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 gas explosion, enzymolysis, fermentation and rectification; the pretreatment method comprises the following steps: S1, winnowing a cellulose raw material to obtain a winnowed material; s2, the materials obtained after winnowing are smashed, and smashed materials are obtained; s3, the crushed materials are subjected to acid pickling and then drained, and drained materials are obtained; and S4, performing primary extrusion on the drained materials. According to the method provided by the invention, the feeding stability of a feeder and the process stability of gas explosion equipment are ensured, so that the efficient utilization of subsequent equipment is realized, the dosage of an enzyme preparation is reduced, and the operating rate is improved.

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] As a biomass material, straw comes from farmland and contains impurities such as large stones, iron blocks, sand, and soil. As a solid material, straw has a relatively low bulk density, with typical data of 45 - 50 g / L (in the case of 15 - 20% moisture). During transportation, it has a large volume, and the raw materials are prone to fluctuations, the materials are easy to float, and the workshop environment is poor. The water content in the straw raw materials is also unstable. Throughout the year, the water content of straw fluctuates with climate change, ranging from 10 - 45%, and the change in moisture also affects the bulk density. The ratio of straw leaves, stems, and straw pith in the raw materials also varies with different round bales / square bales or batches, resulting in different bulk densities. The instability and non-uniformity of moisture affect the stability and uniformity of acid addition in subsequent cooking equipment; thus, affecting the gas explosion recovery rate and effect of the steam generator, and the instability of the material bulk density directly affects the stability and load of the key equipment in the pretreatment process.

[0003] One of the core equipment in the pretreatment section is the feeder of the gas explosion equipment. Straw under normal pressure is pressurized in this equipment and then enters the gas explosion equipment for gas explosion. This feeder requires a stable, uniform, and continuous supply of straw. However, in practical operation, in the dry pretreatment process, due to the low bulk density of straw, the volume of the straw material fluctuates greatly, and the material transportation is in a pulsating fluctuation, resulting in large fluctuations in the operation of the feeder, unable to feed evenly and stably, and prone to blockage. The blockage of the feeder correspondingly affects the process stability of the cooking reactor, and the discharge port of the gas explosion equipment is prone to coking and blockage. Subsequently, it affects the stable and efficient operation of subsequent units such as enzymatic hydrolysis and the start-up rate of the entire device.

[0004] Therefore, there is an urgent need for a fuel ethanol preparation process that can improve the stability of the feeder feeding, thereby improving the process stability of the gas explosion equipment, and further enabling subsequent equipment to be efficiently utilized, reducing the dosage of enzyme preparations, and increasing the start-up rate. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems in the prior art that the bulk density of biomass raw materials is relatively low and unstable, resulting in the inability of the gas explosion equipment to operate stably and continuously, and thus the subsequent equipment has low utilization efficiency and high dosage of enzyme preparations. A method for preparing fuel ethanol is provided. In this preparation method, the cellulose raw material after pretreatment has a relatively high and stable bulk density, thereby improving the stability of the feeder feeding and the process stability of the gas explosion equipment.

[0006] To achieve the above purpose, the present invention provides a method for preparing fuel ethanol, wherein the preparation method includes the following steps: pretreating the cellulose raw material, and then performing gas explosion, enzymatic hydrolysis, fermentation, and rectification; wherein,

[0007] The pretreatment method includes:

[0008] S1. Conduct air separation on the cellulose raw material to obtain the material after air separation;

[0009] S2. Crush the material after air separation to obtain the crushed material;

[0010] S3. Pickle the crushed material, and then drain the water to obtain the material after draining;

[0011] S4. Conduct the first extrusion on the material after draining.

[0012] Through the above technical solution, the beneficial effects of the present invention at least include:

[0013] The method provided by the present invention removes heavy impurities such as stones, iron blocks, and sand in the cellulose raw material through air separation, ensuring the cleanliness of the material, the stable start-up of the device, reducing valve blockage and pipeline wear, and ensuring the continuity of the device operation; through the pickling process and extrusion equipment, the uniformity of adding acid to the material and the moisture uniformity of the material in the feeder are ensured, thereby ensuring the stability of air explosion and the yields of cellulose and hemicellulose, realizing the efficient utilization of subsequent equipment, reducing the dosage of enzyme preparation, and increasing the start-up rate. The start-up rate is increased from 60 - 70% to over 85%; the yield of cellulose after air explosion is increased to over 90%, and the yield of hemicellulose is increased to over 80%; the device load is also increased from 60 - 70% to over 85% full load; the dosage of enzyme preparation is reduced by over 8%. In addition, after the material is pickled, the bulk density increases, the volume is compacted, and there is no longer the situation that the material floats in the air and part of it lands during the conveying process, ensuring the safety of the device and improving the environment of the device.

