Recent progress in supercritical fluid science for biofuel production from woody biomass

1 Introduction Due to global warming caused by excessive use of fossil fuel resources, renewable biomass resources will become more important in the future as alterna- tives to fossil resources. Therefore, technologies that can convert biomass to valuable liquid fuels and chemicals will be important for solving our energy and environmental problems.Thus, in our laboratory, several research projects on biofuels have been carried out in order to establish bioenergy systems, by means of supercrit…     

Cost structure of and competition for forest-based biomass

Abstract

Biomass has become a popular alternative to satisfy expanding energy demand and as a substitute for fossil fuels and phased-out nuclear energy in Europe. The European Union White Paper stipulates that the utilization of biomass shall increase to 1566 TWh by 2010. However it is often overlooked that the forest resources are already, to a large extent, used by the forest industries. When promoting biomass for energy generation the consequences for the forest industries also need to be considered. Sweden is an excellent case study, as there are vast quantities of forest resources, nuclear power is starting to be phased out, there are restrictions on expanding hydropower and the political desire exists to “set an example” with respect to carbon dioxide emissions. This paper attempts to estimate and analyse the supply of two types of forest resource, namely, roundwood and harvesting residues derived from final harvesting and commercial thinnings. Two separate supply curves are estimated: one for roundwood and one for harvesting residues. The cost structure is based on an economic-engineering approach where the separate cost components are constructed from the lowest cost element into aggregates for labour, capital, materials and overhead costs for each forest resource. The results indicate an unutilized economic supply of 12 TWh of harvesting residues in Sweden. However, after these 12 TWh have been recovered it becomes more profitable to use roundwood for energy purposes than to continue extracting further amounts of harvesting residues.     

Biomass energy in industrialised countries—a view of the future

Biomass fuels currently (1994) supply around 14% of the world's energy, but most of this is in the form of traditional fuelwood, residues and dung, which is often inefficient and can be environmentally detrimental. Biomass can supply heat and electricity, liquid and gaseous fuels. A number of developed countries derive a significant amount of their primary energy from biomass: USA 4%, Finland 18%, Sweden 16% and Austria 13%. Presently biomass energy supplies at least 2 EJ year⁻¹ in Western Europe which is about 4% of primary energy (54 EJ). Estimates show a likely potential in Europe in 2050 of 9.0–13.5 EJ depending on land areas (10% of useable land, 33 Mha), yields (10–15 oven-dry tonnes (ODt) ha⁻¹), and recoverable residues (25% of harvestable). This biomass contribution represents 17–30% of projected total energy requirements up to 2050. The relative contribution of biofuels in the future will depend on markets and incentives, on continuous research and development progress, and on environmental requirements. Land constraints are not considered significant because of the predicted surpluses in land and food, and the near balance in wood and wood products in Europe.There is considerable potential for the modernisation of biomass fuels to produce convenient energy carriers such as electricity, gases and transportation fuels, whilst continuing to provide for traditional uses of biomass; this modernisation of biomass and the industrial investment is already happening in many countries. When produced in an efficient and sustainable manner, biomass energy has numerous environmental and social benefits compared with fossil fuels. These include improved land management, job creation, use of surplus agricultural land in industrialised countries, provision of modern energy carriers to rural communities of developing countries, a reduction of CO₂ levels, waste control, and nutrient recycling. Greater environmental and net energy benefits can be derived from perennial and woody energy cropping than from annual arable crops which are short-term alternative feedstocks for fuels. Agroforestry systems can play an important role in providing multiple benefits to growers and the community, besides energy. In order to ameliorate CO₂ emissions, using biomass as a substitute for fossil fuels (complete replacement, co-firing, etc.) is more beneficial from social and economic perspectives than sequestering the carbon in forests.Case studies are presented for several developed countries and the constraints involved in modernising biomass energy along with the potential for turning them into entrepreneurial opportunities are discussed. It is concluded that the long term impacts of biomass programmes and projects depend mainly on ensuring income generation, environmental sustainability, flexibility and replicability, while taking account of local conditions and providing multiple benefits, which is an important attribute of agroforestry-type systems. Biomass for energy must be environmentally acceptable in order to ensure its widespread adoptions as a modern energy source. Implementation of biomass projects requires governmental policy initiatives that will internalise the external economic, social and environmental costs of conventional fuel sources so that biomass fuels can become competitive on a ‘level playing field’.     

