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.     

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.     

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.     

Co-firing switchgrass in a 60-megawatt pulverized coal-fired boiler: Effects on combustion behavior and pollutant emissions

Switchgrass was co-fired with coal in an industrial scale boiler to investigate the co-firing effects on boiler performance and pollutant emissions. Comparing with firing coal alone, co-firing with switchgrass slightly lowered boiler efficiency by 0.6 to 1% under full-load and low-load conditions, respectively. Net carbon dioxide and SO₂ emissions were reduced with co-firing. Nitrogen oxides (NOx) emissions were similar with co-firing to firing coal alone under both high and low loading amounts of switchgrass. Varying the nitrogen content by changing switchgrass type and harvest time revealed no significant effect on NOx emission in the range of tested conditions.     

玉米秸秆与煤掺烧锅炉运行性能分析

基于ASPEN PLUS软件,对玉米秸秆与煤的掺烧过程进行建模与模拟,研究在不同的生物质掺混比例及含水率下,锅炉运行性能以及污染物排放的变化规律。结果表明:与单独燃烧煤粉相比,随着掺烧比例的增大,生成的理论烟气量和烟气热损失增大,锅炉效率有所降低,气体污染物NO及SO2减少;随着生物质含水率的增大,NO的排放量减少,而SO2的排放量增加。     

Influence of coal co-firing on the particulate matter formation during pulverized biomass combustion

Biomass is regarded as CO₂-neutral, while the high contents of potassium and chlorine in biomass induce severe particulate matter emission, ash deposition, and corrosion in combustion facilities. Co-firing biomass with coal in pulverized-combustion (PC) furnaces is able to solve these problems, as well as achieve a much higher generating efficiency than grate furnaces. In this work, the particulate matter (PM) emission from biomass co-firing with coal was studied in an entrained flow reactor at a temperature of 1623 K simulating PC furnace condition. PMs were sampled through a 13-stage impactor, and their morphology and elemental composition were characterized by scanning electron microscopy and electron dispersive X-ray spectroscopy. SO₂ emissions were measured to interpret the possibility of potassium sulfation during co-firing. Results show that PMs from the separated combustion of both biomass and coal present a bimodal particle size distribution (PSD). The concentration and size of fine-mode submicron particles (PM_1.0) from biomass combustion are much higher than those from coal combustion because of the high potassium content in biomass. For the co-firing cases, with the coal ratio increasing from 0% to 50%, the PM_1.0 yield is reduced by more than half and the PM_1.0 size becomes smaller, in contrast, the concentration of coarse-mode particles with the size of 1.0–10 μm (PM_1.0-10) increases. The measured PM_1.0 yields of co-firing are lower than the theoretically weight-averaged ones, which proves that during the biomass and coal co-firing in PC furnaces, the vaporized potassium from biomass can be efficiently captured by these silicon-aluminate oxides in coal ash. In the studied range of coal co-firing ratio (≤50 wt.%), the chlorides and sulfates of alkali metals from biomass burning are the dominating components in PM_1.0, and a certain amount of silicon is observed in PM_0.1-1. The analysis of chemical composition in PM_1.0, together with that of SO₂ emission, indicates a marginal sulfation of alkali metal chloride occurring at high temperatures in PC furnaces.     

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.     

A review on thermo-chemical characteristics of coal/biomass co-firing in industrial furnace

Biomass should be considered as one of the promising sources of energy for mitigating greenhouse gas (GHG) emissions. Co-firing biomass with coal has become a solution for meeting the power crisis as well as to reduce the pollutant emissions. The biomass fuels typically found from woody to grassy and solid recovered fuels depending on its origin and properties. It is suggested that co-firing coal with biomass has a substantial effect on SO_x and NO_x emission level. The ashing process, fly ash quality depends on the conversion technology, capture technology and the properties of the biomass. In order to control the furnace efficiency and production, burnout, optimum injection of biomass sharing with specific information of particle ignition properties are also important. A number of small/laboratory scale and industrial scale experiments have been conducted by different researchers. Different experimental studies performed are reviewed, grouped and summarized based on the fuel processing technology, burnout performance, emission level, environmental aspect, ash information and deposit characteristics, effect of co-firing ratios and adoption of oxy-fuel co-firing. Overall, this paper will highlight existing technologies and emerging trends in co-firing of different types of biomass which will be helpful for future investigations.     

