Environmental, Energy and Economic Aspects and Sustainability in Thermal Processing of Wastes from Pulp Production

conference paper

English

Pulp and paper plants produce large amount of sludge. Environmental problems connected with this waste were not solved satisfactorily in the past. Landfilling is not a suitable way from the environmental point of view. A thermal treatment process proved itself to be the most appropriate solution. Let us show a concrete way how to solve the above-described problems with emphasis on sustainability aspects. A thermal treatment unit with a capacity more than 100 tons of wet sludge per day had been built in one large pulp and paper plant some years ago. This pulp and paper plant is located in mining area. When built, this unit was quite modern. However, because of more and more sweeping environmental laws affecting the process industry, the unit needed a complete retrofit. The retrofit has been realized in three stages. A brief description of the unit for the thermal treatment of sludge is as follows (see also [1]): The waste sludge (after a transport from a sludge storage system) is burnt in a multiple hearth incinerator with a fluidized-bed combustion chamber. Then the flue gas enters a secondary combustion chamber (afterburner chamber). During the first stage of retrofit only a part of heat from flue gas was utilized for heat recovery (pre-heating air for combustion and fluidization) and a contact cooler was involved into the unit. The second stage of retrofit can be characterized as a waste-to-energy one. The contact cooler was replaced by a system for preheating water for steam generation. Off-gas cleaning system consists of a filter for particulates removal and a three stages scrubber system. (Several alternatives of retrofit were considered and simulated and the most promising one was selected.) The third stage of retrofit consist in substituting the currently used fuel by mining gas containing approximately 50 to 60% of CH4. Utilizing this waste gas represents an important contribution from both environmental and economic points of view. Last but not least removing the gas from mines decreases risk of creating an explosive mixture with air and thus it is also important from safely reasons. The unit for thermal treatment of sludge after retrofit can be considered as one of the most up-to-date incinerators with waste-to-energy system at present. Landfilling of sludge costs approximately US$0.5 mil. per annum (and in case of high ambient temperatures when biological processes in sludge are more intensive even US$1.4 mil.). If we have not considered the waste-to-energy system, incineration would be more expensive than landfilling. However, after installing heat recovery and steam generation systems US$0.16 mil. can be saved per annum. Using mining gas as a primary as well as stabilizing fuel represents another savings. Moreover, fuel gas emissions from the local power and heating plant are reduced due to the above-described complex approach.

pulp production, fluidization, sludge incinerator

ORAL, J.; ŠIKULA, J.; PUCHÝŘ, R.; HAJNÝ, Z.; TRUNDA, P.; STEHLÍK, P.; BÉBAR, L.

1. 1. 2002

Dubrovnik, Croatia

953-6759-16-0

Dubrovnik Conference on Sustainable Development of Energy, Water and Environment Systems

61

61

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