Cost Effectiveness in Textile Processing
By: Abhishek jadhav & Nitin AjmeraPresented by www.fibre2fashion.com
Cost effectiveness in textile processingBy: Abhishek jadhav & Nitin AjmeraIndian Textile Industry has great potential to dominate the Global Textile Market. We have a strong tradition of textiles and vastly talented persons in the trade. The textile industry has to strive and put in some real work towards fulfilling such expectations. Hence wet processing of the future should be cost effective, environmentally friendly and gentle to the textile material. Innovative efficient strategies to achieve these goals are needed. This paper reports various such innovative techniques like Right first time dyeing, super critical CO2 dyeing, foam finishing and various measures of energy and water conservation which makes Textile Processing eco-friendly and cost effective in future.
Introduction: Steps taken at various stages of wet processing of textiles to ensure quality of products, particularly in the decentralized sector. A few important guidelines for various cost saving measures by process modifications and adopting new concepts based on modern technological changes are also given. The special importance of using eco-friendly dyes and chemicals is also highlighted in view of latest ban on the export of textiles using such dyes.
ENERGY AND WATER CONSERVATION: Conservation is derived from the Latin words con (together) and servare (guard). 1 In every country, the growing needs of energy in various fields of activities have led to the necessity of finding out ways and means to avoid wastage and conserve the energy. Water is expensive to buy, treat, and dispose. Textile industries are consuming large quantity of water. Major portion of water is used for wet processing of textile (60 to 70 %). Keeping this in mind there is acute need of energy and water conservation programmed to implement as earlier as possible.
Energy conservation: Energy is one of the most important ingredients in any industrial activity. However, its availability is not infinite. Global energy crisis, as well as high cost of fuels resulted in more activities to conserve energy to maximum extent. The textile industry retains a record of the lowest efficiency in energy utilization and is one of the major energy consuming industries. About 34% of energy is consumed in spinning, 23% in weaving, 38% in chemical wet processing and another 5% for miscellaneous purposes. Power dominates consumption pattern in spinning and weaving, while thermal energy is major for chemical wet processing. Preventive energy conservation - finding-energy losses and solutions of them: Following are the major sources from where energy is lost in various forms:
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Energy loss through hot vapours and hot water discharge: A large amount of thermal energy, either in the form of hot exhaust gases or hot vapours is ejected into the atmosphere or down the drain as waste from various processing machinery in the textile mills. The recovery of such waste for reuse is estimated to effect 5 to 7% saving in the cost. For example: Flue gases in plain and thermic fluid boilers. Liquor, water and their vapours in the kiers, agers, jiggers, jet dyeing and beam dyeing machines. Exhaust gases from the stenters.1 Major sources of hot wastewater discharge are desizing washes, scouring, mercerization, dying and steam condensate wastage. Most of the wastewater streams are discharged at the temperature of 60-70 0C. Heat energy can be recovered from the hot wastewater streams originating from different processes by installing heat exchanger between the wastewater and fresh water to be used for different process. The capacity of the heat exchanger will vary with the discharge of the machine. The temperature rose of the cold water would be in the range 40-50oC. This measure will reduce steam consumption for heating the baths. Different types of heat exchangers are available and its choice depends on number of factors. Steam condensate discharges are hot and clean water streams. These streams can be used as boiler feed water or for preparation of dye baths. These options not only reduce water consumption and wastewater quantities, but also results into substantial energy savings. Energy loss through leakages and improper maintenance: In most of the textile industries it was found that there are number of pipelines and equipment from where steam, steam condensate and hot water is lost through leakages. It is difficult to asses the quality of leakages but obvious that leakage of hot water and steam results in substantial energy loss. Generally the condition of piping and insulation is not up to the standard due to the fact that preventive maintenance is not being given due consideration. One of the reasons for this negligence may be due to production load in which machine shut sown for repair is difficult. Steam usage is generally not optimum, reasons for excess usage and wastage of steam are the unnecessary supply of steam to the bath even after attaining required temperature. Steam traps are generally malfunctioning, resulting into escape of steam along with steam condensate. At most of the places, out of order steam traps are disconnected, rather being repaired or replaced. Corroded pipes and valves, as a result of improper maintenance, also contribute in steam and hot water loss. Steam control valves are generally not found in the machines and old machines are not equipped with energy controllers. Preventive maintenance should be given due consideration. Routine maintenance schedule should be maintained and followed properly. Workers should be aware of the fact that substantial money is lost through leakages and improper maintenance practices. Energy loss through lack of insulation on pipelines and machines: Most of steam, steam condensate and hot water carrying pipelines are not equipped with proper insulation. Insulation found to be eroded at various places because of improper maintenance and upkeep. Machines conducting reactions, washing and drying at hot states especially desizing, bleaching, jiggers and dryers are mostly not insulated, that cause heat dissipation to ambient air. The quantity of heat dissipation is the function of the temperature difference between inside hot machine and outside cold air and the surface area of the machine. However, proper insulation provides resistance to convectional heat transfer with the advantage of less steam and fuel consumption in heating contents up to the required temperature.
