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Round robin test of a wood stove: The influence of standards, test procedures and calculation procedures on the emission level
Abstract
As a part of the IEA Bioenergy, Task X-Conversion, Combustion activity, an international round robin test of a wood stove supplied with a catalytic afterburner (JØTUL 3TDCI-2) has been performed to investigate and compare the emission level of CO, particles/tar, hydrocarbons and NOx. The participating countries were Austria, Canada, Denmark, Finland, the Netherlands, Norway, Sweden. U.K. and U.S.A. The wood stove was tested according to national standards and test procedures. In addition, a comparison of the calculation procedures used to convert measured transient volumetric emission levels into average emission levels in g/kg dry fuel was performed, based on both arithmetic and weighted averaging. The results uncovered significant differences in ways of doing environmental evaluation. Particle emission measurements were found to be the best method to evaluate the environmental acceptability of the tested stove, since the particle emission level was least dependent of the national standards, test procedures and calculation procedures used. Finally, transient particle emission measurements are presented, which reveal a close relationship between particle and hydrocarbon emissions.
... Several previous studies of wood stove emissions have measured the emission factors for fine particle mass as well as for certain organic compound classes such as PAH, dioxins, and phenolic compounds (Hall and DeAngelis, 1980;Burnet et al., 1986;Hawthorne et al., 1989; McCrillis and Burnet, 1990;McCrillis et al., 1992;Vikelsoe et al., 1994;Skreiberg et al., 1997;McDonald et al., 2000). The current study focuses on the wood stove combustion of the five most prevalent tree species in the United States. ...
... ranging from about 1 to 7 g kg Ϫ1 wood burned (Hall and DeAngelis, 1980;Skreiberg et al., 1997;McDonald et al., 2000), others are much higher, surpassing 20 g kg Ϫ1 wood burned (Burnet et al., 1986). The lower emission factors observed in this and other studies may be due to the dilution techniques employed, or other differences in testing or sampling procedures. ...
Residential wood combustion is an important contributor to ambient fine particle levels in the United States. About one-half to two-thirds of the residential wood combustion in the United States occurs in wood stoves as opposed to fireplaces. Thus, any differences between these two sources must be accounted for in chemical mass balance receptor models which attempt to determine the contribution of wood smoke sources to ambient fine particle samples. To fully characterize the fine particle emissions from wood stoves and compare the emissions profiles to those determined from previous fireplace experiments, a series of source tests were conducted on the burning of the most prevalent U.S. tree species in wood stoves. The catalyst-equipped wood stove chosen for these tests was operated under both noncatalytic and catalytic conditions to assess the effects of the catalyst on fine particle emissions. Analysis of the wood smoke includes fine particle mass emission factors, organic and elemental carbon content, ionic and elemental composition, and detailed organic speciation by GC/MS. Between 60 and 90% of the fine particle mass emissions were attributed to measured chemical species. The fine particle emissions from wood stoves show the same general patterns as those from the fireplace combustion of the same tree species; important differences between hardwood and softwood combustion are seen among the substituted phenols and diterpenoids, and levoglucosan is the most abundant individual organic compound emitted. However, fine particle mass emission factors from wood stoves are significantly lower than those from fireplaces. The elemental carbon content of the fine particle mass is generally higher in wood stove smoke than in fire-place smoke, and is even higher when the catalyst was employed. Furthermore, a greater fraction of the organic compounds is identifiable by GC/MS methods in the wood stove smoke vs. the fireplace smoke. These results suggest that differences in the source profiles between wood stove and fireplace combustion merit consideration in source apportionment calculations using organic compounds as tracers.
... A pesar de que esta tecnología cuenta ya con algunas décadas de creación y aplicación, poco se ha hecho en el ámbito de su estudio, el cual puede seccionarse en los siguientes rubros de manera general: ambiental [8][9][10][11][12], combustión y reacciones químicas de la combustión [13], energético [14,15] y transferencia de calor [16,17]. El Instituto Nacional de Ecología (INE) ha reportado resultados de evaluaciones de funcionamiento [18], sobre consumos de leña, elaboración de tortillas por unidad de leña consumida así como análisis de emisiones [12,[19][20]. ...
