Experimental investigation of wood combustion in a fixed bed with hot air

Waste combustion on a grate with energy recovery is an important pillar of municipal solid waste (MSW) management in the Netherlands. In MSW incinerators fresh waste stacked on a grate enters the combustion chamber, heats up by radiation from the flame above the layer and ignition occurs. Typically, the reaction zone starts at the top of the waste layer and propagates downwards, producing heat for drying and devolatilization of the fresh waste below it until the ignition front reaches the grate. The control of this process is mainly based on empiricism.MSW is a highly inhomogeneous fuel with continuous fluctuating moisture content, heating value and chemical composition. The resulting process fluctuations may cause process control difficulties, fouling and corrosion issues, extra maintenance, and unplanned stops. In the new concept the fuel layer is ignited by means of preheated air (T > 220 °C) from below without any external ignition source. As a result a combustion front will be formed close to the grate and will propagate upwards. That is why this approach is denoted by upward combustion.Experimental research has been carried out in a batch reactor with height of 4.55 m, an inner diameter of 200 mm and a fuel layer height up to 1 m. Due to a high quality two-layer insulation adiabatic conditions can be assumed. The primary air can be preheated up to 350 °C, and the secondary air is distributed via nozzles above the waste layer. During the experiments, temperatures along the height of the reactor, gas composition and total weight decrease are continuously monitored. The influence of the primary air speed, fuel moisture and inert content on the combustion characteristics (ignition rate, combustion rate, ignition front speed and temperature of the reaction zone) is evaluated.The upward combustion concept decouples the drying, devolatilization and burnout phase. In this way the moisture and inert content of the waste have almost no influence on the combustion process. In this paper an experimental comparison between conventional and reversed combustion is presented.     

Sources of heavy metal contamination in Swedish wood waste used for combustion

In this paper, wood waste (RWW) recovered for heat production in Sweden was studied. Previous research has concluded that RWW contains elevated amounts of heavy metals, causing environmental problems during waste management. This study extends previous work on RWW by analysing which pollution sources cause this contamination. Using existing data on the metal contents in various materials, and the amounts of these materials in RWW, the share of the elevated amounts of metals in RWW that these materials explain was quantified. Six different materials occurring in RWW were studied and the results show that they explain from 70% to 100% of the amounts of arsenic, chromium, lead, copper and zinc in RWW. The most important materials contributing to contamination of RWW are surface-treated wood, industrial preservative-treated wood, plastic and galvanised fastening systems. These findings enable the development and evaluation of strategies aiming to decrease pollution and resource loss from handling RWW. It is argued that source separation and measures taken further downstream from the generation site, such as treatment, need to be combined to substantially decrease the amount of heavy metals in RWW.     

Color analysis of combustion ashes of seawater-soaked wood: estimation of salt concentration

The color of wood ash is normally white, but black color ash was observed when seawater-soaked wood was combusted. In order to check the conditions for generation of black ash, we examined both ashing temperatures from 500 to 800 °C and seawater salt densities for wood soaking. As seawater salt densities rose, the ash color got black at ashing temperatures of 500 and 700 °C. The colors of the ash were analyzed by a spectrophotometer, and color space L* a* b* was measured. The L* value and wood ash yield showed a negative correlation when the ashing temperature was at 600 °C. Salt concentration in wood (SC) was practicably estimated from the L* value (R ² = 0.51) by the approximation formula [SC (%) = 11.82e^?0.038L*]. By scanning electron microscope (SEM) observation, black ash of 600 °C was fully covered by translucent material. It was composed of Na, Mg and Cl by energy dispersive X-ray spectroscopy analysis, and seemed to be crystallized seawater salt. Washed black ash was also observed by SEM, translucent seawater salt was removed and the wood tissue was observed. Black ash was found to be carbonized wood tissue residue, and it was generated when seawater salt exists with a woody biomass.     

Reuse of wood ash from biomass combustion in non-structural concrete: mechanical properties,durability, and eco-efficiency

Journal of Material Cycles and Waste Management - Wood biomass fly ash can contribute to a more sustainable urban infrastructure, but requires efficient recycling strategies. This paper...     

