SEAWATER REPLACES COAL

In 2018, the Danish parliament decided to phase out coal in Combined Heat and Power plants (CHP) by 2030. However, it was not fast enough for Ørsted, the owner of the CHP plant in Esbjerg.

By Claus A. Nielsen, Business Development Director, DIN Forsyning

They wanted to phase out the coal in 2023 already – even though the CHP capacity was 300 MW district heating (DH) – equivalent to half the DH in Esbjerg, and two smaller villages. The other half of the DH was supplied by the local waste incinerator. In total, about 130,000 inhabitants are living in the distribution area.

In Denmark CHP for DH was mandatory by law – for 30 years.
– The mandatory CHP was introduced at a time when large amounts of heat from electricity generation was wasted. The cogeneration was a good idea then because it ensured the efficient use of coal and gas, needed for both electricity and heat production. Now we have good alternatives for renewable electricity generation. CHP production should not be mandatory anymore but planned separately, says business development manager Claus A. Nielsen from DIN Forsyning (DIN Utility).

Smaller units create new opportunities

Claus A. Nielsen and DIN have launched a plan for converting the coal based heat production to sustainable heat production.
– We will combine many small and different solutions, linked to a central distribution network. It provides a flexible electricity powered utilization of surplus heat from waste incineration, local industry, wastewater treatment, seawater, future data centers, and eFuel plants.

It is a modular solution, as each part is only used, when reasonable – economically and environmentally. When the wind blows and electricity is supplied from wind turbines, the heat pumps start, or when industrial production is high, surplus heat is utilised. As the electricity in Northern Europe becomes more based on wind, water, and solar, balancing power is even
more important.

The next generation must be modular and hybrid DIN believes “modular” is the right solution for the next DH generation. Instead of a few large units, Claus A. Nielsen believes the heat should be supplied by several smaller sustainable units. DIN’s plan involves a new seawater heat pump too – the largest in Denmark with a capacity of 50 MW.

The overall production system will include a new biomass heat plant, electric boilers, gas boilers, and surplus heat. The goal is the optimal utilization of surplus heat, perhaps containing new seasonal storage capacity and brand-new technologies.
– The “modular” idea requires planning, but it allows us to implement sustainable energy easier – even if just small heat sources. To be ready when the coal fired CHP plant closes in 2023, we had to use well-known technologies, less sustainable than desired. But we will phase them out when possible following the changes in the entire energy system. An important design parameter is to have investment flexibility thus minimizing the risk of stranded costs. The next generation
of DH will be hybrid and decentralized solutions.

Seawater replaces coal

In September 2023, the work begins in the port of Esbjerg. Construction of a large seawater heat pump station. A biomass heat plant will follow, replacing the coal-fired CHP for DH.
– We don’t want to build one large unit depending on for the next 30 years. We only have a short deadline, and after September 2023, there is just no more heat coming from the CHP plant, says Claus A. Nielsen, and continues.
– The opportunities we had, time and legislation considered, we decided to build a biomass heat plant and a seawater heat pump with 50 MW DH capacity.

A mile of pipe is supplying water

Even though the seawater heat pump (HP) location is in the port, it needs to get the water about a mile away.
– During the design phase, we became aware of the importance of placing intakes and outlets far from each other – avoiding cold water outlets mixing with hot water intakes. Pumps run 4,000 liters per second! By placing them far apart, we prevent the water in the port from freezing in winter when the temperature falls and the pump runs at full power.

The HP system is electrically powered and produces DH by cooling the seawater at a maximum of 4oC locally at the outlet. It is planned to operate from September to May, provided the right electricity price and temperature conditions for running the HP at the lowest possible production costs. In the case of shut down at the local waste incinerator, the heat pump can supply all the heat for DH from June to August.

The future must be green

Although DIN can meet the demands of today with their new construction, they do not stop finding green alternatives for DH.
– We want to bring the modular idea to life. After all, waste incineration may not cover 50% of DH needs in the future. So, we talk to local businesses and the local wastewater treatment plant about using their surplus heat.

Likewise, if any new data centers show up in our district. All of us try to act according to sustainability, but circumstances can force us to act otherwise to replace a large supplier in a short time. The modular idea is good for the environment and also for the security of supply, concludes Claus A. Nielsen.

In total, DIN expects to invest more than DKK 1 billion (130 million €) in the green transition within the next 5 years.