A method for burning furfural residue from biomass solid waste

Abstract

The present invention discloses a method for burning furfural residue, a biomass solid waste. Bentonite is added to the furfural residue, mixed evenly, and then stacked. The residue is passed through a 200-mesh sieve. The oversize material is the low-moisture furfural residue, and the undersize material is the water-absorbed bentonite. The water-absorbed bentonite is dried, recovered, and recycled. Calcium-based bentonite and sodium-based bentonite are added to the furfural residue in a certain proportion, taking advantage of their strong water absorption properties. These materials can absorb moisture from the furfural residue, thereby obtaining low-moisture furfural residue. The moisture content of the furfural residue is reduced to below 30%, and the residue can be directly used as a biomass fuel without drying.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass fuel preparation, in particular to a method for burning biomass solid waste furfural residue. Background Art

[0002] Furfural residue is a by-product of producing furfural (furfural) by hydrolysis of corn cobs. It contains a large amount of lignin, cellulose, etc. It has a high secondary utilization value and can be used as biomass fuel.

[0003] However, furfural slag is large (average particle size approximately 15mm) and has a high moisture content (30-40%), resulting in a low burnout rate and slow combustion. Furthermore, furfural slag contains high levels of alkali metals such as potassium and sodium, which easily form low-melting-point silicates during boiler combustion, causing it to stick to the bed material surface and form lumps.

[0004] The current treatment method is to increase the combustion speed and burnout rate by reducing the moisture content and controlling the particle size distribution range. Conventional methods to reduce moisture content are mostly baking and heating, reducing the moisture content of furfural residue to below 30%. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for burning furfural residue from biomass solid waste, so as to solve the problems of low burnout rate, slow combustion speed and compacted particles of furfural residue in the prior art.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for burning furfural residue from biomass solid waste comprises the following steps:

[0008] (1) Mixing: Mix high-moisture furfural residue with low-moisture water absorbent;

[0009] (2) Moisture transfer: transfer part of the water in the high-moisture furfural residue to the low-moisture water absorbent to obtain a mixture of low-moisture furfural residue and high-moisture water absorbent;

[0010] (3) Screening: The mixture of low-moisture furfural residue and high-moisture water absorbent is screened, the sieve-surface material is low-moisture furfural residue, and the sieve-surface material is high-moisture water absorbent;

[0011] (4) Combustion: compressing low-moisture furfural slag into biomass fuel for combustion, or directly burning low-moisture furfural slag in bulk as biomass fuel;

[0012] (5) Drying and recovery: The high-moisture water absorbent obtained in step (3) is dried using the waste heat of the flue gas generated by the combustion of the low-moisture furfural slag in step (4), and then returned to step (1) as a low-moisture water absorbent.

[0013] In the above-mentioned method for burning furfural slag of biomass solid waste, in step (1): the low-moisture water absorbent is a mixture of calcium-based bentonite and sodium-based bentonite, and the water absorption expansion multiple of the calcium-based bentonite is smaller than the water absorption expansion multiple of the sodium-based bentonite.

[0014] In the above-mentioned method for burning furfural residue of biomass solid waste, in step (1): in the low-moisture water absorbent, the mass ratio of calcium-based bentonite to sodium-based bentonite is 2 to 3:1.

[0015] In the above-mentioned method for burning furfural residue of biomass solid waste, the calcium-based bentonite is carboxymethyl starch-modified calcium-based bentonite.

[0016] The above-mentioned method for burning furfural residue from biomass solid waste and the method for preparing carboxymethyl starch-modified calcium-based bentonite are as follows:

[0017] Step (1-1), adding sodium carboxymethyl starch to acetic acid, stirring thoroughly, adding water, adjusting the pH to 2 with hydrochloric acid solution and continuing to stir; then performing solid-liquid separation, washing the precipitate obtained by solid-liquid separation with anhydrous ethanol and drying to obtain carboxymethyl starch;

[0018] Step (1-2): adding carboxymethyl starch and calcium bentonite to an ethanol solution, then adding cetyltrimethylammonium bromide and ammonium molybdate and stirring to mix evenly, and then placing in a water bath and stirring to fully react; after the water bath ends, filtering and drying to obtain carboxymethyl starch modified calcium bentonite.

