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A computational fluid dynamics (CFD) model was coupled with an advanced statistical strategy combining the response surface method (RSM) and the propagation of error (PoE) approach to optimize and test the robustness of the co-firing of ammonia (NH3) and coal in a fluidized bed reactor for coal phase-out processes. The CFD model was validated under experimental results collected from a pilot fluidized bed reactor. A 3k full factorial design of nine computer simulations was performed using air staging and NH3 co-firing ratio as input factors. The selected responses were NO, NH3 and CO2 emissions generation. The findings were that the design of experiments (DoE) method allowed for determining the best operating conditions to achieve optimal operation. The optimization process identified the best-operating conditions to reach stable operation while minimizing harmful emissions. Through the implementation of desirability function and robustness, the optimal operating conditions that set the optimized responses for single optimization showed not to always imply the most stable set of values to operate the system. Robust operating conditions showed that maximum performance was attained at high air staging levels (around 40%) and through a balanced NH3 co-firing ratio (around 30%). The results of the combined multi-optimization process performance should provide engineers, researchers and professionals the ability to make smarter decisions in both pilot and industrial environments for emissions reduction for decarbonization in energy production processes. [ABSTRACT FROM AUTHOR]

Co-firing wood pellets with coal is an attractive alternative energy generation method with economic, social, and environmental benefits for the US energy generation sector. One way to sustainably use wood pellets for co-firing is to create consumer-supported green pricing programs (GPPs). Our study surveyed residents of five states (Alabama, New Jersey, New York, Pennsylvania, and Virginia) to investigate preferences for the attributes of a hypothetical GPP. The study applied the Best Worst Choice method, which employs the Best Worst Scaling (BWS) and binary choice (BC) task. The BWS analysis showed that residents of all five states most value the flexibility of contracts, the location of energy generation, and the reduction of carbon emissions as attributes of GPPs. The BC analysis, however, showed that residents are willing to pay a premium for length of contract, followed by reduction of carbon emissions and variability of payments. This study shows that the adoption of optimal GPP attributes can create real customer value. The success of GPPs will depend on increasing enrollment and public support; hence, the next step will be to increase awareness levels and green consciousness through sensitization in the form of public education exercises and media campaigns. Such measures will serve to inform and educate residents on the benefits of GPPs and lessen the gap between intrinsic value and willingness to pay for select attributes. [ABSTRACT FROM AUTHOR]

The simultaneous firing characteristics of woodchips and spent mushroom substrates (SMS) were studied in a stoker-type industrial boiler. The type of spent substrate intended for combustion consisted of oyster mushrooms. SMS from mushroom farms generally have a high water content. Dryers are therefore used for combustion. The moisture content of SMS was reduced to achieve low moisture to combust sufficiently at about 20%. First, the basic characteristics of the boiler were confirmed by conducting a woodchip combustion test under various operating loads of 30, 50, 70, and 100%. Thereafter, a simultaneous combustion test of woodchips and SMS was performed. During the experiment, exhaust gas concentrations in the boiler combustion chamber were measured, such as the temperature of oxygen (O2), carbon monoxide (CO), and nitrogen oxides (NOx). In addition, industrial and basic analyses were performed on woodchips and SMS. The main differences in the fuel analysis results between woodchips and SMS were ash, nitrogen, sulfur content and net calorific value. According to the analysis, the nitrogen content of SMS was 2.6%, which was 8.7 times higher than that of woodchips, and the ash content was also 14.8%, which was 18.5 times that of woodchips. As a result of the combustion experiment, the woodchip experiment revealed that the values of O2 and CO decreased and the combustion chamber temperature increased as the amount of fuel increased. Due to higher combustion temperature, thermal NOx also increased. When comparing this combustion test with the co-firing test, there was no significant difference in O2, CO, and combustion chamber temperature. However, with regard to the NOx value, the results showed a sharp increase from 64 ppm to 135 ppm. Although the NOx value increased, SMS had enough heat to be burned as fuel. Therefore, the utility of various agricultural byproducts as fuel has prospects for achieving an effective approach to energy cost reduction. [ABSTRACT FROM AUTHOR]

