Wood Heating Research Articles

Modeling and simulation of heat-mass transfer and its application in wood thermal modification

Abstract Wood is a type of renewable and natural material, with most of its end application related to building materials. However, hygroexpansion and anisotropy in wood markedly shorten its service life and value. In this study, wood thermal modification was used to improve wood quality, and a heat-mass transfer model was established based on practical production process. The software COMSOL Multiphysics was used to solve this coupling transfer model. Relationships between temperature and moisture content, temperatures of the medium under thermal treatment, and treatment time, were established. Results indicated that this coupling model and method can be used to simulate and solve heat-mass transfer during wood thermal treatment, and the simulation results were found to be consistent with the measured results. The temperatures at the wood surface could achieve the target temperature within a considerably short time, whereas that at the wood central point was difficult to obtain. The cross-section of the heat convection boundary obtained the highest temperature and the lowest moisture content, whereas the cross-section of the symmetry boundary obtained the lowest temperature and the highest moisture content. These results can be used to devise a wood thermal treatment schedule, determine the heat and moisture distribution, and control the wood heat treatment process. Consequently, guidance for wood thermal treatment is provided to reduce energy and time consumption.

Nilai Kalor Briket Limbah Kayu Sengon Dengan Perekat Maizena Lebih Tinggi Di Bandingkan Tapioka, Sagu Dan Tepung Singkong

Bio-briquette is a solid fuel made from organic waste and mixed with other ingredients and then printed using certain pressures so that the desired shape and characteristics are obtained. This study focused on determining the effect of adhesive on density, moisture content and heating value on sengon wood charcoal bio-briquette with variations of tapioca, sago, cornstarch and cassava flour with a pressure of 115 kg / . The results showed that the highest density was 0.56 g/ in the bio-briquette of sengon wood waste charcoal with cassava flour adhesive, the lowest water content was 6.52% in the bio-briquette of sengon wood waste with cornstarch adhesive and the highest heating value was found in briquettes maizena adhesive sengon wood waste is 5,868 cal / gr. Keywords: sengon wood waste briquettes, adhesive, density, moisture content and heating value

EXPERIMENTAL STUDY OF MICROWAVE SLOW WAVE COMB APPLICATORS FOR TIMBER TREATMENT AT FREQUENCIES 2.45 AND 0.922GHz

Slow wave comb applicators for timber (and other materials) treatment at frequencies 2.45GHz (Comb1) and 0.922GHz (Comb2), designed for surface layer heating, modification and sterilization, were experimentally studied. Experiments showed that the Comb1 applicator released 83-88% of applied MW energy in wet wood on the depth up to 30mm, in zones with maximum energy application. In other zones, energy application efficiency is higher. The Comb2 applicator releases about 60% of the applied energy on the depth up to 30mm in the zones of maximum energy release. Energy distribution from the comb applicators, in the wet wood, allows the most significant part of the energy to be released in surface layers and increases efficiency of energy use, compared to other MW radiators. Comb1 and Comb2 are recommended for practical use in wood heating, MW modification and sterilization processes. They can be used for soil, concrete, plaster, bricks, plastics and other materials were required heating of surface layers.

Numerical Investigation of a Wood-Chip Downdraft Gasifier

Biomass gasification is regarded as one of the most promising technology in the renewable energy field. The outcome of such operation, i.e. the synfuel, can be exploited in several ways, for example powering engines and turbines, and is considered more flexible than the biomass itself. For this reason, a careful analysis of the gasification performance is of paramount importance for the optimization of the process. One of the techniques that can be used for such a purpose, is the numerical analysis. CFD is indeed a tool that can be of great help in the design and study of the operation of the gasifier, allowing for an accurate prediction of the operating parameters. In this work, a downdraft gasifier is considered, and the biomass is made of wood chip. The present analysis is devoted to build the numerical model and simulate all the reactions that happen inside an actual gasifier, considering the drying of the wood chip, heating, pyrolysis, and combustion. Good match with experimental results is found, making the numerical model here presented a reliable virtual test bench where investigating the effects of variation in the working parameters.

