盐及其系列产品、包装材料、防伪“碘盐标志”、无水硫酸钠的开发、制造和销售；盐业技术的开发、咨询和应用服务；非金属矿采选及其他采矿业；金属制品、通用设备、专用设备、无机盐、专用化学产品、日用化学产品、食品、调味品、化妆品、饮料和精制茶、医药的制造和销售；农产品及农副产品加工和销售；仓储业（不含易燃、易爆及危险化学品）；金属制品、机械和设备修理业；土木工程建筑及安装业；压力容器制造、安装，锅炉安装、维修，压力管道安装；水、热力等的生产和供应；现代物流配送；酒类、日用百货、预包装食品、散装食品、农产品、农副产品、橡胶、粮油制品、饲料、仪器仪表、机械设备、电子产品、有色金属矿产的批发和零售；机械设备租赁、道路货物运输及铁路专用线共用业务；软件和信息技术服务、商务服务业；盐文化博物馆及自有房地产经营活动；货物及技术进出口贸易。（依法须经批准的项目，经相关部门批准后方可开展经营活动）
This paper mainly describes the basic principle of frequency converter, and frequency conversion constant pressure air supply system energy saving situation, around its practical application in the fan are discussed and analyzed. And combined with the current salt-making process of frequency conversion energy-saving problems were analyzed, according to the practice of using frequency converter in salt-making system, finally put forward the improvement scheme.