Numerical study on coal/ammonia co-firing in a 600 MW utility boiler

Co-firing NH₃ in coal-fired power plants is an attractive method to accelerate the pace of global decarbonization. However, the contradiction between achieving elevated temperature within the furnace and maintaining low NO_x emission constrains the utilization of NH₃ as fuel. In this study, 3-dimensional numerical simulations on coal/NH₃ co-firing cases were conducted in a full-scale boiler for the first time. The influences of NH₃ blending ratio, O₂ enrichment combustion and deep air-staging technology were investigated. The results show that the burnout properties of NH₃ are excellent in co-firing boiler. Higher NH₃ blending ratio leads to lower temperature in the furnace. Enriching O₂ concentration to 30% in the secondary air can compensate the temperature decline caused by 50% NH₃ co-firing, while it brings an undesired surge in NO_x concentrations. The high temperature and strong reducing atmosphere (HT&SRA) could be created by combining the O₂ enrichment and deep air-staging combustion. The NO emission drops by 49.6% due to HT&SRA. Then, high flue gas temperature and low NO_x emission can be achieved simultaneously. HT&SRA improves the overall exergy efficiency for 50% NH₃ co-firing case from 51.65% to 51.78%. The findings open up a promising strategy for utilizing NH₃ as a stationary fuel.     

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.     

Current and future financial competitiveness of electricity and heat from energy crops: A case study from Ireland

It has been demonstrated that Miscanthus and willow energy-crop cultivation could be economically competitive with current agricultural land uses at a farm-gate biomass price ranging from €70 to €130 t⁻¹ dry matter [Styles, D., Thorne, F., Jones, M.B., in review. Energy crops in Ireland: An economic comparison of willow and Miscanthus production with conventional farming systems. Biomass and Bioenergy, May 2006]. This paper uses the same farm-gate prices to calculate the economic competitiveness of energy crop electricity and heat production, using a net-present-value (NPV) approach (20-year period, 5% discount rate). Direct and gasified co-firing of willow wood with coal would result in electricity generation 30% or 37% more expensive than coal generation, at current coal and CO₂ allowance prices and a farm-gate biomass cost of €100 t⁻¹. ‘Break-even’ CO₂ allowance prices are €33 and €37 t⁻¹, respectively. However, co-firing of Miscanthus with peat is close to economic competitiveness, and would require a CO₂ allowance price of €16 t⁻¹ to break-even (against a current price of €12 t⁻¹). NPV analyses indicate that wood heat is significantly cheaper than oil, gas or electric heat, excluding existing wood-boiler installation subsidies. Discounted annual savings range from €143 compared with gas to €722 compared with electric heating at the domestic scale and from €3454 to €11,222 at the commercial scale. Inclusion of available subsidies improves the comparative economics of domestic wood heat substantially. The economic advantage of wood heat is robust to variation in fuel prices, discount rates and heat loads. The greatest obstacles to energy-crop utilisation include: (i) a reluctance to consider long-term economics; (ii) possible competition from cheaper sources of biomass; (iii) the need for a spatially coordinated supply and utilisation network.     

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.     

Computational Modelling of Retrofitting a Coal Fired Boiler Type OP-230 for Predicting NO<Subscript>X</Subscript> Reduction

This study focuses on a CFD modelling of biomass-derived syngas co-firing with coal in an older mid-sized PC-fired boiler of type OP-230 with low-emission burners on the front wall. The simulations were performed to determine whether the boiler can be retrofitted for the fulfilment of the prospective environmental protection regulations relating to levels of NO_X emissions. The improvement of the air staging via the dual-fuel technique was based on the indirect co-firing technology. The impact of two arrangements of dedicated syngas nozzles (below and above the existing coal burners), two syngas compositions and two heat replacements (5% and 15%) on the course of thermal processes in a furnace was tested. The reductions in NO_X emissions were predicted relative to the baseline when only coal is combusted. The highest reduction of about 38% was achieved with the syngas nozzles below the existing coal burners and 15% heat replacement. This arrangement of nozzles offers the residence time sufficient to co-fire coal with waste derived syngas. A lower reduction in NO_X emissions was obtained with the nozzles above the burners as the enlargement of local fuel rich zone near syngas injection becomes significant for 15% heat replacement. Results provide for the decreasing impact of methane content along with the increase of syngas heat input. The avoided CO₂ emissions through the syngas indirect co-firing with coal in the boiler are linear function of heat replacements.     

生物质与煤混合燃烧成灰特性研究进展

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.生物质与煤混燃存在的结渣积灰等问题制约着混燃技术的推广利用,因此研究生物质与煤混合燃烧的成灰特性具有现实意义.文章详细介绍了生物质与煤混合燃烧成灰特性的影响因素和分析方法,认为温度是影响生物质与煤混合燃烧成灰特性的主要因素;生物质与煤的混合比例对灰渣成分有一定影响,但二者间不存在明显的线性关系.燃料中的碱金属、氯、硫是引起结渣积灰的主要物质.由于生物质与煤的成灰特性相近,只是灰渣成分的含量差异较大,因此可以利用已有的煤结渣特性研究成果,分析混燃的成灰特性,但须要考虑生物质灰分的特征.     