[0014] In the preferred embodiment of the present invention, the method provided by the present invention makes full use of heat. The wet distillers grains are separated and the syrup is evaporated and sent to the biomass boiler. The biomass boiler provides steam for the whole device, providing steam heat sources for the circulating acid solution, the air explosion unit, and the rectification unit. The whole device does not need to provide steam separately, reducing energy consumption and saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flow chart of the preparation method of fuel ethanol in a preferred embodiment of the present invention

[0016] DESCRIPTION OF THE REFERENCE NUMERALS

[0017] T1 Air Separator T2 Crusher T3 Rotary Drum Washer T4 Acid Solution Recovery Plate Frame

[0018] T5 Extrusion Unit T6 Air Explosion Unit T7 Enzymatic Hydrolysis Unit T8 Fermentation Unit

[0019] T9 Rectification Unit, T10 Separation Unit, T11 Evaporation Unit, T12 Biomass Boiler Detailed Implementation Manner

[0020] In the ranges disclosed herein, the endpoints and any values 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, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0021] 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 air explosion, enzymatic hydrolysis, fermentation and rectification; among them,

[0022] The pretreatment method includes:

[0023] S1. Perform air separation on the cellulose raw material to obtain the air-separated material;

[0024] S2. Crush the air-separated material to obtain the crushed material;

[0025] S3. Perform acid washing on the crushed material, and then perform water drainage to obtain the water-drained material;

[0026] S4. Perform the first extrusion on the water-drained material.

[0027] The method provided by the present invention removes heavy impurities such as stones, iron blocks and sand through air separation, ensuring the cleanliness of the material, ensuring the stable start-up of the device, and also reducing the wear of equipment and pipelines and the blockage of the equipment by materials; through the acid washing process and the first extrusion, the uniformity of adding acid to the cellulose raw material and the moisture uniformity of the material in the feeder are ensured. Due to the stability and uniformity of the feeding, the feeding stability of the feeder and the process stability of the air explosion equipment are ensured, thereby realizing the efficient utilization of subsequent equipment, reducing the dosage of enzyme preparations, and improving the start-up rate. In addition, after the material is acid-washed, the bulk density increases, the volume is compacted, and there is no longer the situation that the material floats in the air and part of it lands during the transportation process, ensuring the safety of the device and improving the environment of the device.

[0028] According to the present invention, preferably, the cellulose raw material is straw, preferably corn straw and / or wheat straw.

[0029] In the present invention, air separation can adopt conventional equipment in the art. For example, an air separator can be used for air separation to remove heavy impurities such as stones, iron blocks and sand, and preliminarily ensure the cleanliness of the material. Preferably, the air separator operates at normal temperature and pressure.

[0030] In order to further improve the removal rate of heavy impurities such as stones, iron blocks, and sand, and further improve the yield of cellulose raw materials, preferably, the aperture of the sieve holes of the screen of the air classifier is 5-8 mm.

[0031] The present invention does not particularly limit the material of the screen of the air classifier. For example, a screen made of 304 stainless steel can be used.

[0032] In order to further improve the removal rate of heavy impurities such as stones, iron blocks, and sand, and further improve the yield of cellulose raw materials, preferably, the air separation speed of the air classifier is 5-20 m / s, preferably 10-15 m / s.

[0033] In the preferred case, the yield of cellulose raw materials in the material after air separation is greater than or equal to 98%; the removal rate of heavy impurities such as stones, iron blocks, and sand is 95-98%.

[0034] 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. Preferably, the crusher operates at normal temperature and pressure.

[0035] In order to further increase the bulk density of the material, preferably, in S2, the crushing conditions are such that the content of the material with a length of 3-5 cm in the crushed material is greater than or equal to 85 wt%, preferably 85-95 wt%.

[0036] Furthermore, the crushing conditions are such that the content of the material with a length greater than or equal to 10 cm in the crushed material is less than or equal to 10 wt%, preferably 2-5 wt%; the content of the material with a length less than or equal to 2 cm in the crushed material is less than or equal to 10 wt%, preferably 2-5 wt%.