This paper presents a research on ash-related problems and emissions during co-firing low-rank Bosnian coals with different kinds of biomass; in this case woody sawdust and herbaceous energy crops Miscanthus. An entrained-flow drop tube furnace was used for the tests, varying fuel portions at a high co-firing ratio up to 30%wt woody sawdust and 10%wt Miscanthus in a fuel blend. The tests were supposed to optimize the process temperature, air distribution (including OFA) and fuel distributions (reburning) as function of SO2 and NOx emissions as well as efficiency of combustion process estimated through the ash deposits behaviors, CO emissions and unburnt. The results for 12 co-firing fuel combinations impose a reasonable expectation that the coal/biomass/Miscanthus blends could be successfully run under certain conditions not producing any serious ash-related problems. SO2 emissions were slightly higher when higher content of woody biomass was used. Oppositely, higher Miscanthus percentage in the fuel mix slightly decreases SO2 emissions. NOx emissions generally decrease with an increase of biomass co-firing rate. The study suggests that co-firing Bosnian coals with woody sawdust and Miscanthus shows promise at higher co-firing ratios for pulverized combustion, giving some directions for further works in co-firing similar multi-fuel combinations. [ABSTRACT FROM AUTHOR]

The firing and co-firing of biomass in pulverized coal fired power plants around the world is expected to increase in the coming years. Torrefaction may prove to be a suitable way of upgrading biomass for such an application. For transport and storage purposes, the torrefied biomass will tend to be in pellet form. Whilst standard methods for the assessment of the milling characteristics of coal exist, this is not the case for torrefied materials--whether in pellet form or not. The grindability of the fuel directly impacts the overall efficiency of the combustion process and as such it is an important parameter. In the present study, the grindability of different torrefied biomass pellets was tested in three different laboratory mill types; cutting mill (CM), hammer mill (HM) and impact mill (IM). The specific grinding energy (SGE) required for a defined mass throughput of pellets in each mill was measured and results were compared to other pellet characterization methods (e.g., durability, and hardness) as well as the modified Hardgrove Index. Seven different torrefied biomass pellets including willow, pine, beech, poplar, spruce, forest residue and straw were used as feedstock. On average, the particle-size distribution width (across all feedstock) was narrowest for the IM (0.41 mm), followed by the HM (0.51 mm) and widest for the CM (0.62 mm). Regarding the SGE, the IM consumed on average 8.23 Wh/kg while CM and HM consumed 5.15 and 5.24 Wh/kg, respectively. From the three mills compared in this study, the IM seems better fit for being used in a standardized method that could be developed in the future, e.g., as an ISO standard. [ABSTRACT FROM AUTHOR]

The increasing global demand for palm oil and its products has led to a significant growth in palm plantations and palm oil production. Unfortunately, these bring serious environmental problems, largely because of the large amounts of waste material produced, including palm kernel shell (PKS). In this study, we used computational fluid dynamics (CFD) to investigate the PKS co-firing of a 300 MWe pulverized coal-fired power plant in terms of thermal behavior of the plant and the CO2, CO, O2, NOx, and SOx produced. Five different PKS mass fractions were evaluated: 0%, 10%, 15%, 25%, and 50%. The results suggest that PKS co-firing is favorable in terms of both thermal behavior and exhaust gas emissions. A PKS mass fraction of 25% showed the best combustion characteristics in terms of temperature and the production of CO2, CO, and SOx. However, relatively large amounts of thermal NOx were produced by high temperature oxidation. Considering all these factors, PKS mass fractions of 10%-15% emerged as the most appropriate co-firing condition. The PKS supply capacity of the palm mills surrounding the power plants is a further parameter to be considered when setting the fuel mix. [ABSTRACT FROM AUTHOR]

The two major pathways for energy utilization from biomass are conversion to a liquid fuel (i.e., biofuels) or conversion to electricity (i.e., biopower). In the United States (US), biomass policy has focused on biofuels. However, this paper will investigate three options for biopower: low co-firing (co-firing scenarios refer to combusting a given percentage of biomass with coal) (5%-10% biomass), medium co-firing (15%-20% biomass), and dedicated biomass firing (100% biomass). We analyze the economic and greenhouse gas (GHG) emissions impact of each of these options, with and without CO2 capture and storage (CCS). Our analysis shows that in the absence of land use change emissions, all biomass co-combustion scenarios result in a decrease in GHG emissions over coal generation alone. The two biggest barriers to biopower are concerns about carbon neutrality of biomass fuels and the high cost compared to today's electricity prices. This paper recommends two policy actions. First, the need to define sustainability criteria and initiate a certification process so that biomass providers have a fixed set of guidelines to determine whether their feedstocks qualify as renewable energy sources. Second, the need for a consistent, predictable policy that provides the economic incentives to make biopower economically attractive. [ABSTRACT FROM AUTHOR]

