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 acid gas explosion, enzymolysis, fermentation and rectification; the pretreatment method comprises the following steps: sequentially carrying out winnowing, primary crushing, roller washing, secondary crushing and water washing on a cellulose raw material. By means of the method, valve blockage and pipeline abrasion can be effectively reduced, the operation continuity of the device is guaranteed, the use amount of acid is reduced, and the operating rate is increased. In addition, the yield of cellulose and hemicellulose after gas explosion is improved, and the dosage of an enzyme preparation is 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 control of air pollution. It is mainly made from grains (such as corn and wheat), tubers (such as sweet potato, cassava, and potato), sugars (such as molasses), or cellulose (such as crop straws, waste wood, and waste 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] Biomass materials represented by straw come from farmland and contain impurities such as large stones, iron blocks, sand, and soil. These impurities can cause valve blockage, wear of equipment pipelines, and blockage of the feeder during feeding, seriously affecting the start-up rate of the device. The floating soil on the straw can also adsorb some acid ions, thus increasing the amount of acid used in the subsequent air explosion process.

[0004] As a solid material, straw has a relatively low bulk density. Typical data shows that for corn straw, it is 45 g / L - 50 g / L (under the condition of 15% - 20% moisture), and for wheat straw, it is 60 g / L - 70 g / L (under the condition of 20% - 30% moisture). During transportation, it has a large volume, and the raw materials are prone to fluctuations, the materials are easy to float and fall, and the workshop environment is poor. The water content in the straw raw materials is also unstable. Throughout the year, the water content of the straw fluctuates with climate change in the range of 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 unevenness of moisture affect the stability and uniformity of acid addition in the subsequent cooking equipment, thus affecting the air explosion recovery rate and effect of the digester. The instability of the material bulk density directly affects the stability and load of the key equipment in the pretreatment.

[0005] One of the core equipment in the pretreatment part is the feeder for the air explosion equipment. Straw under normal pressure is pressurized in this equipment and then enters the air explosion equipment for air 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 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 also affects the process stability of the cooking reactor, and the discharge port of the air 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.

[0006] The dry production process is as follows: After the straw is crushed once, it undergoes roller dust removal, and about 50% of the dust can be 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 the acid mixing screw, where acid liquid is sprayed in. After acid mixing, the material enters the air explosion equipment. Under the extrusion of the feeder, the straw undergoes an acidic air explosion reaction in the digester. After air explosion, the material enters the enzymatic hydrolysis unit, the material of the enzymatic hydrolysis unit enters the fermentation unit, the material of the fermentation unit enters the rectification unit, and the material of the rectification unit enters the separation unit. The separated clear liquid enters the evaporation unit, and the evaporation condensate is recycled. The syrup and the wet cake are mixed and enter the biomass boiler. The biomass boiler generates steam to provide heat sources for air explosion and rectification. There is still a 20% surplus in the biomass boiler providing heat sources for air explosion and rectification. If there is a nearby factory, it can be sent out as a heat source. However, generally, it can only be vented.

[0007] Therefore, there is an urgent need for a preparation method of fuel ethanol that can effectively remove impurities in the raw material, improve the stability of the bulk density of the raw material after pretreatment, thus avoiding valve blockage and equipment pipeline wear, reducing the amount of acid used in the air explosion process, increasing the startup rate of the device, and reducing the dosage of enzyme preparations. Summary of the Invention

[0008] The purpose of the present invention is to overcome the problems existing in the dry production of fuel ethanol in the prior art, where impurities easily cause valve blockage, equipment pipeline wear, and the unstable bulk density of the raw material leads to uneven and unstable feeding. The feeder in the air explosion unit is prone to blockage, thus affecting the air explosion recovery rate and effect of the cooking reactor in the air explosion unit. A preparation method of fuel ethanol is provided. The pretreatment process in this preparation method can effectively reduce the impurities in the raw material and effectively improve the stability of the bulk density of the raw material after pretreatment.