[0019] The above-mentioned biomass solid waste furfural residue combustion method comprises the following steps: in step (1-1), the mass volume ratio of sodium carboxymethyl starch to acetic acid is (0.75-1.0) g / mL; the volume ratio of water to acetic acid is (0.75-1.0):1; the concentration of the hydrochloric acid solution is 1-1.5 mol / L, the pH is adjusted to 2, and stirring is continued for 20-30 minutes; after solid-liquid separation, the precipitate is washed 2-3 times with anhydrous ethanol and dried at 60°C for 1-2 hours; the dried solid product is passed through a 200-mesh sieve, and the sieve-screened product is the carboxymethyl starch;

[0020] In step (1-2), the mass ratio of carboxymethyl starch to calcium bentonite is 1:10-20; the mass volume ratio of calcium bentonite to ethanol solution is (0.15-0.50) g / mL, and the ethanol solution is prepared by mixing water and anhydrous ethanol in a volume ratio of (1-3):1; the amount of cetyltrimethylammonium bromide added is 1-2% of the total mass of the carboxymethyl starch and calcium bentonite, and the amount of ammonium molybdate added is 0.5-1.0% of the total mass of the carboxymethyl starch and calcium bentonite; the water bath stirring conditions are: stirring in a water bath at 50-60° C. for 2-3 hours; and the drying conditions are drying at 80-90° C. for 6-10 hours.

[0021] The above-mentioned biomass solid waste furfural residue combustion method comprises the following steps: in step (1-1), the mass volume ratio of sodium carboxymethyl starch to acetic acid is 1.0 g / mL; the volume ratio of water to acetic acid is 0.75:1; the concentration of the hydrochloric acid solution is 1.0 mol / L, the pH is adjusted to 2, and stirring is continued for 30 minutes; after solid-liquid separation, the precipitate is washed three times with anhydrous ethanol and dried at 60°C for 1.5 hours; the dried solid product is passed through a 200-mesh sieve, and the sieve-through material is the carboxymethyl starch;

[0022] In step (1-2), the mass ratio of carboxymethyl starch to calcium bentonite is 1:10; the mass volume ratio of calcium bentonite to ethanol solution is 0.20 g / mL, and the ethanol solution is prepared by mixing water and anhydrous ethanol in a volume ratio of 2:1; the amount of cetyltrimethylammonium bromide added is 1.0% of the total mass of the carboxymethyl starch and calcium bentonite, and the amount of ammonium molybdate added is 0.5% of the total mass of the carboxymethyl starch and calcium bentonite; the water bath stirring conditions are: stirring in a water bath at 60° C. for 2 hours; and the drying conditions are: drying at 80° C. for 4 hours.

[0023] In the above-mentioned biomass solid waste furfural slag combustion method, in step (1): the amount of low-moisture water absorbent added is 15-20% of the mass of the high-moisture furfural slag; the particle size of the furfural slag is controlled to be 0.5-1 mm; and the low-moisture water absorbent is passed through a 400-mesh sieve. When preparing the low-moisture water absorbent, calcium-based bentonite and sodium-based bentonite are first passed through a 400-mesh sieve respectively, and then the undersize of the calcium-based bentonite and the undersize of the sodium-based bentonite are mixed to form the low-moisture water absorbent.

[0024] In the above-mentioned method for burning furfural residue from biomass solid waste, in step (3), the mixture of low-moisture furfural residue and high-moisture water absorbent is passed through a 200-mesh sieve during screening.

[0025] In the above-mentioned method for burning furfural residue from biomass solid waste, in step (2), the method for transferring moisture is as follows: the stacking time at room temperature is 3-4 days.

[0026] In the above-mentioned method for burning furfural slag of biomass solid waste, in step (4): the calcium-based bentonite and sodium-based bentonite remaining in the low-moisture furfural slag can effectively reduce the adhesion of biomass combustion ash particles on the surface of the fluidized bed at high temperature.

