JP4028588B2 - How to use lignocellulosic biomass - Google Patents

Description

The present invention relates to a method for using lignocellulosic biomass such as wood, and more particularly to a method for using lignocellulosic biomass for recovering combustible gas mainly composed of methane from lignocellulosic biomass such as wood. is there.

Biomass, which is the total of organic matter synthesized from carbon dioxide and water by using photosynthetic organisms, and the organic matter produced by converting them with other organisms, allows the organisms involved in the production of organic matter to grow By maintaining the environment, it can be repeatedly reproduced. In addition, even when biomass is burned to obtain thermal energy, the generated carbon dioxide (CO ₂ ) can be fixed again as the same organic matter, increasing the concentration of carbon dioxide in the atmosphere, which is a cause of global warming. Does not cause. In this sense, biomass is considered to be a renewable and carbon-neutral fuel source, like solar and wind power.
In particular, lignocellulosic biomass, in which fiber cells mainly composed of cellulose and hemicellulose are combined by an intercellular layer composed mainly of lignin, has a high photosynthetic efficiency and is a tree that thrives widely throughout the earth including Japan. Therefore, it is expected to be used more widely as a renewable and carbon neutral fuel source in the future.

However, lignocellulosic biomass has a lower calorific value per unit weight than fossil fuels such as coal, oil, and natural gas, and is usually a solid and has a low bulk density. It is not suitable for long-distance transportation or storage in large quantities from when it is sampled to when it is consumed, and it cannot be used as fuel for internal combustion engines such as automobile engines. For this reason, there are restrictions on the use of lignocellulosic biomass as fuel as it is, and in order to be used more widely in the future, the calorific value per unit weight is large and easy to transport. It is required to switch to a fluid fuel that can also be used as fuel.
By the way, in general, an organic fuel containing carbon and hydrogen can be uniformly burned as the ratio of hydrogen to carbon increases. Therefore, nitrogen oxides generated during combustion, unburned hydrocarbons or There is a tendency that the amount of pollutants such as carbon monoxide (CO) is also low. For this reason, methane (CH ₄ ) having 4 hydrogen atoms per carbon atom is considered to be the cleanest fuel after hydrogen with zero carbon content. In addition, since methane can be easily reformed into hydrogen and carbon dioxide, it can be used as a fuel for a fuel cell which is a clean and highly efficient power generator.
For the above reasons, when lignocellulosic biomass is used as a fuel, it is preferably once converted into a combustible gas mainly composed of methane or hydrogen.

  In order to recover flammable gas mainly composed of methane and hydrogen from lignocellulosic biomass, conventionally, the lignocellulosic biomass is supplied with heat obtained from another heat source with almost no oxygen supplied. By making the temperature sufficiently high, it decomposes into combustible gas and char mainly composed of low molecular gases such as hydrogen and methane (hereinafter referred to as thermal decomposition), or lignocellulosic biomass is completely burned. By supplying oxygen less than the required amount, incomplete combustion is performed, and the heat generated is brought to a sufficiently high temperature to obtain a combustible gas mainly composed of low molecular gases such as hydrogen and methane. (Hereinafter referred to as gasification) was normal.

However, lignocellulosic biomass contains a relatively large amount of oxygen, unlike hydrocarbon fuels such as coal, which hardly contain oxygen. For this reason, when lignocellulosic biomass is heated to a temperature necessary to obtain a combustible gas mainly composed of low molecular gases such as hydrogen and methane, gasification is performed by supplying a small amount of oxygen. Of course, even in the case of pyrolysis with little oxygen supply, most of the carbon contained is converted to carbon monoxide instead of methane. Carbon monoxide itself is not only toxic but also has a low calorific value, and further has a problem of degrading the electrolyte when used as a fuel for a fuel cell.
Therefore, in order to use a gas containing carbon monoxide as fuel, it is preferable to convert it to hydrogen or methane by the reaction of the following formulas (1) and (2). There is a problem that a process different from the process is required, and that an expensive catalyst and a very high temperature are required in the process.
CO + H ₂ O → H ₂ + CO ₂ (1)
CO + 3H ₂ → CH ₄ + H ₂ O (2)

Further, in such a conventional method, the pyrolysis or gasification step for obtaining a gas mainly composed of hydrogen and carbon monoxide is usually performed with lignocellulosic biomass at a high temperature of about 1000 ° C. . And the member exposed to such a high temperature state needs to be composed of an expensive heat-resistant material, and the heat-resistant material that can be used industrially has a short life and has to be frequently maintained. .
Furthermore, when lignocellulosic biomass is pyrolyzed or gasified at a relatively low temperature, a tar content is generated, but at a temperature around 1000 ° C., the generated tar content cannot be completely decomposed. For this reason, in a normal operation state, a tar content is contained in a combustible gas mainly composed of hydrogen and carbon monoxide. The tar content is condensed after the gas is cooled, and the gas is It adheres to flowing ducts and gas storage containers. In order to prevent this, there is a problem that it is necessary to further increase the temperature after using an expensive heat-resistant material or to separately provide a step of removing tar before or simultaneously with cooling of the gas.

In general, lignocellulosic biomass such as wood has a high water content, but in the conventional method, all the water contained in the lignocellulosic biomass is evaporated at the same time in the pyrolysis or gasification step. Become. For this reason, in the process of pyrolysis, it is necessary to obtain extra heat necessary for water evaporation from another heat source, while in the gasification process, it is generated to evaporate water. Since heat is taken away, in order to obtain a necessary high temperature state, a combustion aid must be supplied from the outside to raise the combustion temperature. In any case, there is a problem that energy is lost to evaporate the water contained in the lignocellulosic biomass.
In order to avoid such problems, it is necessary to dry the lignocellulosic biomass in advance and then pyrolyze or gasify it, but even in that case, heat is required for drying or it is very long. There is a problem that it is necessary to store in a dry place for hours.

Special table hei 09-508663 JP2001-131560

  In the present invention, the above-mentioned problems of the conventional techniques are solved, and from lignocellulosic biomass such as wood, combustible gas containing methane as a main component and not containing carbon monoxide and tar content, an expensive heat-resistant material. It can be obtained without passing through a high temperature state as required, and without adding a process for removing carbon monoxide and tar content, and by evaporating the water contained in the lignocellulosic biomass It aims at providing the utilization method of lignocellulosic biomass without the loss of energy.

  In order to achieve the above object, a first invention relating to a method for using lignocellulosic biomass is to disaggregate cellulosic fibers by immersing lignocellulosic biomass in a cooking chemical containing sodium hydroxide as a main active ingredient. A cooking step for obtaining a cooked mixture, a washing step for adding water, an aqueous solution or a suspension containing water as a medium to the cooked mixture, and separating into a cellulosic fiber suspension and a cooking waste solution, the cellulose -Based fiber suspension, or a monosaccharide solution obtained by hydrolyzing cellulose-based fibers in the cellulose-based fiber suspension, or an organic acid solution obtained by acid-generating and decomposing monosaccharides in the monosaccharide solution Is treated with anaerobic microorganisms, and consists of a methane fermentation process in which a combustible gas mainly composed of methane is generated.

  The second invention according to the method of using lignocellulosic biomass, the cooking waste liquid is transferred to a concentration and separation step, and in the concentration and separation step, separated into a sodium ion high-concentration containing liquid and a sodium ion low-concentration containing liquid, The active ingredient of the cooking chemical solution is recovered from the solution containing a high concentration of sodium ions.

  The third aspect of the invention relates to a method for utilizing lignocellulosic biomass, wherein the liquid containing a high concentration of sodium ions is combusted in a recovery boiler, and the active ingredient of the cooking chemical is recovered from the generated combustion residue, and the recovery boiler Then, combustion heat is recovered as steam or hot water.

  Moreover, 4th invention which concerns on the utilization method of lignocellulosic biomass is the said methane fermentation after mixing the said sodium ion low concentration containing liquid with the said cellulose fiber suspension, a monosaccharide solution, or an organic acid solution. It is transferred to the process and treated with anaerobic microorganisms.

  Moreover, 5th invention which concerns on the utilization method of lignocellulosic biomass returns the processed liquid of the said methane fermentation process to the said digestion process or a washing | cleaning process, and is made to reuse.

  Moreover, 6th invention which concerns on the utilization method of lignocellulosic biomass is made to contact the said combustible gas produced | generated in the said methane fermentation process with the said digested liquid mixture, cooking waste liquid, or a sodium ion high concentration containing liquid, This combustible Carbon dioxide and / or hydrogen sulfide in the gas is absorbed into the digested mixture, in the cooking waste, or in a solution containing a high concentration of sodium ions.

  Moreover, 7th invention which concerns on the utilization method of lignocellulosic biomass collect | recovers part of the heat | fever supplied in the said cooking process and / or a concentration separation process, and uses the recovered heat for the process liquid of the said methane fermentation process. It is designed to warm up.

  In the method for using lignocellulosic biomass according to any one of the first to seventh inventions, the combustible gas containing methane as a main component is finally generated when organic substances are decomposed by anaerobic microorganisms. Therefore, carbon monoxide and tar content are not included in the combustible gas. In addition, the process that constitutes the method of using the lignocellulosic biomass of the present invention is performed at about 200 ° C. or less even in the cooking process or the concentration separation process where the temperature is highest, so that an expensive heat-resistant material is required. Absent. Furthermore, since the steps constituting the method of using the lignocellulosic biomass of the present invention all proceed in an aqueous solution or a suspension using water as a medium, it is not necessary to evaporate the water contained in the lignocellulosic biomass, Therefore, there is an effect that no energy is lost due to evaporation of the moisture.

Among these, in particular, the method for using lignocellulosic biomass of the second invention has an effect of reducing the amount of chemicals used as the raw material of the active ingredient of the cooking chemical.
In particular, in the method for using lignocellulosic biomass of the third invention, the effective components of the cooking chemical can be recovered in a simple process, and the chemical energy of the organic matter that has not been transferred to the methane fermentation process can be used effectively. There is an effect.

Furthermore, in particular, in the method for using lignocellulosic biomass of the fourth invention, organic substances such as methanol contained in the low concentration sodium ion-containing liquid can be converted into a combustible gas mainly composed of methane. There is an effect that can be done.
In particular, in the method of using lignocellulosic biomass of the fifth invention, the amount of waste water that may cause water pollution problems when discharged and discharged outside the system is reduced. There is an effect that it is possible to further reduce the amount of chemicals used as the raw material of the active ingredient.

