Cement plant supplies 25 percent of district heating in Aalborg: “We could supply 50 percent”

In 2020, Aalborg Forsyning and Aalborg Portland began an expanded collaboration for the utilization of the cement plant’s surplus heat. Illustration: Aalborg Forsyning

In northern Jutland, we find Aalborg Portland, which as the country’s largest CO2 emitter is well aware that its surplus heat can actually be useful.

“We have installed a system on our white kiln line that collects the flue gas that would otherwise have been released into the atmosphere. Then we added a combined flue gas cleaning and heat recovery system. It removes, among other things, sulphur from the smoke, and then it collects the heat,” says Søren Lausen, production director at Aalborg Portland.

From there, the heat is sent on to Aalborg Forsyning, which uses for district heating. In addition to the white kiln line, Aalborg Portland also has a production line for gray cement that does not have such a system today:

“We supply about 1500 TJ—that is about 25 percent of the district heating in Aalborg. If we installed a similar system on the gray line, we would be able to supply twice as much of the surplus heat to the district heating network,” Søren Lausen says.

Aalborg Portland is in dialogue with Aalborg Forsyning about utilizing the surplus heat from the gray line as well, but the temperature of the flue gas represents a problem for phasing out the heat from the coal-fired power plant, Nordjylland Power Station, which is located on the other side of the fjord.

The cement kilns at Aalborg Portland which supply part of the surplus heat to Aalborg. Illustration: Aalborg Portland

“The excess heat we supply is about 65 to 75 degrees Celsius. If we were to replace the Nordjylland Power Station, the surplus heat would be a bit too cold, but it can be used as a stepping stone to heat pumps that can increase the temperature enough to be used for district heating.”

In order to be used for district heating, the flue gas must be over 80 degrees Celsius. Here we find another example of the lacking incentive structure: Aalborg Portland does not want to install a heat pump itself, as this would mean that the company would become a district heating provider instead of a company that supplies surplus heat to the district heating network. And that would mean that they would have a different level of responsibility and be taxed higher.

From Leca blocks to district heating

If we head south to Hinge between Randers and Hadsten, we find the headquarters of Leca, a company that produces building materials from clay. An energy-intensive process that requires combustion at up to 1150 degrees Celsius. At the same time, it generates 200 GWh of surplus heat per year.

Right now, the heat is going to waste, but it is not because of Leca’s unwillingness to take advantage of it. In 2017, the company installed a system for flue gas cleaning, which enables the utilization of surplus heat.

“But as it is today, it’s just wasted away,” says Mogens Meiniche Madsen, plant manager at Leca Denmark.

Leca and Aalborg Portland are just two of the many Danish companies with an abundance of surplus heat.

According to an analysis on green conversion of the heating sector carried out by the Aalborg University, it would already be possible for the industry to deliver between 3.2 and 7.2 TWh per year if the framework conditions allowed it. In practice, however, there are often a number of obstacles that make it difficult to utilize the surplus heat—and this is also the case at Leca.

This week, the Confederation of Danish Industry for Energy (DI Energi) published a current analysis of the potential for surplus heat together with consulting company Rambøll. They estimate that there is a potential of 3 TWh per year, which is in line with Aalborg University’s low-end scenario of 3.2 TWh per year.

In the analysis, DI Energi points out that the framework conditions for utilizing surplus heat are today better than they have ever been. Until 2021, the tax was 33 percent of the total remuneration, but it has now been reduced to DKK 25 per GJ, with the possibility of being exempted from the tax if the company is certified by the Danish Energy Agency.

Aalborg Portland’s plant conducts surplus heat from “kiln 87 clinker cooler” to kiln 76. Illustration: Aalborg Portland

This is recognized by Mogens Meiniche Madsen, plant manager at Leca, who also believes that the new tax rates will make it more attractive to utilize the surplus heat:

“If we are to supply district heating, then it requires an extra investment of between DKK 80 and 90 million and an extension to be able to extract the heat and send it over to the district heating network. And so far, there have been some tax structures that have stood in the way of those investments, but some changes have been made recently that should help move them along,” Mogens Meiniche Madsen says.

Bad business case

In connection with “IDA’s Climate Response 2045”, Aalborg University has prepared the analysis “Heat Plan Denmark 2021”, which examines which heat sources should constitute the sustainable heating sector of the future.

In 2021, industrial surplus heat accounted for 1.2 TWh per year of the district heating supply, corresponding to about 3 percent of the total supply of 27 TWh per year last year. If the entire estimated potential of the industry’s surplus heat was utilized, which according to the analysis is 6.8 TWh per year, it could cover more than 25 percent of the total district heating demand.

Henrik Lund, professor in energy planning at Aalborg University and one of the authors behind the analysis, says that several things have stood in the way of better utilization of surplus heat. Specifically, he points to three factors:

“In many cases, the taxes were a showstopper for utilizing surplus heat because they made it expensive to send surplus heat to the district heating network,” he mentions first.

Danish Crown tells Ingeniøren that the taxes are precisely the reason why the company does not deliver to the district heating network. The system required to be able to send heat to the district heating network would simply take too long to be depreciated.

In addition, Henrik Lund points out that much of the surplus heat that comes from industry does not have a sufficiently high temperature to be used as is in the district heating network:

“Some surplus heat has low temperatures that require a heat pump to make it usable for district heating. Today, the heat must be 80 degrees Celsius when it’s sent out into the network. And it’s not always that temperature when it comes from the industry,” he says.

The third thing that Henrik Lund points out is a lack of motivation from a political point of view. But now the green transition has put focus on the surplus heat potential as a replacement for the combined heat and power plants that are currently being phased out, such as the coal-fired Nordjylland Power Station.

Uncertainty may be the explanation

Better utilization of surplus heat is a good idea from a climate perspective, but it may be subject to some uncertainty. According to Marie Münster, professor in energy planning at DTU, this is a difficult trade-off:

“There’s a bit of a dilemma here,” she says and elaborates:

“It’s a very costly investment to make. And at the same time, there can be a great deal of uncertainty about how long the company in question or the source of surplus heat will exist, and whether the investment will pay for itself.”

For example, as mentioned, Leca estimates that it would cost the company between DKK 80 and 90 million to build the necessary infrastructure to be able to supply district heating to either Hadsten or Randers Municipality.

Ingeniøren has tried to get a comment from Minister for Climate, Energy and Utilities Dan Jørgensen (S), but the ministry did not respond to the inquiry before the newspaper’s deadline.