生物质直燃发电厂锅炉炉型选择探讨

目前生物质直接燃烧发电是生物质利用的主流技术之一,锅炉设计选型是生物质发电厂技术的主要核心,选择什么样的炉型,不仅影响着生物质电厂的投资、经济型,还影响着生物质电厂的使用寿命。对生物质直燃发电厂的几个炉型比较研究,为生物质直燃发电厂的炉型选择提出建议,供生物质发电厂设计时参考。     

Prevention of Tibetan eco-environmental degradation caused by traditional use of biomass

Tibet is short in fossil energy, but rich in renewable energy sources, such as biomass, hydro, solar, geothermal, and wind power. This potential energy supply in Tibet can be juxtaposed to what drives Tibetan energy consumption its economic motivation and its cultural traditions. Currently, biomass heavily dominates Tibet's energy consumption. In 2003, total energy consumption was about 2 million tce (ton coal equivalent), traditional biomass accounting for nearly 70%. The rarified atmosphere and use of outdated stoves, make for a very low combustion efficiency, utilizing 10–15% of the potential energy of biomass. With population and economic growth, traditional use of biomass has become the principal factor responsible for deforestation, grassland degradation, desertification, and soil erosion. To eradicate the negative impact of the traditional use of biomass on the eco-environment in Tibet, a series of effective countermeasures are investigated. Among these are improved efficiency of stoves, widespread use of solar energy, hydroelectricity as a substitute for traditional biomass, and the development of biogas.     

发展中国家农村民用炉灶的温室气体和污染物排放因子研究

在发展中国家，农村民用炉灶是消耗生物质能的主要设备。为了确定民用炉灶的温室气体和其它污染物的排放因子，从上世纪90年代开始，国际社会选择中国、印度等发展中国家进行了一系列测试。文中对这些测试结果进行了总结和比较。研究表明，除了个别燃料和炉灶组合，生物质能源在节能炉灶中的CO2排放因子都有所降低，而不完全燃烧产物的排放因子比传统炉灶高。     

Health and climate benefits of cookstove replacement options

The health and climate impacts of available household cooking options in developing countries vary sharply. Here, we analyze and compare these impacts (health; climate) and the potential co-benefits from the use of fuel and stove combinations. Our results indicate that health and climate impacts span 2 orders of magnitude among the technologies considered. Indoor air pollution is heavily impacted by combustion performance and ventilation; climate impacts are influenced by combustion performance and fuel properties including biomass renewability. Emission components not included in current carbon trading schemes, such as black carbon particles and carbon monoxide, can contribute a large proportion of the total climate impact. Multiple ‘improved’ stove options analyzed in this paper yield roughly equivalent climate benefits but have different impacts on indoor air pollution. Improvements to biomass stoves can improve indoor air quality, which nonetheless remains significantly higher than for stoves that use liquid or gaseous hydrocarbons. LPG- and kerosene-fueled stoves have unrivaled air quality benefits and their climate impacts are also lower than all but the cleanest stoves using renewable biomass.     

Wood fuel use in the traditional cooking stoves in the rural floodplain areas of Bangladesh: A socio-environmental perspective

A study was conducted, using a multistage simple random sampling design, to determine the structural characteristics of the traditional cooking stoves, amount of wood fuel consumed in the rural floodplain areas in Bangladesh, and also to figure out the socio-economic and environmental consequences of wood fuel usage in the traditional cooking stove. The study showed that family size, income, amount cooked and burning hours significantly affected the amount of wood fuel used per family per year. Taking into account different family sizes, the study observed that 4.24 tonne fuelwood were consumed per family per year. The study showed that 42% of families used only biomass fuel, 5% used liquefied petroleum gas (LPG) and 53% used kerosene along with biomass fuels. The main source of biomass fuel was homestead forests (40%). It has been figured out that the incomplete combustion of biomass in the traditional cooking stove poses severe epidemiological consequences to human health and contributes to global warming. The study also showed that 83% of the respondents would prefer improved cooking stoves over traditional cooking stoves.     

The emissions from a space-heating biomass stove

In this paper, the flue gas emissions of carbon monoxide (CO), nitrogen oxides (NO_X), sulphur dioxide (SO₂) and soot from an improved space-heating biomass stove and thermal efficiency of the stove have been investigated. Various biomass fuels such as firewood, wood shavings, hazelnut shell, walnut shell, peanut shell, seed shell of apricot (sweet and hot seed type), kernel removed corncob, wheat stalk litter (for cattle and sheep pen), cornhusk and maize stalk litter (for cattle pen) and charcoal were burned in the same space-heating biomass stove. Flue gas emissions were recorded during the combustion period at intervals of 5 min. It was seen from the results that the flue gas emissions have different values depending on the characteristics of biomass fuels. Charcoal is the most appropriate biomass fuel for use in the space-heating biomass stoves because its combustion emits less smoke and the thermal efficiency of the stove is approximately 46%.     

