| Title | Iron sulfide deposition and inhibition and its impact on geothermal brine pumps |
|---|---|
| Authors | F. Monterozo, G. Mendoza |
| Year | 2024 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | brine pump, iron sulfide, mineral scaling |
| Abstract | In geothermal systems, iron sulfide can be considered as one of the most challenging scales because of the impacts of the deposits formed. This type of scale is usually intermixed with amorphous silica and metal silicates, which in turn, forms tenacious and hard deposits that can be observed in both surface and subsurface facilities. In one case in the Philippines, deposition of iron sulfide along the brine reinjection system negatively impacts the capacity of the brine pump. Aside from scaling along the pipelines, iron sulfide deposition was also observed inside the pump casing which causes the rapid decline of pump capacity. Without operable pumps, the plant is forced to shut down and do manual cleaning to regain normal operations. Dumping of the brine to maintain separator level was also being done because of limited reinjection capacity due to pump capacity decline. Deposition mechanism of iron sulfide was studied, and it was confirmed that existing chemical and mechanical conditions were conducive in the precipitation of this scale. A new inhibition program was studied based on existing cases for metal silicate and sulfide inhibition to check if the same principle can show positive impact on this type of application. The goal of the inhibition program is to preserve the capacity of the brine pump by minimizing scaling. This will maintain existing or reduce (or to some extent, eliminate) brine dumping rate. It can be observed that before the new inhibition program, the brine dumping rate increases steeply over time. The new inhibition program was able to slow down the steep increase of the dumping rate. This was further demonstrated after the silencer cleaning where it can be observed that the brine dumping rate was consistently controlled for 1 month at 25 kg/s compared to 43 kg/s. Comparing to the baseline, monomeric silica retention increased during the trial which is a good indicator of lesser scaling potential. It was observed that monomeric silica retention increased by 300%. Silica may not be visible in the XRF or XRD analyses because the sample was limited to the brine pump internals only. Aside from quantitative measurements, qualitative observations were also made during the trial. It is worth noting that during an outage were the brine pump was put out of service, no manual barring was done to restart the pump. It was a good indication of the chemical program difference in comparison to the previous experiences of the site. |