Preparation method of low-carbon biomass methanol dimethyl ether fuel

Abstract

The invention relates to the technical field of methanol dimethyl ether fuel synthesis processes, in particular to a preparation method of a low-carbon biomass methanol dimethyl ether fuel. Biomass thermal cracking charcoal, tar, pyroligneous liquor and an additive are blended into neutral charcoal slurry according to a certain proportion, and then the neutral charcoal slurry is converted into the low-carbon biomass methanol dimethyl ether fuel. According to the biochar particles, a grading technology is adopted, namely, biochar with different particle sizes is mixed in proportion for pulping, so that the pulping concentration of biochar pulp can be effectively improved; according to the method, the pH of the wood vinegar is adjusted to be neutral, particulate matter in the solution is filtered out, and then pulping is conducted, so that the pulping concentration and the pulp quality can be effectively improved, and meanwhile pipeline blockage and nozzle abrasion are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of methanol dimethyl ether fuel synthesis process, and more specifically, to a method for preparing low-carbon biomass methanol dimethyl ether fuel. Background Art

[0002] my country has abundant coal reserves, but mainly low-grade coal with a low degree of metamorphism. Its inherent characteristics of being difficult to slurry make it difficult to prepare it into water-coal slurry that meets the needs of coal chemical industry and combustion. As my country's high-quality coal resources become increasingly scarce, the advantages of biomass as a renewable green energy source are gradually emerging.

[0003] With the increasing demand for renewable energy, biomass pyrolysis technology has received extensive attention and development. Compared with other biomass conversion technologies, biomass pyrolysis technology has the advantages of simple operation, low equipment investment, and product diversification. It is widely used in the fields of biomass energy utilization and solid waste treatment. Converting waste biomass resources into raw materials for preparing biochar slurry can not only increase agricultural output, but also reduce pollution, promote a virtuous cycle of ecology, and reduce dependence on coal resources.

[0004] The preparation of neutral biochar slurry from biomass and the preparation of low-carbon methanol dimethyl ether fuel through the entrained flow process are innovative and environmentally friendly technologies that provide an effective way to solve the problems of sustainable production of chemicals such as methanol and the treatment of waste biomass. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing low-carbon biomass methanol dimethyl ether fuel, which uses biochar and tar with high grindability and high volatility obtained by slow thermal cracking of green biomass, wood vinegar adjusted to neutrality and pulping additives to prepare neutral biochar slurry in a certain proportion, and effectively converts the neutral biochar slurry into low-carbon biomass methanol dimethyl ether fuel efficiently, stably and economically.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a method for preparing a low-carbon biomass methanol dimethyl ether fuel, the method comprising the following steps:

[0008] (1) thermally cracking the pretreated biomass at 380-450° C. in an air-tight manner to obtain biochar and cracking liquid;

[0009] (2) Grind the biochar obtained in step (1) in a ball mill, mix the biochar particles with particle sizes a and b in a mass ratio of 4:6, or mix the biochar particles with particle sizes a, b and c in a mass ratio of 1:8.5:0.5, wherein: 25 μm <a≤45μm,45μm<b≤75μm,c≤25μm;

[0010] (3) allowing the lysate obtained in step (1) to stand and separate to obtain an upper layer liquid and a lower layer tar, adding a pH adjuster to the upper layer liquid to adjust its pH to 6 to 8, filtering to obtain wood vinegar, adding an additive to the wood vinegar, and then mixing with the lower layer tar to obtain pulping water;

[0011] (4) adding the biochar particles mixed in step (2) to the pulping water obtained in step (3), stirring, and obtaining a neutral biochar slurry;

[0012] (5) mixing the neutral biochar slurry obtained in step (4) with oxygen to perform a gasification reaction to obtain a crude synthesis gas, and then removing sulfide and CO2 from the crude synthesis gas using a low-temperature methanol washing technology to obtain a purified crude synthesis gas;

