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Dyeing Printing & Finishing

Dwindling Resources -- Put Need To Your Benefit

Energy utilization in traditional finishing processes may be optimized through the use of innovative technologies.

Kurt van Wersch, Head of Product Development, A. Monforts Textilmaschinen GmbH & Co. KG

This article describes how energy costs are incurred and how with simple means and methods maximum energy utilisation can be achieved through the use of innovative technologies in traditional finishing processes.

Dryer configurations, minimum application processes, measuring and control technology, and fabric examples are described.

Discussing dwindling resources is no longer relevant today. No matter how alternative energies are generated, it is necessary to use less energy more effectively.

The parliamentary state secretary at the German Federal Ministry for Economics and Technology, Dagmar Wöhrl, said during the opening of a congress last year:
"Energy is the motor for economic growth and development worldwide. The conservative use of energy and raw materials is not only a major factor for climate protection, but also and more particularly an important competitive advantage for companies and national economies. Using resources efficiently allows you to produce more cost-effectively than the competition. The awareness that the best energy is the energy that is not used is gaining more and more significance, particularly in the light of the ever-increasing energy and raw material prices."

Where Do Costs Occur, And How Can They Be Measured?
If one considers the tenter as one of the main dryers used in textile finishing, then certain demands are made on this dryer and its configuration.

Modern tenters today should offer the following:
•    a high drying capacity;
•    good insulation;
•    variable-frequency circulating air fans;
•    variable-frequency exhaust air fans;
•    high-efficiency motors for fans, drives and auxiliary motors;
•    long-term lubrication for the chain and minimum maintenance requirements;
•    measuring, control and regulating elements;
•    heat-recovery system;
•    if necessary, an exhaust air scrubber; and
•    upline facilities to permit universal application.

If your tenter meets these requirements, you have already taken the first step in the right direction.If one considers the classic tenter drying process, one can see here how much heat energy is required to dry a damp textile (See Figure 1).

Figure 1

The damp textile web enters the tenter at production speed and is heated. The water is vaporized and evaporates. The dried textile leaves the tenter with a certain residual moisture content and at a certain temperature.

The evaporated water is absorbed by the circulating air. Part of this moist air is drawn out of the machine as exhaust air and is replaced by fresh air. This fresh air has to be heated to drying temperature. The energy required to evaporate the water, heat the fresh air and compensate the losses is supplied to the machine by the heater with the circulating air serving as energy medium. A small part of the energy is normally fed into the system by the rotating fan blades of the circulating air fans.

This can be expressed by the following formula:

The process heat flow and the heat flow to heat the fresh air are the most significant elements in the drying process.

The process heat flow is here the most important heat flow for which energy has to be input:

The specific energy consumption for each application can then be calculated using the following formulae:

From these calculation bases, it is possible to determine the specific energy consumption per kilogram (kg) of textile during the drying process in the tenter as a function of the water volume to be evaporated — the parameter is the drying temperature (See Figure 2).


Figure 2: This specific energy consumption holds true for 100-percent cotton (Co), 200 grams per square meter (g/m2), 1.5 meters (m) wide

This then gives the following hourly energy consumption during the drying process:


The enormous influence of the initial moisture content on the drying process is shown below, again from a different perspective for emphasis (See Figure 3).


The graph shows the effect of a variation in the initial moisture content. The starting point is 70 percent. A reduction in the initial moisture content results in an increase in production speed and a reduction in energy consumption and production costs. An increase naturally results in the opposite effect. Overall costs and thermal energy have practically the same-percentage relative deviation.

In summary, this means first of all that the greatest contribution to energy savings is made by a reduction in the initial moisture content. Wherever possible, alternative liquor application systems should be employed. The liquor application should be as low as possible, but as high as necessary.

Examples Of Cost Reductions During The Drying Process


In Example 1, only Step 1 is considered, as Step 2 is a process without water evaporation.
•    Drying process 1: classic
•    Drying process 2: reduced initial moisture content
•    Drying process 3: reduced initial moisture content and modified machine setting


In Example 2a, Δf = 19 percent. Additional costs for drying are 73,022 euros per year, plus a softener loss of more than 180,000 euros.


In Example 2b, Δf = 6 percent. Additional costs for drying are 35,402 euros per year.


Figure 4: The range configuration for the wet-in-wet process.


Figure 5: Monforts’ soft-coating production range enables energy usage and drying cost reductions as well as increased production speed, among other advantages


Figure 6: A tenter inlet section with various upline elements

Final Considerations
This article is intended to show where the problems lie during drying, and how maximum energy utilization can be achieved with simple means and methods through the use of innovative technologies in traditional finishing processes. Energy efficiency is a step in the right direction. What can be eliminated doesn’t require disposal, and what isn’t applied doesn’t require drying.

In order to optimize work flow, older-generation dryers can be redesigned electrically to use frequency controllers, high-efficiency motors and measuring instruments. It is very important to reconcile economy and ecology by using affordable technology to reduce energy consumption and costs and reduce wastewater.


[1] R. Fischer    Zur energetischen Beurteilung von Spannrahmen und den entsprechenden thermischen Prozessen [On the energetic evaluation of stenters and the corresponding thermal processes], VTCC Seminars 1994, Order No. 18

[2] M. Pabst, K. van Wersch    Maschinentechnische Realisierung der Trockenvorbehandlung [Machine engineering implementation of the drying pretreatment], VTCC Seminars 1981, Order No. 8

[3] K. van Wersch    Trockenprozesse verstehen und steuern [Understanding and controlling drying processes], Paper for the University of the Lower Rhine on 25.05.2005, Presentation at VDTF Further Training Seminars

[4] K. van Wersch    Der Einsatz von Dampf-Luft-Gemischen in der Textilveredlung [The use of steam/air mixtures in textile finishing], ITB-International Textile Bulletin 2/2004 and 4/2004