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The vast majority of homes in Europe are heated by natural gas or oil. Switching to alternative, sustainable fuels – such as bio-oil made from farm and forestry waste – would significantly reduce greenhouse gas emissions and help to fight global warming.
In Germany alone, it has been calculated that altering just 10 % of the country’s old-fashioned boilers to run on bio-oil could cut carbon dioxide (CO2) emissions by around 5.5 million tonnes per year.
The goal of the EU-funded RESIDUE2HEAT project was to produce a useful liquid fuel from a wide range of waste biomass, which could be used in small-scale boilers to provide affordable, more sustainable residential heating.
The researchers took a two-stage approach. First, they searched for ways to improve liquid biofuel produced via a process known as fast pyrolysis. The challenge with this type of fuel – known as fast pyrolysis bio-oil (FPBO) – is that even the most advanced residential heating systems are unable to handle its inconsistent properties. Thus, the project team worked to produce a standardised product, regardless of the raw materials used to make it.
RESIDUE2HEAT then looked into adapting residential boilers to render them capable of burning this fuel.
‘Our novel FPBO-fuelled boiler meets most operational and environmental demands in the actual intended environment,’ explains project coordinator Herbert Pfeifer of RWTH Aachen University in Germany and scientific head of the OWI Oel-Waerme-Institut gGmbH, affiliated to the university. ‘And an environmental impact assessment has confirmed the positive impacts of FPBO heating compared to fossil alternatives, especially when it comes to reducing greenhouse gas emissions (80-94 %).’
Redesigning heating for homes
Using the fast pyrolysis process, waste biomass – such as wheat straw, forest resides, bark, elephant grass and clean wood – can be converted into bio-oil. Starting by modelling how FPBO breaks down and burns, the RESIDUE2HEAT team then used the resulting information to tailor the fuel to suit residential heating.
By ensuring consistency in the fuel’s chemical properties, such as water content, they succeeded in improving its stability and quality.
Next, they looked at adapting and optimising existing residential heating systems to enable the use of FPBO. A complex process, this required the redesign and manufacture of suitable burner components to optimise the burning of this fuel.
Typical components used in heating systems, such as pumps and fuel nozzles, were tested for their FPBO compatibility. Since so little was known about FPBO combustion, RESIDUE2HEAT researchers studied the fuel’s behaviour in laboratory-scale burners before scaling up the process.
Switch to biomass
The team has also completed a step-by-step roll-out plan for the use of FBPO in residential heating, interviewing gas, oil, and pellet heating system owners to ensure a positive public acceptance. Importantly, they have shown that the concept is cost-competitive with current fossil fuels without the need for incentives, making it economically viable.
‘Ashes recovered from the FPBO production process have great potential for providing soil nutrients and could therefore be recycled for agricultural applications,’ adds Pfeifer.
The team expect that their techniques for creating high-quality FPBO will offer a head start to other research programmes, such as the EU-funded SmartCHP project, which aims to develop small-scale units for producing heat and electricity from biomass.