[0027] The technical solution of the present invention achieves the following beneficial technical effects:

[0028] 1. The present invention utilizes the strong water absorption characteristics of calcium-based bentonite and sodium-based bentonite, which are added to furfural residue in a certain proportion, thereby absorbing moisture in the furfural residue to obtain furfural residue with low moisture content, and reducing the moisture content in the furfural residue to below 30%, so that it can be directly used as biomass fuel without drying.

[0029] 2. Calcium bentonite and sodium bentonite are selected as low-moisture water absorbents in the present invention because: calcium bentonite has a small water absorption capacity, which is no more than 200%, an expansion multiple of only several to more than ten times, and a fast water absorption rate, and a colloid value of about 60%; sodium bentonite has a large water absorption capacity, which is up to more than 500%, and an expansion multiple of up to 20 to 30 times, but its water absorption rate is slow, takes a long time, and the colloid value is as high as 100%. The present invention rationally controls the ratio of calcium-based bentonite to sodium-based bentonite based on their respective characteristics. A certain proportion of sodium-based bentonite and calcium-based bentonite are evenly added to the furfural slag as a low-moisture absorbent during stacking when the furfural slag is discharged, thereby naturally reducing the moisture content of the furfural slag. Therefore, the method of the present invention enables moisture in a large-volume material with poor thermal conductivity (high-moisture furfural slag) to be transferred to a small-volume material with good thermal conductivity (a mixture of calcium-based bentonite and sodium-based bentonite as a low-moisture absorbent). The method eliminates the need for a complex process of drying the furfural slag before combustion, and only requires the use of low-temperature flue gas to dry the small-volume sodium-based bentonite and calcium-based bentonite with good thermal conductivity.

[0030] 3. Since sodium bentonite has the characteristics of slow water absorption and high colloid price, while calcium bentonite has the characteristics of fast water absorption and low colloid price, after mixing the two with furfural residue in a specific ratio, calcium bentonite can quickly reduce the moisture content at the bentonite-furfural residue interface, thereby effectively avoiding the adhesion or adhesion of sodium bentonite to furfural residue after water absorption when the moisture content of furfural residue is high in the initial stage, thereby avoiding the problem of difficulty in recycling most of the sodium bentonite after water absorption.

[0031] 4. Calcium bentonite can quickly absorb water and saturate and expand to several to ten times its own volume, while the particle size of furfural residue is usually in the millimeter range. Therefore, sodium bentonite with a smaller particle size can fill the "small gaps formed between calcium bentonite particles or between calcium bentonite particles and furfural residue particles" during the initial water absorption, further preventing the sodium bentonite from adhering or sticking to the furfural residue in the early stage of water absorption. As the sodium bentonite slowly absorbs water and expands dozens of times, it gradually fills these small gaps. Although the contact area between the sodium bentonite particles and the furfural residue increases, the contact area ratio is small relative to the total surface area of the expanded sodium bentonite, and the adhesion or sticking force is far less than the gravity of the expanded sodium bentonite. Moreover, the moisture content of the furfural residue is further reduced at this time, making it easy to separate the sodium bentonite and calcium bentonite by screening before combustion. The overall recovery rate of sodium bentonite and calcium bentonite can reach 84.7%.

[0032] 5. Sodium bentonite and calcium bentonite have the property of reversible dehydration and rehydration, and compared with furfural slag, sodium bentonite and calcium bentonite have strong thermal conductivity. By utilizing the waste heat of flue gas to dry sodium bentonite and calcium bentonite, the material can be rapidly heated from the outside to the inside. The bound water adsorbed by sodium bentonite and calcium bentonite can be lost within 60 minutes at a temperature between 100-200°C. Therefore, the present invention utilizes the waste heat of low-temperature flue gas (below 200°C) generated by the combustion of furfural slag to quickly dry and dehydrate the sodium bentonite and calcium bentonite after absorbing water, and then continue to put them into use. It is only necessary to replenish the sodium bentonite and calcium bentonite lost during the circulation process to realize the circulation of the furfural slag combustion process.