[0037] According to the present invention, preferably, in S3, the pickling method includes: rinsing the crushed material with an acid solution; wherein, the amount of the acid solution is such that the weight ratio of the crushed material to the acid solution is (3-5):100.

[0038] In order to further improve the pickling effect and further improve the uniformity of adding acid to the cellulose raw material, preferably, the acid content in the acid solution is less than or equal to 5 wt%, preferably 1-3 wt%.

[0039] In order to further improve the pickling effect and further improve the uniformity of adding acid to the cellulose raw material, preferably, the temperature of the acid solution is 40-50 °C, preferably 43-46 °C.

[0040] In the present invention, pickling can be carried out using conventional equipment in the art. For example, pickling can be carried out in a drum washer.

[0041] To further remove excess moisture, preferably, the conditions for draining water are such that the solid content in the material after draining water is 10 - 20 wt%, preferably 12 - 20 wt%.

[0042] In the present invention, draining water can be carried out using conventional equipment in the art. For example, a draining screw machine can be used for draining water. In a preferred embodiment of the present invention, the acid solution drained out is recovered and reused in the drum washer for pickling.

[0043] To further improve the moisture uniformity of the material entering the feeder, so that equipment such as a digester can operate more stably for a long time, preferably, in S4, the conditions for the first extrusion are such that the solid content in the material after the first extrusion is 20 - 30 wt%, preferably 25 - 30 wt%.

[0044] In the present invention, the first extrusion can be carried out using conventional extrusion equipment in the art. For example, a screw extrusion equipment can be used for extrusion.

[0045] According to the present invention, preferably, the method of steam explosion includes: subjecting the material after the first extrusion to a second extrusion to obtain the material after the second extrusion, and then steaming the material after the second extrusion in the presence of medium-pressure steam.

[0046] According to the present invention, preferably, the second extrusion is carried out in the feeder of the steam explosion device, and the material after the second extrusion enters the steamer of the steam explosion device for steaming; the conditions for the second extrusion are such that the solid content in the material after the second extrusion is 40 - 60 wt%, preferably 45 - 55 wt%. The second extrusion extrudes the excess moisture, which is beneficial for forming a solid plug in the feeder, preventing the steam in the steamer from spraying back from the feeder inlet, and providing stable feeding for the reaction under high temperature and high pressure in the digester.

[0047] Adopting the pickling process and extrusion equipment (for the first extrusion) ensures the moisture uniformity of the material entering the feeder and the uniformity of acid addition. Due to the stability and uniformity of the feeding, the process stability and high efficiency of the steam explosion equipment are ensured.

[0048] To further improve the steam explosion efficiency, further increase the content of cellulose and hemicellulose in the product after steam explosion, and thus further improve the enzymatic hydrolysis effect, preferably, the conditions for steaming include: the pressure of the medium-pressure steam is 0.6 - 1 MPa, the temperature of the medium-pressure steam is 160 - 200 °C, and the steaming time is 10 - 60 min.

[0049] Furthermore, the conditions for steaming include: the pressure of the medium-pressure steam is 0.6 - 0.8 MPa, the temperature of the medium-pressure steam is 170 - 180 °C, and the steaming time is 15 - 30 min.

[0050] Preferably, the solid content in the material after air explosion is 30-50 wt%, and more preferably, the solid content in the material after air explosion is 32-36 wt%.

[0051] Preferably, the yield of cellulose in the material after air explosion is greater than or equal to 90%, and the yield of hemicellulose is greater than or equal to 80%.

[0052] According to the present invention, after the cellulose raw material is pretreated and subjected to air explosion, cellulose and hemicellulose have a high yield. Then, the cellulose and hemicellulose in the material obtained by acid air explosion are enzymatically hydrolyzed, and the cellulose and hemicellulose are mainly decomposed into glucose and pentose.

[0053] According to the present invention, preferably, the enzyme used for the enzymatic hydrolysis is cellulase.

[0054] In order to further improve the enzymatic hydrolysis efficiency, when performing the enzymatic hydrolysis, based on the production of 1 ton of fuel ethanol, the dosage of the cellulase preparation is 100-300 kg, preferably 180-220 kg.

[0055] According to a preferred embodiment of the present invention, the cellulase used for the 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%.

[0056] According to a preferred embodiment of the present invention, the product obtained after air 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 performed.

[0057] According to the present invention, preferably, the temperature of the enzymatic hydrolysis is 50-55 °C, and the time is 60-80 h.

