TPU Creates Unique Geothermal Power Plant Prototype

Engineers from Tomsk Polytechnic University have designed a 25 kW geothermal power plant (GeoPP) prototype, and conducted the first tests of the prototype. Contrary to extant geothermal power plants in Russia, TPU's GeoPP employs an organic Rankine cycle, enabling it to function at reduced temperatures. Prospective applications of such plants include power and heat supply. The project is supported by the Priority 2030 program of the Russian Ministry of Science and Higher Education.

The geothermal energy industry in Russia, a relatively nascent field, currently boasts four operational geothermal power plants in the Kamchatka and Kuril Islands regions. A significant proportion of these power plants rely on direct steam utilization. The approach advocated by TPU entails the development of binary GeoPPs, underpinned by the organic Rankine cycle. Notably, Russia currently lacks industrially operating facilities that leverage this innovative approach. The Rankine cycle constitutes a thermodynamic cycle that involves the conversion of heat into work through the agency of a specific working body. Depending on the parameters of the heat source, hydrocarbons, silicone oils, or refrigerants can act as working bodies.

"In the proposed project, the working body is a refrigerant, ozone-safe Freon R245fa. Moreover, since the GeoPP operates on a closed or binary cycle technology, the refrigerant boils at lower temperatures from 47°C and above. This enables the potential expansion of the regions suitable for GeoPP utilization, as existing GeoPPs are constrained to temperatures above 100°C,” says Stanislav Yankovsky, project manager, associate professor at the Butakov Research Center.

In their study, the researchers examined the existing data on the geothermal industry in Russia and other countries, subsequently creating a map delineating the regions within Russia deemed most suitable for the development of geothermal energy technologies. These regions include Kamchatka, Sakhalin, the Kurils, the North Caucasus, and Western Siberia. The analysis confirmed that the Tomsk region holds significant potential for the development of geothermal energy.

"In constructing this map, we took into account geological criteria and the Tomsk region's demand for affordable electricity. Our analysis encompassed factors such as the density of geothermal resources, the temperature at depths ranging from one to four kilometers, the intensity of heat flow, population density, and the cost of energy produced by diesel power plants," elucidated Gleb Shishaev, a project team member and an engineer at TPU's Heriot-Watt Center.

The analysis, facilitated by the digital model, yielded algorithms to select the necessary above-ground equipment, alongside the development of methodologies for selecting the optimal refrigerant, considering the thermal water temperature.

The GeoPP prototype has been installed at Tomsk Polytechnic University, and initial full-scale launches have been conducted using a real physical model of a geothermal well.
The GeoPP is composed of multiple modules, including a heater unit, an evaporator, a condenser, a screw expander, and a generator. It is equipped with essential measuring equipment and a control system, enabling remote control and monitoring. The prototype was constructed using domestic components.

"The GeoPP's operational mechanism involves the following: the fluid from the geothermal source ascends from the well under pressure, transferring heat to the refrigerant through the heat exchanger. The refrigerant, undergoing a phase transition, transfers energy to a screw expander, which is mounted on a shaft that houses a generator. The generator then converts the energy into electricity. Concurrently, the spent refrigerant undergoes a phase change and is prepared for the subsequent cycle. Additionally, the heat from the fluid can be utilized in parallel for heating consumers,” adds Stanislav Yankovsky.

The technology has the potential to address two pressing problems concurrently: the supply of electricity and heat. A notable benefit of closed-cycle technology is its capacity to minimize environmental emissions.

"The project's distinctiveness lies in the innovative utilization of screw expanders for GeoPPs, a novel application that has rarely been seen in existing plants that predominantly use turbines. The screw expander's effectiveness in a limited power range, its capacity to operate in mixed mode, and its economic superiority over turbines are notable advantages,” adds the project manager.

The experimental prototype facilitates comprehensive process modeling and analysis of critical parameters by scientists. The minimum geothermal source temperature required for the plant to operate efficiently and generate electricity has been determined to be at least 60°C.

"The test runs have demonstrated the operability and efficiency of the technology, enabling us to proceed with its development to expand electric capacity and conduct full-scale tests on a real well," explains Stanislav Yankovsky.

The TPU research initiative involves a collaborative effort among researchers from the university's Heriot-Watt Center and the School of Energy and Power Engineering. The preliminary findings of this research endeavor have been documented in an article, and patents have been secured for the innovative design and methodologies (No. 2 804 793, No. 2 810 329). Additionally, software program registration certificates have been obtained for the same inventions.