[0033] 6. The present invention utilizes carboxymethyl starch to modify calcium bentonite. The carboxymethyl starch-modified calcium bentonite prepared by the method of the present invention is mixed with sodium bentonite and then used as a low-moisture water absorbent to mix with furfural residue. The recovery rate of screening after moisture transfer is significantly improved, and its water absorption capacity remains essentially unchanged after drying in the low-temperature flue gas generated by combustion of furfural residue, and it can be used repeatedly. The method of modifying calcium bentonite with carboxymethyl starch of the present invention can make the hydrophobic end of carboxymethyl starch firmly adsorbed on the surface of calcium bentonite, while its hydrophilic end can combine with water molecules in furfural residue, thereby establishing a bridge connection between calcium bentonite and furfural residue, significantly improving the affinity of calcium bentonite and furfural residue, and effectively preventing sodium bentonite with high colloid value from adhering to furfural residue, so that the overall recovery rate of sodium bentonite and calcium bentonite reaches 92.5%. DETAILED DESCRIPTION

[0034] Example 1

[0035] The method for burning furfural slag from biomass solid waste in this embodiment comprises the following steps:

[0036] (1) Mixing: 1000 g of high-moisture furfural residue with a moisture content of 40% is mixed evenly with 150 g of a low-moisture water absorbent; the low-moisture water absorbent is made by mixing 100 g of calcium-based bentonite and 50 g of sodium-based bentonite, and the water absorption expansion multiple of the calcium-based bentonite is smaller than that of the sodium-based bentonite;

[0037] The low-moisture water absorbent is prepared by: firstly passing calcium-based bentonite and sodium-based bentonite through a 400-mesh sieve respectively, and then taking 100 g of the calcium-based bentonite undersieve and 50 g of the sodium-based bentonite undersieve to mix, thereby obtaining the low-moisture water absorbent;

[0038] In this embodiment, the particle size of furfural residue is controlled within the range of 0.5 to 1 mm;

[0039] (2) Moisture transfer: The mixture of high-moisture furfural residue and low-moisture water absorbent is piled up at room temperature for 3 days to allow the water in the high-moisture furfural residue to be fully transferred to the low-moisture water absorbent, thereby obtaining a mixture of low-moisture furfural residue and high-moisture water absorbent;

[0040] (3) Screening: The mixture of low-moisture furfural residue and high-moisture water absorbent is screened through a 200-mesh sieve. The sieve-surface material is low-moisture furfural residue (the moisture content of which is 21% after testing), and the sieve-surface material is a mixture of high-moisture water absorbent - calcium-based bentonite and sodium-based bentonite after water absorption and expansion;

[0041] (4) Combustion: compressing low-moisture furfural slag into biomass fuel for combustion, or directly burning low-moisture furfural slag in bulk as biomass fuel;

[0042] (5) Drying and recovery: The high-moisture water absorbent obtained in step (3) is dried for 60 min using the flue gas waste heat (less than 200° C.) generated by the combustion of the low-moisture furfural slag in step (4) to obtain 127 g of a mixture of calcium-based bentonite and sodium-based bentonite. After drying, the mixture is returned to step (1) as a low-moisture water absorbent.

[0043] In this example, the overall recovery rate of the low-moisture water absorbents (sodium bentonite and calcium bentonite) was 84.7%. In step (4), the screened oversize material, in addition to the furfural residue, also contained a small amount of high-moisture water absorbents (calcium bentonite and sodium bentonite). These bentonites can effectively reduce the adhesion of biomass combustion ash particles on the surface of the fluidized bed at high combustion temperatures.

[0044] Example 2

[0045] The method for burning furfural slag from biomass solid waste in this embodiment comprises the following steps:

[0046] (1) Mixing: 1000 g of high-moisture furfural residue with a moisture content of 45% was mixed evenly with 200 g of a low-moisture water absorbent; the low-moisture water absorbent was prepared by mixing 150 g of carboxymethyl starch-modified calcium-based bentonite and 50 g of sodium-based bentonite, and the water absorption expansion multiple of the calcium-based bentonite was smaller than that of the sodium-based bentonite;

[0047] The low-moisture water absorbent is prepared by: first, passing carboxymethyl starch-modified calcium-based bentonite and sodium-based bentonite through a 400-mesh sieve respectively, and then taking 150 g of the carboxymethyl starch-modified calcium-based bentonite under the sieve and 50 g of the sodium-based bentonite under the sieve to mix, thereby obtaining the low-moisture water absorbent;

