(192e) Analysis of Heat Transfer Fouling Characteristics During Evaporation of Lignocellulosic Biomass Process Streams

Lignocellulosic feedstocks such as pine wood waste are becoming viable biomass sources for liquid fuel production.  Within the ethanol production process, concentrating the sugar-rich hydrolysate stream by evaporation prior to fermentation can enhance the fermentation productivity and reduce downstream distillation costs. Similarly, evaporation can be used to concentrate the lignocellulosic thin stillage during solids recovery/water treatment.  However, fouling of the evaporator surface by soluble and suspended solids within the process steams can become problematic.  This can reduce the heat transfer rate and ultimately increase energy consumption of the process. In this study we analyzed fouling characteristics of pine wood hydrolysate and thin stillage using an annular fouling probe containing a heated surface to mimic a continuous evaporator operation. The heated region of the probe caused solids in the hydrolysate to adhere to the surface, thus fouling the probe over time. 3.5 L batches of process liquor were circulated through the annulus of the fouling probe while temperatures and power supplied to the probe were measured over time and used to calculate fouling resistance, rate of fouling and induction period. Hydrolysate samples were collected at regular intervals to monitor the sugar and inhibitory compound concentrations. Liquor pH, Reynolds number (laminar region 440 and 880 Re) and feed composition were analyzed for their effects on fouling rate, induction period and fouling deposit ash concentration. Two analytical methods: Inductively Coupled Plasma (ICP) and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) were used to evaluate and compare the mineral composition analysis of fouled material, while ash was determined by the dry ash method. Due to an elevated concentration of inhibitory compounds in solution following evaporation, an adsorption/polyelectrolyte removal operation was performed prior to fermentation analysis.  Optimizing operating conditions and evaporator materials of construction will lead to enhanced biorefinery process efficiencies.