[0013] (6) purifying the raw synthesis gas to perform a water-gas shift reaction, followed by hydrogen addition to adjust the hydrogen-to-carbon ratio to 2.05 to 3.10:1;

[0014] (7) The synthesis gas obtained in step (6) is fed into a methanol synthesis tower to produce methanol;

[0015] (8) The outlet stream of the methanol synthesis tower is evenly divided into two streams, one of which is sent to the dimethyl ether synthesis tower for methanol dehydration to produce dimethyl ether to obtain a mixture of methanol, dimethyl ether and water, which is then dehydrated to obtain methanol and dimethyl ether, which is mixed with the other stream to obtain methanol dimethyl ether fuel.

[0016] In the above technical solution, further, in step (1), the biomass pretreatment method is: crushing the biomass into particles of 3 to 5 mm, and heating and drying the particles to make the moisture content reach 10 to 20%;

[0017] The heating rate of the thermal cracking is 10 to 100°C / min.

[0018] The biomass described in the present invention is one or more of agricultural wastes such as rice straw, rice husk, corn straw, and forestry wastes such as felling residues, forest clearing and tending residues, and wood processing residues.

[0019] In the above technical solution, further, in step (1), the biochar has a dry ash-free volatile matter content greater than 30%.

[0020] In the above technical solution, further, in step (2), the rotation speed of the ball mill is 200 to 400 r / min, and the grinding time is 20 to 60 min.

[0021] In the above technical solution, further, in step (3), the pH adjusting agent is selected from one or more of sodium hydroxide, quicklime, and slaked lime;

[0022] The additives include dispersants, stabilizers and surfactants. The dispersants are selected from one or more of naphthalene sulfonates, lignin sulfonates and sulfonated humates; the stabilizers are selected from one or more of polyacrylamide flocculants, carboxymethyl cellulose salts and soluble starch; and the surfactants are selected from one or more of dodecylbenzene sulfonates and dodecyl sulfates.

[0023] In the above technical solution, further, in step (4), the stirring speed is 200 to 2000 r / min.

[0024] The obtained neutral biochar slurry comprises, by mass fraction, 38-65% biochar, 20-40% wood vinegar, 1-10% tar, 0.1-3% additives, and the balance is water.

[0025] In the above technical solution, further, in step (5), the gasification reaction conditions are: the gasification pressure is 1.0MPa to 9.0MPa, and the gasification temperature is 800°C to 1600°C;

[0026] The removal agent used in the low-temperature methanol washing technology is methanol.

[0027] In the above technical solution, further, in step (6), the water-gas shift reaction conditions are: pressure of 2-3 MPa and temperature of 180-350°C.

[0028] In the above technical solution, further, in step (7), the reaction conditions for preparing methanol from synthesis gas are: pressure of 2.5-5 MPa, temperature of 200-300° C., space velocity of 3000-10000 ml / (g cat·h), and methanol selectivity of >80%.

[0029] In the above technical solution, further, in step (8), the reaction conditions for dehydrating methanol to produce dimethyl ether are: pressure of 3-5 MPa and temperature of 220-400°C.

[0030] The beneficial effects of the present invention are:

[0031] 1. The biochar particles of the present invention adopt a grading technology, that is, biochars of different particle sizes are mixed in proportion to make pulp, which can effectively improve the pulping concentration of the biochar slurry. The increase in the pulping concentration will increase the overall calorific value of the slurry, which is beneficial to combustion and gasification in a gasifier, improve gasification efficiency, and reduce gasification energy consumption; the present invention first adjusts the pH of the wood vinegar to neutral, filters the particulate matter in the solution, and then makes pulp, which can effectively improve the pulping concentration and slurry quality, while avoiding pipeline blockage and wear on the nozzle.

