Process monitoring distributed control system

The reactor pressure is reduced to 0 psig to flash off any remaining water after a desired temperature is reached. Simultaneous ramp up of the heat source to a new setpoint is also carried out. The duration spent at this second setpoint is monitored using CUSUM plots to ensure the batch reaches a desired final reactor temperature within the prescribed batch time. The heat source subsequently is removed and the material is allowed to continue reacting until the final desired temperature is reached. The last stage involves the removal of the finished polymer as evidenced by the rise in the reactor pressure. Each reactor is equipped with sensors that measure the relevant temperature, pressure, and the heat source variable values. These sensors are interfaced to a distributed control system that monitors and controls the processing steps. 

Area 300 is controlled using a distributed control system (DCS). The DCS monitors and controls all aspects of the SCWO process, including the ignition system, the reactor pressure, the pressure drop across the transpiring wall, the reactor axial temperature profile, the effluent system, and the evaporation/crystallization system. Each of these control functions is accomplished using a network of pressure, flow, temperature, and analytical sensors linked to control valves through DCS control loops. The measurements of reactor pressure and the pressure differential across the reactor liner are especially important since they determine when shutdowns are needed. Reactor pressure and temperature measurements are important because they can indicate unstable operation that causes incomplete reaction. 

Packaged units have traditionally had their own progranunable logic controllers (PLCs) and local control panels. This is especially true in the case of units that require extensive sequence controls for stepwise processes such as filtration and ion exchange. Many operators find it more convenient to have control supervised from a central station. From this point of view, these systems are better controlled by a distributed control system (DCS) and monitored from the control room. Some who bought systems equipped with PLCs some years ago have dispensed with the PLCs and moved control to the DCS. Many favor systems which combine local control by PLC with status and alarm signals sent to the DCS. 

As mentioned earlier, the most commonly employed alkylene oxides for producing block nonionic surfactants are the very reactive three-membered cyclic ethers such as EO and PO. Particularly, EO is highly flammable, explosive in some condition, and also toxic and an irritant for skin and eyes. For these reasons, the reactor employed in the synthesis, described earlier, must be equipped with sophisticated safety devices, process monitoring systems, and distributed control systems (DCS) to keep the reaction in safety condition and avoid gas-phase decomposition and the so-called runaway... 

With the rapidly increasing processing power of computers, improved operator interfaces and distributed control systems improved overall controls available to processors. Real-time process and product data and SPC tools became much more accessible and better utilized. However, in this period, perhaps the two most important factors affecting the adoption of process monitoring and control strategies have been... 

The entire system is based on a tiered approach where three layers of technology are integrated into the overall treatment system, as illustrated in Chart 2. First, a distributed process control system is network linked to the various component subunits of the waste management system such as pH control, ion-exchange control, tank level control, etc. Next, are the recovery/treatment processes themselves. The final tier is a monitoring system which controls both the performance of the treatment systems and the discharge assurance of the plant effluent... 

This approach makes the system simple to operate. The entire process is automatically monitored, recorded, and controlled. Operators can run the system from the central console, or from the local control units. And because of the distributed control, each of the local units will continue to do its job, and the waste treatment system will continue to function, even if the central control unit should became disconnected or malfunction. The system also includes a modem for remote diagnostics and program maintenance. 

Network Distributed Process Control System (links treatment system components to central monitor station)... 

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