(92e) The Lp as Utility Systems Design & Optimization Tool

Typically, an LP model of a grassroots refinery project would only be used in the initial configuration studies. After that was done, the LP would be quietly retired early in the Front End Engineering Design (FEED) and only occasionally resurrected to answer the inevitable ?what if' questions. Once FEED was well underway, overall refinery material and utility balances would be performed not with an LP, but with spreadsheets. This resulted in only a limited number of balances for select point in the operating envelope.

Although this approach was common in the past, increased computing power and enhanced LP software has allowed the LP to keep pace with and even lead the FEED work. By continuously updating the LP model with the latest unit yields, blending properties and utility consumption/production figures as developed by the licensors and the FEED contractor, the LP can now quickly produce unlimited balances for the overall refinery as well as for individual units. This allows a complete assessment of the operating envelope which in turn leads to enhanced knowledge of and better designs for OSBL utility systems, including steam, power, water and hydrogen.

The extreme design cases for the utility systems were determined by carefully examining and comparing the utility balances produced by the LP for many operating scenarios. These included partial and total shutdown of various process units during various motor gasoline blending seasons for both expected and guaranteed hydrogen production/consumption across the CCR and hydroprocessing units. An MS Excel workbook was then prepared that used LP produced spreadsheets as input and produced simplified, easy to view summaries for the fuel gas system (including composition and composite btu/scf data), the SMR feed system (including rate and btu content of each feed stream), and all major utility systems (including boiler duty, break over station duty, LP steam condensing duty, fuel gas, cooling water, BFW, cooling water and electrical power used/consumed, imported fuel requirement, condensate flash steam produced, etc). All parameters required to close the major utility balances was provided by the LP. A careful evaluation of all cases then revealed the extreme design points for all major utility systems. Traditional spreadsheet balances for these identified cases were then prepared in order to verify the LP output and to document the utilities and off sites design decisions.

This approach provided a high level of confidence that the offsite systems would not be over or under designed and would be capable of handling a wide range of operating scenarios. This is a degree of confidence and design efficiency not possible with the traditional methods.