Further, particularly in the method of using lignocellulosic biomass of the sixth invention, the concentration of methane in the combustible gas is increased, and in particular, carbon dioxide and hydrogen sulfide (particularly harmful hydrogen sulfide) are slightly present. Or there exists an effect that the combustible gas which hardly contains can be obtained.
Finally, in the method of using lignocellulosic biomass of the seventh invention in particular, in order to promote the progress of the methane fermentation process and convert the organic matter in the liquid to be treated into a combustible gas mainly composed of methane. There is an effect that the required time can be shortened.

In the method of using lignocellulosic biomass of the present invention, lignocellulosic biomass is crushed for large ones such as wood and necessary for small ones such as rice straw, wheat straw, bagasse and the like. According to the above, it is cut and supplied to the digester, mixed with an aqueous solution in which cooking chemicals containing sodium hydroxide as a main active ingredient are dissolved, or mixed with a suspended suspension (hereinafter collectively referred to as a cooking chemical) and soaked. Hold for a certain period of time. At that time, the lignocellulosic biomass is brought into contact with steam prior to immersing it in the cooking chemical solution, the moisture content is increased to about 60% and degassing to increase the rate of penetration of the cooking chemical into the lignocellulosic biomass. be able to. The cooking chemical solution has a sodium ion (Na ⁺ ) weight ratio (dry basis) to lignocellulosic biomass of 5 to 50% in terms of Na ₂ O, and the sodium ion concentration in the cooking chemical solution is in terms of Na ₂ O. It may be adjusted to 2 to 100 g / l.
In this cooking step, the lignocellulosic biomass lignin, which is the main component of the intercellular layer, is cleaved and decomposed mainly by the hydroxide ions (OH ⁻ ) generated by dissociation of sodium hydroxide, thereby producing a cooking chemical solution. Dissolve in. As a result, fiber cells mainly composed of cellulose and hemicellulose are disaggregated, and a part thereof is dispersed in the cooking chemical liquid while being reduced in molecular weight by a peeling reaction or the like, thereby obtaining a cooked product mixture.
In the digested liquid mixture, in addition to fiber cells mainly composed of cellulose and hemicellulose (hereinafter referred to as cellulosic fibers), inorganic components such as sodium ions derived from the cooking chemical liquid, decomposition products of lignin, It contains organic components such as exfoliated products resulting from the peeling reaction of cellulosic fibers. In particular, sodium ions are mainly contained as weak acid-strong alkali sodium salts together with anions such as carbonate ions (CO ₃ ²⁻ ) and organic acid ions, and some are not neutralized as sodium hydroxide. Contained. For this reason, the pH of the cooked mixture is usually 10 or more.

In the cooking step, after the digester composed of the pressure vessel is sealed, the cellulosic fibers of the lignocellulosic biomass are sufficiently disaggregated by heating to 100 ° C. or higher without boiling the cooking chemical. Therefore, the time to be held in the digester can be shortened, and the capacity and installation space of the digester can be reduced. At that time, prior to raising the cooking chemical to a temperature suitable for disaggregation of the cellulosic fibers, the cooking chemical can be sufficiently and uniformly permeated into the lignocellulosic biomass by holding it at a relatively low temperature for a certain period of time. it can.
The cooking chemical solution is heated by blowing steam directly into the digester or by extracting the cooking chemical solution into a circulation line and supplying the indirect heat exchanger provided in the circulation line to indirectly connect the steam and the cooking chemical solution. Heat by exchanging heat and return to the inside of the digester or by supplying steam to the heat exchange pipe provided inside the digester and indirectly exchanging heat between the steam and the cooking chemical it can.

In the above cooking step, by using a cooking chemical liquid containing sodium sulfide as an active ingredient in addition to sodium hydroxide, it is possible to further shorten the time during which lignocellulosic biomass should be held in the cooking kettle. In this case, the sodium sulfide dissolved in the cooking solution is hydrolyzed into sodium hydroxide and sodium hydrogen sulfide as shown in the following formula (3).
Na ₂ S + H ₂ O → NaOH + NaSH (3)
Of these, sodium hydroxide functions as the main active ingredient in cooking, while sodium hydrogen sulfide is dissociated and the hydrogen sulfide ions (SH ⁻ ) produced by dissociation are not sufficient in the lignin bonding sites. Delignification is promoted by cleaving the sites that cannot be cleaved or by preventing condensation of degradation products of lignin.
As a result, after the cooking chemical has been infiltrated into lignocellulosic biomass at a temperature of about 110 to 120 ° C, the inside of the digester is used to disaggregate the cellulosic fibers under the operating conditions of heating to about 160 ° C or higher. The time to be maintained in can be set to about 1 to 5 hours. At this time, in order to further shorten the necessary holding time, the cooking chemical solution may be heated and held at 180 ° C. or higher, preferably 200 ° C. or higher.
In such a relatively high temperature condition, cellulose and / or hemicellulose, which are the main components of the cellulosic fiber, have a lower polymerization degree and molecular weight due to depolymerization. It is possible to reduce the necessity of hydrolysis of the cellulosic fibers in the pretreatment step, that is, the step of hydrolyzing the cellulosic fibers into monosaccharides and the step of acid-generating and decomposing the monosaccharides into organic acids.

In the above cooking process, when providing lignocellulosic biomass containing a decayed portion in which cellulosic fibers are cut, and lignocellulosic biomass crushed into fragments that are not uniform in size prior to the cooking process, The length of the cellulosic fiber disaggregated in the cooking process tends to be non-uniform and the strength tends to decrease. However, in the method of using lignocellulosic biomass of the present invention, the cellulosic fiber is finally sent to the methane fermentation process or its pretreatment process and decomposed into a combustible gas mainly composed of methane, There is no need to manage the length or strength of the cellulosic fibers. For this reason, in the method of using lignocellulosic biomass of the present invention, it is not necessary to store it in a dry state to prevent decay, or to strictly conduct screening of crushed pieces, but rather to partially decay. Waste materials that are available can be used as raw materials.
In addition, even when living cell biomass containing many components other than cellulose, hemicellulose, and lignin is mixed, such as tree bark and leaves, the length of cellulosic fibers disaggregated in the cooking process becomes uneven. The strength also tends to decrease, but there is no problem in the present invention as described above. Rather, nutrient components such as nitrogen, phosphorus, and potassium that are contained in the bark and leaves and migrate into the digested mixture in the cooking process are finally passed through the downstream process, and finally the methane fermentation process or its proper amount. By shifting to the pretreatment step, a nutrient source for microorganisms to be propagated there can be supplied. For this reason, branches that are generated by tree pruning or pruning and difficult to peel off can be widely used as raw materials, or the bark and branches and leaves that have become waste in sawmills etc. are actively used as nutrients. Can also accept. In particular, pruned trees such as street trees that are not often used and are often treated as waste can be used effectively.

The digested liquid mixture generated in the above cooking process is sent to the washing process, and after adding water, an aqueous solution or a suspension containing water as a medium (hereinafter referred to as washing liquid), the cellulosic fibers are in the liquid. It is separated into a dispersed suspension (hereinafter referred to as cellulosic fiber suspension) and cooking waste liquid. At this time, the concentration of the solid content dissolved or dispersed in the cleaning liquid (hereinafter collectively referred to as dissolved solid content including the dispersed solid content) is the dissolved solid excluding the cellulosic fibers in the digested liquid mixture. Ideally, only the cellulosic fibers are transferred from the digested liquid side to the washing liquid side without mixing the liquid part other than the cellulosic fibers in the digested liquid and the cleaning liquid. Can be separated into a cellulosic fiber suspension having a low concentration of dissolved solids other than cellulosic fibers and a cooking waste liquid containing almost no cellulosic fibers and having a high concentration of dissolved solids other than cellulosic fibers. it can.
Here, the dissolved solid content contained in the digested liquid mixture and most of which remains in the digested waste liquid includes inorganic components such as sodium ions and organic components such as lignin decomposition products as described above. Also in the cooking waste liquid, sodium ions are contained as a weak acid-strong alkali sodium salt or sodium hydroxide, so that the pH of the cooking waste liquid is usually 10 or more.

In the actual washing process, the cellulosic fiber suspension and cooking waste liquid are separated by dilution washing, displacement washing, or a combination of dilution washing and substitution washing. In dilution washing, the concentration of cellulosic fibers is increased by removing the liquid portion other than cellulosic fibers from the digested mixture, and the cellulosic fiber concentrate is diluted with the washing solution to obtain cellulosic fibers. A fiber suspension is obtained, while the removed liquid part becomes cooking waste. In the replacement cleaning, the digested liquid mixture is brought into contact with a cleaning liquid of a necessary amount or more as a medium for the cellulosic fiber suspension. The cellulosic fibers are diffused and transferred to the cellulose fiber suspension medium side of the cleaning liquid while suppressing the transfer to the medium fiber suspension medium side, while the remaining cleaning liquid is digested. It becomes a cooking waste liquid with the remaining part which the cellulose fiber detach | desorbed among the mixed liquid. At this time, in dilution washing, liquid components other than cellulosic fibers remain in the cellulose fiber concentrate, and in substitution washing, liquid parts other than cellulosic fibers in the digested liquid mixture are present on the washing liquid side. Since it cannot completely prevent the migration, the concentration of dissolved solids other than the cellulosic fibers in the cellulosic fiber suspension obtained in the actual washing process is lower than the original digest mixture, but the washing solution Higher than.
In order to lower the concentration of dissolved solids other than cellulose fibers in the cellulosic fiber suspension, the amount of the cleaning liquid is increased after using water or a liquid having a sufficiently low concentration of the dissolved solids as the cleaning liquid, If necessary, a plurality of stages of dilution cleaning and / or replacement cleaning may be performed. When performing multiple stages of washing, in the last stage of washing, a liquid having a sufficiently low concentration of water or dissolved solids is used as the washing liquid, and the washing waste liquid separated from the cellulosic fiber suspension is used as a washing liquid there. By using the cleaning liquid in cascade, such as using the cleaning liquid in the previous stage cleaning and using the cleaning waste liquid generated there as the cleaning liquid in the previous stage cleaning, The amount of cooking waste liquid generated can be suppressed.

In the method of using lignocellulosic biomass of the present invention, the cellulosic fiber suspension is transferred to the subsequent methane fermentation step or its pretreatment step and treated with anaerobic microorganisms, but the washing in the washing step is not complete. In the case of the cellulosic fiber suspension, a part of sodium ions contained in the cooked mixture is mainly a weak acid-strong alkali sodium salt or other dissolved solids in the cooked mixture. Migrate as sodium hydroxide. When the ratio of sodium ions transferred in this manner to the cellulosic fibers is remarkably high, the sodium ions may be an inhibiting factor in the methane fermentation process or its pretreatment process.
As described above, this problem is caused by increasing the amount of the cleaning liquid after using a liquid having a low concentration of water or sodium ions as the cleaning liquid, and further stacking multiple stages of dilution cleaning and / or replacement cleaning if necessary. The weight ratio of sodium ions to cellulosic fibers in the cellulosic fiber suspension can be avoided by setting it to 1% or less in terms of Na ₂ O.

