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Project Summary

The ERA-NET Bioenergy project “FutureBioTec” aimed to provide a substantial contribution concerning the development of future low emission stoves and automated small- and medium-scale biomass combustion systems (<20 MWth). The project focused on the further development of wood stoves towards significantly decreased CO, OGC and PM emissions by primary measures (air staging and air distribution, grate design and implementation of automated process control systems), the improvement of automated furnaces in the residential and the small to medium-scale (<20 MWth) capacity range towards lower PM and NOx emissions by primary measures (extremely staged combustion, utilisation of additives and fuel blending concerning new biomass fuels, development of a new combustion system for pulverized fuels), as well as the evaluation, development and optimisation of secondary measures for PM emission reduction for residential biomass combustion systems. According to the different working fields addressed, the project is structured into 4 work packages (WP):

  • WP1: Reduction of PM, CO and OGC emissions from wood stoves by primary measures.
  • WP2: Reduction of PM and NOx emissions from automated boilers by primary measures.
  • WP3: PM emission reduction by secondary measures - evaluation of existing particle precipitation technologies for residential biomass combustion systems.
  • WP4: Development of a specially designed condensing heat exchanger for simultaneous heat recovery and efficient particle precipitation.

In order to reach the aims of the project, a consortium of 9 internationally recognised R&D partners as well as 2 industrial partners from 7 European countries has been formed. The project which has been coordinated by the Austrian Competence Centre BIOENERGY 2020+ GmbH has been started in October 2009 and completed in September 2012. In September 2012 the results of the project have been presented at an international workshop in Graz to interested stakeholders (in total 67 participants from 7 countries attended).

Within the scope of work package 1 country reports regarding “Operational influences of hand-charged wood stoves” have been compiled by the partners involved. These country reports have subsequently been summarized in a report prepared by TFZ. In addition, comprehensive tests have been conducted by TFZ, BE2020 and UEF. At TFZ two chimney stoves with exactly the same firebox geometry and volume but with and without grate have been examined. The results show that the presence of a grate can be beneficial regarding gaseous emissions. Furthermore, an universal retrofit air control unit was tested at two different stoves. The results showed that the emissions were not reduced by the device. It was concluded that such units can only perform efficiently if they are an integrated part of a certain stove technology and not just an addon. At BE2020 different strategies regarding air staging as well as an automated control system were developed and tested. The development was accompanied and supported by CFD-simulations. The different measures applied led to a stepwise reduction of the emissions. Partner UEF, in cooperation with Warma-Uunit Ltd., performed combustion experiments using a hybrid masonry heater for both logwood and wood pellets. Finally a “Low emission operation manual for chimney stove users” and “Guidelines for low emission chimney stove design” have been elaborated based on the results gained within this work package.

Within the scope of work package 2 a summary report regarding the evaluation of existing data on air staging strategies has been compiled by BE2020, UEF and UmU. The report summarizes and evaluates available data regarding the influence of air staging on NOx and PM emissions for fixed bed biomass combustion. Furthermore, systematic experimental studies have been conducted by BE2020, UEF and Teagasc at different grate furnace systems (nominal power output between 35 and 180 kW) utilizing different biomass fuels. The results show that the clearest and strongest dependence on NOx emissions is given by the air ratio in the primary combustion chamber (PCC). The optimum regarding NOx emissions seems not to be fuel dependent (for a given technology) but technology dependent to a certain extent. Consequently, the optimum conditions have to be determined for a given technology with dedicated test runs and the process control should be adjusted accordingly. Moreover, NOx emissions increase with decreasing residence time in the PCC. The temperature in the PCC does not seem to be a relevant influencing parameter on NOx emissions within the range investigated (900 – 1,100 °C). PM1 emissions decrease with increasing volume flow through the fuel bed most probably due to lower fuel bed temperatures at higher air flows. The temperature in the PCC is also of relevance for the fuel bed temperature and has an influence on PM1 emissions which is more pronounced at low air ratios in the PCC. Based on the results design and operation concepts for low-emission biomass grate furnaces based on advanced air staging have been compiled.

Regarding the work performed on additives and fuel blending, a state-of-the-art report on “fuel additives and blending as primary measures for reduction of fine ash particle emissions” has been compiled in a first step. Furthermore, dedicated lab-scale (BE2020) and small-scale (Teagasc) test runs were performed using Kaolin additivation to softwood and straw as well as peat/miscanthus and peat/tall fescue fuel blends. The tests at BE2020 were accompanied by thermodynamic high-temperature equilibrium calculations. The results show that PM1 emissions decrease with increasing amounts of Kaolin additivation (up to a certain additivation ratio) and that peat addition reduced slagging tendencies as well as PM1 emissions for the fuels investigated. In addition, studies with small lab-reactors burning single-pellet samples have been performed by UmU and SP. In general, a somewhat higher release of K was seen in the single pellets tests compared to the K found in fine PM from the pellet burners. This is rather expected and presumably explained by "secondary" capture mechanisms in the fuel bed and also by losses on surfaces in the boiler/flue gas systems.

At IEn a new combustion technology for pulverized biomass fuels has been developed. In this respect investigations of fuel ignition and fuel combustion kinetics were performed using two drop tube furnaces and accompanying CFD simulations. In a next step a 5-15 kW and a 0.5 MW burner for pulverized biomass were developed and tested and subsequently the technology was upscaled to 20 MW. The results of the tests performed show that also in pulverized fuel systems air staging has a strong influence on NOx as well as TSP emissions.

Within the scope of work package 3 a survey on the present state in Europe regarding particle precipitation devices for residential biomass combustion (nominal boiler capacity <50 kWth) was compiled. Furthermore, a number of ESPs has been tested by the project partners, namely the chimney-mounted applications Ruff-Kat ESP (by TFZ), Oekotube ESP (by BE2020 and Teagasc) and the R_ESP (by SP) as well as the Al-top ESP (by Teagasc). Finally, the experiences made within the project group from the test runs have been summarized in the document “Guidelines for design and application of electrostatic precipitators for residential biomass combustion”.

UEF has developed a condensing heat exchanger for efficient heat recovery with fine particle reduction. Within the scope of work package 4, a scrubber unit was developed to assist in keeping the heat exchanger inlet as well as walls clean. The aerosol behaviour was simulated with a computational model. Forces affecting the particles were computed under consideration of thermophoresis, diffusiophoresis and Brownian diffusion. Furthermore, test runs have been conducted which show that the condensing heat exchanger generated 32 % and 36 % lower fine particle emissions when compared to the reference boiler cases. The prototype which was tested, is compact in size and has a high heat recovery potential combined with a certain reduction in particulate emissions. The system is especially suitable for low-temperature heating systems (floor heating) and for use with moist fuels, for example wood chips.

Concluding, the project “FutureBioTec” resulted in a considerable know-how gain regarding future low-emission small- to medium-scale biomass combustion systems.