A methodology to compare combined heat and power systems operating under emissions reduction policies considering biomass co-fired,coal- and natural gas-fuelled steam turbines

A steam turbine CHP system with the option for co-firing biomass was examined under current carbon pricing legislation and the proposed emissions reduction policy of the newly elected Federal Government in Australia. When the boiler was fuelled by coal, the system was liable for the carbon price and was unprofitable indicating that the carbon price was successful as an incentive to reduce emissions. This result held only whilst carbon prices were at the values assumed in the analysis. The system would be more financially beneficial under the new Government policy, as it would not be penalized for its high emissions. All systems operating with a natural gas-fuelled boiler were unprofitable. In an attempt to reduce emissions, a co-fired boiler with biomass and coal was proposed. Emissions at 20 % biomass were still above the threshold determining liability; therefore, co-firing was not able to eliminate carbon pricing liability. Due to the high price of biomass, the carbon price could not be offset and was therefore not an economical solution for reducing emissions. However, when biomass pricing was adopted from more established markets, co-firing became somewhat conducive only when the carbon price was repealed.     

Explosion characteristics of pulverised torrefied and raw Norway spruce (Picea abies) and Southern pine (Pinus palustris) in comparison to bituminous coal

Pre-treatments, such as torrefaction, can improve biomass fuels properties. Dedicated and coal co-firing plants, in which pulverised biomass and torrefied biomass can be used, are exposed to explosion hazards during handling, storage and transport from the mills to the boiler. Data on the explosion characteristics of biomass and torrefied biomass are scarce. This study presents explosion characteristics (maximum explosion pressure, deflagration index and minimum explosible concentration) of two torrefied wood samples and compares their reactivity to that of their corresponding untreated biomass materials and to a sample of Kellingley coal. Torrefied biomass samples showed higher reactivity, overpressures were around 9 bar (0.9 MPa, 1 bar = 10⁵ Pa) for all biomass samples irrespective of size or sample composition. Derived laminar burning velocities ranged between 0.1–0.12 m s⁻¹, and were therefore similar to that of coal (0.12 m s⁻¹). The differences in explosion reactivity influence the design of explosion protection measures and can be used to introduce suitable modifications for safe operations with torrefied biomass.     

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.     

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.     

Hydrothermal co-gasification of sorghum biomass and çan lignite in mild conditions: An optimization study for high yield hydrogen production

In this study, response surface methodology (RSM) combined with a 3–factor and 3–level Box–Behnken design (BBD) was performed to obtain high yield hydrogen production from hydrothermal co–gasification of sorghum biomass and low rank Çan lignite in a batch type reactor at 500 °C. The individual and the combined effects of the process parameters of coal amount (%) of the coal/biomass mixtures, initial water volume (mL) of the reactor and amount of the coal/biomass mixtures (kg) on system pressure, total gas yield, hydrogen production and product distribution were determined. Water volume directly affected the system pressure and the reaction medium was supercritical water medium above 48.2 mL with a pressure of 22.06 MPa. The highest values of both total gas volume and hydrogen gas volume were reached by gasification of 5.0 g of feedstock. It has been observed that total gas volume and hydrogen volume were directly affected by the water volume in the reactor and the coal ratio of the coal-biomass mixtures. The highest total gas and hydrogen volumes can be achieved under the conditions where the higher levels of water volume of the reactor and lower levels of coal percentage of the coal/biomass mixture were combined. Optimum conditions for maximum hydrogen production with 5.0 g of coal/biomass mixture were determined with numerical optimization as coal percentage of 25.6% and initial water volume of 68.5 mL. By combining the impregnated K₂CO₃ (3%, (w/w)) and CaO catalysts an excellent hydrogen selectivity was achieved. The hydrogen selectivity was drastically increased from 32.0% to 70.8% by capturing more than 99% of CO₂ with a H₂/CO₂ mol ratio of 88.5.     

Effect of biomass leaching on H2 production,ash and tar behavior during high temperature steam gasification (HTSG) process

The effect of biomass water leaching on H₂ production, as well as, prediction of ash thermal behavior and formation of biomass tar during high temperature steam gasification (HTSG) of olive kernel is the main aim of the present work. Within this study raw olive kernel samples (OK₁, OK₂) and a pre-treated one by water leaching (LOK₂) were examined with regard to their ash fouling propensity and tar concentration in the gaseous phase. Two temperatures (T = 850 and 950 °C) and a constant steam to biomass ratio (S/B = 1.28) were chosen in order to perform the steam gasification experiments. Results indicated that considering the samples' ash thermal behavior, it seemed that water leaching improved the fusibility behavior of olive kernel; however, it proved that water leaching does not favour tar steam reforming, while at the same time decreases the H₂ yield in gas product under air gasification conditions, due to possible loss of the catalytic effect of ash with water leaching.