[0048] In this embodiment, the particle size of furfural residue is controlled within the range of 0.5 to 1 mm;

[0049] (2) Moisture transfer: The mixture of high-moisture furfural residue and low-moisture water absorbent is piled up at room temperature for 3 days to allow the water in the high-moisture furfural residue to be fully transferred to the low-moisture water absorbent, thereby obtaining a mixture of low-moisture furfural residue and high-moisture water absorbent;

[0050] (3) Screening: The mixture of low-moisture furfural residue and high-moisture water absorbent is screened through a 200-mesh sieve. The sieve-surface material is low-moisture furfural residue (the moisture content of which is 20% after testing), and the sieve-surface material is a mixture of high-moisture water absorbent - carboxymethyl starch-modified calcium-based bentonite and sodium-based bentonite after water absorption and expansion;

[0051] (4) Combustion: compressing low-moisture furfural slag into biomass fuel for combustion, or directly burning low-moisture furfural slag in bulk as biomass fuel;

[0052] (5) Drying and recovery: The high-moisture water absorbent obtained in step (3) is dried for 60 min using the flue gas waste heat (less than 200° C.) generated by the combustion of the low-moisture furfural slag in step (4) to obtain 185 g of a mixture of carboxymethyl starch-modified calcium-based bentonite and sodium-based bentonite. After drying, the mixture is returned to step (1) as a low-moisture water absorbent.

[0053] In step (1) of this embodiment, the preparation method of carboxymethyl starch modified calcium bentonite is:

[0054] Step (1-1): 20 g of sodium carboxymethyl starch was added to 20 mL of acetic acid, followed by the addition of 15 mL of water. The pH value was adjusted to 2 with 1 mol / L hydrochloric acid, and the mixture was stirred for 25 min. The mixture was washed with ethanol three times and filtered. The mixture was dried at 60° C. for 1.5 h and passed through a 200-mesh sieve to obtain carboxymethyl starch.

[0055] In step (1-2), 20 g of carboxymethyl starch and 200 g of calcium bentonite were added to 1000 mL of ethanol solution (the ethanol solution was prepared by mixing water and anhydrous ethanol in a volume ratio of 2:1), and then 2.2 g of hexadecyltrimethylammonium bromide and 1.1 g of ammonium molybdate were added. The mixture was stirred in a 60°C water bath for 2 h, filtered, and dried at 80°C for 4 h to obtain carboxymethyl starch-modified calcium bentonite.

[0056] In this embodiment, the overall recovery rate of the low-moisture water absorbent - carboxymethyl starch modified calcium-based bentonite and sodium-based bentonite is 92.5%.

[0057] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A method for burning furfural slag from biomass solid waste, characterized in that: The steps include: (1) Mixing: Mix high-moisture furfural residue with a low-moisture water absorbent; the low-moisture water absorbent is a mixture of calcium-based bentonite and sodium-based bentonite, and the water absorption expansion multiple of the calcium-based bentonite is smaller than that of the sodium-based bentonite; in the low-moisture water absorbent, the mass ratio of the calcium-based bentonite to the mass of the sodium-based bentonite is 2 to 3:1; (2) Moisture transfer: transfer part of the water in the high-moisture furfural residue to the low-moisture water absorbent to obtain a mixture of low-moisture furfural residue and high-moisture water absorbent; (3) Screening: The mixture of low-moisture furfural residue and high-moisture water absorbent is screened, the sieve-surface material is low-moisture furfural residue, and the sieve-surface material is high-moisture water absorbent; (4) Combustion: compressing low-moisture furfural slag into biomass fuel for combustion, or directly burning low-moisture furfural slag in bulk as biomass fuel; (5) Drying and recovery: The high-moisture water absorbent obtained in step (3) is dried using the waste heat of the flue gas generated by the combustion of the low-moisture furfural slag in step (4), and the dried product is returned to step (1) as a low-moisture water absorbent.

2. The biomass solid waste furfural slag combustion method according to claim 1, wherein Calcium bentonite is carboxymethyl starch modified calcium bentonite.

