Pine Pellets Research Articles

Ecotoxicity of Tar from Coffee Grounds and Pine Pellet Gasification Process

This study determined the toxicity of the condensates produced during the gasification of two waste types. Coffee grounds, pine pellets, and a mixture of both substrates at a ratio of 1:1 were used in the study. Two microbiotests were applied for soil plants and aquatic macrophytes, and quantitative analysis of the soil microbiome for primary taxonomic groups of microorganisms was conducted. Three contamination rates were used in the Phytotoxkit test and the microbiological tests, 100, 1000, and 10,000 mg·kg−1 d.m. of soil, while in the aquatic organism studies, successive two-fold serial dilutions of condensates were used. The presence of liquid waste from the gasification process adversely affected the germination and development of terrestrial plants and the vegetative growth of aquatic plants. The condensate components modified the composition of the soil microbiome, adversely affecting soil fertility. The negative impact increased with increasing levels of contamination and primarily depended on the type of substrate from which the gasification process produced the liquid waste.

Preemergence Herbicides and Mulches for Cutting Propagation—Impact on Rooting, Growth after Transplant, and Weed Control

Weed control in cutting propagation is limited to manual hand weeding, which is time-consuming and labor-intensive. Preemergence herbicides and mulches may be viable weed control methods for cutting propagation, but crop safety and weed control efficacy must be better understood. Four preemergence herbicides (indaziflam, isoxaben, isoxaben + dithiopyr, and oxyfluorfen + oxadiazon) and two mulches (pine pellets and rice hulls) were assessed in cutting propagation for their impact on rooting and subsequent liner growth (butterfly bush [Buddleja davidii Franch.] and crape myrtle [Lagerstroemia indica L.]) and control of four common weed species. Butterfly bush cuttings had lower rooting percentage and root dry weight with isoxaben and isoxaben + dithiopyr, but no damage was observed for all other treatments during propagation or after transplant. Crape myrtle cutting root development and liner growth were statistically similar for all treatments compared to the non-treated control. Isoxaben, isoxaben + dithiopyr, oxyfluorfen + oxadiazon, and pine pellets provided excellent control (87 to 100%) of all four weed species tested. Overall, several preemergence herbicides and mulches were safe for use in cutting propagation and effective weed control varied by product and weed species.

Pellets from mixtures of short rotation coppice with forest-derived biomass: Production costs and energy intensity

The demand for feedstock for pellet production is growing, with a consequent increase in the cost of their purchase and the cost of production. The objective of this study was to determine the cost and energy intensity of pellet production from forest biomass (Scots pine, silver birch) and short rotation coppice – SRC (black locust, poplar and willow) and their mixtures. The lowest cost (339.7 € Mg−1) and energy input (1448 kWh Mg−1) for pellet production were determined for Scots pine. The cost of pellet production from poplar and willow was higher by 5–6% compared with Scots pine pellet. The energy input for pellet production from willow, black locust and poplar was higher by 48.1%, 50.4% and 53.2%, respectively. The feedstock purchase cost (50.3–57.8%) and energy input for drying them (74.6–82.6%) accounted for the largest portion. Increasing the share of SRC biomass from 25% through 50%–75% relative to Scots pine and silver birch biomass resulted in a cost and energy intensity increase and decrease in the energy efficiency of pellet production. Three pellet types: produced from Scots pine and those with an addition of 25% of willow or poplar made up one cluster.

Predicting the energy properties of torrefied debarked pine pellets from torrefaction temperature and residence time

Predicting the energy properties of torrefied debarked pine pellets from torrefaction temperature and residence time

Computational and Experimental Studies on Combustion and Co-Combustion of Wood Pellets with Waste Glycerol.

The shortage of fossil fuels and their rising prices, as well as the global demand for renewable energy and the reduction in greenhouse gas (GHG) emissions, result in an increased interest in the production of alternative biofuels, such as biodiesel or biomass pellets. In this study, the possibility of utilizing waste glycerol, as an addition to pine pellets intended for heating purposes, has been investigated. The usefulness of pellets containing glycerol additions has been compared in terms of applicable quality standards for wood pellets. The highest values of moisture (4.58%), ash (0.5%) and bulk density (650 kg/m3) were observed for pellets without glycerin waste. The addition of waste glycerol slightly increases the calorific value of the pellet (17.94 MJ/kg for 7.5% additive). A 10-kW domestic biomass boiler has been employed to burn the tested pellets. The consumption of analyzed fuels during boiler operation was determined. The concentration of CO, CO2 and NOx in exhaust gases has also been examined. It was observed that the addition of 7.5% of waste glycerol contributes to the reduction in NOx concentrations by 30 ppm and CO2 by 0.15%. The obtained experimental results were compared with the numerical calculations made with the use of ANSYS Chemkin-Pro. The conducted research indicates the legitimacy of utilizing waste glycerol as an additive to wood pellets. In addition, this type of addition has a positive effect on, among others, the increase in calorific value, as well as lower emissions of combustion products such as NOx and CO2.

