Evaluate process alternatives to reduce benzene concentrations in the gasoline produced by a petroleum refinery in order to bring operations in compliance with the Mobile Source Air Toxics (MSAT) regulations.
PROCESS ENGINEERING SUPPORT FOR REFINERY MSAT COMPLIANCE PROJECT
The client, an independent oil refiner, is subject to Environmental Protection Agency (EPA) regulations which limit benzene content in gasoline per the Mobile Source Air Toxics (MSAT) program. To comply with this directive, the refiner was required to install new systems and/or modify existing operations to meet an annual maximum average benzene content of 0.62% by volume in their gasoline pool. Process Engineering Associates, LLC (PROCESS) was contracted by the client to provide process engineering services in support of this effort.
PROCESS‘ first task involved screening viable benzene reduction technologies and associated modifications to the refinery’s process configuration. The goal of this initial study was to quantify the impact of the various alternatives on the refinery hydrogen balance and gasoline pool including effects on benzene concentration, product stream volumes, and stream octane values. As part of this task, a baseline gasoline pool balance was completed to identify the primary sources of benzene and to aid in the selection of options for evaluation. This balance included a comprehensive component list to facilitate the tracing of benzene and benzene precursors as well as to allow for the accurate calculation of stream octane and other physical properties. From these baseline results, evaluations were completed to assess potential benzene reduction strategies.
A total of nine (9) benzene reduction strategies were evaluated which incorporated technologies including isomerization, saturation, alkylation, and fractionation. For each case, PROCESS utilized simulation software to develop preliminary mass and energy balances based on generalized literature data available for each technology. The model results were then used to generate process flow schematics outlining the overall process flow, benzene concentrations, stream octane, and net hydrogen consumption. PROCESS presented these results to the client and a set of best cases were chosen for further evaluation.
PROCESS‘ next task involved developing more detailed evaluations for the benzene reduction strategies selected. For each case, the selected technologies were integrated into the refinery’s existing naphtha process units with the purpose of defining required changes to existing units, providing estimates for the new gasoline pool output, and determining installation cost estimates.
As a first step, comprehensive simulations were developed for the existing naphtha Hydrodesulfurization (HDS) and Isomerization units. Using these models, unit capacities were examined for two (2) scenarios involving options for straight run naphtha desulfurization. For each case, the new operating requirements were compared with existing assets to identify bottlenecks, existing equipment modifications, and new equipment requirements. These results were then summarized and a preliminary cost estimate was generated.
Next, PROCESS investigated configurations related to a new naphtha splitter and reformate splitter installation. The purpose of this assessment was to develop capital cost estimates for the fractionation systems and to generate product stream compositions. These streams were then submitted to catalyst vendors who provided yield estimates for the reforming, isomerization, and benzene saturation units. Using these results, simulations were completed for the existing, modified, and/or new units.
From the catalyst yield estimates and process models, cost estimates were generated for five (5) alternatives. These costs, associated flow schemes, and final gasoline pool balances were presented to the client. A final configuration was chosen which included a revamp of the refinery’s existing HDS, installation of a new naphtha splitter, and revamp of the existing Isomerization unit.
PROCESS‘ final task involved developing a process design package for the selected configuration, including:
- Assistance with final catalyst selection
- Design and optimization of the Naphtha Splitter unit
- Development of integrated process simulations for the HDS, Naphtha Splitter, Isomerization, and Reformer units
- Process Flow Diagrams (PFDs) development
- Equipment list development
- Comprehensive evaluation of 41 existing equipment items
- Development of process level data sheets for 23 new pieces of equipment
- Assistance with equipment proposal evaluations and finalized design approval
- Line sizing
- Impact study of refinery utility systems
- Analysis of new and existing relief valve requirements.
- Petroleum Refining
- Gasoline pool balance
- Refinery process alternatives evaluation
- Catalyst evaluation
- Preliminary and final process design