Co-operation of the MIND-method and the Pinch Technology : Energy Efficient Pre-evaporation of Bleach Plant Filtrate Using Waste Heat

• In order to decrease the environmental impacts caused by the pulp- and paper industry it is nowadays more or less common to perform a closure of the mill. The closure of the bleach plant will result in a minimal intake of fresh water and thereby the effluent will be contaminated to a greater extent. The bleach plant filtrate can be mixed with the black liquor and combusted in the soda recovery boilers. The necessity of pre-evaporating the bleach plant filtrate will thereby arise. In this study some alternatives have been investigated how to process integrate a pre-evaporation plant. Three alternatives have been investigated where the pre-evaporation can be fulfilled by using live steam only or live steam combined with waste heat. It can also be achieved by using a mechanical vapour recompression unit, which uses low temperature waste heat to accomplish the pre-evaporation. Due to the complexity of the mill two different methods have been used to evaluate the alternatives for pre-evaporation. The pinch-method is used on a lower aggregation level where the different components for pre-evaporation is considered, while the MIND-method is used on the higher aggregation level to take into account the whole mill. Two different scenarios have been studied, one with the existing electricity prices and one with an increase of the electricity prices with 50%. In both scenarios it is shown preferable to use the live steam/waste heat alternative compared to the ”worst case”, using mere live steam. The investment costs for the live steam/waste heat case will imply that the payback period will be approximately 3.5 years. The mechanical vapour recompression alternative is shown profitable with the existing electricity prices, compared to the live steam case. But due to the high investment costs it gives an unacceptable payback period. When the electricity price is increased by 50% it shows not profitable. In case of an increase of the fuel prices the mechanical vapour recompression alternative will be more profitable due to the usage of less fuel compared to the other cases.

Nyckelord

MIND

Pinch

Industrial energy systems

cooperation

pulp and paper

Energiförsörjning

Cellulosaindustri och pappersmasseindustri

TECHNOLOGY

TEKNIKVETENSKAP

Publikations- och innehållstyp

vet (ämneskategori)

bok (ämneskategori)