Evaluate a refinery wide cooling water system in a challenging desert like environment to identify areas for improvement and recommend corrective measures.
EVALUATION OF REFINERY COOLING WATER SYSTEM
The client, an international specialty engineering company was working for the ultimate client, a major oil refining company located in the Middle East. Process Engineering Associates, LLC (PROCESS) was contracted to evaluate the cooling water system at one of the ultimate client’s refineries located in an extreme desert environment. PROCESS was asked to assess the capabilities of the existing cooling system and to provide recommendations to address any deficiencies found. The scope of study included identification of areas within supply headers with poor water distribution and heat exchangers with inadequate water supply based on current refinery process demands. Additionally, cooling water requirements for upcoming unit revamps and new unit installations were addressed. Air and water cooled condensers were also assessed to identify potential sources contributing to high flare loading. In support of this effort PROCESS completed the following tasks:
- Conducted an on-site tour of the facility to view the current system and gather relevant data.
- Developed a design basis summarizing current operating conditions and baseline performance requirements.
- Developed a hydraulic model of the cooling water distribution system using HYSYS simulation software. To complete this task, supply and return water piping geometries were analyzed from over 800 isometric drawings and input into the simulation. Heat exchanger pressure drop correlations were then rigorously determined based on exchanger geometry using CHEMCAD’s CCTherm simulation software. The resulting exchanger correlations were then incorporated into the HYSYS hydraulic model. To balance the HYSYS model the cooling water rate and supply pressure, as determined by the existing pump curves, was varied until the return pressure at the cooling tower reached actual operating conditions and all points within the system were hydraulically balanced.
- Validation of baseline results was accomplished. To validate the hydraulic model, exchanger models, and system load estimates, the results were compared to available refinery metrics. For exchangers, simulation results for design conditions were compared with the original specifications to verify the equipment models were correctly configured. Simulations for exchangers were then run using water rates determined in the hydraulic balance and compared against available operating data. The overall model prediction was further validated by heat balance.
- Evaluated water distribution within the supply headers and for individual equipment items. To complete this task cooling loads to over 400 users including pumps, compressors, and process exchangers were estimated for current process requirements. The required cooling load was then compared to available cooling capacities based on cooling water supply rates determined in the HYSYS hydraulic model. Cooling loads for water cooled exchangers were determined using CCTherm to model exchanger performance based on the calculated water rates at actual process conditions. From this analysis process units and individual equipment items with an inadequate water supply were identified.
- Evaluated potential water side fouling issues. To complete this task water analyses were used in combination with exchanger simulation results to identify areas with increase scaling or fouling potential. To assess scaling potential the Ryznar Stability Index (RSI – an index that attempts to correlate an empirical database of scale thickness observed in municipal water systems to the water chemistry) was calculated using water side operating temperatures. Based on interpretations of this index exchangers at increased risk for scaling were identified. Exchangers with an increased risk of water side fouling were also identified based on low operating velocities within the exchangers.
- Evaluated air cooled condensers and water cooled trim condensers. Air cooled condensers and associated trim condensers were evaluated in an effort to minimize the venting of uncondensed vapors into the refinery flare header. For this task the capacity of existing air cooled exchangers and trim condensers were found for current operating conditions and at predicted water supply rates. The capacities determined were then compared against cooling requirements. Deficient areas were identified and recommendations made to increase cooling capacity via an increase in cooling water supply, the replacement of existing trim condensers, or the installation of new trim condensers.
- Determined requirements for new installations and unit revamps. For this task cooling water requirements for upcoming unit revamps and new unit installations were incorporated into the hydraulic model. The distribution within the system was then evaluated based on these new loads. Recommendations were provided to allow for adequate water supply and cooling capacity for the new loadings and expanded water network.
The study results were summarized in a report and provided to the client at their corporate headquarters. Included were recommendations to improve water distribution to individual units and equipment items; to address ongoing maintenance issues; to provide for upcoming installations and unit revamps; and to increase cooling capacity at air cooled condensers.
- Petroleum Refining
- Process evaluation
- Process simulation
- Hydraulic modeling
- Heat transfer analysis