Particulate matter emission and K/S/Cl transformation during biomass combustion in an entrained flow reactor

This study aims to demonstrate the effect of ash chemistry, especially, the transformation of potassium (K), chlorine (Cl), and sulfur (S) species, on the fine particle emission during biomass combustion. Biomass was burned in an entrained flow reactor at varied temperature from 1000 to 1300 °C, where fine particles were sampled using a 13-stage low pressure impactor, and the morphology and composition of the fine particles were analyzed. The fates of K, Cl, and S during biomass combustion were compared between the entrained flow reactor and the muffle furnace. Results show that the particle size distributions of PM₁₀ are bimodal for all studied cases. A higher concentration of fine-mode particle is observed at 1000 °C, with the peak position at 0.274 μm. When the temperature is increased from 1000 to 1100 °C or higher, the concentration of fine-mode particle is reduced by about 50%, and its size becomes smaller with a peak position at 0.097 μm. K, Cl and S are enriched as potassium chloride and sulfate, dominantly in PM_1.0; while Mg, Ca and Si are enriched in PM_1.0–10. A certain amount of sulfur in PM_1.0 at 1000 °C is observed, while the sulfur disappears above 1100 °C. This indicates that the process of potassium sulfation tends to occur at a moderate temperature, and affects the emission amount and the particle size distribution of particulate matters. Analyzing results of the fates of K, Cl and S in the particle phase indicate a completed sulfur-release from biomass ash above 1200 °C, as well as a maximum capture efficiency for potassium-containing vapors at 1100 °C, which results in a minimum PM_1.0 emission at 1100 °C.     

Evaluation of feasibility of pelletized wood co-firing with high ash Indian coals

To reduce anthropogenic CO₂ emissions from power plants, biomass is an immediate alternative fuel which has similar properties as coal. In this regard, the present study discusses about pelletized wood (PW) co-firing with high ash Indian coal by conducting co-milling and co-firing trials in a 1000 kg/hr of pilot scale test facility. Indian coals are typically high ash content and low calorific value fuels, therefore, its interaction with coal during combustion and ash deposition have studied in detail. Based on co-milling trails of PW and coal, it was observed that as PW proportion in coal increases, the quantity of particles of size below 50 μm and as well above 500 μm were increased. From co-firing studies, it was observed that higher volatile content in PW helping in stabilizing flames while co-firing. At lower proportions, up to 10% weight PW co-firing with coal, the flame temperature and heat flux values are very close to base test of 100% coal firing. However, beyond 10% by weight of PW co-firing with coal, the flame temperature and heat flux values were increased significantly from 100% coal tests. This is because of higher calorific value of PW than coal. The CO emission was decreased with increase in PW proportion in coal but at 30% of PW in coal, CO emission was increased suddenly. However, NO and SO₂ concentrations were decreased up to 8% and 16% respectively with increase in PW proportion in coal due to lower fuel nitrogen and sulphur content in PW than coal. Analytical analysis of slagging indices suggest that the slagging potential for PW co-firing with coal is increasing as the PW proportion in coal increases.     

Numerical modeling of the gasification based biomass co-firing in a 600 MW pulverized coal boiler

Gasification based biomass co-firing was an attractive technology for biomass utilization. Compared to directly co-firing of biomass and coal, it might: (1) avoid feeding biomass into boiler, (2) reduce boiler fouling and corrosion problem, and (3) avoid altering ash characteristics. In this paper, CFD modeling of product gas (from biomass gasification) and coal co-firing in a 600 MW tangential PC boiler was carried out. The results showed that NO_x emission was reduced about 50–70% when the product gas was injected through the lowest layer burner. The fouling problem can be reduced with furnace temperature decreasing for co-firing case. The convection heat transfer area should be increased or the co-firing ratio of product gas should be decreased to keep boiler rated capacity.     

