CO and dust reduction with catalytic converters integrated into the combustion chamber

Blue Angel for wood-burning stoves; catalytic converters are an important tool here

. The Blue Angel eco-label will be introduced for wood-burning stoves in 2020
. With the introduction of the Blue Angel eco-label, there are criteria for particularly low-emission stoves. Among other things, special requirements are set for CO, VOC and dust emissions.
If these emissions are undercut and if manufacturers of wood-burning stoves have this confirmed by accredited testing bodies, then the user can be sure of purchasing an environmentally friendly stove that can be operated cleanly for many years.

In order to efficiently reduce CO and VOC emissions from the emissions of such stoves, appropriate aids such as catalytic converters are needed.
CO and VOC can react by combining with oxygen to form CO2. When wood is burned, only as much CO2 is released as the tree has stored during its growth.
CO compounds are weakly reactive molecules that can only react with oxygen at very high temperatures. The exhaust gases in stoves cool down very quickly after the combustion chamber and then leave the stove via the exhaust pipe on their way to the chimney. Therefore, a reduction of CO / VOC can only take place in a very hot environment. In the case of stoves, this is the combustion chamber, where the temperatures are high enough for the CO to react with oxygen. By adding secondary and tertiary air and also by installing flue gas baffles, one can support the reaction of CO / VOC with oxygen in the combustion chamber. However, due to the flow velocity of the exhaust gases in the combustion chamber, no sufficient reaction takes place between CO or VOC and oxygen. The CO compounds flow to the exhaust pipe without sufficient reaction with oxygen and leave the hot zone of the combustion chamber.

It is precisely this problem that the Blue Fire catalytic converter for wood-burning stoves addresses. Thanks to the catalytically active coating specially developed for wood burning, the Blue Fire catalytic converter provides the already cooled flue gas with a reaction surface downstream of the hot combustion chamber and it enables CO or VOC and oxygen to react to form CO2 in a downstream phase. The CO compounds flow through the Blue Fire catalyst on their way to the exhaust pipe. In the process, the activation energy of the CO molecules is reduced so that CO or VOC is ready to absorb oxygen, although the corresponding temperature of the exhaust gases is already too low. The specially developed catalytic surface of the Blue Fire catalytic converter is responsible for this renewed readiness to react, into which, depending on the application, different precious metal components can be incorporated. Through the contact of the exhaust gas with the surface of the Blue Fire catalyst, a large proportion of the CO compounds present are converted to CO2. A prerequisite for this is the presence of oxygen, which the CO compounds need as a reaction partner. In addition, Blue Fire catalytic converters must be installed in such a way that the exhaust gases flow slowly into the catalytic converter to ensure a long reaction time of the exhaust gas with the catalytic converter surface.
Legislation requires the installation of a bypass in case the catalytic converter would be blocked. When designing and positioning the bypass, it is very important to ensure that the exhaust gas does not flow directly through it. Exhaust gas that escapes directly through the bypass cannot participate in the reaction at the catalytic converter.

In addition to these gaseous oxidisable pollutants, there is also the problem that dusty pollutants are emitted. Up to now, it has been possible to reduce dust emissions by up to 20 % through oxidative catalytic degradation at the catalytic converters without adapting or modifying the firing system. Blue Fire GmbH's solution therefore provides for a multi-stage catalytic system that can significantly reduce both dust and gaseous emissions.
In the first stage, the particles with a high soot content are first retained. In the next stage, a part of the carbonaceous components is oxidatively decomposed in stage 1 and then discharged again by the flow from stage 1 in order to prevent blocking of stage 1. In the second catalyst stage, the gaseous pollutants CO and VOC are reduced.

In order to significantly increase the dust reduction of integrated catalytic converters in wood fires, a two-stage catalytic converter module developed by the company Blue Fire GmbH was integrated in a simple and high-emission stove of the lower price segment and tested by the DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH under simulated natural draught conditions. With this two-stage catalyst module, the pollutants carbon monoxide (CO) were reduced by more than 80 %, hydrocarbons (VOC) by 50 to 70 % and dust by more than 50 %.

The two-stage catalyst module is available at a reasonable price and can be adapted to various different stove models.
The measurement data is freely available for download at https://data.mendeley.com/datasets/2xcp6rytgw/1 and was presented at the 9th Separator Expert Meeting on 21.03.2018 in Leipzig.
Blue Fire GmbH
Blue Fire GmbH, based in Saterland-Ramsloh, was founded in 2015 as a joint venture between the companies ETE EmTechEngineering GmbH from Leipzig and Emission Partner GmbH & Co. KG from Ramsloh, was founded.
Blue Fire GmbH develops and sells catalytic converters for all types of wood combustion systems. Blue Fire catalytic converters are manufactured in the production facility of the parent company Emission Partner GmbH & Co. KG in Ramsloh. Due to the two parent companies, Blue Fire GmbH has in-depth knowledge in the fields of combustion technology, combustion chemistry, emission reduction technologies as well as catalyst technology and catalyst manufacturing. The shareholders of Blue Fire GmbH have acquired their in-depth knowledge through many years of professional experience in positions at research institutes, the automotive industry and in heating technology.
We advise our customers from the initial idea, through the calculation of the catalytic converters and the determination of the integration measures, right up to design support and the selection of materials or, with pleasure, right up to obtaining a type approval. Our customers and their products are always the focus of our actions. Our engineers support our customers in word and deed and accompany the emission reduction measures until the product has been successfully type-approved. Laboratory tests and long-term tests on our own or external test benches are naturally also part of our range of tasks. We provide proof of the catalytic converter function in accordance with standards and provide evidence of this.

Original article:Blue Angel for wood-burning stoves; catalytic converters are an important tool here.