However, in the method of using lignocellulosic biomass of the present invention, the ratio of sodium ions to cellulosic fibers in the cellulosic fiber suspension need not be extremely low. Rather, as long as the ratio of sodium ions to cellulosic fibers is not a hindrance factor in the methane fermentation step or its pretreatment step, sodium ions remain in the cellulosic fiber suspension. When the cellulosic fiber suspension is transferred to the methane fermentation step or its pretreatment step, the following advantageous effects are brought about.
First, sodium ions become a nutrient source for microorganisms to be propagated in the methane fermentation process or its pretreatment process. Moreover, since sodium ions migrate to the cellulose fiber suspension as a weak acid-strong alkali sodium salt or sodium hydroxide as described above, the cellulose fiber suspension exhibits alkalinity. By the way, in the acid production / decomposition process in the methane fermentation process or its pretreatment process, the pH of the liquid to be treated is lowered due to the generation of the organic acid, and thus the processes after the acid production / decomposition process may be hindered. Therefore, the fact that the cellulosic fiber suspension is alkaline has an effect of suppressing the inhibition of the methane fermentation process due to the decrease in pH due to the generation of the organic acid.
On the other hand, an attempt to weight ratio of at terms of Na ₂ O of sodium ions to cellulosic fibers of the cellulosic fiber suspension in less than 0.01%, extremely increases the amount of washing liquid used in the cleaning step, moreover cleaning stages It is necessary to have more than 3 stages. And if the amount of washing liquid is increased, the amount of cooking waste liquid will increase, so the burden on the processing process of cooking waste liquid such as the subsequent concentration separation process will increase, and if the number of washing stages is increased, the equipment cost and operation cost for washing will increase accordingly. Expense increases.
For the above reasons, the weight ratio of sodium ions to cellulose fibers in the cellulosic fiber suspension in terms of Na ₂ O is preferably 0.01% or more and 1% or less.

At least a part of the washing step can be performed in the same digester as the cooking step. Specifically, by supplying the cleaning liquid from the supply port at the bottom of the digester, a region of the cleaning liquid is formed near the bottom, and the cellulosic fibers in the mixture of the digested material staying at the top are diffused into the cleaning liquid region. -The cellulosic fiber suspension formed and withdrawn from the outlet at the bottom, while the remaining cooking waste liquid is withdrawn from another outlet located above the washing liquid region, or the cellulosic fiber suspension. By extracting the suspension from the same outlet as the cellulosic fiber suspension after the extraction of the turbid liquid, the cellulosic fiber suspension and the cooking waste liquid can be separated.
In particular, when using a continuous digester that continuously supplies lignocellulosic biomass and cooking chemicals and continuously extracts the digested liquor as the digester, supply the cleaning solution continuously from the supply port at the bottom. The cellulosic fiber suspension is continuously drawn out from the bottom outlet and the cooking waste liquid is continuously drawn out from another outlet located above the washing liquid region. Suspension and cooking waste liquid can be separated. On the other hand, after supplying lignocellulosic biomass and cooking chemical liquid, after holding for a set time at the set temperature, and in the case of a batch type digester that discharges the cooked mixture, the washing liquid is placed at the bottom after the holding time is over. The cellulosic fiber suspension and the cooking waste liquid can be separated by separately feeding the cellulosic fiber suspension produced by the transfer of the cellulose fiber into the cleaning liquid and the remaining cooking waste liquid.
In addition, when supplying a washing | cleaning liquid from a bottom part in order to perform at least one part of a washing | cleaning process inside a digester, when the temperature of a washing | cleaning liquid is low, the temperature of the cellulosic fiber suspension discharged | emitted from a digester will also become low. However, cellulose and / or hemicellulose, which are the main components of cellulosic fibers, depolymerize as the temperature of the cellulosic fiber suspension extracted from the digester increases and the degree of polymerization and molecular weight decrease. The necessity of hydrolysis of cellulosic fibers in the methane fermentation process or its pretreatment process is reduced. For this reason, it is preferable to raise the temperature by heating the cleaning liquid supplied into the kettle and raising the temperature of the cellulosic fiber suspension to be discharged.

  The cellulosic fiber suspension separated from the cooking waste liquid in the washing step is freed from uncooked parts such as knots and foreign matters if necessary, and further if necessary, a pretreatment step such as hydrolysis of cellulosic fibers. And then transferred to the methane fermentation process. In the methane fermentation process, the organic matter that is treated by the anaerobic microorganisms propagated in the anaerobic treatment container and contained in the cellulosic fiber suspension is finally mainly methane, carbon dioxide. And the component which cannot be melt | dissolved in water is discharge | released as a gas body, and the combustible gas which has methane as a main component is obtained.

  In general, the step of obtaining methane from an organic substance by an anaerobic microorganism includes an organic acid mainly composed of volatile fatty acids such as acetic acid by decomposing the organic substance by an acid-producing bacterium, or an acid generation and decomposition step of obtaining hydrogen and oxygen dioxide, It consists of a methane production step of obtaining methane from organic acids, hydrogen and carbon dioxide, or methanol by the producing bacteria. However, since cellulose, which is the main component of cellulosic fibers, is generally difficult to be degraded by acid-producing bacteria, it is preferably hydrolyzed to monosaccharide glucose in advance. The same applies to hemicellulose which constitutes cellulose-based fibers together with cellulose, but in the case of hemicellulose, it is hydrolyzed to other monosaccharides such as manrose and xylose in addition to glucose.

Cellulose and hemicellulose can be hydrolyzed with strong acids such as hydrochloric acid and sulfuric acid, but it is most economical to hydrolyze, ie enzymatic saccharification, using a group of hydrolases collectively called cellulase and hemicellulase. It is. However, these enzymes are not only capable of degrading lignin, which is the main component of the intercellular layer of lignocellulosic biomass, but also have a very large molecular weight, so that the capillary voids with an average diameter of about 10 mm that fiber cells have It cannot pass through the surface cells and penetrate the cells inside. For this reason, it is practically impossible to enzymatically saccharify cellulose and hemicellulose, which are the main components of the fiber cells constituting the lignocellulosic biomass, to the extent that the lignocellulosic biomass is mechanically crushed.
However, in the method of using lignocellulosic biomass of the present invention, since the lignin is decomposed and the cellulosic fibers are disaggregated in the above cooking step, the hydrolase group can be easily contacted, and therefore Cellulose and hemicellulose, which are the main components of cellulosic fibers, are rapidly enzymatically saccharified. For this reason, in the method of using lignocellulosic biomass of the present invention, a cellulase or hemicellulase-producing microorganism, that is, a cellulase-producing bacterium or a hemicellulase-producing bacterium is propagated in the cellulosic fiber suspension, or cellulose Cellulase-based suspensions by adding cellulase-containing liquids or hemicellulase-containing liquids, such as cellulase-producing bacteria or hemicellulase-producing bacteria culture solutions, culture filtrates, culture extracts, or cellulase preparations or hemicellulase preparations Cellulosic fibers in the fiber suspension can be hydrolyzed to monosaccharides.
In particular, when the cellulosic fiber suspension is not completely washed and the cellulosic fiber suspension contains some sodium ions and exhibits alkalinity, the cellulosic fiber suspension contains an alkaliphilic solution. Cellulose and / or hemicellulose are preferably hydrolyzed by breeding cellulase-producing bacteria and hemicellulase-producing bacteria, or adding alkali-resistant cellulase or hemicellulase to the cellulosic fiber suspension.

Such a hydrolysis step is carried out by allowing an anaerobic cellulase-producing bacterium or hemicellulase-producing bacterium to coexist with an acid-producing bacterium in an anaerobic treatment container, or an acid-producing bacterium having cellulase activity or hemicellulase activity. Or by adding a cellulase-containing liquid or hemicellulase-containing liquid, or a cellulase preparation or a hemicellulase preparation under the growth of acid-producing bacteria. it can. Alternatively, by causing anaerobic cellulase-producing bacteria and hemicellulase-producing bacteria to coexist with acid-producing bacteria and methanogens, or by causing cellulase activity and hemicellulase activity to have acid-producing bacteria and methanogens, or By adding a cellulase-containing liquid or hemicellulase-containing liquid, or a cellulase preparation or a hemicellulase preparation under the growth of acid-producing bacteria and methanogenic bacteria, the process may be integrated with the acid-generating decomposition process and the methane-generating process. it can.
However, generally, cellulase activity and hemicellulase activity possessed by acid-producing bacteria and methanogens are weak, and cellulase-producing bacteria with strong cellulase activity and hemicellulase-producing bacteria with strong hemicellulase activity are prone to breed, Conditions under which producers and methanogens are likely to reproduce are different. For this reason, when anaerobic microorganisms are propagated in one processing vessel, hydrolysis and acid generation processes, or hydrolysis and acid generation processes and methane fermentation processes are performed in parallel. There is a problem that the process becomes rate-determining and the process after the acid generation decomposition process does not proceed. In addition, the method of adding an externally produced cellulase-containing liquid or hemicellulase-containing liquid, or a cellulase preparation or a hemicellulase preparation is not economical because cellulose or hemicellulose as a raw material must be separately supplied for the production. .
For this reason, the cellulosic fiber suspension is converted into a monosaccharide solution by hydrolyzing the cellulosic fiber into a monosaccharide such as glucose in a separate processing vessel, and then the methane fermentation process after the acid generation decomposition process is performed. Preferably it is done. Alternatively, the cellulosic fiber suspension is partly branched, cellulase-producing bacteria or hemicellulase-producing bacteria are cultured using the branched liquid as a medium, and the resulting culture solution, culture filtrate or culture extract is used as the remaining cellulosic fiber suspension. It is preferable to perform the methane fermentation process after the acid generation decomposition process after hydrolyzing by mixing with a turbid liquid.
In addition, when cellulase-producing bacteria and hemicellulase-producing bacteria are propagated in a processing container different from the processing container in which the steps after the acid generation and decomposition step are performed, the cellulase-producing bacteria and hemicellulase-producing bacteria are not necessarily anaerobic. There is no need to use aerobic microorganisms.