Full-scale co-firing trial tests of sawdust and bio-waste in pulverized coal-fired 230 t/h steam boiler

Co-firing trial tests of sawdust and bio-waste coming from cereal production with hard coal were carried out at Skawina Power Plant in Poland (1532 MW in fuel, currently belonging to CEZ Group). Skawina Power Plant is a tangentially-fired pulverized coal unit with nine boilers (4 boilers of 210 t/h and five boilers of 230 t/h live steam respectively) that produces 590 MW electricity and 618 MW of heat (district heating and process steam).The paper presents an analysis of energy and ecological effects of sawdust and bio-waste co-firing in the existing pulverized hard coal boiler. The mixture of coal and biomass was blended in the coal yard, and fed into the boiler through the coal mills. During the tests, combustion of mixtures composed of hard coal and sawdust (with mass share of 9.5%) and hard coal – bio-waste (6.6% mass basis) were examined. The co-firing tests were successful. Based on the analysis of the test results, the influence of biomass co-firing on specific components of energy balance (e.g. stack losses and boiler thermal efficiency) was discussed, in comparison to combustion of coal alone. The emission indices during coal combustion were calculated and compared to the emission indices for biomass co-firing. It was proved that co-firing of both biomass sorts leads to a decrease of CO and SO₂ emissions. Due to the possibility of considering the part of the energy generated during biomass co-firing as renewable energy, the procedure for biomass based renewable energy share determination is presented and illustrated with an example.     

Experimental study on the formation of ultrafine particulate matters (PMs) during pulverized coal (PC) char combustion in O2/N2 and O2/CO2 atmospheres

Under the force of increasingly strict emission standard of particulate matters (PMs) and serious haze in China, further understanding of the formation of ultrafine PMs during coal combustion is crucial. In this work, the formation characteristics of ultrafine PMs during pulverized coal (PC) char combustion in O₂/N₂ and O₂/CO₂ atmospheres were investigated through a high-temperature drop tube furnace (DTF) with a two-stage dilution sampling system and a 14-stage electrical low pressure impactor (ELPI+). Results showed that in both number-based and mass-based particle size distribution (PSD) the peaks of ultrafine PMs located nearby 0.2 μm under all experimental atmospheres including O₂21%/N₂79%, O₂21%/CO₂79%, O₂27%/CO₂73% and O₂33%/CO₂67% (O21N79, O21C79, O27C73 and O33C67). And the peak values increased with the increase of O₂ concentration in O₂/CO₂ atmospheres because of the high char combustion temperature at elevated O₂ level. However, the mass and number concentration of ultrafine PMs in O₂/CO₂ atmospheres reduced significantly compared with these in O₂/N₂ atmosphere. When O21N79 atmosphere switched to O21C79, O27C73, O33C67 atmosphere, the mass concentration of ultrafine PMs reduced by 80.90%, 76.58% and 14.31%, and the number concentration reduced by 74.16%, 63.17% and 10.50%, respectively. Furthermore, the total mass of the ultrafine PMs was determined by the mass of the ultrafine PMs with larger particle size, whereas the total number of ultrafine PMs was determined by the number of the ultrafine PMs with smaller particle size. In this work, the ultrafine PMs with the aerodynamic size smaller than 0.3 μm were collected on the 1st to 7th impactor surfaces of the ELPI+. Among the ultrafine PMs, the particles on the 7th impactor (PMs with the superior limit of ultrafine PMs size) accounted for more than 94.8% of the total ultrafine PMs by mass, but less than 2.3% of the total ultrafine PMs by number; The particles deposited on the 1st impactor (PMs with the detectable minimum size of ultrafine PMs) accounted for more than 79.6% of the total ultrafine PMs by number, but less than 0.4% of the total ultrafine PMs by mass. In addition, PM_0.1 which accounted for 96% of the total number of the ultrafine PMs was analyzed for chemical composition by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Results showed that the prominent components of PM_0.1 were Ca, Na, and Si in both O₂/N₂ and O₂/CO₂ atmospheres. However, compared with O₂/N₂ atmosphere, Na, Si, Al, and Fe were more enriched in PM_0.1 in O₂/CO₂ atmospheres.     

