Replacing natural gas with agrobiomass in Denmark reduces heating bills

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In Denmark, the successful deployment of district heating from agrobiomass sources enables the shift from fossil fuels towards renewables.

As part of the EU-funded project AgroBioHeat, two towns have made the switch and this has lead to a smaller heating bill for the end-users!

Creating savings to the heating bills of inhabitants of a small rural village in Denmark by switching the district heating from natural gas to straw

Ulbjerg is a 500 inhabitants village located in Central Denmark Region. A gas fired district heating system provided heat to the households and buildings of the village. Natural gas prices grew steady from year 2000, with important peaks more frequent, leading to very high energy bills for Ulbjerg inhabitants in 2010. Conscious of the situation, Ulbjerg Kraftvarme Amba (CHP) applied to obtain support of the Danish rural development program to explore the alternatives to natural gas. Rambøll, one of the most acknowledged consultancy companies in Denmark, performed the work.

Among the energy sources considered (solar, biogas, straw, wood pellets, wood chips, and bio oil) straw was the most economic option (considering both investment and operating costs). At that time, driven by the high prices of natural gas, the Danish government had already published a new regulation where CHP plants above 1 MW were legally allowed to use straw.

It was not till 2014 when certain plants under 1 MW were also allowed; then Ulbjerg Kraftvarme decided to convert from natural gas to straw and wood chips: since both biomass sources had proven over the years to not be influenced by cyclical economic fluctuations and crises, and independent of natural gas prices. The plant was built in 2016 and has caused a significant reduction of heating bill for Ulbjerg inhabitants.

The biggest challenge for Ulbjerg Kraftvarme Amba in the transition from natural gas to biomass has been the change of routines and getting familiar with straw logistics. The boiler is automatic, though ash removal and other checking requires a person to be present few hours twice a week. The REKA boiler is flexible and in case of a biomass shortage it can burn also other agricultural residues or biomass types (up to 30% moisture).

From the side of the Ulbjerg inhabitants, the solution was welcomed, and no social reaction was evidenced. They were informed about the choice and invited to visit a boiler similar to the one selected.

Download the factsheet here.

A Danish town supplements heat from solar panels using a straw boiler and almost phases out natural gas in the district heating system.

Ørnhøj is a town of 738 inhabitants (as of 2022), belonging to the Herning Municipality in Central Jutland Region of Denmark. Until recently, the district heating network of the town (serving 474 customers) was operated primarily with natural gas. In 2015, the district heating plant was acquired by Vildbjerg Tekniske Værker (Technical Works) which embarked on a process of modernizing and improving the overall operation.

Already in 2012, a new solar panel installation covering an area of 5,000 m 2 were installed. Solar energy can provide part of the heat demand of the municipality, but they are not sufficient for the winter months. Therefore, a decision to substitute natural gas by a new straw fired boiler was made.

Construction of the new straw boiler was finished in summer 2017, with the plant entering operation for the first time in the 2017 2018 heating season. A large, 2,500 m 3 storage facility was built next to the solar panels. The storage can house around 600 large square straw bales, which are equivalent to 25 days of heat production. In total, the plant is consuming around 4,000 straw bales per heating season. Straw is supplied in competitive prices by various local providers.

The main equipment for the straw heating plant was provided by Danish manufacturer LINKA, a company with significant expertise in straw combustion. A double shredder is installed in the straw storage area and the shredded straw is transferred with a 30 meter conveyor to the boiler. The boiler itself is fully automatic, with 5 passes ensuring high efficiency and complete burnout. An automatic ash extraction system to an ash storage room is installed, while a bag house filter ensures very low dust emissions to the atmosphere.

Through the installation of the straw fired boiler, the inhabitants of Ørnhøj now get 70 % of their heat from carbon neutral biomass; around 20 % is supplied by the solar panels and only the remaining 10 % by natural gas.

Download the factsheet here.

About AgroBioHeat

The Horizon 2020 funded project AgroBioHeat “Promoting the penetration of agrobiomass heating solutions in European rural areas” aims to produce a mass deployment of improved and market-ready agrobiomass heating solutions in Europe. Agrobiomass is a large, underexploited, and indigenous resource, which can support the achievement of the European Energy and Climate targets while promoting rural development and circular economy.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 818369.

About the campaign

The campaign is powered by Bioenergy Europe and relayed across Europe by both national and international partners supporting the belief that bioenergy is more than a renewable energy source, it is also a reliable path that will lead Europe to achieve its renewable energy transition in the shortest span of time.

Solid Biomass Conversion Processes

Logging, grinding, screening and drying operations are mechanical processes for enhancing solid biomass fuels. These operations help transform biomass into homogeneous fuel that is easy to handle, with a higher energy recovery (eg. woodchips, wood logs, agrofuel). In general, moisture content in woodchips used for energy generation in municipal or industrial plants ranges between 20-30%.

