Development of a Gas Engine Cogeneration System with High-efficiency Steam Recovery from Hot Wastewater

Tokyo Gas Co., Ltd. (President: Michiaki Hirose, hereinafter referred to as "Tokyo Gas"), Mitsubishi Heavy Industries, Ltd. (President: Shunichi Miyanaga, hereinafter referred to as "Mitsubishi Heavy Industries"), Miura Co., Ltd. (President: Yuji Takahashi, hereinafter referred to as "Miura"), and Kobe Steel, Ltd. (President: Hiroya Kawasaki, hereinafter referred to as "Kobe Steel") have developed a cogeneration system (hereinafter referred to as "this system") that recovers hot wastewater with high efficiency from a gas engine in the form of steam. Mitsubishi Heavy Industries and the Tokyo Gas Group plan to begin selling this system in July 2015.

Advertisement

A gas engine cogeneration system uses a gas engine to drive a power generator to generate electricity, while the system's waste heat found in the exhaust gas and the coolant of the gas engine are used as steam and hot water. Such systems have been widely introduced in office buildings, hotels, factories, and the like.

Of such locations where these systems have been introduced, medium- to large-sized gas engine cogeneration systems are most often introduced to factories where the steam can be widely used in heating, sterilization, and other production processes. However, in some cases where the use of hot water is limited, not all of the hot water can be used, and the utilization ratio of waste heat is thus decreased.

This system combines products marketed by the three manufacturers and can use the waste heat of a gas engine to efficiently convert hot water into steam. More specifically, the new system combines 1) a "high-temperature specification gas engine" (manufactured by Mitsubishi Heavy Industries) that heats wastewater to a higher temperature to recover more steam; 2) a "steam generator that uses the heat of wastewater" (manufactured by Miura) to efficiently convert hot wastewater into low-pressure steam; and 3) a "compact screw-type steam compressor" (manufactured by Kobe Steel) that further pressurizes the converted low-pressure steam to make it suitable for use in factory production processes. By combining these technologies, improvements were made to the high-temperature specification gas engine, and controls were developed for the efficient operation of the system.

As a result of this new design, the steam recovery efficiency of this system has improved by approximately 10% compared with that of the system with only an exhaust gas boiler, and a combined efficiency of approximately 71% for power generation and steam use has been realized. Consideration was also given to convenience so that the settings can be changed in accordance with the usage conditions. For example, when the required amount of steam decreases, the user can switch to the operation of a conventional gas engine cogeneration system.

Tokyo Gas, Mitsubishi Heavy Industries, Miura, and Kobe Steel are endeavoring to achieve further energy savings and CO2 reductions through the utilization of cogeneration technology in the future as well.