The drying of abattoir paunch for waste-to-energy conversion

The drying of abattoir paunch for waste-to-energy conversion

Abattoir paunch waste has the potential to become a site-specific, viable, waste-to-energy stream for adoption within the red meat processing industry. While the literature suggests numerous end uses for dried paunch, the high initial moisture content makes undried paunch a waste product of little to no value to the industry. Thus, this thesis aims to determine some of the specific properties of paunch to determine its inherent drying behaviour. If the initial moisture content of paunch can be reduced in a cost effective manner it can become a useful biomass for industrial uses such as co-combustion, pyrolysis, or gasification. Thus, the aim of the thesis is to characterise paunch waste and develop predictive equations to enable assessment of its re-use as a biomass. To achieve the aim this thesis determined drying rates, energy content, equilibrium moisture content, bulk density, and the latent heat of vaporisation of paunch to allow predictive equations to be developed to inform the future design and modelling of a paunch drying method.

To enable characterisation of paunch a new thin layer dryer was developed using an environment chamber with purpose built load cells used to record weight changes over time. The results obtained in this study showed that the thin layer drying constant, k, varied from 0.0002 to 0.0029 min-n with an average n value of 1.42 ± 0.081 for 35 to 55 °C operating air at 40, 50, 60, and 80% relative humidity. The equilibrium moisture content varied from 7.14 to 13.44% moisture content and constants for the Chung-Pfost equation were determined. Calorific values varied from 17 to 20 MJ/kg for grass and grain type paunches respectively. Based on newly derived equations the bulk density for untapped paunch ranged from 106 kg/m3 (dry) to 504 kg/m3 (100%) and for tapped 152 kg/m3(dry) to 862 kg/m3(100%). The energy density values for paunch varied from 4 865 to 2 110 MJ/m3. The latent heat of vaporisation for paunch varied from 3 741 to 2 519 kJ/kg for 6 to 15% moisture content. A solution to the Hukill deep-bed drying equation was found with new coefficients specific to paunch determined for the dimensionless time unit.

The paunch drying characteristics in this study are expected to benefit Australian and international red meat processing plants by allowing a fundamental understanding of paunch behaviour. This understanding will inform the design of paunch dryers and the selection of appropriate end uses based on the intrinsic properties of paunch such as the energy content and energy density.