The Determination of Combustion for Different Pellets Based on Ostwald Diagrams in a Domestic Stove under Experimental Conditions

The global energy scenario is becoming a vital aspect of the sustainable economic development of regions and countries. Current changes in energy production, mainly due to scarcity and geopolitical factors, have proven the need for changes in energy distribution towards a lower energy dependence. Moreover, a considerable amount of biomass waste is generated in many regions, because of agro-industrial activities, whose management could contribute to energy production. The aim of this work was to study the optimization of the combustion process in a biomass stove by using different raw materials as fuels, such as pine, poplar, and plum tree pellets. For that purpose, power, excess air, and biomass content were optimized, among other parameters, and exhaust gases were analyzed with a Testo 335 analyzer, while temperatures were recorded with temperature probes. In conclusion, high yields were found for the optimized parameters of the studied biomass products (ranging from 91.1% for poplar pellets to 92.34% for pine pellets), making these three biomass fuels suitable for combustion in the abovementioned stove. Also, increasing biomass flow by 25% in the stove contributed to a higher efficiency of the process, especially in the case of plum tree pellets.

Thermo‐economic assessment of a bench‐scale pyrolysis unit through a process simulator

AbstractThis article focuses on the holistic appraisal of a pilot‐scale updraft reactor (E1) powered by the processed residue of forest waste (W1) and hog fuel (W2). The detailed analysis of the up‐draft unit includes the availability of energy, economic evaluation, and the determination of the lignocellulose content of the pine waste. The reformed structure of the pine pellet was used for gas, bio‐oil, and char generation. The Aspen HYSYS process simulator was used for simulation purposes and the results were validated with the solution obtained experimentally. For the measurement of the constituent contents of the pine needles, the National Renewable Energy Laboratory (NREL) procedure was adopted. To investigate the similitude of the packed bed reactor, the Soave–Redlich–Kwong model was considered. For comparison of the given prototype, five different reactor types – conversion (R1), equilibrium (R2), Gibbs (R3), continuous stir tank (CST) (R4) and plug flow (R5) – were juxtaposed and their thermodynamic behavior was evaluated. From structural composition, it was noticed that the cellulose and hemicellulose(s) content dropped by 24.95% and 37.37%, respectively, whereas a rise of 23.33% was seen in the acid‐insoluble lignin (AIL) fraction of forest waste after the torrefaction process. Irrespective of the fuel type, the unconsumed fuel percentage was the same for both wood and processed residue pellets for R5. The relative percentage of methane increased by 1% for processed forest residue. The CO2 emission was estimated to be maximum for reactors R3 and R4. The O2 gain was absent in the R2 reactor. Concomitantly, it gained momentum in R1, R3, and R4. The simulated polytropic equations of state for W1 and W2 were PV1.083 = C and PV1.092 = C, respectively. The levelized cost of energy dropped by 12.50% while scaling up a pyrolysis unit.

Integration of thermoelectric generators in a biomass boiler: Experimental tests and study of ash deposition effect

Thermoelectric generators (TEGs) are based on Seebeck effect and produce electricity from a heat flow. They require low maintenance and provide quiet operation. However, they have low efficiency and need suitable temperature values. Accordingly, the integration of TEGs in boilers is a promising approach, since these equipment present high temperature differences between hot gases and water and allows the use of waste heat for water heating. There are experiences of the integration of TEGs in biomass boilers, but almost none with unconventional biomass with a high tendency to ash deposition. The integration of TEG modules in a commercial pellet-fired 25 kWth boiler is described and experimental results, working with pine pellets and with an agropellet (70% of vineyard pruning and 30% of barley straw), are presented. Power produced with only 6 modules can reach 60 W. After quantifying the effect of the temperature on both gas and water sides, the study focuses on analyzing the ash deposition on the exchange surfaces and their effect on TEG modules operation (e.g. power reduction of 0.24 W per hour with pine and 0.78 with agropellet). This effect can be minimized by working with high excess of air or by integrating a cleaning system.

