STEAM DRYLNG OF WOOD FUELS

ABSTRACT

The objective of this work is to investigate some of the important aspects in the design of a steam band dryer for wood fuels. For this purpose the drying of the material in a bench-scale fixed bed dryer has been studied.

Drying times and thermal efficiencies for experiments conducted under different conditions are compared. The investigated materials are soft-and hardwood chips and softwood bark.

The thermal efficiency, the part of the sensible heat which is used during one passage of the steam through the bed, increases with increasing mass load (mass of dry matter per unit area) and with decreasing steam mass flux. At a mass load of 30 kg/m the thermal efficiency is about 0.85 even at steam mass fluxes as high as 0.6 kg/m² s (1.2 m/s). The thermal efficiency proves to be almost independent of pressure and temperature of the steam.

Due to the very inhomogeneous materials the steam mass flow distribution was uneven. This causes a decreased thermal efficiency. When bark     

STEAM DRYING OF WOOD CHIPS IN PNEUMATIC CONVEYING DRYERS

A model for a pneumatic conveying dryer is presented. Although the main emphasis is put on superheated steam drying of wood chips, it can be used for other porous materials as well

The model includes a comprehensive two-dimensional model for the drying of single wood chips which accounts for the main physical mechanisms occurring in wood during drying. The external drying conditions in a pneumatic conveying dryer were calculated by applying the mass, heat and momentum equations for each incremental step in dryer length. A plug flow assumption was made for the dryer model and the single particle and dryer models were solved in an iterative manner. The non-spherical nature of wood chips were accounted for by measuring the drag and heat transfer coefficients

Model calculations illustrate the complex interactions between steam, particles and walls which occur in a flash dryer. The drying rate varies in a very complex manner through the dryer. The internal resistance to mass transfer becomes very important in The drying of less permeable wood species such as spruce. Two effects were observed as the particle size was increased: firstly the heat transfer rate decreased, and secondly the residence time increased. To some extent, these effects compensate for each other, however, the net result is that larger chips have a higher final moisture content.     

STEAM DRYING OF WOOD CHIPS IN PNEUMATIC CONVEYING DRYERS

ABSTRACT

A model for a pneumatic conveying dryer is presented. Although the main emphasis is put on superheated steam drying of wood chips, it can be used for other porous materials as well

The model includes a comprehensive two-dimensional model for the drying of single wood chips which accounts for the main physical mechanisms occurring in wood during drying. The external drying conditions in a pneumatic conveying dryer were calculated by applying the mass, heat and momentum equations for each incremental step in dryer length. A plug flow assumption was made for the dryer model and the single particle and dryer models were solved in an iterative manner. The non-spherical nature of wood chips were accounted for by measuring the drag and heat transfer coefficients

Model calculations illustrate the complex interactions between steam, particles and walls which occur in a flash dryer. The drying rate varies in a very complex manner through the dryer. The internal resistance to mass transfer becomes very important in The drying of less permeable wood species such as spruce. Two effects were observed as the particle size was increased: firstly the heat transfer rate decreased, and secondly the residence time increased. To some extent, these effects compensate for each other, however, the net result is that larger chips have a higher final moisture content.     

DRYING OF WOOD BIOMASS AT HIGH PRESSURE STEAM ATMOSPHERE; EXPERIMENTAL RESEARCH AND APPLICATION

Imatran Voima Oy together with Technical Research Centre of Finland has carried out experimental research on fuel drying at high pressure steam atmosphere. The pilot dryer is a pressurized flash dryer. Since its commissioning in 1991, the dryer has been used for drying experiments of peat and wood biomass for about 1000 h. The dryer operates at 23 bar pressure steam atmosphere with capacity of abt. 1000 kg/h of wet feedstock.

The developed high pressure steam dryer is planned to be used in a power plant process suitable for wet fuels as peat, biomass, and brown coal. The process is based on the connection of a pressurized fuel dryer, a pressurized gasifier, and a gas turbine. The integration of the high pressure steam dryer to the process increases the power generating efficiency of the process essentially.     