When the aqueous solution of monosaccharides obtained by hydrolyzing the cellulosic fibers in the cellulosic fiber suspension is treated with acid-producing bacteria and methanogens in an anaerobic state, methane production by the methanogen is caused. Become rate-limiting. For this reason, in order to increase the processing speed, it is necessary to increase the concentration of methanogenic bacteria in a processing container kept in an anaerobic state.
As a method for increasing the bacterial cell concentration in the processing container, a fixed bed method in which a biofilm of anaerobic microorganisms is attached to and proliferated on the surface of the processing container, or a carrier on which anaerobic microorganisms adhere and grow can be used. There is a fluidized bed that is granulated and fluidized by an upward flow, and in particular, there is a UASB method that uses a self-aggregation action of anaerobic microorganisms to hold cells in a processing vessel as granular sludge having excellent sedimentation properties. The fastest methane production rate.
However, when the UASB method is applied to a monosaccharide solution obtained by hydrolyzing cellulosic fibers in the cellulosic fiber suspension, acid-producing bacteria that decompose monosaccharides into organic acids are negative. There is a problem that a large amount of highly charged biopolymer is produced to prevent the formation of dense granular sludge of methanogens. In order to avoid this problem, the acid generation decomposition step and the methane generation step are separated, and an organic acid solution obtained by decomposing monosaccharides into organic acids in the acid generation decomposition step is used as a methane generation step using the UASB method. Can be processed.
In general, the conditions under which acid-producing bacteria are likely to propagate are different from the conditions under which methane-producing bacteria are likely to propagate. Therefore, even when a method other than the UASB method is used for the methane production process, the acid production decomposition process and the methane production process are separated. However, it is preferable to optimize the operating conditions of each process.

In order to propagate microorganisms such as cellulase-producing bacteria, hemicellulase-producing bacteria, acid-producing bacteria and methanogens, cellulosic fibers, monosaccharides, or organic substances such as organic acids containing only carbon, hydrogen and oxygen It is necessary to supply nutrients such as nitrogen, phosphorus, potassium, and iron. For this reason, it is preferable to add those nutrient components to a process target liquid prior to a methane fermentation process or its pretreatment process.
For this purpose, as described above, the bark and leaves of the tree are supplied to the cooking process, and the nutrient components transferred from these supplies into the cooking mixture are passed through the downstream process to the methane fermentation process or Although it can be transferred to the pretreatment step, the bark and leaves are mixed with the cellulosic fiber suspension separated from the digested mixture in the washing step, and the mixture is put into the methane fermentation step or the pretreatment step. It can also be transported. At that time, the bark and leaves are easily decomposed by fermentation or the like, and then mixed with the cellulosic fiber suspension to facilitate the use of microorganisms.
As a nutrient source, not only bark and leaves of trees, but also organic waste such as wastewater and waste generated in food production processes such as dredging, sewage sludge, manure, and beer production can be used. Of these, especially for organic wastes with a low content of cellulosic fibers such as sewage sludge and manure, it is not necessary to hydrolyze cellulose and hemicellulose, so cellulosic fibers in cellulosic fiber suspensions By mixing with the monosaccharide solution obtained by hydrolyzing and transferring to the acid generation and decomposition step, it is possible to avoid an unnecessarily increase in the amount of the liquid to be treated in the hydrolysis step.

Combustible gas mainly composed of methane obtained by the method of using lignocellulosic biomass of the present invention, if necessary, after being stored in a gas holder, burned in a gas combustion boiler installed adjacently, The generated heat can be recovered and used with steam or the like, and further converted into electric power by rotating the steam turbine if necessary. Or it can burn with a gas engine and can use power directly, or it can connect with a generator and can generate electric power.
Also, carbon dioxide and / or hydrogen sulfide (H ₂ S) is removed from the flammable gas obtained in the methane fermentation process, and flammable gas containing methane as the main component and little or no carbon dioxide and hydrogen sulfide. The combustible gas can be reformed into hydrogen by a reformer and then converted into electric power by a fuel cell installed adjacent thereto, and further, a natural gas vehicle or a reformer is provided. The fuel cell vehicle can be supplied as fuel.
Alternatively, these combustible gases can be transported to a remote consumer by filling the cylinder and transporting the cylinder by truck or the like or by feeding it to a pipeline.

In particular, when a natural gas pipeline is laid in the vicinity of the apparatus using the lignocellulosic biomass utilization method of the present invention, if necessary, from the combustible gas obtained in the methane fermentation process After removing carbon dioxide and / or hydrogen sulfide, making flammable gas containing methane as a main component and little or little carbon dioxide and hydrogen sulfide, pressurizing the combustible gas to a required pressure, It is convenient to supply to the pipeline. In that case, it is possible to use the combustible gas by selling the combustible gas to the owner of the pipeline, such as a gas company. It is possible to use it to sell
At that time, an automatic metering device that measures the flow rate of the combustible gas is installed at the supply port to the pipeline, and the pipeline owner or computer is used by the computer based on the measured supply amount and the preset price. It can be a system that automatically charges remote consumers. In particular, when a consumer has a carbon dioxide emission allowance, the methane-based combustible gas obtained by the method of using the lignocellulosic biomass of the present invention is a carbon neutral fuel. Therefore, a margin is generated in the consumer's carbon dioxide emission allowance, and the margin can be sold as the carbon dioxide emission right.

  Now, sodium hydroxide and sodium sulfide, which are the active ingredients of cooking chemicals, are very expensive chemicals, and sodium carbonate and sodium sulfate as raw materials are also expensive, so the cooking chemicals can be recovered and reused repeatedly. It is preferable to do. For this reason, in one form of the utilization method of the lignocellulosic biomass of the present invention, the cooking waste liquid is transferred to a concentration and separation step, and is separated into a high sodium ion concentration containing solution and a low sodium ion concentration containing solution in the concentration and separation step. Thus, after the sodium ions contained in the cooking chemical liquid and transferred to the cooking waste liquid are transferred to a small amount of sodium ion high-concentration containing liquid, the active ingredient of the cooking chemical liquid is recovered from the sodium ion high-concentration containing liquid. It was decided.

The cooking waste liquid separated from the cellulosic fiber suspension in the washing step is transferred to the concentration separation step and separated into a sodium ion high-concentration containing liquid and a sodium ion low-concentration containing liquid. This separation combines the evaporation step of concentrating by evaporating the water and volatile components in the cooking waste liquid to obtain a sodium ion high concentration liquid, and the condensation step of condensing the evaporated component to obtain a low sodium ion concentration liquid. Can be done. In this concentration and separation process, steam and cooking waste liquid are indirectly heat-exchanged to indirectly evaporate moisture and volatile components, and the generated steam and volatile components are indirectly heat-exchanged with cooling water to condense. An indirect condenser can be used in combination. In particular, the volatile component-containing steam generated by indirect heat exchange with the steam is indirectly heat-exchanged with the remaining liquid to further evaporate moisture and volatile components from the remaining liquid, and the original volatile component-containing steam. The amount of steam used can be reduced by using a multi-effect evaporator that condenses.
In such a concentration and separation process, most of the sodium ions contained in the cooking waste liquid are scattered and transferred to the low concentration sodium ion concentration liquid side, except for a small amount. It is moved to. As a result, sodium ions will be transferred from a large amount of the digested mixture to a small amount of sodium ion high-concentration containing liquid. Can be done easily.
As mentioned above, the cooking waste liquid contains sodium ions mainly as a weak acid-strong alkali sodium salt or sodium hydroxide, so that the pH is usually 10 or more. However, these sodium components are concentrated to a high concentration. In liquids, the pH is even higher. In addition, in the case of a solution containing a low concentration of sodium ions, only a small amount of sodium ions is scattered and transferred, so the pH is lower than that of the cooking waste solution, but it is still mainly a weak acid-strong alkali sodium salt or hydroxide. It exhibits alkalinity because it migrates as sodium.

In the cooking step, when a cooking chemical liquid containing sodium sulfide as an active ingredient in addition to sodium hydroxide is used, the cooking chemical liquid contains hydrogen sulfide ions generated by hydrolysis of sodium sulfide. Most of them are oxidized to sulfate ions (SO ₄ ²⁻ ) and thiosulfate ions (S ₂ O ₃ ²⁻ ) in the cooking process, but some remain as hydrogen sulfide ions in the digested liquid mixture. Hydrogen sulfide ions move into the cooking liquor, except that only a small portion of the hydrogen sulfide ions are transferred to the cellulosic fiber suspension along with the cellulosic fibers. In addition, most of them remain in the high-concentration solution of sodium ions in the evaporation process, but the remaining small amount of hydrogen sulfide ions evaporate from the cooking waste as thiols such as hydrogen sulfide and methanethiol (CH ₃ SH). . In addition, as will be described later, when the cooking waste liquid is brought into contact with the combustible gas generated in the methane fermentation step, and hydrogen sulfide in the combustible gas is absorbed in the cooking waste liquid, it results from the hydrogen sulfide. Some of the hydrogen sulfide ions are also evaporated from the cooking waste liquid again as hydrogen sulfide or as a thiol such as methanethiol in the evaporation step.
Most of the hydrogen sulfide and thiol once evaporated in this way migrate to the low-concentration sodium ion-containing liquid side in the subsequent condensation process, but part of the hydrogen sulfide and thiol remain in the gas phase together with water vapor. When hydrogen sulfide and thiols are released into the atmosphere in the gas phase, the problem of malodor occurs, but these are both acidic or weakly acidic and easily dissolved in an alkaline aqueous solution. Absorption can be removed by gas-liquid contact with a digested product mixture solution, a cooking waste solution or a solution containing a high concentration of sodium ions, or a cooking chemical solution before use in the cooking process.

In the case where sodium sulfide and / or sodium hydrogen sulfide is contained in the cooking waste liquid at a relatively high concentration, the material of the indirect evaporator used in the concentration and separation process may corrode. The problem is that sodium sulfide and sodium hydrogen sulfide are oxidized to sodium thiosulfate (Na ₂ S ₂ O ₃ ) by the reaction of the following formulas (4) and (5) by bringing the cooking waste liquid into contact with air or oxygen. Can be avoided or reduced.
2Na ₂ S + 2O ₂ + H ₂ O → Na ₂ S ₂ O ₃ + NaOH (4)
2NaSH + 2O ₂ → Na ₂ S ₂ O ₃ + H ₂ O (5)
And by passing through such a cooking waste liquid oxidation process before the concentration separation process, the amount of hydrogen sulfide and thiol evaporated in the concentration separation process can be reduced as described above.

