Japan Coke spearheading repair technology to extend life of coke ovens

Japan Coke Industry Co. Ltd., a coke manufacturer specialising in the Japan Steel Group, along with two other companies, has developed a new repair technology that will extend the life of coke ovens. The technology revives COG (coke oven gas) ducts, one of the causes of the aging of coke ovens, using an innovative method which saves energy and increases productivity.

The repair technology, implemented at the company's Kitakyushu plant, promises to extend the life of a coke oven beyond the usual 50 years. Jointly developed with Southeast Trading Co. and Narita Ceramics, the technology focuses on COG ducts that send the gas to the combustion chamber. If a part of the duct is damaged due to aging, it is unable to supply enough COG, or supply will have to be stopped, which will lead to a decrease in the productivity of the coke oven.

Eventually, a complete renewal using the pad-up method will be required. So, if it is possible to extend the life of the duct as much as possible, it would be possible to extend the age of the coke oven. In duct repair, it is common to repair the damaged part with mortar. However, as the deterioration progresses over time, the damaged part expands, making it impossible to repair the mortar. It is possible to completely replace the ducts, but the costs are high.

The three companies have developed a method of passing pipes through the inside of ducts. By sending COG to the combustion chamber through this pipe, it is possible to revive the duct without repairing the damaged part.

The COG duct is about six metres long and is installed vertically at the bottom of the coke oven. The pipe that runs through the duct is made of ceramic, but for the lower part, where the temperature is not so high, a flexible pipe made of stainless steel is used.

With age, the duct becomes curved. In this case, it is easy to pass a stainless steel flexible pipe, but it is difficult to pass a straight ceramic pipe. The partners have developed a construction method that uses ceramic fittings to successfully pass ceramic pipes through the inside of curved ducts.

The Kitakyushu Plant has four coke ovens with a total of 6,000 ducts. The pipe-fitting work started about two years ago, and by last fall pipes had been fitted into about 500 ducts. The advantage of this repair method is that it can be installed without stopping the operation of the coke oven, regardless of where the duct is installed.

According to Japan Coke, energy efficiency has improved by about 5% with the implementation so far and it is claimed that the repair method can restore productivity by 5% even in aging furnaces.

Japan Coke will continue to insert pipes into ducts that are heavily damaged in an effort to extend the life of coke ovens. This new technology is attracting the attention of blast furnace manufacturers and has already been introduced on a trial basis at JFE Steel's West Japan Steel Works and Fukuyama area through Southeast Trading. In the future, the company will also consider installing it in a coke oven at Japan Steel's mill.

With the advancement of repair technology the average age of a coke oven has been extended to over 50 years from around 40 years earlier. However, after about 50 years, the damage to COG ducts and other equipment is so severe that despite repair productivity has to be sacrificed. Although COG ducts are not the only cause of aging, new technologies developed by Japan Coke and others can be used to extend the age of coke ovens at low cost.