Evaluate deflagration mitigation systems on a pressurized syngas vessel.
SYNGAS VESSEL DEFLAGRATION MITIGATION SYSTEM PROCESS DESIGN
Process Engineering Associates, LLC (PROCESS) was tasked with sizing one (1) deflagration rupture disk to be located on a pressurized syngas vessel for a packaged system being engineered by the client, a technology package provider.
PROCESS first developed a sizing basis, which involved collecting the baseline information which was provided by the client. PROCESS, based on the information gathered as well as discussions with project team members, summarized the sizing basis information. This consisted of capacity requirements and operating conditions; and syngas physical and chemical characterizations.
NFPA 68, Explosion Protection by Deflagration Venting and NFPA 69, Explosion Prevention Systems were referenced for the sizing of the rupture disk and it was determined that the application fell outside the scope of NFPA 68. Specifically, the operating pressure was 100 psig compared to a 30 psig limit for application of NFPA 68 vent sizing techniques. Moreover, NFPA 69 (section A10.2.3) cautions that “only limited information is available for deflagration containment of systems with initial gauge pressures exceeding 2 bar (30 psi). Increased initial pressure might increase the potential for detonation.” NFPA 69 consequently does not recommend deflagration containment for systems with initial pressure over 30 psig unless test data specific to the system is available.
A literature survey was conducted to ascertain the existence of explosion studies and/or specific data that might encompass the operating conditions of this application and none were found. As a result, it was concluded that a valid sizing of a deflagration rupture disk could not be performed without the availability of actual system test data.
Based on the information presented in the NFPA standards, PROCESS recommended that an oxidant reduction deflagration prevention system, in accordance with NFPA 69, be incorporated into the design in lieu of sizing the pressure relief for a deflagration.
While the syngas in the process typically did not contain oxygen, there was a remote potential for small amounts to leak into the system upstream of a compressor. The proposed prevention measure consisted of continuous analysis for oxygen concentration with dilution provided as necessary with an automated nitrogen (or other inert gas) purge.
PROCESS further recommended that the required safety integrity level (SIL) for the monitoring/purge system be determined through a Layers of Protection Analysis (LOPA) that should be conducted as part of the Process Hazards Analysis (PHA) for the complete system.
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