Las estufas que se emplean en las zonas rurales o marginadas que han llegado a sustituir a los fogones tradicionales denominados de tres piedras, son una tecnología cada vez más demandada y aplicada, principalmente en los países en desarrollo. Sin embargo, se conoce poco en cuanto a su comportamiento térmico a lo largo de su funcionamiento. En este trabajo, se muestran los resultados obtenidos a través de un monitoreo de perfiles de temperatura en cuatro partes de una estufa de biomasa (EB): comal principal, hornilla derecha, hornilla izquierda y salida de gases en la chimenea. Se realizaron tres pruebas de monitoreo con dos distintos tipos de leña: pino y mezquite. Se concluye que este tipo de pruebas son necesarias para lograr determinar potenciales de mejora en cuanto a la construcción, configuración y materiales, así como para el cálculo del potencial de eficiencia.
ABSTRACT Stoves used in rural or disadvantaged areas that have come to replace the traditional open fires are increasingly demanded and applied, particularly in the developing countries. However, little is known regarding their thermal behavior throughout its operation. In this paper, the results obtained through monitoring of temperature profiles in four parts of a wood biomass (EB) are shown: Main griddle, flat plate right, flat plate left and exhaust through the chimney. Three monitoring tests with two different types of wood were performed: pine and mesquite. This type of testing to determine potential of achieving improvement in the construction, configuration and materials, as well as for the calculation of the potential efficiency are necessary. Página | 0895 Derechos Reservados © 2015, SOMIM
... Grate firing systems without spreader stoker were studied recently in a great extent (Costa et al., 2008, Huai et al., 2008, Kaer et al., 2004, Huttunen et al., 2004, Goh et al., 1998, Skreiberg et al., 1997, Shin and Choi, 2000, Bruch et al., 2003. However, the models of packed bed usually consider fuel feeding from one side. ...
In spreader stoker boilers, solid fuel particles are spread uniformly over the grate area as they are thrown into the furnace. Primary combustion air enters from below through the grate and the fuel on it. Since the fuel has some fine particles, these burn in a suspension as they fall against the airflow moving upward through the grate. Heavier particles burn on the grate and the ash is removed from the discharge end of the grate. This article presents possible modelling approach of woodchips combustion in 25 MW th spreader stoker boiler. It is assumed that all fuel moisture is evaporated in the suspension phase. Present model considers half of the dry wood is burning in the suspension and the rest forms a packed bed on the grate. The fuel used is the mix of several types of wood waste from forest industry. Mean size of woodchips is 150 x 80 x 30 mm, with fine particles (< 3 mm) content less than 5 %. Moisture of the wood is relatively high (up to 50 %), ash content is 3 wt% dry. Combustion of solid particles in suspension is calculated by Lagrangian discrete phase model. The packed bed is considered as a porous media with mass sources of the species released by devolatilization and char oxidation; and energy sources of pyrolysis and char combustion. The CFD model has been calculated by standard k-ε turbulence model, species transport (Eddy Dissipation Concept for turbulence-chemistry interaction) combustion model. The kinetics of chemical reactions is governed by Leroy mechanism of 49 reactions (V. Leroy et al., 2008), adapted for biomass fuel types.
... The average values are approximately at 1000 ppm during most of the experiment's length. SO 2 and NO x emissions are kept below the threshold limits (Skreiberg et al., 1997; Van Loo and Koppejan, 2002). The main reason is the low sulfur and nitrogen contents of olive kernels (Table 1). ...
An innovative combustion unit was designed and implemented, aiming at the production of thermal energy, using different types of biomass fuels. The unit was made out of conventional materials, had a nominal capacity of 65 kWth and comprised a silo, a continuous feedstock supply system, a desiccator, a cutting mill, and a cross flow boiler. Among the two residues tested, olive kernels produced a higher thermal efficiency and lower CO, SO2, and NOx emissions. A series of experiments, conducted at different biomass/air feed rates, showed that at a feedstock mass flow of 14.4 kg/h improved combustion conditions and heat recovery were obtained. Gaseous emissions were kept below the threshold limits and system efficiency was 81.3%. The unit needs to be optimized in terms of air supply and optimal parameters control systems.
