Greening energy plants
Green transition 23 January 2018 Jacob Thysgaard
Heat and power plants are being converted from coal to biomass, especially in Northern Europe. However, going green also poses its challenges.
From 2016 most ships docking at Avedøre Power Station no longer carry coal but wood pellets instead.
The Avedøre plant, located just south of Copenhagen, supplies district heating to more than 200,000 households in the Greater Copenhagen area and power to meet the annual consumption of 1.3 million households. The plant is making the transition to biomass, a move that will reduce its CO2 emissions by about one million tonnes per year.
The switch from fossil fuels to renewables is one of the world’s largest scale bioconversions of a heat or power plant to date, heralding a trend that is likely to pick up speed in the coming years.
“The project’s scale, energy efficiency and safety requirements demonstrate that Denmark has a head start on using biomass as a resource,” says Thomas Dalsgaard, Executive Vice President of DONG Energy/Ørsted, which owns the Avedøre Power Station.
“We have to keep developing the experience we gain and make our solutions more attractive to other countries in their transition to greener energy,” he continues.
Forbes Magazine’s energy expert, Ken Silverstein, agrees. In a recent article titled “Biomass Breathing New Life into Coal Plants”, he concludes that “large-scale power facilities are determined to make the technology both workable and profitable.”
Biomass also has its critics. Their greatest concern is that cutting down a greater number of trees will leave fewer to absorb carbon emissions. Newly planted trees, meanwhile, are unable to absorb carbon as rapidly as older ones.
The green NGO World Wide Fund for Nature (WWF) maintains that since biomass is a limited resource, it must be produced sustainably. To this end, governments should primarily invest in expanding other renewable energy technologies like wind and solar power, according to Hanne Jersild, Senior Advisor on Climate & Energy Policy at WWF.
However, she emphasises that some countries may need to use biomass during the transition period.
"This is why it makes sense in Denmark to convert the large coal-fired plants to biomass as we transition to a fossil-free energy system,” says Hanne Jersild.
Co-firing the most immediate step
Most large-scale bioconversions are taking place in Northern Europe, especially Denmark, the UK and the Netherlands. The EU has issued nonbinding criteria for biomass, because, as the EU Commission writes on its website, “increasing the use of biomass in the EU can help diversify Europe’s energy supply, create growth and jobs and lower greenhouse gas emissions.”
The USA also boasts some bioconversion examples. According to the US Department of Energy, the co-firing of biomass and fossil fuels is the most immediate step that utilities can take to cut their carbon dioxide emissions. Thus far, bioconversions in the USA have typically involved projects that modify coal-fired boilers to burn wood chips as well. Energy companies see co-firing technology as the most economical and easier to use than bioconversions that completely exclude coal.
The bioconversion at Avedøre Power Station certainly poses challenges, but the hurdles can be overcome, stresses Jacob Thysgaard, Chief Project Manager at Ramboll Energy. DONG Energy/Ørsted asked Ramboll to handle the conversion at the Avedøre and Studstrup power stations.
The most pressing problem is that wood pellets can spontaneously combust and explode if wet. So they are kept dry inside gigantic silos, safely protected against the Scandinavian climate. In the unlikely event that the pellets get wet and a fire erupts, the silos have also been redesigned to direct the flames where they cannot harm people or the construction.
The lifetime is extended
Another challenge is to retrieve as much energy from wood pellets as from coal.
“The biomass process involves more tonnes of material, so we had to redesign the entire transport system – bearing in mind that the dust had to be kept at a minimum, as it can also cause explosions and fires,” Jacob Thysgaard explains.
When the bioconversion is completed, the Avedøre Power Station will have the same energy capacity with pellets as it once had with coal. By utilising the excess heat from power production for district heating, the plant achieves an overall energy conversion efficiency of up to 97%, resulting in better fuel economy and a lower CO2 emission per produced kWh.
As part of the bioconversion, the plant’s lifetime will be extended by 15 years, thus enabling it to operate until 2033 instead of 2018. Extending the lifetime of a plant saves both time and money. In Europe, building a new thermal power plant typically costs about EUR 700 million, while modernising and refurbishing an existing plant runs to just under EUR 150 million. Moreover, an existing plant takes less than two years to refurbish, while a new plant can take as long as five years to construct.
More efficient energy plants
Currently, approximately 85% of the world’s energy consumption comes from fossil-fuelled power plants. The plants face the challenge of having to reduce their environmental footprints, and the global challenge is to ensure that new and existing power plants are as energy efficient as possible.
In Denmark, optimising existing coal-fired power plants is one solution that significantly improves efficiency rates. The efficiency rate of the average power plant is below 40%. The Nordjylland Power Station in Denmark, however, uses 94% of the energy in fuel, exploiting high pressure, extreme heat and optimised processes to attain the highest coal fuel efficiency rate in the world. Like Avedøre, Nordjylland is a Combined Heat and Power (CHP) station that is close to a big city, so the surplus heat can be used for district heating.
To keep pace with the green transition and other developments, energy plants must often also be capable of swiftly changing between the fuels that are currently politically and economically viable, whether coal, natural gas, oil, straw or wood pellets.
Written by Michael Rothenborg.