Carbonizing Furnaces in Japan February 2002

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Introduction: In recent years, regulations on waste incineration have become increasingly strict, including revisions to the Law Concerning Special Measures against Dioxin and the Waste Disposal and Public Cleansing Law. On the other hand, various recycling laws have been enacted to realize a resource-recycling society, and the cost of waste disposal has skyrocketed due to the tightness of final disposal sites. There is a strong demand for a shift from incineration and landfill to recycling in waste disposal.

In line with this trend, there is an emerging need for an alternative recycling method to simple incineration for organic wastes (construction waste wood, food waste, sewage sludge, livestock manure, etc.), which were originally disposed of in landfills after intermediate treatment such as dehydration, drying, and incineration. Carbonization" is suddenly coming into the limelight as one such method.

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Current Status and Direction of Carbonization Furnace Development: Charcoal production is a typical example of carbonization. So far, for its production, traditional charcoal-making techniques (e.g., Tsuki Kiln and Proc Furnace) and flat furnaces, screw furnaces, rotary kilns, and fluidized bed furnaces for industrial mass production have been used. However, while the need for dioxin countermeasures is low for thinned wood, sawmill waste, and other materials with well-defined properties, and can be handled with conventional technologies, dioxin is an unavoidable problem when carbonization equipment is used as an alternative to waste incineration or as a recycling device.

What is required of carbonization equipment for the purpose of recycling is how to obtain good quality carbonized material at low cost without generating dioxin. In other words, the furnace must be sealed and oxygen-free (or low oxygen) to suppress the formation of dioxin while allowing steaming at high temperatures, and the contents must be stirred to ensure homogeneous carbonization.

The rotary kiln is the most widely used carbonization equipment that satisfies these requirements. In the rotary kiln method, materials are placed in a rotating cylindrical furnace and carbonized by internal or external heat. One drawback of rotary kiln incinerators is that the residual material (carbide) must be post-combusted in a stoker until it is completely reduced to ash. This is an advantage of the carbonization process.

The organic content in the raw material is converted into combustible dry distillation gas, from which the heat necessary for carbonization is obtained, thus saving fuel. (2) The furnace has a simple structure with no mechanical parts, which minimizes breakdowns.

(iii) Although advanced sealing technology is required to seal the furnace, the dioxin removal system and stoker are not necessary, making it superior in terms of installation space and equipment cost. (4) The raw materials are fed into the kiln by the rotation of the kiln.

(4) The raw materials are cut back and forth by the rotation of the kiln, so there is no unevenness in baking. Since the basic technology has already been established in this field, many companies, from major machinery manufacturers to small and medium-sized companies and venture businesses, have entered the carbonization equipment market, and equipment ranging in scale from 10OO kilograms per day to several tens of tons per day has been developed. This section looks at examples of carbonization processes for various organic wastes, the carbonization furnaces used for each, and marketability.

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Charcoal Market Expansion, Organic: One of the major reasons why carbonization is attracting attention from both sides of the development of new applications for waste is the expansion of applications for charcoal. While there are many cases in which various recycling projects face difficulties in distributing their products, the prospects for carbonized materials are relatively bright. Charcoal, which was produced at a rate of about 2.7 million tons per year in the 1940s and used as a major fuel along with coal, has been gradually declining in production.

In recent years, however, new demand has emerged for non-fuel uses, and production has been increasing. Currently, 58,835 tons of charcoal sold in Japan is used for purposes other than fuel (1999 results).

The reason for this is charcoal's excellent functionality as a material, namely its ability to absorb odorous substances in the air and water and pollutants in water through the numerous micropores on its surface, and its ability to improve soil quality through the propagation of soil microorganisms and the improvement of air and water permeability (designated as soil improvement material under the Soil Energy Promotion Law enacted in 1984). Recently, the adsorption of volatile organic compounds such as toluene, xylene, and formaldehyde, which are believed to be factors in sick building syndrome, has also been proven.

In response, the use of charcoal from wood waste, such as thinned lumber, pruning branches, sawdust, and mill scraps, is on the rise. Such charred products are expected to be widely used as substitutes for conventional charcoal products, with high added value. For example, it can be used for drinking water, bedding and pillows, odor control, and baths, as well as a soil conditioner and a humidity regulator for housing (regulates under-floor humidity to prevent the growth of capiocarps and termites).

