生物质与煤混烧技术的应用

生物质是一种可在再生、低污染的清洁能源，在能源系统中占有重要地位。本文综述了世界上生物质与煤混烧的应用状况，包括直接利用和气化利用，总结了目前生物质与煤混烧中存在的问题，并根据我国的实际情况，提出了在我国发展生物质混烧技术的建议。     

Technological aspects of sunflower biomass and brown coal co-firing

The technological problems occurring in the co-firing of biomass and brown coal (lignite) prompted this research project. During the fuel preparation, accidental self-ignition and explosions were several times reported by power plants operators. The aim of this study was to evaluate brown coal, sunflower husks and sunflower husk pellets as fuels for co-firing in energetic boilers. Sunflower husk had a lower ash content and calorific value than the pellets. The range of the combustion temperatures of the biomass (200–300 °C) was narrower than that of brown coal (200–800 °C). The formation of highly alkaline ash from the biomass resulted in the formation in boiler of agglomerates of ash. The elemental composition, thermogravimetric and biological analyses suggested that the pellets contained synthetic additives difficult to identify. The biological method was proposed for evaluating biomass additives. The use of additional agents in the pelletizing process may influence on the combustion parameters. Mixing biomass with brown coal may occasionally result in self-ignition in the logistic chain. Plastic additives and biological activity may contribute to self-ignition.     

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.     

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.     

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.     

大容量煤粉锅炉生物质混燃技术探讨

针对当前发达国家正在兴起的生物质混燃发电技术,结合实际调研情况,研究分析了该技术在大容量煤粉炉中的几种典型相关系统的配置方案和国内外应用现状,指出了该技术具有高效率、低造价,同时能规模化实现二氧化碳有效减排的优势,在未来有广阔的应用前景。     

我国生物质与煤混烧发电的可行性分析

通过对生物质发电政策法规、混烧发电优势、原料保障的分析,对生物质混烧发电技术方案进行讨论,并结合一些实例,分析得出生物质混烧发电适合我国国情,应大力发展.     

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.     

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.     

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.     

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.     

Biofuels and biochemicals production from forest biomass in Western Canada

Biomass can be used for the production of fuels, and chemicals with reduced life cycle (greenhouse gas) emissions. Currently, these fuels and chemicals are produced mainly from natural gas and other fossil fuels. In Western Canada, forest residue biomass is gasified for the production of syngas which is further synthesized to produce different fuels and chemicals. Two types of gasifiers: the atmospheric pressure gasifier (commercially known as SilvaGas) and the pressurized gasifier (commercially known as RENUGAS) are considered for syngas production. The production costs of methanol, (dimethyl ether), (Fischer-Tropsch) fuels, and ammonia are $0.29/kg, $0.47/kg, $0.97/kg, and $2.09/kg, respectively, for a SilvaGas-based gasification plant with a capacity of 2000 dry tonnes/day. The cost of producing methanol, DME, F-T fuels, and ammonia in a RENUGAS-based plant are $0.45/kg, $0.69/kg, $1.53/kg, and $2.72/kg, respectively, for a plant capacity of 2000 dry tonnes/day. The minimum cost of producing methanol, DME, F-T fuels, and ammonia are $0.28/kg, $0.44/kg, $0.94/kg, and $2.06/kg at plant capacities of 3000, 3500, 4000, and 3000 dry tonnes/day, respectively, using the SilvaGas-based gasification process. Biomass-based fuels and chemicals are expensive compared to fuels and chemicals derived from fossil fuels, and carbon credits can help them become competitive.     

低温热解生物质与煤共燃的结渣、积灰和磨损特性分析

利用灰分的结渣性指数t2、B／A、S／A、G,积灰沾污特性指数比和磨损指数‰对低温热解生物质单燃和与煤共燃时的结渣、积灰和磨损特性进行了研究和分析。认为：(1)低温热解生物质(锯屑、谷壳和花生壳)都不适合在电厂锅炉中直接燃烧。(2)热解生物质与煤共燃时的结渣、积灰和磨损特性取决于热解生物质灰分含量、灰成分,煤的灰分含量、灰成分以及混合比例等因素。(3)三种熬解生物质与煤共燃能够改善它们的结渣、积灰沾污和磨损性能,但又增加了煤的结渣、积灰沾污和磨损性。(4)热解生物质灰分含量越低。煤的灰分含量越高,煤的结渣、积灰沾污性能越好,越有利于提高混燃比例。(5)三种热解生物质中,热解锯屑与煤可混性最好。其他两种则相对较差。     

The feasibility of co-firing biomass for electricity in Missouri

Bioenergy is one of the most significant energy resources with potential to serve as a partial replacement for fossil. As an agricultural state, Missouri has great potential to use biomass for energy production. In 2008, Missouri adopted a renewable portfolio standard (RPS) yet about 80% of its power supply still comes from coal. This paper describes a feasibility study of co-firing biomass in existing coal-powered plants in Missouri. Specifically, this study developed a linear programming model and simulated six scenarios to assess the economic feasibility and greenhouse gas impacts of co-firing biomass in existing qualified coal power plants in Missouri.The results of this study indicate that although co-firing can reduce the emissions of GHG and environmental pollutants, it is still not an economically feasible option for power generation without additional economic or policy incentives or regulations which could take environmental costs into account. Based on these results, strategies and policies to promote the utilization of biomass and to increase its competitiveness with fossil fuels are identified and discussed.     

生物质气掺烧对煤污染物排放特性影响的Aspen Plus数值计算研究

为了分析生物质气与煤混合燃烧对锅炉燃烧产物的影响,基于Aspen Plus建立了生物质气化以及合成气与煤混合燃烧模型,对含水率为20%的松木气化的合成气与不同品质的煤种的混合燃烧过程以及污染物排放特性进行研究。改变生物质气的掺烧比例,随着输入锅炉空气流量的变化,确定出各种工况下的锅炉最高燃烧温度,得到对应燃烧温度下的NOx,SO2等污染物的排放值。结果表明,随着煤种质量的降低和掺烧比例的增加,煤与生物质气混烧后的最高燃烧温度均降低;无论是优质煤还是劣质煤,与生物质气掺烧后,均可以使污染物NOx,SO2随生物质气掺烧比例的增加而减少,即减排率随掺烧比例的增加而增加。     

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.     

Sequential development of correlated projects: An application to coal liquefaction

In this paper, a sequential research and development programme is considered for which several categories of related technologies are available to develop, each having the potential to produce some final product. At each stage of the programme, an optimal portfolio of technologies is chosen, given the information acquired from the previous stages, and those contingent optimal plans are followed in all subsequent stages. The model is applied to coal liquefaction technologies to emphasize the costs that may be incurred by erroneously approaching the development programme as a once-and-for-all endeavour rather than in a sequential framework. The results of the synthetic oil application indicate that the acceleration of the programme may be optimal when the probability of successful development decreases. Under these conditions, adoption of a ‘crash programme’ in which all projects are researched simultaneously, may lead to deferral of synthetic oil development.     

花生壳与煤共燃的燃烧特性研究

用热重分析法,对花生壳与煤以相同比例掺混后在不同升温速率下进行了共燃试验。研究表明,生物质的加入改善了煤的燃烧性能,且随升温速率的升高,着火温度呈下降趋势;各试样的挥发分最大释放速率、固定炭最大燃烧速率、燃尽温度均呈增加趋势,它们的燃烧特性均随升温速率的升高而变好。     

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。