[0058] According to a preferred embodiment of the present invention, continuous enzymatic hydrolysis process is used for the enzymatic hydrolysis.

[0059] 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 fed into a fermentation tank for batch fermentation; preferably, the inoculation amount for the expansion is 12-18 V%.

[0060] Preferably, the temperature for the expansion is 25-30 °C, and the time for the 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 the expansion is 16-32 h. Preferably, the budding rate of Saccharomyces cerevisiae is above 20%, and the mortality rate is less than or equal to 10%.

[0061] Preferably, the temperature of the fermentation is 30-33 °C, and the time is 50-70 h.

[0062] According to a preferred embodiment of the present invention, an intermittent C5 and C6 fermentation process is used for fermentation.

[0063] Preferably, based on the total volume of the fermentation broth, the alcohol content in the fermented product is 6-8V%.

[0064] 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 preheating the mash through a mash preheater and then introducing it into a rough distillation column for rough distillation, then introducing the side-drawn material from the rough distillation column into the first rectification column for the first rectification, and then introducing the side-drawn material from the first rectification column 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 by a condenser, and the condensate enters the ethanol product tank as finished alcohol.

[0065] According to a specific embodiment of the present invention, the rough distillation column operates under negative pressure. The mature mash in the cellulosic ethanol section is preheated through a mash preheater respectively and then enters from 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 side-drawn from the rough distillation column enters the first rectification column.

[0066] 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.

[0067] According to a specific embodiment of the present invention, the first rectification column operates under slightly positive pressure. The rough liquor side-drawn from 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, and the alcohol vapor overflows from the top of the column. Part of the top gas is condensed and cooled by the reboiler and after-cooler of the rough distillation column as the reflux of the column, and the other part enters the molecular sieve for dehydration and then goes to the ethanol product tank. The side-drawn material from the first rectification column enters the second rectification column.

[0068] 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.

[0069] According to a specific embodiment of the present invention, the second rectification column operates under pressure. The side-draw material of the first rectification column enters the second rectification column. Under the action of steam, alcohol vapor continuously overflows from the top of the second rectification column. A part of the alcohol vapor enters the first rectification column as reflux through the first rectification column reboiler, 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.

[0070] 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 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.

[0071] 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.

[0072] After the molecular sieve adsorption dehydration, the molecular sieve can be regenerated. In a specific embodiment of the present invention, the molecular sieve regeneration is carried out under the condition of a pressure of -0.09 MPaG to -0.07 MPaG.

[0073] The finished product alcohol vapor overflows from the upper part of the molecular sieve column. After the finished product alcohol vapor exchanges heat through the product cooler, it is sent to the ethanol product tank.

[0074] In a specific embodiment of the present invention, most of the finished product alcohol vapor coming out from the top of the molecular sieve column is taken out as a product after passing through the cooler, and a small part of the finished product alcohol vapor enters another molecular sieve column to be regenerated for regenerating the molecular sieve. The light alcohol formed by the molecular sieve regeneration enters the light alcohol tank. Two sets of molecular sieve columns are provided. One set of molecular sieve column is used for dehydration, and the other set of molecular sieve column is for regeneration. The two sets of molecular sieve columns are used for dehydration alternately.

[0075] According to the present invention, preferably, the finished product alcohol vapor used for molecular sieve regeneration accounts for 20 - 40% of the total volume of the finished product alcohol vapor.

[0076] 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 circulating acid liquid in the pretreatment part, the air explosion unit, the rectification unit, etc. The device no longer needs to provide a separate steam heat source, thereby reducing energy consumption and saving costs.

[0077] 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%.

[0078] Preferably, the clear liquid after plate-and-frame separation is evaporated in an evaporation system under the following conditions. The evaporation system is a quadruple-effect evaporation system. 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 21 - 30 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. In the preferred case, the concentration of syrup in the syrup-containing feed liquid obtained after evaporation is 50 - 60 wt%.

