Featuring energy-saving and emission reduction, BDC batch displacement cooking is an extended delignification process used in chemical pulp mills. A displacement cooking system can be equipped with 1-5 digesters, 2 pressure liquid recovery accumulators and several ordinary pressure tanks. In addition to the batch replacement operation, there are other continuous operations, such as: heat transfer within tank zone, fiber separation, condensate water treatment and gas collection. This cooking system is suitable for non-woody fibers including wood chips, bamboos, straws and others.