Thermal Energy and Exhaust Emissions of a Gasifier Stove Feeding Pine and Hemp Pellets

This paper presents the results of research on the energetic use of self-combusted hemp pellets and co-firing with pine pellets. The tests were carried out with the use of a boiler equipped with a Lester Projekt Company gasifying burner and an automatic fuel feeding system. The boiler is equipped with an additional heat exchanger that enables the simulation of any heat load. The experimental stand so built guaranteed to obtain results adequate to the real operating conditions. The research material consisted of pellets made of waste biomass of the Futura 75 sowing hemp and pine sawdust pellets. The experiment was carried out in five proportions by mass of mixtures of both fuels (C-hemp, P-pine): 0:100 (P100), 25:75 (C25/P75), 50:50 (C50/P50), 75:25 (C75/P25), 100:0 (C100). For each variant, the following were determined: effective boiler power, boiler energy balance, boiler energy efficiency, the volumetric composition of flue gas (carbon monoxide, carbon dioxide, hydrogen, sulfur dioxide, nitrous oxide), excess air coefficient and the dust content of particle matter—PM10, PM2.5. The heating value was also determined for hemp pellets and pine sawdust pellets, accordingly 17.34 and 19.87 MJ·kg−1. The obtained test results were related both to the volume of exhaust gases leaving the boiler and to one kilowatt hour of heat produced. The obtained test results showed that the boiler fed with pine pellets achieved the highest thermal power (P100)—14.17 kW, while the smallest—hemp pellets (C100)—4.92 kW. The CO2 emissivity increased with the addition of pine pellets, from 26.13 g (C100) to 112.36 g (P100) relating to 1 m3 and from 430.04 g (C100) to 616.46 g (C25/P75) relating to 1 kWh of heat. In terms of dust emissions, it was found that the combustion of hemp pellets and mixtures thereof is a little worse than that of pine pellets.

Effect of Mulch Type and Depth on Rooting of Stem Cuttings and Weed Control in Containers

Weeds are a major problem in cutting propagation and compete with the main crop for water, sunlight, and nutrients, thus reducing growth and marketable quality of rooted cuttings. Due to the high labor cost of hand weeding, mulches can be an alternative method for weed control in the propagation environment. The objective of this research was to determine the effect of mulches (coarse vermiculite, rice hulls, paper pellets, and pine pellets) on rooting of stem cuttings and weed control when applied at 0.5- and 1-inch depths. Cuttings of three plant species [‘Nanho Blue’ butterfly bush (Buddleja davidii), ‘Catawba’ crape myrtle (Lagerstroemia indica), ‘Phantom’ hydrangea (Hydrangea paniculata)] were stuck in 2.5-inch-diameter containers filled with pine bark substrate and treated with mulch. In a separate study, seeds of four weed species [creeping woodsorrel (Oxalis corniculata), hairy bittercress (Cardamine hirsuta), large crabgrass (Digitaria sanguinalis), mulberry weed (Fatoua villosa)] were sown onto the mulch surface. Rooting percentage was unaffected by mulch type or depth for any of the three crop species (‘Nanho Blue’ butterfly bush, ‘Catawba’ crape myrtle, ‘Phantom’ hydrangea). Pine pellets did not affect root dry weight of any crop species, but root length and volume of ‘Catawba’ crape myrtle was reduced by pine pellets at 1-inch depth. Rice hulls slightly reduced the root length and volume of ‘Catawba’ crape myrtle, but the reduction was less than 50%. Pine pellets and paper pellets (both depths) reduced growth of all four weed species. Even though weed seeds germinated in pine and paper pellets, seedlings did not grow large enough to potentially affect crop rooting. In conclusion, pine pellets and paper pellets at 0.5-inch depth can be effective in suppressing weed populations with minimal effect on rooting.

