerated for regenerating the molecular sieve. The pressure for molecular sieve regeneration is -0.08 MPaG, and the formed weak wine enters the weak wine tank. The finished wine gas used for molecular sieve regeneration accounts for 30% of the total volume of the finished wine gas.

[0096] Waste mash separation:

[0097] The rectified spent mash liquid is subjected to plate and frame filtration to obtain a filter cake (solid content of 50 wt%) and a clear liquid (solid content of 2.5 wt%); the clear liquid is subjected to four-effect evaporation in an evaporation system. The temperature of the first-effect evaporation is 98 °C and the pressure is 95 kPa, the temperature of the second-effect evaporation is 70 °C and the pressure is 45 kPa, the temperature of the third-effect evaporation is 55 °C and the pressure is 20 kPa; the temperature of the fourth-effect evaporation is 53 °C and the pressure is 18 kPa, to obtain a syrup-containing feed liquid (syrup concentration of 60 wt%) and evaporation condensate. The evaporation condensate is recycled as dilution water for the enzymatic hydrolysis unit, and the filter cake and the syrup-containing feed liquid enter a biomass boiler. The steam generated in the biomass boiler serves as the heat source for the rectification unit, the air explosion unit and the drying unit.

[0098] Example 2

[0099] Fuel ethanol is prepared according to the method of Example 1, except that during the pretreatment of corn stover, the degree of the first pulverization is different. Specifically, "in the material after the first pulverization, the content of the material with a particle size of 3 - 5 cm is 90 wt%, the content of the material with a particle size less than 3 cm is 3 wt%, and the content of the material with a particle size greater than 5 cm is 7 wt%" is used to replace "in the material after the first pulverization, the content of the material with a particle size of 3 - 5 cm is 85 wt%, the content of the material with a particle size less than 3 cm is 5 wt%, and the content of the material with a particle size greater than 5 cm is 10 wt%". The fuel ethanol is obtained.

[0100] Example 3

[0101] Fuel ethanol is prepared according to the method of Example 1, except that during the pretreatment of corn stover, the degree of flaking is different. Specifically, "the particle size of the material after flaking is 5 cm, the thickness is 10 mm, and the bulk density of the material after flaking is 500 kg / m 3 " is used to replace "the particle size of the material after flaking is 4 cm, the thickness is 6 mm, and the bulk density of the material after flaking is 650 kg / m 3 ". The fuel ethanol is obtained.

[0102] Example 4

[0103] Fuel ethanol is prepared according to the method of Example 1, except that during the pretreatment of corn stover, the degree of the first pulverization is different. Specifically, "in the material after the first pulverization, the content of the material with a particle size of 3 - 5 cm is 80 wt%, the content of the material with a particle size less than 3 cm is 10 wt%, and the content of the material with a particle size greater than 5 cm is 10 wt%" is used to replace "in the material after the first pulverization, the content of the material with a particle size of 3 - 5 cm is 85 wt%, the content of the material with a particle size less than 3 cm is 5 wt%, and the content of the material with a particle size greater than 5 cm is 10 wt%". The fuel ethanol is obtained.

[0104] Example 5

[0105] Fuel ethanol was prepared according to the method of Example 1, except that during the pretreatment of corn stover, the degree of drying was different. Specifically, the content of water in the material at the outlet of the drum dryer was 30 wt% was used to replace the content of water in the material at the outlet of the drum dryer was 20 wt%. Fuel ethanol was obtained.

[0106] Example 6

[0107] Fuel ethanol was prepared according to the method of Example 1, except that during the pretreatment of corn stover, the degree of the second pulverization was different. Specifically, the content of the material with a particle size of 3 - 5 cm in the material after the second pulverization was 80 wt%, the content of the material with a particle size less than 3 cm was 10 wt%, and the content of the material with a particle size greater than 5 cm was 10 wt% was used to replace the content of the material with a particle size of 3 - 5 cm in the material after the second pulverization was 88 wt%, the content of the material with a particle size less than 3 cm was 4 wt%, and the content of the material with a particle size greater than 5 cm was 8 wt%. Fuel ethanol was obtained.