Investigation on PM formation from combustion of lignite with high contents of AAEMs (alkali and alkaline earth metals) and Fe: Effect of the reaction temperature

Coal-fired power plants require higher flexibility and a broader range of the operating temperature than before to accommodate the load regulation of the power grid. The relationship between the reaction temperature and the characteristics of particulate matter (PM) need to be better understood. In this study, Zhundong coal combustion was conducted in a drop tube furnace at different reaction temperatures in air. The PM characteristics and elemental contributions are investigated in detail. The experimental results show that the mass yields of PM_0.4 and PM_0.4-10 are non-monotonic with the reaction temperature. The competition between the generation of inorganic fumes and the removal of inorganic fumes by Si–Al-bearing minerals governs the mass yield of PM_0.4. At higher reaction temperature, generation of Ca, Mg, Fe-containing fumes increases, contributing most to the increment of PM_0.4; while the sulfation of chlorides is inhibited, resulting in more Cl in PM_0.4. The S content in PM_0.4 is mainly affected by the sulfation of AAEMs (alkali and alkaline earth metals) oxides. The mass yield of PM_0.4-10 is controlled by the competition between the fragmentation of char or mineral particles and the coalescence of mineral particles. For Zhundong coal combustion, the reaction temperature is recommended to be 1273K–1373K to control PM emission.     

生物质与煤混燃燃烧特性研究进展

基于能源与环境的双重压力,以及生物质与煤单独燃用存在的问题,生物质与煤混燃已成为一种发展趋势,但其利用方面还面临着许多困难。因此,研究混合燃料燃烧过程中的燃烧特性及污染物规律,对于生物质与煤混燃技术的利用具有重要的意义。本文重点介绍了近年来国内外在生物质与煤混燃燃烧特性,及污染物排放的方面研究现状,并提出了研究过程中存在的问题,以期为后续的研究工作提供有价值的参考。     

Preliminary study of trace element emissions and control during coal combustion

Hazardous trace element emissions have caused serious harm to human health in China. Several typical high-toxic trace element coals were collected from different districts and were used to investigate the emission characteristics of toxic trace elements (As, Se, Cr, Hg) and to explore preliminary control methods. Coal combustion tests were conducted in several bench-scale furnaces including drop tube furnace (DTF), circulating fluidized bed (CFB) combustion furnace, and fixed-bed combustion furnace. Calcium oxide was used to control the emission of arsenic and selenium. The granular activated carbons (AC) and activated-carbon fibers (ACF) were used to remove mercury in the flue gas from coal combustion. The chemical composition and trace element contents of ash and particulate matter (PM) were determined by X-ray fluorescence (XRF) spectrometry and inductively coupled plasma-atomic emission spectrometry (ICP-AES), respectively. The speciation and concentration of mercury were investigated using the Ontario-Hydro method. X-ray diffraction spectrometry (XRD) was used to determine the mineral composition of production during combustion experiments. With the addition of a calcium-based sorbent, arsenic concentration in PM₁ sharply decreased from 0.25–0.11 mg/m³. In fixed-bed combustion of coal, the retention rates of selenium volatiles were between 11.6% and 50.7% using lime. In the circulating fluidized-bed combustion of coal, the content of selenium in ash from the chimney was reduced to one-fourth of its original value and that in leaching water from the chimney decreased by two orders of magnitude using lime. Calcium-based sorbent is an effective additive to control the emission of As and Se during coal combustion. The emission of chromium is influenced by the occurrence mode of Cr in coal. Chromium emission in PM_2.5 during coal combustion is 55.5 and 34.7 μg/m³ for Shenbei coal and mixed Pingdingshan coal, respectively. The adsorptive capacity of granular activated carbon for Hg⁰ is significantly enhanced through ZnCl₂-impregnation. The activated carbon fibers showed decent efficiency in mercury adsorption, on which surface oxygen complex showed positive effects on mercury adsorption.     

