Moisture Content Of Wood Chips Research Articles

NIR-based models for the evaluation of basic density, moisture and higher heating value of industrial wood chips

ABSTRACT The quick and efficient classification of wood is crucial for optimizing processes in forestry industries, which highlights the use of near infrared (NIR) spectroscopy. This study investigated the application of NIR spectroscopy for estimating the basic density, moisture content and calorific value of wood chips of Eucalyptus urophylla × E. grandis hybrids directly in the company yard. Using two lots of industrial chips collected in the company’s yard (Lots A and B), the NIR signatures were correlated with the results obtained by standard methods via Partial Least Squares Regression (PLS-R). The predictive models presented coefficients of determination (R²) of 0.83 for basic density (Lot A), 0.81 to 0.90 for moisture content (Lots A and B) and 0.74 for calorific value (Lot A). Variations in the moisture content of wood chips impacted the information quality of spectral signatures and thus the model accuracy, highlighting the difficulty of applying this technology in field conditions. However, the NIR models can be used as a solution for fast estimation of wood chips quality in the company yard, optimizing industrial processes.

Utilizing the Heat Waste from Biomass Power Generation to Reduce the Moisture Content of Woodchips

This paper is to study the drying method to reduce the moisture content (MC) of the woodchip. The methods used are to utilize the heat from solar and waste heat from the Biomass Power Plant (BioPP). By using a 250 °C heat waste from the BioPP, and stirring on the woodchip inside the drying equipment, the results obtained to reduce the MC from more than 40 % to MC around 20 % will take 2 h and 4 h faster than that which was not done on woodchips. Reducing MC from 40 % to 20 % will save 25.44 % on the woodchip consumption for combustion in the boiler of the BioPP. An analysis related to MC, CV, and woodchip consumption in generating electricity is also carried out. When MC is 26.70 %, the CV is 13.5 GJ T-1, and the woodchip consumption becomes 4.62 T h-1 and 1.31 T MWh-1, the energy produced is 764.7 kWh T-1. When the MC is higher, 47.68 %, causing the CV to become 9.8 GJ T-1, it is found that the consumption of the woodchips becomes 6.41 T h-1 and 1.81 T MWh-1, the energy produced is 551.3 kWh T-1.

Dielectric meter for moisture content determination of wood chips

The aim of this study was to evaluate the efficiency of the dielectric meter in predicting moisture content in wood chips based on the input parameter (capacitance) which yields the measured value (moisture). A database was constructed from twelve sets of measurements using the dielectric moisture meter on wood chips of Pinus sp. and Eucalyptus sp. from eight different suppliers. This database was then used to produce a specific curve for each supplier through linear regression. Consequently, a positive linear correlation was observed, with the data points showing a 45° trend in their dispersion on the graph for each curve. It was noted that the dielectric constant decreased as the moisture content reduced during the drying process. With a determination coefficient R² exceeding 80% on the curves, it's feasible to predict the moisture content based on the dielectric properties of each group of wood chips in a swift, practical, and cost-effective manner.

Experimental studies of wood chips charactristics influence on boiler performance and pollutant emissions

Wood chips are often used as solid fuel in modern biomass boilers. Experiments were conducted on 22 boilers located in Serbia burning wood chips as fuel. The influence of wood chips characteristics is analyzed in relation to the flue gas losses and the thermal efficiency of the boiler. Measured useful heat output of the tested boilers was 460-2585 kW. Moisture content of the wood chips was 19.21-38.23% with a net calorific value of 10177-14139 kJ/kg and ash content of 0.84-3.59%. Thermal efficiency of the boilers was 88.78-94.06%, flue gas losses 5.84-11.13% and flue gas temperature 121.83-188.44?C. Experimental research and analysis of the results showed that an increase in moisture content of wood chips lead to a decrease of net calorific value i.e., decrease in flue gas temperature. Moisture content of wood chips has an influence on both useful heat output and boiler thermal efficiency. The experimental results showed that for a given boiler construction, this impact is not negative. Based on regression analysis, mathematical expressions were derived for the calculation of thermal efficiency and flue gas losses. Throughout the experiments, pollutant emissions were measured, NOx, CO, and particulate matter.