Fossil fuels comprise 93% of Malaysia's electricity generation and account for 36% of the country's 2010 Greenhouse Gas (GHG) emissions. The government has targeted the installation of 330 MW of biomass electricity generation capacity by 2015 to avoid 1.3 Mt of CO2 emissions annually and offset some emissions due to increased coal use. One biomass option is to co-fire with coal, which can result in reduced GHG emissions, coal use, and costs of electricity. A linear optimization cost model was developed using seven types of biomass residues for Peninsular Malaysia. Results suggest that about 12 Mt/year of residues are available annually, of which oil-palm residues contribute 77%, and rice and logging residues comprise 17%. While minimizing the cost of biomass and biomass residue transport, co-firing at four existing coal plants in Peninsular Malaysia could meet the 330 MW biomass electricity target and reduce costs by about $24 million per year compared to coal use alone and reduces GHG emissions by 1.9 Mt of CO2. Maximizing emissions reduction for biomass co-firing results in 17 Mt of CO2 reductions at a cost of $23/t of CO2 reduced. [ABSTRACT FROM AUTHOR]

Switchgrass is a high yielding, low-input intensive, native perennial grass that has been promoted as a major second-generation bioenergy crop. Raw switchgrass is not a readily acceptable feedstock in existing power plants that were built to accommodate coal and peat. The objective of this research was to elucidate some of the characteristics of switchgrass biochar produced via carbonization and to explore its potential use as a solid fuel. Samples were carbonized in a batch reactor under reactor temperatures of 300, 350 and 400 °C for 1, 2 and 3 h residence times. Biochar mass yield and volatile solids decreased from 82.6% to 35.2% and from 72.1% to 43.9%, respectively, by increasing carbonization temperatures from 300 °C to 400 °C and residence times from 1 h to 3 h. Conversely, biochar heating value (HV) and fixed carbon content increased from 17.6 MJ kg-1 to 21.9 MJ kg-1 and from 22.5% to 44.9%, respectively, under the same conditions. A biomass discoloration index (BDI) was created to quantify changes in biochar colors as affected by the two tested parameters. The maximum BDI of 77% was achieved at a carbonization temperature of 400 °C and a residence time of 3 h. The use of this index could be expanded to quantify biochar characteristics as affected by thermochemical treatments. Carbonized biochar could be considered a high quality solid fuel based on its energy content. [ABSTRACT FROM AUTHOR]

CO2 emissions reduction from coal-fired power plants is an urgent issue in Japan, as well as around the world. The purpose of this study is to estimate the CO2 emissions and economy of using carbonized wood pellets produced overseas and co-fired at coal-fired power plants in Japan. We examined carbonized wood pellets produced in Canada and Vietnam, since those countries are major exporters of wood pellets for Japan. The results obtained are as follows: (1) The CO2 emissions and calculated cost per calorific value of carbonized wood pellets (CP25), which have a fixed carbon content of 25 wt.%, are lower than those of wood pellets at the port of import in Japan. When the fixed carbon of carbonized biomass is controlled at 25 wt.% or more via a carbonizer, sufficient pyrolysis gas (the heat source used for drying and carbonization without auxiliary fuel) can be obtained. (2) Carbonized wood pellets manufactured in Vietnam are more economical than those manufactured in Canada, since the resource of wood is less expensive and the transportation distance is shorter from Vietnam compared to Canada. (3) When carbonized wood pellets at CP25 are co-fired in coal-fired power plants, they do not affect the cost of the electricity generated, even if the carbonized pellets are blended at a high ratio. [ABSTRACT FROM AUTHOR]