[0032] 2. The neutral biochar slurry proposed by the present invention mainly consists of raw materials of biochar, wood vinegar and tar, all of which are products obtained by pyrolysis of renewable biomass. Compared with the non-renewable water-coal slurry currently used in industry, it can realize the sustainable production of synthesis gas and low-carbon biomass methanol dimethyl ether fuel; the carbon source of the neutral biochar slurry comes from organic matter and tar in biochar, wood vinegar, and its diversity of sources reduces the amount of biochar added while ensuring the carbon content in the slurry, thereby avoiding the problem of biochar being prone to agglomeration and poor pulping in the existing biochar pulping technology; compared with coal and coke, the sulfur content in biochar is low, only 5-10% of that in coke. Therefore, the sulfur content in the synthesis gas produced by using biochar slurry as raw material is greatly reduced, so that the energy consumption of acid gas separation is low, the loss of removal reagents is less, and the subsequent process cost can be reduced.

[0033] 3. The present invention uses wood vinegar instead of water to prepare biochar slurry, reducing the amount of water used in pulping. At the same time, due to the presence of organic matter in wood vinegar, it is more conducive to producing synthesis gas with a higher proportion of hydrogen during the gasification process, reducing the need for hydrogen supplementation in the subsequent synthesis of methanol dimethyl ether from synthesis gas.

[0034] 4. The present invention utilizes the products obtained by slow thermal cracking of biomass to prepare biochar slurry, and all products are fully utilized, that is, the carbon, hydrogen and other elements in the biomass can be recycled, and no organic waste is produced as a by-product, which can effectively reduce the pulping cost of biochar, and has important social significance in terms of low-carbon energy and environmental protection.

[0035] 5. The biochar used in pulping of the present invention has a higher dry ash-free volatile matter than general biochar. The dry ash-free volatile matter of ordinary biochar is generally 5% to 20%, and the dry ash-free volatile matter of the biochar used in the present invention is 30% to 40%, which can better improve the gasification efficiency and product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a process flow chart of the method for preparing low-carbon biomass methanol dimethyl ether fuel. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0038] Figure 1 The process flow chart of the preparation method of low-carbon biomass methanol dimethyl ether fuel of the present invention comprises the following steps:

[0039] (1) thermally cracking the pretreated biomass at 380-450° C. in an air-tight manner to obtain biochar and cracking liquid;

[0040] (2) Grinding the biochar obtained in step (1) in a ball mill, mixing the biochar particles with particle sizes a and b in a mass ratio of 4:6, or mixing the biochar particles with particle sizes a, b and c in a mass ratio of 1:8.5:0.5, wherein: 25 μm <a≤45μm,45μm<b≤75μm,c≤25μm;

[0041] (3) allowing the lysate obtained in step (1) to stand and separate to obtain an upper layer liquid and a lower layer tar, adding a pH adjuster to the upper layer liquid to adjust its pH to 6 to 8, filtering to obtain wood vinegar, adding an additive to the wood vinegar, and then mixing with the lower layer tar to obtain pulping water;

[0042] (4) adding the biochar particles mixed in step (2) to the pulping water obtained in step (3), stirring, and obtaining a neutral biochar slurry;

[0043] (5) mixing the neutral biochar slurry obtained in step (4) with oxygen to perform a gasification reaction to obtain a crude synthesis gas, and then removing sulfide and CO2 from the crude synthesis gas using a low-temperature methanol washing technology to obtain a purified crude synthesis gas;

[0044] (6) purifying the raw synthesis gas to perform a water-gas shift reaction, followed by hydrogen addition to adjust the hydrogen-to-carbon ratio to 2.05 to 3.10:1;

[0045] (7) The synthesis gas obtained in step (6) is fed into a methanol synthesis tower to produce methanol;

[0046] (8) The outlet stream of the methanol synthesis tower is evenly divided into two streams, one of which is sent to the dimethyl ether synthesis tower for methanol dehydration to produce dimethyl ether to obtain a mixture of methanol, dimethyl ether and water, which is then dehydrated to obtain methanol and dimethyl ether, which is mixed with the other stream to obtain methanol dimethyl ether fuel.

