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Udomsirichakorn J.,Asian Institute of Technology | Basu P.,Dalhousie University | Abdul Salam P.,Asian Institute of Technology | Acharya B.,Greenfield Research Incorporated
Fuel Processing Technology | Year: 2014

Steam gasification of biomass undergoes the problem of undesirable CO 2 and tar formation. Calcium oxide (CaO), when added to the gasification, could play the dual role of tar reforming catalyst and CO 2 sorbent, and thereby produce more hydrogen. However, the deactivation of CaO after carbonation reaction is challenging for continuous hydrogen production and economical perspective. The concept of CaO-based chemical looping gasification (CaO-CLG) plays a key role in overcoming such a challenge. This work primarily aims at studying steam gasification of biomass with the presence of CaO in a uniquely designed chemical looping gasification (CLG) system for hydrogen production with in situ CO2 capture and tar reduction. The effect of solid circulation rates on gas and tar production is studied. A comparison of CaO-CLG, sand-based chemical looping gasification (Sand-CLG) and CaO-based bubbling fluidized bed gasification (CaO-BFBG) is presented mainly focusing on gas and tar production. The maximum H2 and minimum CO2 concentrations as well as maximum H2 yields of 78%, 4.98% and 451.11 ml (STP)/g of biomass, respectively, are obtained at the solid circulation rate of 1.04 kg/m2s. At the same point, the maximum total gas yield was 578.38 ml (STP)/g of biomass and the tar content of 2.48 g/Nm3 was the lowest. 30% higher concentration of H2 and triple yield of H2 were found in CaO-CLG compared to Sand-CLG. Compared to CaO-BFBG, CaO-CLG resulted in 15% higher concentration of H2 and almost double yield of H2. Moreover, the lowest tar content of 2.48 g/Nm3 was obtained for CaO-CLG while the tar content was 68.5 g/Nm3 for Sand-CLG and 26.71 g/Nm3 for CaO-BFBG. CO2 concentration obtained for CaO-CLG also significantly reduced by 13-17% as compared to both Sand-CLG and CaO-BFBG. © 2014 Elsevier B.V.


Udomsirichakorn J.,Asian Institute of Technology | Basu P.,Dalhousie University | Salam P.A.,Asian Institute of Technology | Acharya B.,Greenfield Research Incorporated
International Journal of Hydrogen Energy | Year: 2013

Previous studies showed that calcium oxide (CaO), when added to a biomass steam gasifier, could play the role of both CO2 sorbent and tar reforming catalyst, and thereby produce more hydrogen. However, most of these works focused on the former role with little attention to tar reforming aspect of CaO. Therefore, this work aims primarily at studying the tar reforming effect of in-bed CaO. To this end, an in-depth analysis of the effect of CaO on tar yield and composition is presented. The present work also studies the role of CaO as a CO2 sorbent to enhance hydrogen production from steam gasification of biomass in a bubbling fluidized bed. The influence of different operating parameters, temperature (T) and steam to biomass (S/B) ratio, as well as the effect of using in-bed CaO on gas and tar production is investigated. Results show that the maximum H2 and minimum CO2 concentration of 63.07% and 18.68%, respectively are obtained at T = 650 C and S/B = 3.41. The maximum H2 yield of 256.81 ml g-1-biomass was obtained at T = 700 C and S/B = 3.41, at which the minimum tar content of 6.45 g N m-3 was also received. Compared to a bed of sand alone, a 20% higher H2 concentration, an almost double H2 yield and a 67% reduction in tar content were obtained when a bed of CaO was used. Moreover, shifting the tar species from higher to fewer ring structures as a result of in-bed CaO can reduce tar dew point by 11 C and tar carcinogenic potential by almost 60%. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Basu P.,Dalhousie University | Acharya B.,Greenfield Research Incorporated | Cheng L.,Zhejiang University
CFB-11: Proceedings of the 11th International Conference on Fluidized Bed Technology | Year: 2014

Sustained supply of fuel from a single source and at a predicted price has been a major concern for the power generation. To address these issues, power industries are considering a fuel mix. This is motivating the power industries to move towards fluidized bed boilers. However, due to the nature of operation of fluidized bed boilers where solid particles are moving at higher velocity, the chances of occurrence of erosion becomes higher along with the corrosion problems seen in other type of boiler as well. This paper discusses about such erosion and corrosion issue in circulating fluidized bed boilers.


