Best Practice: Waste Stream Reduction
Klamath Cogeneration Plant
Challenge. The facility uses reclaimed water for cooling of the condenser and all auxiliary equipment including direct contact cooling of two HRSG flash tanks and one auxiliary boiler (AXB) flash tank (Fig 1). The flash tanks are the final gathering point for all HRSG and AXB drains prior to their disposal to the underground oily/water separator. From the oily/water separator the water is collected and sent to the City Water Treatment Facility’s (CWTF) head works.
Direct contact cooling caused recycling of the reclaimed water back to the CWTF. Chemicals and heavy metals started to accumulate and became difficult to manage for the CWTF. An independent engineering firm calculated that we were causing greater than 13% of their chemicals and heavy-metals loading.
The drain system was installed by the OEM, and the underground piping was made of a PVC type material that has an upper temperature limit of 160F. The plant’s water discharge permit limits water temperature to 140F. Elimination of the cooling system was not an option. Also, the average monthly sewer bill for the plant exceeded $20,000, which included sending this waste stream back to the CWTF.
Solution. The three existing flash tanks were retrofitted with tube and shell heat exchangers, and minor piping changes were incorporated to eliminate the mixing of the flash tank fluids and the reclaimed cooling water (Fig 2). The heat exchangers were oversized to ensure that pumps, level switches, and associated logic would not be necessary. The gravity drain system remained intact.
The blowdown drains reject their heat to the reclaimed water in the heat exchangers. The reclaimed water flows into the storm drains and is collected in the evaporation pond. From there it makes its way back into the cooling tower where it began.
Results. Since the reclaimed water now is returned to the circ water system where it originated, the plant no longer discharges chemicals and heavy metals to the CWTF. CWTF bills are now averaging less than $5,000/month, resulting in a payback time for the modifications of 4.5 months. These mods also eliminated the need for the CWTF to buy additional equipment to handle the heavy metals.
