Straw and wood chips are set to provide district heating for two small towns in Denmark using the new concept.
Industrial cooling technology heats district heating water
With new type district heating concept, the evaporate is turned back into water while simultaneously liberating heat for the district heating water. The injected water has thus been used to transfer energy from very hot flue gases to district heating water.
At traditional district heating works, flue gases are cooled in a heat exchanger, which typically cools the flue gas to 130°C or so to prevent corrosion. With the new concept, flue gas is cooled to about 35°C, thereby increasing the fuel's energy utilisation rate by 10-15 per cent.
Better utilisation of energy and cheaper operation
Jens Dall Bentzen, a project manager from COWI and originator of the idea, says about his expectations:
"I expect this type of district heating works to provide higher energy utilisation of the fuel together with better, cheaper operation. In addition, it is kinder to the environment, as efficient scrubbing of the flue gas is an integral part of the concept."
The projects, which are being subsidised by the Danish Energy Agency, are scheduled to go into operation during 2007. One plant will be fuelled by straw while the other will run on wood chips. Both will be connected to the existing district heating network. By Kathrine Schmeicel, kats@cowi.dk Published: 26.04.2007
The idea for this new district heating technology came to Jens Dall Bentzen as he was performing calculations with an IT computation tool, also developed by COWI. The IT tool, which is freely available on COWI's website, can analyse operating economy, energy and environmental parameters for the individual works, providing a more qualified basis on which to make decisions about fuel or boiler types, for example.
The computation tool allows free scope to enter the temperature to which the flue gas is to be cooled in a traditional heat exchanger and offers the option of inputting data for a condensing unit (in which steam is converted to water). During program testing, Jens Dall Bentzen allocated a substantial proportion of energy production to a condensing unit and was thus inspired to devise the water injection system.
Initially, he thought the water injection technique would need to be developed, but after having investigated the market, he learned that such a technique already existed in industry. Bentzen subsequently embarked on a dialogue with a number of such industries. Several have shown an interest in supplying equipment for district heating plants. Together with two heating stations, COWI has now applied to the Danish Energy Agency's Research Programme for a subsidy to fund actual demonstration, but the outcome of the application is still pending.Find out more about, or download, the computational tool by clicking on the links at the top of this page.