Now, not only organic acid ions are dissolved as sodium salt in the high concentration sodium ion concentration liquid separated from the cooking waste liquid, but also non-volatile organic substances are dissolved in high concentration. . The organic matter containing these organic acid ions is combusted and oxidatively decomposed into water and carbon dioxide to generate combustion heat. In particular, the water content of the high concentration sodium ion-containing liquid is 50% in the concentration and separation step. If it is suppressed to about a level or less, the combustion heat of the organic substance exceeds the latent heat of vaporization of the water contained in the liquid containing high concentration of sodium ions, and the heat of combustion can be recovered and used. In order to effectively use the chemical energy of the lignocellulosic biomass of the present invention, in the form of the method for using lignocellulosic biomass of the present invention, the liquid containing sodium ions at a high concentration is combusted in a recovery boiler, and the cooking chemical liquid is formed from the generated combustion residue. While recovering the active ingredients, the recovery boiler recovers the combustion heat as steam or hot water. In particular, when steam is generated at the water pipe wall of the recovery boiler and the steam turbine is rotated, the recovered thermal energy can be converted into electric power.

When the sodium ion high-concentration liquid is burned in the recovery boiler, the organic acid sodium is converted to sodium carbonate (Na ₂ CO ₃ ) and recovered as a combustion residue together with the sodium carbonate originally contained in the sodium ion high-concentration liquid. Is done. When this combustion residue is dissolved in water and calcium hydroxide (Ca (OH) ₂ ) is added to the resulting aqueous solution, the poorly soluble calcium carbonate (CaCO ₃ ) is dissolved together with sodium hydroxide by the reaction of the following formula (6). By removing the calcium carbonate formed and dispersed in the aqueous solution, an aqueous solution or suspension of sodium hydroxide can be obtained.
Na ₂ CO ₃ + Ca (OH) ₂ → 2NaOH + CaCO ₃ (6)

In the cooking step, when using a cooking chemical solution containing sodium sulfide as an active ingredient in addition to sodium hydroxide, the sodium sulfide is changed to sodium sulfate or sodium thiosulfate by the above cooking step and cooking waste liquid oxidation step, and sodium ions Move to the high concentration solution side. These sulfur-containing sodium components are converted into sodium sulfide when combusting a liquid containing a high concentration of sodium ions and transferred into the combustion residue, and finally coexist with sodium hydroxide in the aqueous solution or suspension. It will be dissolved or dispersed in. For this reason, this mixed aqueous solution or mixed suspension can be used again as a cooking chemical.
At that time, particularly, when sodium sulfide and / or sodium hydrogen sulfide is contained in a relatively high concentration in the liquid containing a high concentration of sodium ions, those sulfur-containing sodium components are represented by the following formulas (7) and (8). It reacts with carbon dioxide in the combustion gas of the high ion concentration liquid to produce hydrogen sulfide.
Na ₂ S + CO ₂ + H ₂ O → Na ₂ CO ₃ + H ₂ S (7)
_{2NaSH + CO 2 + H 2 O} → Na 2 CO 3 + 2H 2 S (8)
This problem can be avoided by going through the step of oxidizing sodium sulfide and sodium hydrogen sulfide to sodium thiosulfate by the reaction of the above formula (4) or (5) prior to the combustion step of the liquid containing high concentration of sodium ions. Can do. In addition, this oxidation may be performed at the stage of the cooking waste liquid before concentration separation of the high concentration sodium ion solution as described above, or may be performed after concentration concentration separation of the high concentration sodium ion solution. .

  However, even in the above process, it is usually impossible to completely recover all the sodium ions and sulfur originally contained in the cooking chemical. It can be supplemented by replenishing sodium carbonate prior to burning the high concentration liquid in the recovery boiler or when dissolving the combustion residue in water. Or when using the cooking chemical | medical solution which uses sodium sulfide as an active ingredient in addition to sodium hydroxide, it can supplement by replenishing sodium sulfate before burning a sodium ion high concentration content liquid with a recovery boiler.

A device for obtaining combustible gas containing methane as a main component and a cooking waste liquid (hereinafter referred to as a methane gas generator) using the steps from the cooking step to the methane fermentation step of the method of using the lignocellulosic biomass of the present invention, An apparatus (hereinafter referred to as a cooking chemical recovery apparatus) for burning the liquid containing a high concentration of sodium ions obtained by concentrating and separating from the cooking waste liquid to obtain an active ingredient of the cooking chemical liquid (hereinafter referred to as a cooking chemical recovery apparatus) must be installed close to each other. In addition, it is not necessary to install a cooking chemical recovery device set for the methane gas generator set.
Rather, lignocellulosic biomass, as described above, is not suitable for long-distance transportation or storage in large quantities from when it is collected in a growing place such as a forest until it is consumed. In view of the fact that the cooking liquor is liquid and is relatively easy to transport and store, and that it is more economical to enlarge the recovery boiler that burns the liquid containing a high concentration of sodium ions, the methane gas generator Is installed at a location relatively close to the location where lignocellulosic biomass is collected, such as forests, and for the cooking chemical recovery device, concentrated sodium ion-concentrated liquid concentrated from the cooking waste liquid generated from multiple methane gas generators is concentrated. It is preferable to install an apparatus for processing automatically.
At that time, the concentration separation device that separates the high-concentration sodium ion-containing liquid and the low-concentration sodium ion-containing liquid from the cooking waste liquid may be installed close to the methane gas generator, or close to the cooking chemical recovery device. It is also possible to install and collect the cooking waste liquid generated from a plurality of methane gas generators, and then concentrate and separate it. In particular, when collecting and separating cooking waste liquids generated from a plurality of methane gas generators, the cooking waste liquid oxidation process may also be performed after collecting the cooking waste liquids generated from a plurality of methane gas generators. preferable.

In the method of using lignocellulosic biomass of the present invention, particularly when using a cooking chemical containing sodium sulfide as an active ingredient in addition to sodium hydroxide, black liquor installed in a kraft pulp factory as a cooking chemical recovery device A cooking chemical recovery device after the concentrator or after the recovery boiler can be used. That is, the high-concentration sodium ion-containing liquid or cooking waste liquid produced by the method of using lignocellulosic biomass of the present invention is mixed with the dark or dilute black liquor of the kraft pulp factory, and is left as it is or after being concentrated. Further, if necessary, sodium sulfide and / or sodium hydrogen sulfide in the mixed solution is oxidized and burned in a recovery boiler. The generated combustion residue is dissolved in water, and the resulting aqueous solution is causticized by adding calcium hydroxide, and the by-product hardly soluble calcium carbonate is removed to remove the active ingredient of the cooking chemical liquid. An aqueous solution, that is, a mixed aqueous solution or suspension (white liquor) of sodium hydroxide and sodium sulfide is obtained. And a part of this mixed aqueous solution or suspension is used in the utilization method of the lignocellulosic biomass of the present invention, and the rest is used as white liquor in the kraft pulp manufacturing process.
Thus, when the utilization method of lignocellulosic biomass of the present invention is combined with the kraft pulp manufacturing process, the necessity to newly install equipment used for reusing cooking waste liquid when implementing the utilization method of lignocellulosic biomass of the present invention. There is an advantage that it can be reduced. On the other hand, in the kraft pulp factory, the amount of organic matter burned in the recovery boiler is increased by the amount of organic matter contained in the cooking waste liquid obtained in the method of using the lignocellulosic biomass of the present invention. There is an advantage that the amount of fossil fuel burned to obtain the heat or power to be reduced can be reduced. In particular, in order to prevent global warming due to carbon dioxide, when each kraft pulp manufacturing company or factory has a carbon dioxide emission allowance according to the amount of kraft pulp produced, it is obtained from lignocellulosic biomass and therefore carbon. Since there is a margin in the emission allowance by using a cooking waste liquid or a solution containing a high concentration of sodium ions, which is a neutral fuel, it is also possible to sell the margin as carbon dioxide emission rights.
Thus, in the case of the utilization method which combined the utilization method of lignocellulosic biomass of the present invention and the kraft pulp manufacturing process, the acceptance of the mixed aqueous solution or suspension (white liquor) of sodium hydroxide and sodium sulfide in the methane generator And an automatic metering device that measures the amount of each of the cooking waste in the kraft pulp manufacturing process, and a methane gas generator using a computer based on the measured amount received and a preset price. It can be a system that automatically calculates the amount of payment between the owner and the kraft pulp mill.

Moreover, another method is also possible as a method of combining the utilization method of lignocellulosic biomass of the present invention and the kraft pulp manufacturing process. That is, a part of a pulp suspension which is a cellulosic fiber suspension is extracted from the kraft pulp manufacturing process, and the pulp suspension is converted into a monosaccharide solution or further an organic acid solution if necessary. By transferring to a methane fermentation process and processing with anaerobic microorganisms, combustible gas which has methane as a main component can be generated. At that time, the generated combustible gas can be used as a fuel for obtaining heat and electric power used in the kraft pulp manufacturing process, or the existing owner of the pipeline or the remote Can be sold to consumers.
In this method as well, the amount of black liquor generated in the kraft pulp factory is increased by the amount of black liquor produced compared to the conventional operating state in which only the kraft pulp was produced by transferring the pulp suspension to the methane fermentation process. There is a merit that the consumption of fossil fuel per production amount can be reduced and the carbon dioxide emission allowance can be afforded. When combustible gas is sold to the pipeline owner or remote consumer, it can be a system that automatically charges the pipeline owner or remote consumer as described above. In addition, when a carbon dioxide emission allowance is set for a consumer, it is possible to sell the margin of the emission allowance as carbon dioxide emission rights. it can.

Now, the said sodium ion low concentration containing liquid contains several thousand ppm of volatile organic substances which have methanol as a main component. Therefore, if the sodium ion low-concentration containing liquid is discharged out of the system and released into the river or the sea as it is, not only the chemical energy of the organic substance is not effectively used, but also a problem of water pollution may occur.
For this reason, in one form of the utilization method of the lignocellulosic biomass of the invention, the liquid containing a low concentration of sodium ions is mixed with the cellulosic fiber suspension, monosaccharide solution, or organic acid solution, and then the methane. They were transferred to the fermentation process and treated with anaerobic microorganisms. As a result, the organic matter contained in the low-concentration sodium ion-containing liquid is treated by anaerobic microorganisms after being subjected to pretreatment such as acid generation and decomposition, if necessary, and converted to a combustible gas mainly composed of methane. The
At this time, since methanol is directly converted to methane by the methanogen, it is not necessary to go through a hydrolysis step and an acid generation decomposition step. Therefore, it is preferable to mix the sodium ion low-concentration liquid with the organic acid solution, thereby avoiding an increase in the amount of the treatment liquid in the hydrolysis step and the acid generation decomposition step by the amount of the sodium ion low-concentration liquid. be able to.
Moreover, since the sodium ion low concentration containing liquid is alkaline as described above, mixing this with a cellulosic fiber suspension, a monosaccharide solution, or an organic acid solution prior to the methane fermentation process, The production of the organic acid in the acid generation / decomposition step has an effect of suppressing the pH of the liquid to be treated from being lowered and inhibiting the steps after the acid generation / decomposition step.