木质生物质直接液化研究现状及趋势

木质生物质可以再生利用、能量密度相对较高、易运输和储存, 是实现大规模替代石化燃料的理想生物资源。直接液化是近年来迅速发展起来的一门新兴的生物质能利用技术, 具有反应条件较为温和、反应设备简单、产品可部分生物降解等特点, 发展潜力较大。阐述了木质生物质直接液化的分类, 总结了该技术的国内外研究状况, 探讨了木质生物质直接液化技术的发展趋势。     

工业锅炉生物质燃烧应用现状

介绍了工业锅炉中生物质燃料各种燃烧技术的技术特点和发展现状,重点分析了各种燃烧技术对不同生物质的适应性,展望了生物质燃烧技术的发展趋势,提出了生物质燃烧技术发展和应用的建议.     

森林防火隔离带技术的变革与优势

以消减可燃物的方式预防和阻隔森林火灾是林火管理工作的核心。传统阻隔技术向遮荫型防隔火技术的演变已成为近10余年西方多林国家林火管理工作的重要走向。从林火的特点和蔓延基本规律出发, 遮荫型防火隔离带技术通过局部消减可燃物载量和规则化可燃物分布, 显著降低其可能形成的林火强度, 使大多数火灾自行熄灭。该项技术的实施不受区域和气候条件限制; 与传统全光式防火隔离带和生物防火林带相比, 不但工作量较小, 对林分植被和生态环境的干扰也较小。该项技术实现了偶发性林火的防控、森林健康及生态维护的有机结合, 以此替代传统防火隔离带技术效益显著。针对遮荫型防隔火技术的进一步研究工作应包括不同稀化程度林带潜在火行为和其防隔火效能的量化评估、林地局部可燃物稀化的高效作业机具以及伴随该项技术实施产生的大量生物质副产品的有效利用问题。     

Social preferences toward energy generation with woody biomass from public forests in Montana,USA

In Montana, USA, there are substantial opportunities for mechanized thinning treatments on public forests to reduce the likelihood of severe and damaging wildfires and improve forest health. These treatments produce residues that can be used to generate renewable energy and displace fossil fuels. The choice modeling method is employed to examine the marginal willingness of Montanans' to pay (MWTP) for woody biomass energy produced from treatments in their public forests. The survey instrument elicited social preferences for important co-benefits and costs of woody biomass energy generation in Montana, namely the extent of healthy forests, the number of large wildfires, and local air quality. Positive and statistically significant MWTP is found for woody biomass energy generation, forest health and air quality. MWTP to avoid large wildfires is statistically insignificant. However, MWTP for woody biomass energy diminishes quickly, revealing that Montanans do not support public forestland management that produces more than double the current level of woody biomass harvested for energy generation. These findings can be used by policy makers and public land managers to estimate the social benefits of utilizing residues from public forest restoration or fuel treatment programs to generate energy.     

Bringing Agroforestry Technology to Farmers in Leyte, the Philippines: A Comparison of Two Extension Assistance Regimes

The response of farmers to personalised forestry and agroforestry extension assistance has not been well documented in the Philippines, thus providing the impetus for this research in which the effectiveness of extended on-farm assistance was compared with more limited assistance. In four municipalities in Leyte Island, farmers responded positively to an extended program which helped them overcome problems in germinating and growing seedlings and establishing trees on their land. A limited assistance program which sought to make use of farmers’ familiarity with growing and raising plants was relatively unsuccessful, with less preparation of tree planting sites and a higher rate of abandonment. Allowing farmers freedom to select planting sites and aspects of technical advice which suited their personal circumstances, encouraged a high degree of cooperation between extension staff and farmers, but 38% of farmers neglected post-planting weed control and 35% of sites were inappropriate for growing trees. Destruction of sites by flooding and grazing also caused farmers to blame extension staff even though these risks had been discussed with them beforehand. This suggested that a more interventionist approach would be appropriate for site selection although it may reduce recruitment. The number of farmers recruited through local government staff was low, but attendance by neighbours at locally held demonstrations was high, suggesting an avenue for further recruitment. Overall, the program was successful in shifting the initiative for further planting from extension staff to those farmers who received extended extension assistance.     

