Combustion Of Logs Research Articles

Contribution of brown carbon to light absorption in emissions of European residential biomass combustion appliances

Abstract. Residential biomass combustion significantly contributes to light-absorbing carbonaceous aerosols in the atmosphere, impacting the earth's radiative balance at regional and global levels. This study investigates the contribution of brown carbon (BrC) to the total particulate light absorption in the wavelength range of 370–950 nm (BrC370–950) and the particulate absorption Ångström exponents (AAE470/950) in 15 different European residential combustion appliances using a variety of wood-based fuels. BrC370–950 was estimated to be from 1 % to 21 % for wood log stoves and 10 % for a fully automatized residential pellet boiler. Correlations between the ratio of organic to elemental carbon (OC / EC) and BrC370–950 indicated that a one-unit increase in OC / EC corresponded to approximately a 14 % increase in BrC370–950. Additionally, BrC370–950 was clearly influenced by the fuel moisture content and the combustion efficiency, while the effect of the combustion appliance type was less prominent. AAE470/950 of wood log combustion aerosols ranged from 1.06 to 1.61. By examining the correlation between AAE470/950 and OC / EC, an AAE470/950 close to unity was found for pure black carbon (BC) particles originating from residential wood combustion. This supports the common assumption used to differentiate light absorption caused by BC and BrC. Moreover, diesel aerosols exhibited an AAE470/950 of 1.02, with BrC contributing only 0.66 % to the total absorption, aligning with the assumption employed in source apportionment. These findings provide important data to assess the BrC from residential wood combustion with different emission characteristics and confirm that BrC can be a major contributor to particulate UV and near-UV light absorption for northern European wood stove emissions with relatively high OC / EC ratios.

Global warming and human health effects of wood heating life cycle in the Grand-Est region in France

In France, residential wood heating represents 52% of the share of energy produced from renewable resources for heat production. The forest of the Grand Est region (FR) covers one third of the regional territory and 12% of the national forest area. The main purpose of this study is to assess and to compare the global warming and the human health effects of the wood energy sector at domestic and regional scales. Five scenarios systems were studied. S1 (wood-log scenario and S2 (pellet scenario) were compared in real conditions of use. S3 studies in details the pellet manufacturing process. The novelty of the study compares S1 and S2 at the regional scale with two new scenarios S4 and S5 considering the entire log inserts and pellets stoves listed in the region. A cradle-to-grave approach was applied including all stages from forestry operations to heat production by combustion. Scenario S2 leads to a higher global change than S1 with values of 73.7 and 44.1 kg CO2eq per ton of green wood, respectively. If the combustion stage of pellets emits less greenhouse gases than the combustion of logs, the stage production contributes for 67% of the total impact. The packaging was the main process having the highest health and environmental impacts. At regional scale, the combustion stage mainly enhances all impacts due to the presence of old appliances with low environmental efficiency. Public policies must continue their efforts to promote the replacement of old household appliances.

Numerical investigations of soot generation during wood-log combustion

• Particle-scale biomass combustion model with soot formation is established. • Virtual-particle-based thermally-thick model and two-equation soot model are integrated. • Improved prediction of soot volume fraction for a single-particle combustion experiment is achieved. • Soot generation during wood log combustion depends highly on flame structure and the packing of wood logs. Soot formation is an important challenge in the design of modern wood stoves, as soot not only deteriorates the combustion efficiency but also poses threats to human health. Although soot formation in biomass combustion has been studied previously, the investigation at wood stove level is still rare due to its complex nature. In this paper, numerical simulations are performed to uncover the basic trends of soot formation during wood log combustion. The soot formation model is developed based on a particle-resolved biomass combustion algorithm, where the intraparticle heat and mass transfer effect, soot mass fraction and particle size are all resolved. Besides, simplified tar and precursor models are used in solving the reaction kinetics of soot formation. The integrated model is first validated through the combustion simulation of a micron-sized coal particle in air, where the predicted flame temperature and the soot volume fraction show improved agreement with experimental data compared to a previous modeling work. Thereafter, the soot formation during wood-log combustion in a confined stove is studied. Different combustion behaviors are observed for varying numbers of wood logs and for variations in the wood-log stacking. Additionally, the flow field temperature, tar, soot, and oxygen concentrations during the combustion are analyzed. Finally, the influences of the air intake rate, the relative distance between wood logs, and temperature boundary condition on the soot formation are discussed. This work provides useful information for the design and the optimization of modern wood stoves.

