Combustion of biomass

Most electricity from biofuels is generated by direct combustion. Wood fuels are burned in stoker boilers, and mill waste lignin is combusted in special burners. Plants are generally small, being less than 50 MW in capacity. There is considerable interest in combustion of biomass in a process called cofiring, when biomass is added to traditional fuels for electricity production. Cofiring is usually done by adding biomass to coal, but biomass also can be cofired with... 

The primary solid byproduct of combustion processes is bottom ash, which primarily consists of mineral matter and minor amounts of unreacted carbon. Because the leaching property of the ash, the bottom ash from combustion of most material is considered hazardous. An exception is the bottom ash from combustion of biomass. 

The majority of these operations use boiler technology, which involves the direct combustion of biomass materials... 

In this evaluation only C02 from the combustion of fossil fuels is considered. The combustion of biomass is assumed to be C02 neutral because the amount of C02... 

In the case of biomass-derived fuels, the C02 emitted by carbon-containing fuels is absorbed from the atmosphere during the growth of the plants. As a result, the combustion of biomass-derived fuels is assumed to be C02 neutral at a global scale. 

Currently, the ID model describes the essential features of the propagation of a combustion front in the reverse combustion mode. With an adapted version of the model, the combustion of biomass could be modeled accurately. To obtain... 

High-temperature processes, based on pyrolysis, gasification or combustion of biomass are the preferred conversion routes for non-food competing biomass conversion processes to secondary energy. 

This appendix presents a review of experimental work in the field of packed-bed combustion of biomass. It deals with the measurement methods used to analyse the thermochemical conversion of the biomass. This implies that thermochemical conversion studies of coal is outside the scope of this literature study. Wood stove research is not considered in this review either. Of special interest in this survey is the choice of sought physical quantities (target quantities) and measurands of interest in each study and how they are modelled and verified, and if uncertainty analysis is carried out. 

Below, the experimental work in the field of packed-bed combustion of biomass is presented in chronological order. The authors original terminology is used as much as possible. Each work is reviewed with respect to objective, apparatus, fuel, measurement methods, theory, procedure, and results and conclusions. 

Saastamoinen J.J., Huttunen M., and Kjaldman L., Modelling of Pyrolysis and Combustion of Biomass Particles , the fourth European Computational Fluid Dynamics Conference, 7-11 Sept, Athens, Greece, (1998)... 

Gronli M.G., Experimental and Modelling Work on the Pyrolysis and Combustion of Biomass - A review of the Literature , in Project Reports lEA Bioenergy Agreement, Task X, Biomass utilisation, 1992-1994, prepared by Sonju O.K, Hustad J.H and Gronli M.G., Trondheim (Norway), March, (1995). 

Yokelson, R. J., R. Susott, D. E. Ward, J. Reardon, and D. W. T. Griffith, Emissions from Smoldering Combustion of Biomass Measured by Open-Path Fourier Transform Infrared Spectroscopy, . /. Geophys. Res., 102, 18865-18877 (1997). 

It is estimated that in the year 2020, about 200,000,000 MW hours of electricity will be produced from the combustion of biomass. How much power is this in units of MW Hint there are 8760 hours in a year.)... 

An alternative to the above described approaches is the radiocarbon method that allows a distinction of contemporary carbon (from biogenic emissions and combustion of biomass) and carbon from combustion of fossil fuels in particulate carbonaceous matter [15, 41,42]. In contrast to fossil fuels where the 14C isotope is completely depleted, CM emitted from WB shows a contemporary radiocarbon level. Radiocarbon measurements are often combined with measurements of complementary source specific tracers (macro-tracer) for additional information of source impacts [14, 43, 44]. 

The combustion of biomass, which invariably contains carbon and chloride, produces CHCI3, although the amount is much less than that recorded for CH3C1 and CH2C12 (283, 286) and is a minor emission source of CHC13 (<1%) (303-305) (Table 3.3). The high temperature (700°C) reaction of methane, HC1, and oxygen furnishes trichloromethane (232). 

It is natural to wonder why the combustion of biomass is an example of sustainable technology, as combustion releases COz in the atmosphere and therefore does not seem to close the material cycles. While the combustion does release COz into the atmosphere, the growth of biomass consume C02 (see Figure 16.2). Therefore, the final result is that there is no net release or consumption of COz if the biomass is replenished. For example, consider that a certain unit of active biomass absorbs one unit of C02 per unit time while growing. If one unit of this biomass is combusted, thus releasing one unit of C02, the result is that there is no net increase or decrease in COz emission. 

Fluidized-bed systems combust the fuel that has been fluidized by high-velocity air. In general, fluidized-bed systems are flexible in terms of fuel requirements. As a result, they are quite suitable for the simultaneous combustion of biomass and other fuels. 

Absorption of water has serious implications for any process such as direct combustion that converts absorbed liquid water in the fuel into emitted water vapor in the flue gas, in that it reduces the lower heating value (LHV) of the biomass and requires more biomass per unit of heat released by combustion, an effect also noted by Yoshida et al. (10). Figure 5 shows the loss in LHV and the corresponding increase in biomass that must be delivered to a direct combustion-based biomass operation at 67% moisture level. Werther et al. (11) note some other problems with increasing moisture in the direct combustion of biomass reduced combustion temperature, delayed release of volatiles, poor ignition, and higher volumes of flue gas. These secondary impacts on efficiency and operability of a direct combustion unit are not considered in Fig. 5. 

DC Direct Combustion of Biomass Gasif Gasification for power feneration... 

DC Dirccl Combustion of Biomass Gas if GasiticjMion for power generation s-fluesM... 

Shihadeh, A. and Hochgreb, S., Diesel engine combustion of biomass pyrolysis oils. Energy Fuels 2000, 14 (2), 260-274. 

Nussbaumer, T., Combustion and co-combustion of biomass Fundamentals, technologies, and primary measures for emission reduction. Energy Fuels 2003, 17 (6), 1510-1521. 

Losses from the system due to combustion of biomass can be quite high for carbon, nitrogen, and sulfur, and less for major nutrients like phosphorus, potassium, and calcium (Ewel et al. 1981, Frost and Robertson 1985, Kauffman et al. 1995, Sanchez 1976, Wright and Bailey 1982). However, immediate improvement in the soil chemical characteristics - higher pH, reduced aluminum toxicity, and higher nutrient content— is usually observed after forest cutting and burning in the Amazon basin (Buschbacher 1984, Dantas 1989, Dantas and Matos 1980, Diez et al. 1991, Falesi 1976, Seubert et al. 1977, Smyth and Bastos 1984). 

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