生物质热解产物综合利用方案及经济可行性

通过收集秸秆类生物质热解数据,构建热解产物数据库,从而建立SVM生物质热解产物模型,提出基于农业园区的生物质分级利用一体化方案,同时利用产物模型基于该方案进行个性化种植优化调节。在处理量400 kg/h的情况下,与传统秸秆还田方案相比,该方案能够处理掉25%～50%的还田秸秆。在秸秆处理和肥料采买项目上,园区可节省相关支出近30%,采取优化方案可在此基础上再减少支出近4%。     

高温干旱下毛竹林受灾状况和自恢复能力研究

2013年夏季,我国东南部地区发生了严重的高温干旱天气,毛竹林受灾严重。通过设置固定样地研究了高温干旱后毛竹林的受灾状况以及灾后竹林的自恢复能力。结果表明:在高温灾害发生以后,胸径较大的毛竹抵御灾害的能力高于胸径较小的毛竹;受灾毛竹地上部分生物量80%以上分布在竹秆中,因此竹枝和竹叶受损对毛竹地上生物量的影响不大;毛竹林受灾后的恢复能力在很大程度上取决于受灾当年新生竹的株数。因此,在毛竹林经营中应加强林地的水肥管理,培育大径竹材,同时应保持较高的立竹密度和较多的新生竹数量,以抵御旱灾并加快林分的灾后恢复。     

Potential for climate change mitigation through afforestation: an economic analysis of fossil fuel substitution and carbon sequestration benefits

The impetus for this paper is Canada's commitment under the Kyoto Protocol to reduce national greenhouse gas emissions as well as reducing dependency on fossil fuels. This research assesses the economic viability of using biomass from afforested lands and industrial wood waste as a feedstock for ethanol production to substitute for fossil fuels in the transportation sector. Afforestation can increase the size of the carbon sink and also provide a source of renewable energy. Ethanol offers an excellent opportunity for greenhouse gas mitigation due to market potential, an ability to offset significant emissions from the transportation sector, and reduce emissions from CO₂-intensive waste-management systems. A case study of the economics of a hypothetical ethanol production facility found that a facility capable of producing 122 million litres of ethanol annually could have a net present value of CDN$245 million over a planning horizon of 36 years. This facility would require a supply of up to 960 oven-dry tonnes of wood-biomass per day and would result in net annual reductions of greenhouse gas emissions of approximately 349,000 tonnes of CO₂. This includes the carbon sequestered through the afforestation as well as emissions avoided through fossil fuel substitution. Using biomass from afforested lands and industrial wood waste as a fuel for energy production can be an economically viable tool for reducing greenhouse gas levels in the atmosphere, reducing reliance on fossil fuels and reducing the sensitivity of transportation fuel prices to changes in gasoline prices. This revised version was published online in August 2006 with corrections to the Cover Date.     

木质生物原料的液化

随着石油资源的日近枯竭,加上石油制品不易生物降解而造成的环境污染,寻求石油替代品,开发新能源、新材料迫在眉睫。利用产量巨大、可再生、可生物降解的木质生物原料(森林和作为农业废弃物的秸杆等)通过物理、化学方法获取燃料、化学品及新型材料的研究日益受到人们的关注。通过液化制备各种新型高分子材料和燃油,是替代石油制品,提高木材的利用价值、有效利用劣质和废弃森林资源及农业废弃物、减轻环境与能源压力的全新途径。本文综述了木质资源液化的研究开发与现状。     

Leaf physiology, production, water use, and nitrogen dynamics of the grassland invader Acacia smallii at elevated CO(2) concentrations