Emission factors and chemical characterization of particulate emissions from garden green waste burning

This work provides an evaluation of the emission factors (EFs) of typical garden waste burning (fallen leaves and hedge trimming) in terms of particulate matter (PM), elemental and organic carbon (EC-OC) together with a detailed chemical characterization of 88 particle-bound organic species including polycyclic aromatic hydrocarbons (PAHs), levoglucosan and its isomers, lignin breakdown products (methoxyphenols), cholesterol, alkanes, polyols and sugars. Furthermore, wood-log based burning experiments have been performed to highlight key indicators or chemical patterns of both, green waste and wood burning (residential heating) sources, that may be used for PM source apportionment purposes. Two residential log wood combustion appliances, wood stove (RWS) and fireplace, under different output conditions (nominal and reduced) and wood log moisture content (mix of beech, oak and hornbeam), have been tested. Open wood burning experiments using wood logs were also performed. Green waste burning EFs obtained were comparable to the available literature data for open-air biomass burning. For PM and for most of the organic species studied, they were about 2 to 30 times higher than those observed for wood log combustion experiments. Though, poor performance wood combustions (open-air wood log burning, fireplace and RWS in reduced output) showed comparable EFs for levoglucosan and its isomers, methoxyphenols, polyols, PAHs and sugars. Toxic PAH equivalent benzo[a]pyrene EFs were even 3–10 times higher for the fireplace and open-air wood log burning. These results highlighted the impact of the nature of the fuel burnt and the combustion performances on the emissions. Different chemical fingerprints between both biomass burning sources were highlighted with notably a predominance of odd high-molecular weight n-alkanes (higher carbon preference index, CPI), lower levoglucosan/mannosan ratio and lower sinapylaldehyde abundance for green waste burning. However, the use of such indicators seems limited, especially if applied alone, for a clear discrimination of both sources in ambient air.

Biomass burning combustion efficiency observed from space using measurements of CO and NO<sub>2</sub> by the TROPOspheric Monitoring Instrument (TROPOMI)

Abstract. The global fire emission inventories depend on ground and airborne measurements of species-specific emission factors (EFs), which translate dry matter losses due to fires to actual trace gas and aerosol emissions. The EFs of nitrogen oxides (NOx) and carbon monoxide (CO) can function as a proxy for combustion efficiency to distinguish flaming from smoldering combustion. The uncertainties in these EFs remain large as they are limited by the spatial and temporal representativeness of the measurements. The global coverage of satellite observations has the advantage of filling this gap, making these measurements highly complementary to ground-based or airborne data. We present a new analysis of biomass burning pollutants using space-borne data to investigate the spatiotemporal efficiency of fire combustion. Column measurements of nitrogen dioxide and carbon monoxide (XNO2 and XCO) from the TROPOspheric Monitoring Instrument (TROPOMI) are used to quantify the relative atmospheric enhancements of these species over different fire-prone regions around the world. We find spatial and temporal patterns in the ΔXNO2 ∕ ΔXCO ratio that point to distinct differences in biomass burning behavior. Such differences are induced by the burning phase of the fire (e.g., high-temperature flaming vs. low-temperature smoldering combustion) and burning practice (e.g., the combustion of logs, coarse woody debris and soil organic matter vs. the combustion of fine fuels such as savanna grasses). The sampling techniques and the signal-to-noise ratio of the retrieved ΔXNO2 ∕ ΔXCO signals were quantified with WRF-Chem experiments and showed similar distinct differences in combustion types. The TROPOMI measurements show that the fraction of surface smoldering combustion is much larger for the boreal forest fires in the upper Northern Hemisphere and peatland fires in Indonesia. These types of fires cause a much larger increase (3 to 6 times) in ΔXCO relative to ΔXNO2 than elsewhere in the world. The high spatial and temporal resolution of TROPOMI also enables the detection of spatial gradients in combustion efficiency at smaller regional scales. For instance, in the Amazon, we found higher combustion efficiency (up to 3-fold) for savanna fires than for the nearby tropical deforestation fires. Out of two investigated fire emission products, the TROPOMI measurements support the broad spatial pattern of combustion efficiency rooted in GFED4s. Meanwhile, TROPOMI data also add new insights into regional variability in combustion characteristics that are not well represented in the different emission inventories, which can help the fire modeling community to improve their representation of the spatiotemporal variability in EFs.

