It puts forward suggest that control the pressure of air cooler and exhaust equipment respectively. To realize the suggestion, it fixes the regulating valve in the vacuum pipe of exhaust equipment. So the vacuum of the unit is optimized and the economy is improved. Furthermore, continuous air exhaust system is assembled in the vertical downcomer from the air cooler to the exhaust equipment. It can prevent strenuously vibrating for mixed air. And this is favorable to the operation stability of the unit.