Techno‐economic analysis of a production‐scale torrefaction system for cellulosic biomass upgrading

Abstract

Torrefaction of biomass early in the supply chain is one method of enhancing or preservin biomass quality during storage; reducing storage and transportation costs; attaining uniformity among different feedstock types; and meeting biorefi neries' quality and quantity demands for feedstock in a cost effective and sustainable manner.The main objectives of this study were to analyze the mass and energy balance, to assess the techno-economic feasibility of a production-scale torrefaction system, and to quantify the sensitivity of energy and cost results to changes in initial feedstock moisture content, torrefaction process temperature, plant operating window, and initial capital investment. The output from this analysis provides clear guidance on the opportunities and costs associated with production-scale torrefaction of biomass as a feedstock intermediate. Analysis of energy results indicated that the net external energy required for the torrefaction process increased and energy effi ciency of the torrefaction system decreased with increasing moisture contents. However, both of these energy metrics exhibited a decreasing trend with increasing process temperatures. In addition to the energy results, unit torrefaction process cost exhibited a decreasing trend with decreasing initial moisture contents of feedstock and decreasing torrefaction process temperatures. For the typical moisture content of 30% wb , process temperature of 240°C, plant operating window of 6 mo.yr −1 and initial capital investment of $7.5 million for the system with rated capacity of 25 Tton.hr -1 , unit torrefaction process cost was estimated to be 17.5 $-Tton −1 . Additional system improvements through capital cost reduction and wider operating windows can yield a torrefaction product cost of ~12 $-Tton -1 . Overview of the mass and energy balance modelA model was developed to simulate the mass and energy balance and the techno-economic aspects of a production-scale continuous-fl ow torrefaction system under diff erent initial conditions. Model input parameters included initial moisture content of biomass, torrefaction process temperature,

Some Chemical Compositional Changes in Miscanthus and White Oak Sawdust Samples during Torrefaction

“…In addition, it has been noted that torrefaction of biomass not only increases biomass energy properties, but produces some higher hydrocarbons as well, which can typically be used for producing chemicals or for improving overall energy efficiency [31]. Some recent experimental and techno-economical studies on torrefaction include: (a) the effects of particle size, different corn stover components, and gas residence times on the torrefaction of corn stover by Medic et al [32]; (b) the techno-economic analysis of a production-scale torrefaction system for cellulosic biomass upgrading by Shah et al [33]; (c) biomass upgrading by torrefaction for the production of biofuels by van der Stelt et al [34]; (d) the study of particle size effect on biomass torrefaction and densification by Peng et al [35]; (e) recent advances in biomass pretreatment, torrefaction fundamentals, and technology by Chew and Doshi [36]; and (f) studies by Tumuluru et al [37] on the response surface analysis of elemental composition and energy properties of corn stover during torrefaction. In general, response surface methodology (RSM) is the commonly used method to understand the effect of process variables on the product properties.…”

Biomass supply curves for western juniper in Central Oregon, USA, under alternative business models and policy assumptions

“…The scale of a torrefaction plant discussed for development in Prineville is planned to produce 36,290 tonnes year −1 (Simet, 2012). This pyrolysis technology bakes off volatiles that result in a weight reduction of the original inputs by approximately 20% when operating with optimal conditions, which would require approximately 45,360 ODT year −1 in raw juniper (Shah et al, 2011). When considering only this one source of juniper as the primary feedstock input, the stock would last for nearly 6.5 years.…”

“…When considering only this one source of juniper as the primary feedstock input, the stock would last for nearly 6.5 years. The estimated life of the torrefaction capital is 30 years (Shah et al, 2011). The rate at which juniper is removed from the landscape will be dependent on the price that is offered for delivered chips, higher prices will lead to faster depletion of juniper biomass on the landscape.…”

Integration of torrefaction in CHP plants – A case study

“…However, varying moisture content and feedstock compositions results in changes in the gas volume and composition, which results in variation of energy supply to the reactor. Consequently, the quality of the torrefied product could be risked [21]. The amounts of gas released which could be used for heating of the reactor varies and does not always equal the required heat.…”