"Wood is a fuel for eternity, being the most widely used kind of biomass for supplying heat and domestic hot water in households," states Dr.-Ing. Mohammad Aleysa, leader of the working group 'Exhaust Systems' at the Fraunhofer Institute for Building Physics IBP. "Any effort that contributes to advance the development of suitable and improved combustion technologies is worthwhile to be undertaken. There is a growing tendency to prefer wood over other fuels due to increasing prices for fossil energy carriers and, above all, due to the energy turnaround in Germany." Unlike fossil energy carriers, wood releases only the amount of carbon dioxide it had previously incorporated during growth. "This fact theoretically makes wood a CO2 neutral source of energy," as Aleysa underlines, "but it takes advanced technical systems to bring to bear the environmental advantages in the combustion area."
Despite being carbon neutral, the use of biomass as an energy carrier has its drawbacks, too. According to the German Federal Environmental Agency (UBA) residential combustion sources are emitting particulate matter and many gaseous pollutants like carbon monoxide (CO), volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs), which are associated with noxious effects. In 2012, about 24,000 tons of dust were emitted from domestic chimneys, stoves and boilers to be released into the atmosphere.
"There are three key factors," says Aleysa, "which determine the efficiency and the pollutant emission of combustion sources: the combustion technology, the fuel, and the user." Requirements on combustion technology as the first factor of influence have been defined and specified in the respective test standards. Here, engineers continue to puzzle out improvements and further refine methods. The German Federal Immission Control Ordinance (1. BImSchV) specifies the parameters for the fuels used. Merely user behavior has not yet been subject to controls or regulations. In the course of their investigations, Aleysa and his team of scientists found that it was very difficult to ensure correct operation of the furnaces, even though advanced combustion technologies and fuels perfectly suited for combustion were used. In plain text this means: there is further potential for minimizing pollutant emissions, namely regarding user behavior. Dust emissions from incomplete combustion are mainly due to obsolete technical systems and handling errors. It is up to the user to ensure high thermal efficiency (which is a key prerequisite for minimized pollutant emission), for instance by using only well-dried wood or by providing sufficient supply of combustion air in the burning phase.
Aleysa acts one step ahead. In his opinion, the consistent and continuous monitoring of small combustion systems will provide opportunities to contribute substantially to establishing efficient and environmentally compatible energy supplies from biomass. A sophisticated combustion technology involving intelligent systems is to minimize the influence of user behavior and to ensure that the firing plants will work faultlessly. Operating errors will then belong to the past – optimizing operations and minimizing pollution are the goals for the future. A project designed by Fraunhofer IBP takes up this idea, doing research on this unique innovative system. The principle of this so-called "Monitoring and Emission Assessment System for Biomass Boilers" (iÜBS) is based on the application of new gas sensors, which are combined with the control of the firing plant. This involves not only controlling combustion quality and pollutant emission - special attention is also given to the mode of operation. For instance, this includes assessments regarding the quality of the fuel and the user-friendly operation of the system or the efficiency achieved. By analyzing the emissions, the plant also records polluting mistakes like burning wet wood or even garbage in residential combustion sources. If combustion is not optimal, immediate counter-measures can be taken. This environmental and economic approach can only be implemented, however, if the user can be convinced of the advantages. Technology is to relieve and support users, who should just enjoy watching the fire burn.
In the scope of further research activities of the "Heating and Chimney Systems" group two innovative combustion concepts were designed, which are suited for both biomass-fueled single-room combustion plants and for centralized boilers (like gasification boilers and wood chip firing systems). These combustion concepts are intended to advance the combustion and emissions performance such that present and future emission requirements of the 1st BImSchV will be met without taking any secondary measures. The tests that were performed at Fraunhofer IBP promised a successful outcome. Partners from industry and science are welcome to join in the above described research projects, which are still at a planning stage.
Fraunhofer IBP's Heating Systems researchers are not only focusing on the development of low-emission combustion technologies, but also on the use of waste gas products. In a current research project the parallel supply of heat and CO2 to greenhouses is being investigated, where carbon dioxide is used as a fertilizer: In addition to light, water and supply of nutrients it fosters optimum plant growth. This involves the application of an innovative, high-modulation technology: flameless combustion ensures equal zero-emission, i.e. practically no pollutants will be released during the burning process - which closes the cycle of a sustainable, optimal energy supply based on biomass.
(schw)
Fraunhofer Institute for Building Physics IBP