[0108] Example 7

[0109] Fuel ethanol was prepared according to the method of Example 1, except that the conditions of neutral explosion were different. Specifically, in the presence of medium-pressure steam with a pressure of 1.5 MPa and a temperature of 160 °C was used to replace in the presence of medium-pressure steam with a pressure of 1.5 MPa and a temperature of 220 °C. Fuel ethanol was obtained.

[0110] Comparative Example 1

[0111] A traditional method for preparing fuel ethanol was adopted, with a 30,000-ton / year cellulose ethanol plant designed for 8,000 hours of operation time.

[0112] Corn stover with a flow rate of 20 dry tons / hour (straw moisture content 15 wt%, impurity content about 10 wt%, bulk density 25 kg / m 3 ) was pulverized. In the pulverized material, the content of the material with a length of 3 - 5 cm was 30 wt%, the content of the material with a length greater than or equal to 10 cm was 20 wt%, and the content of the material with a length less than 3 cm was 30 wt%; the bulk density of the pulverized material was 30 kg / m 3 .

[0113] Then, a roller sieve is used for rolling dust removal, which is carried out under normal pressure and normal temperature. The rotation speed of the roller sieve is 12 revolutions, and 50% of the dust is removed. After impurity removal, the material enters the silo for buffer storage. The crushed material is transported to a pin drum meter for metering, and then enters a mixed acid screw. Sulfuric acid with a concentration of 2.5 wt% is sprayed into the mixed acid screw, and the dosage of sulfuric acid makes the weight ratio of the crushed material to sulfuric acid 1:1. After mixing with the acid, the material enters the air explosion equipment. The straw is extruded by a feeder (the solid content in the extruded material is 50 wt%), and undergoes an acidic air explosion reaction with the acid in a digester. The air explosion reaction conditions are the same as those in Example 1.

[0114] Enzymatic hydrolysis:

[0115] The acidic air explosion product is diluted with water to obtain the material to be enzymatically hydrolyzed, and the dilution degree makes the solid content in the material to be enzymatically hydrolyzed 20 wt%. A continuous enzymatic hydrolysis process is adopted, and cellulase solution (the composition of the enzyme solution is the same as that in Example 1) is used to carry out enzymatic hydrolysis at a temperature of 50 °C for 64 h. An enzymatic hydrolysate is obtained.

[0116] Fermentation:

[0117] Saccharomyces cerevisiae (Angel yeast) is inoculated into the enzymatic hydrolysate (inoculation amount 15 V%), and expanded cultivation is carried out at a temperature of 25 °C for 15 h. The viable cell count in the material after expanded cultivation is 200 million cells / ml, the budding rate of Saccharomyces cerevisiae is 20%, and the mortality rate is 10%. Then, the material after expanded cultivation is fermented by an intermittent C5 fermentation process at a temperature of 32 °C for 60 h.

[0118] The method for separating anhydrous alcohol and waste mash liquor by rectification extraction is the same as that in Example 1.

[0119] Test example

[0120] The start-up rate of the device, the dosage of enzyme preparation, the yields of cellulose and hemicellulose after air explosion, the ethanol content in the fermentation broth, and the operation load of the device in each example and comparative example are measured respectively. The results are shown in Table 1.

[0121] 1) Start-up rate % = start-up time (hours) ÷ 8000 × 100%;

[0122] 2) Cellulose yield % = (mass of dry matter in the material after air explosion per hour × mass percentage of cellulose) ÷ (mass of the material after tabletting per hour × mass percentage of cellulose) × 100%;

[0123] 3) Hemicellulose yield % = (mass of dry matter in the material after air explosion per hour × mass percentage of hemicellulose) ÷ (mass of the material after tabletting per hour × mass percentage of hemicellulose) × 100%;

[0124] 4) The ethanol content in the fermentation broth was measured by liquid chromatography;

[0125] 5) Operating load % = (amount of fuel ethanol produced per hour) ÷ (designed amount of fuel ethanol per hour) × 100%.

[0126] Table 1

[0127]

[0128] It can be seen from the results in Table 1 that Examples 1-7 of preparing fuel ethanol by using the method provided by the present invention have a relatively high plant start-up rate and operating load, a relatively high cellulose and hemicellulose yield after air explosion, a relatively high ethanol content in the obtained fermentation broth, and a relatively low enzyme preparation dosage. For Comparative Example 1 of preparing fuel ethanol by using a traditional method, the plant start-up rate and the operating load of the plant are significantly reduced, the cellulose and hemicellulose yields after air explosion are significantly reduced, the ethanol content in the obtained fermentation broth is significantly reduced, and the enzyme preparation dosage also increases.