Measurement of the moisture content in woodchips through capacitive sensing and data driven modelling

In this paper, a helical capacitive sensor is developed to measure the moisture content (MC) in woodchips. Firstly, based on the orthogonal test method, the structure of the capacitive sensor is optimized to obtain the best possible uniform sensitivity. Then, the effect of the type and random distribution of woodchips on the capacitive MC measurement is investigated. Finally, three different algorithms, including support vector machine, random forest and deep neural network, are employed to establish the data driven models. Experimental results demonstrate that the proposed system is capable of measuring the MC in woodchips with absolute error within ±5%. The generalization capability is verified using the cedarwood with three size ranges, with R2, RMSE and MAE of 0.95, 1.69% and 1.28%, respectively. The absolute error of the predicted MC in cedarwood over the range 24.3% and 25.2% is found to be within ±2% for a range of packing densities.

Effects of microwave irradiation on the moisture content of various wood chip fractions obtained from different tree species

The paper proposes the use of microwave irradiation to lower the initial moisture content of wood chips. The study involved willow and fir chips fractionated by means of a sieve separator and unfractionated ash chips. The wood chips were exposed to a constant microwave power of 800 W for 30 s, 60 s, 120 s and 180 s. The chips were weighed before and after irradiation to measure loss of moisture. It was found that the decline in moisture content increased with wood chip size for a given irradiation time and microwave power. The initial moisture content of wood chips was not found to significantly affect loss of moisture as the drying rates of wood chips with higher and lower moisture content exposed to microwaves were not statistically different. The results showed that irradiation intensity increased with the time of exposure to microwaves and unit radiant energy per unit of evaporated moisture decreased with increasing wood chip size in the 3.15–31.50 mm range.

An Analysis of the Current Status of Woody Biomass Gasification Power Generation in Japan

Forests cover two-thirds of Japan’s land area, and woody biomass is attracting attention as one of the most promising renewable energy sources in the country. The Feed-in Tariff (FIT) Act came into effect in 2012, and since then, woody biomass power generation has spread rapidly. Gasification power generation, which can generate electricity on a relatively small scale, has attracted a lot of attention. However, the technical issues of this technology remain poorly defined. This paper aims to clarify the problems of woody biomass gasification power generation in Japan, specifically on the challenges of improving energy utilization rate, the problem of controlling the moisture content, and the different performance of power generation facilities that uses different tree species. We also describe the technological development of a 2 MW updraft reactor for gasification and bio-oil coproduction to improve the energy utilization rate. The lower heating value of bio-oil, which was obtained in the experiment, was found to be about 70% of A-fuel oil. Among the results, the importance of controlling the moisture content of wood chips is identified from the measurement evaluation of a 0.36 MW-scale downdraft gasifier’s actual operation. We discuss the effects of tree species variation and ash on gasification power generation based on the results of pyrolysis analysis, industry analysis for each tree species. These results indicate the necessity of building a system specifically suited to Japan’s climate and forestry industry to allow woody biomass gasification power generation to become widespread in Japan.

Estimation of moisture in wood chips by Near Infrared Spectroscopy

In order to assess the moisture content of wood chips on an industrial scale, readily applicable techniques are required. Thus, near infrared (NIR) spectroscopy was used to estimate moisture in wood chips by means of partial least squares regressions. NIR spectra were obtained in spectrometer with an integrating sphere and optical fiber probe, on the longitudinal and transverse surface of Eucalyptus wood chips. The specimens had their masses and NIR spectra measured in 10 steps during drying from saturated to anhydrous condition. Principal Component Analysis was performed to explore the effect of moisture of wood chip on NIR signatures. The values of moisture content of chips were associated with the respective NIR spectra by Partial Least Squares Regression (PLS-R) and Partial Least Squares Discriminant Analysis (PLS-DA) to estimate the moisture content of wood chips and its moisture classes, respectively. Model developed from spectra recorded on the longitudinal face by the integrating sphere method presented statistics slightly better (R²cv = 0,96; RMSEcv = 7,15 %) than model based on optical fiber probe (R²cv = 0,90; RMSEcv = 11,86 %). This study suggests that for calibration of robust predictive model for estimating moisture content in chips the spectra should be recorded on the longitudinal surface of wood using the integrating sphere acquisition method.

Production of Chips from Logging Residues and Their Quality for Energy: A Review of European Literature

Wood chips from logging residues are a renewable solid fuel that has become widely used in the energy sector. The current work presents a review of European papers on various aspects of wood chips production published in the years 2005–2018. The effects of the comminution method on the quality and energy parameters of the resulting wood chips were analysed. Most authors identified terrain and roadside chipping as the optimum technologies from the energy viewpoint. Furthermore, seasonal changes in the moisture content of wood chips have implications for their ash content and calorific value and determine the annual patterns of supplies to energy plants. In general, logging residues should be chipped approximately five to seven months after harvesting and delivered over economically feasible distances, which have increased in recent years due to the large dispersion of forest areas and energy plants. In a number of cases, logging residue chips did not meet the quality specifications contained in the relevant ISO standards, which may result in technological problems with their burning, especially in small to medium energy plants.