A greener approach to byproducts from the production of heat-treated poplar wood: Analysis of volatile organic compound emissions and antimicrobial activities of its condensate

Although many properties of plantation wood are greatly enhanced by heat treatment, large quantities of volatile organic compounds (VOCs) are released from this process, resulting in potential problems for the environment and human health. Volatile byproducts were collected from Populus tomentosa wood that was treated at 160, 180, 200, and 220 °C for 2 h. The VOC gases were partly collected at the heating, holding, and cooling stages of the process and were then analyzed by gas chromatography-mass spectrometry and thermogravimetry. The results show that over 90% of the volatiles from the first and third stages were alkane compounds. The mass losses in the heating and holding stages were almost at the same level, and the liquid byproduct contained approximately 48% phenolic products at 160 °C. The volatiles at 180 °C were mainly alkanes, terpenes, and aromatic compounds, and the absolute amount of VOCs released in the holding stage was much higher than that in the heating stage. The concentrations of phenols and ketones in the liquid byproducts decreased when the treatment temperature was increased, and more complex chemicals such as N-containing compounds emerged. Ester and aromatic compounds increased with the treatment temperature. The condensate collected at 160 °C exhibited considerable biological activity in the bacterial and mildew resistance tests. These results suggest that thermally treated byproducts can be turned into wood preservatives, which would also make the wood heat treatment cleaner.

EFFECTS OF IRRIGATION, PLANTATION DENSITY AND clonal composition ON WOODY BIOMASS QUALITY FOR BIOENERGY IN A SHORT ROTATION CULTURE SYSTEM WITH WILLOWS (Salix spp.)

ABSTRACT A short rotation intensive system with willows was analyzed with the following aims: a - to determine the effects of irrigation, genotype and plantation density on wood anatomy, wood density, moisture content, lower heating value, total ash content and energy accumulated in the woody biomass; b - to explore the relationships between anatomical and physical wood properties and the parameters determining their quality as a biofuel. A complete factorial experiment was set up, with three factors and two levels for each factor. The factors were: irrigation, plantation density and clone (genotype). The clones were Salix matsudana Koidz. x Salix alba L. ‘Barrett 13-44 INTA´ (B) and Salix alba L. ‘Yaguareté INTA - CIEF´ (Y). 46 stools of 1 m long were sampled, on which the following determinations were carried out: vessel diameter and frequency, fiber wall thickness and area, wood density, moisture content, ash content and heating values. Clone B had higher wood density than clone Y (0.406 vs. 0.395 g/cm3) and lower moisture content (47.11 vs. 50.53 %). The plantation density did not affect any of the variables analyzed. Irrigation increased the energy yield to 393.2 Gj/ha, compared to 309.15 Gj/ha without irrigation. A system with clone B planted at a lower density (13,000 plants/ha) and under irrigation has the best advantage as an energetic crop over the other alternatives evaluated in this work.

Economic analysis of a field monitored residential wood pellet boiler heating system in New York State

An economic and environmental benefit analysis have been performed using data from the field monitoring of a 25-kW wood pellet boiler heating system with thermal energy storage (TES) tanks installed in a home using a low temperature heat distribution system and radiant heat emitters in northern New York State (NYS). Pellet fuel demand was a linear function of daily average ambient temperature. It was used to predict total seasonal fuel and heat demand from the beginning of October to the end of April. A cost of heat (COH) analysis was performed considering all costs associated with the system including capital cost, operation, maintenance, other costs, and final system disposal (or salvation) cost. Sensitivity analysis showed that initial capital cost, wood pellet fuel price, and boiler heating system seasonal efficiency were the top three key factors determining the final COH with seasonal efficiency becomes more significant when pellet price increases. A life cycle annualized cost method was used to determine and compare the costs of heat using natural gas, No. 2 fuel oil, and propane. The study found that at the current seasonal efficiency of 75.8% (based on gross heating value), pellet fuel price of 240 $/ton, and maximum government incentives of $10,000, wood pellet boiler heating is able to replace intermediate efficiency (83%) propane heating systems in NYS at current fuel price of 2.48 $/gal. With a 3.6% fuel price increase to 2.57 $/gal, wood pellet heating is comparable with high efficiency (95%) propane heating systems. In addition, a heating oil price above 3.22 $/gal would make it economically possible to switch from oil heating to wood pellet heating in NYS. It was found that major emissions reductions can be achieved by switching from inefficient wood heating technology to wood pellet heating in terms of reductions in CO2, particulate matter (PM), and CO emissions. Greenhouse gas emissions reductions are also achieved when switching from fossil fuels to wood pellets, but PM and CO emissions increased significantly.

Symptoms of chronic bronchitis in individuals without chronic obstructive pulmonary disease: prevalence, burden, and risk factors in southern Poland.

