(574e) Experimental Studies On Gasification of Pine Wood Shavings in a Downdraft Biomass Gasifier

Biomass is the oldest form of energy used by human beings, mainly in the form of wood. It is a renewable source of energy and has many advantages from an ecological point of view (Babu and Sheth, 2006). The direct combustion of biomass generates a concern among the environmentalists, as it is incomplete and inconsistent and may produce organic particulate matter, carbon monoxide and other organic gases. If high temperature combustion is used, oxides of nitrogen would also be produced. The biomass gasification has come to prominence as it offers higher efficiencies compared to combustion and pyrolysis. Gasification is a process of conversion of solid carbonaceous fuel into combustible gas by partial combustion (Sheth and Babu, 2009b). The resulting gas, known as producer gas, is a mixture of carbon monoxide, hydrogen, methane, carbon dioxide and nitrogen (Sheth and Babu, 2009a). The concentration of hydrogen in producer gas depends upon many factors such as moisture content of biomass, type and composition of biomass, operating conditions, configuration of the biomass gasifier etc. (Sheth and Babu, 2010).

Experimental studies on downdraft biomass gasifier have been carried out with different biomass materials such as wood, wood chips, hazelnut shell, agricultural wastes, saw dust, etc. Zainal et al. (2002) reported that bridging of biomass loaded in the gasifier is a common problem in the gasifier operation. It occurs mainly in the pyrolysis zone of the downdraft biomass gasifier. As soon as the biomass in combustion zone gets consumed, the biomass in the pyrolysis zone flows downwards due to its gravity. If the biomass doesn't flow downward easily, it leads to bridging. There are mainly two reasons for bridging: (1) the bulk density of the biomass is too low, and (2) the cone angle is less than angle of repose of the biomass. The second reason is generally addressed while designing the downdraft biomass gasifier. However, while using light weight biomass such as wood shavings, moist saw dust, rice husk etc. with down draft biomass gasifier, it leads to a practical operating problem of bridging.

In the present study, the experimental study on downdraft biomass gasifier with wood shavings of pine wood as a biomass is used. The wood shavings of the pine wood are collected from the carpentry section of the institute's workshop. During the initial experimental runs, the bridging is found to occur and gasifier was not operable in continuous mode for more than 10 minutes. It is due to the low bulk density of the wood shavings of the pine wood. To overcome the bridging, the design of the biomass gasifier is modified by incorporating the shaking mechanism. The ?L' shape steel rod is placed in the gasifier, the one end of which is extended along the axis of the gasifier up to the oxidation zone. Some small rods (in the radial directions up to the wall of the gasifier) are welded on its axial part of ?L' shaped rod at different heights. The other part of the rod is positioned to protrude through the side wall to the outside of the gasifier. Mechanical fitting is carried out to ensure the negligible leakage and free movement while facilitating the shaking of the biomass of pyrolysis zone from outside the gasifier. During the experimental runs, this mechanism is used once in every five minutes to break the bridging of biomass in the pyrolysis zone.

With this modified design of the biomass gasifier, the experiments are carried out with pine wood shavings as biomass, covering a wide range of operating conditions. The effects of air flow rate and moisture content on biomass consumption rate and the quality of the producer gas generated are studied. The performance of the biomass gasifier system is evaluated in terms of equivalence ratio, producer gas composition, calorific value of the producer gas, gas production rate, zone temperatures and cold gas efficiency. Material balance is carried out to examine the reliability of the results generated.

References:

Babu, B.V., Sheth, P.N., 2006. Modeling and simulation of reduction zone of downdraft biomass gasifier: effect of char reactivity factor. Energy Conversion and Management 47, 2602?2611.

Sheth, P.N., Babu, B.V., 2009a. Differential evolution approach for obtaining kinetic parameters in non isothermal pyrolysis of biomass. Materials and Manufacturing Processes 24, 47?52.

Sheth P.N., Babu, B.V., 2009b. Experimental studies on producer gas generation from wood waste in a downdraft biomass gasifier. Bioresource Technology, 100, 3127-33.

Sheth P.N., Babu, B.V., 2010. Production of hydrogen energy through biomass (waste wood) gasification. International Journal of Hydrogen Energy, Article in Press. doi:10.1016/j.ijhydene.2010.03.009

Zainal, Z.A., Ali, R., Quadir, G., Seetharamu, K.N., 2002. Experimental investigations of a downdraft biomass gasifier. Biomass and Bioenergy 23, 283?289.