A novel cascade refrigeration process using waste heat and its application to coal-to-SNG

To efficiently develop coal-based chemical processes in China faces many challenges. A large amount of waste heat in the process is not efficiently employed. The proportion of energy that is fully utilized is extremely low. This paper proposes cascade refrigeration technology (CRT) that combines a LiBr absorption refrigeration with a NH3 absorption refrigeration. The CRT is driven by low-grade waste heat below 150 °C and produces high-grade cold energy. The CRT is applied to a coal-to-SNG project as a case study. In a 4 billion Nm3/a coal-to-SNG plant, the CRT is integrated to use low-grade heat taken from the methanation unit. Produced cold energy is used in the Rectitsol unit to remove CO2. Results show that it reduces the compression refrigeration by 16%. The absolute gain is 3.4 × 107 million CNY per year.