In addition to emission level reduction, combustion process optimization by modifications of pyrolysis boilers is aimed at fuel cost decrease. Knowledge of fuel composition and fuel combustion properties is important to the optimum and economical combustion process. The levels of emissions caused by the process can be reduced by several designs and operational modifications. This paper deals with modifications of combustion equipment in order to reduce harmful flue gas emissions in a boiler MA 23. The hot water boiler MA 23 belongs to gasification boilers for dry lump wood combustion; it is intended primarily for the heating of family houses, cottages, small office buildings and other small buildings and has the maximum required heat output of 23 kW. The boiler was tested in several modes, based on the requirements of the standard EN 303-5 dealing with emission limits. A basic requirement was the implementation of technical measures described in the paper and a proposal of method of regulation of flue gas volumetric flow rate and of installation in order to keep emission levels below the required limit.
The main combustion systems for biomass fuels are presented and the respective requirements are discussed. Wood stoves and stick wood boilers are used for individual house heating. Under stoker furnaces are used for wood chips from native wood with low ash content. Combustors for pulverized wood are used for dry wood residues (saw dust etc.) in industrial boilers or for co-combustion in power plants. For fuels with high ash content an efficient ash removal system is needed and mainly moving grate firings are used. Fluidized bed combustion is an option if a wide variety of fuels (including biomass fuels) is burnt. However, fluidised bed combustors are only used for large scale combustion. For biofuels with low ash fusion temperature like grass, straw, miscanthus etc., slagging on the grate and at the combustion chamber walls can cause severe operation problems usually above 850 °C - 1000 °C, depending on the fuel. For straw and similar biofuels, furnaces for whole bales like cigar burners can be used. The main functions of a biomass combustion system and the respective requirements are discussed in the paper.
New emission standards for wood stoves have been developed and introduced in several countries. To meet these emission regulations, new technology such as wood stoves with catalytic combustors and staged combustion units have been developed and introduced into the stove market. Three traditional wood stoves, one fireplace, one stove with a catalytic afterburner on the norwegian market have been tested in accordance with national testing procedures. In addition also a new none catalytic stove, two catalytic stoves and a non catalytic laboratory stove have been tested. The emissions of CO, particles, tar and hydrocarbons have been measured at different average wood consumption.
The amount of CO emissions for the traditional wood stoves/fireplace were found to vary from 100 to 250 g CO/kg dry wood fired (5.1-12.6 g/MJ input) at an average wood consumption below 1 kg/hour. Particle emissions from the traditional stoves were found to vary from 40 to 100 g/kg dry wood fired (2.0-5.1 g/MJ input) at below same average wood consumption. At higher wood consumptions the emissions were reduced considerably compared with low wood consumptions. For new types of stoves like the catalytic stove and the non catalytic laboratory stove, the particle emissions are 30–40 times lower than the traditional stoves at an average wood consumption
of approximately 1 kg/hour. The level of tar emissions were approximately the same as for the particle emissions. It is concluded in the paper that the particles mainly contain tar. Correlations were found between CO and emissions of hydrocarbons, CH, and H2. Low concentrations of CO gave in general low concentrations of particles, tar, hydrocarbons, CH4 and H2. The details of the experimental results and analysis of these results are presented in the paper.
Two main groups of pollutants from wood firings can be distinguished: unburnt pollutants as carbon monoxide, hydrocarbons and soot; and oxidized pollutants such as NOx and CO2.
It is shown that the unburnt pollutants can be diminued effectively if the firing system follows the rules of the two stage combustion by gasification of the wood with primary air and oxidation of the combustible gases with secondary air. Modern wood firings which fit these requirements can reach a high combustion quality, e.g. CO emissions < 250 mg/m3 at 11 Vol.% 02, if they are operated correctly. To avoid an increase of the emissions due to incorrect air settings or changes of the fuel parameters in practice an adequate combustion control is necessary.
Nitric oxides as an oxidation product cannot be avoided by a complete combustion. It is shown that the emissions of NOx from wood firings originate mainly from the fuel bound nitrogen, thermal NOx are not of great importance. The following concepts to reduce the formation of fuel NOx are presented: two stage combustion with separate reduction chamber, air staging, (process internal) fuel staging, flue gas recirculation.