Based on the existing biomass co-firing technologies and the known innate drawbacks of dedicated biomass firing, including slagging, corrosion and the dependence on fuel, a new model of agro/forestry residue pellets/shreds and coal co-fired in a large Pulverized Coal (PC) furnace was proposed, and the corresponding technical and economic assessments were performed by co-firing testing in a 300 MW PC furnace and discounted cash flow technique. The developed model is more dependent on injection co-firing and combined with co-milling co-firing. Co-firing not only reduces CO2 emission, but also does not significantly affect the fly ash use in cement industry, construction industry and agriculture. Moreover, economic assessments show that in comparison with dedicated firing in grate furnace, agro/forestry residues and coal co-firing in a large PC furnace is highly economic. Otherwise, when the co-firing ratio was below 5 wt%, the boiler co-firing efficiency was 0.05%-0.31% higher than that of dedicated PC combustion, and boiler efficiencies were about 0.2% higher with agro/forestry residues co-firing in the bottom and top burner systems than that in a middle burner system. [ABSTRACT FROM AUTHOR]

This paper presents a concise overview of ash deposition in combustion or co-firing of biomass (woody biomass, agricultural residues, peat, etc.) with other fuels for power/heat generation. In this article, the following five research aspects on biomass combustion ash deposition are reviewed and discussed: influence of biomass fuel characteristics, deposit-related challenges, ash deposition monitoring and analysis of ash deposits, mechanisms and chemistry of fly ash deposition, and key technologies for reducing ash deposition and corrosion in biomass-involved combustion. [ABSTRACT FROM AUTHOR]

CO2 emissions are a major contributor to global warming. Biomass combustion is one approach to tackling this issue. Biomass is used with coal combustion in thermal power plants or with blast furnaces (BFs) because it is a carbon-neutral fuel; therefore, biomass provides the advantage of reduced CO2 emissions. To examine the effect of co-firing on pulverized coal injection (PCI) in BFs, two coals of different ranks were blended with the biomass in different proportions, and then their combustion behaviors were examined using a laminar flow reactor (LFR). The PCI combustion primarily functions as a source of heat and CO to supply the upper part of the BF. To create a similar PCI combustion environment, the LFR burner forms a diffusion flat flame with an oxygen concentration of 26% with a flame temperature of ~2000–2250 K at a heating rate of 105 K/s. The combustion characteristics, such as the flame structure, burning coal particle temperature, unburned carbon (UBC), and CO and CO2 emissions were measured to evaluate their effect on PCI combustion. With the increase in the biomass blending ratio, the brightness of the volatile cloud significantly increased, and the particle temperature tended to decrease. The fragmentation phenomenon, which was observed for certain coal samples, decreased with the increase in the biomass blending ratio. In particular, with an increase in the biomass blending ratio, the optimum combustion point occurred, caused by the fragmentation of coal and volatile gas combustion of biomass. [ABSTRACT FROM AUTHOR]

Straw is treated as agricultural waste, and it is available in almost every region of Poland. A total of 30 million tons of straw is produced per year, of which there is a surplus of approximately 13.5 million tons of undeveloped straw. For energy purposes, straw from cereals or rapeseed is most often used. When analyzing scientific publications, it was noticed that, in Poland, large amounts of oat straw are produced, and there is no alternative use for it. Hence, we conducted research to determine the energy value of oat straw. Raw material was obtained from an individual farm from 2018 to 2020. Selected energy parameters for straw burned alone (100%) or co-fired with coal were analyzed in the following weight proportions: 70/30, 80/20, and 90/10 coal/oat straw. It was shown that changing weather conditions, in particular years, had a modifying effect on some of the energy parameters of straw. The calorific value of straw was lower than that of coal, but its impact on environmental pollution turned out to be significantly lower. The difference in combustion heat between coal and straw was 11.74 MJ·kg−1. Investigations into pollutant concentrations were performed for cubes of compressed straw and hard coal. Mixtures of these fuels were not studied in this part of the work. The combustion of straw resulted in a reduction of harmful NO, NOX, and SO2 pollutants and an increase in CO compared to coal combustion. As for hydrogen content—it was the highest in carbon and the lowest in straw. In the case of analytical moisture, an inverse relationship was observed. In the case of both coal and straw, the ash content varied throughout the years of research. As the boiler power increased from 5 to 25 kW, the consumption of burned raw material increased significantly. The results indicate that the surplus of oat straw can be rationally used to obtain thermal energy, including co-combustion with coal. This will allow one to avoid burning straw in the fields, which causes great harm to the natural environment. [ABSTRACT FROM AUTHOR]