It also shows promise as an activated carbon used in more advanced fields such as dioxin adsorption, industrial water purification, and solvent recovery. Activated carbon is made porous by reacting carbide with oxidizing gas at high temperatures (gas activation method) or by impregnating uncarbonized materials with dehydrating and oxidizing chemicals and carbonizing them in an oxygen-free state (chemical activation method).

Generally, a surface area of less than 800 meters per gram is distinguished as charcoal and a surface area of more than 800 meters is distinguished as activated charcoal, but some carbonized materials calcined at high temperatures (800°C or higher) have a similar surface area, and thus have higher added value as a recycled product. While efforts to carbonize such woody wastes are progressing, applications for organic wastes, including food scraps, as a raw material for charcoal are also beginning to be developed. Currently, organic waste is mostly recycled by converting it into compost or slag and then re-commercializing it.

However, composting is expected to experience an oversupply of products in the future, and incineration sales and molten ash (slag) have limited applications such as roadbed material and construction aggregate. The current prices of charcoal made from waste materials are 30 yen per kg of cucumber charcoal (for soil conditioner), 80 yen per kg of okara charcoal (for fertilizer), and 30 yen per kg of tire charcoal (for deodorizer).

4 Construction waste wood: Charcoal is used as a raw material.

Construction waste wood: Construction waste wood represents the largest business opportunity in the carbonization market, as it is the closest material to the original source of charcoal and has yet to be explored for recycling. In particular, the full enforcement of the Construction Materials Recycling Law in May 2002 will provide a tailwind.

According to the Ministry of Land, Infrastructure, Transport and Tourism's "Survey on Recycling of Construction Byproducts in FY2000," the reuse of asphalt concrete and concrete blocks as recycled aggregate and roadbed material has increased significantly to 98% (85% in FY95) and 96% (65% in FY95), respectively, while the recycling rate for wood has declined to 38% (40% in FY95). However, the percentage of lumber has worsened to 38% (40% in FY95). Demand for fuel chips, which had been the mainstay of construction wood use, has declined due to the aging of wood waste oilers and the closing of a number of public bathhouses.

Recycled chips are in short supply, prices of chips for paper and plywood have dropped across the board, and in the case of chips for fuel, there is an increasing number of cases of so-called reverse debt, in which freight is paid to have the chips brought to the site, making the development of new applications an urgent necessity.

Under the Construction Recycling Law, wood can be reduced in size (by incineration) as a special exception only when the cost is excessive, such as when there is no recycling facility within a certain distance (25 km) from the construction site. However, if it is simply burned, it has no added value as a resource. Considering the social headwind against incineration, it is expected that the trend will be toward resource recycling in the long run, along with the cost advantages of recycling.

Kumagaya Carpon, located in Kumagaya City, Saitama Prefecture, was one of the first companies to develop business in this field. The company was established in October 1998 as a group company of Kamei Sangyo, which holds a license to collect, transport, and dispose of industrial waste, as well as to carbonize wood chips, for which demand had been stagnant.

The reason for the separate company status was that carbonization by Kamei Sangyo, a processor of industrial waste, would fall under the category of incineration under the current law, and the resulting carbonized material would be classified as "fly ash," which could not be sold as a commodity. Therefore, Kamei Sangyo performs the entire carbonization process up to the chipping stage, which is sold as valuable resources, and Kumagaya Carbon purchases the raw materials and processes them at its plant.

The company's carbonization system first removes paints, termite inhibitors, and preservatives from the wood during the chipping process. This is because of the possibility of these materials leaching out if the carbonized material is used as a soil conditioner or other material. The selected waste wood is then chipped in a crusher. Paint chips and metals are thoroughly removed using sieves, magnetic separators, and metal detectors before the raw material chips are finally produced.

