Drying, whether it be of loose fibre, yarn or fabric, is one of the most energy-intensive operations in the dyeing and finishing area.
Moisture is generally accepted as one of the most important factors affecting the processing of fibres, yarns and fabrics. This rings true for both natural and man-made fibres, albeit it is often more significant for natural fibres, as they tend to be more hygroscopic.
The purpose of the drying operation is to drive off the moisture within the fibre, so that when the product (whether it be loose fibre, yarn or fabric) exits the dryer it is at the desired moisture content (or regain).
Each process has different requirements for the moisture content as the product exits the dryer. In some processes the moisture content has no bearing at all, for example heat setting of fabrics. In this process the object is to drive off most of the moisture early in the drying process and then have the material maintain a certain surface temperature for a certain period of time to ensure adequate “setting” of the material.
In other processes, the moisture content of the product as it exits the dryer is critical. To avoid the problems that can be caused by moisture-content variations, most processors tend to over-dry, as this tends to be the “safe” option from a production and quality perspective. But it results in a significant waste of energy. For wool fibre a good “rule of thumb” is that between 15% and 10% regain, for every 1% you over-dry you are wasting 2% to 3% in energy!
Processors without accurate on-line moisture-control systems typically over-dry by 3 to 4% (or more), thus wasting 10% or more in energy. How much does 10% of your drying-energy costs equate to over a year? This could impact significantly on your bottom line – studies have shown that a 1% saving in energy can equate to an improvement in bottom line profits by 10% or more.
Although over-drying is referred to above as a “safe” option from a quality perspective, over-drying can cause quality issues too (fibre damage, static problems, etc). Also, if fibre is sold based solely on weight, you are giving away fibre when you over-dry!
Moisture measurement and control systems are available to ensure that the product moisture content is maintained at the desired level at the exit of the dryer. These systems, such as the Streat Instruments DRYCOM Moisture Control System, continually monitor the moisture of the product at the exit of the dryer and manipulate either the energy supply to the dryer, or the dryer speed, to maintain the product moisture at the desired level. This allows the “safety margin” to be reduced to a much tighter window of moisture-content levels, thus affording the benefits of significant energy and productivity savings.
In response to requests from high-value knitwear processors in Scotland, Streat developed the DRYCOM Tumble Dryer Controller, which is easily retrofitted to existing dryers. By ensuring the garments are removed from the dryer at precisely the right time, product quality (handle and shelf appearance) are optimised and processors benefit from reduced energy and increased productivity.
With a typical payback period of between 6 and 12 months, Streat DRYCOM systems provide processors with a significant opportunity to reduce energy costs, improve productivity and efficiency, and enhance their competitive edge.