Arjunwadkar A.,Greenfield Research Incorporated | Basu P.,Greenfield Research Incorporated | Acharya B.,University of Prince Edward Island
Applied Thermal Engineering | Year: 2016

Circulating Fluidized Bed (CFB) technology has emerged as the most favoured steam generation technology in recent times. The use of CFB boilers is growing exponentially, due to its attractive features such as fuel flexibility, stable operation and low acid gas emissions, to name a few. The design of CFB boilers has developed over the years to meet the demanding availability expectations of the utilities. Proactive operation and maintenance (O&M) helps improve availability and reduce operating costs, which form a crucial component of the final steam cost of the boiler plant. This paper studies some important O&M issues of CFB boilers particularly looking into issues related to components specific to CFB boilers and the methods to avoid them. Operational difficulties like agglomeration, gas refluxing, back-sifting and performance related issues like emission control and bed temperature control are also examined. Refractory failure, which accounts for a considerable portion of the maintenance cost often forces shutdowns. This review is based on compilation of O&M issues of CFB boiler as found mainly in the open literature, but some unpublished information are also included. © 2016 Elsevier Ltd.


Basu P.,Dalhousie University | Dhungana A.,Greenfield Research Incorporated | Rao S.,Greenfield Research Incorporated | Acharya B.,Greenfield Research Incorporated
Journal of the Energy Institute | Year: 2013

Torrefaction, though defined as a low temperature (200-300°C) decomposition of biomass in an oxygen free atmosphere, it is hard to obtain such environment in a commercial unit unless one uses expensive means of nitrogen flushing or indirect heating. Oxygen leakage that adversely affects the product quality is unavoidable in commercial directly heated torrefier. Present work attempts to examine the optimum concentration of oxygen in the torrefier that can be tolerated without greatly compromising the product quality. In this work, torrefaction of relatively large pieces (25·4 and 19 mm diameter) of poplar wood was conducted at different oxygen concentration as well as in inert atmosphere while observing its effect on the temperature profile in the biomass interior, mass yield, energy yield and energy density. Results obtained are in agreement with those obtained in previous work on fine biomass particles that mass yield and energy yield decreases with oxygen presence in the torrefier. It, however, notes a slight increase in energy density. The work observes a sharp decline in mass yield beyond about 14% oxygen concentration suggesting that this may be the practical limit of oxygen in a torrefier. Finally this work notes that the presence of modest amount of oxygen could not only be tolerated but it may have some positive effect on the commercial design of a torrefier. © 2013 Energy Institute.


Basu P.,Dalhousie University | Sadhukhan A.K.,National Institute of Technology Durgapur | Gupta P.,National Institute of Technology Durgapur | Rao S.,Greenfield Research Incorporated | And 2 more authors.
Bioresource Technology | Year: 2014

A competitive kinetic scheme representing primary and secondary reactions is proposed for torrefaction of large wet wood particles. Drying and diffusive, convective and radiative mode of heat transfer is considered including particle shrinking during torrefaction. The model prediction compares well with the experimental results of both mass fraction residue and temperature profiles for biomass particles. The effect of temperature, residence time and particle size on torrefaction of cylindrical wood particles is investigated through model simulations. For large biomass particles heat transfer is identified as one of the controlling factor for torrefaction. The optimum torrefaction temperature, residence time and particle size are identified. The model may thus be integrated with CFD analysis to estimate the performance of an existing torrefier for a given feedstock. The performance analysis may also provide useful insight for design and development of an efficient torrefier. © 2014 Elsevier Ltd.