3. The biomass solid waste furfural slag combustion method according to claim 2, wherein: The preparation method of carboxymethyl starch modified calcium bentonite is as follows: Step (1-1), adding sodium carboxymethyl starch to acetic acid, stirring thoroughly, adding water, adjusting the pH to 2 with hydrochloric acid solution and continuing to stir; then performing solid-liquid separation, washing the precipitate obtained by solid-liquid separation with anhydrous ethanol and drying to obtain carboxymethyl starch; Step (1-2): adding carboxymethyl starch and calcium bentonite to an ethanol solution, then adding cetyltrimethylammonium bromide and ammonium molybdate and stirring to mix evenly, and then placing in a water bath and stirring to fully react; after the water bath ends, filtering and drying to obtain carboxymethyl starch modified calcium bentonite.

4. The biomass solid waste furfural slag combustion method according to claim 3, characterized in that: In step (1-1), the mass volume ratio of sodium carboxymethyl starch to acetic acid is (0.75-1.0) g / mL; the volume ratio of water to acetic acid is (0.75-1.0):1; the concentration of the hydrochloric acid solution is 1-1.5 mol / L, the pH is adjusted to 2, and stirring is continued for 20-30 minutes; after solid-liquid separation, the precipitate is washed 2-3 times with anhydrous ethanol and dried at 60° C. for 1-2 hours; the dried solid product is passed through a 200-mesh sieve, and the sieve-screened product is carboxymethyl starch; In step (1-2), the mass ratio of carboxymethyl starch to calcium bentonite is 1:10-20; the mass volume ratio of calcium bentonite to ethanol solution is (0.15-0.50) g / mL, and the ethanol solution is prepared by mixing water and anhydrous ethanol in a volume ratio of (1-3):1; the amount of cetyltrimethylammonium bromide added is 1-2% of the total mass of the carboxymethyl starch and calcium bentonite, and the amount of ammonium molybdate added is 0.5-1.0% of the total mass of the carboxymethyl starch and calcium bentonite; the water bath stirring conditions are: stirring in a water bath at 50-60° C. for 2-3 hours; and the drying conditions are drying at 80-90° C. for 4-8 hours.

5. The biomass solid waste furfural slag combustion method according to claim 4, characterized in that: In step (1-1), the mass volume ratio of sodium carboxymethyl starch to acetic acid is 1.0 g / mL; the volume ratio of water to acetic acid is 0.75:1; the concentration of the hydrochloric acid solution is 1.0 mol / L, the pH is adjusted to 2, and stirring is continued for 25 minutes; After solid-liquid separation, the precipitate was washed three times with anhydrous ethanol and dried at 60°C for 1.5 hours. The dried solid product was sieved with a 200-mesh sieve, and the residue below the sieve was carboxymethyl starch. In step (1-2), the mass ratio of carboxymethyl starch to calcium bentonite is 1:10; the mass volume ratio of calcium bentonite to ethanol solution is 0.20 g / mL, and the ethanol solution is prepared by mixing water and anhydrous ethanol in a volume ratio of 2:1; the amount of cetyltrimethylammonium bromide added is 1.0% of the total mass of the carboxymethyl starch and calcium bentonite, and the amount of ammonium molybdate added is 0.5% of the total mass of the carboxymethyl starch and calcium bentonite; the water bath stirring conditions are: stirring in a water bath at 60° C. for 2 hours; and the drying conditions are: drying at 80° C. for 4 hours.

6. The method for burning furfural slag from biomass solid waste according to any one of claims 1 to 5, characterized in that: In step (1): the amount of low-moisture water absorbent added is 15-20% of the mass of high-moisture furfural residue; the particle size of the furfural residue is controlled to be 0.5-1 mm; and the low-moisture water absorbent is passed through a 400-mesh sieve.

7. The method for burning furfural slag from biomass solid waste according to claim 6, wherein: In step (3), the mixture of low-moisture furfural residue and high-moisture water absorbent is passed through a 200-mesh sieve during screening.

8. The method for burning furfural slag from biomass solid waste according to claim 7, wherein: In step (2), the method for moisture transfer is: stacking the mixture of high-moisture furfural residue and low-moisture water absorbent at room temperature for 3 to 4 days.