Online elemental analysis of process gases with ICP-OES: A case study on waste wood combustion

A mobile sampling and measurement system for the analysis of gaseous and liquid samples in the field was developed. An inductively coupled plasma optical emission spectrometer (ICP-OES), which is built into a van, was used as detector. The analytical system was calibrated with liquid and/or gaseous standards. It was shown that identical mass flows of either gaseous or liquid standards resulted in identical ICP-OES signal intensities. In a field measurement campaign trace and minor elements in the raw flue gas of a waste wood combustor were monitored. Sampling was performed with a highly transport efficient liquid quench system, which allowed to observe temporal variations in the elemental process gas composition. After a change in feedstock an immediate change of the element concentrations in the flue gas was detected. A comparison of the average element concentrations during the combustion of the two feedstocks showed a high reproducibility for matrix elements that are expected to be present in similar concentrations. On the other hand elements that showed strong differences in their concentration in the feedstock were also represented by a higher concentration in the flue gas. Following the temporal variations of different elements revealed strong correlations between a number of elements, such as chlorine with sodium, potassium and zinc, as well as arsenic with lead, and calcium with strontium.     

Concentrations of organic wood preservatives in wood chips produced from wood wastes

We investigated the concentrations of wood preservatives in the wood chips produced in wood-waste processing facilities in 1988, 1998–1999, and 2001–2002. Among the wood preservatives used in the past in Japan, halophenols, including PCP, chlordane, and chlorpyrifos, had comparatively high detection rates and high average concentrations in the wood chips produced in 2001–2002. Aldrin and endrin were rarely detected, and DDT was already in low concentrations in those wood chips. Although several types of wood preservative were contained in the wood chips, their concentration levels depended on the sources of the wood wastes. In chips produced from wooden pallets, wooden forms for concrete working, or wood discarded from nondemolition sources, no organochlorine wood preservatives were detected, and chlorpyrifos and chlorophenols were detected at one order of magnitude lower than the average concentrations in chips produced from wood wastes discarded in house demolitions.     

Life Cycle Assessment of landfill biogas management: Sensitivity to diffuse and combustion air emissions

Goal and scopeThe life cycle inventory of landfill emissions is a key point in Life Cycle Assessment (LCA) of waste management options and is highly subject to discussion. Result sensitivity to data inventory is accounted for through the implementation of scenarios that help examine how waste landfilling should be modeled in LCA.MethodFour landfill biogas management options are environmentally evaluated in a Life Cycle Assessment perspective: (1) no biogas management (open dump), conventional landfill with (2) flaring, (3) combined heat and power (CHP) production in an internal combustion engine and (4) biogas upgrading for use as a fuel in buses. Average, maximum and minimum literature values are considered both for combustion emission factors in flares and engines and for trace pollutant concentrations in biogas.ResultsBiogas upgrading for use as a fuel in buses appears as the most relevant option with respect to most non-toxic impact categories and ecotoxicity, when considering average values for trace gas concentrations and combustion emission factors. Biogas combustion in an engine for CHP production shows the best performances in terms of climate change, but generates significantly higher photochemical oxidant formation and marine eutrophication impact potentials than flaring or biogas upgrading for use as a fuel in buses.Interpretation and discussionHowever the calculated environmental impact potentials of landfill biogas management options depend largely on the trace gas concentrations implemented in the model. The use of average or extreme values reported in the literature significantly modifies the impact potential of a given scenario (up to two orders of magnitude for open dumps with respect to human toxicity). This should be taken into account when comparing landfilling with other waste management options. Also, the actual performances of a landfill top cover (in terms of oxidation rates) and combustion technology (in terms of emission factors) appear as key parameters affecting the ranking of biogas management options.     

Characterization of municipal solid waste combustion in a grate furnace

The objective of this paper is to evaluate the combustion process of municipal solid waste combustion in a grate furnace both experimentally and numerically by using data of a reference experiment with over-stoichiometric primary air supply. Measurements were carried out inside the combustion chamber of a pilot plant by monitoring temperatures and sampling gaseous combustion products along the bed surface. The data were assessed using elemental and energy balances. Experimental data of the axial temperature profiles of the flue gas, the fuel bed and the grate bars, as well as local gas flows and the flue gas composition measured above the fuel bed along the grate were used to describe the conversion process, including drying and carbon burnout. These data served as input to model the thermo- and fluid dynamic processes of the gas phase above the bed inside the combustion chamber. For this purpose the commercial code FLUENT was employed to carry out the simulations. Thus, the turbulent temperature, flow and species distributions in the combustion chamber of the pilot waste incinerator TAMARA were predicted. The results of the FLUENT modeling showed that under the prevailing conditions the flue gas burnout is almost completed before entering the first flue due to high temperatures, effective mixing and sufficient residence times of the flue gas inside the combustion chamber. This agrees well with the experimental results inside the first flue. On the basis of the above mentioned results, design and parametric studies can be carried out in a more efficient way by saving cost and time.     

