Total hydrocarbon relief capacity for safety valves of major units of typical refinery complex
S.No.
Unit name
Unit capacity
Relief valves hydrocarbon
1 2
CDU/VDU with sat. LPGTU and Sat. FGTU 9 MMTPA/162 KTPA/1425 TPD
909,000 kg/hr 918,000 kg/hr 1,168,000 kg/hr 6,133,500 kg/hr
DCU with unsat. LPGTU
2.4 MMTPA
3 4
DHDT/HGU
4.1 MMTPA/55 KTPA
PFCCU/PFCC gasoline HDT MS block (NHT/ISOM/ semi-regenerative reforming)
2.9 MMTPA/0.53 MMTPA 1.8 MMTPA/0.26 MMTPA/
5
0.115 MMTPA
143,650 kg/hr
Table 1
upsets, they are unable to measure leaks. This is because these devices are usually designed for handling very high flow rates (for example, during entire unit trips) and, as a result, they offer very poor accuracy in leak detection and measurement. Also, no mechanism exists to pinpoint such leaks, and they continue for very long periods. In contrast, wireless leak detection Edge devices represent a significant advancement in flare system monitoring. These devices can accurately identify and locate leaking valves, as well as quantify the extent of leakage. By providing real-time data on leakage events, they enable prompt corrective actions, thereby enhancing the overall efficiency and safety of refinery operations. A systematic approach to estimating hydrocarbon leakage at the unit level involves considering the relief capacities of various types of safety valves used in refinery operations. The three predominant types are conventional relief valves, bellows-type relief valves, and pilot- operated relief valves. Industry data indicate that the majority of leakage incidents are attributable to conventional and bellows-type relief valves, with pilot-operated valves exhibiting a lower propensity for leaks due to their inherent design. In this study, the relief capacity of in-service conventional and bellow-type safety valves have been listed for various units of a typical refinery complex, such as crude distillation unit (CDU)/ vacuum distillation unit (VDU), delayed coker unit (DCU), diesel hydrotreater (DHDT), fluid catalytic cracking unit (FCCU), and motor spirit (MS) block. The leakage rates and percentage of valves exhibiting leakage have been established based on conservative industry practices.
To provide a conservative estimate, the following has been done: • The required relief capacity has been considered in place of the actual relieving capacity. • If multiple relief valves are present, the relieving capacity of the standby relief valves has not been considered. Table 1 captures the total hydrocarbon relief capacity for the safety valves of major units of a typical refinery complex. For hydrocarbon leakage estimation, on average, 5% of relief valves have been considered with minor leaks (leakage rate 0.02%) and 1% relief valves have been considered with major leaks with (leakage rate of 1%). These values have been considered conservative. The estimated time for leak detection is set at two months. Figure 4 serves as a foundational basis for estimating potential hydrocarbon leakage and implementing targeted mitigation strategies. The cumulative hydrocarbon loss amounts to a staggering 2,500 tonnes per annum for the units considered. Financial analysis The integration of IIoT technologies for flare relief system leakage detection in refineries requires a comprehensive cost analysis encompassing both hardware and software components. This assessment provides a unit-wise estimation based on standardised pricing, acknowledging that actual costs may vary depending on specific project requirements and regional factors. The system comprises of the following components: • Edge devices on discharge of relief valves. • Wireless gateways.
Refining India
29
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