[0009] To achieve the above purpose, the present invention provides a preparation method of fuel ethanol. The preparation method includes the following steps: pretreating the cellulose raw material, and then performing acidic air explosion, enzymatic hydrolysis, fermentation, and rectification; wherein,

[0010] The pretreatment method includes sequentially performing winnowing, first crushing, drum washing, second crushing, and water washing on the cellulose raw material.

[0011] Through the above technical solutions, the beneficial effects of the present invention at least include:

[0012] In the preparation method of fuel ethanol provided by the present invention, a pneumatic separation unit is set up to remove heavy impurities such as stones and iron blocks; a drum washing device is set up to remove small sand and soil, and the floating soil on the straw is cleaned by water washing technology, ensuring the cleanliness of the materials, ensuring the stable start-up of the device, reducing the wear of equipment and pipelines and the blockage of equipment by materials, and reducing the acid usage in the subsequent air explosion process. After the materials are washed with water, the bulk density increases, the volume is compacted, and there is no longer a situation where materials fly in the air and part of them fall to the ground during the conveying process, ensuring the safety of the device and improving the environment of the device.

[0013] In a preferred embodiment of the present invention, the acid solution required in the air explosion reaction is added to the cooking equipment from the front end of the equipment, and is fully mixed with the high dry matter materials after being extruded by the feeder, ensuring the feeding stability of the feeder and the process stability of the air explosion equipment. On this basis, the efficient utilization of subsequent equipment is realized, the dosage of enzyme preparation is reduced, and the start-up rate is increased.

[0014] In a preferred embodiment of the present invention, the method provided by the present invention makes full use of heat. The waste mash liquor after rectification is separated, and the wet distillers grains and evaporated syrup enter the biomass boiler, and the biomass boiler provides steam for the whole device, and the whole device does not need to provide steam separately. The new process reduces energy consumption and saves costs. Brief Description of the Drawings

[0015] Figure 1 It 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 in the Drawings

[0017] T1 Pneumatic Separation; T2 First Crushing; T3 Drum Washing; T4 Second Crushing

[0018] T5 Water Washing; T6 Water Recovery; T7 Acidic Air Explosion; T8 Enzymatic Hydrolysis

[0019] T9 Fermentation; T10 Rectification; T11 Waste Mash Liquor Separation; T12 Evaporation

[0020] T13 Biomass Boiler Detailed Embodiments

[0021] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values 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.

[0022] The present invention provides a method for preparing fuel ethanol, and the preparation method includes the following steps: pretreating a cellulose raw material, and then performing acid explosion, enzymatic hydrolysis, fermentation and rectification; wherein,

[0023] The pretreatment method includes successively performing winnowing, first pulverization, drum washing, second pulverization and water washing on the cellulose raw material.

[0024] According to the present invention, through winnowing of the cellulose raw material successively, heavy impurities such as stones, iron blocks and sand are removed, initially ensuring the cleanliness of the material; after the first pulverization, the material after the first pulverization enters a drum washing device to remove small stones and soil, etc.; after the second pulverization, the material after the second pulverization is washed with water to clean the floating soil on the cellulose raw material, ensuring the cleanliness of the material, and the bulk density of the material increases after water washing, and there is no longer any floating of the material, which falls to the ground. This ensures the safety of the device, improves the environment of the device. It ensures the stable start-up of the device, reduces the wear of equipment and pipelines and the blockage of equipment by materials, and moreover reduces the acid usage amount in the subsequent explosion process. The material after water washing enters the explosion unit for acid explosion, and the excess water after water washing can be recycled.

[0025] In the present invention, winnowing can adopt conventional equipment in the art. For example, a winnowing machine can be used for winnowing to remove heavy impurities such as stones, iron blocks and sand, initially ensuring the cleanliness of the material. Preferably, the winnowing machine operates under the conditions that the temperature is 15 - 35°C; the inlet of the fan has a slightly negative pressure, and the pressure is 85 - 95 kPA; the outlet of the fan has a slightly positive pressure, and the pressure is 105 - 115 kPa.

[0026] In order to further improve the removal rate of heavy impurities such as stones, iron blocks and sand and further improve the yield of the cellulose raw material, preferably, the aperture of the sieve holes of the sieve mesh of the winnowing machine is 5 - 7 mm.

