Current Status and Prospects of Carbonization Technology 2002.02 (92)

In recent years, the Law Concerning Special Measures against Dioxin and the Waste Disposal and Public Cleansing Law have been revised, resulting in stricter regulations on waste incineration. At the same time, various recycling laws have been legislated to realize a resource-recycling society, and the cost of waste treatment has skyrocketed as final disposal sites become increasingly tight. As a result, there is a strong demand to shift waste disposal from incineration and landfill to recycling.

As a result, the need for an alternative recycling method to simple incineration has emerged for organic wastes (construction waste wood, food waste, sewage sludge, livestock manure, etc.), which were previously disposed of in landfills after intermediate treatment such as dehydration, drying, and incineration. In particular, “carbonization” is attracting attention.

Current Status and Direction of Carbonization Furnace Development

A typical example of carbonization is the production of charcoal. Currently, traditional charcoal-making techniques (e.g., tsuki-kilns and prock furnaces) as well as flat furnaces, screw furnaces, rotary kilns, and fluidized bed furnaces for industrial mass production are used for its production. However, for materials with well-defined properties, such as thinned wood and sawmill waste, there is little need for dioxin control and conventional technologies can be used. However, for carbonization equipment used as an alternative to waste incineration, the problem of dioxin is unavoidable.

What is required of carbonization equipment for recycling purposes is to obtain good quality carbonized material at low cost without generating dioxin. To achieve this, the furnace must be sealed and oxygen-free (or low oxygen), steamed at high temperatures, and the contents stirred to ensure homogeneous carbonization.

Characteristics and Advantages of Carbonization Equipment

Rotary kilns are currently the most highly regarded carbonization equipment available. In the rotary kiln method, the material is placed in a rotating cylindrical furnace and carbonized by internal or external heat. This method has the following advantages

Various organic materials can be carbonized: Anything with organic content can be carbonized, and the organic content in the raw material can be converted into combustible dry distillate gas to save fuel.

Simple structure and fewer breakdowns: Fewer breakdowns are required because there are no mechanical parts in the furnace.

No need for dioxin countermeasures: Although advanced sealing technology is required, dioxin removal equipment and stoker are no longer necessary, making the kiln superior in terms of installation space and equipment price.

Homogeneous carbonization: Rotation of the kiln eliminates uneven baking.

Because this is a well-established field of technology, a large number of companies, from major machinery manufacturers to small and medium-sized companies and venture businesses, have entered the carbonization equipment market, developing equipment ranging in scale from 100 kilograms per day to several tens of tons per day.

Expanding Charcoal Market and New Applications for Organic Waste

One of the reasons carbonization is attracting so much attention is the expanding range of applications for charcoal. While it is often difficult to distribute products in the recycling business, the prospects for carbonized products are relatively bright. Charcoal, which was produced at a rate of about 2.7 million tons per year in the 1940s, has been used as a primary fuel, but in recent years, new demands other than fuel have arisen and production has increased.

The excellent functionality of charcoal as a material has expanded its diverse applications to include soil conditioners, humidity regulators, deodorizers, and activated carbon. In particular, charcoal has been proven to adsorb toluene, xylene, and formaldehyde, which are substances that cause sick building syndrome, and the use of charcoal in wood waste, such as thinned lumber, pruned branches, mill ends, and saw dust, is increasing.

Carbonization of Construction Wood Waste

Construction waste wood is the most suitable raw material for charcoal. In particular, the full enforcement of the Construction Materials Recycling Law in May 2002 will provide a tailwind. According to a survey by the Ministry of Land, Infrastructure, Transport and Tourism, there is an urgent need to develop applications for construction waste wood, as its reuse has not progressed. Kumagaya Carpon and other companies in Kumagaya City, Saitama Prefecture, are developing businesses in this field, adding value through carbonization.

Carbonization of Municipal Solid Waste

Of the approximately 51 million tons of general waste generated annually, about 39 million tons are incinerated. Although the recycling rate is increasing due to the expansion of sorted collection by municipalities, there is a need to strengthen dioxin countermeasures as incinerators are upgraded. Carbonization of municipal solid waste is expected to be a means of obtaining high added value, and Itoigawa City in Niigata Prefecture plans to introduce a carbonizing furnace and use it as an alternative fuel to coal.

Carbonization of Sewage Sludge

Japan's sewage penetration rate reached 62% at the end of 2000, and recycling of sewage sludge generated at sewage treatment plants is being promoted. A sewage sludge carbonization facility is in operation at the Lake Biwa Konan Chubu Purification Center in Kusatsu City, Shiga Prefecture, and is used as a soil conditioner and deodorizing material.

Carbonization of Food Waste

The Food Recycling Law enacted in 2001 mandates the control of food waste generation and recycling. Food waste is often used as fertilizer or feed, but new applications are being developed through the use of carbonization technology. For example, technology has been developed to produce activated carbon by using limonene extracted from citrus fruits for pretreatment to remove salt and oil.

Carbonization of Livestock Excrement

Proper treatment and recycling of livestock excrement is also important. At a poultry farm in Hokkaido, chicken manure is carbonized to produce high-value-added fertilizer, creating a recycling system.

Conclusion

Carbonization is effective as a device for reducing the volume of organic waste that is difficult to dispose of due to its high water content. In addition, the generated charcoal has a higher commercial value than compost or molten slag, making it easy to establish a recycling business. In addition, new demands are expected for sick house syndrome countermeasures and greening projects. In the future, carbonizing furnaces are expected to expand their market as “calcination furnaces” as their performance is required to meet various organic waste recovery methods and product applications.