PLC Batch Process Control Design and Implementation Fundamentals

Batch process control is typically used for repeated chemical reaction tasks. It starts with a measured liquid material filling operations followed by a controlled reaction leading to the discharge or transport of processed quantities of material. The input materials is contained in vessel reactor and subjected to a sequence of processing activities over a recipe predefined duration of time. Batch systems are designed to measure, process, and discharge a varying volume of liquid from drums, tanks, reactors, or other large storage vessel using a programmable logic controller (PLC). These systems are common in pharmaceutical, chemical packaging, Beverage processing, personal care product, biotech manufacturing, dairy processing, soap manufacturing, and food processing industries. This paper briefly discusses the fundamental techniques used in specifying, designing, and implementing a PLC batch process control [1, 2]. A simplified batch process is used to illustrate key issues in designing and implementing such systems. In addition to the structured PLC ladder design; more focus is given to safety requirements, redundancy, interlocking, input data validation, and safe operation. The Allen Bradley (AB) SLC 500 PLC along with the LogixPro simulator are used to illustrate the concepts discussed in this paper. Two pumps are used to bring in material during the tank filling and a third pump is used to drain processed product. The three pumps are equipped with flow meters providing pulses proportional to the actual flow rate through the individual pipes. The tank material is heated to a predefined temperature duration followed by mixing for a set time before discharge. Batch control systems provides automated process controls, typically and universally using PLC’s networked to HMI’s and other data storage, analysis, and assessment computers. The overall system perform several tasks including recipe development and download, production scheduling, batch management and execution, equipment performance monitoring, inventory, production history and tracking functionalities. Flexible batch control systems are designed to accommodate smaller batches of products with greater requirements / recipes variation, efficiently and quickly. In addition to providing process consistency, continuous batch process control quality improvements are attained through the automatic collection and analysis of real-time reliable and accurate event performance data [3, 4].