Technical-economic estimation of geothermal resources

Abstract

Tremendous underground heat resources and simplicity of geothermal installations attracts ever more attention of power engineers in many countries of the world. To determine conditions and possible scale of earth heat effective utilization it is necessary to compare thoroughly geothermal sources with other energy sources. 1. 1. Classification of geothermal installation schemes. When utilizing thermal water for purposes of heat supply four different schemes can be used: 1) direct use of thermal water; 2) rising of geothermal temperature level in peak boiler shops; 3) rising of geothermal temperature level in heat pump installations; 4) combined schemes. There are comparative characteristics of these schemes given and conditions of their expedient application considered in the paper. Two schemes of geothermal power stations differ principally: 1) with vapour cycle of thermal water; 2) with secondary fluid cycle. Comparison of these schemes from the point of view of their power effectiveness, possibility of using water with different composition and operational conditions shows that none of the schemes is absolutely predominant. The choice of this or that scheme must be done with regard to local conditions. 2. 2) Technical-economical indices of geothermal heat sources. The direct heat source in systems of geothermal heat supply is the operational drill-well. Its useful heat output is determined by yield, depth, temperature gradient and geothermal conditions of the region. With increasing depth the thermal water temperature rises as well as the heat output of the well. Non-linearity of the well cost dependence from its depth predetermines the presence of optimal depth at which the best technical-economical characteristics of the well as an energy source are achieved. Generalization of data on investment in oil and gas wells drilling allows to obtain empirical dependences for determination of wells cost in prospected areas of thermal water utilization. Equations for determination of optimal well depth, of specific rated expenses and net cost of thermal water are obtained. Data on geothermal conditions, well's yield and the influence of the depth on basic economical characteristics of geothermal heat sources are presented in the paper. 3. 3. Comparison of geothermal heat sources with installations using organic fuels. As a criterion of the energy source effectiveness the value of specific reduced expences is accepted, which is determined as the relation of rated annual expenses sum to the annual power output. Comparing the specific reduced expenses for geothermal installations, heating boiler shops and thermal power stations it became possible to find conditions of economically expedient use of thermal water for heat supply and electric power generation. The main factors are geothermal conditions, well yield, drilling cost and the economical conditions of the region.