Transient CFD simulation of wood log combustion in stoves

Wood log stoves are a common residential heating technology that produce comparably high pollutant emissions. Within this work, a detailed CFD model for transient wood log combustion in stoves was developed, as a basis for its optimization. A single particle conversion model previously developed by the authors for the combustion of thermally thick biomass particles, i.e. wood logs, was linked with CFD models for flow and turbulence, heat transfer and gas combustion. The sub-models were selected based on a sensitivity analysis and combined into an overall stove model, which was then validated by simulations of experiments with a typical wood log stove, including emission measurements. The comparison with experimental results shows a good accuracy regarding flue gas temperature as well as CO2 and O2 flue gas concentrations. Moreover, the characteristic behavior of CO emissions could be described, with higher emissions during the ignition and burnout phases. A reasonable accuracy is obtained for CO emissions except for the ignition phase, which can be attributed to model simplifications and the stochastic nature of stove operation. Concluding, the CFD model allows a transient simulation of a stove batch for the first time and hence, is a valuable tool for process optimization.

Differences between co-cultures and monocultures in testing the toxicity of particulate matter derived from log wood and pellet combustion.

BackgroundIn vitro studies with monocultures of human alveolar cells shed deeper knowledge on the cellular mechanisms by which particulate matter (PM) causes toxicity, but cannot account for mitigating or aggravating effects of cell-cell interactions on PM toxicity.MethodsWe assessed inflammation, oxidative stress as well as cytotoxic and genotoxic effects induced by PM from the combustion of different types of wood logs and softwood pellets in three cell culture setups: two monocultures of either human macrophage-like cells or human alveolar epithelial cells, and a co-culture of these two cell lines. The adverse effects of the PM samples were compared between these setups.ResultsWe detected clear differences in the endpoints between the mono- and co-cultures. Inflammatory responses were more diverse in the macrophage monoculture and the co-culture compared to the epithelial cells where only an increase of IL-8 was detected. The production of reactive oxygen species was the highest in epithelial cells and macrophages seemed to have protective effects against oxidative stress from the PM samples. With no metabolically active cells at the highest doses, the cytotoxic effects of the PM samples from the wood log combustion were far more pronounced in the macrophages and the co-culture than in the epithelial cells. All samples caused DNA damage in macrophages, whereas only beech and spruce log combustion samples caused DNA damage in epithelial cells. The organic content of the samples was mainly associated with cytotoxicity and DNA damage, while the metal content of the samples correlated with the induction of inflammatory responses.ConclusionsAll of the tested PM samples induce adverse effects and the chemical composition of the samples determines which pathway of toxicity is induced. In vitro testing of the toxicity of combustion-derived PM in monocultures of one cell line, however, is inadequate to account for all the possible pathways of toxicity.

