7 Day Emergency Intervention

7-Day Trial Demonstrates BCP™ 5030’s Ability to Disrupt and Disperse Sulfur Deposits in a Heavily Fouled Geothermal Power Plant Cooling Water System

Demonstrated BCP 5030’s performance to start clean up by removing sulfur deposits in a heavily sulfur and microbiologically fouled geothermal power plant cooling water system.

Sulfur Fouling and the Impact on Geothermal Plant Power Output

Two 660,000 gallon cooling water systems associated with a 106 MW geothermal power plant complex in Southeast Asia were experiencing declining cooling system efficiency due to fouling by elemental sulfur. 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 “low clog” PVC fill. Sulfur fouling in the hot water distribution lines reduces the lines’ internal diameter and restricts flow, causing hot water to be diverted to the tower basin without cooling. Sulfur fouling on the spray nozzles also restricts flow and contributes to increased pressure which in turn increases the amount of hot water diverted to the tower basin.

Hot water returned to the tower basin without cooling reduces the efficiency of the cooling water system. Gradual loss of cooling efficiency due to sulfur fouling will result in an increase in the plant’s cold water temperatures, which in turn produces higher condenser pressures (less vacuum), resulting in less efficient steam turbine operation. Reduced turbine operating efficiency has a direct impact on the power output of the plant.

Faced with declining cooling system efficiency, the plant’s operator requested the water treatment service provider to conduct a trial to demonstrate BCP 5030’s ability to remove existing sulfur deposits, and maintain clean system components free of sulfur deposition.

7-Day Trial Demonstrates BCP 5030’s Ability to Remove Existing Sulfur Deposits and Prevent Sulfur Deposition on Clean System Components

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 sulfur deposits in the Cerro Prieto IV (Mexico) geothermal power plant, a 7-day a trial was conducted in order to demonstrate BCP 5030’s ability to remove existing sulfur deposits, and prevent the formation of new sulfur deposits in one of two units at the Southeast Asia geothermal power plant complex.

A pre-trial inspection showed sulfur accumulation in and on hot water distribution piping in the upper tower, on hot water spray nozzles, on wooden structural beams in the upper tower, and on the tower fill (fouled piping, spray nozzles and fill are shown below). The tower basin and lower tower wooden structure were free of sulfur deposits but showed evidence of algal fouling in areas with adequate sunlight.

A number of spray nozzles were cleaned and reinstalled before the trial. These spray nozzles were to be inspected after the trial to assess BCP 5030’s ability to prevent the formation of new sulfur deposits.

BCP 5030 was dosed into the system in 9 slugs (two slugs of 100 ppm and one slug of 50 ppm of BCP 5030 on the first day; 50 ppm of BCP 5030 on all subsequent days of the trial). A total of 365 gallons of BCP 5030 was added to the 660,000 gallon system during the 7 day trial period.

Dosing over the first three days of the trial generated significant amounts of dirty foam as biofouling deposits and particulate elemental sulfur were removed from tower surfaces.

These observations were supported by water quality data indicating increasing turbidity, elevated dipslide aerobic bacteria counts and elevated ATP levels in the recirculating water.

Disruption of biofilm-based sulfide-oxidizing bacteria populations reduced sulfate concentrations in the water, and temporarily eliminated the requirement for caustic to maintain an alkaline pH in the system.

A post-trial inspection was conducted two days after the trial. Significant sulfur deposit had been removed from wooden structural beams in the upper tower.

Spray nozzles cleaned before the trial were judged to be cleaner after the trial. Spray nozzles with significant sulfur deposit accumulation before the trial (below, left) showed evidence of initial sulfur removal at the end of the 7-day trial (below, right).

Significant quantities of sulfur deposit chips (“flakes”) had detached within the hot water distribution lines, and accumulated at the bottom of the line. Shown below are detached deposits in a distribution line, and flushed from the end of a distribution line during the post-trial inspection.

Larger, thicker pieces of sulfur deposit were also found in the distribution lines (below, left and center). Accumulation of larger sulfur deposit pieces and smaller sulfur “flakes” in the bottom of main hot water supply header will plug bottom-of-the-line spray nozzles on the headers (below, right), and therefore must be flushed from the lines following a clean-up program.

Prior to the trial all sulfur deposits found in the cooling system were very hard, and required high pressure washing or mechanical scraping for effective removal. After the trial sulfur deposits were softened to the extent that they could be removed easily by hand, or with low pressure water washing. Shown below at left, deposits break away from a spray nozzle during handling. At center, a gloved finger wipes deposits off a wooden beam. At right, deposits are easily removed from a distribution pipe with a gloved hand.

Shown below, flow from a low pressure utility hose is sufficient to wash sulfur deposits off of wooden beams (left) and tower fill (unwashed fill left, washed fill right). If BCP 5030 treatments had been continued, it is very likely that normal water flows through the tower would eventually have washed sulfur deposits from all surfaces.

Biofouling deposits were disrupted by BCP 5030 treatments. Elevated ATP readings, shown earlier, indicated significant biomass removed from cooling system surfaces and dispersed into the recirculating water. During the post-trial inspection shut-down it was evident that algal fouling deposits were also affected by BCP 5030 treatments. Algal deposits on wood surfaces in the lower part of the tower were beginning to detach at the end of the 7-day trial.

Despite large amounts of detached sulfur deposits accumulating in the hot water distribution lines, sufficient dispersion had occurred such that no hot water was diverted directly to the tower basin at the end of the trial, and for several weeks thereafter.

Conclusions

BCP 5030 treatments removed and dispersed large quantities of preformed hard sulfur deposits from the cooling tower structural beams, spray nozzles and hot water distribution lines in a 7-day trial at this 106 MW geothermal power plant.

Sulfur deposits remaining in place at the end of the trial were sufficiently softened that they could be easily removed by hand or low pressure washing. It is believed that if the trial had continued another one to two weeks, these softened deposits would have been removed by normal water flows in the system.

BCP 5030 treatment prevented the formation of new sulfur deposits on pre-cleaned hot water spray nozzles, and in fact removed additional sulfur from these cleaned nozzles.

BCP 5030 treatments removed and dispersed biofouling deposits in the system as indicated by elevated ATP levels in the water following treatments, and the visible stripping of algal deposits from surfaces in the lower tower.

Removal and dispersion of sulfur deposits in the hot water distribution lines allowed sufficient flow through the lines so that no hot water was diverted directly to the basin. Operating with all hot water passing through the tower fill promotes more effective cooling, and through this, more efficient plant operation.