Biomass moisture content

Dryer cost data were obtained from manufocturers as a function of dryer volume, the latter being calculated by the model assuming the volumetric heat transfer coefficient to be a function of mean biomass moisture content. The form of the function was derived from manufacturers data. 

The study assumes that all cases have a drying stage. Therefore the cases with 50% biomass moisture content both to the dryer and to the gasifier (implying no requirement for a dryer) are omitted firom the analysis. 

Figure 7 shows CoE plotted against air oxygen concentration to the gasifier, for a system with an RFSG and a band conveyor dryer. The biomass feed rate is 1.5 dt/h, the pre-dryer biomass moisture content 75% and the biomass cost 630/dt. 

Similar results are seen at other feed rates, pre-dryer biomass moisture contents and biomass costs. If the RFSG has to operate with oxygen-enriched air however, its superiority in CoE is rapidly eroded. For an oxygen concentration of 0.28 the difference in CoE is negligible for an oxygen concentration above 0.28 the UGETC is usually superior. 

With one or two exceptions, an increase in biomass moisture content to the gasifier results in an increase in tfo. This is despite a fell in electrical output, which is outweighed by increased hot water production. The increase in hot water production conies fiom the product gas water heater, where a fall in gasifier cold gas efficiency gives rise to more sensible heat in the product gas. 

CoE however always rises with increasing biomass moisture content to the gasifier, as the net benefits of a smaller dryer and increased heat revmue are outweighed fay reduced electrical output (see Figure 7). 

Figure 12 shows the effect of biomass feed rate on CoE for sy ems with an unoiriched air RFSG and a UGETC. The systm has a rotary cascade dryar with integral burner, a biomass moisture content to and frcsn the dry of 7S% and 10%, and a biomass cost of 630/dt. 

The effect of the cost ofbioma at the plant gate on CoE is illustrated in Figure 13 for systems with an RFSG with unenriched air and a UGETC, In each case, the system has a band conveym- dryer and a biomass feed rate of 1,5 dt/h, with biomass moisture content to and fr n the dryer 75% and 10%. 

Taking a biomass moisture content to the dryer of 75% as typical, and the largest size of plant considered (2.0 dt/h), the maximum rfo obtained is 79.7%, for a system incMporating a UGETC and a rotary cascade dryer with integral burner, drying the... 

As biomass moisture content delivered to the dryer rises, rjo fells and CoE rises. As biomass moisture content delivered to the gasifier rises, tjo (generally) and CoE both rise. Moisture content delivered to the plant should be minimised, but provided a drying stage is required the drying carried out should be maximised at the expense of heat exported. 

There are many interacting parameters and possible feedstock—process—product combinations, but all are not feasible from a practical standpoint eg, the separation of small amounts of metals present in biomass and the direct combustion of high moisture content algae are technically possible, but energetically unfavorable. 

Eor certain types of study, e.g., soil dissipation, additional factors may need to be recorded, e.g., soil biomass, specific soil moisture content, soil conductivity, and pH. 

Demirbas, A., Effect of initial moisture content on the yields of oily products from pyrolysis of biomass. Journal of Analytical and Applied Pyrolysis 2004, 71(2), 803-815. 

Uncertainties with the availability and suitability of biomass resources for energy production are primarily due to their varying moisture content, and to a lesser degree to their chemical composition and heating value. As the moisture content of biomass increases, the efficiency of thermal conversion process decreases. At some point more energy may have to be expended to dry the biomass than it contains. Uncertainties can be reduced by conducting a detailed chemical and physical analysis of the biomass sources. 

Table 5.3 Mean biomass yield, moisture content and heating value of appropriated energy crop species in Germany according to Schmitz (2003), BMELV (2006), KTBL (2006), Friihwirth et al. (2006), Rosillo-Calle et al. (2007), BMELV (2007a) and own data...

Decreased soil phosphatase activity and total P in aboveground plant biomass Increased microbial P mineralization (approx. 0.8 mg P kg-1 day1) and immobilization (approx. 6 mg P kg-1 day1) with higher moisture content No effect on soil phosphatase activities, plant P concentrations, or N/P ratios No effect on colonization of roots with mycorrhizae... 

The direct combustion of wood and other plant matter has been a primary energy source in the past. Any type of biomass can be burned to produce heat or steam to turn a generator or perform mechanical work. Direct combustion is used in large power plants that produce up to 400 megawatts. Most direct combustion systems can use any type of biomass as long as the moisture content is less than 60%. Wood and wood residues are commonly used along with a number of other agricultural residues. 

Many available biomass feedstocks have a high moisture content, which lowers their heat value. Preprocessing can help, but adds to the cost. There are also some biomass conversion technologies that are only marginally beneficial and this keeps them from being cost-competitive. 

The biomass is fed overbed through multiple feed chutes using air jets to help distribute the fuel over the surface of the bed. Variable-speed screw conveyors are usually used to meter the fuel feed rate and control steam output. Feedstocks such as bark and waste wood are chipped to a top size of 25 mm (1 in) to ensure complete combustion. The bed usually consists of sand around 1 m (3 ft) deep. This serves to retain the fuel in the furnace, extending its in-furnace residence time and increasing combustion efficiency. It also provides a heat sink to help maintain bed temperature during periods of fluctuating fuel moisture content. 

The biomass characteristics already described, namely 50% moisture content and heterogeneity, introduce many materials handling problems. The importance of scale should also be noted—the largest biomass processing plants are pulp mills of around 2000 ton/day of product or about 6000 t/day of dry feed stock. In electrical energy terms, the average Canadian pulp mill of 1200 t/day would correspond to an electrical station of 150 MWq (70-85% utilisation) or the production of about 1100... 

Methane, hydrocarbons and carbon monoxide can be converted into hydrogen using SMR, partial oxidation and gas shift reactions respectively. Gasification is generally used for biomass with a moisture content less than 35%. 

Coal is a rich source of carbon and has been a valuable source of fuel for centuries. It is classified by both coal type and coal rank. Coal type is determined by the nature of the original biomass that led to the formation of the coal. Coal rank signifies the degree of maturation or chemical change in coal and usually determines coal quality. The calorific value, moisture content, elemental analysis, volatile matter, ash, and fixed carbon content are important qualities of coal. 

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