For economic reasons, a refinery desires to maintain refining capacity during periodic maintenance shutdown of their sulfur recovery unit (SRU). A temporary caustic scrubber had been used to remove sulfur from sour fuel gas during shutdown but was quite expensive and logistically difficult. Several technologies were evaluated to replace the temporary scrubber for a permanent, lower cost solution. Considered technologies included a reverse jet scrubber, fiber film contactor, and an Envitech packed bed caustic scrubber.Envitech’s packed bed scrubber was selected. The scope of supply includes a type 316SS packed bed absorber, instruments, redundant ANSI Goulds recirculation pumps (1 operating, 1 spare), pre-assembled recirculation pump skid, redundant caustic recirculation pumps, and access platforms. Instruments and motors meet class 1, division 2 group D area classification. Pre-mounted instruments are pre-wired to a junction box on board the skid. The scrubber vessel is 3 ft DIA by 38 ft tall with 300# flanges, pipe supports, and is designed for 200 psig and full vacuum per ASME VIII division 1 with code stamp. A detailed hazardous operations review was performed with the customer during the project design phase.
The fuel gas enters the absorber horizontally at the bottom of the vessel and travels vertically upward, counter-current to downward flowing water. Scrubbing water is collected in the sump and is re-circulated to the top of the packed bed. A dilute solution of plant-supplied sodium hydroxide is metered into the scrubber recirculation line to neutralize H2S and is controlled by the recirculation liquid pH. A blowdown stream from the recirculation line purges the system of reaction products. A mist eliminator at the top of the vessel removes droplets before exiting the scrubber.
The system will be installed and utilized during a planned maintenance shutdown in 2023. The design parameters are summarized below.
- Inlet flow rate – 1,000 acfm, 7,300 scfm
- Inlet temperature – 110oF
- Inlet pressure - 117 psia
- Design pressure - 200 psig, full vacuum
- Vessel - T316SS per ASME VIII division 1 or 2 with code stamp
- Inlet H2S - 8,200 ppmv
- Removal efficiency > 99.3%
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