[0047] In step (1), the biomass is pretreated by: crushing the biomass into particles of 3 to 5 mm, and heating and drying the particles to make the moisture content reach 10 to 20%;

[0048] The heating rate of thermal cracking is 10-100°C / min;

[0049] Biomass is one or more of agricultural wastes such as rice straw, rice husk, corn straw, and forestry wastes such as logging residues, forest clearing and tending residues, and wood processing residues;

[0050] In step (1), the dry ash-free volatile matter of the biochar is greater than 30%;

[0051] In step (2), the rotation speed of the ball mill is 200 to 400 r / min, and the grinding time is 20 to 60 min;

[0052] In step (3), the pH adjusting agent is selected from one or more of sodium hydroxide, quicklime, and slaked lime;

[0053] The additive is selected from one or more of naphthalene sulfonate, lignin sulfonate, sulfonated humate, polyacrylamide flocculant, carboxymethyl cellulose salt, soluble starch, dodecylbenzene sulfonate, and dodecyl sulfate;

[0054] In step (4), the stirring speed is 200 to 2000 r / min;

[0055] The obtained neutral biochar slurry comprises, by mass fraction, 38-65% biochar, 20-40% wood vinegar, 1-10% tar, 0.1-3% additives, and the balance is water;

[0056] In step (5), the gasification reaction conditions are: gasification pressure is 1.0MPa to 9.0MPa, and gasification temperature is 800°C to 1600°C;

[0057] The removal agent used in low-temperature methanol washing technology is methanol;

[0058] In step (6), the water-gas shift reaction conditions are: pressure of 2-3 MPa and temperature of 180-350° C.;

[0059] In step (7), the reaction conditions for preparing methanol from synthesis gas are: pressure of 2.5-5 MPa, temperature of 200-300° C., space velocity of 3000-10000 ml / (g cat·h), and methanol selectivity of >80%;

[0060] In step (8), the reaction conditions for dehydrating methanol to produce dimethyl ether are: pressure of 3-5 MPa and temperature of 220-400°C.

[0061] All process flows of the present invention use renewable electricity to achieve the goal of controllable carbon intensity; hydrogen is produced by electrolyzing water.

[0062] The following are specific embodiments.

[0063] The fluidity of neutral biochar slurry is determined by visual inspection:

[0064] Grade A: Flow is continuous, smooth and uninterrupted; Grade B: Flow is relatively continuous but the fluid surface is not smooth; Grade C: Flows better with the help of external force; Grade D: Flows in a muddy state without slurry.

[0065] Example 1

[0066] (1) crushing corn stalks into particles of 3 to 5 mm, heating and drying them to a moisture content of 10 to 20%, heating at a rate of 30° C. / min, and thermally cracking them at 400° C. in an air-tight environment to obtain biochar and cracking liquid, and using cracking gas obtained by thermal cracking to supplement the electricity consumption of biomass thermal cracking;

[0067] The Hardgrove grindability index of the biochar produced by thermal cracking in this example is 138, the dry ash-free volatile matter is 36.45%, and the charcoal yield is 41.65%;

[0068] (2) grinding the biochar obtained in step (1) in a ball mill at a speed of 300 r / min for 30 min, sieving the ground biochar particles to obtain biochar particles with a particle size range of 25 to 45 μm and 45 to 75 μm, and mixing the above biochar particles at a mass ratio of 4:6;

[0069] (3) allowing the lysate obtained in step (1) to stand and separate to obtain an upper layer liquid and a lower layer tar, adding slaked lime to the upper layer liquid, adjusting its pH to 6-8, filtering to obtain wood vinegar, adding additives to the wood vinegar, and then mixing with the lower layer tar to obtain pulping water;