Thermal rating and design of woodstoves: A new approach

The paper is divided into two parts. In the first part, the results of tests on 13 stoves currently being marketed in India, compared with two traditional stoves, are presented. The bulk of the tests (about 140) pertain to variation of efficiency against fuel burning rate. Also, a few tests on the variation of chimney heights (18 tests) and damper position (20 tests) were conducted. The levels of efficiency were quite low on account of improper dimensioning of the stoves. Except for two stoves, all recorded consistently low efficiency figures. In the second part of the paper, the results of tests on combustion chambers of different sizes, ranging from a diameter of 180 mm to 500 mm, are presented in the form of design equations. The optimum length to diameter ratio is about 0.35, and optimum height of the ash chamber is 0.2 times the height of combustion chamber. A new approach to the sizing of combustion chambers is presented.     

Performance evaluation of three types of forced draft cook stoves using fuel wood and coconut shell

Many cook stove programs implemented in South Asia and Africa were aimed at reducing fuel wood consumption and pollutants through the use of improved cook stoves. The research work presented in this paper is focused on evaluation of improved cook stoves with respect to thermal efficiency and emission levels. Since the type of biomass fuel varies in different geographical regions, the improved cook stoves must be compatible to use different types of fuel. The present research work is aimed at evaluating three types of forced draft cook stove with two types of biomass fuels. Water boiling tests were conducted to evaluate the stove performance with respect to efficiency and fuel flexibility. The findings of the study are used to evaluate the stove's performance with respect to fuel flexibility, efficiency and user acceptance. The performance results of three types of forced draft stoves tested with fuel wood and coconut shell are presented in this research paper.     

户用生物质炉具热效率试验方法研究

针对国内外主要热效率试验方法进行对比与研究,通过控制试验操作方法及条件,得出6组影响因素,对实测热效率结果进行了评价。尝试找出适用于国内户用生物质炉具的试验方法,且使操作更加便捷,测试结果更加准确。     

Combustion Systems for Biomass Fuel

Abstract

Biomass is one of humanity's earliest sources of energy. Traditionally, biomass has been utilized through direct combustion, and this process is still widely used in many parts of the world. Biomass thermo-chemical conversion investigations are certainly not the most important options at present; combustion is responsible for over 97% of the world's bio-energy production. Biomass combustion is a series of chemical reactions by which carbon is oxidized to carbon dioxide, and hydrogen is oxidized to water. Biomass fired domestic stoves are commonly used for space heating and cooking in the rural areas. Biomass residues are now widely used in many countries to provide centralized, medium and large-scale production of process heat for electricity production. Biomass is burned by direct combustion to produce steam, the steam turns a turbine and the turbine drives a generator, producing electricity.     

小型卧式燃煤热风炉内流动与传热过程的数值模拟及实验

为了研究第三挡板长度对热风炉燃烧性能的影响,以热风炉燃烧室为研究对象,利用FLUENT软件对其进行了数值模拟,模拟分析了燃烧室内的温度分布、速度分布及颗粒物浓度分布等情况,最后搭建了试验台对数值模型进行了验证。结果表明：燃烧室温度模拟值与实验值的相对误差在10%以内;燃烧高温区位于第一挡板和第二挡板顶部之间的区域;大部分颗粒物集中在炉排底部附近,随着烟气绕挡板流动,颗粒物浓度逐渐降低;热风炉燃烧室内第三挡板长度为270mm时,可以减少炉膛出口处颗粒物的排放,使燃烧更充分。     

Biomass availability, energy consumption and biochar production in rural households of Western Kenya

Pyrolytic cook stoves in smallholder farms may require different biomass supply than traditional bioenergy approaches. Therefore, we carried out an on-farm assessment of the energy consumption for food preparation, the biomass availability relevant to conventional and pyrolytic cook stoves, and the potential biochar generation in rural households of western Kenya. Biomass availability for pyrolysis varied widely from 0.7 to 12.4 Mg ha⁻¹ y⁻¹ with an average of 4.3 Mg ha⁻¹ y⁻¹, across all 50 studied farms. Farms with high soil fertility that were recently converted to agriculture from forest had the highest variability (CV = 83%), which was a result of the wide range of farm sizes and feedstock types in the farms. Biomass variability was two times lower for farms with low than high soil fertility (CV = 37%). The reduction in variability is a direct consequence of the soil quality, coupled with farm size and feedstock type. The total wood energy available in the farms (5.3 GJ capita⁻¹ y⁻¹) was not sufficient to meet the current cooking energy needs using conventional combustion stoves, but may be sufficient for improved combustion stoves depending on their energy efficiency. However, the biomass that is usable in pyrolytic cook stoves including crop residues, shrub and tree litter can provide 17.2 GJ capita⁻¹ y⁻¹ of energy for cooking, which is well above the current average cooking energy consumption of 10.5 GJ capita⁻¹ y⁻¹. The introduction of a first-generation pyrolytic cook stove reduced wood energy consumption by 27% while producing an average of 0.46 Mg ha⁻¹ y⁻¹ of biochar.     

