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Recovering Waste Heat from Genset Power Plants

What is a genset

A genset consists in short of a reciprocating engine connected to a generator. The internal combustion engine generates the rotational force that spins the rotor within the generator or alternator, which in turn generates electricity. For more information have a look at this site. The advantages of a genset setup are features such as: the reliability and robustness of the engines, fuel efficiency, quick start and stop, and modular scaling.Why are we using gensets?

Perhaps now the first thing you can think of is a diesel generator, providing power in an emergency situation or at a construction site. But our focus for this piece are larger installations, usually comprised of several megawatt sized gas engines, as the use of these are increasing. These larger installations play a part in many grid supporting functions and are increasingly popular for a stable power supply.

The greatest advantages with genset power plants is their efficiency and quick response. Because of this they are often used to balance intermittent renewables, such as wind and solar power. Gensets can provide backup power when the wind stops blowing or the sun isn’t out. Another great advantage is peak shaving, where the genset supplies power for the hours of peak demand.

The other role it shares with decentralized heat power, is its positive impact on the grid. Gensets are often used for smaller island-grids, be it a physical island or a larger industrial park. Industries that have the need for stable power generation and/or a desire to have a micro-grid. The second decentralized benefit is using gensets in remote areas of the grid, far from traditional centralized power generation. In these cases it helps the grid and can provide backup power in the case of an interruption somewhere along the transmission lines.

A Wärtsilä genset power plant. photo via wartsila.com

While the traditional gensets use diesel or fuel oil, the growing market is heavily dominated by methane gas powered engines. These engines reach high efficiencies, up to 45 percent, as they grow into megawatt size. Rivaling and even outperforming traditional steam power plants in terms of efficiency. While not beating combined cycle gas turbines, gas gensets are far quicker to respond to demand. In addition the modular nature of a genset power plant gives it a higher redundancy.

Natural gas has long been regarded as a transition fuel from dirtier fossil fuels like coal and oil. Gas powered gensets are the perfect example on how this can occur in practice. The natural gas can seamlessly be replaced by any methane gas, such as low carbon landfill gas or renewable biogas produced from sewage or agricultural waste. It may even be possible to use a gas mixture of methane and hydrogen to power the engines.

Efficient, but still wasteful

Energy flow in an engine can typically be explained by the rule of thirds, where one third is converted into useful mechanical energy, one third is lost in the exhaust and the final third in the engine cooling system. The more efficient large gas engines convert more of the fuel to mechanical energy, increasing electrical efficiencies up to 45 percent. But that means they still waste more than half of the energy. Either it goes up the chimney, literally, or with the engine cooling water, wasted away in conventional cooling towers. So, the follow up, the question must be, how can we make these engines even more efficient?

To recover energy from the exhaust, a first step is to fit turbochargers much like in cars. These are often used to decrease fuel usage while maintaining the power output. But recall the rule of third, that there is often equally as much waste heat in the engine cooling circuit. While the exhaust is high grade heat, often several hundred degrees centigrade. The engine cooling water is low grade heat, below 100 degrees centigrade. Lower grade heat is usually more difficult to transform into useful energy. The best use of heat is almost always direct heating purposes, such as to warm up a building. Using the heat in this way you have created a combined heat and power (CHP) plant.

Where does Climeon fit in

However, what if you do not have any need for heating but still want to make use of that low temperature waste heat? This is where Climeon’s modular heat power units can provide a great addition to a genset power plant. By converting the low temperature waste heat into electricity, it increases the fuel and electrical efficiency of the entire power plant. Climeon's modular units fit great onto larger genset engines (one megawatt and above) and will reduce the fuel use or increase the electrical output for your power plant. An advantage of converting low-grade heat into electricity is its already the main product of the plant, and that electricity is very versatile and can support a multitude of end uses.