First Step: CLEANING IT UP (First Clean It Up & Then Keep It Clean!)
28-Day Evaluation Demonstrates BCP 5030 Disrupts, Removes and Disperses Hard Sulfur Fouling in a Geothermal Power Plant Cooling Water System
Clean up in Progress Using BCP 5030
Sulfur Fouling and the Impact on Geothermal Plant Power Output
Four 400,000 gallon cooling water systems associated with a 100 MW geothermal power plant were experiencing declining cooling system efficiency due to fouling by elemental sulfur. This plant (Cerro Prieto IV) is one of four plants with a combined capacity of 720 MW operated by CFE (Federal Electricity Commission) in the Cerro Prieto (Mexico) Geothermal Field.
Sulfur enters the geothermal plant’s cooling system as hydrogen sulfide, one of a number of non-condensable gasses associated with the steam produced from the geothermal reservoir. Condensation of the steam in a direct contact condenser results in low levels of H2S in the [steam condensate + cooling water] mixture which is returned to the cooling tower. In the fully oxygenated cooling tower environment the H2S is oxidized to elemental sulfur, sulfuric acid and several other oxidized forms of sulfur by a combination of microbiological and abiotic oxidation processes.
Elemental sulfur accumulates in the system as hard sulfur deposits in the direct contact condenser, the hot water distribution lines, on hot water spray nozzles and in the cooling tower’s high efficiency cross-corrugated film fill. Sulfur fouling in the hot water distribution lines reduces the lines’ internal diameters and restricts flow. Sulfur fouling on the spray nozzles results in a confined/ineffective spray pattern which produces areas of heavy sulfur fouling in the upper fill. Sulfur fouling in flow lines, on spray nozzles and on tower fill appears in the photos below.
The pattern of uneven heavy sulfur deposit accumulation in the upper fill results in channeled flow through the fill (see photos below). Channeled flow reduces air-water mixing, resulting in a loss of cooling efficiency (see temperature variation across water curtain for uniform vs. channeled flow, below).
Gradual loss of cooling efficiency due to sulfur fouling resulted in a gradual increase in the plant’s cold water temperatures (see graph, below), which in turn produces higher condenser pressures (less vacuum), resulting in less efficient steam turbine operation. Loss in turbine operating efficiency has a direct impact on the power output of the plant.
28-Day Trial Demonstrates BCP 5030’s Impact on Preformed Sulfur Deposits
BCP 5030 is a highly effective deposit penetrant, dispersant and cleaner. It is used in industrial water systems to clean fouled systems, and maintain clean systems free of inorganic, organic and microbiological fouling. Based on BCP 5030’s proven abilities to disrupt and disperse difficult-to-remove deposits, a trial was conducted in one of four 25 MW units at Cerro Prieto Plant IV in order to demonstrate BCP 5030’s ability to disrupt and disperse hard sulfur fouling deposits.
BCP 5030 was dosed into the system in slugs ranging from 137.5 ppm (3x on the first day) to 50 ppm (1x per day on most subsequent days). A total of 825 gallons of BCP 5030 was added to the 400,000 gallon system during the 28 day trial period.
The treatments resulted in increasing turbidity of the recirculating cooling water as biomass and particulate elemental sulfur were dispersed into the system (see photo tower basin water and graph of turbidity, below). Microbiological monitoring showed high numbers of microorganisms dispersed from deposits in the system.
An inspection at the end of the trial showed clear evidence of sulfur deposit removal, with the larger pieces of deposit detached from the hot water distribution lines, and sulfur cylinders detached from spray nozzle orifices collecting on the top surface of the tower fill (see photos below). Detachment of sulfur deposits is not observed under pre-trial routine operating conditions.
In the inspection it was also observed that detachment of algal fouling deposits was initiated during the trial (see photos of biomass on screens and sloughing algal deposits, below). Continuation of BCP 5030 treatment beyond the 28-day trial would eventually have resulted in removal of all algal fouling deposits from the system.
At the conclusion of the trial, BCP 5030 treatments were stopped. A subsequent inspection showed that in the absence of daily BCP 5030 treatments, sulfur deposition resumed in the orifices of the spray nozzles.
Conclusions
Hard elemental sulfur deposits which develop in certain geothermal cooling water systems impact the system in ways which result in loss of cooling efficiency, and declining plant power output.
BCP 5030 attacks preformed hard sulfur fouling deposits in geothermal power plant cooling water systems, resulting in detachment and dispersion of the deposits.
BCP 5030 removes and disperses biofouling deposits in the cooling system, thereby minimizing biofilm-based microbial processes in the system.
BCP 5030 treatments initiated detachment of algal fouling deposits.
Continued application of online BCP 5030 cleaning treatments has the potential to remove all sulfur and biofouling (microbial and algal) deposits from the system, thereby restoring cooling system efficiency and enabling plant operation at design power output.