Basu P.,Dalhousie University | Rao S.,Greenfield Research Incorporated | Acharya B.,Greenfield Research Incorporated | Dhungana A.,Greenfield Research Incorporated
Canadian Journal of Chemical Engineering | Year: 2013

This work provides preliminary data on the effect of torrefaction on the apparent density of biomass. It also examines how the shape of wood is affected by torrefaction. Experiments conducted on cylinders of poplar wood showed that torrefaction reduced both density and volume of the wood, and the extent of reduction increased with increase in severity of torrefaction. The shape of the wood appears to have some effect on the extent of density change. The shrinkage in radial direction was 3-4%, while reduction in longitudinal direction was 6.5-8.8%. The mass yield decreased with torrefaction severity. © 2013 Canadian Society for Chemical Engineering.


Basu P.,Dalhousie University | Rao S.,Greenfield Research Incorporated | Dhungana A.,Greenfield Research Incorporated
Canadian Journal of Chemical Engineering | Year: 2013

Present work examines an important practical aspect of torrefaction that is, the effect of size and shape of biomass on torrefaction. Experiments were conducted on different sizes of Poplar and Oak wood in directly heated torrefaction reactors. Experiments were conducted with 13, 19 and 25mm diameter Poplar wood with lengths varying from 8 to 65mm long. Most of the experiments were conducted at 250°C for 60min in a directly heated convective reactor with limited few in a fluidised bed reactor. Results showed increase in mass and energy yield with increasing particle length but opposite with particle diameter. © 2012 Canadian Society for Chemical Engineering.


Dhungana A.,Dalhousie University | Dhungana A.,Greenfield Research Incorporated | Basu P.,Dalhousie University | Dutta A.,Dalhousie University | Dutta A.,University of Guelph
Journal of Energy Resources Technology, Transactions of the ASME | Year: 2012

Torrefied biomass is a green alternative to coal, and thus the interest in the torrefaction process is rising fast. Different manufacturers are offering different patented designs of torrefier with data on varying operating and process conditions each claiming their superiority over others. The choice of torrefaction technology has become exceptionally difficult because of a near absence of a comparative assessment of different types of reactors on a common base. This work attempts to fill this important knowledge gap in torrefaction technology by reviewing available types of reactors, and comparing their torrefaction performance common basis and examining the commercial implication of reactor choice. After reviewing available patent and technologies offered, torrefiers are classified broadly under two generic groups: indirectly heated and directly heated. Four generic types of reactors, convective heating, fluidized bed, rotating drum and microwave reactor were studied in this research. Convective and fluidized beds have direct heating, rotating reactors has indirect heating while microwave involves a volumetric heating (a subgroup of direct heating) mechanism. A standard sample of biomass (25 mm diameter 64 mm long poplar wood) was torrefied in each of these types of reactors under identical conditions. The mass yield, energy density and energy yield of the wood after torrefaction were measured and compared. Rotating drum achieved lowest mass yield but highest energy density. The difference between two direct heating, convective heating and fluidized beds was small. Microwave provided only localized torrefaction in this series of tests. Indirectly heated reactors might be suitable for a plant near the biomass source while directly heated plant would give better value at the user end. © 2012 American Society of Mechanical Engineers.


Dhungana A.,Dalhousie University | Dutta A.,University of Guelph | Basu P.,Greenfield Research Incorporated
Canadian Journal of Chemical Engineering | Year: 2012

Torrefaction of some non-lignocellulose waste biomass was attempted to examine if such materials could benefit from this process as conventional lignocellulose biomass does. Experiments were conducted on chicken litter, digested sludge, and undigested sludge from a municipality in Canada. Effects of two important torrefaction process parameters: temperature and residence time on the torrefaction yield were studied. For reference, torrefaction of three lignocellulose biomass (switch grass, coffee husk, and wood pellet) was also carried out in the same apparatus under identical conditions. A comparison of torrefaction yield and other properties of these biomass showed that in spite of the large difference in their constitution the torrefaction behaviour of non-lignocellulose and lignocellulose biomass were similar. The increase in energy density after torrefaction and the effect of temperature and residence time on torrefaction were also similar for these two types. The present research made an important addition to the existing database on torrefaction of biomass by adding missing information on torrefaction of sludge and poultry litter. Additionally, this work unearthed a potential option for production of composite pellets of waste (e.g., sludge) mixed with biomass (e.g., switch grass). © 2011 Canadian Society for Chemical Engineering.

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