[0027] The present invention has no particular limitation on the material of the sieve mesh of the winnowing machine. For example, a sieve mesh made of 304 stainless steel can be used.

[0028] In order to further improve the removal rate of heavy impurities such as stones, iron blocks and sand and further improve the yield of the cellulose raw material, preferably, the winnowing speed of the winnowing machine is 5 - 20 m / s, preferably 10 - 15 m / s.

[0029] Under the preferred conditions, the yield of the cellulose raw material in the material after winnowing is greater than or equal to 98%, and the material loss is less than or equal to 2%; the removal rate of heavy impurities such as stones, iron blocks and sand is 95 - 98%.

[0030] According to the present invention, preferably, the cellulose raw material is straw, preferably corn straw and / or wheat straw.

[0031] 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 under normal temperature and pressure conditions.

[0032] In order to further improve the effect of subsequent drum washing to remove impurities such as small stones and soil, preferably, the conditions of the first crushing are such that in the material after the first crushing obtained by the first crushing, the content of the material with a length of 2 - 8 cm is greater than or equal to 85 wt%.

[0033] Furthermore, the conditions of the first crushing are such that in the material after the first crushing obtained by the first crushing, the content of the material with a length of 8 - 10 cm (excluding 8 cm) is less than or equal to 5 wt%, the content of the material with a length greater than 10 cm is less than or equal to 5 wt%, and the content of the material with a length of 0.5 - 2 cm (excluding 2 cm) is less than or equal to 10 wt%.

[0034] According to a preferred embodiment of the present invention, a cylindrical screen is used for drum washing, the cylindrical screen is rotated, and an appropriate amount of water is used as a detergent for drum washing, so that impurities such as sand and soil are removed through the sieve holes. Preferably, the cylindrical screen operates under normal temperature and pressure conditions.

[0035] In order to further improve the removal rate of impurities such as sand and soil, preferably, the aperture of the sieve holes of the cylindrical screen is 4 - 5 mm; and / or, the rotation speed of the cylindrical screen is 6 - 15 r / min; and / or, during drum washing, the temperature of the detergent is 15 - 50 °C; and / or, based on the total weight of the material after the first crushing, the dosage of the detergent during drum washing is 2 - 5 wt%.

[0036] When a cylindrical screen is used and water is used for drum washing, in the preferred case, the impurity removal rate of impurities such as sand and soil is 60% - 80 wt%, and the cellulose raw material yield is greater than or equal to 98 wt%.

[0037] A smaller crushing particle size is beneficial to the increase of the bulk density of the material, so that the bulk density of the material entering the feeder is increased, meeting the requirements of the design load. In order to increase the bulk density of the material, the material after drum washing needs to be crushed for the second time. Preferably, the conditions of the second crushing are such that in the material after the second crushing obtained by the second crushing, the content of the material with a length of 3 - 5 cm is greater than or equal to 85 wt%.

[0038] Furthermore, the conditions of the second crushing are such that in the material after the second crushing obtained by the second crushing, the content of the material with a length greater than or equal to 10 cm is less than or equal to 3 wt%, and the content of the material with a length less than 3 cm is less than or equal to 5 wt%.

[0039] In the present invention, the water washing can be carried out using conventional equipment in the art. For example, a drum washer can be used to rinse the material with water. The material tumbles in the drum washer, and the circulating water rinses the material.

[0040] To further improve the water washing effect, preferably, when carrying out the water washing, the weight ratio of the material after the second pulverization to the washing water is (3 - 5):100.

[0041] According to the present invention, preferably, when carrying out the water washing, the temperature of the washing water is 40 - 50°C, preferably 43 - 46°C.

[0042] According to the present invention, preferably, the pretreatment method further includes: draining the water from the material after the water washing, and the draining conditions are such that the solid content in the drained material after draining is 10 - 20 wt%, preferably 12 - 20 wt%.

[0043] In the present invention, the draining can be carried out using a conventional draining device in the art. For example, a draining screw device can be used for draining.