Impact of the wood combustion in an open fireplace on the air quality of a living room: Estimation of the respirable fraction

Presently, both in rural areas and in cities open fireplaces are still present and large quantities of wood are combusted every year. The present study aims to characterize aerosol size distribution, chemical composition and deposition in the human respiratory tract of particles emitted during the combustion of logs of oak in an open fireplace installed in the living room of a typical village house. CO2 and CO levels and aerosol size distribution have been continuously monitored and a PM10 sampler with two types of filters for chemical and microscopic analysis was also installed. The increment, between the operating periods and the indoor background, in the organic carbon and PM10 concentration due to the use of the fireplace is 15.7±0.6 (mean±standard deviation) and 58.5±6.2μgm−3, respectively. The two main polluting processes during the operation of the fireplace are the ignition with the subsequent refueling and the final cleaning of the residual ashes. In both phases mean values around 1800 particles cm−3 with CMD of 0.15μm were measured. However, while PM10 levels of 130±120μgm−3 were estimated for the ignition stage, values of 200±200μgm−3 were obtained during the final cleaning step. Assessment conducted according to ISO standard 7708:1995, demonstrated that a person who stays in a living room when an open fireplace is lit will inhale, on average, 217μgm−3 and 283μgm−3 during the ignition and the refueling stages, respectively. Subsequent refueling proved to be much less polluting. The ashes removal can also be very polluting and dangerous to health if there are hidden small incandescent embers among the ashes (estimated PM10 of 132μgm−3), reaching a CO2 level of 1940ppm and a dangerous level of CO of 132ppm.

Analysis of the chemical composition of ultrafine particles from two domestic solid biomass fired room heaters under simulated real-world use

Two common types of wood (beech and fir) were burned in commercial pellet (11.1 kW) and wood (8.2 kW) stoves following a combustion cycle simulating the behavior of a real-world user. Ultrafine particulate matter (UFP, dp < 100 nm) was sampled with three parallel multistage impactors and analyzed for metals, main water soluble ions, anhydrosugars, total carbon, and PAH content. The measurement of the number concentration and size distribution was also performed by a fourth multistage impactor. UFP mass emission factors averaged to 424 mg/kgfuel for all the tested stove and wood type (fir, beech) combinations except for beech log burning in the wood stove (838 mg/kgfuel). Compositional differences were observed for pellets and wood UFP samples, where high TC levels characterize the wood log combustion and potassium salts are dominant in every pellet sample. Crucial aspects determining the UFP composition in the wood stove experiments are critical situations in terms of available oxygen (a lack or an excess of combustion air) and high temperatures. Whereas for the automatically controlled pellets stove local situations (e.g., hindered air-fuel mixing due to heaps of pellets on the burner pot) determine the emission levels and composition. Wood samples contain more potentially carcinogenic PAHs with respect to pellets samples. Some diagnostic ratios related to PAH isomers and anhydrosugars compiled from experimental UFP data in the present study and compared to literature values proposed for the emission source discrimination for atmospheric aerosol, extend the evaluation usually limited to higher particle size fractions also to UFP.

Correlation between air flow rate and pollutant concentrations during two-stage oak log combustion in a 25 KW residential boiler

Abstract It can be expected that there is a considerable correlation between combustion air flow rate and the concentrations of carbon monoxide, hydrocarbons and nitrogen oxide in the flue gas. The influence of temperature and oxygen concentration in the combustion zone on the concentrations of carbon monoxide, hydrocarbons and nitrogen oxide in the flue gas, for high and low combustion air flow, was analysed. Oxygen concentration for which the concentration of carbon monoxide is the lowest was determined, as well as the mutual relation between carbon monoxide and nitrogen oxide concentration.

