The calcium looping cycle for large-scale CO2 capture

Torrefaction is a mild pyrolysis, which has been explored for the pretreatment of biomass to increase the heating value and hydrophobicity. Due to its potential applications for making torrefied pellets, which can be used as a high quality feedstock in gasification for high quality syngas production and as a substitute for coal in thermal power plants and metallurgical processes, torrefaction and densification have attracted great interest in recent years from both academia and bioenergy industry. This paper provides a comprehensive review of research progresses in this area, drawing on major contributions from two major research groups of the authors on torrefaction and densification at Canada and Taiwan as well as literatures. It is revealed that torrefaction of various biomass species and their major components, lignin, cellulose and hemicelluloses have been extensively studied in thermogravimetric apparatus (TGA) under both inert (N 2 ) and oxidative (O 2 , H 2 O) environments to elucidate the weight loss as a function of temperature, particle size and time. It was found that the higher heating value and saturated water uptake of torrefied biomass were a strong function of weight loss, which represents the degree of torrefaction. When torrefied sawdust is compressed into torrefied pellets, more mechanical energy is consumed and higher die temperature is required to make torrefied pellets of similar density and hardness as regular pellets. Simple economics analyses based on laboratory scale experimental data showed that because of the potential savings from pellets transport, handling and storage logistics, the overall cost for torrefied pellets can be lower than regular pellets in European market for both European and Canadian pellets. The gasification could be improved in terms of both energy efficiency and syngas quality because of the removal of oxygenated volatile compounds from torrefied biomass.

A state-of-the-art review of biomass torrefaction, densification and applications

Calcium oxide can be an effective sorbent to separate CO2 at high temperatures. When coupled with a calcination step to produce pure CO2, the carbonation reaction is the basis for several high-temperature CO2 capture systems. The evolution with cycling of the capture capacity of CaO derived from natural limestones is experimentally investigated in this work. Long series of carbonation/calcination cycles (up to 500) varying different variables affecting sorbent capacity have been tested in a thermogravimetric apparatus. Calcination temperatures above T > 950 °C and very long calcination times accelerate the decay in sorption capacity, while other variables have a comparatively modest effect on the overall sorbent performance. A residual conversion of about 7−8% that remains constant after many hundreds of cycles and that seems insensitive to process conditions has been found. This residual conversion makes very attractive the carbonation/calcination cycle, by reducing (or even eliminating) sorbent purge ra...

CO2 Capture Capacity of CaO in Long Series of Carbonation/Calcination Cycles

Review—calcination and carbonation of limestone during thermal cycling for CO2 sequestration

Thermochemical conversion of microalgal biomass into biofuels: A review

Sulfation and reactivation characteristics of nine limestones

The particle size effect on torrefaction of pine particles and formation of torrefied pellets has been studied in a thermogravimetric analyzer (TGA) and a tubular fixed bed reactor. The fixed bed reactor was also used to produce torrefied samples for a single-die press unit for the densification test. Both the TGA and fixed bed reactor torrefaction test results showed that the torrefaction rate was affected by the particle size, especially at high temperatures. Although the temperature gradient inside particles smaller than 1 mm is very small during torrefaction, the internal diffusion of generated vapors inside particles imposes an impact on the global torrefaction reaction rate. The hard core or nonshrinkage particle model with a first order torrefaction reaction can predict the reaction data reasonably well, with the data-fitted effective vapor diffusivity coefficient. The densification tests showed that more energy was required to make pellets from larger torrefied particles, while the water uptake an...

A Study of Particle Size Effect on Biomass Torrefaction and Densification

Crystallization and fracture: formation of product layers in sulfation of calcined limestone

Steam treatment of four softwood species and bark to produce torrefied wood

This study systematically examined the current and future wood pellet market, estimated the cost of Canadian torrefied pellets, and compared the torrefied pellets with the conventional pellets on the basis of literature and industrial data. The results showed that the wood pellet industry has been gaining significant momentum due to the European bioenergy incentives and the rising oil and natural gas prices. With the new bioenergy incentives in USA, the future pellets market may shift to North America, and Canada can potentially become the largest pellet production centre, supported by the abundant wood residues and mountain pine beetle (MPB)-infested trees.

Jim Lim

Papers

Sulfation and reactivation characteristics of nine limestones

A Study of Particle Size Effect on Biomass Torrefaction and Densification

Crystallization and fracture: formation of product layers in sulfation of calcined limestone

Steam treatment of four softwood species and bark to produce torrefied wood

An Economical and Market Analysis of Canadian Wood Pellets