by Simon Schneebeli
In the Swiss village of Beznau, heat losses from a nearby nuclear power plant are being used in a district heating system. Although this is still nuclear energy, even the “green†politicians should love such a system.
It is known that common nuclear power plants have an efficiency coefficient of only about 30 percent (newer power plants may increase this up to 60%). This means, that twice the amount of electrical energy that it produces, is lost to the atmosphere. In the case of the nuclear power plant at Beznau in Switzerland, with its two reactors of 365 MW each, 1460MW are lost to the environment.
The Oil Crisis In 1979
The idea to use heat losses from the nuclear power plant for a district heating system was born after the oil crisis of 1979. In 1983 a neighbouring research institute was successfully supplied with heat for the first time. In the subsequent years, district heating network was expanded step by step. Today, REFUNA (Regionales Fermwärmenetz Unteres Aaretal) supplies heat to over 2300 clients, ranging from small individual houses to large industrial buildings and hospitals.
The Heat Exchange Process
In the nuclear reactors of Beznau, water is heated to a temperature of 312°C. Through the first heat exchanger, the water of the second cycle is vaporised at a temperature of 260° and a pressure of 55 bar. The water then powers first the high pressure turbines and then the low pressure turbines, where a part of the energy is converted into electricity.
At this level, there is enough energy available to heat the water of the district heating network to a temperature of 85°C and if this is not enough to meet the demand, the temperature can be further raised to 125°C through a heat exchanger between the high and the low pressure turbine.
The District Heating Network
The remaining district heating network is the same as the conventional heating networks. Pumps push the heated water through the main network (total length: 31 km) and then through the local secondary network (total length: 99 km). This way, the hot water reaches the buildings where the heat again passes through heat exchangers and then into the buildingâ€TMs heating system.
The whole system is backed by an emergency heating station and a connection with the neighbouring districtâ€TMs heating system. This guarantees the availability of energy even in the case of nuclear reactors of Beznau being switched off.
Still Nuclear Power
The REFUNA district heating network sells about 130 000 MWh of energy every year and is thus by far the largest district heating system of Switzerland. Many technical obstacles had to be overcome before its effective implementation. However an equally difficult task was to convince people that nuclear district heating is safe and non-polluting. Many people are sceptical when they hear the word “nuclear”. Indeed the energy extracted from the reactors is not just “heat loss†. If the heat that is extracted after the low pressure turbine is not enough to meet the demand, energy is extracted from between the high and the low pressure turbine. This leads to a decrease in electricity production. This is the reason why it is not possible to talk of a “clean heating energy†system.
Why Is This Still A Good Solution?
The main argument in favour of such a heating system is that resources are scarce (even Uranium) and the resources we consume must be consumed in the most efficient way. This means that if it is possible to improve the efficiency of a system, it must be done.
The other argument is that with this system, the consumption of heating oil could be reduced drastically. The amount of heat that is sold to consumers can be converted into heating oil and then into CO2 emissions. To produce 130 000 MWh, around 12 600 t of heating oil is required. Burning this much amount of oil would emit 44 000 t of CO2.
Given the amount of energy that is produced by nuclear power plants and considering the fact that energy sources are scarce, it would simply be irrational not to use these in the best possible way. District heating systems powered by heat from nuclear power plants is one such logical option.
February 21st, 2010 at 11:45 am
I agree on the last argument that resources are scarce and they should be used in the most efficient way. But there is a bunch of arguments not being touched.
Nuclear co-generation (heat and power) as an efficient energy conversion technology is is not generally right because, a) not all the heat produced can be used for district heating as the water systems have to be separated carefully due to the danger of nuclear pollution (in other words: the efficiency of heat production is very low compared to other co-generation technologies) and b) there is a huge amount of heat produced centrally – more than generally can be used in the neighborhood. Background of this is that heat cannot be transported over an arbitrary distance (energy for pumping and heat losses increase with distance). In other words there are generally not enough consumers close by, which leads to the potential solution that nuclear power plants should be built very close to places where many people live or work, which will not happen as opposition in big cities is too big.
This shows that the advantage of increasing the efficiency of electricity producing power plants by utilizing their excess heat by applying a district heating system does not or only to a limited extent account for nuclear power plants. I would like to see the rise of efficiency of the plant in Beznau through it’s district heating system. I bet it is very little.
And there is one more strategic danger. If this argument of nuclear district heating will be used to build more nuclear power plants it will support a legacy technology, which should be replaced by cheaper solutions, which are additionally much more flexible for uncertain future developments of markets/resources and environmental impacts.