HOT|COOL NO.1/2021 - "Fuel, Flexibility & Green Transition"

Ringsted DHC’s heat recovery kickstarts a new era of greener district heating

Ringsted District Heating Company (DHC), a large district heating utility in Denmark, has reduced its reliance on fossil fuels by 97% after installing an innovative heat recovery system using heat pumps. The heat pumps – built with oil-free compressor technology – recover surplus heat from the plant’s equipment that would otherwise be wasted.

By Drew Turner, Director of Global Business Development and Market Research, Danfoss

Three new heat pumps In 2020, the DHC introduced four new electric heat pumps – three of which use Turbocor® oil-free techno- logy – and a new scrubber to remove SO 2 from the straw boilers’ flue gas. The new pumps help to capture what would other- wise be wasted heat from its existing infrastructure and

This is a significant step forward for the utility, and for district heat suppliers everywhere looking to providemoreefficient, environmen- tally friendly heat. Traditionally, district heating net- works have relied on fossil fuel- sourced heat generation to supply consumers with comfort space and water heating. But with regulation

and costs growing, district heat plants are turning to renewable energy and innovative technology like electric heat pumps and heat recovery – to reduce their environmental impact and give consumers an affordable price. In this article, we will examine Ringsted DHC’s new system, and how implementing new heat pump technology has enabled the station to hit key heat efficiency and decarbonization goals. We’ll also explore how oil-free technology is paving the way for greener, more efficient district heating.

the outside air, and put it to good use – increasing COP, maximizing heat capacity, and further reducing its environ- mental impact. The first heat pump (HP1) recovers heat from the outside air, then heats up the district’s returning

flow to 57°C. This is mixed with water from the biomass boilers at 95°C, then sent back out via the district heating network.

Keeping Ringsted warm – and hitting decarbonization goals

But this was just the beginning. Ringsted DHC realized that the flue gas from the straw boiler was a significant source of wasted heat, and that this needed to be cooled significantly from its escape temperature of 120-140°C for the scrubber to be effective. So, it introduced a scrubber and two Geoclima heat pumps (HP02 and HP03) with a total 1000kW heat capacity, powered by Danfoss Turbocor oil-free compressor technology. These new heat pumps perform an important double job – recovering energy for the district, while also eliminating the need to provide the scrubber with an expensive external water supply. As a result, the overall system is efficient and cost- effective. Finally, the DHC wanted to recover heat from the new heat plant equipment room, the CHP, and the variable speed drives for the ambient air-sourced heat pumps (HP01). So it introduced an additional 350kW heat pump (HP03), using oil-free compressors, to recover a further 310kW from its equipment, put it to use for the city and further improve the plant efficiency.

Ringsted DHC delivers heat to the city of Ringsted across a 124kmdistrict heating network, withmost of the heat supplied from one centralized heating station. With the equivalent of 7,000 one-family homes to keep warm, heat needs to be transmitted safely, without interruption, and at the best price for the consumer. Before last year, the station generated its heat using two straw- fuelled biomass boilers a gas-powered Combined Heating and Power (CHP) plant, and a heat accumulator. This meant that 75% of its heat was generated from renewable sources. However, the DHC had also promised the city that its heat production would be 95% CO 2 free by 2020. What’s more, the exhaust gas from its straw-fired boilers contained harmful sulphur dioxide – as did the oxidization catalyst used in its gas- driven CHP. Nearly all (97%) of this needed to be removed. It was a significant challenge. But by making smart use of heat pumps to ensure no surplus heat goes to waste, Ringsted DHC has been able to meet its goals, while keeping its consumer heat prices low.

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