Invasion by woody legumes can alter hydrology, nutrient accumulation and cycling, and carbon sequestration on grasslands. The rate and magnitude of these changes are likely to be sensitive to the effects of atmospheric CO(2) enrichment on growth and water and nitrogen dynamics of leguminous shrubs. To assess potential effects of increased atmospheric CO(2) concentrations on plant growth and acquisition and utilization of water and nitrogen, seedlings of Acacia smallii Isely (huisache) were grown for 13 months at CO(2) concentrations of 385 (ambient), 690, and 980 micro mol mol(-1). Seedlings grown at elevated CO(2) concentrations exhibited parallel declines in leaf N concentration and photosynthetic capacity; however, at the highest CO(2) concentration, biomass production increased more than 2.5-fold as a result of increased leaf photosynthetic rates, leaf area, and N(2) fixation. Measurements of leaf gas exchange and aboveground biomass production and soil water balance indicated that water use efficiency increased in proportion to the increase in atmospheric CO(2) concentration. The effects on transpiration of an accompanying decline in leaf conductance were offset by an increase in leaf area, and total water loss was similar across CO(2) treatments. Plants grown at elevated CO(2) fixed three to four times as much N as plants grown at ambient CO(2) concentration. The increase in N(2) fixation resulted from an increase in fixation per unit of nodule mass in the 690 micro mol mol(-1) CO(2) treatment and from a large increase in the number and mass of nodules in plants in the 980 micro mol mol(-1) CO(2) treatment. Increased symbiotic N(2) fixation by woody invaders in response to CO(2) enrichment may result in increased N deposition in litterfall, and thus increased productivity on many grasslands.     

典型生物质快速热解工艺流程及其性能评价

生物质液体燃油被认为是替代日益枯竭的化石能源的一个重要生长点,快速热解液化已经具有了一定的研究基础和工程应用。首先分析快速热解前进行干燥和粉碎等预处理的原因,接着分析几种典型的热解工艺的流程和性能,最后得出要加大生物质热解机理研究力度的结论。     

生物质固化成型技术研究进展

生物质固化成型技术是目前利用生物质能比较普遍且效果显著的技术之一。它是将生物质压制为便于运输和贮存的棒状或颗粒燃料, 可以提高燃烧效率。文中综述了国内外生物质固化成型技术的开发利用现状, 从成型工艺、成型设备、影响因素和燃料炉具4个方面进行了总结, 并针对我国生物质能源现状提出了合理、充分开发生物质固化成型技术的相关问题和建议。     

Higher growth temperatures decreased net carbon assimilation and biomass accumulation of northern red oak seedlings near the southern limit of the species range

If an increase in temperature will limit the growth of a species, it will be in the warmest portion of the species distribution. Therefore, in this study we examined the effects of elevated temperature on net carbon assimilation and biomass production of northern red oak (Quercus rubra L.) seedlings grown near the southern limit of the species distribution. Seedlings were grown in chambers in elevated CO(2) (700 μmol mol(-1)) at three temperature conditions, ambient (tracking diurnal and seasonal variation in outdoor temperature), ambient +3 °C and ambient +6 °C, which produced mean growing season temperatures of 23, 26 and 29 °C, respectively. A group of seedlings was also grown in ambient [CO(2)] and ambient temperature as a check of the growth response to elevated [CO(2)]. Net photosynthesis and leaf respiration, photosynthetic capacity (V(cmax), J(max) and triose phosphate utilization (TPU)) and chlorophyll fluorescence, as well as seedling height, diameter and biomass, were measured during one growing season. Higher growth temperatures reduced net photosynthesis, increased respiration and reduced height, diameter and biomass production. Maximum net photosynthesis at saturating [CO(2)] and maximum rate of electron transport (J(max)) were lowest throughout the growing season in seedlings grown in the highest temperature regime. These parameters were also lower in June, but not in July or September, in seedlings grown at +3 °C above ambient, compared with those grown in ambient temperature, indicating no impairment of photosynthetic capacity with a moderate increase in air temperature. An unusual and potentially important observation was that foliar respiration did not acclimate to growth temperature, resulting in substantially higher leaf respiration at the higher growth temperatures. Lower net carbon assimilation was correlated with lower growth at higher temperatures. Total biomass at the end of the growing season decreased in direct proportion to the increase in growth temperature, declining by 6% per 1 °C increase in mean growing season temperature. Our observations suggest that increases in air temperature above current ambient conditions will be detrimental to Q. rubra seedlings growing near the southern limit of the species range.     

