Automated overfill protection system (AOPS)

The Automated Overfill Protection System (AOPS), a safety instrumented system (SIS) by SIS-Tech can prevent dangerous overfill conditions in terminals, tank farms and process vessels. The AOPS incorporates a non-programmable Logic Solver (suitable up to SIL-3) that receives signals from switches or transmitters, determines if an abnormal process condition is present, and provides outputs to close isolation valves, shut down transfer pumps, or open diversion valves. The system operates independently of the plant’s process control system with the capability to communicate to the control system via hardwire, Modbus, Ethernet or wireless communications. The AOPS prevents overfill conditions that can result in vessel damage and release of hazardous chemicals to the environment. It can also be configured to prevent underfill conditions. Underfill conditions can cause loss of suction to transfer pumps with the potential for pump damage, or cause significant hazards when a floating roof tank is used and level is too low. Automated trips ensure protection even when the operator is focused on other duties. A SIS, such as the AOPS, can detect high level and prevent filling beyond the safe fill limit. The system uses independent sensors such as a switch or transmitter to detect high level, and independent final elements such as a motor control circuit or block valve to divert or terminate feed. The SIS trip action is automatically initiated at a setpoint that allows sufficient time for the action to be completed safely. Risk analysis determines the safety integrity level (SIL), typically SIL-1 or SIL-2, required to ensure that the overfill risk is adequately addressed. The AOPS is a low-cost, stand-alone, independent, non-PE logic solver suitable for use up to SIL 3.  Rated for –30 to 75°C and constructed using Class I Div 2 components, the AOPS can be installed in the harshest process units near the tank. Further, the number of inputs and voting architecture (1oo1, 1oo2, 2oo2 or 2oo3), can be adjusted for each process variable to meet any SIL or reliability requirement.  The AOPS is flexible and can be customized for any specific level application. For the ultimate in remote, stand-alone installation—solar power provides SIL protection without the need for utilities, while wireless communication sends system status to centralized control rooms. As compared to safety PLCs, total lifecycle costs are 50% less.