Integrated Process Air Compressor Control System Overcomes Unique Problem at a Pure Terephthalic Acid (PTA) Plant in India

摘要

Two process air compressors (steam and electrical power driven) having unequal capacity and operating in parallel provide the main air duty for the Pure Terephthalic Acid (PTA) plant, Patalganga unit at Reliance, India. During fouled rotor conditions, the compressor surged due to rapid grid frequency dips or at low frequency periods unloaded the motor driven compressor. With reductions in air supply to the reactor, the plant production was interrupted in a few cases. Projected annual savings, based on gain in PTA production under compressor-fouled conditions and the elimination of unscheduled shutdowns during low frequency periods of operation, were the main factors considered to justify the OEM control system replacement. After trying out various available options with the OEM supplied control system, The END USER decided to implement the Integrated Turbomachinery Control System (ITCS) solution. ITCS is a multivariable control system that provides anti-surge control, coordinated header pressure control, and parallel load sharing for energy efficient operation. The paper discusses the problems overcome at the END USER after the process air compressors were retrofitted with Integrated Turbomachinery Control System (ITCS) in January 2004. The paper also addresses: control system design for various operational modes, control system implementation, deficiencies inherent in earlier control systems, automation of plant startup, surge protection algorithm for low grid frequency operation, and energy conservation. Data collected before & after installation is used to highlight the benefits of the new system.