[0079] According to a preferred embodiment of the present invention, in combination with Figure 1 The preparation method of fuel ethanol is described as follows. The preparation method includes the following steps: Biomass straw is sequentially subjected to air separation in an air separator T1, crushing in a crusher T2, pickling in a rotary drum washer T3. After pickling, the material is drained by a draining screw conveyor and then enters an extrusion unit T5 for the first extrusion. The acid solution drained by the draining screw conveyor enters an acid solution recovery plate-and-frame T4 for acid solution recovery and is reused in the rotary drum washer T3 for pickling. After the first extrusion, the material enters the feeder of a pneumatic explosion unit T6 for the second extrusion, and then enters the steamer of the pneumatic explosion unit T6 for cooking. The material after pneumatic explosion is introduced into an enzymatic hydrolysis unit T7 for enzymatic hydrolysis to obtain an enzymatic hydrolysate. Then, Saccharomyces cerevisiae is inoculated into the enzymatic hydrolysate for expansion culture. The expanded material is fermented in a fermentation unit T8, and then the fermented mash 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 reused as dilution water for the enzymatic hydrolysis unit T7. 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 T12 is used as the heat source for the rectification unit T9, part is used as the heat source for the pneumatic explosion unit T6, and part is used as the heat source for the circulating acid solution. The waste gas after pneumatic explosion in the steamer of the pneumatic explosion unit T6 is used as the heat source for the evaporator of the evaporation unit T11, realizing the heat utilization of the waste gas and saving steam consumption.

[0080] The pressures in the present invention are all gauge pressures.

[0081] 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.

[0082] The following examples are used to illustrate the preparation method of fuel ethanol.

[0083] Example 1

[0084] A 30,000-ton / year cellulose ethanol plant with an annual operating time of 8,000 hours.

[0085] Cellulose raw material pretreatment:

[0086] Corn straw (corn straw flow rate: 20 dry tons / hour, moisture content: 20 wt%, impurity content: 10 wt%) is subjected to air separation by an air separator at normal temperature and pressure. The aperture of the sieve holes of the sieve mesh of the air separator is 6 mm, the material of the sieve mesh is 304 stainless steel, and the air separation speed of the air separator is 13 m / s. Heavy impurities such as stones, iron blocks, and sand are removed. The yield of corn straw in the material after air separation is 98%; through weight measurement, the removal rate of heavy impurities such as stones, iron blocks, and sand is measured to be 96%.

[0087] The air-separated corn straw is crushed by a crusher. The content of the material with a length of 3 - 5 cm in the crushed material is 85 wt%, the content of the material with a length greater than or equal to 10 cm is 5 wt%, and the content of the material with a length less than or equal to 2 cm is 5 wt%.

[0088] The crushed material enters a drum washer and is rinsed with a sulfuric acid aqueous solution with a concentration of 2 wt% and a temperature of 45°C. The dosage of the sulfuric acid aqueous solution is such that the weight ratio of the crushed material to the sulfuric acid aqueous solution is 4:100. After pickling, the material enters a draining screw conveyor, and the drained sulfuric acid aqueous solution is recycled to the drum washer for pickling. The solid content in the material after draining is 15 wt%. The material after draining enters a screw extrusion device for the first extrusion, and the solid content in the material after the first extrusion is 27 wt%.

[0089] Explosion puffing:

[0090] The material after the first extrusion enters the feeder of the explosion puffing device for the second extrusion, and the solid content of the material after the second extrusion is 50 wt%. The material after the second extrusion enters the steamer of the explosion puffing device, and in the presence of medium-pressure steam, the material after the second extrusion is cooked; the pressure of the medium-pressure steam is 0.7 MPaG, the temperature of the medium-pressure steam is 175°C; the cooking time is 20 min. After cooking, the material is discharged through a blow-off valve to obtain an explosion-puffed product. The yield of cellulose in the explosion-puffed product is 90%, the yield of hemicellulose is 85%, and the solid content is 35 wt%.

[0091] Enzymatic hydrolysis:

[0092] The explosion-puffed product is diluted with water to obtain a 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 used, and the material to be enzymatically hydrolyzed is enzymatically hydrolyzed with a cellulase solution (the content of cellulase preparation in the enzyme solution is 15 wt%) at a temperature of 50°C for 70 h to obtain an enzymatic hydrolysate.

[0093] Fermentation:

[0094] Saccharomyces cerevisiae (Angel Yeast) was inoculated into the enzymolysis solution (inoculation amount 15V%), and the culture was expanded at a temperature of 25°C for 20 h. After the expansion, the viable cell count in the material was 200 million cells / ml, the budding rate of Saccharomyces cerevisiae was 20%, and the mortality rate was 10%. Then, the expanded material was fermented using an intermittent C5 fermentation process at a temperature of 32°C for 60 h. The ethanol content in the obtained fermentation broth was 6.5V%.