[0070] The additive includes the following components in weight percentage: 50% of naphthalene sulfonate and 50% of polyacrylamide flocculant;

[0071] (4) adding the mixed biochar particles in step (2) to the pulping water obtained in step (3), stirring at 200 to 2000 r / min to obtain a neutral biochar slurry with Class A fluidity, continuous flow, and smooth and uninterrupted flow;

[0072] The neutral biochar slurry obtained in this embodiment has a composition, by mass fraction, of 47% biochar, 39% wood vinegar, 8% tar, 1% additive, and the balance is water; after testing, the viscosity of the biochar slurry is 735 mPa·s;

[0073] (5) mixing the neutral biochar slurry obtained in step (4) with oxygen to carry out a gasification reaction, wherein the gasification reaction conditions are: a gasification pressure of 5.7 MPa and a gasification temperature of 1150° C. to obtain a crude synthesis gas, wherein the crude synthesis gas includes two or more of CO, CO2, H2 and CH4, and then using methanol as a removal agent and adopting a low-temperature methanol washing technology to remove sulfide and CO2 from the crude synthesis gas to obtain a purified crude synthesis gas;

[0074] (6) Purifying the crude synthesis gas to carry out a water-gas shift reaction, the water-gas shift reaction conditions being: a pressure of 2 MPa, a temperature of 250° C., a Ni-based catalyst, and subsequently supplementing hydrogen to adjust the hydrogen-to-carbon ratio to 2.05 to 3.10:1;

[0075] (7) The synthesis gas obtained in step (6) is fed into a methanol synthesis tower to produce methanol. The reaction pressure is 3 MPa, the temperature is 250° C., the space velocity is maintained at 8000 ml / (g cat·h), and the catalyst used is a Cu-Zn-Al based catalyst;

[0076] (8) The stream at the outlet of the methanol synthesis tower is evenly divided into two streams, one of which is sent to the dimethyl ether synthesis tower at 240°C, and the methanol is dehydrated to produce dimethyl ether at a temperature of 280°C and a pressure of 3.0 MPa using modified alumina as a catalyst to obtain a mixture of methanol, dimethyl ether and water. The mixture is cooled to 0°C and then separated to obtain methanol, dimethyl ether and water. The mixture is then dehydrated to obtain methanol and dimethyl ether (the water content after dehydration is <0.8%), which are mixed with the other stream to obtain methanol dimethyl ether fuel;

[0077] The calorific value of the methanol dimethyl ether fuel obtained in this embodiment is 18.7 MJ / L, and its purity is greater than 99.5%. The carbon emission intensity of the process flow is 5 to 20 g CO2 / MJ.

[0078] Example 2

[0079] (1) crushing corn stalks into particles of 3 to 5 mm, heating and drying them to a moisture content of 10 to 20%, heating at a rate of 30° C. / min, and thermally cracking them at 400° C. in an air-tight environment to obtain biochar and cracking liquid, and using cracking gas obtained by thermal cracking to supplement the electricity consumption of biomass thermal cracking;

[0080] The Hardgrove grindability index of the biochar produced by thermal cracking in this example is 124, the dry ash-free volatile matter is 36.45%, and the charcoal yield is 41.65%;

[0081] (2) grinding the biochar obtained in step (1) in a ball mill at a speed of 300 r / min for 30 min, sieving the ground biochar particles to obtain biochar particles with particle sizes ranging from 0 to 25 μm, 25 to 45 μm, and 45 to 75 μm, and mixing the above biochar particles at a mass ratio of 0.5:1:8.5;

[0082] (3) allowing the lysate obtained in step (1) to stand and separate to obtain an upper layer liquid and a lower layer tar, adding slaked lime to the upper layer liquid, adjusting its pH to 6-8, filtering to obtain wood vinegar, adding additives to the wood vinegar, and then mixing with the lower layer tar to obtain pulping water;

[0083] The additive includes the following components in weight percentage: 48.5% of naphthalene sulfonate and 51.5% of polyacrylamide flocculant;

