Heat and power plants are being converted from coal to biomass, especially in Northern Europe. President Obama’s Clean Power Plan will probably enhance the transition process in the United States. However, going green also poses its challenges.
Beginning in 2016 most ships docking at Avedøre Power Station located in Denmark will no longer carry coal but wood pellets instead. The Avedøre plant, located just south of the Danish capital 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 accelerate in the coming years.
“The project’s scale, energy efficiency and safety requirements demonstrate that Denmark has a headstart on using biomass as a resource,” says Thomas Dalsgaard, Executive Vice President of DONG Energy, which owns the Avedøre Power Station.
Like hydroelectric power, biomass is a renewable form of power that can be generated as baseload power. Because biomass is not intermittent like wind or solar, it poses fewer operational or technical challenges to the grid, thus better ensuring grid reliability without accompanying significant expenditures on transmission.
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.
Most large-scale bioconversions are taking place in Northern Europe, especially Denmark, the UK and the Netherlands. The EU has issued non-binding 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 one of the most immediate steps that utilities can take to cut their carbon dioxide emissions.
Bioconversion has the potential to play a significant role in President Obama’s Clean Power Plan, which calls for a 32% reduction in carbon emissions from the power sector from 2005 levels by 2030.
Thus far, bioconversions in the United States have typically involved projects that modify coal-fired boilers to also burn wood chips. Energy companies see co-firing technology as more economical and practical 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’s power division. DONG Energy hired Ramboll to handle the conversion at the Avedøre and Studstrup power stations. Headquartered in Copenhagen, Ramboll is a leading engineering, design and consultancy company with 13,000 experts and an established presence in Europe and the United States.
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 do damage.
Another challenge is to retrieve as much energy from wood pellets as from coal. When the bioconversion is completed, the Avedøre Power Station will have the same energy capacity with pellets as it once had with coal. In addition, by utilizing 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 kWh produced.
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 modernizing 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.
Amid the transition to greener power, power plants will increasingly need to be able to modify their fuel source. The Avedøre Power Station provides an excellent example of how this can best be accomplished.