Feasibility of Using Wood Chips to Regulate Relative Humidity Inside a Building: A Numerical Study

The use of bio-based materials in buildings has become more and more significant last years. In most of the cases, their health properties and natural provenance have made them a great solution to face global climate warming and the new policies to reduce building energy consumption. In many thermal problems, bio-based materials can allow to optimize the building thermal behavior according to its energy consumption and inside comfort conditions. So it is when they are used as an insulation material in the building. However, it is not the case in this paper. In fact, the bio-based matter is rather used as a desiccant wheel to control air conditioning inside the building. The aim of this paper is to numerically verify if it is possible to use a bed of wood chips as a hygroscopic material (or a desiccant matter) in order to modify the relative humidity inside the building in Reunion Island and so improve thermal comfort. A simple model of heat and mass transfer between a bed of wood chips and building inside air has been set up and implemented into a validated building simulation code named ISOLAB. Numerical simulations were set up for the four climate zones of the island regulations and a focus has been made on the low altitude one (with high, solar irradiation, temperature and relative humidity). Simulation results give the thermal behavior of the building particularly the temperature and relative humidity of inside air temperature, and temperature and moisture content of wood chips. The obtained results lead to determine if the wood chips bed is suitable for the reference building and to verify its technical feasibility (wood species, size of the bed, integration to the building, etc.). The results show that the use of a WCB help to decrease the building inside air temperature and water content up to 10°C less and 11.6 g.kg-1 less. These are the ways to improve inside comfort conditions. Indeed, comfort analysis have shown the possibility to significantly increase building users’ thermal comfort when coupled with a fan and natural ventilation, like the regulation needs for low altitude climate. In this case, a gain of 68% of year time is achieved for a building equipped with WCB system compared to one without it (6308 hours of comfort over a year with the WCB against 350 hours without WCB). So the WCB seems to be able to help reducing cooling loads in tropical climate conditions.

UWB Radio Measurement and Time-Domain Analysis of Anisotropy in Wood Chips

Ultra-wideband (UWB) radio transmission measurements have been used to determine the moisture content of wood chips using a time-domain technique. Wood chips have been found to have birefringent dielectric properties acting as an anisotropic dielectric effective medium. Birefringence in wood chips occurs because of the orientation and the shape of wood chips and microscopic structures of these objects, such as wood fibers. The birefringence gives rise to two different wavefronts along the principal axes, which have different dielectric properties. Each wavefront has a specific time-domain signal that can be used to determine the moisture content. In industrial applications, for example, in measurement on wood chips in trucks, the vertical polarization direction is the preferable polarization because this signal has higher signal-to-noise ratio, which makes the signal more identifiable at longer distance (2–3 m). Thus, UWB radio transmission measurement and time-domain analysis is a robust technology to investigate larger containers of wood chips and to determine the moisture content with high accuracy.

Planning woody biomass supply in hot systems under variable chips energy content

The growing economic importance of the biomass-for-bioenergy in Europe motivates research on biomass supply chain design and planning. The temporally and geographically fragmented availability of woody biomass makes it particularly relevant to find cost-effective solutions for biomass production, storage and transportation up to the consumption facility. This paper addresses tactical decisions related with optimal allocation of wood chips from forest residues at forest sites to terminals and power plants. The emphasis is on a “hot-system” with synchronized chipping and chips transportation at the roadside. Thus, decisions related with the assignment of chippers to forest sites are also considered. We extend existing studies by considering the impact of the wood chips energy content variation in the logistics planning. This is a key issue in biomass-for-bioenergy supply chains. The higher the moisture content of wood chips, the lower its net caloric value and therefore, a larger amount of chips is needed to meet the contracted demand. We propose a Mixed Integer Programming (MIP) model to solve this problem to optimality. Results of applying the model in a biomass supply chain case in Finland are presented. Results suggest that a 20% improvement in the supplier profit can be obtained with the proposed approach when compared with a baseline situation that relies on empirical estimates for a fixed and known moisture content in the end of an obliged storage age.