[0084] (4) adding the mixed biochar particles in step (2) to the pulping water obtained in step (3), stirring at 200 to 2000 r / min to obtain a neutral biochar slurry with Class A fluidity, continuous flow, and smooth and uninterrupted flow;

[0085] The neutral biochar slurry obtained in this embodiment has a composition, by mass fraction, of 49% biochar, 37% wood vinegar, 8% tar, 1% additive, and the balance is water; after testing, the viscosity of the biochar slurry is 789 mPa·s;

[0086] (5) mixing the neutral biochar slurry obtained in step (4) with oxygen to carry out a gasification reaction, wherein the gasification reaction conditions are: a gasification pressure of 5.7 MPa and a gasification temperature of 1150° C. to obtain a crude synthesis gas, wherein the crude synthesis gas includes two or more of CO, CO2, H2 and CH4, and then using methanol as a removal agent and adopting a low-temperature methanol washing technology to remove sulfide and CO2 from the crude synthesis gas to obtain a purified crude synthesis gas;

[0087] (6) Purifying the crude synthesis gas to carry out a water-gas shift reaction, the water-gas shift reaction conditions being: a pressure of 2 MPa, a temperature of 250° C., a Ni-based catalyst, and subsequently supplementing hydrogen to adjust the hydrogen-to-carbon ratio to 2.05 to 3.10:1;

[0088] (7) The synthesis gas obtained in step (6) is fed into a methanol synthesis tower to produce methanol. The reaction pressure is 3 MPa, the temperature is 250° C., the space velocity is maintained at 8000 ml / (g cat·h), and the catalyst used is a Cu-Zn-Al based catalyst;

[0089] (8) The stream at the outlet of the methanol synthesis tower is evenly divided into two streams, one of which is sent to the dimethyl ether synthesis tower at 240°C, and the methanol is dehydrated to produce dimethyl ether at a temperature of 280°C and a pressure of 3.0 MPa using modified alumina as a catalyst to obtain a mixture of methanol, dimethyl ether and water. The mixture is cooled to 0°C and then separated to obtain methanol, dimethyl ether and water. The mixture is then dehydrated to obtain methanol and dimethyl ether (the water content after dehydration is <0.8%), which are mixed with the other stream to obtain methanol dimethyl ether fuel;

[0090] The calorific value of the methanol dimethyl ether fuel obtained in this embodiment is 19.5 MJ / L, and its purity is greater than 99.5%. The carbon emission intensity of the process flow is 5 to 20 g CO2 / MJ.

[0091] Example 3

[0092] (1) crushing rice husk into particles of 3 to 5 mm, heating and drying the particles to a moisture content of 10 to 20%, heating at a rate of 30° C. / min, and thermally cracking the particles in an airtight state at 400° C. to obtain biochar and cracking liquid, and using cracking gas obtained by thermal cracking to supplement the electricity consumption of biomass thermal cracking;

[0093] The Hardgrove grindability index of the biochar produced by thermal cracking in this example is 156, the dry ash-free volatile matter is 30.05%, and the charcoal yield is 40.90%;

[0094] (2) grinding the biochar obtained in step (1) in a ball mill at a speed of 300 r / min for 30 min, sieving the ground biochar particles to obtain biochar particles with a particle size range of 25 to 45 μm and 45 to 75 μm, and mixing the above biochar particles at a mass ratio of 4:6;

[0095] (3) allowing the lysate obtained in step (1) to stand and separate to obtain an upper layer liquid and a lower layer tar, adding slaked lime to the upper layer liquid, adjusting its pH to 6-8, filtering to obtain wood vinegar, adding additives to the wood vinegar, and then mixing with the lower layer tar to obtain pulping water;

[0096] The additive includes the following components in weight percentage: 50% of naphthalene sulfonate and 50% of polyacrylamide flocculant;