Biomass co-firing options on the emission reduction and electricity generation costs in coal-fired power plants

Co-firing offers a near-term solution for reducing CO₂ emissions from conventional fossil fuel power plants. Viable alternatives to long-term CO₂ reduction technologies such as CO₂ sequestration, oxy-firing and carbon loop combustion are being discussed, but all of them remain in the early to mid stages of development. Co-firing, on the other hand, is a well-proven technology and is in regular use though does not eliminate CO₂ emissions entirely. An incremental gain in CO₂ reduction can be achieved by immediate implementation of biomass co-firing in nearly all coal-fired power plants with minimum modifications and moderate investment, making co-firing a near-term solution for the greenhouse gas emission problem. If a majority of coal-fired boilers operating around the world adopt co-firing systems, the total reduction in CO₂ emissions would be substantial. It is the most efficient means of power generation from biomass, and it thus offers CO₂ avoidance cost lower than that for CO₂ sequestration from existing power plants. The present analysis examines several co-firing options including a novel option external (indirect) firing using combustion or gasification in an existing coal or oil fired plant. Capital and operating costs of such external units are calculated to determine the return on investment. Two of these indirect co-firing options are analyzed along with the option of direct co-firing of biomass in pulverizing mills to compare their operational merits and cost advantages with the gasification option.     

Co-firing—A strategy for bioenergy in Poland?

Biomass provides the largest reduction of carbon dioxide (CO₂) emission when it replaces coal, which is the dominating fuel in heat and electricity production in Poland. One means of replacing coal with biomass is to co-fire biofuels in an existing coal-fired boiler. This paper presents an analysis of the strengths and weaknesses of co-firing biofuels in Poland with respect to technical, environmental, economical and strategic considerations. This analysis shows that co-firing is technically and economically the most realistic option for using biofuels in the large pulverized fuel (PF) boilers in Poland. However, from an environmental perspective, co-firing of biofuels in large combined heat and power (CHP) plants and power plants provides only a small reduction in sulphur dioxide (SO₂) emission per unit biofuel, since these plants usually apply some form of desulphurization technology. In order to maximize the SO₂ emission reduction, biofuels should be used in district heating plants. However, co-fired combustion plants can handle disruptions in biofuel supply and are insensitive to moderate changes in fuel prices, which makes them suitable utilizers of biofuels from perennial energy crops. Co-firing could therefore play an important role in stimulating perennial crop production.     

Ash-related issues during biomass combustion: Alkali-induced slagging,silicate melt-induced slagging (ash fusion), agglomeration,corrosion, ash utilization,and related countermeasures

Biomass is available from many sources or can be mass-produced. Moreover, biomass has a high energy-generation potential, produces less toxic emissions than some other fuels, is mostly carbon neutrality, and burns easily. Biomass has been widely utilized as a raw material in thermal chemical conversion, replacing coal and oil, including power generation. Biomass firing and co-firing in pulverized coal boilers, fluidized bed boilers, and grate furnaces or stokerfed boilers have been developed around the world because of the worsening environmental problems and developing energy crisis. However, many issues hinder the efficient and clean utilization of biomass in energy applications. They include preparation, firing and co-firing, and ash-related issues during and after combustion. In particular, ash-related issues, including alkali-induced slagging, silicate melt-induced slagging (ash fusion), agglomeration, corrosion, and ash utilization, are among the most challenging problems. The current review provides a summary of knowledge and research developments concerning these ash-related issues. It also gives an in-depth analysis and discussion on the formation mechanisms, urgent requirements, and potential countermeasures including the use of additives, co-firing, leaching, and alloying.Alkali species, particularly alkali chlorides and sulfates, cause alkali-induced slagging during biomass combustion. Thus, the mechanisms of generation, transformation, and sequestration of alkali species and the formation and growth of alkali-induced slagging, formed as an alternating overlapping multi-layered structure, are discussed in detail. For silicate melt-induced slagging (ash fusion), the evolutions of chemical composition of both the elements and minerals in the ash during combustion and existing problems in testing are overviewed. Pseudo-4D phase diagrams of (Ma₂O)-MaeO-P₂O₅-Al₂O₃ and (Ma₂O)-MaeO-SiO₂-Al₂O₃ are proposed as effective tools to predict ash fusion characteristics and the properties of melt-induced slagging. Concerning agglomeration that typically occurs in fluidized bed furnaces, melt-induced and coating-induced agglomeration and coating-forming mechanisms are highlighted. Concerning corrosion, seven corrosion mechanisms associated with Cl₂, gaseous, solid/deposited, and molten alkali chlorides, molten alkali sulfates and carbonates, and the sulfation/silication of alkali chlorides are comprehensively reviewed. The effects of alloying, salt state (solid, molten, or gaseous), combustion atmosphere, and temperature are also discussed systematically. For ash utilization, potential approaches to the use of fly ash, bottom ash, and biomass/coal co-fired ash as construction and agricultural materials are explored.Several criteria or evaluation indexes are introduced for alkali-induced slagging and agglomeration, and chemical equilibrium calculation and multicomponent phase diagrams of silicate melt-induced slagging and agglomeration. Meanwhile, remedies, including the use of additives, co-firing, leaching, alloying, and the establishment of regulations, are discussed.It is suggested that considerable attention should be focused on an understanding of the kinetics of alkali chemistry, which is essential for the transformation and sequestration of alkali species. A combination of heterogeneous chemical kinetics and multiphase equilibrium modeling is critical to estimating the speciation, saturation levels, and the presence of melt of the ash-forming matter. Further practical evaluation and improvement of the existing criterion numbers of alkali-induced slagging and agglomeration should be improved. The pseudo-4D phase diagrams of (Ma₂O)-MaeO-P₂O₅-Al₂O₃ and (Ma₂O)-MaeO-SiO₂-Al₂O₃ should be constructed from the data derived from real biomass ashes rather than those of simulated ashes in order to provide the capability to predict the properties of silicate melt-induced slagging. Apart from Cr, research should be conducted to understand the effects of Si, Al, and Co, which exhibit high corrosion resistance, and heavy metals such as Zn and Pb, which may form low-melting chlorides that accelerate corrosion. Regulations, cooperation among biomass-fired power plants and other industries, potential technical research, and logistics should be strengthened to enable the extensive utilization of biomass ash. Finally, alkali-induced slagging, silicate melt-induced slagging, agglomeration, and corrosion occur concurrently, and thus, these issues should be investigated jointly rather than separately.     

