Project SynopsisExecute a process design for the caustic scrubbing system, evaluate existing and new columns for use as the scrubber and evaluate fired heater.
ASPHALT REFINERY CAUSTIC SCRUBBING SYSTEM PROCESS DESIGN
The client contracted with Process Engineering Associates, LLC (PROCESS) for the process design of a caustic scrubber for a petroleum refinery. The refinery facility is an asphalt topping refinery that distills the lighter portions of heavy crude oils to produce asphalt as the primary product. The refinery acid gas was being routed to the flare, resulting in SOx emissions. The purpose of the design was to re-route the acid gas through a caustic scrubber and then feed the purified gas to the crude furnace as supplemental fuel gas. PROCESS was contracted primarily to execute a process design for the caustic scrubbing system and to evaluate an existing column for use as the scrubber. Project tasks included:
- Computer process simulation and the development of heat and material balances (H&MBs) for scrubber column baseline operation
- Evaluation of caustic strength, circulation rates, and spent caustic waste to achieve the purification target and minimize capital and operating costs
- Mass transfer evaluation of the existing column
- Design of a new column and column internals
- Development of the scrubbing system and fired heater process control schemes
- Design of auxiliary process equipment and the preparation of equipment and instrument specifications
- Development of preliminary process flow diagrams (PFDs)
- Development of piping and instrumentation diagrams (P&IDs) and markup modifications of existing P&IDs.
PROCESS was provided with the normal and maximum inlet stream conditions as well as the scrubber performance requirements as the design basis. PROCESS then used its licensed commercial process simulation software to model the system to determine the caustic strength and caustic rates necessary to achieve the H2S removal requirement. PROCESS also simulated and evaluated the heat of reaction and the spent caustic strength to determine heat removal needs and to minimize caustic usage costs. PROCESS then simulated and evaluated the existing column for feasibility in achieving the objectives and determined that the existing column would not provide adequate vapor-liquid contact due to the large column diameter. PROCESS next simulated and designed a new column that was sized appropriately for the application. Finally, PROCESS provided the design and preliminary equipment specifications for the associated pumps, control valves, instrumentation, relief valves, piping, and column internals as well as a preliminary capital cost estimate for project implementation.
PROCESS was also asked to evaluate the fired heater, burners, and controls for combusting the purified gas. PROCESS developed a control scheme that would dedicate 2 out of 8 burners to the purified gas and provide supplemental fuel gas to increase the net heating value and provide stable gas pressure to the burners.
The deliverables resulting from this project, including the process design basis; H&MBs, PFDs, preliminary and markup P&IDs; column and equipment specifications; process control schemes; control valve and instrument specifications; pressure relief valve (PRV) specification; and screening cost estimate, were assimilated in a project report submitted to the client.
- Petroleum Refining
- Computer process simulation
- Scrubber design
- Column design
- Heat & Material balances
- P&ID and PFD preparation
- Equipment specification
- Capital cost estimate
- Schedule A package