Impact of drying-grinding sequence on loblolly pine chips preprocessing effectiveness

The high amount of energy consumed during the processing of biomass inflates the production cost of bio-fuels and bio-products. This study was therefore carried out to evaluate the influence of drying and grinding sequence on biomass energy consumption and properties (specific grinding energy requirement, specific drying energy requirement, particle size distribution, bulk density, tap density, aspect ratio, and flow index of grinds). Among the six drying-grinding sequences (12-S, 30-S, 50-S, 30-L-12-S, 50-L-12-S, and 50-L-30-S), sequence 50–S had the lowest geometric mean diameter and sequence 30–S had the highest geometric mean diameter. Drying-grinding sequence significantly affected the bulk density and tap density of grinds. The bulk density of grinds varied from 267.1kg/m3 (sequence 12-S) to 98.0kg/m3 (sequence 50-S) while the tap density ranged from 342.6kg/m3 (sequence 12-S) to 153.7kg/m3 (sequence 50-S). This variation in the densities followed the changes the particle morphology and aspect ratio distribution. A trade-off was noted between specific grinding energy requirement and specific drying energy requirement. The grinding of samples at higher moisture content consumed higher grinding energy than the grinding of samples at lower moisture content. Moisture loss during grinding however increased as the moisture content of woodchips increased, hence resulted in lower drying energy requirements. The least specific drying energy consumption was (1581kJ/kg d.b.) for sequence 50-S and the highest specific drying energy consumption was (3933kJ/kg d.b.) for sequence 12-S.

The effect of storage time and moisture content on grindability of loblolly pine (Pinus taeda L.)

Specific grinding energy and particle size distribution of grinds are usually used to assess the efficiency of grinding equipment and material grindability. The objective of this study was to quantify the effects of moisture content and storage time on the specific grinding energy of loblolly pine woodchips and the physical properties of the resulting grinds. Samples were ground in a hammer mill fitted with 3.18 and 6.35 mm screen sizes. The specific grinding energy, moisture loss during grinding, particle size distribution, and bulk density of the grinds were measured. Moisture loss during grinding increased with increase in moisture content of woodchips and decreased with increase in hammer mill screen size. Bulk density of grinds reduced from 273.64 to 106.03 kg/m3 and from 251.14 to 131.40 kg/m3 (for 3.18 mm and 6.35 mm hammer mill screen size, respectively), when the moisture content of woodchips was increased from 13.6 to 100.0 % (dry basis). Results also showed that storage time did not significantly affect (p < 0.05) the specific grinding energy. However, specific grinding energy was significantly affected (p < 0.05) by the moisture content of woodchips and hammer mill screen size. The specific grinding energy of woodchips ground through 3.18 mm hammer mill screen size increased with increase in moisture content of woodchips. However when loblolly pine woodchips were ground through 6.35 mm hammer mill screen size, the specific grinding energy initially increased as moisture of woodchips increased from 13.6 to 42.9 % (dry basis), then decreased with further increase in moisture content of woodchips from 42.9 to 100.0 % (dry basis).

Capacitance Sensing of Moisture Content in Fuel Wood Chips

Moisture content of wood chips is an important factor to be known in their utilization as a biomass material. Several moisture measuring instruments are available in the market, but for most of these instruments, some sort of sample preparation is needed that involves sizing, grinding, and weighing. The samples in this process are usually destroyed, and the measurement involves considerable time and labor. The standard methods of oven drying and Karl Fisher also fall in the destructive and laborious category. In this paper, estimation of moisture content of hardwood chips, from the measurement of certain electrical properties of a parallel-plate capacitor, holding the samples of these materials between them at two radio frequencies, is presented. The wood chip samples tested were in the moisture range of 3%–50%. The standard error of prediction was 2.0, and the prediction accuracies were better for the samples with moisture contents below 25%. The construction and performance of a prototype moisture sensing instrument working on these principles is briefly described. This method being nondestructive and rapid would be useful in the biofuel industry.

Predicting moisture content of chipped pine samples with a multi-electrode capacitance sensor

Woody biomass is currently sold on a weight basis, practical moisture sensors are essential for fair sales, especially in energy markets. To address this need, an 8-electrode electrical capacitance tomography (ECT) sensor was built and tested for predicting moisture content of wood chips and compared with the near infrared spectroscopy (NIR) method. The goal was to find an optimal means of measuring moisture content of woody biomass in the form of chips in two situations: individual chips and bulk samples. Tests were made on chips ranging in moisture content from 4% to 140% (d.b.). Results indicated that NIR had better performance in measuring moisture of single wood chips, while ECT was more accurate and rapid in bulk moisture determination. Knowledge of the mass of wood chips under test was required in the ECT moisture prediction model, unlike in the case of NIR. Both methods had the capability to measure moisture content of biomass while in motion. From a practical standpoint, however, only a portion of the material flowing past a near-infrared sensor could be practically scanned and the sub-sampled biomass would have to be representative of the entire population to be accurate. The ECT sensor, on the other hand, could likely be designed to scan the entirety of a large quantity of moving material and provide an accurate bulk average moisture content. Compared to a single paired-plate capacitance sensor, the ECT system also provided images, through its tomography function, that displayed permittivity distribution variability throughout bulk biomass samples.