Synergy effects of co-firing wooden biomass with Bosnian coal

The paper presents synergy effects found during the co-firing of wooden biomass with Bosnian coal types in an experimental reactor. The co-firing tests used spruce sawdust in combination with Kakanj brown coal and a lignite blend of Dubrave lignite and Sikulje lignite. Coal/biomass mixtures at 93:7 and 80:20 wt% were fired in a 20 kW pulverized fuel (PF) entrained flow reactor. Over 20 test trials were performed to investigate ash deposition behavior and emissions under different conditions, varying the process temperature, excess air ratio, and air distribution. During the tests, the temperature in the experimental facility varied between 880 and 1550 °C, while the excess air ratio varied between 0.95 and 1.4. There was sufficient combustion efficiency under all co-firing regimes, with burning out at 96.5–99.5% for brown coal–sawdust co-firing. Synergy effects were detected for all co-firing regimes with regard to SO₂ emission, as well for slagging at the process temperature suitable for the slag tap furnace. CO₂ emissions were also calculated for the blends tested and significant reductions of CO₂ found, due to the very low ranking of Bosnian coals.     

Environmental analysis of bio-CCS in an integrated oxy-fuel combustion power plant with CO2 transport and storage

Oxy-fuel combustion (OFC) belongs to one of the three commonly known clean coal technologies for which practical application may be in the offing. Similarly to conventional power plants, there is a possibility of biomass co-firing, thus an additional reduction of CO₂ emission is possible. Including the biomass in the fuel mixture of an integrated OFC power plant allows to obtain the so called “neutral” CO₂ status as biomass combustion does not contribute to anthropogenic CO₂ emissions. In OFC power plants without biomass co-firing, even if 100% of CO₂ is captured, there are still additional CO₂ emissions in processes like fossil fuel extraction, transportation and preparation. The same assumption applies also to biomass and other materials (e.g. limestone or raw water). A higher share of biomass in the fuel mixture can lead to “negative” CO₂ emissions with may be helpful to compensate the unfulfilled goals in other sectors where reduction is required. The paper presents the system approach to the environmental analysis based on the “input–output” method and both the index of the thermoecological cost and cumulative CO₂ emissions. Thermoecological cost includes, the cumulative exergy consumption of non-renewable energy sources and additional exergy consumption due to harmful emissions to the atmosphere. In order to investigate the impact of bio-CCS (both biomass co-firing and dedicated biomass boilers) on the net thermoecological cost of electricity production and cumulative CO₂ emissions five cases have been analyzed.     