Degradation effect of diatomite on pyrolysis volatility of pine pellets

Degradation effect of diatomite on pyrolysis volatility of pine pellets

Densification of Wood—Influence on Mechanical and Chemical Properties when 11 Naturally Occurring Substances in Wood Are Mixed with Beech and Pine

The need to increase the use of renewable biomasses for energy supply, such as fuel pellets is significant. However, different types of biomasses have different mechanical properties to be pelletized, which entails a limitation in available raw materials for pellet producers. Within this study eleven different pure substances from biomasses were separately mixed with European beech and Scots pine, to identify its impact on the densification process. Beech and pine pellets were used as control materials against their corresponding pellets mixed with substances representing: cellulose, hemicelluloses, other polysaccharides, lignin, protein, and extractives. The mechanical properties were investigated as well as FT-IR and SEM analyses on the pellets. The results showed that the addition of the substances xylan and galactan created the hardest pellets for both pine and beech and that adding extractives to wood affects pine more than beech in relation to hardness. The FT-IR data could not provide clear explanations as to the variation in hardness and springback behavior through the identification of major functional groups in each pellet. It can be concluded that biomass residues rich in xylan and galactan increase pellet quality in terms of strength and durability without affecting the production process.

The effect of biomass pyrolysis temperature on the performance of biochar-fed molten hydroxide direct carbon fuel cells

Biomass derived biochar is a promising fuel for direct carbon fuel cells, and the pyrolysis process to produce biochar has significant influence on the performance of said biochar-fed cells. In the present study, pine pellets were utilized as the fuel feedstock, and by using a molten hydroxide direct carbon fuel cell, the effect of the pyrolysis temperature on the fuel performance of pine biochar pellets obtained from fast pyrolysis was explored. The results revealed high pyrolysis temperature was beneficial to the fuel performance of pine biochar pellets in terms of peak power density and electrochemical impedance spectroscopy. To illustrate the observed results, a mechanism was proposed based on the physical and chemical characterizations. The proposed mechanism indicated that high pyrolysis temperature would result in high carbonization degree, amorphous microstructure, and smooth surface morphology of the pine biochar pellets, as well as high reactivity of carbon fuel in the cell operating conditions, which in turn would be conducive to the extension of triple phase boundaries and the improvement of charge transfer at/near triple phase boundaries. According to the results, the cells fed with the pine biochar pellets produced at 800 °C achieved the highest peak power density of 76.6 mW/cm2 at 400 °C.

Mechanical and Combustion Properties of Agglomerates of Wood of Popular Eastern European Species.

The objective of the reported project was to produce wood agglomerates from popular East European species to determine their strength and combustion properties. Closed-die pellets were produced from sawdust of six types of wood common on the East European market: pine, willow, oak, poplar, birch, and beech. The properties of pellets, determined by the type of wood, were influenced by the compaction pressure and the moisture content of the sawdust. The highest average pellet density was obtained for oak sawdust, while the lowest density was obtained for poplar pellets. Expansion of pellets after removing from the die was found to be dependent on the wood species, and as expected, on compaction pressure. The pellet expansion increased after 2 h of conditioning in the laboratory and with an increase in moisture content. The highest and the smallest strength were obtained for oak pellets and for birch sawdust, respectively. The strength of the pellets increased by more than 100% with an increase in the compaction pressure from 60 MPa to 120 MPa. The average strength decreased by 65% with increasing moisture content. For all tested materials, drop resistance remained at a high level, acceptable in industrial practice. The highest calorific value of 18.97 MJ/kg was obtained for pine pellets. The highest ash value of 1.52% was obtained for willow pellets and the lowest value of 0.32% for pine pellets.

Modelling of a Torrefaction Process Using Thermal Model Object

So far, the torrefaction process has been merely discussed based on the physical and chemical characteristics of the final product, but the mechanism has not been yet pondered and investigated. Thus far, microwave torrefaction has been predominately used for thermal pre-treatment; therefore, a paradigm shift in the methodology has been introduced by using a Joule heating system. The article mainly focuses on the thermal engineering aspect of the torrefaction process. The densified black pine underwent thermal pre-treatment at a temperature of 523 K. The furnace used for torrefaction was initially improvised to carry out thermal degradation at quasi-static/dynamic conditions. A 3D PDE thermal model was developed to determine the numerical solution and temperature distribution across a black pine pellet. To compare the effect of the linear ramping profile, time-dependent as well as fixed Dirichlet conditions were applied to the proposed model. The mass distribution, duration of the torrefaction process, the effect of Nusselt and Reynold’s number of inert gas, and thermal history are some of the factors whose influence on the numerical solution was investigated. The simulation of thermal pre-treatment and its effect on the heat transfer characteristic was examined with help of a PDE thermal model, whereas the numerical solution of diffusion of the product of reactions was determined by solving the partial differential equations with the help of the discretisation method (PDEPE). The densification of black pine was performed in a ring die, whereas initial milling of biomass was carried out using a 1.5 mm sieve size. The system was found to have a homogeneous distribution in energy and temperature with time, whereas the amplitude of heat flux along the radial direction was reduced by 15% if the same pellet underwent torrefaction for a duration of 5 min in dynamic mode. Similarly, a 64.46% drop in amplitude of heat flux along the azimuth plane could be seen while performing torrefaction in a time-dependent thermal history. However, the relative amplitude of the heat flux at the centre of the pellet was estimated to be lowered by 98.41% along the vertical axis for heating a pellet in a quasi-static condition. The net change in the mass fraction of carbon dioxide across the boundary film was seen to be 40% higher than that of carbon monoxide. The rate of change of mass fraction of carbon monoxide across the boundary film was increased by 7–11% with the increase in torrefaction time. A 6.8% rise in the evaporation of water was noticed during the first half interval of torrefaction (from 5 min to 10 min). In the second half, from 10 min to 15 min, it was merely increased by 5.8%. A relative drop of 17.24% in water evaporation was estimated in the dynamic state of the system.

