Production of bio-syngas and biohydrogen via gasification

A. DUTTA, University of Guelph, Canada and

B. ACHARYA, Dalhousie University, Canada

Abstract: Gasification is becoming a most attractive conversion technology for energy production from fossil fuels, as well as an alternative source of biomass. This chapter gives an insight into gasification, beginning with a general introduction. It discusses different types of gasifier, as well as some of the innovative approaches. The last section of this chapter reviews design methods for different types of gasifier.

Key words: gasification, gasifier types, gasifier design methods, gasifier modeling.

16.1 Introduction

Gasification, once extensively used for transportation and lighting during the Second World War, lost its merits because cheap and easy fuels were commercialized for power production. At present oil reserves are diminishing and coal combustion is creating the problem of environmental contamination with greenhouse gases. Gasification technology is again getting new life. Its growth in the past has been slow but future predictions show a sharp rise. It has become more modern and sophisticated, such that technically it can easily compete with the existing power generation technologies. Rises in fossil fuel prices, their scarcity and penalties for environmental contamination could be other forces driving the economics of gasification and making the technology more attractive, technically, as well as economically.

Gasification is a thermo-chemical process that converts solid carbonaceous feed into a gaseous fuel product in the presence of steam and/or sub-stoichiometric oxygen. The result of gasification is the producer gas, containing carbon monoxide, hydrogen, methane, and some other inert gases. When it is mixed with air, the producer gas can be used in gasoline or diesel engines with little modification. The gaseous product is applied mainly as fuel gas for electricity generation and direct heating. It can also be used as a synthetic gas in the process industry to produce methanol or ammonia. The idea of gasification power generation fits well with the decentralized energy generation concept. A small-scale gasifier system (10-30 KW) would be appropriate for many applications in villages in developing countries.

Theoretically, almost all kinds of biomass can be gasified but, practically, various properties of the materials impose limitations on the quality of gases that can be

produced. Higher volatile matter results in higher tar content, an undesirable product of gasification. Similarly, large particle size, higher moisture content, and ash content pose a lot of technical challenges. The key to successful design of a gasifier is to understand the properties and thermal behavior of the fuel fed to the gasifier.