Co-firing Coal and Municipal Solid Waste

Abstract

The aim of this study was to experimentally investigate how different the organic fraction of municipal solid waste (OFMSW) or municipal solid waste (MSW) utilizing strategies affects the gas emission in simple fluidized bed combustion (FBC) of biomass. In this study, ground OFMSW and pulverized coal (PC) were used for co-firing tests. The tests were carried out in a bench-scale bubbling FBC. Coal and bio-waste fuels are quite different in composition. Ash composition of the bio-waste fuels is fundamentally different from ash composition of the coal. Chlorine (Cl) in the MSW may affect operation by corrosion. Ash deposits reduce heat transfer and also may result in severe corrosion at high temperatures. Nitrogen (N) and carbon (C) assessments can play an important role in a strategy to control carbon dioxide (CO₂) and nitrogen oxide (NO_x) emissions while raising revenue. Regulations such as subsidies for oil, liquid petroleum gas (LPG) for natural gas powered vehicles, and renewables, especially biomass lines, to reduce emissions may be more cost-effective than assessments. Research and development (R&D) resources are driven by energy policy goals and can change the competitiveness of renewables, especially solid waste. The future supply of co-firing depends on energy prices and technical progress, both of which are driven by energy policy priorities.     

Reprint of: Studies on formation and control of combustion particulate matter in China: A review

Airborne particulate matter (PM) now exceeds sulfur dioxide and nitrogen oxides to become principal urban pollutant in most major cities of China. This paper gives an overview of fundamental studies on the formation and control of combustion PM from many research groups in China. About 62.8% major cities in China have lowered their annual mean PM₁₀ concentrations to less than 100 μg/m³ as of year 2006. The coal combustion source contributes 15–20% to fine particulates in Beijing because of the coal-dominant energy consumption structure. Overall, in mainland China the PM emission from coal-fired power plants totals 3.81 million tonnes per year, accounting for 44.6% of the total PM. Then, the characteristics of PM₁₀ from both pulverized coal plants and circulated-fluidized bed coal plants are discussed. Finally, the R&D of emission control technologies of PM₁₀ including combustion modification, electrically enhanced fabric filtration and novel agglomeration approaches are reviewed in detail.     

Assessing plantation biomass for co-firing with coal in northern Indiana: A linear programming approach

Tightening environmental regulations and the signing of the Kyoto Protocol have prompted electric utilities to consider co-firing biomass with coal to reduce the levels of CO₂, SO₂, and NO_x in stack emissions. This analysis examines the cost competitiveness of plantation produced woody biomass and waste wood with coal in electricity production. A case study of woody biomass production and co-firing in northern Indiana is presented. A Salix (willow) production budget was created to assess the feasibility of plantation tree production to supply biomass to the utility for fuel blending. Co-firing with waste wood from primary and secondary wood processing activities and local municipalities also is considered. A linear programming model was developed to examine the optimal co-firing blend of coal and biomass while minimizing variable cost, including the cost of ash disposal and material procurement costs. This model was used to examine situations where coal is the primary fuel and waste wood, willow trees, or both are available for fuel blending. The results indicate that co-firing woody biomass is cost-effective for the power plant. Sensitivity analysis explored the effect of waste wood prices on co-firing cost.     

Studies on formation and control of combustion particulate matter in China: A review

Airborne particulate matter (PM) now exceeds sulfur dioxide and nitrogen oxides to become principal urban pollutant in most major cities of China. This paper gives an overview of fundamental studies on the formation and control of combustion PM from many research groups in China. About 62.8% major cities in China have lowered their annual mean PM₁₀ concentrations to less than 100 μg/m³ as of year 2006. The coal combustion source contributes 15–20% to fine particulates in Beijing because of the coal-dominant energy consumption structure. Overall, in mainland China the PM emission from coal-fired power plants totals 3.81 million tonnes per year, accounting for 44.6% of the total PM. Then, the characteristics of PM₁₀ from both pulverized coal plants and circulated-fluidized bed coal plants are discussed. Finally, the R&D of emission control technologies of PM₁₀ including combustion modification, electrically enhanced fabric filtration and novel agglomeration approaches are reviewed in detail.     