[0044] According to the present invention, preferably, the pretreatment method further includes: performing a first extrusion on the drained material, and the conditions of the first extrusion are such that the solid content in the material after the first extrusion is 25 - 45 wt%, preferably 30 - 40 wt%.

[0045] According to a preferred embodiment of the present invention, the first extrusion of the material is carried out by a screw extrusion device.

[0046] According to the present invention, the water remaining after draining and the water remaining after the first extrusion can be returned to the water washing section for recycling.

[0047] According to the present invention, preferably, the method of acid gas explosion includes: performing a second extrusion on the extruded material to obtain a material after the second extrusion, and then, in the presence of medium-pressure steam, mixing the material after the second extrusion with acid liquor for cooking.

[0048] According to a specific embodiment of the present invention, the second extrusion is carried out in the feeder of the gas explosion device, and the material after the second extrusion enters the cooking equipment (steam generator) of the gas explosion device. The acid liquor required in the gas explosion reaction is added to the equipment from the top of the cooking equipment, and is fully mixed with the high-dry material (material after the second extrusion) extruded by the feeder (second extrusion) and medium-pressure steam in the cooking equipment for material cooking. After the material is discharged through the blow-off valve, the material after acid gas explosion is obtained. This ensures the stability of the feeder feeding and the process stability of the gas explosion device. On this basis, the efficient utilization of subsequent equipment is achieved, the dosage of enzyme preparation is reduced, and the operating rate is increased.

[0049] After the material is washed with water, a draining device is used for draining, and then the material is first extruded by a screw extrusion device. The extruded material enters a feeder. The internal acid addition process is adopted to add the acid solution to the material after the feeder, ensuring the moisture uniformity of the material in the feeder and the uniformity of acid addition. Due to the stable and uniform feeding of the feeder, the process stability and yield of the air explosion device are ensured. Due to the long-term stable operation of equipment such as the digester, the high-efficiency utilization of subsequent equipment is achieved, the dosage of enzyme preparation is reduced, and the operating rate is increased.

[0050] According to the present invention, preferably, the conditions of the second extrusion are such that the solid content in the material after the second extrusion obtained by the second extrusion is 25 - 70 wt%, preferably 45 - 55 wt%.

[0051] According to the present invention, preferably, the dosage of the acid solution is such that the weight ratio of the material after the first extrusion to the acid solution is 1:(1.2 - 3.5), preferably 1:(1.5 - 2.5).

[0052] In order to further increase the content of cellulose and hemicellulose in the product after acid addition and air explosion, thereby further improving the enzymatic hydrolysis effect, preferably, the acid content in the acid solution is 0.5 - 5 wt%, preferably 1 - 2.5 wt%.

[0053] According to the present invention, preferably, the conditions of cooking include: the pressure of medium-pressure steam is 0.6 - 1 MPa, preferably 0.6 - 0.8 MPa; the temperature of medium-pressure steam is 160 - 200 °C, preferably 170 - 180 °C; the cooking time is 10 - 60 min, preferably 15 - 30 min.

[0054] In the preferred case, the yield of cellulose in the material obtained by acid air explosion is greater than or equal to 90%, and the yield of hemicellulose is greater than or equal to 80%.

[0055] In the preferred case, the solid content in the material obtained by acid air explosion is 30 - 50 wt%, and in the more preferred case, the solid content is 32 - 36 wt%.

[0056] According to the present invention, after the cellulose raw material is pretreated and subjected to acid 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.

[0057] According to the present invention, preferably, the enzyme used for the enzymatic hydrolysis is cellulase.

[0058] In order to further improve the enzymatic hydrolysis efficiency, preferably, when carrying out the enzymatic hydrolysis, based on the production of 1 ton of fuel ethanol, the dosage of the cellulase preparation is 200 - 230 kg.

[0059] According to a preferred embodiment of the present invention, the cellulase used in 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%.

[0060] According to a preferred embodiment of the present invention, the product obtained after acid 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.

[0061] Preferably, the temperature of the enzymatic hydrolysis is 50-55 °C, and the time is 60-80 h.

