Design And Development Of Computer Control System For Steam-Water Heat Exchanging Process

Heat exchange stations are the key elements in the whole heating processes. Stable, reliable operation of heat exchange stations is vital important for normal production of enterprises in winter. Therefore the design and development of computer control system for steam-water heat exchanging process have important significance.Supported by the National Science and Technology Supporting Program (Advanced Control Technology of Whole production Line of Mineral Processing 2012BAF19G01) and the Key Automation Project (Synthetic Automation System of Newly Built 4 Million t/a Mineral Processing Plant), this thesis has presented design and development of the computer control system for a steam-water heat exchanging process. In order to ensure heating quality, the control system of heat exchange station must keep the temperature of the secondary network feed water stable around its setpoint. However, the heat exchanging process is time-variant, with large time delay and large inertia. There are coupling between different parameters. It is difficult for the conventional PID controller to eliminate the disturbance quickly and to keep the temperature stable. Considering the above problems, the main works of this thesis are summarized as follows:1) The control strategy based on cascade control and feedforward-feedback control for the steam-water heat exchanging process has been presented. The ultimate purposes of steam-water heat exchanging control system are to keep the temperature and pressure of the feed water stable. Because the steam pressure will influence the steam flow as disturbance, and the heat exchanging process is multivariable and with large inertia, the cascade control strategy should be adopted in controlling the temperature of feed water. Also the make-up water pressure acted as measurable disturbance to the feed water pressure, a feedforward-feedback controller has been employed. The mathematical model of the steam-water heat exchanging process has been established, and simulations has shown the feasibility and effectiveness of the proposed control strategy.2) The PLC control system for the steam-water heat exchanging process has been designed. The hardware design included not only the selection of the required instrumentations for temperatures and pressures, and the actuators in the process of heat exchanging, but also the control system network configuration, the PLC cabinets and the engineer stations. The software design for monitoring functions in upper computers consists in status monitoring, alarming and historical trends. The software design for operation and control functions contains equipment control, interlock control and loop control. The communication function has also been designed.3) The software of PLC system for the steam-water heat exchanging process has been developed. Employing the RSview32 Software, we have developed the upper monitoring software whose functions are status monitoring, alarming and historical trends. With the RSlogix5000 Software, we have completed the lower PLC software which is responsible for equipment control, interlock control and loop control. Also the communication software has been configurated.4) The computer control system of the steam-water heat exchanging process has been functionally verified. The PLC control system has been successfully applied in the engineering practice, and the application results have shown the effectiveness of such monitoring, operation and control functions.