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2 GRC Transactions, Vol. 31, 2007 Technical Experiences of Brine Injection Pumping Stations in El Salvador s Geothermal Fields Cristo Umanzor LaGeo S.A. de C.V., Colonia Utila, Nva. S.S., El Salvador, C.A. cumanzor@lageo.com.sv Keywords Injection, Ahuachapan, Berlín, pumping station, pumps, silica scaling ABSTRACT In the history of Berlín and Ahuachapán geothermal fields, injection has always been an important and complex issue to consider. The growing injection capacity demand and low wells injection capacity have resulted in the design and installation of brine injection pumping stations in both geothermal fields. This paper describes the main experiences acquired during the design and operations of these pumping systems. These experiences were obtained from the injection pumping station of Ahuachapán Geothermal Field, a injection pumping test and a projected injection pumping station in Berlín Geothermal Field. The main issue and problem to consider in a pumping station design is the silica scaling. This matter can be carefully discussed with pump manufacturers through a well defined quality management plan specifically detailed for the project. 1.2 Experiences with Hot Brine Injection Pumping Set The set of hot brine injection pumps have been working continuously and the following representative problems were observed: After around two years of operation, pressurized brine penetrated the bearing housing and was mixed with the bearings lubrication oil. Brine and oil mixing caused damages to the bearings and operation trips were generated due to relatively high bearing temperature and high vibration. Brine penetration was caused by the deflector between the volute housing and bearings housing which was made of aluminum (See figure 3). Silica scaling damaged aluminum deflectors and permitted brine access to the bearing housing. The deflectors were changed by components fabricated with stainless steel 316. The problem was not observed again after the change. Silica scaling sealed some gaps between pump casing and casing covers. This problem complicated dismantling operations because higher forces were necessary to apply and, these forces might damage the pump casing (See Figure 4, overleaf). 1. Experiences in Ahuachapán Geothermal Field 1.1 General Description of Ahuachapán Pumping System Ahuachapán brine pumping injection station started its operation on May, This pumping station is conformed by three (3) different sets of pumps with the following functions: a. Hot brine injection (3x300 kw - Figure No 1) b. Emergency brine injection (2x500kW - Figure No 2) c. Cooling tower blow-down injection (2x100kW - Figure No 1) Figure 1. Hot brine and condensate injection pumps. 207

3 axis bushing material was changed to graphite bronze and axis was changed to Stainless Steel 316. The problem was not observed again. The original design considered that axis and axis bushing adjustments were going to be auto-lubricated with the same pumped brine. Silica scaling sealed these adjustments and the lubrication was diminished. This might be a potential additional cause of the recorded failure. Figure 2. Emergency brine injection pumps (2x500 kw). 1.3 Experiences with the Emergency Brine Pumping Set The set of emergency brine injection pumps shown material hardness problems. The pump axis failed after a year of operation. The failure analysis detected an abrasive wear in the external axis diameter (0.25 in approx.) due to different hardness materials between the axis and axis bushing. The 1.4 Experience Mixing Pumped Brines with Different Temperature The three injection pumping systems merge their pumped fluids at different operation temperatures. This is an important issue to consider for the operation procedures. To introduce cold water into a empty hot pipe system generates thermal shocks and potential serious damages over the pipe, accessories, and supports. The installation of additional sensors to detect pressure and temperature working as pipe system protection might mitigate the risk. 2. Berlin Brine Injection Pumping Test A brine injection pumping test was developed in Berlin geothermal field to verify the effect of high pressure brine injection over the reservoir. The system consisted of two 750 kw barrel type pumps and motors, driven by a set of three 1300 HP Diesel generators. The test was executed continuously during 4 months. 2.1 Problems Observed with the Control Flow Valves The brine injection flow control was performed by a couple of butterfly valves located at the pump discharge pipe. Silica scaling inside the valve clogged flow control many times dur- Figure 3. Deflector pump component made of aluminum. Figure 4. Extraction of internal pump components from its casing. Figure 5. Pumping station for injection test in Berlin geothermal field. 208

4 Figure 6. Flow control valve clogged with silica scaling. Figure 8. Silica deposits inside one of the pump stage impellers. ing the operation. This problem did not allow operators to control injection flow. In the design of permanent pumping stations this problem was solved with the installation of variable frequency drivers (VFD) to control the flow instead of control valves. 2.2 Silica Scaling Inside the Injection Pumps Silica scaling inside the pumps created serious problems during the dismantling process. The silica scaling sealed the gaps among all the pump components and relatively high forces were applied to dismantle the pump, taking the risk of Figure 7. Radial-split type pump casing. potential damages over the pump casing and internal parts. The pump casing design is radial-split type and this issue makes the dismantling process even more complicated. Due to electrical generators trip, auxiliary pumps for mechanical seals lubrication stopped and depressurized the mechanical seals chamber, brine penetrated into that chamber. Hence, silica scaling affected the mechanical seals lubrication. After months of continuous operation, mechanical seals were damaged. 3. Berlín Projected Pumping Injection System A new brine injection pumping station is projected in Berlín geothermal field (Figures No 9 and 10, overleaf). The design of this projected station considers the previous experiences. The most important design issues are as follows: a. The pumping station includes three Variable Frequency Drivers (VFD) for injection flow control. b. Pumps casing design is axially-split type. This issue will facilitate maintenance operations. c. Wider gaps between impellers and pump casing will be considered to allocate potential silica scaling. Nevertheless, this issue has to be discussed very carefully with the pump manufacturers because it might affect the pump mechanical efficiency. d. Additional insertion points for inspection and drainage were included in the pump casing design. 209

5 b. Pump manufacturers experience for geothermal brine injection is not common and, some manufacturing standards do not apply integrally to geothermal processes. It is important to define a Quality Management Plan specifically for the project s pump fabrication. With this plan, materials and design aspects can be revised periodically along the whole manufacturing process. Figure 9. General view of brine injection station in Berlin, currently in construction. References Maintenance Reports for injection pumps in Ahuachapán Geothermal Field, Internal Report, López Godofredo, Departamento de mantenimiento mecánico de Ahuachapán, LaGeo S.A. de C.V. (2005) Operation and maintenance reports of brine injection pumping test in Berlin Geothermal Field, Internal Report, Equipo de Proyecto RTB, LaGeo S.A. de C.V. (2006) e. Auxiliary pumps for mechanical seals lubrication will operate constantly to avoid brine from penetrating inside the mechanical seal chambers. f. Maintenance procedures consider periodical pump cleaning operations to reduce silica scaling inside the pumps. g. A system of silica inhibitors will be installed to reduce scaling along the brine injection piping system. h. A Quality Management Plan was implemented along the whole pump fabrication to control the customized design aspects. Conclusions a. Silica scaling is always the main issue to deal with the design of brine injection pumping stations. Figure 10. Brine injection pump Berlin Geothermal Field. 210