Experiments have been performed in three different wood stoves based on batch combustion with natural draught; a traditional stove, a stove equipped with a catalytic afterburner and a staged air unit with downdraught combustion and good insulation of the secondary combustion chamber. The average wood consumption was varied between 0.8–3.8 kg dry wood/h, the average excess air ratio varied between 1.5–5, and the average CO emission level varied between 5–190 g/kg dry fuel (300–12000 ppm). The average NOx emission level varied between 0.5–1.8 g NO2/kg dry fuel (16–110 ppm), giving a fuel-N to NOx conversion factor between 0.23–0.55 depending on the wood species (spruce, birch or pine), the operating principle of the wood stove and the operating conditions. The NOx emission level is traditionally correlated with excess air ratio, temperature, initial fuel-N content and combustion quality. Using the CO emission level as an indicator of the combustion quality, an empirical model has been developed for the total fuel-N to NOx conversion factor based on average input variables. The excess air ratio and the temperature were found to be the most important input variables, while the CO emission level and the initial fuel-N content only were of minor importance.
Nitric oxide emissions from biomass combustion originate mainly from the fuel bound nitrogen, thermal NOx are only of minor importance. Since biomass combustion leads to higher NOx emissions than gas or light fuel oil combustion primary or secondary measures for NOx reduction are necessary for future combustion plants.
To minimize NOx emissions by primary measures, the fuel nitrogen must be reduced to molecular nitrogen in zones with an excess air ratio < 1. The following techniques for the reduction of fuel NOx have been investigated: Air staging with and without separate reduction chamber, fuel staging and flue gas recirculation. It is shown that an NOx reduction of 40% to 75% can be reached by air staging with separate reduction chamber if the following conditions are met: Primary excess air ratio ≈ 0.7 –0.8, temperature in the reduction chamber ≈ 1’100° – 1’200°C, residence time ≈ 0.3 –0.5 s. Fuel staging shows a similar potential of NOx reduction. As for air staging the NOx reduction is mainly influenced by the excess air ratio in the reduction chamber. Fuel staging can only be used for large combustion plants while air staging can be used for automatic wood furnaces from app. 200 kW up to large scale combustion.
If primary measures are not sufficient, secondary measures as the selective catalytic and non-catalytic reduction (SCR, SNCR) through the injection of sal ammoniac, ammonia or urea can be taken. The NOx reduction in the SNCR process is limited by the ammonia slippage. Further an accurate process control is neceassary to ensure the temperature window of app. 840°C – 920°C. To operate the combustion at low excess air ratio without exceeding the temperature limit, a partial extraction of heat before the SNCR process is necessary. By the SNCR process 60% – 80% reduction can be reached, depending on the fuel composition and the operation conditions. With SCR more than 80% (up to 95%) reduction can be achieved. However there is only little experience with the long term behaviour of catalysts in wood combustion systems.
For large combustion plants combinations of low NOx and denox-techniques are considered.
The objectives of the International Energy Agency (IEA) bioenergy
program are: (1) to encourage cooperative research, development and use
of energy and the increased utilization of alternatives to oil; and (2)
to establish increased program and project cooperation between
participants in the whole field of bioenergy. There are four Task
Annexes to the Implementing Agreement during the period 1992-1994:
Efficient and Environmentally Sound Biomass Production Systems;
Harvesting and Supply of Woody Biomass for Energy; Biomass Utilization;
and Conversion of Municipal Solid Waste Feedstock to Energy. The report
describes the following biomass combustion activities during the period
1992-1994: Round robin test of a wood stove; Emissions from biomass
combustion; A pilot project cofiring biomass with oil to reduce SO2
emissions; Small scale biomass chip handling; Energy from contaminated
wood waste combustion; Modeling of biomass combustion; Wood chip
cogeneration; Combustion of wet biomass feedstocks, ash reinjection and
carbon burnout; Oxidation of wet biomass; Catalytic combustion in small
wood burning appliances; Characterization of biomass fuels and ashes;
Measurement techniques (FTIR).
Bioenergy use and potential, biofuels and bioenergy systems including combustion equipment and technology development are reviewed in the IEA member countries participating in the combustion activity. Focus has been put on pollutant emissions, emission measurement and reduction techniques, energy and emissions from contaminated wood combustion and fuel reactivity and modelling of pyrolysis and combustion. The paper describes the status on these topics within the IEA cooperation agreements.
Projects and achievements within the activity “Wood Combustion and Oxidation of Wet Biomass” in the triennium 1992–1994 are reviewed. The projects include modelling of wood combustion and pyrolysis, characterisation of biomass fuels and ashes, emission comparisons, emission reduction techniques, measurement techniques, comparison of test standards, utilisation of contaminated wood waste, oxidation of wet biomass, condensing systems and co-generation and co-firing techniques.
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Greenhouse gas emissions from woodstoves
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