Concentrated animal feeding operations (both slaughter and dairy cattle) lead to land, water, and air pollution if waste storage and handling systems are not effectively managed. At the same time, cattle biomass (CB), which includes both slaughter/feedlot biomass (FB) and dairy biomass (DB), have the potential to be a source of green energy at coal-fired power plants. Part I presented results on NOx reductions with pure FB or Coal: FB blends as reburn fuels. Part II deals with results from reburning with pure DB or Coal: DB blends as reburn fuels. A mixture of NG with a small amount of NH3 was used to generate the baseline NOx of 400–420 ppm (or 185–194 g/GJ). NOx emissions were found to be reduced by as much as 96% when reburning with FB. The effects of reburn fuel type, equivalence ratio (ERRBZ) in the reburn zone, vitiated air, several injection configurations of reburn fuel and initial NO concentrations on NOx emissions were investigated. The ERRBZ shows a significant effect on the NOx reduction. The 20% heat input by reburning was the better operating condition for the long-term operation due to its ash production. The results reveal that reburn with DB fuels is an effective technology for NOx emission control when the initial NOx emission is higher than 275 ppm (or 127 g/GJ or 0.3 lb/MMBtu). [ABSTRACT FROM AUTHOR]

Cattle biomass (CB or manure from cattle) is proposed as reburn fuel under slightly fuel-rich conditions. The CB includes wastes from cattle feedlots (cattle grown in feedlots to slaughter weights of 450–640 kg) termed as Feedlot Biomass (FB) and cattle wastes from dairy farms termed as Dairy Biomass (DB). NOx emissions from coal-fired power plants can be reduced by using pure CB and Coal:CB mixtures as reburn fuels (10~30% by heat) injected after the primary combustion region. Experiments with Coal:CB mixtures as reburn fuels were performed using the 30 kW burner facility. Part I deals with results from experiments using pure FB and Coal:FB blends as reburn fuels while Part II presents results on extent of NOx reduction using pure DB and Coal:DB blends as reburn fuels (RF). In the current work, results on NOx emission are presented with FB and Coal:FB blends as RF. The parametric studies include: equivalence ratio in reburn zone (ERRBZ), vitiated air, angle of reburn nozzles, presence and absence of heat exchangers (HEXs), and baseline NOx concentration. The optimum operating conditions for FB reburning were found to be conditions with vitiation at ERRBZ = 1.1 with 45° upward counter-current injection in the presence of HEXs. NOx emissions were reduced by as much as 96%. [ABSTRACT FROM AUTHOR]

Despite the technology for wood biomass combustion being much more advantageous when compared to traditional burners, such as the Stoker or fluidized burner, there has been scant research on the topic of wood biomass cyclone burners. The purpose of this paper is to review biomass cyclone burner technology, which includes theory, design, and combustion, in terms of the chemistry and properties of wood biomass, emission related to NOx and CO, and application of the burner, such as co-firing with coal and gasification firing. The design factors for type 2 cyclone burners have been identified through the following three dimensionless numbers: swirl intensity (S), Strouhal number (St), and Reynolds number (Re). The lowest CO and NOx of type 2 cyclone burners have been sought for pulverized and non-pulverized wood biomass. The benefits of the co-firing of wood biomass in a cyclone burner with coal, have been presented in respect to combustion efficiency, alkali retention, and the amount of K and Na. The results evidently reveal the reduction in clinker and slag generation, which are the biggest concern to wood biomass combustion. The recent results of gasification studies using type 2 cyclone burners are compared, in terms of producer gases and syngases (H2, CO, CO2, CH4). [ABSTRACT FROM AUTHOR]