秸秆类生物质燃烧动力学特性实验研究

生物质能的利用越来越受到重视。直接燃烧技术由于其操作简单、取材方便、成本适宜等特点是一种符合我国国情的生物质能利用方式。采用热重分析的研究方法,对水稻秸秆、玉米秸秆和玉米芯三种秸秆类生物质的燃烧动力学特性进行了实验,研究了不同升温速率、氧浓度对不同种类的秸秆生物质燃料燃烧动力学特性的影响,并对着火温度、燃烧稳定性、挥发分析出特性、燃烧特性指数等相关特性参数进行定量分析,为设计秸秆工业锅炉燃烧设备,合理选择生物质种类、优化燃烧、提高锅炉效率提供了理论支撑。     

Study of a TE (thermoelectric) generator incorporated in a multifunction wood stove

Replacing traditional open fire stoves, characterized by low efficiency, with improved ones is an important challenge for developing countries. Adding TE (thermoelectric) generators can provide electricity that permits not only the use of an electric fan increasing the ratio air to fuel to achieve a complete combustion in the stoves but also the satisfaction of basic needs: light, phones and other electronic devices. A review of existing TE generators for stoves is presented. To test the TE modules, an experimental device has been carried out in our laboratory where a gas heater simulates the stove. The generator set-up is described including the switching electric regulator that stabilizes the fluctuating voltage from the modules and stores the energy in a battery. The performance of the generator mostly depends on the heat transfer through the modules and especially on the thermal contact resistances. First experiments show the influence of the pressure on these resistances. Then a study of temperatures and electrical power measurements is compared to a theoretical analysis using TE and heat transfer equations. The very reasonable value of the obtained contact resistances shows that the mechanical design of the generator is almost optimized. The TE generator has produced up to 9.5 W.     

Low greenhouse gas biomass options for cooking in the developing countries

Large quantities of biomass fuels are used for cooking in the developing countries. Although biomass is a renewable source of energy, traditional biomass-fired stoves cause significant greenhouse gas (GHG) emissions due to formation of products of incomplete combustion; also, exposure to smoke from these stoves causes serious health problems. This paper presents an analysis of a number of selected options available for developing countries in the context of reducing total greenhouse gas emission per unit of useful energy for cooking. It is assumed that biomass as an energy carrier is CO₂—neutral. However, other GHGs emitted from biomass combustion cause a net greenhouse effect; accordingly, in this study only the non-CO₂ greenhouse gases i.e. CH₄ and N₂O are considered in estimating GHG emission for different biomass-based cooking options. The total GHG emission from traditional wood-fired stoves is estimated to be about $\text{110}\text{g}$ of CO₂ equivalent per mega joule of useful energy (g CO₂-e MJ_useful⁻¹) delivered to the cooking pot; this can be compared with 42, 5, 2, 350, 166 and $\text{196}\text{g}\text{CO}{}_2$-e MJ_useful⁻¹ in case of improved wood-, biogas-, producer gas-, kerosene-, natural gas- and LPG-fired stoves, respectively. Modern biomass based cooking options such as improved biomass-, biogas- and producer gas-fired stoves can potentially play an important role in mitigating GHG emission from domestic cooking by providing an alternative to kerosene-, natural gas- and LPG-fired stoves.     

Review of technology in small-scale biomass combustion systems in the European market

This work studied the importance of wood pellets, chips and wood logs for small- and medium-scale heat production. Pellet use can contribute substantially to reaching the renewable heat and electricity goals set by the European Union (EU) Renewable Energy Directive. Consequently, to integrate into European energy markets, pellet use must be a key piece of the EU energy policy.This study provides a wide perspective on the state-of-the-art small-scale biomass combustion units, particularly those that use pellets for fuel. Small-scale combustion units include stoves and boilers with capacities less than 200 kW. A wide market review has been conducted, including a review of the literature and information from manufacturers and test institutes. A database has been created, which includes 186 companies and offers 995 different models, providing an extensive view of the European market. The large number of new companies shows that the solid-fuel boiler market is continuously increasing across Europe. The technologies that are currently the most widely used are described and compared.     