DRYING OF WOOD BIOMASS AT HIGH PRESSURE STEAM ATMOSPHERE; EXPERIMENTAL RESEARCH AND APPLICATION

ABSTRACT

Imatran Voima Oy together with Technical Research Centre of Finland has carried out experimental research on fuel drying at high pressure steam atmosphere. The pilot dryer is a pressurized flash dryer. Since its commissioning in 1991, the dryer has been used for drying experiments of peat and wood biomass for about 1000 h. The dryer operates at 23 bar pressure steam atmosphere with capacity of abt. 1000 kg/h of wet feedstock.

The developed high pressure steam dryer is planned to be used in a power plant process suitable for wet fuels as peat, biomass, and brown coal. The process is based on the connection of a pressurized fuel dryer, a pressurized gasifier, and a gas turbine. The integration of the high pressure steam dryer to the process increases the power generating efficiency of the process essentially.     

SIMULATION OF SUPERHEATED STEAM DRYING CONSIDERING INITIAL STEAM CONDENSATION

A heat and mass transfer model was proposed for the superheated steam drying, focusing on phenomena which occur during the initial stage of drying, i.e., condensation of superheated steam on material surfaces and subsequent shift from condensation to evaporation leading to the beginning of the actual drying (Reverse Process Model). Next, drying equations considering the reverse process were formulated for a shrinking/swelling infinite flat plate to calculate moisture content and temperature distributions in a material, changes in mass of a material with time, and a characteristic drying curve. Then, the influence of the initial thickness of a material and the heat transfer coefficient were investigated. In addition, calculation results were compared with experimental ones with regard to the change in mass of material with time and the characteristic drying curve, and good conformance was obtained for the initial stage of drying.     

SIMULATION OF SUPERHEATED STEAM DRYING CONSIDERING INITIAL STEAM CONDENSATION

A heat and mass transfer model was proposed for the superheated steam drying, focusing on phenomena which occur during the initial stage of drying, i.e., condensation of superheated steam on material surfaces and subsequent shift from condensation to evaporation leading to the beginning of the actual drying (Reverse Process Model). Next, drying equations considering the reverse process were formulated for a shrinking/swelling infinite flat plate to calculate moisture content and temperature distributions in a material, changes in mass of a material with time, and a characteristic drying curve. Then, the influence of the initial thickness of a material and the heat transfer coefficient were investigated. In addition, calculation results were compared with experimental ones with regard to the change in mass of material with time and the characteristic drying curve, and good conformance was obtained for the initial stage of drying.     

二氧化碳压缩机汽轮机蒸汽消耗增大原因分析

二氧化碳压缩机汽轮机蒸汽消耗大，对其影响因素逐项进行分析、论证，针对主要原因采取相应处、理措施，使汽轮机蒸汽消耗恢复到正常。     

中国发展合成燃料可能性的探讨

当前国际石油市场供过于求，价格疲软，显然不可能兴建煤革合成燃料工厂。但中国的情况有很大的差异，在可预见的时期内，中国能源仍将以煤为主要支柱（＞７５％），从国内能源的探明资源及生产实际看，煤炭相对缓和而石油严重不足，随着货运及民用车辆的急剧增加，发动机燃料短缺已成为最突出矛盾，因而在中国一些无油或严重贫油但却多煤的省份，发展合成燃料工业是可行的。在分析发建设资金筹集的可能性，技术成熟程度和经济竞争能     

CONTACT DRYIXG OF WOOD VENEER

A model for contact drying of wood veneer is presented and compared with experimental results. The model is and-dimensional and assumes that convective transport of liquid and vapor is dominant for the drying conditions examined. Model results are in good agreement with the experimental data.

A parameter study indicates that total drying time is a strong function of platen temperature and veneer thickness. The model indicates that the spacing of ventilation grooves does not affect drying rate significantly, but has a large effect on pressure buildup in the veneer. Veneer permeability shoved a similar effect--with lover permeabilities resulting in slightly slower drying, but significantly higher internal pressure.     