Densification is another popular way to transform woody material into an advanced fuel with high calorific value. This process involves compressing biomass and lowering moisture levels to a range of 8-10%, allowing for an homogenous fuel – either in the form of pellets or briquettes. The heat during compression fuses the lignin in the biomass, naturally binding the biomass together in a new, enhanced shape. Thanks to densification, the homogenous biomass fuel is easier to transport and can be used in automated biomass installations, such as pellet stoves and boilers.

Thermo-chemical conversions are now used to produce fuel with even higher calorific value, utilising torrefaction or steam explosion technologies. During the torrefaction process, wood is subjected to temperatures of 230°C-300°C at atmospheric pressure without oxygen. Comparable to some extent to coffee torrefaction, this method creates a fuel with unique characteristics. As compared to conventional wood, torrefied wood has very low (>5%) moisture content, is easily grindable and is relatively hydrophobic.

Thanks to advanced technologies, woody biomass can also produce liquid and gaseous fuels. Pyrolysis, for instance, is a thermal-chemical conversion that requires a high temperature (>400°C) and little oxygen to convert solid biomass into gas, liquid fuels (pyrolysis oil) and/or biochar. Gasification is another thermo-chemical conversion that takes place at high temperatures (>800°C), with limited oxygen and/or steam, and converts solid biomass into synthesis gas, known as syngas – which contains carbon and hydrogen and can be used to produce liquid fuels such as biodiesel.

Wet Biomass Conversion Processes

Wet biomass is present in high volume across Europe (manure, agricultural waste and by-products). As it contains too much moisture to be converted efficiently into energy via a direct combustion process, other conversion pathways and energy outputs have been developed by the biogas (eg. anaerobic digestion) and biofuel sectors (eg. fermentation). Anaerobic digestion and fermentation are the two main conversion pathways used for converting wet biomass feedstock into advanced fuel.

Anaerobic digestion is the microbiological process of decomposition of organic matter, in the absence of oxygen, and is common to many natural environments; it is largely applied today in order to produce biogas in airproof reactor tanks, commonly referred to as digesters. A wide range of micro-organisms are involved in the anaerobic process which has two main end products: biogas and digestate. Biogas is a combustible gas consisting of methane, carbon dioxide and small amounts of other gases and trace elements. Biogas can be used in direct combustion to produce heat, but also power if converted within a cogeneration plant or in adapted gas motors. Biogas can also be upgraded via purification processes to a biomethane that can be injected into the existing natural gas networks, used as a chemical product and/or vehicle fuel. Digestate is the decomposed substrate, rich in macro- and micro-nutrients and therefore suitable for use as plant fertiliser.

Fermentation is a biochemical conversion whereby microorganisms, including yeast and bacteria, convert matter into products such as ethanol and liquid transport fuel (biodiesel). This process is done in several stages. First, sugary and starchy feedstock such as corn must be crushed and combined with water, allowing enzymes to convert this starch into sugar. This ferments along with the addition of yeast and is distilled into bioethanol. Bioethanol can also be produced from cellulosic biomass, such as grass, wood and stalks, via fermentation; however, this process is more complex and involves a mechanical pre-treatment and the addition of enzymes, or the breakdown of the lignocellulose into sugar through hydrolysis, followed by the same procedure.

Solid bioenergy feedstock

Renewables represent 8,0% of EU-27 total energy consumption (22.473 kilotonnes of oil equivalent) in transportation, of which 68% is provided by biofuels in 2018. It is rather challenging to foresee how biofuels (in particular first-generation biofuels) will continue to develop, since recent EU legislation established a quota for these biofuels. EU statistics on renewables in transportation can also be misleading regarding the actual level of production, because multiple counting rules are applied in accordance with the EU renewable energy directive. Looking at it in more detail, the biofuel market is driven by biodiesel and bioethanol. Biodiesel was the first biofuel developed and used in the EU in the transport sector in the 1990s. EU-27 remains the world’s largest biodiesel producer and it consumed 13,303 Ktoe in 2018. By comparison, bioethanol consumption in 2018 reached 2,620 Ktoe for an actual production of 2,365 Ktoe (Biofuels Report, 2020).

Bioenergy comes in all shapes and sizes

Within our close environment, a great source of organic materials such as plants, algae, or organic wastes, can be valuable fuels as soon as a technology makes it possible to efficiently extract all of its energy potential. Bioenergy players traditionally refer to biomass to describe those usable feedstocks. Biomass currently used in Europe includes wood from forests, agricultural crops and residues, by-products from the wood and agricultural industry, herbaceous and woody energy crops, municipal organic wastes and manure, and could potentially integrate algae and marine biomass in the future.

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