[0062] According to a preferred embodiment of the present invention, continuous enzymatic hydrolysis process is adopted for enzymatic hydrolysis.

[0063] 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 enters a fermentation tank for batch fermentation; preferably, the inoculation amount for expansion is 5-15 V%.

[0064] 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. In the preferred case, the budding rate of Saccharomyces cerevisiae is above 20%, and the mortality rate is less than or equal to 10%.

[0065] Preferably, the temperature of the fermentation is 30-33 °C, and the time is 50-70 h.

[0066] According to a preferred embodiment of the present invention, batch C5 and C6 fermentation process is adopted for fermentation.

[0067] In the preferred case, based on the total volume of the fermentation broth, the content of the alcohol fraction obtained by fermentation is 6-8 V%.

[0068] 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 introducing the mash into a rough distillation column for rough distillation, then introducing the side-draw material from the rough distillation column into a first rectification column for the first rectification, and then introducing the side-draw material from the first rectification column into a second rectification column for the second rectification; part of the alcohol vapor at the top of the first rectification column and part of the alcohol vapor at the top of the second rectification column enter a molecular sieve column for dehydration, and after dehydration, the ethanol gas is condensed and cooled, and the condensate is used as finished alcohol and enters an ethanol product tank.

[0069] 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 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.

[0070] 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 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.

[0071] 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 it undergoes mass transfer with the rising steam from the bottom on the trays. The alcohol vapor overflows from the top of the column. A part of the top 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 for 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.

[0072] 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 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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 conditions of a pressure of -0.09 MPaG to -0.07 MPaG.

[0077] The finished alcohol vapor overflows from the upper part of the molecular sieve tower. After heat exchange in the product cooler, the finished alcohol vapor is sent to the ethanol product tank.

[0078] 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 weak wine formed by the molecular sieve regeneration enters the weak 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 regenerated. The two sets of molecular sieve towers are alternately used for dehydration.

[0079] 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.

[0080] According to the present invention, preferably, the preparation method of fuel ethanol further includes: subjecting the waste mash after rectification 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 recycled water 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.

[0081] 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%.

[0082] 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. In the preferred case, the concentration of the syrup in the syrup-containing feed liquid obtained after evaporation is 50-60 wt%.

[0083] 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: Biomass straw is successively subjected to air separation T1, first crushing T2, drum washing T3, second crushing T4, and water washing T5; After water washing, the material is successively subjected to water draining and first extrusion. The water remaining after water draining and the water remaining after first extrusion are subjected to water recovery T6 and returned to the water washing section for recycling. After the material after first extrusion enters the feeder for second extrusion, it is introduced into the air explosion unit for acidic air explosion T7. After acidic air explosion, the material is introduced into the enzymatic hydrolysis unit for enzymatic hydrolysis T8, and then Saccharomyces cerevisiae is inoculated into the enzymatic hydrolysate for expansion culture. The material after expansion culture is fermented in the fermentation unit T9, and then the mash obtained after fermentation is introduced into the rectification unit for rectification T10 to extract anhydrous alcohol. The waste mash after rectification is introduced into the separation unit for separation T11 to obtain filter cake and clear liquid; The clear liquid is introduced into the evaporation unit for evaporation T12 to obtain syrup-containing feed liquid and evaporation condensate. The evaporation condensate is reused as the dilution water for the enzymatic hydrolysis unit, and the syrup-containing feed liquid and filter cake are introduced into the biomass boiler T13. Part of the steam generated by the biomass boiler is introduced into the rectification unit, part is introduced into the air explosion unit, and part is introduced into the recycled water for use as the heat source for water washing.

[0084] The pressures in the present invention are all gauge pressures.

[0085] The present invention will be described in detail below through examples and comparative examples. In the following examples, unless otherwise specified, they are all conventional methods; The reagents and materials used, unless otherwise specified, can be obtained from commercial channels.

[0086] The following examples are used to illustrate the method for preparing fuel ethanol.

[0087] Example 1

[0088] An ethanol plant with a scale of 30,000 tons / year and an operating time of 8,000 hours.