[0095] Rectification to extract anhydrous alcohol:

[0096] The mature mash after fermentation was preheated by a mash preheater and then entered the middle-upper part of the rough distillation column for rough distillation. The waste liquid at the bottom of the column was discharged from the bottom of the rough distillation column. The top pressure of the rough distillation column was -0.068 MPaG, and the bottom pressure was -0.048 MPaG; the top temperature was 52.4°C, and the bottom temperature was 83°C; the ethanol content in the bottom of the column was 0.04 wt%; the reflux ratio was 1; the number of trays was 26.

[0097] The rough alcohol drawn from the side line of the rough distillation column entered the first rectification column for the first rectification. The top pressure of the first rectification column was 0.07 MPaG, and the bottom pressure was 0.0935 MPaG; the top temperature was 93°C, and the bottom temperature was 119.5°C; the ethanol content in the bottom of the column was 0.04 wt%; the reflux ratio was 2.6; the number of trays was 64. Under the action of steam, the alcohol vapor overflowed from the top of the first rectification column. Part of it entered the first rectification column as reflux through the reboiler of the rough distillation column, and the other part of the alcohol vapor was heated by the alcohol vapor superheater and then entered the molecular sieve column for dehydration at a temperature of 125°C and a pressure of 0.045 MPaG.

[0098] The material drawn from the side line of the first rectification column entered the second rectification column for the second rectification. The top pressure of the second rectification column was 0.42 MPaG, and the bottom pressure was 0.445 MPaG; the top temperature was 126.6°C, and the bottom temperature was 155.4°C; the ethanol content in the bottom of the column was 0.04 wt%; the reflux ratio was 3.8; the number of trays was 72. Mass transfer occurred with the rising steam at the bottom of the column on the trays, and the alcohol vapor overflowed from the top of the column. The alcohol vapor at the top of the column was used as the heat source for the first rectification. After heating the reboiler at the bottom of the first rectification column, the alcohol vapor at the top of the column entered the cooler for condensation and cooling. Part of the cooled liquid material was used as the reflux of the first rectification column, and the other part was drawn out and entered the molecular sieve column for dehydration at a temperature of 125°C and a pressure of 0.045 MPaG.

[0099] After the alcohol vapor overflowing from the top 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 25V% is obtained at the top of the molecular sieve column. After a part of the finished wine gas is heat-exchanged through a product cooler, it enters the ethanol product tank for storage. Another part of the finished wine gas enters another molecular sieve column to be regenerated, which is used to regenerate 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.

[0100] Spent mash separation:

[0101] The rectified spent mash is separated by a plate and frame filter 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 65 °C, and the pressure is 25 kPa. The temperature of the third-effect evaporation is 55 °C, and the pressure is 23 kPa. The temperature of the fourth-effect evaporation is 50 °C, and the pressure is 20 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 the biomass boiler. The steam generated in the biomass boiler is used as a heat source for the circulating acid solution, the air explosion unit, the rectification unit, etc.

[0102] Example 2

[0103] Fuel ethanol is prepared according to the method of Example 1, except that the degree of pulverization is different. Specifically, "the content of the material with a length of 3 - 5 cm in the pulverized material is 90 wt%, the content of the material with a length greater than or equal to 10 cm is 3 wt%, and the content of the material with a length less than or equal to 2 cm is 5 wt%" is used to replace "the content of the material with a length of 3 - 5 cm in the pulverized material is 85 wt%, the content of the material with a length greater than or equal to 10 cm is 5 wt%, and the content of the material with a length less than or equal to 2 cm is 5 wt%". Fuel ethanol is obtained.

[0104] Example 3

[0105] Fuel ethanol is prepared according to the method of Example 1, except that "the material after draining water enters a screw extrusion device for the first extrusion, and the solid content in the material after the first extrusion is 30 wt%; the material after the first extrusion enters the feeder of the air explosion device for the second extrusion, and the solid content of the material after the second extrusion obtained is 55 wt%" is used to replace "the material after draining water enters a screw extrusion device for the first extrusion, and the solid content in the material after the first extrusion is 27 wt%; the material after the first extrusion enters the feeder of the air explosion device for the second extrusion, and the solid content of the material after the second extrusion obtained is 50 wt%". Fuel ethanol is obtained.

