落叶松树皮喷动循环流化床快速热解的影响因素

对喷动循环流化床落叶松树皮快速热解过程中反应温度、物料粒径、进料速率及气体流量对热解产物产率的影响以及这4个因素共同作用对生物油产率的影响进行研究.结果表明:反应温度是影响热解产物产率的主要因素,气体流量影响较显著,在试验范围内物料粒径、进料速率影响不显著;喷动循环流化床最佳制备液体产物--生物油快速热解工艺条件为:反应温度550℃,物料粒径0.2～0.3 mm,进料速率20 r·min-1,气体流量25m3·h-1.     

高酚类含量生物油喷动循环流化床快速热解工艺

采用喷动循环流化床快速热解系统对落叶松树皮进行快速热解制备高酚类物质含量生物油,考察反应温度、粒径、进料速率和气体流量对生物油中酚类物质含量的影响,以生物油中酚类物质含量为目标,优化快速热解工艺.结果表明:反应温度、粒径是影响生物油中酚类物质含量的关键因素;制备高酚类物质含量生物油的喷动循环流化床快速热解最佳工艺为:反应温度823K,粒径0.3～ 0.45mm,进料速率50 r/min,气流量15 m3/h.     

喷动循环流化床生物质快速热解设备的特性分析与发展研究综述

简要综述了生物质快速热解设备研究的国内外现状,继而详述了喷动床和循环流化床,重点对喷动循环流化床作了较深入的探析,探讨了喷动循环流化床快速热解设备研究的发展方向。     

喷动循环流化床快速热解动力学方程研究

目前生物质热解动力学方程的研究主要集中在低升温速率工况,实验和模拟数据不能完全反映极高升温速率下商业规模级别热解反应器生物质快速热解动力学特征。以喷动循环流化床快速热解系统为研究对象,分析落叶松树皮快速热解过程,结合气固等温反应理论,通过生物油产率及不凝气体产率,获得落叶松树皮快速热解、生物油转化、不凝气体转化的动力学参数及其动力学方程。     

木质生物质快速热解生物油产率影响因素分析

木质生物质能是可再生能源的重要组成部分,快速热解技术是国内外木质生物质能源化的热点研究课题.本文在简要总结木质生物质快速热解技术的基础上,着重对快速热解过程中热解温度、升温速率、压力、气相滞留时间、木质生物质物料特性、催化剂、热解反应器等因素对生物油产率的影响进行了论述,阐明了提高生物油产率的快速热解工艺条件.     

甘蔗渣热解气化特性的研究

在实验条件下,考察反应温度、升温速率、物料颗粒大小等因素对蔗渣在水蒸气中的热解气化特性的影响。实验结果表明,热解终温越高,物料粒径越小,越有利于产生高质量的热解气。在先到达热解终温,再通入水蒸气的操作条件下,升温速率的改变对气化效果的影响并不突出,而热解终温是热解气化过程主要的决定因素。实验在最佳条件,温度采用粉末物料在1 000℃进行热解可以得到高热值合成气10 M J/Nm3,和较高的产气率1.7 m3/kg。     

热过滤对流化床快速热解制取生物油产率和品质的影响

在1 kg/h的小型鼓泡流化床热解反应装置中增设一热过滤装置,对杉木快速热解制取生物油进行了研究,考察了热过滤装置对生物油产率和品质的影响。结果表明:热解油(未经热过滤)和过滤油(经过热过滤)的产率随热解温度的升高先上升后下降,并都在475℃时达到最大值,分别为58.1%和50.7%。热过滤装置的引入降低了生物油的产率(下降5%~10%),且热解温度越高,过滤油产率下降越明显。相比于热解油Ⅰ,过滤油Ⅰ的含水率从13.77%增加到15.83%,p H值从2.18上升到2.23,热值由20.47 MJ/kg降低到19.53 MJ/kg,但固体含量、碱金属和碱土金属均有显著下降,总体下降约75%,减少了生物油中自聚反应的发生。在老化实验过程中,过滤油Ⅰ的含水率、黏度分别增加了10.2%和57.6%,但较热解油Ⅰ变化幅度小;通过GC-MS分析其组成变化,发现过滤油Ⅰ中各组分含量变化幅度较热解油Ⅰ小,表明热过滤使其中不利反应的发生得到了抑制,稳定性较好,显示出热过滤装置对生物油品质提升的良好促进作用,有利于生物油的储存、运输和使用。     

基于机器学习的生物质热解三态产物产率提升研究

通过挖掘文献中木质纤维素类生物质鼓泡流化床快速热解实验数据并建立随机森林(RF)回归模型,以生物质原料特性与热解条件对生物质热解生物油、生物炭、气体的产率进行预测。从影响生物质热解产物分布的5类关键因素中整理出15个特征变量,将输入变量进行了组合得到7个模型,均能很好地预测生物质热解三态产物,回归系数(R²)大于0.9。模型6的输入变量最少且准确度最高,对生物炭、生物油、生物质热解气产率预测的R²分别为0.942 8、 0.956 1、 0.939 1,均方根误差(RMSE)分别为2.679 1、 2.939 5和3.108 3。通过模型贡献度分析可知,热解条件(Ⅴ)为影响热解产物产率的最重要因素,其对生物炭、生物油、生物质热解气产率预测的贡献度分别为0.332 7、 0.220 4和0.214 7。采用部分依赖图(PDP)结合各个特征变量的分布箱线图分析,结果表明：热解温度(HT)、木质素质量分数(Lig)、颗粒粒径(PS)为影响生物炭产率的主要因素;生物油与生物质热解气产率则由HT、纤维素质量分数(Cel)与半纤维素质量分数(Hem)、进...     

流化床式生物质快速热解生产线热质衡算北大核心

生物质快速热解技术被国际上公认为最具发展潜力的生物质能源转换技术之一。笔者在北京林业大学平泉实验基地中试生产线试验数据的基础上,进行了年处理1万t流化床式生物质快速热解生产线的热质衡算,研究热解生产线各个工序的物料变化及能量流动情况,获得生物质原料与生物油、热解炭等产品之间的转化关系,定量反映出热解工艺中反应、冷凝等关键过程的能量变化,为确定热解工艺条件及热负荷、生产线关键设备设计及选型提供依据。     

流化床式生物质快速热解生产线热质衡算

生物质快速热解技术被国际上公认为最具发展潜力的生物质能源转换技术之一。笔者在北京林业大学平泉实验基地中试生产线试验数据的基础上,进行了年处理1万t流化床式生物质快速热解生产线的热质衡算,研究热解生产线各个工序的物料变化及能量流动情况,获得生物质原料与生物油、热解炭等产品之间的转化关系,定量反映出热解工艺中反应、冷凝等关键过程的能量变化,为确定热解工艺条件及热负荷、生产线关键设备设计及选型提供依据。     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.