木粉对PVC木塑复合材料力学性能影响

采用电镜扫描观察了3种木粉的纤维细胞尺寸及其木粉微观形态。研究了木粉粒度、微观特性以及木粉添加量对了聚氯乙烯（PVC）木塑复合材料力学性能的影响。结果表明，木粉表面裸露的微细纤维增加和粒度减小，有助于提高木塑复合材料力学强度；加入少量木粉使木塑复合材料力学性能降低，但随着木粉添加量的增大，木塑复合材料的抗弯性能和拉伸强度上升；木塑复合材料的冲击强度随木粉含量增加而下降。     

CONTACT DRYIXG OF WOOD VENEER

A model for contact drying of wood veneer is presented and compared with experimental results. The model is and-dimensional and assumes that convective transport of liquid and vapor is dominant for the drying conditions examined. Model results are in good agreement with the experimental data.

A parameter study indicates that total drying time is a strong function of platen temperature and veneer thickness. The model indicates that the spacing of ventilation grooves does not affect drying rate significantly, but has a large effect on pressure buildup in the veneer. Veneer permeability shoved a similar effect--with lover permeabilities resulting in slightly slower drying, but significantly higher internal pressure.     

汽轮机高速齿轮受损后的处理及机组运行

介绍汽轮发电机组特点,减速箱齿轮坏的原因与修复方法,说明稳定机组安全运行的工艺措施     

优化动力配煤

简述优化动力配煤的工艺流程，指出配煤的种类配比，燃烧性和结渣性，通过优化配比，总结出动力煤技术是值得推广的，经济实用和洁净煤技术。     

KBR蒸汽系统的优化

介绍了中海石油化学股份有限公司二期合成氨装置KBR蒸汽系统,分析了原设计中存在的缺陷和不足,通过采取一系列的改造和优化措施,使问题得以解决.     

IMPINGEMENT STEAM DTYING OF PAPER

A mathematical model is presented to predict the drying rates and energy consumption for the process of impingement steam drying of paper during the constant-rate drying period. Preliminary experiments have verified the validity of the simulation model. The predicted results show consumption may be as low as 640 kJ/kg water evaporated while hot air Yankee dryers typically consume 5020 to 7100 kJ/kg water evaporated     

表面处理对木粉增强PVC发泡复合板材性能的影响

研究表面处理的木粉对发泡聚氯乙烯(PVC)板材的增强改性效果。使用铝酸酯偶联剂、丙烯酸丁酯预聚物对木粉进行表面处理，将其混合到聚氯乙烯发泡板材配料中进行板材加工生产，结果表明，经处理的木粉能提高发泡PVC板材的拉伸强度和冲击强度。用铝酸酯偶联剂处理木粉的发泡板材力学性能好于用丙烯酸丁酯预聚物处理的板材；而用丙烯酸丁酯预聚物处理木粉的复合材料在流变加工性能优于用铝酸酯处理木粉的复合材料。     

浅析外用S100蒸汽对合成气压缩机高压汽轮机的影响

分析目前二化肥合成装置引用S100过热蒸汽后,对合成气压缩机高压汽轮机(103-JAT)的影响,同时考虑到二化肥扩能的因素,提出解决问题的办法.     

EVALUATION OF SOME TRANSPORT AND THERMODYNAMIC PROPERTIES OF SUPERHEATED STEAM: EFFECTS OF STEAM TEMPERATURE AND PRESSURE

For machine computation of drying, humidification and dehumidification processes it is necessary to have reliable correlations to predict transport and thermodynamic properties of the drying medium as functions of temperature and pressure. In this paper empirical correlations for specific volume, dynamic viscosity, thermal conductivity as well as specific isobaric heat capacity of superheated steam over the temperature range of 160-500^° C and the pressure range of 100-500 kPa are presented. The Prandtl numbers at various temperatures and pressures are also presented. Comments on the properties and the use of these correlations are given.     

EVALUATION OF SOME TRANSPORT AND THERMODYNAMIC PROPERTIES OF SUPERHEATED STEAM: EFFECTS OF STEAM TEMPERATURE AND PRESSURE

ABSTRACT

For machine computation of drying, humidification and dehumidification processes it is necessary to have reliable correlations to predict transport and thermodynamic properties of the drying medium as functions of temperature and pressure. In this paper empirical correlations for specific volume, dynamic viscosity, thermal conductivity as well as specific isobaric heat capacity of superheated steam over the temperature range of 160-500^° C and the pressure range of 100-500 kPa are presented. The Prandtl numbers at various temperatures and pressures are also presented. Comments on the properties and the use of these correlations are given.