Introduction Chronic bronchitis (CB) symptoms are commonly reported in individuals without chronic obstructive pulmonary disease (COPD), but CB is rarely diagnosed in this population. Objectives We aimed to determine the prevalence and burden of CB, as well as its risk factors, in a population of patients without COPD. Patients and methods Data from the "Health Action" program (a lung cancer prevention and health care improvement program conducted in Proszowice County, Poland) were used. All county inhabitants aged 40 years or older without COPD were invited to participate. As part of the program, a questionnaire was administered to assess CB symptoms and risk factors. Spirometry at baseline and after the bronchodilator test was also performed. Results CB symptoms were present in 9.1% of the 3558 participants. The prevalence of CB in the study population was 7.12% (95% CI, 6.70-7.56). Patients with CB had more dyspnea and more often received medical treatment for lung disease or were hospitalized for respiratory disorders than patients without CB. CB was associated with worse lung function and a worse score in the modified Medical Research Council Dyspnea Scale even after adjustment for possible confounders. In a multivariate analysis, male sex, age over 70 years, current smoking, passive exposure to tobacco smoke, gas or wood heating, occupational exposure to chemical agents, lower forced expiratory volume in 1 second, and asthma correlated with an increased risk of CB. Conclusions CB symptoms are common in individuals without COPD aged 40 years or older and are associated with more dyspnea irrespective of lung function and comorbidities.

Characterization and reactivity of charcoal from high temperature pyrolysis (800–1600 °C)

This study presents the effect of wood origin and heat treatment temperature on the CO2 reactivity, nanostructure and carbon chemistry of chars prepared at 800, 1200, and 1600 °C in slow pyrolysis reactors. The structure of charcoal was characterized by transmission electron microscopy, Raman spectroscopy, mercury intrusion porosimetry and N2 adsorption. The CO2 reactivity of char was investigated by thermogravimetric analysis. Results showed that spruce and oak chars have similar reactivity at all heat treatment temperatures. The oak char prepared at 1600 °C contained long and flat graphene layers and interplanar distance that is similar to graphite and thus, was more ordered than the spruce char. The TEM analysis showed that charcoal had structural characteristics of non-graphitizing carbon. Thus, increasing heat treatment temperature increases the graphitization of char structure, leading to the reactivity that is nearly similar to that of low reactive metallurgical coke. The wood origin, heat treatment temperature, nanostructure, differences in porosity and pore size of char influenced the CO2 reactivity less than the differences in CO2 concentrations.

Assessment of a Woodstove Changeout Program on PM2.5 Levels in Keene, New Hampshire, U.S.A.

In local airsheds, wood smoke from residential woodstoves is a major source of PM2.5 pollution. Exposure to PM2.5 can cause a variety of health problems and complications. Communities situated in valleys that experience cold winters are especially susceptible to poor air quality during inversion events on calm winter nights. Keene, New Hampshire, USA is one such community where the widespread use of outdated residential woodstoves frequently resulted in PM2.5 exceeding national standards. Seeking to improve air quality, the City of Keene partnered with the New Hampshire Department of Environmental Services from 2009-2010 to facilitate a woodstove changeout program which replaced 86 inefficient woodstoves with newer or alternate heating appliances. Despite the fact that many U.S. communities have enacted similar programs, research on their effectiveness is limited. This research assessed Keene’s program and determined that Keene has experienced a significant reduction in PM2.5 on calm winter nights. When winds are below 2 miles per hour (3.22 kilometers per hour), PM2.5 dropped 7% to 52% (1.28 to 7.30 µg/m3) after the woodstove changeout; a mean decrease of 23%. It therefore appears that Keene’s woodstove changeout program successfully improved air quality on the nights that are most likely to violate national air quality standards. This provides evidence that such programs can be an effective means to moderating the effects of wood heating in communities susceptible to inversions.

Effect of Temperature of Heat Treatment on Energetic Intensity of Flat Milling of Picea Abies

Abstract The paper deals with the research of the influence of thermal modification temperature of spruce wood on the electric energy consumption of its face milling. Samples of spruce wood heat treated at temperatures of 160, 180, 200 and 220°C were milled at the cutting speed of 20, 40 and 60 m.s-1, the feed rate of 6, 10 and 15 m.min-1, the rake angle of 15° with the depth of the cut of 1 mm. The energy consumption was evaluated from the cutting power, which was based on the difference during milling and idle cycle. The analysis of variance showed a decrease in cutting power with an increasing temperature of thermal modification. The average cutting power value is 137.7 W at the native sample and 80.8 W at the sample treated at 220°C. The Duncan’s test of statistical significance has shown that the thermal modification has a statistically significant effect on the cutting power values.

