Coal Bed Pressure Drop

If a one-dimensional flow through a packed bed of granular material is assumed (e.g., in moving-bed gasifiers), the pressure drop over a certain bed height Hbed complies to Equation (3.77). It uses the representative diameter based on equivalent specific surface ds, the density of the gas p, the superficial velocity in the bed u, and the dimensionless bed void fraction e for pressure drop calculation (see also Section 3.12.3.2). 

The dimensionless drag function is composed of a viscous (laminar) and inertial (turbulent) term and can be specified according to bed material properties. The Ergun correlation [127] found wide application for coal bed characterization, which is 

The Reynolds number Rchyd must be adapted to the flow conditions in the bed and is calculated by 

Equation (3.77) is known to systematically underestimate the pressure drop of industrial moving-bed gasifiers. Several studies traced the Sauter diameter to be the main source of the errors, which seems not representative in the case of very broad particles size distributions [114,128-130]. However, it remains a proven measure to evaluate and study the complex phenomena in a moving bed in a simple way. 

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