Recovering heat across the globe

Recovering heat across the globe

Kazuki Ao, Kawasaki Heavy Industries, Ltd., details the supply of waste heat recovery power generation systems to cement plants around the world.

In both Japan and South Korea’s cement sectors, Kawasaki Heavy Industries’ waste heat recovery (WHR) power generation systems have a very high market share. Kawasaki’s cement plant WHR solution has a long history in South Korea, with a total of five units installed after an initial delivery to the Tongyang Cement Corporation (Sampyo Cement at present) in 2004. Kawasaki also has strong ties in South Korea in the field of steam turbines, with a delivery record of more than 30 units. This article provides an outline of cement plant WHR systems, Kawasaki’s new VEGA® boiler, the company’s track record of supplying WHR solutions in South Korea and beyond, and a description of Kawasaki’s steam turbine technology.

Outline of the cement plant WHR system

The history of Kawasaki’s cement plant WHR system traces back over 40 years. For example, the WHR unit delivered to Taiheiyo Cement Corporation’s Kumagaya plant in 1982 is still operating smoothly today.

Kawasaki group has been continuously developing new technologies to meet the needs of the times, and has received orders for more than 270 WHR units for cement plants in Japan as well as 14 other countries including South Korea, Germany, and Turkey. As a result, the total power output of installed Kawasaki WHR units has reached about 2880 MW, with a CO2 emissions reduction of about 15 million tpy.

The steam Rankine cycle (SRC) is the most efficient WHR system and has been adopted in Kawasaki’s solutions, which use WHR boilers to recover unused heat from two heat sources in the clinker manufacturing process: a preheater (PH) and a clinker cooler (AQC). Using only one heat source from either the PH or AQC is also possible. The recovered heat generates electricity through the combination of a steam turbine and a generator. Both the PH boiler and AQC boiler consist of an evaporator and a superheater. The AQC boiler is also equipped with an economiser commonly used in both boilers, and this combination with a flasher enables the maximum heat recovery from the clinker cooler, which then maximises total power output.

An estimated 20 – 40% of the electricity needed by a cement factory can be produced by Kawasaki’s WHR system. This not only enables a reduction in the cost of purchasing electricity from external sources such as power companies, but also contributes to a reduction in CO2 emissions by reducing the amount of fossil fuels which would have been used for the unconsumed electricity.

In addition, unlike renewable energy power sources, WHR systems are not subject to changeable weather conditions such as sunshine and wind speed, so their availability is much higher. The use of a highly efficient waste heat recovery system can also allows the operation of the kiln system during power interruptions that are becoming more frequent in some countries.

New boiler technology

Starting in around 2000, cement plants began using alternative fuels and alternative raw materials such as wood chips, waste plastics, sludge, incineration ash from sewage sludge, and ash from municipal waste, among others. These materials, however, generate a far more adherent, sticky dust, necessitating better dust removal performance from waste heat recovery boilers. Moreover, due to layout restrictions within cement plants, the need to install WHR units in limited spaces has been increasing. Kawasaki developed and launched the second-generation PH boiler in the middle of the 2010s with a view to address these issues. The VEGA boiler is designed to spread WHR systems to cement plants that have difficulties in achieving economic feasibility (due to factors such as low kiln capacity) using alternative fuels and alternative raw materials, and to replace the existing poorly performing PH boilers.

The first VEGA boiler was delivered in 2017. The power output has been exceeding the guaranteed level for more than 5 years although sludge has been used as an alternative fuel at the rate of 15% (calorific value basis, 15 – 30% in 2022) of total fuel in the clinker production process.

The operation of this first unit demonstrated the high dust removal performance and durability of the VEGA boiler. Since then, the first VEGA boiler in Japan was delivered to the Saitama Plant of Taiheiyo Cement Corporation in 2022, and orders for VEGA boilers to date have exceeded 50 units around the world.