Fungicidal value of wood tar from pyrolysis of treated wood

The objective of the paper was to estimate the fungicidal value of wood tar extracted as a product of pyrolysis of wood previously treated with either creosote oil or CCB-type salt preservative. The effectiveness of wood treated with one of these two wood tar residuals was compared to the effectiveness of wood treated with virgin creosote oil (type WEI-B) and an untreated control. Wood was impregnated with alcohol solutions of the two extracted preservatives or virgin creosote oil and then subjected to the Coniophora puteana, Poria placenta and Coriolus versicolor fungi. The fungicidal values of the investigated preservatives were determined with the use of the short agar-block method and the aging test according to the standard EN 84. It was found that wood tar extracted by pyrolysis of old creosote-treated wood and then used to treat wood may have potential as a preservative for wood protection or as a component of preservatives.     

CFD simulation of MSW combustion and SNCR in a commercial incinerator

A CFD scheme was presented for modeling municipal solid waste (MSW) combustion in a moving-grate incinerator, including the in-bed burning of solid wastes, the out-of-bed burnout of gaseous volatiles, and the selective non-catalytic reduction (SNCR) process between urea (CO(NH₂)₂) and NO_x. The in-bed calculations provided 2-D profiles of the gas–solid temperatures and the gas species concentrations along the bed length, which were then used as inlet conditions for the out-of-bed computations. The over-bed simulations provided the profiles of incident radiation heat flux on the top of bed. A 3-dimensional benchmark simulation was conducted with a 750 t/day commercial incinerator using the present coupling scheme incorporating with a reduced SNCR reduction mechanism. Numerical tests were performed to investigate the effects of operating parameters such as injection position, injection speed and the normalized stoichiometric ratio (NSR) on the SNCR performance. The simulation results showed that the distributions of gas velocity, temperature and NO_x concentration were highly non-uniform, which made the injection position one of the most sensitive operating parameters influencing the SNCR performance of moving grate incinerators. The simulation results also showed that multi-layer injections were needed to meet the EU2000 standard, and a NSR 1.5 was suggested as a compromise of a satisfactory NO_x reduction and reasonable NH₃ slip rates. This work provided useful guides to the design and operation of SNCR process in moving-grate incinerators.     

Spontaneous combustion of shale spoils at a sanitary landfill

Shale deposits excavated from the Upper Cretaceous, Eagle Ford Formation for a sanitary landfill near Dallas, Texas spontaneously combusted. The shale is dark gray in color, with 3-4% fractional organic carbon, and no lignite seams. Gradual sifting and segregation of fine particles, having high surface area per unit volume, along with moisture trapped in the pile as it accumulated led to spontaneous combustion. Hot summer temperatures compounded the problem by heating the pile and preventing heat from efficiently venting to the atmosphere. Maximum temperatures exceeded 960 degrees F (516 degrees C) at several hot spots located approximately 4 m beneath the pile surface. The ongoing combustion problem, which has lasted for approximately 1 year, eventually will be extinguished by spreading the deposits in thin layers, and compacting them to reduce air circulation and segregation of fines.     

Conversion of CCA-treated wood to ethanol: a method to reduce leaching of metals from disposed treated wood prior to disposal

The objective of this paper is to evaluate the feasibility of producing ethanol from CCA-treated wood that is highly leachable. Following the initial tests, CCA-treated wood was hydrolysed and fermented and the results showed not only that ethanol was produced during the fermentation process but that metals were taken up by the yeast. Toxicity characteristic leaching procedure tests of the hydrolysed wood leached less than 4 mg/L of As while minimal amounts of Cr and Cu remained in the hydrolysed wood which makes landfilling of hydrolysed wood acceptable and less hazardous. A slightly lower amount of ethanol from CCA-treated than untreated wood was produced (6 and 7 g/L, respectively). In general, it suggests that production of ethanol as a source of energy from a hazardous waste (CCA-treated wood) is feasible.     

Removal and recovery of creosote sludge at a wood treatment plant

Off-site reclamation and incineration of residues proved to be the most efficient and cost-effective solution for remediation of the Broderick Wood Products Superfund site, a closed-down wood-preserving plant outside of Denver, Colorado. More than 3,200 cubic yards of hazardous K001 creosote sludge were removed and recovered at a total cost of only $3.1 million.     

