Incorporation of Geothermal Heat Sources in Latvian Heat Supply Systems

Abstract

The main objective of this study is a comprehensive evaluation of the geothermal potential of Latvia and the solution of practical problems in conjunction with the incorporation of geothermal plants into the existing heat supply systems.

The Latvian geothermal resources are concentrated in the Lower Devonian (D1km) and Cambrian (Cm2dm) aquifers in the form of low enthalpy water. Noteworthy heat power could be obtained from the water of the Cambrian aquifers, located in the area of 12,000 km2 in the Central and south-western parts of Latvia at the depth 1,350-1,730 m. During the recent years, the economically usable heat resources were evaluated, reaching the total of 36exp18 J.

The geothermal plants in Latvia are feasible only using the systems of thermal water circulation with reinjection in combination with the heat pump technology and peak load boiler plants. Taking into consideration the existing fuel and energy prices in Latvia and the tendencies of their changes in the near future, it was concluded, based on calculations, that the above geothermal plants can have the pay-back time of up to 8-10 years, if the following conditions are fulfilled:

- there should be certain heat consumption in the summer, at least 25-30% of the winter peak load; - there should be a district heat supply system in good working condition; - the total heat consumption (the winter base load) should be at least 3.5-4.0 MW.

After the analysis of heat demand volume and dynamics for different consumers in the geothermal zone, complying with the above conditions, we have come to the conclusion that bigger cities are more suitable for the use of geothermal water for district heating and hot water supply: Liepaja (population 98,000), Jurmala (60,000), Jelgava (71,000) and Dobele (16,000). There are no suitable consumers in the rural areas, and such consumers are unlikely to appear in the near future, except in the virgin coastal areas suitable for the establishment of spas, where ecologically friendly geothermal plants could be used for the heat supply. The schemes most suitable for current conditions, have been selected. The computer modelling of the working conditions is carried out with the objective to optimise the compatibility of the construction and technological parameters of the proposed plant equipment in order to minimise the operation costs. This work is still in progress, although the power of the main items of basic equipment, the interrelation between them and the limiting values of the work regimes have already been determined.