Bark beetles,fuels, fires and implications for forest management in the Intermountain West

Bark beetle-caused tree mortality in conifer forests affects the quantity and quality of forest fuels and has long been assumed to increase fire hazard and potential fire behavior. In reality, bark beetles, and their effects on fuel accumulation, and subsequent fire hazard, are poorly understood. We extensively sampled fuels in three bark beetle-affected Intermountain conifer forests and compared these data to existing research on bark beetle/fuels/fire interactions within the context of the disturbance regime. Data were collected in endemic, epidemic and post-epidemic stands of Douglas-fir, lodgepole pine and Engelmann spruce. From these data, we evaluated the influence of bark beetle-caused tree mortality on various fuels characteristics over the course of a bark beetle rotation. The data showed that changes in fuels over time create periods where the potential for high intensity and/or severe fires increases or decreases. The net result of bark beetle epidemics was a substantial change in species composition and a highly altered fuels complex. Early in epidemics there is a net increase in the amount of fine surface fuels when compared to endemic stands. In post-epidemic stands large, dead, woody fuels, and live surface fuels dominate. We then discuss potential fire behavior in bark beetle-affected conifer fuels based on actual and simulated fuels data. Results indicated that for surface fires both rates of fire spread and fireline intensities were higher in the current epidemic stands than in the endemic stands. Rates of spread and fireline intensities were higher in epidemic stands due, however, to decreased vegetative sheltering and its effect on mid-flame wind speed, rather than changes in fuels. Passive crown fires were more likely in post-epidemic stands, but active crown fires were less likely due to decreased aerial fuel continuity. We also discuss the ecological effects of extreme fire behavior. Information is presented on managing forests to reduce the impact of bark beetle outbreaks and the interplay between management, bark beetle populations, fuels and fire hazard and behavior.     

我国桉树生物质能源林研究与利用综述

开发利用林业生物质能源是改善能源结构、保障能源安全和保护生态环境的重要途径之一.桉树不仅是工业原料林生产的重要树种,也是林业生物质能利用的良好原材料.本文从品种研究、评价指标(热值、灰分、生物量、能量现存量)、造林技术(立地条件、整地方式、造林密度、混交造林、收获周期、效益分析)和利用方式等方面阐述了我国桉树生物质能源林研究与利用现状,简要总结了我国发展桉树生物质能源存在的不足并提出今后加强研究的重点,以期为我国合理开发和利用桉树生物质能源提供参考.     

Increased utilization of different tree parts for energy purposes in the Nordic countries

The review gives an overview of the increased utilization of forest biomass for energy. The emphasis is on Nordic countries, especially on Sweden and Finland with large biomass potentials and a high share of renewable energy in gross final energy consumption. The utilization and potential of forest chip sources such as logging residues, small-size tree stems and stumps that are normally not harvested in conventional harvesting are described. Environmental potential and impacts that may reduce the utilization of forest biomass are discussed based on recent publications. Finally, the review summarizes the future developments based on their relationship to policies, certifications and guidelines and forest owners' decisions.     

生物质直接燃烧利用现状

随着社会经济的发展,环境问题和能源问题日益严重,人类开始加紧寻找可再生能源的步伐。在众多的能源中,生物质能以其清洁、可再生性等优点受到了世界各国的广泛关注,人们开始研究采用不同的方法及技术来燃烧生物质,以其获取寻找最佳的燃烧利用方法,提高生物质的利用率。为了更有效地开发生物质能源,本文详细分析了目前生物质的来源组成及直接燃烧的过程。在此基础上,本文提出了今后在生物质利用方面林业工作的研究内容。