The carbonization equipment used by the company is called the repetitive rocking type, which was jointly developed by Gyoko Giken and Chiyoda Engineering. Basically, it performs dry distillation gasification under low-oxygen conditions as in the rotary kiln method, but instead of rotating the furnace, it oscillates it like a cradle. This method is designed to keep the charcoal even and finely shaped without losing its shape. Only a small amount of fuel (kerosene or heavy oil A) is used as an igniter when the material is fed into the furnace, and the rest of the process is done with the material burning on its own for about 40 minutes at a temperature of over 1000 degrees Celsius.

The dry distillate gas emitted during carbonization is not used for carbonization, but is mixed with air in a dry distillate gas firing furnace and re-burned. This exhaust gas is also used for drying when materials with high moisture content are used, as it is over 1,000°C. Even so, there is still a large amount of heat left over. The plant produces 2,000 liters of charcoal from 2,500 kilograms of chips per hour. The company also commercializes "Sukoyaka Mokkun," an underfloor humidity conditioner, and "Irodori," a soil conditioner, both of which are packaged in bags by the company.

5 Municipal Solid Waste

Municipal waste: Approximately 51 million tons of general waste is generated annually. Although the percentage of recycled waste has been increasing recently due to the expansion of sorted collection by local governments, about 39 million tons are still directly incinerated. Under such circumstances, some municipalities are considering the introduction of carbonizing furnaces to strengthen their dioxin countermeasures in conjunction with the replacement of incinerators.

Since a variety of substances may be mixed in, and since a large amount of municipal waste is generated at one time, the use of the product is limited to the extension of thermal recycling, such as as fuel, cemented carbide, or raw fuel for steelmaking. However, once carbonized, the aim is to improve the quality of the product as fuel and obtain high added value. The Itoigawa Regional Municipal Waste Recycling Association (Itoigawa City, Niigata Prefecture), which was the first in Japan to introduce a carbonizing furnace as a method for recycling municipal waste, has adopted a carbonizing furnace that Hitachi, Ltd. introduced from TIDO of France.

The furnace, which will be completed in March of this year, will be able to process 70 tons of waste per day in continuous 24-hour operation. The carbonized material obtained from the furnace has a high calorific value of 4,000 to 5,000 calories per kilogram, so it is planned to be used as an alternative fuel to coal. Kurimoto Iron Works also received an order from Ena City, Gifu Prefecture, for a refuse derived fuel (RDF) conversion facility with carbonization equipment.

After drying combustible general waste and converting it to RDF, the plant will dry distill and carbonize the waste, which will also be used as fuel. If the heat from the incineration of municipal waste is used to generate electricity by turning a steam turbine, the energy recovery efficiency will be more than twice as high as when the waste is burned directly. Recycling as energy is one way to achieve this.

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Sewage sludge: Japan's sewage system penetration rate was 62% at the end of 2000. Sewage sludge generated at sewage treatment plants amounts to approximately 1.86 million tons nationwide (based on the dried weight of the sludge when it is generated). Sewage sludge, which is difficult to recycle due to its high moisture content (75-80%) and tendency to corrode, is increasingly being used for cement and melt-solidified construction materials, and together with its return to green farmland, the recycling rate is 57%, and 3% is effectively used for other purposes such as energy.

However, more and more carbonization plants are actually being introduced for higher value-added utilization. The Lake Biwa Konan Chubu Purification Center (Kusatsu City, Shiga Prefecture) has been operating a sewage sludge carbonization facility since April 2001. The system consists of a sludge hopper, dryer, carbonizing furnace, and carbonized sludge storage and conveying equipment.

The system processes 20 tons of dewatered sludge per day and produces approximately 1.7 tons of carbide. The carbide is effectively used within the center as a dehydration aid and deodorizer, and is also returned to the surrounding community as a soil conditioner, snow moderator, and other materials.

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Food Waste: Under the Food Recycling Law enacted in April 2001, food-related businesses that generate 100 tons or more of food waste per year are required to reduce their emissions by 20% by 2006 through methods such as curtailment, curtailment, and recycling. Food waste generated in Japan amounts to 19.4 million tons per year (according to a 1996 survey by the Ministry of Health and Welfare). Of this amount, 3.4 million tons is industrial waste from food manufacturing industries and 6 million tons is business-related waste from food distribution and food service industries, for a total of 9.4 million tons.

