Each discharge to the disposal system is defined in terms of flow rate, pressure, temperature, and composition to enable accurate modeling of the collection and disposal system performance. In many cases, the discharge conditions will correspond to a specific causes of overpressure that has already been evaluated during the determination of the pressure relief requirements of the refinery’s equipment (see Section 1220). In addition to these cases, guidelines are presented here for evaluating discharges from other types of devices.
Where a system is protected by more than one of the devices listed below, the total relief requirement from the process should be allocated to the various devices to achieve a conservative result. For example, conventional pressure relief valves are affected by much lower back pressures than control valves are. Therefore, when both a conventional pressure relief valve and a control valve to the disposal system are installed on an equipment item, a conservative evaluation of the disposal system performance will be obtained by assuming the relief flow is entirely through the pressure relief valve.