Unconventional techniques for energy conservation in ... techniques for energy conservation in textile wet processing Dr. S. R. Shah and Dr. J. N. Shah Department of Textile Chemistry,

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  • Unconventional techniques for energy conservation in textile wetprocessing

    Dr. S. R. Shah and Dr. J. N. ShahDepartment of Textile Chemistry, Faculty of Technology & Engineering. The M. S. University of Baroda, Vadodara 390

    001, Gujarat, INDIA.E-mail: srshah24263@yahoo.co.in

    Keywords : Unconventional technique, ultrasound, plasma, supercrtical fluid, electrochemical, textile wet processing

    1. Introduction

    Power and utility plays a vital role and their cost contributes significantly on total cost of finished textile product. Beingbasic and the oldest industry, it grows with the population rate, so is the need of power. Among all the industries, textilesector consumes about 5 - 8% of the total energy mainly in the form of electrical and thermal. Out of this about 40-45%energy consumed in manufacturing of yarn and fabric and 35-60% energy utilized in wet processing. Textile wetprocessing involved pretreatment, dyeing, printing and finishing, on grey fiber to impart aesthetic values andmarketability. All the four conventional energy sources namely, coal, electricity, oil and gas are utilized in the wetprocessing of textile. Table 1 shows the pattern of steam consumption in a typical composite textile sector. Wetprocessing of textile consumes very small proportion of electrical energy mainly for running of machineries. Fuel interms of coal or oil is used extensively, mainly to generate steam or heat. International energy crisis and escalating costof fuels have diverted all the researchers and industrialists to think for the ways to conserve energy [1-3]. Variousapproaches have been developed and practiced to conserve energy in wet processing namely,

    Developments of machines with low material to liquor ratio. Efficient heat recovery and processing. Developments in specialty chemicals and dyes to reduce processing time or cycles. Optimize wet pickup on fabric to reduce drying energy. Adoption of e-control to minimize unnecessary leakages. Development of techniques to reduce process cycle.

    Table 1 Steam consumption in a typical textile composite mill [1]

    Department Steam consumption (%)Humidification 10Sizing 15Boiler house 05Wet processing 60Leakage 10

    Innovation of unconventional techniques have opened a new era of energy conservation in textile wet processing[4,5]. The important benefits to textile industry of the said technologies are:

    The apparent increase in diffusion rate of chemicals Energy saving s as process operate at lower temperature Increased efficiency of process leads to less effluent Preserved drapability, luster and finish of fiber Overall cost reduction of process

    2. Application of ultrasound [6-9]

    Normal audible sound frequency range for human is about 16 18 Hz (1 Hz = 1 Cycle for second). Ultrasound (US) isa cyclic sound pressure wave with a frequency greater than the upper limit of human hearing. US is thus not separatedfrom "normal" (audible) sound based on differences in physical properties, only the fact that humans cannot hear it. USmainly divided into two groups, namely, power ultrasound (20 KHz 2 MHz) and diagnostic ultrasound (5MHz 10 MHz). The various range of sound shown in figure 1. Power US induces cavitation in liquors, mainly used in textilewet processing while diagnostic US does not induce any cavitation and used mainly in medical imaging.

    Materials and processes for energy: communicating current research and technological developments (A. Mndez-Vilas, Ed.)____________________________________________________________________________________________________

    FORMATEX 2013 747

  • Figure 1: US range diagram

    US radiation requires medium with electric properties for propagation and with this respect, it differs from light andother form of electromagnetic waves, which travel freely in vacuum. During the propagation of ultrasonic waves, theparticles in the electric medium oscillate and transfer energy through the medium in the direction of propagation. Theycan be propagated either longitudinally or transverse. In gas and liquid medium only longitudinal waves are transferredwhile in solid medium both longitudinal and transverse waves can be transmitted. The longitudinal vibration in liquidproduces the phenomenon of cavitations. This cavitations, is the form of microscopically small bubbles, which duringprocess, expand and collapse violently and generating shock wave. The cavitation formation depends on many factors,namely, frequency and intensity of waves, temperature and vapor pressure of liquid. The important phenomenon intextile wet processing, with respect to ultrasonic waves is micro steaming i.e. large amount of vibration energyaccommodated in relatively small volumes with little heating. The combine effects of cavitations and micro steaminglead to inter molecular tearing and surface rubbing. This reaction behaves as catalyst for the actual process i.e. increasesthe rate of processing.