Currently, only 1.65 million tons (17%) of this business-related food waste is recycled, and the remaining 7.75 million tons is incinerated or landfilled, so improving the recycling rate is an urgent issue. However, food waste from the food distribution and food service industries must undergo a secondary processing process because it has few effective components relative to its volume, even if it is used as fertilizer or feed.

In addition, the salt content mixed in at the food processing and cooking stages is concentrated by composting. The adverse effects of salt damage have been pointed out, and the product value as a fertilizer or feedstuff may be low. On the other hand, large companies that generate large amounts of organic waste, notably in the beer industry, are promoting recycling and methane fermentation as biomass energy as part of their efforts to achieve zero emissions at their plants.

However, many food manufacturing industries are concentrated in rural and fishing areas where the raw materials are produced, and small and medium-sized enterprises are responsible for these industries. For these businesses, which have limited emissions and cannot economically afford to install very large equipment, small-scale carbonization equipment is an option. Yasuhara Chemical (Fuchu City, Hiroshima Prefecture) and Vid (Shinjuku-ku, Tokyo) have solved the problem of salt residue, which is also a concern in carbonization, by using limonene extracted from citrus fruits for pretreatment. Limonene has the property of dissolving and removing salt and oil.

In V-BOX J, which was jointly developed by the two companies, limonene is added to food waste at a ratio of 1% by weight, stirred at 50°C for 24 hours, and then dehydrated to reduce the volume to about 10% of its original volume, while salt and oil are removed. Activated carbon is obtained by steaming at 300~400 degrees C. The company plans to deliver 100 units to an onion farmer on Awaji Island, Hyogo Prefecture, where they will be used to process onions, such as their stems and peels, and the activated carbon will be mixed with non-woven fabric and used as a culture medium for rooftop greening.

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Livestock excrement: 9.152 million tons of animal feces and urine (livestock excrement) is generated annually, of which 96% is recycled as compost, and only 1% is ultimately disposed of as it is. However, there are many facilities that are sloppy in their management of manure until it is transported to a composting facility, or that do not take appropriate measures to prevent odors and leakage into the environment, such as composting boards (natural fermentation on a concrete floor), causing water contamination of rivers and groundwater by nitrate nitrogen in some cases.

In response to this current situation, the Livestock Excrement Law has required livestock farmers to properly treat and store livestock excrement since November 2004, and the majority of small-scale livestock farms (10 cows, 100 pigs, 2000 chickens, and more than ID horses) under private management are also subject to this law. In the case of one lowland farm in Hokkaido, chicken manure is usually used as fertilizer, and was incinerated in an incinerator at the farm.

However, the dioxin problem made it difficult to renew the incinerator, so they decided to install a carbonizer. For every 100 kg of chicken manure, 30 kg of granular charcoal was produced. Analysis of the charcoal showed that it contained nitrogen, phosphoric acid, and potassium, the three major elements necessary for the growth of crops, and a recycling system has been established in which this is mixed with chicken manure to produce value-added fertilizer for sale, the proceeds of which are used to produce grain for bird feed.

In summary, for food waste, sludge, and livestock excrement, which have a high water content and are difficult to dispose of, carbonization can reduce the amount of waste input to 1/5 to 1/20 by weight. In addition, the product itself, charcoal, has a higher commercial value than compost or molten slag, making it easier to establish a recycling business, which is also a tailwind for its introduction.

However, the current charcoal production capacity is about 50,000 tons. Even if half of this amount could be replaced by charcoal made from organic waste, the amount of blackened blackened charcoal produced would still be negligible. Unless further applications are developed, it is inevitable that there will be an oversupply, as with compost. Fortunately, however, demand is expected to continue to grow, as the use of charcoal for building materials such as underflooring and wall materials, slope and spreading greening projects, and gardening is beginning to take off against the backdrop of the shithouse problem.

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Furthermore, in the future, carbonizing furnaces will need to be more specific, with performance tailored to how various types of organic waste are recovered, the associated waste properties, and the intended use of the product. This will expand the market for carbonizing furnaces, which, while certainly processing waste, will not be an extension of the all-purpose incinerators of the past, but rather will be positioned as an industrial "firing furnace" for producing charcoal.