The fluidized bed combustion (FBC) of biomass and solid recovered fuel (SRF) is globally emerging as a viable solution to achieve net-negative carbon emissions in the heat and power sector. Contrary to conventional fossil fuels, alternative fuels are highly heterogeneous, and usually contain increased amounts of alkaline metals and chlorine. Hence, experimental studies are mandatory in order to thoroughly characterize the combustion behavior and pollutant formation of non-conventional fuels in novel applications. This work gives an overview of experimental investigations on the oxy-fuel combustion of hard coal, wheat straw, and SRF with a limestone bed in a semi-industrial circulating fluidized bed (CFB) pilot plant. The CFB combustor was able to be operated under different fuel blending ratios and inlet O2 concentrations, showing a stable hydrodynamic behavior over many hours of continuous operation. The boundary conditions introduced in this study are expected to prevail in carbon capture and storage (CCS) processes, such as the oxy-fuel combustion in the CFB calciner of a Calcium Looping (CaL) cycle for post-combustion CO2 capture. [ABSTRACT FROM AUTHOR]

Torrefied empty fruit bunch (EFB) co-firing is a promising technology to reduce emissions from coal-fired power plants. However, co-firing can influence the combustion and heat transfer characteristics in a coal boiler. In order to study the feasibility of co-firing application of torrefied EFB (T-EFB) in boilers, the combustion characteristics, gas emissions and heat flux distribution were analyzed, respectively. First, the kinetic parameters of T-EFB devolatilization and char oxidation were obtained by experimental analysis. Second, the computational fluid dynamics (CFD) analysis was applied to the actual 500 MWe boiler simulation to further evaluate the differences in the co-firing performance parameters (combustion characteristics and emissions) of the T-EFB and the heat transfer characteristics within the boiler. Numerical results show that T-EFB co-firing can improve the ignition characteristics of pulverized coal, reduce the formation of unburned particles. When the blending ratio was increased from 10% to 50%, significantly NOx (oxides of nitrogen) reduction (levels from 170 to 98 ppm at 6% O2) was achieved. At a blending ratio above 40%, boiler combustion efficiency decreases as the total heat flux of the boiler decreases due to an increase in the amount of unburned carbon. In addition, T-EFB co-firing can affect the heat transfer characteristics of the boiler. [ABSTRACT FROM AUTHOR]

One of the ways used to reduce the emission of carbon dioxide and other harmful substances is the implementation of biomass co-firing processes with coals. Such processes have been implemented for many years throughout many countries of the world, and have included using existing high-power coal boilers. Despite numerous experiments, there are still no analyses in the literature allowing for their generalization. The purpose of this paper is to determine the generalized energy and ecological characteristics of dust steam boilers co-firing hard coal with biomass. The energy characteristics determined in the paper are the dependence of the gross energy efficiency of boilers on such decision parameters as their efficiency and the share of biomass chemical energy in fuel. However, the ecological characteristics are the dependence of emission streams: CO, NOx, SO2, and dust on the same decision parameters. From a mathematical point of view, the characteristics are approximation functions between the efficiency values obtained from the measurements and the emission streams of the analysed harmful substances and the corresponding values of the decision parameters. Second-degree polynomials are assumed in this paper as approximation functions. Therefore, determining the characteristics came down to determining the constant coefficients occurring in these polynomials, the so-called structural parameters. The fit of the determined characteristics was assessed based on the coefficients of random variation and the test of estimated significance of structural parameters. Boiler characteristics can be used when forecasting the impact of changes in operating conditions on the effects achieved in existing, modernized, and designed boilers. The generalization of the characteristics was obtained from the measurement results presented in 10 independent sources used to determine them. [ABSTRACT FROM AUTHOR]

The aim of this study was to provide more effective use of straw for energy production by co-firing wheat straw pellets with solid fuels (wood, peat pellets) under additional electric control of the combustion characteristics at thermo-chemical conversion of fuel mixtures. Effects of the DC electric field on the main combustion characteristics were studied experimentally using a fixed-bed experimental setup with a heat output up to 4 kW. An axisymmetric electric field was applied to the flame base between the positively charged electrode and the grounded wall of the combustion chamber. The experimental study includes local measurements of the composition of the gasification gas, flame temperature, heat output, combustion efficiency and of the composition of the flue gas considering the variation of the bias voltage of the electrode. A mathematical model of the field-induced thermo-chemical conversion of combustible volatiles has been built using MATLAB. The results confirm that the electric field-induced processes of heat and mass transfer allow to control and improve the main combustion characteristics thus enhancing the fuel burnout and increasing the heat output from the device up to 14% and the produced heat per mass of burned solid fuel up to 7%. [ABSTRACT FROM AUTHOR]