Optimizing reduced energy resources to meet finishing
requirements
by Dipl.-Ing Kurt van
Wersch, A. Monforts Textilmaschinen GmbH & Co. KG,
Monchengladbach (Germany).
1. Abstract
Energy utilization in traditional finishing processes has to
be optimized through the use of innovative technologies. This
article describes how energy costs are incurred and how with
simple means and methods maximum energy utilization 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.
2. Introduction
Discussing dwindling resources is no longer relevant today.
No matter how alternative energies are generated, we have 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.”
3. Where do costs occur, and how can
they be measured?
If we consider the stenter as one of the main driers used in
textile finishing, then certain demands are made on this drier
and its configuration.
Modern stenters today should
- Have a high drying capacity.
- Have good insulation.
- Have variable-frequency circulating air fans.
- Have variable-frequency exhaust air fans.
- Be equipped with high-efficiency motors for fans, drives
and auxiliary motors.
- Have long-term lubrication for the chain and require
minimum maintenance.
- Be equipped with measuring, control and regulating
elements
- Have a heat recovery system.
- If necessary, have an exhaust air scrubber, and
- Have upline facilities to permit universal application.
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(Fig.1) |
If your stenter meets these requirements, you have already
taken the first step in the right direction. If we now consider
the classic stenter drying process [Fig. 1], we can see here how
much heat energy is required to dry a damp textile.
The damp textile web enters the stenter at production speed
and is heated up. The water is vaporized and evaporates. The
dried textile leaves the stenter with a certain residual
moisture content and at a certain temperature.
The evaporated water is absorbed by the circulating air
(=energy medium). 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 up 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 [1]:
The process heat flow and the heat flow to heat up the fresh
air are the most significant elements in the drying process. The
importance of the heat flow for heating up the fresh air has
already been described many times, so that here reference is
made merely to citations [2-4] on the above subject.
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 these formulae.
From these calculation bases it is possible to determine the
specific energy consumption per kg textile during the drying
process in the stenter as a function of the water volume to be
evaporated (the parameter is the drying temperature). [Fig. 2]
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[Fig. 2] |
This specific energy consumption holds true for 100% Co, 200
g/m², 1.50 m wide.
tDü = 150°C, xD = 15 Vol%
Example 1 f1 =
70% initial moisture content.
f2 = 8% residual moisture content.
qT 2400 kJ/kg textile.
Example 2 f1 = 40%
initial moisture content.
f2 = 8% residual moisture content.
qT 1250 kJ/kg textile
This then gives an hourly energy consumption during the
drying process of
The enormous influence of the initial moisture content on the
drying process is shown here again from a different perspective
for emphasis.
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[Fig. 3] shows the effect of a
variation in the initial
moisture content. |
[Fig. 3] shows the effect of a variation in the initial
moisture content. Starting point here is 70%. A reduction in the
initial moisture content results in an increase in the
production speed and a reduction in the 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: 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.
4. Examples of cost reductions
during the drying process to suit your needs
In this example, 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.
(Δf = 19%) Additional costs for drying 73,022 EUR/year
(better than 180,000 EUR softener loss).
|
[Fig. 4] shows the range
configuration for
the wet-in-wet process. |
|
[Fig. 5] shows a soft-coating production range. |
|
[Fig. 6] shows a stenter inlet section with various upline
elements. |
(Δf = 6%) Additional costs for drying 35,402 EUR/year.
5. 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
avoided doesn’t need to be disposed of, and what isn’t applied
doesn’t need to be dried.
Our motto is “Put need to your benefit”.
Redesign dryers electrically (use of: frequency controllers,
high-efficiency motors, measuring instruments). Reconcile
economy and ecology (use affordable technology to reduce energy
consumption and costs, reduce the waste water).
Use our resources conservatively, because our children's
children will also need energy.
Bibliography
- R. Fischer: On the energetic evaluation of stenters and
the corresponding thermal processes, VTCC Seminars 1994, Order
No. 18
- M. Pabst, K. van Wersch. Machine engineering
implementation of the drying pretreatment, VTCC Seminars 1981,
Order No. 8
- K. van Wersch : Understanding and controlling
drying processes, Paper for the University of the Lower Rhine
on 25.05.2005, Presentation at VDTF Further Training Seminars
- K. van Wersch : The use of steam/air mixtures
in textile finishing], ITB-International Textile Bulletin
2/2004 and 4/2004.
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