[0089] Raw material pretreatment: Corn straw with a flow rate of 20 dry tons / hour (straw moisture content 15wt%, sand content 10wt%, bulk density 25kg / m 3 ) is subjected to air separation at normal temperature and pressure using an air separator. The aperture of the sieve holes of the sieve mesh of the air separator is 6mm, the material of the sieve mesh is 304 stainless steel, and the air separation speed of the air separator is 13m / s to remove heavy impurities such as stones, iron blocks, and sand. The corn straw yield of the material after air separation is 99%; By weight measurement, the removal rate of heavy impurities such as stones, iron blocks, and sand is measured to be 98%.

[0090] The corn straw after air separation is first crushed by a crusher. In the material after the first crushing, the content of materials with a length of 2 - 8 cm is 85 wt%, the content of materials with a length of 8 - 10 cm (excluding 8 cm) is 2 wt%, the content of materials with a length greater than 10 cm is 5 wt%, and the content of materials with a length of 0.5 - 2 cm (excluding 2 cm) is 5 wt%. The bulk density of the material after the first crushing is 32 kg / m 3 . The drum washing is carried out at normal temperature and pressure using a cylindrical sieve. The aperture of the sieve holes of the cylindrical sieve is 5 mm, the rotational speed of the cylindrical sieve is 12 r / min, and the temperature of the detergent (water) is 25°C. Based on the total weight of the material after the first crushing, the dosage of the detergent is 3 wt%. Thus, impurities such as sand and soil are removed. Through weight measurement, the impurity removal rate of sand and soil and other impurities is 80 wt%, and the cellulose raw material yield is 98 wt%.

[0091] The material after drum washing is secondarily crushed by a crusher. In the material after the second crushing, the content of materials with a length of 3 - 5 cm is 85 wt%, the content of materials with a length greater than or equal to 10 cm is 2 wt%, and the content of materials with a length less than 3 cm is 2 wt%. The bulk density of the material after the second crushing is 42 kg / m 3 .

[0092] A rotary drum washer is used to rinse the material after the second crushing with water. The weight ratio of the material after the second crushing to the washing water is 4:100, and the temperature of the washing water is 45°C. The water-washed material is drained using a draining screw machine, and the solid content in the drained material is 20 wt%. The drained material is first extruded using a screw extrusion device, and the solid content in the material after the first extrusion is 35 wt%. The water remaining after draining and the water remaining after extrusion can be returned to the water-washing section for recycling.

[0093] Acid gas explosion:

[0094] The material after the first extrusion is secondarily extruded in the feeder of the gas explosion device, and the solid content of the material after the second extrusion is 50 wt%. Then, in the presence of medium-pressure steam, the material after the second extrusion and sulfuric acid with a concentration of 2.5 wt% are introduced into the cooking equipment of the gas explosion device, fully mixed, and cooked; the dosage of sulfuric acid makes the weight ratio of the material after the first extrusion to sulfuric acid 1:2. The pressure of the steam is 0.7 MPa, the temperature of the steam is 175°C; the cooking time is 20 min. After the cooked material is discharged through a blow-off valve, an acid gas explosion product is obtained. The cellulose yield in the acid gas explosion product is 92%, the hemicellulose yield is 80%, and the solid content is 35 wt%.

[0095] Enzymatic hydrolysis:

[0096] The acidic gas explosion products are 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 enzymatically hydrolyzed solution is obtained.

[0097] Fermentation:

[0098] Saccharomyces cerevisiae (Angel yeast) is inoculated into the enzymatically hydrolyzed solution (inoculation amount 10 V%), and expanded cultivation is carried out at a temperature of 25 °C for 10 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%.

[0099] Rectification to extract anhydrous alcohol:

[0100] The mature mash after fermentation is preheated by a mash preheater respectively and then enters the upper middle part of the rough distillation column for rough distillation. 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.

[0101] 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 rough distillation column reboiler, 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.