Evaluation of Gas Composition Obtained from Gasification of Pellets and Blends with Agricultural Wastes

The gas produced by gasification is more versatile than the original solid biomass and can be applied as raw material for chemical industry and as fuel for the electrical and thermal energy production. Small gasification plants are being considered as an option for electrical energy generation in remote areas where agriculture wastes can be found easily. In this way, the aim of this work was to evaluate the characteristics of the gas composition of co-gasification using pine pellets and blends with agricultural wastes. The experiments were carried out in duplicate in a pilot scale fixed bed downdraft gasifier, GEK Power Pallet 20kW. It was performed experimental runs with 100 % pine pellets, 80 % pine pellets and 20 % agriculture wastes, and 80 % pine pellets with 15.4 % agriculture wastes and 4.6 % of glycerol used as an agglutinant agent. The samples were analyzed by GC-FID/TCD. The moisture of different feedstocks varied between 8.00 and 10.88. The results of the produced gas show an average composition of 37.45% CO and 15.79% H2, and LHV 7,155 kJ/kg for gasification of 100 % pine pellets. While the mixture of pine pellets and agriculture wastes resulted in a gas with 32.13% CO and 20.10% H2, and LHV of 6,663.4 kJ/kg. When added glycerol, the gas composition to CO was 20.52 % and to H2 11.21 % with LHV of 4,507.4 kJ/kg. The results indicate that the gasifier is compatible with the mixture of agricultural residues and pines pellets in co-gasification.

Evaluation of Gas Composition Obtained from Gasification of Pellets and Blends with Agricultural Wastes

The gas produced by gasification is more versatile than the original solid biomass and can be applied as raw material for chemical industry and as fuel for the electrical and thermal energy production. Small gasification plants are being considered as an option for electrical energy generation in remote areas where agriculture wastes can be found easily. In this way, the aim of this work was to evaluate the characteristics of the gas composition of co-gasification using pine pellets and blends with agricultural wastes. The experiments were carried out in duplicate in a pilot scale fixed bed downdraft gasifier, GEK Power Pallet 20kW. It was performed experimental runs with 100 % pine pellets, 80 % pine pellets and 20 % agriculture wastes, and 80 % pine pellets with 15.4 % agriculture wastes and 4.6 % of glycerol used as an agglutinant agent. The samples were analyzed by GC-FID/TCD. The moisture of different feedstocks varied between 8.00 and 10.88. The results of the produced gas show an average composition of 37.45% CO and 15.79% H2, and LHV 7,155 kJ/kg for gasification of 100 % pine pellets. While the mixture of pine pellets and agriculture wastes resulted in a gas with 32.13% CO and 20.10% H2, and LHV of 6,663.4 kJ/kg. When added glycerol, the gas composition to CO was 20.52 % and to H2 11.21 % with LHV of 4,507.4 kJ/kg. The results indicate that the gasifier is compatible with the mixture of agricultural residues and pines pellets in co-gasification.

