Torrefaction of Pulp Industry Sludge to Enhance Its Fuel Characteristics

Abstract

Recently, under COP26, several countries agreed to phase-out coal from their energy systems. The torrefaction industry can take advantage of this, as the fuel characteristics of torrefied biomasses are comparable to those of coal. However, in terms of economic feasibility, torrefied biomass pellets are not yet competitive with coal without subsidies because of the high price of woody biomass. Thus, there is a need to produce torrefied pellets from low-cost feedstock; pulp industry sludge is one such feedstock. In this context, this study was focused on the torrefaction of pulp industry sludge. Torrefaction experiments were carried out using a continuous reactor, at temperatures of 250, 275, and 300 °C. The heating value of the sludge increased from 19 to 22 MJ/kg after torrefaction at 300 °C. The fixed carbon content increased from 16 wt.% for dried pulp sludge to 30 wt.% for torrefied pulp sludge. The fuel ratio was in the range of 0.27 to 0.61. The ash content of the pulp sludge was comparable to that of agricultural waste, i.e., around 12 wt.% (dry basis). The cellulose content in the sludge was reduced from 35 to 12 wt.% at 300 °C. Ash related issues such as slagging, fouling, and bed agglomeration tendency of the sludge were moderate. This study shows that torrefaction treatment can improve the fuel properties of pulp industry sludge to a level comparable to that of low-rank coal.

The Evaluation of Torrefaction Efficiency for Lignocellulosic Materials Combined with Mixed Solid Wastes

“…Biomass is considered a carbon neutral source that is almost always available; in addition, it is available in large quantities [10]. It is believed that biomass energy has the potential for energy or power generation [11], despite the fact that its direct application is not always feasible due to several discovered issues [12]. Raw biomass is characterized by a high moisture content, high hygroscopy, low bulk density, low energy density, high ash content, low carbon content, and poor grindability [13].…”

Integrating torrefaction of pulp industry sludge with anaerobic digestion to produce bioenergy and biochemicals: Techno-economic and environmental feasibility analysis

“…The mass and energy flows were calculated for a plant capacity of 60,000 tons of wet sludge per year. The experimental results from our previous studies on pulp sludge torrefaction [12] and anaerobic digestion of pulp sludge derived condensate [10] was used as a base to simulate the product flow at each stage of the process for the selected capacity of the plant. The moisture content of the wood chips was selected as 40%.…”

“…It was assumed that both pulp sludge and wood chips are thermally dried at 110 • C to a moisture level of 10% in the dried product. For energy balance, it was assumed that both dried sludge and the water vapor leaves the dryer at 110 • C. The methodology presented in [12] was followed to calculate the drying energy requirement.…”

The Thermochemical Conversion of Municipal Solid Waste by Torrefaction Process

“…As noted in the work of Doddapaneni et al [37] mass and energy yields are two most important parameters for evaluating the performance of the torrefaction process. In this work, mass (MY) and energy yields (EY) of the selected MSW samples were calculated using the following Equations ( 2) and (3).…”