| The large-scale exploitation of geothermal energy is associated primarily with high-temperature geothermal brines that constitute a considerable portion of the existing energy sources [1]. However, a high content of salts and gases dissolved in the brines determines their high corrosive activity and inclination to salt deposition, as a result of which one of the essential tasks of using the waters of this kind is the development of methods for corrosion and salt deposition control. To prevent the above adverse processes in the power-generating equipment and service lines, twocircuit systems are used; in the first circuit, saline thermal water circulates, while fresh water or a low-boiling working medium circulate in the second circuit. The basic component of the two-circuit system is the heat exchanger manufactured of alloyed steel grades in very short supply and titanium, which impairs the technical and economic characteristics of the geothermal heat supply systems. Therefore, the necessity of manufacturing heat exchangers from cheap carbon steels capable of resisting the corrosive impact of geothermal brines, which is achieved by protecting the metal with corrosion-resistant coatings, is economically sound. The practice of operating the geothermal systems shows that the use of both shell-and-tube and plate heat exchangers in the second circuit causes great difficulties. The performance of such heat exchangers becomes impaired with time; they fail frequently and require periodical cleaning from salt-deposition and corrosion products. This results in considerable extra costs and causes frequent stops of geothermal wells, which also reduces the cost-efficiency of the geothermal production. To utilize the heat of geothermal brines, a heat exchanger of a simple design of the “tube-in-tube” type is proposed. It is assembled out of components that represent two concentrically positioned tubes of a definite length, 3–۶ m, serially connected with each other and placed one above the other (see Fig. 1). The internal tubes are joined with return bends and the external tubes are joined with connecting branches. A heat exchanger of this design was installed in Ternair geothermal steam field in Makhachkala and has been successfully operated there for several years. The heat of saline (to 23 g/dm3 ) thermal water (100°C) is transferred to fresh water of the second circuit that circulates in the heating system of apartment houses. |