[0097] (4) adding the mixed biochar particles in step (2) to the pulping water obtained in step (3), stirring at 200 to 2000 r / min to obtain a neutral biochar slurry with Class A fluidity, continuous flow, and smooth and uninterrupted flow;

[0098] The neutral biochar slurry obtained in this embodiment has a composition, by mass fraction, of 38% biochar, 48% wood vinegar, 8% tar, 1% additive, and the balance is water; after testing, the viscosity of the biochar slurry is 697 mPa·s;

[0099] (5) mixing the neutral biochar slurry obtained in step (4) with oxygen to carry out a gasification reaction, wherein the gasification reaction conditions are: a gasification pressure of 5.7 MPa and a gasification temperature of 1150° C. to obtain a crude synthesis gas, wherein the crude synthesis gas includes two or more of CO, CO2, H2 and CH4, and then using methanol as a removal agent and adopting a low-temperature methanol washing technology to remove sulfide and CO2 from the crude synthesis gas to obtain a purified crude synthesis gas;

[0100] (6) Purifying the crude synthesis gas to carry out a water-gas shift reaction, the water-gas shift reaction conditions being: a pressure of 2 MPa, a temperature of 250° C., a Ni-based catalyst, and subsequently supplementing hydrogen to adjust the hydrogen-to-carbon ratio to 2.05 to 3.10:1;

[0101] (7) The synthesis gas obtained in step (6) is fed into a methanol synthesis tower to produce methanol. The reaction pressure is 3 MPa, the temperature is 250° C., the space velocity is maintained at 8000 ml / (g cat·h), and the catalyst used is a Cu-Zn-Al based catalyst;

[0102] (8) The stream at the outlet of the methanol synthesis tower is evenly divided into two streams, one of which is sent to the dimethyl ether synthesis tower at 240°C, and the methanol is dehydrated to produce dimethyl ether at a temperature of 280°C and a pressure of 3.0 MPa using modified alumina as a catalyst to obtain a mixture of methanol, dimethyl ether and water. The mixture is cooled to 0°C and then separated to obtain methanol, dimethyl ether and water. The mixture is then dehydrated to obtain methanol and dimethyl ether (the water content after dehydration is <0.8%), which are mixed with the other stream to obtain methanol dimethyl ether fuel;

[0103] The calorific value of the methanol dimethyl ether fuel obtained in this embodiment is 18.3 MJ / L, and its purity is greater than 99.5%. The carbon emission intensity of the process flow is 5 to 20 g CO2 / MJ.

[0104] Comparative Example 1

[0105] The preparation method of low-carbon biomass methanol dimethyl ether fuel is similar to that of Example 1, except that in step (2), the biochar particles are not graded, and the sieved particle size range is less than 100 μm.

[0106] The obtained neutral biochar slurry has a composition, by mass fraction, of 44% biochar, 42% wood vinegar, 8% tar, 1% additive, and the balance is water; after testing, the viscosity of the biochar slurry is 727 mPa·s.

[0107] Comparative Example 2

[0108] The preparation method of low-carbon biomass methanol dimethyl ether fuel is similar to that of Example 3, except that in step (2), the biochar particles are not graded, and the biochar particles are sieved to have a particle size range of less than 100 μm.