[0102] The side-draw material from the first distillation column enters the second distillation column for the second distillation. The top pressure of the second distillation 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 is 0.04 wt%; the reflux ratio is 3.8; the number of trays is 72. Mass transfer occurs on the trays with the rising steam from the bottom of the column. The alcohol vapor overflows from the top of the column. The alcohol vapor at the top is used as the heat source for the first distillation. After heating the reboiler at the bottom of the first distillation column with the alcohol vapor at the top, it is condensed and cooled by a cooler. Part of the cooled liquid material is used as the reflux of the first distillation 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.

[0103] After the alcohol vapor overflowing from the tops of the first and second distillation columns 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. 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 resulting 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.

[0104] Spent mash separation:

[0105] The spent mash after distillation 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 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, obtaining 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. The filter cake and the syrup-containing feed liquid enter the biomass boiler. The steam generated in the biomass boiler is used as the heat source for the circulating recovered water, the air explosion unit, and the distillation unit, etc.

[0106] Example 2

[0107] Fuel ethanol is prepared according to the method of Example 1, except that the particle size distribution of the material after the second pulverization is different. Specifically, the content of the material with a length of 3 - 5 cm in the material after the second pulverization is 60 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 3 cm is 20 wt%; the bulk density of the material after the second pulverization is 30 kg / m 3”The content of materials with a length of 3 - 5 cm in the "replaced" material after the second crushing is 85 wt%, the content of materials with a length greater than or equal to 10 cm is 2 wt%, and the content of materials with a length less than 3 cm is 2 wt%; the bulk density of the material after the second crushing is 42 kg / m 3 ”. Fuel ethanol is prepared.

[0108] Example 3

[0109] Fuel ethanol is prepared according to the method of Example 1, except that the solid content in the material after the second extrusion is different. Specifically, replace "the solid content of the material obtained after the second extrusion is 50 wt%" with "the solid content of the material obtained after the second extrusion is 60 wt%". Fuel ethanol is prepared.

[0110] Example 4

[0111] Fuel ethanol is prepared according to the method of Example 1, except that the dosage of the acid solution is different. Specifically, replace "the weight ratio of the material after the first extrusion to sulfuric acid is 1:2" with "the weight ratio of the material after the first extrusion to sulfuric acid is 1:0.6". Fuel ethanol is prepared.

[0112] Example 5

[0113] Fuel ethanol is prepared according to the method of Example 1, except that the cooking conditions are different. Specifically, replace "the steam pressure is 0.7 MPa and the steam temperature is 175 °C; in the acidic explosion product, the solid content is 35 wt%" with "the steam pressure is 0.6 MPa and the steam temperature is 150 °C; in the acidic explosion product, the solid content is 40 wt%". Fuel ethanol is prepared.

[0114] Comparative Example 1

[0115] A traditional method for preparing fuel ethanol is adopted, with a 30,000 - ton / year cellulose ethanol plant designed for 8,000 hours of operation time.

[0116] Corn straw with a flow rate of 20 dry tons per hour (straw moisture content 15 wt%, sand content 10 wt%, bulk density 25 kg / m 3 ) is crushed. In the crushed material, the content of materials with a length of 3 - 5 cm is 30 wt%, the content of materials with a length greater than or equal to 10 cm is 20 wt%, and the content of materials with a length less than 3 cm is 30 wt%; the bulk density of the crushed material is 30 kg / m 3 .

[0117] Then, a roller screen is used for roller dust removal, which is carried out under normal pressure and normal temperature. The rotation speed of the roller screen 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 the 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 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.

[0120] Fermentation:

[0121] 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 adopted for an intermittent C5 fermentation process and fermented at a temperature of 32 °C for 60 h.

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

[0123] Test example

[0124] 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 output of fuel ethanol products are measured for each example and comparative example 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 straw after the second crushing 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 straw after the second crushing per hour × mass percentage of hemicellulose) × 100%;

[0128] 4) The ethanol content in the fermentation broth was measured by liquid chromatography.

[0129] Table 1

[0130]

[0131]

[0132] From the results in Table 1, it can be seen that compared with Comparative Example 1 for preparing fuel ethanol by the traditional method, in Examples 1 - 5 of preparing fuel ethanol by the preparation method of the present invention, the operating rate, the ethanol content in the fermentation broth, and the yield of the fuel ethanol product have all increased, and the dosage of the enzyme preparation has decreased.

