Double stage coal gasifier, also known as two stage coal gasifier, double stage gas generator, double stage gas producer, was designed in the 1990s and gradually introduced to the market. The engineer adds a dry distillation section  to gasify bituminous coal in a single stage gas generator, using the heat of the gas itself to dry distill coal, producing a mixture of dry distillation gas and gasification gas, therefore, the calorific value of mixed gas is high. At the same time, the tar produced by dry distillation has better fluidity and can be recycled as an industrial by-product. 

  Compared with a single-stage gas generator, a two-stage gas generator has multiple advantages such as high thermal efficiency, high gas calorific value, and recyclable tar.