Through three links of design, construction and monitoring, a closed cycle system is set up for the monitoring of stability of high slope of three Gorges Prject permanent lock.

This system is the closed cycle cooling water system applicable for turbine and boiler's auxiliary machines.

By means of an example of controlling the tail gas from the production of arsenic acid, this paper introduced the pretreatment, desulfurization and wastewater closed cycle of the control system.