Pilot scale steam-oxygen CFB gasification of commercial torrefied wood pellets. The effect of torrefaction on the gasification performance

Torrefaction is a promising biomass upgrading technology as it makes biomass more coal alike and offers benefits in logistics and handling operations. Gasification is an attractive thermochemical conversion technology due to its flexibility in the product gas end-uses. Therefore, it is valuable to investigate whether additional benefits are foreseen when torrefaction is coupled with gasification. Therefore, two commercial torrefied wood fuels and their parent materials are gasified at 800-850 degrees C under atmospheric steam-oxygen circulating fluidized bed gasification conditions and magnesite as bed material. The torrefied feedstocks consisted of wood residues torrefied by Topell at 250 degrees C (Topell black), and mixed wood and wood residues torrefied by Torrcoal at 300 degrees C (Torrcoal black). The gasification results show that torrefaction resulted in an increased gas quality, as it yielded higher H-2 and CO contents, a decrease of the CO2 content, increased gas yield and a significant decrease of the total tar content for both feedstocks. For the Torrcoal samples, torrefaction resulted in a decrease in the carbon conversion efficiency (CCE). In addition, the cold gas efficiency (CGE) remained approximately the same due to the increase in the H-2 and CO contents. The Topell samples showed an increase in the CCE and CGE upon torrefaction, but this could be attributed to a significant grinding in the screw feeder. It is generally concluded that both torrefied fuels may offer benefits as a feedstock for steam-oxygen blown circulating fluidized bed gasification, in particular in terms of gas quality and yield. (C) 2017 The Author(s). Published by Elsevier Ltd

The effect of torrefaction on the process performance of oxygen-steam blown CFB gasification of hardwood and softwood.

Torrefaction is a promising biomass upgrading method, offering advantages in logistics and handling. Gasification is an attractive thermochemical conversion technology due to its flexibility in the product gas end-use. The aim of this paper is to investigate the impact of torrefaction on the gasification performance of a softwood (spruce) and a hardwood (ash). Spruce and ash were torrefied at 260 and 280 °C, and at 250 and 265 °C, respectively, and pelletized. All feedstocks were gasified at 850 °C and atmospheric pressure under oxygen-steam circulating fluidized bed gasification conditions, with magnesite as bed material and with an equivalence ratio (ER) of 0.3 and a steam-to-biomass mass ratio (SBR) of 1.0. Only the torrefied feedstocks were gasified varying ER and SBR values. The results show that torrefaction affected the gasification performance of both feedstocks leading to decreasing the cold gas and carbon conversion efficiencies. For spruce, torrefaction did not affect the permanent gas composition but led to a decrease of the total tar content for both spruce 260 and spruce 280. For ash, torrefaction resulted in decreasing the CH4 volume fraction, and increasing the H2 volume fraction and the total tar content for both torrefaction temperatures. Varying the ER and SBR affected only the Class 3 tars of ash 250. Conclusively, torrefaction of spruce and ash did not offer substantial benefits on the gasification performance under the investigated conditions. It is suggested that research of torrefied wood gasification includes feedstock's chemical analysis and characterization of products obtained under fast devolatilization conditions

Moving torrefaction towards market introduction:Technical improvements and economic-environmental assessment along the overall torrefaction supply chain through the SECTOR project

AbstractThe large-scale implementation of bioenergy demands solid biofuels which can be transported, stored and used efficiently. Torrefaction as a form of pyrolysis converts biomass into biofuels with according improved properties such as energy density, grindability and hydrophobicity. Several initiatives advanced this development. The first pilot-scale and demonstration plants displayed the maturity and potential of the technology.The European research project SECTOR intended to shorten the time-to-market. Within the project 158 Mg of biomass were torrefied through different technologies (rotary drum, toroidal reactor, moving bed). Their production led to process optimization of combined torrefaction-densification steps for various feedstocks through analysing changes in structure and composition. The torrefied pellets and briquettes were subjected to logistic tests (handling and storage) as well as to tests in small- and large-scale end-uses. This led to further improvement of the torrefied product meeting logistics/end-use requirements, e.g. durability, grindability, hydrophobicity, biodegradation and energy density. Durability exceeds now 95%.With these test results also international standards of advanced solid biofuels were initiated (ISO standards) as a prerequisite for global trade of torrefied material. Accompanying economic and environmental assessment identified a broad range of scenarios in which torrefied biomass perform better in these areas than traditional solid biofuels (e.g. white pellets), depending e.g. on feedstock, plant size, transport distances, integration of torrefaction in existing industries and end use. The implementation of industrial plants is the next step for the technology development. Different end user markets within and outside Europe can open opportunities here

Influence of Torrefaction Pretreatment on Reactivity and Permanent Gas Formation during Devolatilization of Spruce

Torrefaction has shown potential for improving biomass properties and converting biomass to a more coal-like fuel. In this paper, both fast and slow devolatilization behaviors of untreated spruce and spruce torrefied at 290 °C and 20–30 min holding time have been studied by conducting experiments in a bench-scale heated foil reactor and a thermogravimetric analyzer, respectively. The former has been applied to estimate the permanent gas formation for biomass entering a fluidized bed reactor, and the latter has been used to determine the effect of torrefaction on (slow) devolatilization reaction kinetics. The reaction kinetics were derived using the Reaction Rate Constant Method and the Senum and Yang Temperature Integral Approximation. The gases produced during fast devolatilization, applying a constant heating rate and a final temperature in the range of 500–1000 °C, were analyzed by Fourier transform infrared spectroscopy, and tars were collected and quantified gravimetrically. Results show that the activation energy and pre-exponential factor increased for the global devolatilization reaction. The former increased by 25% due to torrefaction pretreatment. The yield of the produced permanent gases CO, CH₄, and CO₂ increased with increasing final devolatilization temperature. CO is the dominant gas at temperatures higher than 600 and 800 °C for untreated and torrefied spruce, respectively. At lower temperatures, CO₂ has the highest mass yield. CH₄ shows the lowest yield for each final temperature and fuel sample. The results reported in this paper provide basic information for thermochemical reactor design when using (torrefied) spruce as a feedstock. The findings confirm that torrefied spruce is more coal-like than the parent material with respect to activation energy, char production, respective evolution of CO and CO₂, and O/C and H/C atomic ratios