An evaluation of biomass co-firing in Europe

Reduction of the emissions of greenhouses gases, increasing the share of renewable energy sources (RES) in the energy balance, increasing electricity production from renewable energy sources and decreasing energy dependency represent the main goals of all current strategies in Europe. Biomass co-firing in large coal-based thermal power plants provides a considerable opportunity to increase the share of RES in the primary energy balance and the share of electricity from RES in gross electricity consumption in a country. Biomass-coal co-firing means reducing CO₂ and SO₂, emissions and it may also reduce NO_x emissions, and also represents a near-term, low-risk, low-cost and sustainable energy development. Biomass-coal co-firing is the most effective measure to reduce CO₂ emissions, because it substitutes coal, which has the most intensive CO₂ emissions per kWh electricity production, by biomass, with a zero net emission of CO₂. Biomass co-firing experience worldwide are reviewed in this paper. Biomass co-firing has been successfully demonstrated in over 150 installations worldwide for most combinations of fuels and boiler types in the range of 50–700 MWe, although a number of very small plants have also been involved. More than a hundred of these have been in Europe. A key indicator for the assessment of biomass co-firing is intrduced and used to evaluate all available biomass co-firing technologies.     

The effect of coal size on PM2.5 and PM-bound polycyclic aromatic hydrocarbon (PAH) emissions from a domestic natural cross-draft stove

Residential coal combustion has played an important role in the domestic energy supply of Northern China for many decades and will do so for the foreseeable future, although it is also an important contributor to severe air pollution. Meeting the daily cooking and spacing-heating demands of rural residents in an eco-friendly manner necessitates cleaner-burning technologies for residential coal combustion. Several reports have suggested that appropriately sized coal be beneficial for optimizing the performance of domestic coal-fired stoves. The effects of coal size (<1.6 cm, 1.6–2.0 cm, 2.0–2.5 cm and >2.5 cm) on fine particulate matter (PM_2.5) and sixteen U.S. Environmental Protection Agency (EPA) priority polycyclic aromatic hydrocarbons (16-PAHs) emissions from a natural cross-draft stove, operating in different phases (ignition, high power heating, low power heating, ramping up and high power cooking) were analyzed in this study. Results indicated that decreasing the coal size enhanced thermal efficiency and reduced pollutant emissions. When the coal size decreased from >2.5 cm to <1.6 cm, the average emission factor (EF) of PM_2.5 over a complete combustion sequence decreased from 3.12 to 1.42 mg/MJ_net, and the EF of PM-bound total PAHs decreased from 44.9 to 10.9 μg/MJ_net. The corresponding toxic equivalent quantity (TEQ) decreased from 1.25 to 0.38 μg/MJ_net. Emissions and energy efficiencies varied markedly between the various combustion phases, adequate air supply during the high power heating and cooking phases reduced the EFs of PM_2.5 and PAHs, while the low power heating phase produced relatively more pollutants due to a fuel-rich condition.     

Technoeconomic assessment of beetle kill biomass co-firing in existing coal fired power plants in the Western United States

Widespread mortality of forests in the western United States due to a bark beetle epidemic provides a source of biomass for power generation. This study assessed availability and economics of co-firing beetle kill biomass with coal in power plants in the western U.S. Since biomass may be considered carbon neutral under careful management, co-combustion of biomass with coal provides power plants a way to meet emission reduction requirements, such as those in the EPA Clean Power Plan (CPP). Cost has been a barrier to co-firing, but the economics are altered by emission reduction requirements, such as CPP guidelines. The present study assessed beetle kill biomass availability in national forests in Wyoming and Colorado through Geographic Information System (GIS) analysis of U.S. Forest Service (USFS) data. Power plants near beetle kill mortality were identified as candidates for co-firing. An economic assessment of costs to implement co-firing was conducted. Co-firing reduces the need for the USFS to manage beetle kill trees when they are harvested for energy use, and these mitigated treatment costs were considered as an effective subsidy of co-firing. The results of this analysis include beetle kill availability, costs, and annual CO₂ emissions reductions that can be met by co-firing.