Boiler Combustion Optimization of Vegetal Crop Residues from Greenhouses

This work presents an alternative for adding value to greenhouse crop residues, used for (1) heating and (2) as a CO2 source. Both options are focused on greenhouse agricultural production, but could be applied to other applications. The influence of factors, such as the air/fuel rate and turbulence inside the combustion chamber, is studied. Our results show that for pine pellets, olive pits, tomato-crop residues, and a blend of the latter mixed with almond prunings (75–25%), the thermal losses ranged from 19.5–53.1, 20.5–58.9, 39.9–95%, and 29.4–75.5%, respectively, while the NOX emissions were 30–247, 411–1792, and 361–2333 mg/Nm3, respectively. The above-mentioned blend was identified as the best set-up. The thermal losses were 39.2%, and the CO, NOX, and SO2 concentrations were 11,690, 906, and 1134 mg/Nm3, respectively (the gas concentration values were recalculated for 0% O2). Currently, no other work exists in the literature include a similar analysis performed using a boiler with a comparable thermal output (160.46 kW). The optimal configurations comply with the relevant local legislation. This optimization is important for future emission control strategies relating to using crop residues as a CO2 source. The work also highlights the importance of ensuring a proper boiler set-up for each case considered.

Development of a small-scale reactor for upgraded biofuel pellets

The comprehensive investigation of a pyrolysis reactor has been conducted on the basis of thermal engineering design. The gas dynamics, thermodynamic, and psychrometric behaviour of the producer gas have been thoroughly assessed. The pilot-scale reactor has been programmed to operate at the temperature 973 K in the absence of an inert medium. The concentric casing of the heating filament has been used as an external source of energy. The experimental task is divided into two parts: upgradation of biomass and the decomposition of pellets in a developed small-scale pyrolysis unit for the possible gas, char, and pyrolysis oil generation. The fuel upgradation is performed via quasi-static torrefaction of pine pellets using Joule heating in the presence of nitrogen gas. The volumetric gas of nitrogen flowing across the improvised furnace is 0.70 L·min−1. The obtained results are compared with the wood pellets. The unsaturated producer gas has been found to vary accordingly to the following gas equation pv0.25=C and pv−0.69=C for the processed pine pellets and wood pellets, respectively. A relative increase of 21.00% has been seen while running the reactor with the processed pine pellets. The percentage yield of the pyrolytic oil for the processed pine and wood pellets is 10.48% and 30.00% respectively. The flame temperature and adiabatic flame temperature of the producer gas (processed pine) is lowered by 8.10% and 17.00% respectively. The energy yield of processed pinechar is found to be 122.58% higher than that of wood char.

Комплексная эффективность применения древесных гранул в энергоустановках

In advanced countries, the dramatic impact of greenhouse gases on the global climate is reduced by replacing fossil fuels with biofuels. This method is being actively encouraged. However, by-products of logging, processing and conversion of wood are classified as difficult to burn fuels due to their high moisture content, low energy density and extremely heterogeneous granulometric composition. A promising direction to increase the energy density and transportability of the timber industry by-products is their granulation. Wood pellet fuel burning in heat-generating plants results in significant increase in their energy and environmental performance. The purpose of the paper is an experimental and calculation study of the energy and environmental performance of 4 MW hot water boilers produced by Polytechnik Luft- und Feuerungstechnik GmbH in the process of burning pine and spruce wood pellets obtained from by-products woodworking. When performing studies, the components of the boiler’s heat balance, gas release, and particulate emissions were determined. Numerical modeling of thermochemical and aerodynamic processes taking place in the boiler combustion chamber was carried out by using the Ansys Fluent three-dimensional simulation software. Together with industrial-operational tests it showed the possibility to reduce the total share of flue gas recirculation into combustion chambers of boiler units to values not exceeding 0.45, in providing an acceptable temperature of combustion products at the combustion chamber outlet and maintaining minimum emissions of carbon and nitrogen monoxides. At the same time, the share of gases fed by recirculation smoke exhausters to the over-bed area of the burner should have higher values than under the reciprocating grates of boilers. Guidelines for comprehensive improvement of wood pellet combustion efficiency in combustion chamber of 4 MW hot water boilers have been developed and implemented. The priorities are: using the air passed through the cooling channels of the setting as secondary air; reducing the rarefaction in the combustion chambers to 30–70 Pa; optimizing the ratio of primary and secondary air, herewith, the share of primary air in the total flow should be 0.26–0.35. Implementation of the developed guidelines allowed to increase the boiler gross efficiency by 0.5–1.8 %, to reduce the aerodynamic resistance of the gas path by 15–20 % and to ensure consistently low emissions of carbon and nitrogen monoxides and soot particles. When designing boiler units for burning wood pellet fuel it is advisable to place heating surfaces in the combustion chamber, included in the circulation circuit of the boiler. This will increase the efficiency and life cycle of the boiler unit.