Numerical simulation of municipal solid waste combustion in a novel two-stage reciprocating incinerator

A mathematical model was presented in this paper for the combustion of municipal solid waste in a novel two-stage reciprocating grate furnace. Numerical simulations were performed to predict the temperature, the flow and the species distributions in the furnace, with practical operational conditions taken into account. The calculated results agree well with the test data, and the burning behavior of municipal solid waste in the novel two-stage reciprocating incinerator can be demonstrated well. The thickness of waste bed, the initial moisture content, the excessive air coefficient and the secondary air are the major factors that influence the combustion process. If the initial moisture content of waste is high, both the heat value of waste and the temperature inside incinerator are low, and less oxygen is necessary for combustion. The air supply rate and the primary air distribution along the grate should be adjusted according to the initial moisture content of the waste. A reasonable bed thickness and an adequate excessive air coefficient can keep a higher temperature, promote the burnout of combustibles, and consequently reduce the emission of dioxin pollutants. When the total air supply is constant, reducing primary air and introducing secondary air properly can enhance turbulence and mixing, prolong the residence time of flue gas, and promote the complete combustion of combustibles. This study provides an important reference for optimizing the design and operation of municipal solid wastes furnace.     

Analysis of the combustion of sewage sludge-derived fuel by a thermogravimetric method in China

The treatment and disposal of sewage sludge are significant environmental problems in China. The reuse of sewage sludge for fuel could be an effective solution. The aim of this study was to characterize the behavior of sludge-derived fuel during combustion by a thermogravimetric method. The combustion profiles obtained showed four obvious weight loss regions. The results of dynamics analysis showed that first-order reactions together with Arrhenius’ law explained reasonably well the different stages of weight loss in the samples. Three temperature regions (162–327 °C, 367–445 °C, and 559–653 °C for sawdust and 162–286 °C, 343–532 °C, and 609–653 °C for coal) in each derivative thermogravimetry (DTG) curve corresponded well with the Arrhenius equation. The reactivity of sludge was lower than that of samples containing sawdust, but higher than that of coal-containing samples. These data demonstrate that sludge-derived fuel has better combustion characteristics than sludge, sawdust, or coal.     

燃烧过程中氮氧化物的生成机理

简述了自然界氮氧化物的来源及其对环境的危害，重点介绍了燃烧过程产生NOx的3条主要途径，详细介绍了NOx的生成机理，可作为控制NOx排放的参考。     

Natural biodegradation of wood preservatives

Natural biodegradation can contain groundwaters impacted by creosote and pentachlorophenol. Using natural biodegradation for such sites is attractive because groundwater restoration is often impracticable, but the dissolved plumes are biodegradable and exert relatively low oxygen demands. Three case studies of its successful use are presented, with emphasis on the types of evidence needed, the rates and extents of removal, and the strategies for incorporating natural biodegradation into a remediation approach. Natural biodegradation was proven at all three sites, using a combination of field geochemical measurements, laboratory simulations, and computer modeling. Contaminant plumes at these three sites were contained within 100 to 700 feet downgradient of the apparent sources, although the rates of biodegradation varied widely. Natural biodegradation should be considered as part of an overall remedial strategy for most sites contaminated by creosote and/or pentachlorophenol.     

Potential resources of post-consumer wood waste in Poland

Journal of Material Cycles and Waste Management - This article presents the results of studies, whose aim was to determine the volume of post-consumer wood waste resources in Poland and propose a...     

Designing a purification process for chromium-, copper- and arsenic-contaminated wood

The disposal of chromated copper arsenate (CCA)-treated wood is becoming a serious problem in many countries due to increasing levels of contamination by the hazardous elements, chromium, copper and arsenic. The present experiment was conducted as a preliminary step toward one-step solvent extraction of CCA-treated wood. Because chromium, copper and arsenic have different chemical characteristics, it is best to consider them separately prior to designing a one-step extraction process. As a basis, various two-step extraction processes were first designed and tested experimentally to determine feasibility. Among these combinations, the treatment combining oxalic acid as the 1st step and a sodium oxalate solution under acidic conditions (pH 3.2) as the 2nd step was found to be an effective way of extracting CCA elements from treated wood. Extraction efficiency reached 100% for arsenic and chromium and 95.8% for copper after a 3-h sodium oxalate treatment, following a 1-h pre-extraction process with oxalic acid. On the other hand, the same combination under alkaline conditions (pH 11.2) during the 2nd step was ineffective for copper removal, indicating that pH plays an important role in complexation with sodium oxalate solution. The present results suggest that the extraction of CCA elements using a combination of oxalic acid and acidic sodium oxalate solution is a promising basis for application to a one-step extraction method.