Performance and emissions characteristics of compressed spent coffee ground/wood chip logs in a residential stove

Spent coffee grounds (SCG), a processing by-product from the soluble coffee industry, was evaluated as a potential feedstock for preparing compressed logs for energy production. Hence, a blend of SCG/wood chips was transformed into densified logs using an industrial press. Chemical properties such as calorific value, ash content and elemental analysis were obtained. Combustion tests were carried out with a five-star–labeled stove in a French industrial research and development laboratory. Three different configurations were tested: a densified log containing 20wt% of SCG blended with pine wood chips, another containing a mixture 50/50wt% of SCG/pine wood chips and a classical beech log. This study is the first one that focuses on the potential of compressed logs as a new biocombustible for wood stoves. The obtained results show that the combustion of logs containing SCG leads to better yield of combustion. Nevertheless, CO and particle emissions increase when increasing the rate of SCG although the exhaust gas emissions and combustion yields always lead to the “five-star Flamme Verte” label achievement. Such attainment is essential to sell these densified biofuel logs in the French market. Results indicate that the blended densified logs are combusted rapidly leading to higher stove efficiency and therefore good heat recuperation from the stove walls. On the contrary, the addition of SCG leads to lower CO2 concentrations (7.7% and 9.05% for 20wt% and 10wt% of SCG, respectively). This behavior indicates that the combustion of compressed logs is not suitable for the stove design and may lead to an uncomfortable heating. One should be reminded that the evaluated stove was designed for the combustion of conventional wood logs (with respect to the NF Bois de Chauffage standard). This means that the results obtained during this study with the different densified fuel logs could be improved after an adjustment of the stove conception.

Optimization of a log wood boiler through CFD simulation methods

This paper describes the steady-state modeling and simulation of a wood log fired boiler. It is designed and manufactured by THERMODYNAMIKI S.A. (KOMBI), a company based on Northern Greece. Its nominal fuel power is around 32kW and its efficiency is close to 75%. A specific operating case, selected and experimentally investigated by the manufacturer, is examined. Due to the highly transient and complex nature of wood log combustion, an ad-hoc model has been developed. Its main characteristic is the fuel division into three components: water vapor, volatiles and fixed char. The latter is considered to form a layer, which is treated as a porous medium thus forming a volumetric source zone adjacent to the firebed area. Volatiles and water vapor are modeled as volumetric mass sources, whereas a two-step reaction mechanism of the former is considered. The numerical results are compared against corresponding experimental data for the nominal load as far as flue gas characteristics (temperature and species concentration) at the boiler exit, are concerned. Based on the validated model, a proposed optimization pattern of the boiler is undertaken and examined by means of CFD.

Emission formation during wood log combustion in fireplaces part I: volatile combustion stage

A CFD-based tool for the analysis of combustion and emissions in batch-fired wood log combustion is introduced. It consists of submodels for drying and pyrolysis of a wood log, for combustion of volatilised fuel and char, for radiative heat transfer, and for NO formation implemented in a commercial CFD-programme (Fluent) for turbulent flows. Comparing model predictions to experimental data in a test oven shows the applicability of the different submodels and combination of them.

Emission formation during wood log combustion in fireplaces part II: char combustion stage

A simplified simulation model of heat storing fireplaces during combustion of residual thin char bed was developed. When the bed model is coupled with CFD calculations for the furnace above the bed, the emissions can be predicted. Especially the time instant of maximum CO emissions is considered. The following results (output quantities) can be calculated with the coke-bed model: bed temperature, composition of gases leaving from the bed (CO, CO2, O2 and NO), and release of carbon from the bed. The following input data are required: primary air rate, particle size, grate-area, bed thickness, bed porosity, and effective furnace radiation.

Spatial distribution and properties of ash and thermally altered soils after high-severity forest fire, southern California

After a century of fire suppression, dense forests in California have fueled high-severity fires. We surveyed mixed conifer forest with 995–1178 trees ha−1 (stems &gt; 10 cm diameter at breast height), and nearby pine–oak woodland having 175–230 trees ha−1, 51 days after a severe burn, to contrast the spatial extent and properties of thermally altered soil at sites with different tree densities. Water-repellent soils were more extensive in forest than woodland. Deposits of white ash, composed largely of calicite, covered at most ~25% of the land surface, in places where large fuel items (e.g. logs, branches, exfoliated oak bark) had thoroughly combusted. At least 1690 kg ha−1 of CaCO3 in ash was deposited over the forest, and at least 700 kg ha−1 was added to the woodland. Combustion of logs and large branches also reddened the underlying yellow-brown soil as deep as 60 mm (average 8 mm), and over ~1–12% of the land surface. The reddened soils have magnetic susceptibilities that are three to seven times greater than surrounding unreddened soils within the burn, indicating thermal production of maghemite. Such fire-altered conditions persist over spatial and temporal scales that influence soil genesis in Mediterranean-type climate regions.