In addition, when a liquid containing organic substances containing methanol as the main component and having a concentration of several thousand ppm, such as a liquid containing a low concentration of sodium ions, is treated in the methane fermentation process, hydrogen sulfide, thiol, and dimethyl sulfide When sulfur compounds such as (CH ₃ SCH ₃ ) and dimethyl disulfide (CH ₃ SSCH ₃ ) coexist on the order of several hundred ppm, the methane production process may be particularly disturbed in the methane fermentation process. However, in the method of using lignocellulosic biomass of the present invention, a sulfur compound is used to treat a cellulosic fiber suspension, monosaccharide solution or organic acid solution having an organic substance concentration of several to several tens of percent in the methane fermentation step. The ratio of to organic matter becomes sufficiently small, and the influence on the methane production process can be ignored.

In the methane fermentation process, not all organic substances in the liquid to be treated are completely decomposed. Therefore, the BOD of the treated liquid in the methane fermentation process is usually several hundred to several thousand ppm. If the spent solution is discharged out of the system and released into the river or the sea as it is, it may cause water pollution problems.
Further, in the liquid to be treated in the methane fermentation process, the sodium ion migrates from the digested liquid mixture into the cellulosic fiber suspension in the washing process as described above. In the case of transferring to the methane fermentation process, sodium ions are also contained by the sodium ions scattered in the concentration / separation process moving into the low-concentration sodium-containing solution. This sodium ion is transferred to the treated liquid except that a part thereof is transferred to the sludge generated in the methane fermentation process. If the treated liquid is discharged, the sodium ions are undesirably lost.

For this reason, in one form of the utilization method of the lignocellulosic biomass of this invention, the processed liquid of the said methane fermentation process shall be returned to the said cooking process or a washing | cleaning process, and shall be reused. As a result, most of the sodium ions transferred to the liquid to be treated in the methane fermentation step are again subjected to the “cooking step, washing step and concentration / separation step” or “washing step and concentration / separation step”. In particular, sodium salts such as organic acid sodium and sodium carbonate are converted to sodium hydroxide, which is the main active ingredient of cooking chemicals in the cooking chemical recovery process, and used again as cooking chemicals. Will be. In addition, when using a cooking chemical solution containing sodium sulfide as an active ingredient in addition to sodium hydroxide, most of the sulfur content such as sulfate ions and hydrogen sulfide ions transferred to the liquid to be treated in the methane fermentation process After passing through the “cooking process, washing process and concentration / separation process” or “washing process and concentration / separation process” again, the solution is transferred to the sodium ion high-concentration containing liquid, converted to sodium sulfide in the cooking chemical solution recovery process, and digested again. It will be used as a medicine.
As a result, even if a relatively large amount of sodium ions migrates to the cellulosic fiber suspension side, the sodium ion loss from the cellulosic fiber suspension can be suppressed to a very low level. In order to prevent the loss, it is not necessary to suppress the concentration of sodium ions that migrate to the cellulosic fiber suspension side to a remarkably low level in the washing step. For this reason, it is possible to avoid an increase in equipment costs and operating costs by extremely increasing the amount of cleaning liquid used in the cleaning process or increasing the number of cleaning stages.

In the methane fermentation process, carbon dioxide is generated in the acid generation and decomposition process in which monosaccharides such as glucose produced by hydrolysis of cellulose and hemicellulose are decomposed into organic acids, and a part of the carbon dioxide is also produced as acid. It is converted into methane together with the hydrogen generated in the cracking process, but the rest is released as gas. Carbon dioxide is also generated when a portion of the generated methane is oxidized. Thus, although the combustible gas generated in the methane fermentation process contains carbon dioxide, since carbon dioxide is nonflammable, the calorific value per unit volume of the combustible gas is reduced due to the presence of carbon dioxide. become.
On the other hand, when lignocellulosic biomass contains sulfur, or when live cell biomass containing a relatively large amount of sulfur such as bark and leaves is mixed, the sulfur content is mainly sulfate ions or It is converted into thiosulfate ion and transferred to a cellulosic fiber suspension through a washing step. In particular, when sodium sulfide is used together with sodium hydroxide as a cooking chemical, hydrogen sulfide ions generated from sodium sulfide according to the above formula (3) are oxidized mainly into sulfate ions and thiosulfate ions in the cooking process, and also cellulose. Transition to system fiber suspension. This sulfate ion eventually moves into the liquid to be treated in the methane fermentation process, but in the methane fermentation process, sulfate-reducing bacteria produce hydrogen sulfide using sulfate ions, thiosulfate ions, methanol, and organic acids as raw materials. The portion that cannot be completely dissolved in the liquid is released as a gas, and as a result, hydrogen sulfide is contained in the combustible gas generated in the methane fermentation process. In particular, when the cellulosic fiber suspension or the low concentration sodium ion-containing liquid contains hydrogen sulfide ions, and as a result, the liquid to be treated in the methane fermentation process contains hydrogen sulfide, the sulfide generated in the methane fermentation process. Since there is less room for hydrogen to dissolve, the concentration of hydrogen sulfide contained in the combustible gas tends to increase.
Hydrogen sulfide is not only odorous and toxic in itself, but when flammable gas containing it is burned, toxic and corrosive sulfur oxides such as sulfur dioxide are generated. It is not preferable to be contained in the gas used.

Therefore, in one form of the method of using lignocellulosic biomass of the present invention, the combustible gas generated in the methane fermentation step is brought into contact with the digested liquid mixture, the cooking waste liquid or the liquid containing a high concentration of sodium ions, and the combustible By absorbing carbon dioxide and / or hydrogen sulfide in a sex gas into the digested liquid mixture, cooking waste liquid or liquid containing a high concentration of sodium ions, little or almost no carbon dioxide and hydrogen sulfide are mainly composed of methane. We decided to obtain combustible gas which did not contain.
As described above, the digested liquid mixture, the cooking waste liquid, and the liquid containing a high concentration of sodium ions contain sodium ions mainly as a weak acid-strong alkali sodium salt or sodium hydroxide, and therefore the pH is usually 10 or more. On the other hand, both carbon dioxide and hydrogen sulfide are acidic gases that are easily soluble in alkaline aqueous solutions, and methane, which is the main component of flammable gases, is hardly soluble in aqueous solutions. By bringing the gas into contact with the cooking waste liquid, carbon dioxide and hydrogen sulfide in the combustible gas can be selectively absorbed and removed.
Carbon dioxide and hydrogen sulfide absorbed in the digested liquor mixture, digested waste liquor or liquid containing a high concentration of sodium ions are dissolved in the digested liquor mixed liquor, digested waste liquor or high concentration of sodium ions in the reaction of the following formulas (9) and (10). It reacts with unreacted sodium hydroxide contained in the contained liquid, and is converted into sodium carbonate and sodium hydrogen sulfide, respectively.
CO ₂ + 2NaOH → Na ₂ CO3 + H ₂ O (9)
H ₂ S + NaOH → NaSH + H ₂ O (10)
In particular, when the combustible gas mainly composed of methane is brought into contact with the digested liquid mixture or the cooking waste liquid, sodium carbonate and sodium hydrogen sulfide generated in the digested liquid mixture or the cooking waste liquid are washed. Then, after passing through the concentration / separation step, or the concentration / separation step, the solution is transferred to the liquid solution containing a high concentration of sodium ions, and only a small part is transferred to the cellulosic fiber suspension or the solution containing a low concentration of sodium ions.

  In addition, when the sodium hydroxide in the cooking chemical liquid is almost consumed in the cooking process and the concentration of sodium hydroxide in the cooking liquid mixture, cooking waste liquid or liquid containing a high concentration of sodium ions is not so high, the cooking liquid mixture In some cases, the hydrogen sulfide concentration in the combustible gas after being brought into contact with the cooking waste liquid or the liquid containing a high concentration of sodium ions cannot be lowered to a significantly low level. In this case, the gas after being brought into contact with the digested liquid mixture, the cooking waste liquid or the liquid containing a high concentration of sodium ions is brought into contact with the cooking chemical before being used in the cooking process containing sodium hydroxide at a high concentration. Can reduce the hydrogen sulfide concentration in the combustible gas to a significantly low level. In this case, the hydrogen sulfide absorbed in the cooking chemical is converted to sodium hydrogen sulfide by the above formula (6), and the generated hydrogen sulfide ions contribute to the decomposition of lignin in the cooking process.

A gas absorption device such as a gas absorption tower can be used for gas-liquid contact between the digested liquid mixture, cooking waste liquid or high concentration sodium ion-containing liquid and combustible gas. Spray system for spraying the digested liquid mixture, digested waste liquid or liquid containing high concentration of sodium ions, providing a packing in the gas absorber, and contacting the liquid surface on the surface of the packed material A method of bringing gas into liquid contact, or a method of bubbling a combustible gas in a digested liquid mixture, a cooking waste liquid or a liquid containing a high concentration of sodium ions can be used.
Since the equilibrium partial pressure of carbon dioxide and hydrogen sulfide is lower as the temperature of the absorbing solution is lower, the equilibrium partial pressure is obtained in the methane fermentation process after cooling the digested product mixture, cooking waste solution, or solution containing a high concentration of sodium ions. The concentration of carbon dioxide and hydrogen sulfide in the combustible gas after contact can be lowered by contacting with the combustible gas generated. At that time, it is preferable that the temperature of the digested liquid mixture, the cooking waste liquid, or the liquid containing a high concentration of sodium ions is 50 ° C. or less.

Now, when cellulosic fiber suspension is treated by methane fermentation process and flammable gas mainly containing methane is recovered, the rate-limiting process is usually the methane production process by methane producing bacteria. In the production step, the methanogenic rate can be increased by using a mesophilic methanogen or a thermophilic methanogen having a high metabolic rate as the methanogen. However, since the optimal temperature of mesophilic methanogen is 30-40 ° C and the optimal temperature of thermophilic methanogen is 50-57 ° C, to heat or maintain the liquid to be treated up to that temperature The heat source is necessary.
For this reason, in one form of the utilization method of the lignocellulosic biomass of the present invention, a part of the heat supplied in the cooking step and / or the concentration and separation step is recovered, and the liquid to be processed in the methane fermentation step is recovered by the recovered heat. Was to be heated. Thereby, it is not necessary to prepare a new heat source for heating the liquid to be treated in the methane fermentation process, or even if a new heat source is required, the necessary amount is small. In addition, when separating a methane production | generation process from a hydrolysis process and an acid production | generation decomposition process, the heating of the process target liquid of the methane fermentation process by the said collection | recovery heat is a cellulase production bacterium, a hemicellulase production bacterium, and / or an acid production bacterium. It is also possible to carry out before the hydrolysis step or before the acid generation decomposition step by selecting one having an optimum temperature comparable to that of the methanogen.

