Heliyon (Jul 2020)
A feasibility assessment of the production of char using the slow pyrolysis process
Abstract
There is a growing need for the production and use of sustainable biofuels worldwide. One noteworthy approach is the production of biofuels via the thermochemical conversion of lignocellulose biomass. This work studied the production of char via the slow pyrolysis of corn-stover as a suitable supplement or replacement of coal in industrial processes. The char quality was assessed according to the ASTM D388 (American Standard Testing Method), which ranks coals according to their higher heating value (HHV), volatile matter and fixed carbon. Furthermore, an evaluation of the techno-economic feasibility of an industrial scale 30 t/day slow pyrolysis plant was conducted. The techno-economic study was conducted at a char baseline price of $100/ton. A two-level three-factor central composite design (CCD), with response surface methodology (RSM) was used to study the slow-pyrolysis process conditions. Optimisation experiments were conducted at bench-scale gram-level to study the influences of the process condition of char higher heating value (HHV) and yield. Furthermore, this study assessed the techno-economic feasibility of a 30t/day processing plant. The results showed process temperature had the most significant influence on char HHV and yield. Optimal conditions for char production were at a reactor temperature of 453 °C, and 5 °C/min and 29 min for heating rate and holding time respectively. Under these conditions char with HHV of 26.25 ± 1.5 MJ/kg and yield of 34.5% were produced. These chars are comparable to sub-bituminous A coals. A high energy efficiency of ~82% was also associated with the process. The economic feasibility of the plant is highly sensitive to the cost of CS feedstock. The process had a net present value (NPV) of -$1.17 million at the $20/ton CS baseline assumption. A cost sensitivity analysis showed that when the cost of CS was lowered to $3/ton, the NPV was zero. Uncertainties in the price estimation of the volatile by-products remained a concern.