    The use of US in textile wet processing was commenced in 1941 by Sokolov and Tumanski (Japan). Application ofUS in textile wet processing can be divided into two categories.

    2.1 Application in auxiliary bath preparation

    This application mainly related to the preparation of auxiliary bath such as preparation of sizing bath, emulsion solutionpreparation, dye dispersion preparation and thickener preparation for printing. In conventional process the starch andthickener paste/solution are mixed with water and heated at gelatinizing temperature and held for long period at the saidtemperature. With the help of US, the operation can be conducted more rapidly, even at lower temperature. Further, thequality of solution prepared by US usage is superior in terms of homogeneity. Similarly, US techniques are used toprepare emulsion solution used for lubricants. Ramaszeder prepared water-oil emulsion using US and found stabilitymore than 212 hours. Whereas those prepared by conventional method is only 12 hours. US techniques are widely usedfor dye dispersion preparation either in dyestuff industries or at shop floor in dyeing department.

    2.2 Application in chemical processing of textiles

    Application of US in this category involves, heterogeneous systems (textile subtract and liquor) and used in variousprocesses such as desizing, scouring, bleaching, dyeing and finishing.In the pretreatment and washing operations, the main object is to remove natural and added impurities from the fibersurface while in dyeing and finishing is to transfer or diffuse dyes or chemicals into the fiber structure.

    Dyeing of textile materials with US has been subject to many studies likes, effects of low and high frequency soundwaves, quality of dispersion, solubility of dyes, dye uptake by subtract etc. The frequency suitable for inducing UScavitation is in the range of 20 to 50 KHz. The mechanism of US in dyeing can be explained as follows: When ultrawaves are induced in liquor, the phenomenon cavitation starts and liberates entrapped gases from liquid or porousmaterials (textiles) as a result three dimension reactions occurs, namely, dispersion (breaking up of miscells and highmolecular weight aggregates into uniform dispersion ), degassing (expulsion of dissolved or entrapped gases or airmolecules from fiber capillaries) and diffusion (accelerating the rate of dye diffusion inside the fiber by piercing theinsulating layer covering the fiber and accelerating the interaction between dye and fiber). Dispersion and degassingeffects are catalyzed by mechanical action of cavitations while diffusion is catalyzed by both mechanical action ofcavitations and heating of fiber surface.

    US application in textile finishing can be explored for various types of fabric lamination. For this purpose Kuster,Germany has developed US Laminating Calendars. The important significance of US in textile processing can besummarized as:

    Improved quality products obtained mainly in paste preparation process. Better dye penetration, improved uniformity and fastness properties of dyeing. Energy saving as the process is possible at low temperature compared to conventional process. Consistent and uniform bonding in the finishing process.

    Materials and processes for energy: communicating current research and technological developments (A. Mndez-Vilas, Ed.)____________________________________________________________________________________________________

    FORMATEX 2013748

  • 3. Application of plasma [10-14]

    Plasma technology was first developed by M. Faraday in 1880s and had been proposed by I. Langmuir in 1926. Plasmais an ionized gas with equal density of positive and negative charges which exist over an extremely wide range oftemperature and pressure. Plasma consists of free electrons, ions, radicals UV-radiation and other particles dependingupon the gas used. In order to maintain a steady state, it is necessary to apply an electric field to the gas plasma, whichis generated in a chamber at low pressure. Plasma is the 4th state of matter and a gas becomes plasma when the kineticenergy of the gas particles rises to equal the ionisation energy of the gas. When this level is reached, collisions of thegas particles cause a rapid cascading ionisation, resulting in plasma(figure 2b). When the neutral molecules of a gasare energized, e.g. by exposing to high electric field, to a point when some electrons become free and the gas turns intoa mixture of electrons, ionised atoms and molecules, photons and residual neutral species. In this state it behaves as achemically very active environment and there is a high likelihood of surface interaction with organic substrates. It isalso possible to genetate plasma at room temperature. Plasma is generated when an electrical current is applied across adielectric gas or fluid (an electrically non-conducting material) (figure 2a) or in air a