[0133] In addition, in Example 2, the particle size distribution of the material after the second pulverization was changed; in Example 3, the solid content in the material after the second extrusion was changed; in Example 4, the dosage of the acid solution during acid explosion was changed; in Example 5, the cooking conditions during acid explosion were changed. Compared with Example 1, the operating rate of the device in Examples 2 - 5 has decreased, the dosage of the enzyme preparation has increased, the yields of cellulose and hemicellulose after explosion have decreased, and the ethanol content in the fermentation broth and the yield of the fuel ethanol product have decreased. This shows that when the pretreatment conditions, the dosage of the acid solution during acid explosion, and the cooking conditions meet the preferred conditions, the operating rate of the device, the yields of cellulose and hemicellulose after explosion, the ethanol content in the fermentation broth, and the yield of the fuel ethanol product can be further improved, and the dosage of the enzyme preparation can be further reduced.

[0134] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept 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 includes the following steps: pretreating the cellulose raw material, and then performing acid explosion, enzymatic hydrolysis, fermentation, and rectification; wherein, The pretreatment method includes: subjecting the cellulose raw material to air separation, first pulverization, drum washing, second pulverization, and water washing in sequence.

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, the air separation is performed by an air separator, and the aperture of the sieve holes of the sieve of the air separator is 5-7 mm; and / or, the air separation speed of the air separator is 5-20 m / s, preferably 10-15 m / s; Preferably, the drum washing is performed by a cylindrical sieve, and the aperture of the sieve holes of the cylindrical sieve is 4-5 mm; and / or, the rotational speed of the cylindrical sieve is 6-15 r / min; and / or, during drum washing, the temperature of the detergent is 15-50 °C; and / or, based on the total weight of the material after the first pulverization, the dosage of the detergent during drum washing is 2-5 wt%.

3. The preparation method according to claim 1 or 2, characterized in that, The conditions of the first pulverization are such that in the material after the first pulverization obtained by the first pulverization, the content of the material with a length of 2-8 cm is greater than or equal to 85 wt%; Preferably, the conditions of the first pulverization are such that in the material after the first pulverization obtained by the first pulverization, the content of the material with a length of 8-10 cm is less than or equal to 5 wt%, the content of the material with a length greater than 10 cm is less than or equal to 5 wt%, and the content of the material with a length of 0.5-2 cm is less than 10 wt%.

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

5. The preparation method according to claim 4, characterized in that, When performing the water washing, the weight ratio of the material after the second pulverization to the washing water is (3-5):100; Preferably, when performing the water washing, the temperature of the washing water is 40-50 °C, preferably 43-46 °C.

6. The preparation method according to any one of claims 1-5, characterized in that, The pretreatment method further includes: draining the material after water washing obtained by the water washing, and the draining conditions are such that the solid content in the material after draining obtained by the draining is 10-20 wt%, preferably 12-20 wt%; Preferably, the pretreatment method further includes: performing a first extrusion on the material after draining, and the conditions of the first extrusion are such that the solid content in the material after the first extrusion obtained by the first extrusion is 25-45 wt%, preferably 30-40 wt%.

7. The preparation method according to claim 6, characterized in that, The acid explosion method includes: performing a second extrusion on the extruded material to obtain a material after the second extrusion, and then, in the presence of medium-pressure steam, mixing the material after the second extrusion with an acid solution for cooking.

8. The preparation method according to claim 7, wherein The conditions of the second extrusion are such that the solid content in the material after the second extrusion obtained by the second extrusion is 25-70 wt%, preferably 45-55 wt%; Preferably, the dosage of the acid solution is such that the weight ratio of the material after the first extrusion to the acid solution is 1:(1.2 - 3.5), preferably 1:(1.5 - 2.5); Preferably, the acid content in the acid solution is 0.5 - 5 wt%, preferably 1 - 2.5 wt%; Preferably, the cooking conditions 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 cooking time is 10 - 60 min, preferably 15 - 30 min.

9. The preparation method according to claim 7 or 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 200 - 230 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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