Heat treatment kinetics using three-stage approach for sustainable wood material production

The purpose of this study is to develop a numerical tool to predict the mass loss of a wood board during heat treatment as a marker of the process advancement. Mass loss dynamics during the wood heat treatment is experimentally obtained using a specially conceived equipment. The investigation method is applied on large scale wood samples whose radial and transvers dimensions are close to the boards used in industry. A two-step reaction mechanism is adopted to describe the behavior of wood thermodegradation. Model parameters are obtained by fitting the experimental data according to a new approach developed in this study for their optimal determination. The originality of the implemented modelling strategy is the establishment of a three-stage approach based on the analysis of wood thermal sensitivity depending on the treatment temperature range. Model equations are solved numerically by the commercial package Matlab® software. A good agreement is achieved between the numerical predictions and the experimental data. The developed model and established kinetics can be used for heat treatment process and reactor design in industry to produce wood materials for their applications.

Heat and Mass Transfer Properties of Sugar Maple Wood Treated by the Thermo-Hygro-Mechanical Densification Process

This study investigated the evolution of the density, gas permeability, and thermal conductivity of sugar maple wood during the thermo-hygro-mechanical densification process. The results suggested that the oven-dry average density of densified samples was significantly higher than that of the control samples. However, the oven-dry density did not show a linear increase with the decrease of wood samples thickness. The radial intrinsic gas permeability of the control samples was 5 to 40 times higher than that of densified samples, which indicated that the void volume of wood was reduced notably after the densification process. The thermal conductivity increased by 0.5–1.5 percent for an increase of one percent moisture content for densified samples. The thermal conductivity of densified wood was lower than that of the control samples. The densification time had significant effects on the oven-dry density and gas permeability. Both densification time and moisture content had significant effects on thermal conductivity but their interaction effect was not significant.

AN ANALYSIS OF HEATING UNIFORMITY IN WOOD HIGH-FREQUENCY DRYING

The high-frequency heating temperature field simulation model was built using finite element method and validated by experiments. Under the premise of ensuring model accuracy, the model parameters (plate spacing and area, wood dielectric constant, stack length and width, and heating time) were individually varied to assess the impact of these parameters on wood heating uniformity. The results showed the following: 1) The model has good accuracy as verified by experiments. 2) In the thickness direction, the middle layer temperature was higher than the upper and lower surface temperatures; in the length and width directions, the center temperature was lower than those of both ends and both sides, and the temperature at the corners was the highest. 3) The smaller the distance between the plates, the better the heating uniformity; with the plate area increasing, the heating uniformity first increased and then decreased; the smaller the wood dielectric constant, the better the heating uniformity; as the continuous heating time increased, the heating uniformity first decreased, then increased, and then again decreased; as the length and width of the stack increased, the heating uniformity decreased first, then increased, and then again decreased; when they were the same size as the plate, the heating uniformity was the best.

To adopt or not to adopt? Insights on energy transitions from a study of advanced wood heating

The study of energy system transitions requires research methods that incorporate multilayered systemic factors that span shifts in time, contexts, and actor groups. To integrate this complexity into energy transition research can be a daunting methodological challenge. However, it can illuminate how an energy system operates and help identify the levers that influence a transition to sustainable energy sources. This article describes how a multistate study of the strategies and policies to promote advanced wood heating technology in the northeastern United States encountered methodological challenges indicative of the broader problems faced in energy system transitions. In particular, we found that changes in macrolevel systemic factors (e.g. price of oil) and the early stage of diffusion of this particular technology complicate sampling and ultimately affect the application of results. While a participatory research approach and use of key informants helped in developing the sampling strategy, survey questions and access to study participants, it also introduced logistical difficulties and the potential for pro-innovation bias. We describe the mixed methods used to capture the systemic factors that affect adoption of this technology and highlight implications for research on interventions that seek to promote alternative energy technologies.