[0109] The resulting neutral biochar slurry has a composition by mass fraction, including: 36% biochar, 50% wood vinegar, 8% tar, 1% additives, and the balance is water. After testing, the viscosity of the biochar slurry is 632 mPa·s. The above-described embodiments only express several implementation methods of the present invention, and the descriptions are relatively specific and detailed, but they cannot be understood as limitations on the scope of the patent application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, several variations and improvements can be made, which all belong to the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for preparing low-carbon biomass methanol dimethyl ether fuel, characterized in that: The method comprises the following steps: (1) thermally cracking the pretreated biomass at 380-450° C. in an air-tight manner to obtain biochar and cracking liquid; (2) Grinding the biochar obtained in step (1) in a ball mill, mixing the biochar particles with particle sizes a and b in a mass ratio of 4:6, or mixing the biochar particles with particle sizes a, b and c in a mass ratio of 1:8.5:0.5, wherein: 25 μm <a≤45μm,45μm<b≤75μm,c≤25μm; (3) allowing the lysate obtained in step (1) to stand and separate to obtain an upper layer liquid and a lower layer tar, adding a pH adjuster to the upper layer liquid to adjust its pH to 6 to 8, filtering to obtain wood vinegar, adding an additive to the wood vinegar, and then mixing with the lower layer tar to obtain pulping water; (4) adding the biochar particles mixed in step (2) to the pulping water obtained in step (3), stirring, and obtaining a neutral biochar slurry; (5) mixing the neutral biochar slurry obtained in step (4) with oxygen to perform a gasification reaction to obtain a crude synthesis gas, and then removing sulfide and CO2 from the crude synthesis gas using a low-temperature methanol washing technology to obtain a purified crude synthesis gas; (6) purifying the raw synthesis gas to perform a water-gas shift reaction, followed by hydrogen addition to adjust the hydrogen-to-carbon ratio to 2.05 to 3.10:1; (7) The synthesis gas obtained in step (6) is fed into a methanol synthesis tower to produce methanol; (8) The outlet stream of the methanol synthesis tower is evenly divided into two streams, one of which is sent to the dimethyl ether synthesis tower for methanol dehydration to produce dimethyl ether, thereby obtaining a mixture of methanol, dimethyl ether and water, which is then dehydrated to obtain methanol and dimethyl ether, which is mixed with the other stream to obtain methanol dimethyl ether fuel.

2. The preparation method according to claim 1, characterized in that: In step (1), the biomass pretreatment method is: crushing the biomass into particles of 3 to 5 mm, and heating and drying the particles to make the moisture content reach 10 to 20%; The heating rate of the thermal cracking is 10 to 100° C. / min.

3. The preparation method according to claim 1, characterized in that: In step (1), the biochar has a dry ash-free volatile matter content greater than 30%.

4. The preparation method according to claim 1, characterized in that: In step (2), the rotation speed of the ball mill is 200 to 400 r / min, and the grinding time is 20 to 60 min.

5. The preparation method according to claim 1, characterized in that: In step (3), the pH adjusting agent is selected from one or more of sodium hydroxide, quicklime, and slaked lime; The additive is selected from one or more of naphthalene sulfonate, lignin sulfonate, sulfonated humate, polyacrylamide flocculant, carboxymethyl cellulose salt, soluble starch, dodecylbenzene sulfonate and dodecyl sulfate.

6. The preparation method according to claim 1, characterized in that: In step (4), the stirring speed is 200 to 2000 r / min. The obtained neutral biochar slurry comprises, by mass fraction, 38-65% biochar, 20-40% wood vinegar, 1-10% tar, 0.1-3% additives, and the balance is water.

7. The preparation method according to claim 1, characterized in that: In step (5), the gasification reaction conditions are: gasification pressure of 1.0-9.0 MPa, gasification temperature of 800-1600° C.; The removal agent used in the low-temperature methanol washing technology is methanol.

8. The preparation method according to claim 1, characterized in that: In step (6), the water-gas shift reaction conditions are: pressure of 2-3 MPa and temperature of 180-350°C.

9. The preparation method according to claim 1, characterized in that: In step (7), the reaction conditions for preparing methanol from synthesis gas are: pressure of 2.5-5 MPa, temperature of 200-300° C., space velocity of 3000-10000 ml / (g cat·h), and methanol selectivity of >80%.

10. The preparation method according to claim 1, characterized in that: In step (8), the reaction conditions for dehydrating methanol to produce dimethyl ether are: pressure of 3-5 MPa and temperature of 220° C.-400° C.

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