Sandvik Process Systems has supplied 12 dedicated steel belt cooling systems for coal liquefaction to China’s largest coal producer, the Shenhua Group. As noted in IM’s May issue, coal liquefaction technology is likely to become increasingly important in China. The country started an investment program in the 1970s to use local coal stocks for electrical power generation and direct coal liquefaction (DCL). Development of this coalfield and operation of the entire plant, which is China’s single biggest investment since the Yangtze dam, Sandvik reports, is handled by the Shenhua Group.

As part of the DCL process used in China a liquid residual – the Coal Slurry – is produced containing a high heating energy. The slurry is delivered from the DCL process at viscosities of about 100 mPa-s and temperatures up to 310ºC and for economic and environmental reasons is then converted into solid form. Pilot productions demonstrated that the optimum process would be solidification in the form of flakes via a steel belt cooling system.

In 2006, Sandvik and Shenhua signed a contract for the turnkey supply of 12 steel belt cooling systems, each with a solidification capacity of 15 t/h, as part of the first step of the total investment.

The coal slurry is fed onto a continuously running, 1.5 m wide steel belt, which is cooled from beneath with sprayed water. The coal slurry cools and solidifies as it travels the length of the steel belt and at the end is available as a uniform layer. Depending on the quality of the coal and the process parameters the solidified product can show very different physical properties, from brittle to tough through to sticky. Therefore, different discharge and breaking devices are installed at the end of the steel belt before the product is discharged for storage.

Design of the units takes into account the very harsh climatic conditions of the site in Inner Mongolia. Here ambient temperatures can range from -30° C to + 40°C with the likelihood of heavy sandstorms. This challenge was further compounded by the requirement to install the systems in the open air, without any shelter