Effective Usage of Energy in Tissue Drying Part 1: Air System, Heat Recovery and Cogeneration, 2006 Papermaker’s Conference
Increasing energy prices necessitate more careful use of energy in all applications and especially in the drying of tissue paper. Effective usage of energy is needed to minimize operating cost. Considerations of effective energy usage begin with machine design and must be borne in mind during daily operation of a tissue machine. Therefore the topic is split in two parts, the first part deals with design and layout considerations, air system, heat recovery and use of cogeneration exhaust. The second part deals with questions of practical operation in daily business.
Tissue drying uses steam for heating the Yankee, gas for heating impingement air in the hood, and electricity for fans in the hood circulation system. The main heat source on a high performance machine is gas, followed by steam, and with electricity in third place. Gas is not only the main energy source from the thermal point of view but also the main cost factor. It has become more and more important as the development of gas price in the US (fig. 1) during recent years shows. There has been a steady increase in price. The situation changed dramatically in 2005, when gas price doubled in only few months (fig. 2). In other countries the situation has been not as bad – the prices were at a higher level already – but they increased markedly all over the world. High gas usage and its high price focus special attention on possibilities of gas savings, although real energy cost differs from mill to mill due to special tariffs and situations.