Online Calcite Removal, Silca Prevention And Removal, NACE Test And Calcium Acrylate Prevention: An Update On R&D Progress

Abstract

At the 2013 NZGW there were discussions about the need for more R&D and how the chemical industry could contribute to moving the Geothermal industry forward by looking into solutions to chemistry problems some plants are facing. In particular silica and antimony was highlighted. This paper is an update on advances made into a series of issues that are, have been or could be faced by the Geothermal power producers. Some solutions have been found, others are work in progress. The topics covered are: online calcite removal, silica inhibition and removal, NACE testing and calcium acrylate deposition. It was suggested that it is time to work more collaboratively to move our industry forward and be part of the promulgation of clean energy in the face of doubling world energy demand over the next 3 decades. Initial on site online calcite removal trials show that a combination of PMA and copolymers combinations including carboxylates alkyl ethers and sulphonates, have increased soluble calcium levels in treated brines. This indicates online calcite removal whilst the geothermal well remains in production. Silica inhibition has been successfully achieved by similar copolymers in an ORMAT run plant and work is now underway to search for methods of dissolving silica which does not involve strong acid. Initial results are presented. Investigation into the NACE test procedure showed that significant differences in results to screen calcite inhibitors is due to the method used to test the thermal stability of the compounds. As these are used by the industry to make decisions that impact selection of calcite inhibitors and could contribute to calcium acrylate deposition it was thought worthy to uncover the reason for the variances. It was found that the procedure used to test thermal stability is where the inconsistency originates. An oxygenated procedure impacted results from 86% to 540% and varied for each of the 11 inhibitors treated. The advent of calcium acrylate in boiler and binary plants has been solved by initially adding sulphonate side chains onto acrylate polymers. This has been a significant factor in the development of the copolymer technologies which avoid calcium acrylate deposition completely and are showing improved results for the treatment of silica, calcite and metal sulphides. It is concluded that using unmodified polyacrylates increases the risk of calcium acrylate deposition in binary plants.