Biomass heating

Modern biomass Heat and power generation, pyrolysis, gasification, digestion... 

Benestad C, Moeller M, Osvik A, et al. 1985. Air pollution from biomass heated boilers compared with that from waste incineration and oil combustion. Energy Biomass 1985 819-821. 

Small biomass particle sizes are needed to achieve high biomass heating rates, and particle sizes generally need to be less than 2 to 3 mm,... 

An important result of this study is the finding that the work and pressure of compression or extrusion can be reduced by a factor of about two by preheating the feedstock to 200-225 C before densification, This requires extra thermal energy for complete drying and to heat the biomass (heat capacity about 1.8 J/g-C) to the higher temperature however, these are offset by lower electrical power costs, lower equipment costs because of the lower pressure requirements, possibly reduced die wear due to improved lubricity of the biomass at increased temperatures, and increased fuel value due to complete water removal and prepyrolysis. These factors must be tested at the commercial scale before any conclusions can be drawn on the desirability of preheating feedstock. 

The equations in the proposed model have been solved using numerical method to calculate the changes of me, wood temperature, air humidity, and air temperature as a function of location along the bed thickness and drying time. Further improvement of the model has recently been conducted to take into account the biomass heat up in which period the vapor in the drying air may condense on the exposed surface of the biomass when the biomass tanperature is below the wet-bulb temperature. The hot air enters the biomass bed through the conveyor, therefore, the drying air conditions are used as the boundary conditions at the bed bottom surface. The initial conditions of the biomass include the initial me of the woody biomass (chips) and initial biomass temperature. 

Of special interest is the energetic analysis on the basis of photoconversion efficiency (PCE), what is the chemical energy formed as biomass (heat of combustion Hx) per hght energy absorbed in the reactor volume... 

Pyrolysis of biomass, as well as pyrolysis of Salix viminalis wood, yields volatile products besides the mentioned solid product—active carbon (Figure 5). Figure 5 doc-mnents that the proportions between basic products of biomass heat-treatment depend on process dynamics. High speed pyrolysis prefers the formation of non-condensable gases while slow carbonizations increase the share of soUd product (char or active carbon). 

Air-dried wood or other biomass heated in the absence of oxygen can be converted into oil, gas, and other valuable fuels. The biomass feedstock, before it is fed to the pyrolysis reactor, must be ground or shredded into smaller than 14-mesh size units. Flash pyrolysis takes place at 500°C and under high pressure (101 kPa). After processing the solid char is separated from the fluids produced in a cyclone separator. The char is then used as a heating source for the reactor. 

Domestic biomass heating can today be found in the increasing popularity of wood stoves. A wide variety of wood-burning appliances are used by households, particularly in rural areas of countries with traditional forest cultures such as Canada, Austria, Finland and Sweden. Since wood fuel was classified as a carbon-neutral fuel under the Kyoto Protocol, most countries that require winter space heating have begun to look again at wood. 

Biomass heating. If the biomass heating system is based upon a wood-burning stove, then the property must have a chimney or flue system or the facility to install a chimney. I see lots of stainless steel chimneys being installed to provide a flue for a wood burner. A wood burner is a desirable feature in many homes these days, even very modern homes. The stove provides a focal point... 

Biomass heating. A wood burner gives a very cosy focal point to a living space, especially on a cold winter s day. However, unlike gas and electricity heating you must be able to store the fuel on the premises. You must also have a chimney or fiue connecting the wood burner to the outside. Financial payback is not appiicabie here because fuel costs are about the same as coal, oil or gas and the installation of a 7 kW stove and chimney liner if necessary is less than 1,000. 

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