JP2005112960A - Method for producing refuse-derived solid fuel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent abnormal combustion and explosion of RDF by improving a method for producing RDF while using an existing RDF production technique and production apparatus, to collect hydrogen gas or mixed gas consisting essentially of hydrogen gas generated by the method for producing RDF and to effectively use the gas as a resource. <P>SOLUTION: The production method comprises a known process for producing RDF and a post process for promoting fermentation by providing a readily fermentable environment by a specific microorganism. Specifically, moisture is added to RDF in a dry state, wetted RDF is held in a closed container at 25-45°C for a fixed time. Consequently, fermentation is advanced and formed hydrogen gas, etc., is recovered. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a manufacturing method for avoiding the risk of abnormal combustion and gas explosion associated with abnormal heat generation during storage of a solid waste fuel (RDF) manufactured by a known method, and its processing step The present invention relates to an RDF manufacturing technique in which generated hydrogen gas or a mixed gas thereof is collected as a useful resource.

  In recent years, solid waste fuel (RDF) has attracted attention from the viewpoint of effectively using increasingly increasing waste as a resource, and several tens of RDF treatment systems are in operation or constructed throughout the country. So

For an overview of RDF manufacturing technology,
In addition to these reports, RDF processing stem manufacturing companies and some local governments have also made public.

Environmental hygiene management technology system, harmful microorganism management technology Volume 2, Fuji Techno System Co., Ltd., issued on May 23, 2000.

The manufacturing process generally includes a process of crushing garbage containing resin such as raw garbage, paper, fibers, plastics, etc. in two stages, a drying process by heating, a process of removing non-combustible materials such as metals, wind power It consists of a step of removing unsuitable molding by sorting, a step of adding lime (mainly slaked lime), and a step of molding RDF. The RDF produced through these steps has a pH (pH) in the range of 6.5 to 10.5 and a water content of less than 20% by weight, preferably 15% by weight or less, more preferably 10%. It is less than wt%.
Here, the pH of RDF is in the range of 6.5 to 10.5 because lime such as slaked lime is added for the purpose of preventing the halogen compound in the garbage from generating dioxin by combustion. Yes, it becomes neutralized as calcium chloride by the combustion of RDF. The following patents that further improve dioxin generation have been published.

Japanese Patent Application No. 10-184071 "Production Method of Solid Waste Fuel" Japanese Patent Application No. 2000-359970 (P2000-359970) “Waste incineration method that does not generate dioxins, dioxin generation inhibitor, and production method thereof”.

  Next, in order to ensure the strength of RDF, the water content of RDF is controlled to be less than 20% by weight. As a method for achieving this, the crushed waste is heated and dried at a substantial temperature of 60 ° C. to 120 ° C. Later, lime such as slaked lime is added. Through these steps, it is thought that heat-sensitive microorganisms such as Escherichia coli in garbage are killed, and because they are in a dry state, no fermentation or rot occurs, and heat generation and gas generation due to fermentation can be prevented. It was.

  However, recently, there has been a problem that an accident in which RDF being stored burns due to abnormal heat generation, or an explosion in severe cases, particularly at high temperatures in summer, has occurred.

  While using existing RDF manufacturing technology and manufacturing equipment, the RDF manufacturing method is improved to prevent abnormal combustion and explosion of RDF, and the main component is hydrogen gas or hydrogen gas generated by the RDF manufacturing method of the present invention. It is an object of the present invention to collect the mixed gas and effectively use it as a resource.

  In order to solve the above problems, the present inventors have studied the causes of abnormal heat generation, abnormal combustion, and explosion of RDF during storage, and have found the following facts. That is, even when the combustible crushed pulverized material passes through a high temperature state of 60 ° C. to 120 ° C. at the substantial temperature by the heat drying process and is alkalized by the addition of slaked lime, certain heat-resistant microorganisms such as Bacillus genus When the stored RDF is kept at an appropriate temperature, hydrogen gas is produced by fermentation using polysaccharides such as starch and cellulose and / or saccharides such as oligosaccharides contained in the garbage. This was assumed to be the main cause of abnormal combustion and explosion.

  Based on the above discovery, the present invention solves the problem by adding a post-process that promotes fermentation by providing an environment in which specific microorganisms are easily fermented, in addition to the known RDF production process. It was made with the idea of reversal.

