Thu, 26 August, 2021
Geothermal energy offers a flexible source of energy that can help stabilise fluctuations in the grid from other, more intermittent renewable energy sources. However, in order to improve the efficiency of geothermal power, whilst also reducing operating costs, improvements in heat exchangers are vital.
The Geo-Hex Project has been working to develop materials for geothermal power plant heat exchangers to provide improved properties and performance. To find out more about the project and its aims, we spoke with Project Leader, Imran Bhamji.
Can you start by introducing yourself and letting us know how you are involved in the Geo-Hex Project?
I am a project leader in the Materials Performance and Characterisation Section of TWI, having joined the organisation in 2017, and I am technical lead on the GeoHex project. I assist TWI's Industrial Members with failure investigations, materials characterisation, materials testing and performance assessments involving stainless steels and non-ferrous alloys. I graduated from the University of Manchester in 2007 with a Master’s degree in Materials Science and Engineering and then completed an EngD, also at the University of Manchester, sponsored by TWI Ltd, in 2012. Prior to joining TWI, I had a number of academic roles at the Open University and the University of Manchester, investigating cracking in power plant steels and preventing corrosion of nuclear fuel rods.
What role do the heat exchangers play in geothermal power plants, and what are the material challenges they face as a result?
Heat exchangers are crucial components of geothermal power plants, particularly for binary cycle power plants, such as those based on Organic Rankine Cycle (ORC) or Kalina cycle, where preheaters, evaporators, superheaters and condensers are used to exchange heat between geothermal brine and a low boiling point working fluid. These heat exchanger components are responsible for a significant proportion of plant capital costs and therefore also have a major influence on plant profitability and viability. As geothermal energy is considered to be clean and flexible, reductions in heat exchanger costs are therefore an important factor in displacing energy from fossil fuels and playing a role in achieving goals related to climate change.
How is the Geo-Hex Project addressing these issues and what benefits will this deliver to heat exchanger properties and performance?
The aim of the GeoHex project is to address the following factors, which are responsible for the high cost of geothermal power plants:
- Low efficiency: A major issue in geothermal plants is mineral, particularly silica, scale build-up, which can occur as the hot water/wet steam can be supersaturated in these minerals at certain temperatures relevant to the thermal cycle. This must be mitigated by operating at inefficient temperatures, through chemical inhibitors or through frequent downtime and cleaning.
- Corrosion: Geothermal fluids are aggressive and therefore there is a requirement to utilise stainless steels or other corrosion resistant alloys in geothermal plants. These materials are also more expensive then lower alloyed steels.
GeoHex will aim to develop coated heat exchanger tubes and plates to avoid scaling and increase efficiency, whilst also enhancing corrosion resistance so that lower cost materials can be utilised, i.e. low alloy steels instead of stainless steels.
Aside from developing materials, the Geo-Hex project is developing sustainability models and a knowledge based engineering tool – can you tell us more about these aspects of the project?
GeoHex will develop a sustainability model that will determine the environmental impact and cost per meter square of the developed engineered surface. The model will be based on the experimental results of heat transfer performance, scalability and manufacturability issues, and environmental impact and cost. In this way, it will be demonstrated that GeoHex materials are viable for application. All models and experimental results will be integrated into a Knowledge Based Engineering (KBE) tool combined with a multicriteria Decision-Support System (DSS). These tools will allow insights to be provided relative to droplet dynamics, environmental impacts and cost benefits, including Levelised Cost of Energy (LCOE).
What stage is the Project currently at, and what are the next steps to getting the work completed?
We are currently mid-way through the project and have developed coatings which will be further evaluated in small scale and full-scale tests.
++Imran will be representing TWI, alongside Research and Product Development Programme Manager Shiladitya Paul, at the World Geothermal Congress in Reykjavik from 24-27 October ++
The Geo-Hex project has received funding from the European Union's Horizon 2020 research and innovation programme. Grant agreement 851917