Soil properties in fire-consumed log burnout openings in a Missouri oak savanna

Downed logs are known to increase species diversity in many forest ecosystems by increasing resource and structural complexity and by altering fire behavior in fire-prone ecosystems. In a frequently burned oak savanna in central Missouri, combustion of downed logs formed patches that have remained free of herbaceous vegetation for more than 3 years. To assess the influence of “log burnouts” on soil conditions we compared soil chemical, biological and physical properties in log burnout zones and beneath surrounding herbaceous vegetation. Soil pH and extractable soil NO 3 −, P, K + and Ca 2+ were all higher in the log burnouts compared to adjacent soil. There was no difference in total soil N or extractable NH 4 +. An index of plant N availability was lower and the soil C:N ratio was higher in the burnout patches, though the magnitudes of these reductions do not explain the persistence of the bare patches. We suspect that following log combustion degraded soil aggregate structure and decreased soil porosity alters soil water availability and restricts plant colonization into the log burnouts areas. The modified soil conditions associated with fire-consumed coarse woody debris may have a long-term influence on herbaceous species diversity and spatial distribution in fire-maintained oak savannas.

Effects of increased biomass pellet combustion on ambient air quality in residential areas—a parametric dispersion modeling study

Sweden's goals of contemporaneously reducing CO 2 emissions and phasing out nuclear power will require a maximum utilization of biomass fuels. This would imply a significant shift from electricity and fuel oil to biomass generated heat, but must also be accomplished without a deterioration of the local air quality. The most suitable energy carrier seems to be pelletized biomass fuels with their associated low emissions and considerable residential conversion potential. Using an underlying statistical design, a parametric dispersion modeling study was performed to estimate and illustrate the combined effects of source-specific, meteorological and modeling variables on the ambient air quality in a typical residential area for different conversion scenarios. The work nicely illustrated the benefits of combining statistical designs with model calculations. It further showed that the concentration of combustion related ambient THC was strongly related to conditions affecting the source strength, but only weakly to the dispersion conditions and model variables. Time of year (summer or winter); specific emission performance; extent of conversion from electricity; conversion from wood log combustion; and specific efficiency of the pellet appliances showed significant effects in descending order. The effects of local settings and model variables were relatively small, making the results more generally applicable. To accomplish the desired conversion to renewable energy in an ecologically and sustainable way, the emissions would have to be reduced to a maximum advisable limit of 25±7 mg THC / MJ fuel (given as CH 4). Further, the results showed the potential positive influence by conversion from wood log to low emission pellet combustion.

Sources of Fine Organic Aerosol. 9. Pine, Oak, and Synthetic Log Combustion in Residential Fireplaces

Combustion of wood in residential fireplaces contributes approximately 14% on an annual average of the total primary fine particle organic carbon (OC) emissions to the Los Angeles urban atmosphere and up to 30% of the fine particulate OC emissions on winter days. This paper presents comprehensive organic compound source profiles for smoke from burning pine, oak, and synthetic logs in residential fireplaces. Mass emission rates are determined for approximately 200 organic compounds including suites of the n-alkanes, n-alkenes, cyclohexylalkanes, n-alkanals, n-alkanoic acids, alkenoic acids, dicarboxylic acids, resin acids, hydroxylated/methyoxylated phenols, lignans, substituted benzenes/benzaldehydes, phytosterols, polycyclic aromatic hydrocarbons (PAHs), and oxy-PAHs. Wood smoke constituents reflect to a great extent the underlying composition of the wood burned: pine and oak logs produce smoke that is enriched in lignin decomposition products, pine smoke is enriched in resin acids and their thermal alteration products, while smoke from the synthetic log burned here bears the major signature of the petroleum products combined with traces of the sawdust components from which it is made. Resin acids are discussed as potential wood smoke tracers in the environment, and it is shown that the time series of resin acids concentrations in the Los Angeles atmosphere follows the extreme seasonal variation in wood use reported in previous emissions inventories for the Los Angeles urban area.

