Lower heating value moisture content

Because mass flow bins have stable flow patterns that mimic the shape of the bin, permeabihty values can be used to calculate critical, steady-state discharge rates from mass flow hoppers. Permeabihty values can also be used to calculate the time required for fine powders to settle in bins and silos. In general, permeabihty is affected by particle size and shape, ie, permeabihty decreases as particle size decreases and the better the fit between individual particles, the lower the permeabihty moisture content, ie, as moisture content increases, many materials tend to agglomerate which increases permeabihty and temperature, ie, because the permeabihty factor, K, is inversely proportional to the viscosity of the air or gas in the void spaces, heating causes the gas to become more viscous, making the sohd less permeable. 

Fig. 3 The efficiency decreases, when the combustion air ratio or the moisture content of the fuel increases. However, if the outlet temperature of the combustion gases is below the dew point of the water vapour, the efficiency calculated according to LHV lower heating value) begins to increase, when the moisture content of the fuel increases. Temperature of combustion air is 0 C, RH 60%, excess air ratio 1.4 and composition of dry fuel is CH i owOo.m).

LHV = lower heating value of dried coal per unit moist coal M = moisture content (kg of O/kg of coal) m = mass flow rate... 

The second observation is explicitly made by the two authors in their paper. All correlations between chemical availability and lower heating value in terms of either atomic or mass ratios were based on values calculated for dry fuels with no moisture content. However, in applying those equations to fuels whose heating values do not appear on available tables, it is quite possible that the experimental determination of such value would be achieved by burning moist fuel in a calorimeter without first drying the substance. Care should then be exercised not to use the heating value of moist fuel in formulae derived for dry fuels. Nevertheless, the lower heating value of the dried fuel (LHV) can be established in terms of that of the wet fuel (LHV)W by means of the relation... 

Higher Heating Value (HHV)- The maximum heating value of a fuel sample, which includes the calorific value of the fuel (bone dry) and the latent heat of vaporization of the water in the fuel. (See moisture content and net (lower) heating value, below.)... 

Coals of the Western United States tend to have lower heating values, lower sulfur contents, and higher moisture contents relative to bituminous coals from the Eastern United States. The efficiency loss associated with high-moisture- and ash-content coals is more significant for slurry-feed gasifiers. Consequently, dry-feed gasifiers, such as the Shell gasifier, may be more appropriate for low-quality coals. 

Equation (3.4) shows the general recalculation of the LHV in MJ/kg from one moisture content to another here, conversion from air-dried basis to as-received basis. The moisture and ash content are denoted by W and A, respectively, both given in wt%. In Equations (3.5) and (3.6), the conversion from a moist basis, either as-received or air-dried, to a dry and water-and-ash-free basis is shown. For conversions from water-free to water-and-ash-free basis and vice versa, the factor from Table 3.3 can be used as moisture is not involved. All other combinations of basis conversions for lower heating value can be foimd by transposing Equations (3.4) to (3.6). 

The moisture content of freshly mined lignitic coals can be as high as 73%, but it is usually 30—65%. The more mature, consoHdated coals have lower moisture contents and thus a higher heating value. Figure 2 shows moisture and ash contents, as well as net heating values for lignitic coals from the world s principal deposits (19). 

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 temperature of the air in the dryer is usually the primary variable used to control the drying rate. If the air temperature is increased, the increased heat transfer to the product will result in increased evaporation. Lowering the air temperature will decrease the drying rate. If the product is coming out of the dryer too wet, increasing the air tanperature in the dryer will bring the discharge product moisture content back down to the proper value. 

---