  That is, the present invention provides at least a solid waste fuel (RDF) containing at least saccharides and slaked lime, having a pH (pH) in the range of 6.5 to 10.5, and having a moisture content of less than 20% by weight. Moisture is added so that the water content is 20% to 75% by weight to obtain a wet RDF, and then the wet RDF is held for 6 hours or more in a sealed container having an ambient temperature of 25 ° C. to 45 ° C. This is a method for producing a solid waste fuel (RDF).

Furthermore, it is a manufacturing method related to a manufacturing method of re-drying the wetted RDF held for 6 hours or more in a sealed container having an atmospheric temperature of 25 ° C. to 45 ° C.
Next, in the step of holding the wet RDF in a sealed container having an ambient temperature of 25 ° C. to 45 ° C. for 6 hours or more, holding the wet RDF until the pH (pH) of the wet RDF is 6.0 or less. Is a manufacturing method characterized by

  Further, in the step of holding the wet RDF in a sealed container having an ambient temperature of 25 ° C. to 45 ° C. for 6 hours or more, the hydrogen gas generated during the holding or a mixed gas containing hydrogen gas as a main component is sealed. It is a manufacturing method characterized by selectively collecting from a container.

  With the solid waste fuel production method of the present invention, it is possible to produce RDF without the risk of abnormal combustion or explosion, and it is possible to collect hydrogen gas generated in the production process according to the present invention or a mixed gas thereof, thereby effectively utilizing resources. I can plan.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of the invention will be described in detail. However, the technical scope of the invention is not limited by the following embodiment, and various modifications can be made without changing the gist of the invention. can do.

  First, in the present invention, water is added to RDF in a dry state having a water content of less than 20% by weight produced by a known method to obtain a wet RDF having a water content of 20% to 75% by weight. The reason why the wet RDF is held in a sealed container having an ambient temperature of 25 ° C. to 45 ° C. for 6 hours or more will be described below.

  Sugars such as starch, cellulose and fruit juice are decomposed into monosaccharides such as glucose and fructose by microorganisms (bacteria, mold, etc.), and the monosaccharide is finally converted into an organic acid by the fermentation reaction shown in the formula (1). Decomposed into carbon dioxide and hydrogen.

The reaction of formula (1) is anaerobic at the next stage where oxygen is consumed, in the presence of water, at an appropriate temperature and at an appropriate pH, under the initial environment where oxygen is present, and the reaction by aerobic respiration of microorganisms proceeds. Fermentation proceeds.

  The reason for adding water to the RDF in a dry state so that the water content is 20% to 75% by weight is that the fermentation reaction progresses slowly if it is less than 20% by weight, and the strength of RDF decreases if it exceeds 75% by weight. This is because the handling operation of RDF becomes difficult. Therefore, in order to promote the fermentation reaction while maintaining the strength of RDF, the water content of RDF is more preferably 30% by weight to 60% by weight.

  Next, the wet RDF is held in a sealed container having an ambient temperature of 25 ° C. to 45 ° C. for 6 hours or longer. . In addition, if it is less than 6 hours, the fermentation reaction hardly proceeds, and it is more desirable to keep it for 24 hours or more.

  Here, the reason why the wet RDF is stored in the sealed container is that the fermentation for generating hydrogen gas proceeds anaerobically, so that the supply of oxygen is cut off and the generated hydrogen gas is diffused into the atmosphere. This is for the purpose of preventing accidents such as abnormal combustion and explosion, and for collecting the generated hydrogen gas or a mixed gas thereof from a pipe or the like disposed in a sealed container and recovering it as a resource.

  The mixed gas in the sealed container such as hydrogen gas, carbon dioxide gas and nitrogen gas remaining in the container is used as fuel gas. Carbon dioxide gas is pressurized and absorbed with an alkaline liquid such as ethanolamine. It can be recovered as a mixed gas containing hydrogen gas as a main component by a known method such as removal.

  By the way, in the above, the method of adding moisture to the dry RDF includes not only the method of moistening the RDF with watering or moist air before storing it in the sealed container, but also storing the RDF in the sealed container. There is a method of wetting in a humid air atmosphere, and the method is selected in consideration of reaction efficiency, cost and the like.