The distribution of solar radiation throughout southern Africa : Drummond, A. J. and Vowinckel, E., J. Meteor. 14 (4): 343-53, Aug. 1957. Illus.

Spent coffee grounds (SCG), a processing by-product from the soluble coffee industry, was evaluated as a potential feedstock for preparing compressed logs for energy production. Hence, a blend of SCG/wood chips was transformed into densified logs using an industrial press. Chemical properties such as calorific value, ash content and elemental analysis were obtained. Combustion tests were carried out with a five-star–labeled stove in a French industrial research and development laboratory. Three different configurations were tested: a densified log containing 20 wt% of SCG blended with pine wood chips, another containing a mixture 50/50 wt% of SCG/pine wood chips and a classical beech log. This study is the first one that focuses on the potential of compressed logs as a new biocombustible for wood stoves. The obtained results show that the combustion of logs containing SCG leads to better yield of combustion. Nevertheless, CO and particle emissions increase when increasing the rate of SCG although the exhaust gas emissions and combustion yields always lead to the “five-star Flamme Verte” label achievement. Such attainment is essential to sell these densified biofuel logs in the French market. Results indicate that the blended densified logs are combusted rapidly leading to higher stove efficiency and therefore good heat recuperation from the stove walls. On the contrary, the addition of SCG leads to lower CO2 concentrations (7.7% and 9.05% for 20 wt% and 10 wt% of SCG, respectively). This behavior indicates that the combustion of compressed logs is not suitable for the stove design and may lead to an uncomfortable heating. One should be reminded that the evaluated stove was designed for the combustion of conventional wood logs (with respect to the NF Bois de Chauffage standard). This means that the results obtained during this study with the different densified fuel logs could be improved after an adjustment of the stove conception.

Temperature consideration in solar battery development : Halsted, R. E., J. App. Phys. 28 (10): 1131, Oct. 1957. Illus.

Spent coffee grounds (SCG), a processing by-product from the soluble coffee industry, was evaluated as a potential feedstock for preparing compressed logs for energy production. Hence, a blend of SCG/wood chips was transformed into densified logs using an industrial press. Chemical properties such as calorific value, ash content and elemental analysis were obtained. Combustion tests were carried out with a five-star–labeled stove in a French industrial research and development laboratory. Three different configurations were tested: a densified log containing 20 wt% of SCG blended with pine wood chips, another containing a mixture 50/50 wt% of SCG/pine wood chips and a classical beech log. This study is the first one that focuses on the potential of compressed logs as a new biocombustible for wood stoves. The obtained results show that the combustion of logs containing SCG leads to better yield of combustion. Nevertheless, CO and particle emissions increase when increasing the rate of SCG although the exhaust gas emissions and combustion yields always lead to the “five-star Flamme Verte” label achievement. Such attainment is essential to sell these densified biofuel logs in the French market. Results indicate that the blended densified logs are combusted rapidly leading to higher stove efficiency and therefore good heat recuperation from the stove walls. On the contrary, the addition of SCG leads to lower CO2 concentrations (7.7% and 9.05% for 20 wt% and 10 wt% of SCG, respectively). This behavior indicates that the combustion of compressed logs is not suitable for the stove design and may lead to an uncomfortable heating. One should be reminded that the evaluated stove was designed for the combustion of conventional wood logs (with respect to the NF Bois de Chauffage standard). This means that the results obtained during this study with the different densified fuel logs could be improved after an adjustment of the stove conception.