In the cooking step, the cooking chemical is usually heated to 100 ° C. or higher, but the heat supplied at that time is the cooking mixture, and further the cellulosic fiber suspension from which the cooking mixture is separated in the washing step. And shift to cooking waste. And the heat | fever which this digested material liquid mixture etc. hold | maintain can be collect | recovered by exchanging heat with a digested material liquid mixture etc. and cooling water indirectly, and obtaining warm water or a vapor | steam. Or, in particular, when the temperature of the cooked mixture or the like is 100 ° C or higher, the flash steam is generated from the cooked mixture by opening the sealed state, and the sensible heat possessed by the cooked mixture or the like is retained. The flash steam can be recovered as latent heat, and if necessary, the flash steam and cooling water can be indirectly heat-exchanged to obtain hot water or steam.
By indirectly exchanging the hot water or steam thus obtained with the liquid to be treated in the methane fermentation step, the liquid to be treated can be heated. Alternatively, by using the liquid to be treated in the methane fermentation process as cooling water that indirectly exchanges heat with flash steam generated from the digested liquid mixture or the like It is also possible to heat directly without going through.

When a continuous digester is used as the digester, the cellulosic fiber suspension and cooking waste liquid are used when at least a part of the washing process is performed inside the digester, and the digested mixture is used when not used. Therefore, the heat held by the cellulosic fiber suspension and the cooking waste liquid or the cooking liquid mixture is recovered after the discharge is discharged from the cooking tank. In particular, when the temperature of the effluent exceeds 100 ° C, the sensible heat retained by the effluent is recovered as the latent heat of the flash vapor by temporarily storing in the blow tank and opening the sealed state with the blow tank. Can do.
On the other hand, when a batch-type digester is used as the digester, the heat held by the cellulosic fiber suspension and the cooking waste liquid, or the mixture of the digested products is the same as that of the continuous digester. Can be recovered after it has been discharged from the digester, but it is also possible to recover it while the digest mixture is held in the digester. Specifically, flash steam can be generated by opening the relief valve of the digester to open the sealed state, or for the indirect heat exchanger or heat exchange in the digester solution circulation line or in the digester Steam or hot water can be recovered by exchanging heat between the digested liquid mixture and the cooling water through piping. At that time, as the heat exchange pipe, the indirect heat exchanger or the heat exchange pipe used for heating the cooking chemical solution in the cooking step can be diverted, and cooling water can be flowed instead of steam.

As mentioned above, the temperature at which the liquid to be treated in the methane fermentation process should be heated is about 55 ° C., so steam or hot water close to 100 ° C. is always used as a heat source for heating it. It is not necessary, so if steam or high-temperature hot water is obtained in the heat recovery process as described above, use it in a process that requires a higher-temperature heat source, and use hot drainage such as steam condensate generated at that time. Are preferably used in cascade as a heat source for heating the liquid to be treated in the methane fermentation process.
In particular, when recovering the heat of the cooked mixture as steam (including flash steam), the steam is brought into contact with the lignocellulosic biomass prior to immersing the lignocellulosic biomass in the cooking chemical. It can be used as steam or as a heat source for the concentration / separation step, and the generated hot waste water can be used as a heat source for the liquid to be treated in the methane fermentation step.
In addition, when using a batch type digester as a digester, the heat | fever collect | recovered from flash steam or a high-temperature digested liquid mixture has a big fluctuation | variation temporally. In order to absorb this fluctuation and keep the liquid to be treated in the methane fermentation process at a constant temperature, a large amount of water may be used as a heat absorber.

The flash vapor generated in the heat recovery process is condensed by indirectly exchanging heat with cooling water. The flash vapor condensate generated at that time contains not only moisture but also volatile organic substances such as methanol. To do. Therefore, if the flash vapor condensate is discharged out of the system and directly released into a river or the sea, the chemical energy of the organic matter may not be effectively used, and there may be a problem of water pollution.
For this reason, the flash vapor condensate is mixed with the cellulosic fiber suspension or cooking waste liquid separated in the washing step and processed. As a result, the organic matter contained in the flash vapor condensate is eventually converted into a combustible gas mainly composed of methane in the methane fermentation process or burned in the recovery boiler in the cooking chemical recovery process. Combustion heat can be recovered.
In addition, since the property of the flash vapor condensate is similar to that of the low-concentration sodium ion-containing liquid, it is preferably transferred to the methane fermentation step after being mixed with the organic acid solution in the same manner as the low-concentration sodium ion-containing liquid.

In the cooking step, when using a cooking chemical containing sodium sulfide as an active ingredient in addition to sodium hydroxide, the concentration of dissolved solids other than cooking waste liquid, cooked liquor mixture, and cellulosic fibers is not kept sufficiently low. The cellulosic fiber suspension contains hydrogen sulfide ions as described above. Therefore, when flash vapor is released from these liquids, the hydrogen sulfide ions are evaporated as thiols such as hydrogen sulfide and methanethiol. Most of the evaporated hydrogen sulfide and thiol are transferred into the condensate, but some are diffused to the outside in the gas phase, causing odor problems.
In order to avoid this problem, instead of cooling the cooking chemical by opening the flash valve and releasing the steam, the heat exchange pipe is used instead of steam to flow cooling water indirectly. Can be cooled by.

  Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings. However, the present invention is not limited to such an embodiment, and various modifications can be made within the scope of the technical idea.

Example 1
FIG. 1 is a flow process diagram showing an example of a method for utilizing lignocellulosic biomass of the present invention.
Lignocellulosic biomass such as wood is crushed or cut if necessary and cooked in a pressure vessel together with a cooking solution that is an aqueous solution or dispersion in which sodium hydroxide and sodium sulfide are dissolved. It is supplied to the inside of the digester 1 from each supply port provided at the top of the kettle 1. At that time, the supply amount of cooking chemical is adjusted so that the weight ratio of NaOH + 1 / 2Na ₂ S to lignocellulosic biomass in terms of Na ₂ O is 10-30% (dry basis). The dissolved solid content concentration is adjusted to 10 to 50 g / l in terms of Na ₂ O.
The cooking chemical liquid is extracted to a circulation line, and heated to 160 to 200 ° C. by indirectly exchanging heat with steam in the cooking chemical liquid heater 2 which is an indirect heat exchanger provided in the circulation line. Lignocellulosic biomass gradually settles in the region of the cooked cooking solution and stays for 1 to 3 hours until reaching the bottom, while the fiber cells mainly composed of cellulose and hemicellulose disaggregate, and the cellulosic fibers are in the liquid. A cooked product mixture in which other dissolved solids are dissolved or dispersed while being dispersed is obtained.
A cleaning liquid II is supplied from the supply port at the bottom of the digester 1 to form a region of the cleaning liquid in the vicinity of the bottom, and cellulosic fibers are diffused and transferred to the cleaning liquid region to obtain a cellulosic fiber suspension I. . The cellulosic fiber suspension I is discharged from the outlet provided at the bottom of the digester 1, while mixing the digested product from which a part of the washing liquid II supplied from the bottom supply port and the cellulosic fibers are detached. The mixture of the remaining part of the liquid is extracted as cooking waste liquid from another outlet located above the washing liquid region at the bottom of the digester 1.
The cellulosic fiber suspension I is temporarily stored in the blow tank 3, and the pressure is reduced to atmospheric pressure and cooled to 100 ° C. or less by releasing flash vapor. The cooled cellulosic fiber suspension I is supplied to the diffusion washer 4 and is washed by displacement with the washing liquid I. The cellulosic fiber suspension II having a sodium ion concentration lower than that of the cellulosic fiber suspension I and the washing waste liquid. Separated.
Among these, the washing waste liquid is supplied to the digester 1 as the washing liquid II, while the cellulosic fiber suspension II is further reduced in sodium ion concentration by repeating substitution washing and / or dilution washing if necessary. Then, it is supplied to the hydrolysis tank 5. In the hydrolysis tank 5, the cellulosic fibers in the cellulosic fiber suspension II are hydrolyzed into monosaccharides such as glucose by microorganisms containing cellulase-producing bacteria and hemicellulase-producing bacteria. The monosaccharide solution thus obtained is supplied to the acid generation tank 6, where the monosaccharide is decomposed into an organic acid mainly composed of volatile fatty acids such as acetic acid by the acid-producing bacteria. A solution is obtained, and the organic acid solution is sent to a methane generation tank 7 which is a UASB apparatus.
On the other hand, the cooking waste liquid extracted from the digester 1 is transferred to the flash tank 8 where the pressure is reduced to atmospheric pressure by discharging flash steam and cooled to 100 ° C. or lower, and is a multi-effect evaporator. The concentrated separation device 9 is supplied. The cooking waste liquid is indirectly heat-exchanged with the steam in the concentration / separation device 9 to generate steam containing volatile components such as methanol, and the generated volatile-component-containing steam is indirectly heat-exchanged with the remaining liquid. As a result, the volatile component-containing vapor is condensed while the volatile component-containing vapor is generated again from the remaining liquid. To be separated.
Among these, the solution containing a low concentration of sodium ions is sent to the methane generation tank 7 which is a UASB device together with the organic acid solution, and the organic acid and methanol in the liquid are decomposed into methane, carbon dioxide and water by the methanogen. Of these, components that cannot be dissolved in water are released as a gas body, and as a result, a combustible gas I containing methane as the main component, 10 to several tens of percent of carbon dioxide, and some hydrogen sulfide is obtained. This combustible gas I is sent to the gas absorption device 10 which is a packed tower, brought into gas-liquid contact with the high concentration sodium ion containing liquid I transferred from the concentrating / separating device 9, and contained in the combustible gas I. Carbon and hydrogen sulfide are absorbed and removed by the liquid I containing sodium ions at a high concentration. In this way, a flammable gas II containing methane as a main component and little or almost no carbon dioxide and hydrogen sulfide is obtained.
On the other hand, the sodium ion high concentration liquid II obtained by absorbing the carbon ion and / or hydrogen sulfide by the sodium ion high concentration liquid I is added with sodium carbonate and / or sodium sulfate, if necessary. Then, it is sent to the recovery boiler 11 and burned. The combustion residue thus obtained was dissolved in make-up water in the dissolution tank 12 to obtain a residue aqueous solution. Is added, and the cooking chemical solution is recovered by removing the generated calcium carbonate. Further, the recovery boiler 11 is provided with a water pipe wall, and recovers the combustion heat of the liquid II containing sodium ions at a high concentration as steam.
The liquid separated from the combustible gas in the methane generation tank 7 is sent to the dilution tank 14 after removing sludge and diluted with make-up water to obtain the cleaning liquid I. Then, the cleaning liquid I is supplied to the diffusion washer 4 as described above.