Emission factors of wood and charcoal-fired cookstoves

In the developing countries, energy required for cooking often has the biggest share in the total national energy demand and is normally met mostly by biomass. This paper presents the results of experimental studies on emission conducted on a number of traditional and improved cookstoves collected from different Asian countries using wood and charcoal as fuel. The emission factors from this study are comparable to those reported in the literature. In the case of wood combustion, CO₂ emission factor is in the range of 1560–1620 g kg⁻¹. The emission factors for pollutants CO, CH₄, TNMOC and NO_x were in the ranges 19–136, 6–10, 6–9 and 0.05–0.2 g kg⁻¹, respectively. In the case of charcoal combustion, CO₂ emission factor is in the range of 2155–2567 g kg⁻¹. The emission factors for pollutants CO, CH₄, TNMOC were in the ranges 35–198, 6.7–7.8, 6–10 g kg⁻¹, respectively.

Comparison between wood and charcoal fired stoves shows that, CO₂ and CO emission factor values for wood are lower as compared to charcoal. CH₄ and TNMOC emission factors for wood are with the same range as compared to charcoal. Emission factors for NO_x using wood is slightly lower than charcoal. The emission of all the pollutants per unit of useful heat was found to decrease with increasing stove efficiency for both wood and charcoal fired stoves.     

Solid-fuel household cook stoves: Characterization of performance and emissions

In this study, 14 solid-fuel household cook stove and fuel combinations, including 10 stoves and four fuels, were tested for performance and pollutant emissions using a WBT (Water Boiling Test) protocol. Results from the testing showed that some stoves currently used in the field have improved fuel efficiency and lower pollutant emissions compared with traditional cooking methods. Stoves with smaller-mass components exposed to the heat of fuel combustion tended to take lesser time to boil, have better fuel efficiency, and lower pollutant emissions. The challenge is to design stoves with smaller-mass components that also have acceptable durability, affordable cost, and meet user needs. Results from this study provide stove performance and emissions information to practitioners disseminating stove technology in the field. This information may be useful for improving the design of existing stoves and for developing new stove designs. Comparison of results between laboratories shows that results can be replicated between labs when the same stove and fuel are tested using the WBT protocol. Recommendations were provided to improve the ability to replicate results between labs. Implications of better solid-fuel cook stoves are improved human health, reduced fuel use, reduced deforestation, and reduced global climate change.     

Economic evaluation of common reed potential for energy production: A case study in Wuliangsuhai Lake (Inner Mongolia,China)

Wuliangsuhai Lake is one of the largest wetlands in Inner Mongolia, China, half covered by large and highly productive Common Reed (Phragmites australis) stands. However, benefits from current utilization practices do not cover the costs of harvesting. Against this background, Wuliangsuhai Lake is taken as a case study for the assessment of the potential use of reed biomass for energy production. Taking into account, both the present and the potential reed availability, four scenarios are considered, i.e. (1) a decentralized application in household stoves, (2) a centralized reed supplied combined heat and power gasification, (3) a direct combustion plant and (4) a co-firing in existing coal plants. Two field campaigns have been conducted firstly collect information about the current situation of the reed and coal market and secondly to measure reed above-ground biomass. The suitability of reed for thermochemical conversion processes has been evaluated by means of chemical-physical, calorimetric, and thermal analyses of the samples. The potential energy production is valued regarding the profitability on the current Chinese energy market. Possible subsidies for reed as a renewable resource are taken into account. The evaluation has shown that reed has the potential to act as an energy feedstock. In relation to the considered study site, reed energy use can be profitable on the household level, in CHP combustion plants and in co-combustion. Gasification CHP plants are not economic feasible under current conditions. The results show that reed can be a sustainable alternative to highly health and environment damaging coal.     

LCA of domestic and centralized biomass combustion: The case of Lombardy (Italy)

This paper analyzes and compares the environmental impacts of biomass combustion in small appliances such as domestic open fireplaces and stoves, and in two types of centralized combined heat and power plants, feeding district heating networks. The analysis is carried out following a Life Cycle Assessment (LCA) approach. The expected savings of GHG (greenhouse gases) emissions due to the substitution of fossil fuels with biomass are quantified, as well as emissions of toxic pollutants and substances responsible for acidification and ozone formation.The LCA results show net savings of GHG emissions when using biomass instead of conventional fuels, varying from 0.08 to 1.08 t of CO₂ eq. per t of dry biomass in the different scenarios. Avoided GHG emissions thanks to biomass combustion in Lombardy are 1.32 Mt year^?1(1.5% of total regional GHG emissions). For the other impact categories, the use of biomass in district heating systems can again cause a consistent reduction of impacts, whereas biomass combustion in residential devices shows higher impacts than fossil fuels with a particular concern for PAH, VOC and particulate matter emissions. For example, in Lombardy, PM10 emissions from domestic devices are about 8100 t year^?1, corresponding to almost one third of the total particulate emissions in 2005.