| 摘要 |
The flow of air being removed from the dryer section, the flow of process air and the supply of heat to the process air are all controlled so that two of these parameters remain constant whilst the other is varied, in order to alter drying performance. A method for drying a web (1), preferably a paper web, comprises passing the web through a dryer section (20) containing several levels of blowboxes (12, 13), so that the web is supported by a cushion of hot process air on the top side of the lower blowboxes (12), in order to carry out contact-free drying. Steam generated by the water expelled from the web is mixed with and carried away by the process air, at least some of which is recirculated. The non-recirculated air is replaced with a corresponding amount of air having a low moisture content. The flow of non-recirculated air being removed, the flow of the process air and the supply of heat to the process air are all controlled during drying. Under a first condition when there is only a need for low performance drying, the flow of non-recirculated air being removed and the flow of process air are kept essentially constant, whilst the supply of heat to the process air is varied in order to alter drying performance. Under a second condition when there is only a need for medium to high performance drying, the flow of process air and the supply of heat to the process air are kept essentially constant, whilst the flow of non-recirculated air being removed is varied. Under a third condition when there is a need for high performance drying, the flow of non-recirculated air being removed and the supply of heat to the process air are kept essentially constant, whilst the flow of process air is varied. |
