Demonstration of catalytic properties of char from thermo-catalytic reforming (TCR) of deinking sludge

The secondary fibre paper industry is a producer of two types of wastes deinking sludge and rejects produced as a result of paper/card and tissue manufacturing. This creates a significant disposal problem for the paper industry. A typical paper mill produces ~500,000 t of sludge (wet basis) and 50,000 t of rejects each year. With increasing gate fees and the introduction of the waste directive that prohibits organic wastes from sending to landfill, it is becoming increasingly costly and challenging for paper mills to dispose of these waste streams. The current paper mill waste disposal methods are cofiring with natural gas, landfilling and landspreading with minimal environmental advantages. These methods are costly and environmentally undesirable caused by using fossil natural gas. And land-spreading involves the application of pollutants contained in sludge to the soil. Existing technologies cannot convert organic feedstocks with low cellulose, high ash and variable moisture content and are not economical or efficient to implement, as they are energy intensive processes.
Fig.1. TCR reactor at UoB (2 kg/h).
Recently, Fraunhofer UMSICHT in collaboration with the University of Birmingham (UoB) proved the utilisation of organic residues for fuel applications using Thermo-Catalytic Reforming (TCR) [1, 2]. TCR is based on intermediate pyrolysis followed by higher temperature reforming stage. The reactor (Fig.1) consists of a feed hopper, a horizontal TCR reactor, a vertical TCR post-reformer, a condensing unit and a gas filtration system. TCR advances utilisation of wastes from paper mills with additional benefit in the production of bio-oil, syngas and char (with superior quality from the current standard).
Deinking sludge contains high ash content up to 75%, mostly Ca, Mg, Al, Si, Fe and P. A limited work has been done to date on utilisation of those wastes. Our early work [3, 4] presented that deinking char has catalytic properties similar to that of dolomite or limestone. Those catalytic properties affect the biomass thermal degradation and product distribution and influence the product quality during TCR of biomass.
Obtained results will present the catalytic characteristics of char from thermal treatment of deinking sludge. For the better understanding of ash catalytic activity, a comparative study was carried out between deinking sludge (high ash 68%) and wood (low ash 0.7%). TCR results will present the effect of high and low ash contents in biomass on the product yield and quality. Preconditioned deinking sludge was dried, shredded and pelletized. The presented TCR results (scale) were divided into three parts:
• TCR of wood pellets - a baseline,
• TCR of deinking sludge,
• TCR of wood pellets with deinking char addition.
Obtained analyses including mass and energy balance, characterization of feedstock, char, bio-oil and syngas will be discussed in the paper. Obtained results evaluate char production from deinking sludge and char catalytic properties. These variables will help understand the effect of feedstock composition on the catalytic properties of char.