[0106] Example 4

[0107] Fuel ethanol was prepared according to the method of Example 1, except that during the pretreatment of the cellulose raw material, the degree of pulverization was different. Specifically, "the content of the material with a length of 3 - 5 cm in the pulverized material is 85 wt%, the content of the material with a length greater than or equal to 10 cm is 10 wt%, and the content of the material with a length less than or equal to 2 cm is 5 wt%" was used to replace "the content of the material with a length of 3 - 5 cm in the pulverized material is 85 wt%, the content of the material with a length greater than or equal to 10 cm is 5 wt%, and the content of the material with a length less than or equal to 2 cm is 5 wt%". The fuel ethanol was obtained.

[0108] Example 5

[0109] Fuel ethanol was prepared according to the method of Example 1, except that the concentration of the sulfuric acid aqueous solution used during pickling was different. Specifically, "rinsing was carried out with a sulfuric acid aqueous solution with a concentration of 5 wt% and a temperature of 45 °C" was used to replace "rinsing was carried out with a sulfuric acid aqueous solution with a concentration of 2 wt% and a temperature of 45 °C". The fuel ethanol was obtained.

[0110] Example 6

[0111] Fuel ethanol was prepared according to the method of Example 1, except that the amount of the sulfuric acid aqueous solution used during pickling was different. Specifically, "the amount of the sulfuric acid aqueous solution was such that the weight ratio of the pulverized material to the sulfuric acid aqueous solution was 8:100" was used to replace "the amount of the sulfuric acid aqueous solution was such that the weight ratio of the pulverized material to the sulfuric acid aqueous solution was 4:100". The fuel ethanol was obtained.

[0112] Example 7

[0113] Fuel ethanol was prepared according to the method of Example 1, except that the conditions of the steam explosion cooker were different. Specifically, "the pressure of the medium-pressure steam was 0.5 MPaG" was used to replace "the pressure of the medium-pressure steam was 0.7 MPaG". The fuel ethanol was obtained.

[0114] Comparative Example 1

[0115] A traditional method for preparing fuel ethanol was adopted, with a 30,000-ton / year cellulose ethanol plant designed for 8000 hours of operation time.

[0116] The corn straw (corn straw flow rate 20 dry tons / hour, moisture 20 wt%, impurities 10 wt%) 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 .

[0117] Then, a roller screen is used for rolling dust removal at normal pressure and room temperature. The rotation speed of the rolling screen is 12 revolutions, removing 50% of the dust. After impurity removal, the material enters the storage bin 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 the digester. The air explosion reaction conditions are the same as those in Example 1.

[0118] Enzymatic hydrolysis:

[0119] 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 the material to be enzymatically hydrolyzed is enzymatically hydrolyzed at a temperature of 50 °C for 64 h using a cellulase solution (the composition of the enzyme solution is the same as that in Example 1) to obtain an enzymatic hydrolysate.

[0120] Fermentation:

[0121] Saccharomyces cerevisiae (Angel yeast) is inoculated into the enzymatic hydrolysate (inoculation amount 15 V%), and undergoes expansion culture at a temperature of 25 °C for 15 h. The viable cell count in the material after expansion culture is 200 million cells / ml, the budding rate of Saccharomyces cerevisiae is 20%, and the mortality rate is 10%. Then, the material after expansion culture is fermented using an intermittent C5 fermentation process at a temperature of 32 °C for 60 h.

[0122] The method for separating anhydrous alcohol and waste mash liquor by rectification extraction is the same as that in Example 1.

[0123] Test example

[0124] The start-up rate, production load, cellulose and hemicellulose yields, fermented alcohol concentration, and enzyme preparation dosage of each example and comparative example are measured respectively. The results are shown in Table 1.

[0125] 1) Start-up rate % = start-up time (hours) ÷ 8000 × 100%;

[0126] 2) Cellulose yield % = (mass of dry matter in the material after air explosion per hour × mass percentage of cellulose) ÷ (mass of dry matter in the crushed straw per hour × mass percentage of cellulose) × 100%;

[0127] 3) Hemicellulose yield % = (mass of dry matter in the material after air explosion per hour × mass percentage of hemicellulose) ÷ (mass of dry matter in the crushed straw per hour × mass percentage of hemicellulose) × 100%;

[0128] 4) The concentration of fermented alcohol is measured by liquid chromatography;

[0129] 5) Production load % = (amount of fuel ethanol produced per hour) ÷ (designed amount of fuel ethanol per hour) × 100%.