  Now, as shown in the formula (1), as the fermentation reaction proceeds, the amount of organic acid such as organic carboxylic acid increases, the pH shifts to the acidic side, and it becomes difficult for microorganisms to survive. Since the fermentation activity is reduced, there is almost no production of hydrogen gas. Therefore, the fermentation reaction is terminated when pH 6 becomes below, more desirably, below pH 5.5.

  Next, for the purpose of increasing the strength of the wet RDF after the fermentation reaction, it is also an option to add a re-drying step. The re-drying method includes a method by heating, a method of keeping in a dry air atmosphere, a method of vacuum drying, etc., and is selected in consideration of the cost and the like including the case of omitting the re-drying.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Number of microorganisms in dry RDF>
Currently, three types of dry RDF with different pH were obtained from RDF plants in Mie Prefecture from among industrially produced RDFs, and the number of microorganisms living in them was investigated. The obtained RDF was dried at an atmospheric temperature of 280 ° C. (substance temperature was about 80 ° C.), and the water content was 7% by weight.

The results are shown in Table 1. In any dry RDF with different pH, all of aerobic microorganisms (Aerobes), anaerobic microorganisms (Anaerobes) and facultative anaerobes (10 ⁴ to 10 ⁶ cfu / g (cfu is the number of colonies produced by bacteria). In particular, RDF1 (pH 8.33) was higher in number than other RDFs because of the appropriate pH of the living microorganisms.

<Gas generation by fermentation of wetted RDF>
Next, deionized water was added to 1.7 L (100 g) of the above RDF1 sample so that the water content was different, and the mixture was moistened. did. The gas produced by the fermentation was collected in a cylinder by a water displacement method through a pipe led out of the container from the glass bottle, and the gas components were analyzed by gas chromatography.

  The results are shown in Table 2, and the following tendencies were observed. That is, the amount of generated gas increased with an increase in the water content ratio, and the ratio of the amount of hydrogen gas to the total gas amount gradually decreased from 80% to around 65%.

Further, FIG. 1 shows the results of measuring the amount of change in the amount of generated gas with time when the moisture content ratio is 73% and holding for 72 hours. According to this, the amount of gas generated increased rapidly from 12 hours after storing the wet RDF in the container, and reached saturation after about 72 hours. The pH at this time was 5.5.

<Discussion>
Aerobic, anaerobic and amphoteric microorganisms were alive in RDF in a dry state with a pH of about 7-10 neutral to alkaline and a water content of 7%. The moisture content of the RDF is increased and moistened, and the fermentation reaction proceeds by placing it in an appropriate temperature environment of 30 ° C. to 40 ° C., and hydrogen gas is generated after about 12 hours. Although increased, saturation was reached after about 72 hours. The pH was changed from an alkalinity of 8.33 to an acidity of 5.5, and in this state, it was estimated that the activity of microorganisms decreased and the fermentation reaction became inactive.

It is a figure which shows the time change of the gas amount which wetted RDF produces | generates by fermentation.

Claims (4)

Waste solid fuel (RDF) containing at least saccharides and slaked lime, having a pH (pH) in the range of 6.5 to 10.5 and a moisture content of less than 20% by weight, and a moisture content of 20% by weight Moisture is added so as to be ˜75% by weight to obtain a wet RDF, and then the wet RDF is held in a sealed container having an atmospheric temperature of 25 ° C. to 45 ° C. for 6 hours or more. A method for producing solid waste fuel (RDF). 2. The waste solid fuel (RDF) according to claim 1, wherein the wet RDF is held again in a sealed container having an atmospheric temperature of 25 ° C. to 45 ° C. for 6 hours or more and then dried again. Production method. In the step of holding the wet RDF in a sealed container having an ambient temperature of 25 ° C. to 45 ° C. for 6 hours or more, the wet RDF is held until the pH (pH) of the wet RDF is 6.0 or less. The manufacturing method of the solid waste fuel (RDF) of Claim 1 or Claim 2 to do. In the step of holding the wet RDF in a sealed container having an ambient temperature of 25 ° C. to 45 ° C. for 6 hours or more, hydrogen gas generated during the holding or a mixed gas containing hydrogen gas as a main component is removed from the sealed container. The method for producing solid refuse fuel (RDF) according to any one of claims 1 to 3, which is selectively collected.

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