GM Pontiac Cooling Tower System Design
May 07, 2021
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| STATEMENT OF PROBLEM Before the cooling tower system was turned over to the plant, an oily sheen was discovered in the basins by GM. CCC mitigated the issue with oil socks but it was brought up by the plant on why the filter was not running/filtering the oil. This was because the filter is not meant to filter oil (oil will clog the filter strainer). During the design phase in september of 2015 the mechanical subcontractor and CCC held a meeting with the plant and GF team to review the cooling tower submittals (tower, pumps, and filter). At this time the filter changed from a sidestream sand type to a direct-flow strainer type per GM / Orion. The criteria for filtering was derived from the particulate micron-level that Rotem required and that Orion published in their CTW load study (100 micron). The GM mechanical engineer desired for 25 micron filtration, so final design filter installed had 25 micron filtration. It was never discussed to design and build a system which could handle oil in the water, or that oil was an issue in the water due to oil leaks in old press heat exchangers. This would require an oil separator to be designed into the system before the filter. COURSE OF ACTION JEG contacted the filter supplier to determine what steps were available to mitigate any oil presence that could clog the filter strainer in backwash. It was determined from the supplier that changing the strainer to a 100 micron strainer would greatly reduce the risk of oil clogging. CCC and JEG had a meeting with GM to propose the change and reviewed how the water chemical treatment dissipates the oil. LESSON LEARNED 1) For future projects requiring a cooling tower, the team needs to identify any existing conditions in the plant which can impact the performance of the system. If oil leaks are known and a real concern, the team needs to consider including an oil separator in the front end to mitigate the issue. Or, be prepared to take the corrective steps to prevent oil from entering into the system as designed. 2) It may be more feasible for the prime GC to have the AE perform the schematic design of the system with all stakeholders, prior to the mechanical sub finalizing design. |
