Gasification lower heating value

The cost of transporting wood chips by truck and by pipeline as a water slurry was determined. In a practical application of field delivery by truck of biomass to a pipeline inlet, the pipeline will only be economical at large capacity (>0.5 million dry t/yr for a one-way pipeline, and >1.25 million dry t/yr for a two-way pipeline that returns the carrier fluid to the pipeline inlet), and at medium to long distances (>75 km [one-way] and >470 km [two-way] at a capacity of 2 million dry t/yr). Mixed hardwood and softwood chips in western Canada rise in moisture level from about 50% to 67% when transported in water the loss in lower heating value (LHV) would preclude the use of water slurry pipelines for direct combustion applications. The same chips, when transported in a heavy gas oil, take up as much as 50% oil by weight and result in a fuel that is >30% oil on mass basis and is about two-thirds oil on a thermal basis. Uptake of water by straw during slurry transport is so extreme that it has effectively no LHV. Pipeline-delivered biomass could be used in processes that do not produce contained water as a vapor, such as supercritical water gasification. 

Gasification determines to a large extent the cost of indirect liquefaction. Also, the thermal efficiency of gasification contributes largely to the overall thermal efficiency of the entire process. The thermal efficiency is defined as the lower heating value of the products divided by the lower heating value of the feed... 

Table 5.1 Selected properties and heating values of gases occurring in gasification systems [1] (HHV - higher heating value, LHV - lower heating value, M - molar mass, / (STP) - density at standard temperature and pressure, Vmoi-molar volume).

Figure 5.8 Sensitivity analysis of selected variables for single-stage entrained-flow slurry gasification (GE-RC) at 1450°C employing Pittsburgh No. 8 (Pitt 8) coal on (a) cold gas efficiency and (b) change in oxygen consumption (LHV-lower heating value).

Consequently the mass transfer rate during diffusion combustion of polymers is determined by the ratio of the heat of combustion to the effective enthalpy of polymer gasification. The lower the combustion heat and the higher the polymer gasification enthalpy or, in other words the more heat resistant the polymer, the lower is the B value. For polymer combustion in air the B value of e.g., PMMA varies between 1.3-1.4, that of polyethylene between 0.5-0.6, of phenolic resins between 0.14-0.4 74 75). An increase of the oxygen concentration in the oxidative medium and of the oxidant temperature causes a rise of the mass transfer number B. Lower B values have been observed in thermally stable polymers of the carbonizable types. 

Gasification of coal can produce synthesis gas (syngas) not only from coals having a wide range of heat values but also from low-value carbon feedstocks such as petroleum coke, high-sulfur fuel oil, municipal wastes, and biomass. This flexibility increases the economic value of these resources and lowers costs by providing industry with a broader range of feedstock options. 

In the case of fluidized-bed gasifiers, fluidization velocity plays an important role. The higher the fluidization velocity, the higher the temperature and the lower the produced gas heating value (increased amounts of O2 and N2 in the inlet gas for air gasification systems). 

When the air-to-steam ratio is increased, the gas volumetric yield also increases, as well as the gas heating value, but it reaches a peak. The effect is more notorious at lower ratios due to contribution to the gasification process of the steam released at the devolatilization stage even in the case, when steam is not added. 

The rate of thermal diffusion within the particles decreases with increased particle size, thus resulting in a lower heating rate. At constant tanperature, the gasification rate, the produced gas yield, and composition increase with a decrease in particle size. Maximum heating value is reported with smallest particle size. For the largest particle size, the heating value increases, reaches a maximum, and then decreases. Edrich et al. (1985) found the gasification rate to depend on particle size. 

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