[0129] In addition, in Example 4, the degree of the first pulverization during the pretreatment of corn stover was changed; in Example 5, the degree of drying during the pretreatment of corn stover was changed; in Example 6, the degree of the second pulverization during the pretreatment of corn stover was changed. Compared with Example 1, the plant start-up rate and the operating load in Examples 4-6 are both reduced, the cellulose and hemicellulose yields after air explosion are both reduced, the ethanol content in the obtained fermentation broth is both reduced, and the enzyme preparation dosage is both increased; in Example 7, the conditions of neutral air explosion were changed. Compared with Example 1, although the plant start-up rate in Example 7 did not decrease, the operating load of the plant decreased, the cellulose and hemicellulose yields after air explosion decreased, the ethanol content in the obtained fermentation broth decreased, and the enzyme preparation dosage increased. This shows that when the degree of the first pulverization and the second pulverization, the degree of drying, and the conditions of neutral air explosion during the pretreatment of cellulose raw materials meet the preferred conditions, the plant start-up rate and the operating load of the plant can be further improved, the cellulose and hemicellulose yields after air explosion can be further improved, the ethanol content in the fermentation broth can be further improved, and the enzyme preparation dosage can be further reduced.

[0130] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing fuel ethanol, characterized in that, The preparation method comprises the following steps: pretreating the cellulose raw material, followed by medium-pressure explosion, enzymatic hydrolysis, fermentation, and rectification; wherein, The pretreatment method comprises: S1. Crushing the cellulose raw material for the first time to obtain the material after the first crushing; S2. Drying the material after the first crushing to obtain the dried material; S3. Screening the dried material to obtain the first screened material with a particle size less than or equal to 5 cm and the second screened material with a particle size greater than 5 cm; S4. Crushing the second screened material for the second time, and mixing the material obtained after the second crushing with the first screened material to obtain a mixed material; S5. Tabletting the mixed material.

2. The preparation method according to claim 1, characterized in that, In S1, the conditions of the first crushing are such that the content of the material with a particle size of 3 - 5 cm in the material after the first crushing is greater than or equal to 85 wt%; Preferably, the conditions of the first crushing are such that the content of the material with a particle size less than 3 cm in the material after the first crushing is less than or equal to 5 wt%, and the content of the material with a particle size greater than 5 cm is less than or equal to 10 wt%; Preferably, the cellulose raw material is straw, preferably corn straw and / or wheat straw.

3. The preparation method according to claim 1 or 2, characterized in that, In S2, the conditions of the drying are such that the water content in the dried material is 10 - 25 wt%.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In S4, the conditions of the second crushing are such that the content of the material with a particle size of 3 - 5 cm in the material after the second crushing is greater than or equal to 85 wt%; Preferably, the conditions of the second crushing are such that the content of the material with a particle size less than 3 cm in the material after the second crushing is less than or equal to 5 wt%, and the content of the material with a particle size greater than 5 cm is less than or equal to 10 wt%.

5. The preparation method according to any one of claims 1-4, characterized in that, In S5, the conditions of the tabletting are such that the particle size of the material after tabletting is 3 - 5 cm and the thickness is 2 - 10 mm.

6. The preparation method according to any one of claims 1-5, characterized in that, The method of medium-pressure explosion comprises: steaming the material after tabletting in the presence of medium-pressure steam.

7. The preparation method according to claim 6, characterized in that, The pressure of the medium-pressure steam is 1.2 - 2 MPa, and the temperature of the medium-pressure steam is 180 - 250 °C; Preferably, the steaming time is 15 - 30 min.

8. The preparation method according to any one of claims 1-7, characterized in that, The temperature of the enzymatic hydrolysis is 50 - 55 °C, and the time is 60 - 80 h.

9. The preparation method according to claim 8, wherein When carrying out the enzymatic hydrolysis, based on the production of 1 ton of fuel ethanol, the dosage of the cellulase preparation is 180 - 260 kg, preferably 200 - 240 kg.

10. The preparation method according to any one of claims 1-9, characterized in that, The temperature of the fermentation is 30 - 33 °C, and the time is 50 - 70 h.

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