[0130] Table 1

[0131]

[0132]

[0133] 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 device start-up rate and production load, a relatively high cellulose and hemicellulose yield after air explosion, a relatively high alcohol content in the fermentation broth, and a relatively low dosage of enzyme preparation. Comparative Example 1 prepares fuel ethanol by using a traditional method. Compared with Examples 1-7, the device start-up rate and production load of Comparative Example 1 are significantly reduced, the cellulose and hemicellulose yields after air explosion are significantly reduced, the alcohol content in the fermentation broth is significantly reduced, and the dosage of enzyme preparation also increases.

[0134] In addition, in Example 4, the crushing degree during the pretreatment of the cellulose raw material was changed; in Example 5, the concentration of the sulfuric acid aqueous solution used during pickling was changed; in Example 6, the dosage of the sulfuric acid aqueous solution used during pickling was changed; and in Example 7, the pressure of the medium-pressure steam in the digester during air explosion was changed. Compared with Example 1, the device start-up rate and production load of Examples 4-7 are both reduced, the cellulose and hemicellulose yields and the alcohol content in the fermentation broth after air explosion are all reduced, and the dosage of enzyme preparation all increases. This shows that when the crushing degree during the pretreatment of the cellulose raw material, the concentration and dosage of the sulfuric acid aqueous solution used during pickling, and the air explosion conditions meet the preferred conditions, the device start-up rate and production load can be further improved, the cellulose and hemicellulose yields and the alcohol content in the fermentation broth after air explosion can be further increased, and the dosage of enzyme preparation can be further reduced.

[0135] 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, and then performing air explosion, enzymatic hydrolysis, fermentation and rectification; wherein, The pretreatment method comprises: S1. Performing air separation on the cellulose raw material to obtain the air-separated material; S2. Crushing the air-separated material to obtain the crushed material; S3. Pickling the crushed material and then draining the water to obtain the drained material; S4. Performing the first extrusion on the drained material.

2. The preparation method according to claim 1, characterized in that, The cellulose raw material is straw, preferably corn straw and / or wheat straw; Preferably, in S1, the air separation is performed by an air separator, and the aperture of the sieve holes of the sieve of the air separator is 5-8 mm; and / or, the air separation speed of the air separator is 5-20 m / s, preferably 10-15 m / s.

3. The preparation method according to claim 1 or 2, characterized in that, In S2, the conditions of the crushing are such that the content of the material with a length of 3-5 cm in the crushed material is greater than or equal to 85 wt%, preferably 85-95 wt%; Preferably, the conditions of the crushing are such that the content of the material with a length greater than or equal to 10 cm in the crushed material is less than or equal to 10 wt%, preferably 2-5 wt%; the content of the material with a length less than or equal to 2 cm in the crushed material is less than or equal to 10 wt%, preferably 2-5 wt%.

4. The preparation method according to any one of claims 1-3, characterized in that, In S3, the pickling method comprises: rinsing the crushed material with an acid solution; wherein, the dosage of the acid solution is such that the weight ratio of the crushed material to the acid solution is (3-5):

100.

5. The preparation method according to claim 4, characterized in that, The acid content in the acid solution is less than or equal to 5 wt%, preferably 1-3 wt%; Preferably, the temperature of the acid solution is 40-50 °C, preferably 43-46 °C; Preferably, the conditions of the water draining are such that the solid content in the drained material is 10-20 wt%, preferably 12-20 wt%.

6. The preparation method according to any one of claims 1-5, characterized in that, In S4, the conditions of the first extrusion are such that the solid content in the material after the first extrusion is 20-30 wt%, preferably 25-30 wt%.

7. The preparation method according to any one of claims 1-6, characterized in that, The air explosion method comprises: performing a second extrusion on the material after the first extrusion to obtain the material after the second extrusion, and then steaming the material after the second extrusion in the presence of medium-pressure steam.

8. The preparation method according to claim 7, characterized in that, The second extrusion is performed in a feeder; the conditions of the second extrusion are such that the solid content in the material after the second extrusion is 40-60 wt%, preferably 45-55 wt%; Preferably, the conditions of the steaming include: the pressure of the medium-pressure steam is 0.6-1 MPa, preferably 0.6-0.8 MPa; the temperature of the medium-pressure steam is 160-200 °C, preferably 170-180 °C; the steaming time is 10-60 min, preferably 15-30 min.

9. The preparation method according to any one of claims 1-8, characterized in that, The temperature of the enzymatic hydrolysis is 50-55 °C, and the time is 60-80 h; Preferably, when performing the enzymatic hydrolysis, based on the production of 1 ton of fuel ethanol, the dosage of the cellulase preparation is 100-300 kg, preferably 180-220 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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