Biomass gasification with CO2 in a fluidized bed

Biomass gasification with CO2 as the gasifying agent is a promising way to relieve the energy shortage and minimize CO2 emission. In this study, Eulerian method was used to study the CO2 gasification of biomass in a fluidized bed gasifier. It was found that the CO2 percentage in the gasifying mixture with air, the CO2-to-biomass ratio, the moisture content of woodchips, and the woodchip size had great influence on the gasification performance. With the increasing CO2-to-biomass ratio, the mole fraction of CO in the producer gases would be increased while those of H2 and CO2 vary in the opposite trend. When CO2 mass percentage in the gasifying agent was 60%, the fractions of CO and CH4 in the producer gas reached the maximum, as well as the lower heating value and cold gas efficiency, so this was the optimal condition when the gasifier had the best performance. The moisture content and particle size of the woodchips had negative effects on the gasification performance, because of the lower heating value of producer gases, cold gas efficiency and CO2 conversion ratio were both reduced with increasing moisture content and particle size. This study offers a promising way to integrate the gasification of renewable biomass with CO2 capture, and may be helpful in the design and operation of biomass gasifier.

Lumber and wood chips properties of dead and sound black spruce trees grown in the boreal forest of Canada

Little attention has been given to changes in wood properties after isolated mortality events, which characterize the gap dynamics of several forest ecosystems. For the forest industry, dead and sound trees may represent a significant source of timber supply, but of potentially lower quality. The main objective of this study was therefore to compare the properties of wood obtained from dead and sound wood (DSW) trees with those from live trees. In total, 162 black spruce trees (Picea mariana (Mill.) BSP) were felled from three sites comprising three states of tree degradation and three diameter classes. In total, 822 pieces of lumber of different dimensions were produced and visually graded. Full-size lumber pieces of 4.3–5.0 m in length (n 1⁄4 343) were tested for wood stiffness and strength in longitudinal static bending. Samples of wood chips and bark were also collected during the production process at a sawmill. Results indicate that DSW trees produced lumber of significantly poorer mechanical properties than live trees. For the same modulus of elasticity (MOE) value, DSW trees have significantly lower modulus of rupture values than those of live trees, especially for MOE values of ,15 GPa. This suggests that the wood of DSW trees is more brittle, a fact that should be taken into account for the production of machine-stress-rated lumber. Moisture content of wood chips was significantly lower in DSW trees, although it remained above the fibre saturation point. The amount of wood fibre attached to the bark was significantly higher in DSW trees. Considering these differences, DSW trees can be expected to provide wood of inferior quality than live trees but which still meet the technical requirements (Barrett and Lau, 1994) for producing structural lumber.

Design of methodology for wood chips moisture estimation determined for gasification

The moisture content of the charged wood chips is a significant factor affecting the gasification process. The increased moisture content increases the demand on the energy consumption, which is needed to cover the heat consumption related to the water evaporation and adversely affects the wood gas quality and input fuel amount. Monitoring of the moisture content in wood chips is therefore the diagnostic tools suitable to evaluate the operational parameters of the whole gasification process. Present paper describes the design of the suitable methodology to measure and estimate the wood chips moisture content. The issues related to the moisture content estimation include preliminary the selection of the suitable methodology based on the assumed moisture content in the wood chips. Further factor which needs to be considered is the fact that the moisture content in wood chips is time dependent due to the changing parameters of the ambient air (as temperature, pressure and air humidity). Correctly estimated moisture content will enable to improve the wood chips gasification process.

Determination of the moisture content in wood chips of Scots pine and Norway spruce using Mantex Desktop Scanner based on dual energy X-ray absorptiometry

There has been a longstanding interest in developing a fast and accurate method for measuring moisture content in wood. The gravimetric method that is commonly used today is a widely accepted industrial standard but it is time consuming. In this study, we tested and evaluated Mantex Desktop Scanner that is based on dual energy X-ray absorptiometry as a potential technique for fast and accurate determination of moisture content at different temperatures in wood chips of Pinus sylvestris, Picea abies and a variety of mixtures thereof. The results of the study give similar results as the gravimetric method when determining the moisture content in wood. They further show that there was no significant influence on the result if samples were measured while frozen or at room temperature.