(Example 2)
FIG. 2 is a flow process diagram showing another example of the method of using lignocellulosic biomass of the present invention, and in particular, recovery of a part of the heat supplied in the cooking process and the concentration and separation process, and methane by the recovered heat. It is a flow process figure explaining the heating of the process target liquid of a fermentation process.
The steam generated in the gas combustion boiler 15 is supplied to the cooking chemical heater 2 and indirectly heat-exchanged with the cooking chemical and cooking waste liquid, while the other party is heated and condensed to become hot waste water. Further, the steam generated in the gas combustion boiler 15 is also supplied to the concentrating / separating device 9 and indirectly heat-exchanges with the cooking waste liquid to evaporate moisture and volatile components from the other party, while it condenses and warms itself. It becomes drainage. Then, the warm drainage generated in the cooking chemical heater 2 and the concentration separator 9 is collected in the warm drainage tank 16. Note that the volatile component-containing vapor evaporated in the concentration / separation apparatus 9 is condensed and recovered as a sodium ion low-concentration containing liquid.
The flash steam I discharged from the blow tank 3 and the flash steam II discharged from the flash tank 8 are sent to the flash steam I condenser 17 and the flash steam II condenser 18, respectively, and supplied from the cooling water tank 19. While it condenses itself by indirectly exchanging heat with the cooled cooling water, the cooling water is heated to generate hot waste water. These warm wastewaters are collected in the warm drainage tank 16.
Thus, the warm waste water collected in the warm drain tank 16 is supplied to the treatment target liquid heater 20 which is an indirect heat exchanger as warm water for heating, and indirectly heated with the organic acid solution generated in the hydrolysis tank 6. The organic acid solution is heated to 50 ° C. to 55 ° C. by exchanging it, while it is cooled and collected in the cooling water tank 19. The recovered cooling water is supplied to the flash steam I condenser 17 and the flash steam II condenser 18 as described above, and a part thereof is supplied to the gas combustion boiler 15 to be converted into steam.
On the other hand, the heated organic acid solution is sent to the methane generation tank 7 and the combustible gas mainly containing methane is generated by decomposing the organic acid and methanol in the organic acid solution. A part of the gas is sent to a gas-fired boiler and burned, and steam is generated by the heat of combustion.

(Example 3)
FIG. 3 is a flow process diagram showing another example of the method of using lignocellulosic biomass of the present invention, and in particular, the method of using lignocellulosic biomass of the present invention and kraft pulp (abbreviated as KP in the figure). ) It is a flow process diagram explaining a utilization method that combines manufacturing processes.
The cellulosic fiber suspension extracted from the digester 1 undergoes a process not shown in the figure, and then contains methane as a main component, and contains 10 to several tens of carbon dioxide and some hydrogen sulfide. Converted to flammable gas I. The combustible gas I is brought into gas-liquid contact with the cooking waste liquid I extracted from the digester 1, and the gas absorbing device 10, and the carbon dioxide and hydrogen sulfide contained in the combustible gas I are absorbed by the cooking waste liquid I. Removed. In this way, a combustible gas II containing methane as a main component and little or little carbon dioxide and hydrogen sulfide is obtained, while the cooking waste liquid II absorbs carbon dioxide and / or hydrogen sulfide to produce the cooking waste liquid II. can get.
The cooking waste liquid II obtained from a plurality of methane gas generators composed of the above devices and processes is sent to the mixing tank 21 together with the kraft pulp black liquor obtained from the kraft pulp manufacturing process, and the resulting mixed waste liquid is It is a multi-effect evaporator after sodium sulfide and / or sodium hydrogen sulfide in the mixed waste liquid is oxidized to sodium thiosulfate by contacting with air and gas-liquid in the oxidizer 22 which is an aeration tube type aeration tank. The concentrated separation device 9 is supplied.
The mixed waste liquid after oxidation is indirectly heat-exchanged with steam in the concentration / separation device 9 to generate steam containing volatile components such as methanol, and the generated volatile-component-containing steam is indirectly heat-exchanged with the remaining liquid. By repeating that the volatile component-containing vapor is condensed while the volatile component-containing vapor is generated again from the remaining liquid, the sodium ion high concentration liquid and the sodium ion low concentration liquid are finally obtained. Separated. Among these, a liquid containing a high concentration of sodium ions is sent to the recovery boiler 11 and combusted after adding sodium carbonate and / or sodium sulfate, if necessary. The combustion residue thus obtained was dissolved in make-up water in the dissolution tank 12 to obtain a residue aqueous solution. Is added, and the cooking chemical solution is recovered by removing the generated calcium carbonate. Further, the recovery boiler 11 is provided with a water pipe wall, and the combustion heat of the liquid containing a high concentration of sodium ions is recovered as steam.
A part of the cooking chemical obtained in this way is sent to the kraft pulp manufacturing process, and the rest is sent to a plurality of methane gas generators which are the supply sources of the cooking waste liquid II, and supplied to the digester 1 again.

  INDUSTRIAL APPLICABILITY The present invention can be used in industries that produce flammable gas mainly composed of methane. Moreover, it can utilize also in the industry which manufactures a cellulose fiber (pulp) from lignocellulosic biomass as a raw material, and the industry which processes organic waste.

It is a flow process figure showing the utilization method of lignocellulosic biomass. It is a flow process diagram which shows another example of the utilization method of lignocellulosic biomass, and in particular, recovery of a part of the heat supplied in the cooking process and the concentration separation process, and the treatment target liquid of the methane fermentation process by the recovered heat It is a flow process figure explaining heating. It is a flow process figure which shows another example of the utilization method of lignocellulosic biomass, and is a flow process figure explaining the utilization method which combined the utilization method of lignocellulosic biomass of this invention, and the kraft pulp manufacturing process especially. .

Explanation of symbols

1 ... digester 2 ... cooking chemical heater 3 ... blow tank 4 ... diffusion washer 5 ... hydrolysis tank 6 ... acid generator tank 7 ... methane generator tank 8 ... Flash tank 9 ... Concentration separator
10 ... Gas absorber
11 ………… Recovery boiler
12 Melting tank
13 ………… Causticizing tank
14 ………… Dilution tank
15 ... Gas-fired boiler
16 · · · · · Thermal drainage tank
17 ‥‥‥ Flash Vapor I Condenser
18 ………… Flash Vapor II Condenser
19 Cooling water tank
20 · · · · · Liquid heater to be treated
21… Mixing tank
22 ... Oxidizer

Claims (6)

A cellulosic fiber suspension production step for obtaining a cellulosic fiber suspension by decomposing and removing lignin from lignocellulosic biomass;
A live cell biomass mixing step of mixing the cellulosic fiber suspension with a live cell biomass such as a bark or leaf of a tree;
The mixed solution of the cellulosic fiber suspension and the living cell biomass is maintained in an anaerobic state, and the cellulosic material in the mixed solution is propagated in the mixed solution or by the microorganism and hydrolase. A methane production process that produces “flammable gas mainly composed of methane” by decomposing fibers and other organic substances;
A method of using lignocellulosic biomass comprising: The methane production step includes
The mixed solution of the cellulosic fiber suspension and the living cell biomass is kept in an anaerobic state, and the cellulosic fiber and other organic substances in the mixed solution are decomposed by microorganisms or by microorganisms and hydrolases. Acid generating and decomposing step of obtaining an organic acid solution by:
A methane fermentation process in which the organic acid solution is maintained in an anaerobic state, and an organic acid and other organic substances in the organic acid solution are decomposed by microorganisms to generate a “combustible gas mainly composed of methane”;
The method for using lignocellulosic biomass according to claim 1, comprising: A cellulosic fiber suspension production step for obtaining a cellulosic fiber suspension by decomposing and removing lignin from lignocellulosic biomass;
A live cell biomass mixing step of mixing the cellulosic fiber suspension with a live cell biomass such as a bark or leaf of a tree;
A hydrolysis step of obtaining a monosaccharide solution by hydrolyzing a cellulose fiber in a mixed solution of the cellulosic fiber suspension and the living cell biomass using a hydrolase or a hydrolase-producing bacterium; ;
By maintaining the monosaccharide solution in an anaerobic state and decomposing monosaccharides and other organic substances in the monosaccharide solution by microorganisms propagated in the monosaccharide solution, a “flammable gas mainly composed of methane” A methane production process to produce
A method of using lignocellulosic biomass comprising: The methane production step includes
An acid generating and decomposing step of obtaining an organic acid solution by maintaining the monosaccharide solution in an anaerobic state and decomposing monosaccharides and other organic substances in the monosaccharide solution by microorganisms;
A methane fermentation process in which the organic acid solution is maintained in an anaerobic state, and an organic acid and other organic substances in the organic acid solution are decomposed by microorganisms to generate a “combustible gas mainly composed of methane”;
The method for using lignocellulosic biomass according to claim 3, comprising: A cellulosic fiber suspension production step for obtaining a cellulosic fiber suspension by decomposing and removing lignin from lignocellulosic biomass;
A hydrolysis step of obtaining a monosaccharide solution by hydrolyzing the cellulosic fiber in the cellulosic fiber suspension using a hydrolase or a hydrolase-producing bacterium;
A live cell biomass mixing step of mixing the monosaccharide solution with live cell biomass such as tree bark and leaves;
By maintaining the mixed solution of the monosaccharide solution and the living cell biomass in an anaerobic state and decomposing monosaccharides and other organic substances in the monosaccharide solution by the microorganisms propagated in the mixed solution, “methane can be obtained. A methane production process that produces a combustible gas as a main component;
A method of using lignocellulosic biomass comprising: The methane production step includes
An acid generating and decomposing step of obtaining an organic acid solution by maintaining a mixed solution of the monosaccharide solution and the living cell biomass in an anaerobic state and decomposing the monosaccharide and other organic substances in the mixed solution by a microorganism;
A methane fermentation process in which the organic acid solution is maintained in an anaerobic state, and an organic acid and other organic substances in the organic acid solution are decomposed by microorganisms to generate a “combustible gas mainly composed of methane”;
The method for using lignocellulosic biomass according to claim 5, comprising:

Images