The pulp and paper industry uses pulping chemicals for the treatment of bagasse, straw and wood chips. Spent liquor or effluent liquor, with high carbon content is produced and sent to chemical recovery to recover pulping chemicals. In addition, energy from the spent liquor is recovered and utilised to generate steam for electricity supply, thereby reducing fossil fuel power consumption. Spent liquor is destroyed using conventional incineration technology, in a recovery furnace or recovery boiler, which is the heart of chemical recovery. These units have over the past few decades been prone to numerous problems and are a major concern to the pulp and paper industry. They pose a threat to the environment, are expensive to maintain and constitute a safety hazard. Thus the pulp and paper industry is now looking at a replacement technology; an alternative that will effectively regenerate pulping chemicals and recover energy for generating electricity, ultimately to make the plant energy self-sufficient. Gasification technology may be the chosen technology but is yet to be applied to the pulp and paper sector. However, this technology is not new. It has been integrated and used successfully in the petroleum industry for decades, with applications in coal mining and the mineral industry. The overall objective of tills study is to develop a better understanding of gasification using a pilot-scale fluidised bed reactor which was designed and developed at the University of Natal. The reactor, "the Gasifier", is operated at temperatures below the smelt limits of inorganic salts (<750°C) in the spent liquor. In this investigation, spent liquor is injected
directly into an inert bed of alwninium oxide grit, which is fluidised by superheated steam.
The atomized liquor immediately dries when it contacts the grit in the bed, pyrolyses and the
organic carbon is gasified by steam. Pyrolysis and steam gasification reactions are
endothennic and require heat. Oxidised sulphur species are partially reduced by reaction
with gasifier products, which principally consist of carbon monoxide, carbon dioxide and
hydrogen. The reduced sulphur is said to be unstable in the gasifier environment, and reacts
with steam and carbon dioxide to form solid sodium carbonate and gaseous hydrogen sulphide. (Rockvam, 2001). The focus of this study will be to determine the Gasifier's ability to gasify spent liquor, from soda and sulphite pulping of bagasse, at different operating conditions. In addition, the fate of process and non-process elements will be investigated. The product gas generated in the gasification of spent soda and sulphite liquors consisted of
hydrogen, carbon dioxide, carbon monoxide and methane. In the gasification of spent sulphjte liquor, hydrogen sulphide was also produced. The water-gas shift reaction, which
was the main reaction, was found to be temperature dependent. In adilition, organic carbon
conversion increased with temperature. Furthermore, most of the sulphur in the bed
predominated in the form of hydrogen sulphide with very little sulphur in the form of sulphate. This indicated that gasification would reduce sulphate levels, which are responsible
for dead load in a chemical recovery cycle. Finally, an important result was that the aluminium oxide grit was successfully coated. It was previously speculated that this would not be possible. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2004.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/4186 |
| Date | January 2004 |
| Creators | Sewnath, Pravesh. |
| Contributors | Arnold, Dave R. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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