Drying is often one of the most energy intensive operations in a wide range of textile processes. The implementation of an accurate on-line Moisture Control System can offer significant benefits to processors involved in drying operations.
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 of 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. 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 specific 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 and in order 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. This “safe” option can however have disastrous effects on the energy consumption and general productivity of the drying operation.
The installation of an accurate moisture measurement and control system can ensure that the “safety margin” can be reduced to a much tighter window of moisture content levels, thus affording the benefits of significant energy or productivity savings.
There are three major areas to consider with respect to cost justification for the implementation of a moisture control system.
All fibres retain a certain amount of moisture and this can have a significant effect on the total weight of the fibre. As the sale price of the fibre is often based on the weight of the fibre, the amount of moisture can significantly affect the final sales value. Generally the final invoice is adjusted to allow for the moisture content but this is not always the case.
It is also often very important to monitor the moisture content throughout the operation of a production unit in order to keep an accurate record of yields. The effect of moisture variations of even 1% can have a significant effect, especially for high value fibre.
Consider the case of a slipe wool processor in New Zealand:
If the regain could be raised by 1% this would equate to an increase in revenue of NZ$ 20,000.00 per year. In this type of application a regain increase of 2 to 3% is typical after the installation of a Streat system.
Please note that above saving is just the direct cost saving. There will also be considerable savings due to reduced energy usage, increased productivity, and the ability to optimise the operation (perhaps even saving on the cost of new capital plant such as dryers as the old plant can be operated more efficiently).
Consider the case of a yarn spinner processing high value yarn:
A drop in yield of 1% (caused by moisture variation) would result in an apparent loss of NZ$ 6,000,000 per year.
This is an extreme case with very high value yarn (cashmere) but even for a yarn with a value of NZ$ 20.00/kg with the same production the apparent loss would be NZ$ 800,000 per year.
It is very important to note that increased productivity is highly profitable for textile processors. There is virtually no increase in overheads, so that the profit margin on the extra product is very high. There are three main factors to be considered in relation to increased productivity:
In a drying process the elimination of over-drying of product provides the opportunity to increase product throughput rates. We have had instances of productivity increases of 20 to 30%, and 10 to 15 % are typical.
Thus if the optimum regain for a future process (or customer) is 16%, but you dry to 13% “to be safe” and ensure you don’t process fibre above 16% (which will cause processing problems, dissatisfied customers etc.)
you are sacrificing between 6 and 9% of energy. When you consider that many studies have shown that a 1% energy saving can equate to a 10% or more improvement in bottom line profits, this has considerable significance to any drying operation.
For wool between 10 and 15% regain, for every 1% of regain that you over-dry; productivity drops by 2 to 3%.
Often companies are over-drying by up to 3 or 4%, causing a productivity drop of 10% or more!
If the plant down-time could be reduced by 30 minutes/day (a typical stoppage is five minutes) this relates to a potential productivity gain of 2% (based on a 24 hour operation).
In addition there will also be considerable savings due to:
Improved future processing efficiencies are made possible if the product is kept at the desired level of moisture content.
The problems caused by incorrect moisture can be considerable and in extreme cases can result in damage to processing equipment. With the modern high speed machinery optimum processing speeds can only be obtained if the fibre moisture is controlled within tight limits.
Reprocessing and plant down-time reduce the time that the plant is available for normal production, and are thus very expensive.
These benefits can easily be directly related to total production to give annual saving.
Improved quality has many benefits including:
In summary, the implementation of an accurate on-line moisture control system should be considered by all processors looking to improving the efficiency and profitability of their operations.