Evaluation of the buffering capability of B-chloro-propionic acid-sodium B-chloro-propionate system in a low pH geothermal brine

• Main Author: Brondial, Yolanda P.
• Format: text
• Language: English
• Published: Animo Repository 2003
• Subjects: Buffer solutions; Acid base equilibrium; Geothermal brines; Saline waters; Hydrogen-ion concentration; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_doctoral/921
• Institution: De La Salle University

The Philippines being a part of the Pacific Ring of Fire has abundant geothermal energy. However, a substantial number of drilled wells produce acidic geofluid with high enthalpy and high wellhead pressure. It becomes imperative, therefore, to research and develop methods or techniques by which these acidic wells can be used for power generation. The geothermal industry incurs a huge financial loss with the current practice of plugging and abandoning acidic wells. A potential method for commercializing high-enthalpy acidic geothermal wells is explored in this study by raising the pH of the geofluids to equal to or greater than 3.5, pH levels considered by geothermal reservoir engineers to be non-corrosive to low-carbon steel (the material of constuction of the casing and pipeline network of the steam-gathering systems in the Philippines). The non-condensible gases of acidic geothermal wells are relatively high in H2S and CO2, and the brine is high in sulfates. These substances, aside from being potential hazards, account for the acidity of geofluid. In this study, pH buffering is accomplished by adding to a certain volume of geofluid 25 degrees C less than or equal to temp 100 degrees C, BCPH-NaBCP buffering solutions that are stable at high temperature and non-hazardous at low level. The buffer solution preserves the pH of the geofluid at a non-corrosive level until such point that it is fully utilized in terms of available H+. The pH buffering was modeled using stepwise regression with an assumed full model. The procedure used completely randomized block design and was simplified with the use of the software Design-Expert 6. The following were considered: five design factors (pH geofluid, pH BCPH-NaBCP, volume BCPH-NaBCP, concentration BCPH-NaBCP and temperature {t} of solution), and one response factor (pH of resulting solution). Experiments were conducted according to the experimental design at 25 degrees C less than or equal to temp less than or equal to 100 degrees C and the resulting pH of solution for each combination of factors were measured. Experimental laboratory results showed that BCPH-NaBCP could raise the pH to greater than 3.5 and that the initial pH of geofluid, the pH, concentration and volume of BCPH-NaBCP solution significantly influenced the stable pH of the final solution. The best combination of factors was then used in the bench-scale set-up to investigate the possibility of applying pH buffering at high velocity. Results showed that BCPH-NaBCP was useful for fast buffering and could therefore be used to commercialize acidic wells.