An overview of the chemical composition of biomass

Combustion characteristics of different biomass fuels

Currently, fossil fuels such as oil, coal and natural gas represent the prime energy sources in the world. However, it is anticipated that these sources of energy will deplete within the next 40–50 years. Moreover, the expected environmental damages such as the global warming, acid rain and urban smog due to the production of emissions from these sources have tempted the world to try to reduce carbon emissions by 80% and shift towards utilizing a variety of renewable energy resources (RES) which are less environmentally harmful such as solar, wind, biomass etc. in a sustainable way. Biomass is one of the earliest sources of energy with very specific properties. In this review, several aspects which are associated with burning biomass in boilers have been investigated such as composition of biomass, estimating the higher heating value of biomass, comparison between biomass and other fuels, combustion of biomass, co-firing of biomass and coal, impacts of biomass, economic and social analysis of biomass, transportation of biomass, densification of biomass, problems of biomass and future of biomass. It has been found that utilizing biomass in boilers offers many economical, social and environmental benefits such as financial net saving, conservation of fossil fuel resources, job opportunities creation and CO 2 and NO x emissions reduction. However, care should be taken to other environmental impacts of biomass such as land and water resources, soil erosion, loss of biodiversity and deforestation. Fouling, marketing, low heating value, storage and collections and handling are all associated problems when burning biomass in boilers. The future of biomass in boilers depends upon the development of the markets for fossil fuels and on policy decisions regarding the biomass market.

A review on biomass as a fuel for boilers

Potential applications of renewable energy sources, biomass combustion problems in boiler power systems and combustion related environmental issues

Torrefaction is a mild pyrolysis, which has been explored for the pretreatment of biomass to increase the heating value and hydrophobicity. Due to its potential applications for making torrefied pellets, which can be used as a high quality feedstock in gasification for high quality syngas production and as a substitute for coal in thermal power plants and metallurgical processes, torrefaction and densification have attracted great interest in recent years from both academia and bioenergy industry. This paper provides a comprehensive review of research progresses in this area, drawing on major contributions from two major research groups of the authors on torrefaction and densification at Canada and Taiwan as well as literatures. It is revealed that torrefaction of various biomass species and their major components, lignin, cellulose and hemicelluloses have been extensively studied in thermogravimetric apparatus (TGA) under both inert (N 2 ) and oxidative (O 2 , H 2 O) environments to elucidate the weight loss as a function of temperature, particle size and time. It was found that the higher heating value and saturated water uptake of torrefied biomass were a strong function of weight loss, which represents the degree of torrefaction. When torrefied sawdust is compressed into torrefied pellets, more mechanical energy is consumed and higher die temperature is required to make torrefied pellets of similar density and hardness as regular pellets. Simple economics analyses based on laboratory scale experimental data showed that because of the potential savings from pellets transport, handling and storage logistics, the overall cost for torrefied pellets can be lower than regular pellets in European market for both European and Canadian pellets. The gasification could be improved in terms of both energy efficiency and syngas quality because of the removal of oxygenated volatile compounds from torrefied biomass.

A state-of-the-art review of biomass torrefaction, densification and applications

http://www-personal.umich.edu/~mswool/publications/cofire_prog_official_reprint.pdf

Co-firing of coal and biomass fuel blends

The present study was conducted to investigate the tribological and mechanical properties of plasma-nitrided Ti6Al4V alloy. Specimens were nitrided in an H2N2 (1:8 ratio) plasma. The nitrogen concentration along the nitrided zone was obtained using the nuclear reaction analysis technique. The workpiece temperature was varied from 450 to 520 °C during the nitriding process. Pin-on-disc wear tests were carried out to evaluate the wear properties of the resultant samples and a ball-on-disc experiment was conducted to measure the friction coefficient. Microhardness tests, Scanning electron microscopy and X-ray diffraction were carried out to investigate the phases developed in the nitrided zone. It was found that the wear resistance improved considerably after the nitriding process. Three distinct layers were identified: (i) an inner layer where δ-TiN + e-Ti2N phases formed, (ii) an intermediate layer where α-(TiN) with or without e phase developed and (iii) an outer layer where precipitations were dominant.

Plasma nitriding of Ti6Al4V alloy to improve some tribological properties

Laser-induced thermal stresses on steel surface

The laser drilling process is a complex phenomenon. This is especially true after the evaporation process starts. It is experimentally evident that liquid ejection occurs due to drag forces developed around the solid cavity and/or explosion resulting from nucleation of vapour bubbles in the liquid zone. Therefore, study into the ejection of liquid due to vapour bubble formation is necessary. Consequently, the present study examines the liquid ejection mechanism experimentally and possible saturated nucleate boiling is treated theoretically. In the experimental study, streak photography is introduced while a kinetic theory is adopted for the heat transfer model. This enables us to obtain the surface and internal temperature rise due to the laser heating pulse. It is found that the time measured for the liquid expulsion from the heated zone is identical with the time computed corresponding to possible saturated nucleate boiling.

http://iopscience.iop.org/article/10.1088/0022-3727/30/14/006/pdf

M. Sami

Papers

Co-firing of coal and biomass fuel blends

Plasma nitriding of Ti6Al4V alloy to improve some tribological properties

Laser-induced thermal stresses on steel surface

Liquid ejection and possible nucleate boiling mechanisms in relation to the laser drilling process

A comparative evaluation of gray and non-gray radiation modeling strategies in oxy-coal combustion simulations