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A saving of the order of 5-10 % of the energy consumed for steam production can result from this measure. Further this measure will improve the occupational atmosphere, especially during the hot weather, and also increase the safety of the workers, due to covering of the otherwise hot surfaces. Energy loss through flue gases and hot air: Boiler flue gases contain substantial heat energy. This energy can be utilized to preheat the boiler feed water through economizer but at present in most of the industries it is not being utilized. Some industries installed economizer but could not last, may be because of improper material of construction or faulty design. Hot air, from different dryers, is also wasted. The thermal energy, present in the boiler off-gas stream, can be used to preheat the boiler feed water. Savings in boiler fuel consumption can amount to about 5%. Economizer can be boiler stack in which hot flue gases will preheat boiler feed water. Energy loss through singeing machine: Singeing operation is employed to destroy singes and tufts on the surface of the fabric, by its direct exposure to the flame, for a very short time. Fabrics of varying widths are processed in the textile industry. Generally a single multiple port full-width burner is provided in the singeing machine, which results into unnecessary wastage of energy, when fabric of width shorter that that of the singeing flame is being processed. The arrangement required would be the replacement of the single full width burner with a series of burners of shorter widths placed in one row, each with separate fuel gas supply. The number of burners to be fired, during singeing operation, would be according to the width of the fabric. Use of non-conventional energy sources: The different alternative renewable resources of energy are biomass, geothermal energy, tidal energy, wind energy and solar energy. Out of these energy sources, solar energy is abundant and is inexhaustible, in fact, fossil fuel, viz. coal, oil, and natural gas owe to their origin to these energy sources. Indias geographical location favors unlimited and uninterrupted trapping of solar energy and it is the desirable energy available in the environment. The plants serve as the most abundant renewable raw material in nature for production of biogas, as they are rich in carbohydrates. The gas can be produced and consumed at the place of production and hence cost of transportation of raw material and gaseous product is eliminated. The technology is simple and easy to operate, with virtually very little maintenance cost. There will not be any problem of air pollution. In short, nothing is wasted and there is no effluent.2-5 Steam generation and its effective distribution: Steam has become the first source of heat in dye house. The only way to absorb all the heat from the steam is to inject source of heat in dye bath. Heat exchanger of coil, tube or plate type, suitably closed by a steam trap to permit the drainage of condensed steam, are now a days installed in a machine itself. Most of the energy goes for generation of steam and production of power. The efficiency of conversation of fuel into steam is of the order of 75% and that of electricity about 30%. The steam generated from the boiler has to be distributed through proper insulated pipelines wherever required. The loss due to the leakage have to be ventilated properly to avoid the condensing of the steam on the roofs and the machines like jigger and winches may also be covered with covers.
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Drying: Drying is a thermal energy consuming process required at different stages in wet processing. Drying operation is done by different techniques. Cylinder drying can be made more effectively by use of steel cylinders and reducing water contents by vacuum extraction. Hot air stenter, if used by preventing fresh air leakage, running exhaust only when necessary, keeping circulation of air effective and avoiding idle running can save energy. Infrared and RF-drying are also effective due to their specific effects. Microwaves are more energy efficient saving in both capital and operating cost. Microwaves affect polar molecules (such as water) and in a textile material the substrate is generally non polar, hence water is evaporated without affecting the substrate by IMS (Industrial Microwave System).4-5. Process modification: Bleaching and Finishing: Combined preparatory processes save time as well as energy. If the fabric is pretreated by subjecting grey one to steam purging operation, wettability improves, which can be followed by single step desizing, scouring and bleaching. Explore scope for wet-on-wet mercerising and wet-on-wet finishing by using vacuum extractor. Run two or more ends either side-by-side or superimposed on machine like shearing, cropping, sizing, chainless merceriser, cylinder drying rages and calendars, etc. Combined drying and heat setting or optical brightening and heat setting. Dyeing and Finishing: Dyeing of blends in single bath. Combined dyeing and finishing process. Solvent assisted dyeing, supercritical carbon dioxide as a medium of dyeing. Ultrasonic and UV energy for dyeing. Cold pad bath operations wherever possible. Eliminating intermediate drying operation between beam dyeing of polyester and jigger dyeing of cellulose in blends. Resort to drying cum curing of pigment prints Energy audit UKs energy efficiency best practice programmes (EEBPP) show that energy cost can be reduced by 10% without any investments, simply by improving energy management practices. The first logical step towards reducing energy cost is to understand how energy is consumed and then comparing the energy of specific site or process against some established industry norms. One of most common approaches is to calculate the quality of energy used to produce a unit of product. This is known as specific energy consumption (SEC). Toray Textiles Ltd. initiated a major energy management programme along with activities like staff motivation, capital investment programme, training, good house keeping and modern management technique. The results of this programme found very impressive as their annual energy consumption reduced by 27%. Nearly half the saving were made through no cost or low cost good house keeping practices.6 Water usage in textile industry: Presented by www.fibre2fashion.com
Water is used extensively throughout processing operations. Almost all dyes, specialty chemicals, and finishing chemicals are applied to textile substrates from water baths. In addition, most fabric preparation steps, including desizing, scouring, bleaching, and mercerizing, use aqueous systems. Water consumption pattern in textile mills: The requirement for different purposes in a textile mill can be generalized as below: Purpose Steam production Cooling water Deminerialised water for specific purposes Wet process Sanitary use Fire fighting, etc. Water Conservation and Recycle: Water is expensive to buy, treat & dispose and as it is becoming a scarce commodity, sustainable developments of the textile industry needs recycling of waste water generated and conservation of water to reduce the water requirements and also dependency on other water sources. As the cost of water supplied to industry keeps increasing, recycling becomes more important. Many textile industries in water scarce areas are installing water recycle plants. Reduction in waste water volume: Proper water management in mills can achieve this of the water used for various operations, a large portion is consumed in wet processing. Water required for wet processing varies from mill to mill and depends upon: Sources of water Availability of water Quality and quantity of fabric processed Processing sequence adopted Number of washings in processing sequence Type of processing machinery used Water Consumption % 5 6 8 72 8 1
Techniques of conservation: Numerous methods have been developed to conserve water at textile mills. The sections below discuss some of the techniques applicable to a wide variety of firms. Counter-current washing: For both water and energy savings, counter-current washing is employed frequently on continuous preparation and dye ranges. Clean water enters at the final wash box and flows coun...