Development and Validation of a Simulation Model for the Temperature Field during High-Frequency Heating of Wood

In the process of applying high-frequency heating technology to wood drying, controlling the material temperature affects both drying speed and drying quality. Therefore, research on the heat transfer mechanism of high-frequency heating of wood is of great significance. To study the heat transfer mechanism of high-frequency heating, the finite element method was used to establish and solve the wood high-frequency heating model, and experimental verification was carried out. With a decrease in moisture content, the heating rate decreased, then increased, and then decreased again. There was no obvious linear relationship between the moisture content and heating rate; the simulation accuracy of the heating rate was higher in the early and later drying stages and slightly lower near the fiber saturation point. For the central section temperature distribution, the simulation and actual measurement results matched poorly in the early drying stage because the model did not fully consider the differences in the moisture content distribution of the actual test materials. In the later drying stage, the moisture content distribution of the test materials became uniform, which was consistent with the model assumptions. Considering the changes in heating rate and temperature distribution, the accuracy of the model is good under the fiber saturation point, and it can be used to predict the high-frequency heating process of wood.

A comparative study of some of the mechanical properties of pine wood heat treated in vacuum, nitrogen, and air atmospheres

The use of heat treatment to modify wood using different treatment heat transfer media, such as nitrogen, vegetable oil, steam, and vacuum, is preferable in many respects to other methods that use chemical treatments. However, the results of the heat treatment differ based on the heat transfer media that are used. In this study, the thermal modification of black pine wood in vacuum, nitrogen, and air atmospheres was studied. The heat treatments were conducted at temperatures of 180 °C, 200 °C, and 220 °C. After the heat treatments, the density, mass loss, modulus of rupture, modulus of elasticity, and impact of bending of heat-treated black pine wood were determined. The results indicated that the density, modulus of rupture, and impact of bending decreased as the temperature increased. In addition, the greatest decrease in the mechanical properties of the wood occurred in the test samples that were treated in air. The vacuum atmosphere was least harmful to the mechanical properties of the wood, and the differences in the mechanical properties of the wood that were heat treated in vacuum and nitrogen were unnoticeable.

Impact Of Heat Treatment On Weight Loss During Combustion Of Laminated Veneer Lumber (LVL)

This study was performed to determine the effects of heat treatment on weight loss during combustion of the laminated wood materials produced from Oriental beech ( Fagus orientalis L.), scotch pine ( Pinus sylvestris L.), sessile oak ( Quercus petraea L.), and poplar ( Populus nigra L.) veneers bonded with PVAc-D 4 , PUR and MF adhesives. For this aim, the weight loss during combustion of the test samples was determined according to ASTM E 160-50. The results of this study indicated that the weight loss percentage was the highest in poplar wood (89.17%), PVAc-D 4 adhesive (89.79%) and control samples (88.69%). In the interaction of the wood materials and type of adhesive, the highest value was measured in poplar+PUR (90.93%), interaction of the wood materials and heat treatment in poplar + control samples (90.87%), in the interaction of the type of adhesive and heat treatment in PVAc-D 4 + 185 °C (91.10%). In the interaction of the wood material, type of adhesive and heat treatment temperature, the highest value was determined in laminated control poplar samples with PUR adhesive (93%), while the lowest in laminated scotch pine samples with MF and heat-treated at 185 °C (81.83%). The use of laminated and heat-treated wood material in places where in high risk of fire, impregnation of wood material with fire-retardant compounds can be suggested.

Policy incentives for flexible district heating in the Baltic countries

This study analyzes the impacts of taxes, subsidies, and electricity transmission and distribution tariffs and heat storage on the operation and economic feasibility of district heating plants with different flexibility potentials in the Baltic countries. Under 2016 conditions, the lowest levelized cost of heat is achieved by a combination of wood chip boilers, electric boilers, and heat storage. Heat storage enables a higher utilization of least-cost technologies, resulting in greater cost efficiency for all considered scenarios. Current taxes and subsidies are found to have limited impact on the operation of combined heat and power plants and electric boilers.

Physico-mechanical properties of light red meranti (Shorea spp.) and kedondong (Canarium spp.) wood heat treated in convection oven

Physico-mechanical properties of light red meranti and kedondong wood heat treated in a laboratory at 160, 180 and 200 °C for 5, 7 and 9 h were investigated. Weight loss of the treated samples increased along with treatment severity. Heat treatment reduced the hygroscopicity of the wood where reduction in equilibrium moisture content and a positive moisture excluding efficiency was observed. Reduction in bending strength as function of increasing treatment temperature and time were also recorded.