The need of energy conservation has assumed paramount importance due to the rapid growth of process industries causing substantial energy consumptions in textile operations. And this has made pathway to conservation of energy which can be affected through process and machinery modifications and implementation of technological advancements relating to process optimisation as well as development of newer methods to meet the challenge of substantial energy saving in textile wet processing. Thus, there is a necessity for replacing the conventional methods by the latest processes which will lead to considerable savings in terms of energy, money and time.

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 utilisation and is one of the major energy consuming industries. About 34 per cent of energy is consumed in spinning, 23 per cent in weaving, 38 per cent in chemical processing and another 5 per cent for miscellaneous purposes. Power dominates consumption pattern in spinning/weaving, while thermal energy is major for chemical processing. It is known that thermal energy in textile mill is largely consumed in two operations, in heating of water and drying of water. Fuel consumption in textile mills is almost directly proportional to amount of water consumed. Hence, if consumption of water can be reduced, it will also save energy.

It is, therefore, an important aim of industrial fundamental research to develop new technologies to optimise conventional processes to conserve energy by basically adopting novel concepts discussed in the paper.

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 utilisation and is one of the major energy consuming industries. About 34 per cent of energy is consumed in spinning, 23 per cent in weaving, 38 per cent in chemical processing and another 5 per cent for miscellaneous purposes. Power dominates consumption pattern in spinning/weaving, while thermal energy is major for chemical processing.

It is known that thermal energy in textile mill is largely consumed in two operations, in heating of water and drying of water. Fuel consumption in textile mills is almost directly proportional to amount of water consumed. Hence if consumption of water can be reduced, it will also save energy. Conservation of energy can be affected through process and machine modification, proper chemical recipes, and new technologies. The possibilities of utilising new energy resources like solar energy, wind power, tidal power, nuclear energy, etc. are to be explored. But initial cost of production will increase in step with cost of oil, which makes development of such sources doubtful in terms of cost incurred.

Focus Areas for Energy Conservation

Thermal Energy
As already indicated, wet processing of textiles consumes a very high proportion of thermal energy mainly for the evaporation of moisture from textiles. at various stages of wet processing and for heating of process chemicals. Table 1 indicated the department wise percent steam consumption in a composite textile mill.

Steam is generated employing boilers by using either coal or furnace oil and lately low sulphur heavy stock oil available from the refineries as fuel having average calorific values of 4200; 6200; 10,280 and 10,700 Kcal respectively.

Thermal energy in the form of steam is supplied to the various equipment's through pipe for this purpose; steam generated in the boiler is bifurcated into the required branches through the main steam header. The major consumption of steam is for evaporating moisture from treated textiles as compared to that of heating of process chemicals. Following are the tables which gives the average steam consumption in some unit operations and in each stage of wet processing.

Electrical Energy
The wet processing of textiles consumes only a small portion of electrical energy, say around 15 per cent of total electrical energy, mainly for running the various processing machineries. By and large, most of the textile mills draw their power requirements and from respective state electricity boards. However, the supply is adversely affected sometime resulting in severe power cuts for the industry, in order to supplement this; several mills have gone in for their own captive generation in spite of the higher cost. Some mills have tried for steam turbines by taking the advantage of tail race low pressure steam, however non-availability of low to medium turbines, and their maintenance as compared to diesel engines limits their use.

Energy Conservation
The term energy saving or energy conservation can be affected by two ways:

  • The engineer's approach
  • The dyer's approach

To realise this savings, short term as well as long term plans should be developed depending on cost benefit analysis. Some of the measures are enumerated below for fuel conservation.

  • Human factor management
  • Fuel selection
  • Fuel handling and storage
  • Fuel combustion
  • Steam generation
  • Steam distribution
  • Steam utilisation
  • Maintenance of machine
  • Waste heat recovery
  • Alternate sources of fuel
  • Renovation / replacement of existing plants
  • Process modification

At dyer's approach to conserve the heat or energy. As far as, the engineer’s approach is concerned towards the energy conservation above mentioned points 1 to 10 are applicable.

Following is some of the measures from the dyer's approach:

1. Electrical Energy
The major consumption of electrical energy in the textile industry is in the manufacture of yam and cloth, amounting to nearly 3/4th or 4/5th of the total power requirement in a textile mill, whereas hardly 15 to 20 per cent of electrical power is consumed for running various machines in textile wet processing.

As far as the electrical power saving is concerned the following measures can be affected:

Reduce the processing steps by combining some of the constituent wet processing operations in each processing sequence. This may help in reducing number of washings and dryings e.g:

  • One bath bleaching may enable to save around 70 per cent electrical inputs.
  • Reduced number of ends / turns jiggers may help in saving around 20 per cent electrical input.
  • Elimination of curing in printing saves 100 per cent electrical input for curing step.
  • Combined drying - cum - curing in resin finishing saves around 35 per cent electrical input.

Explore the scope for an increased output per unit duration of various electrically driven machines.

  • Use of high efficiency motors in place of standard motors with proper application will save 2 to 4 per cent.
  • Replacement of under size and over size motors - saving depending upon the percentage of loading on the motors.
  • Use of high temperature grease according to insulation class of motors
  • No load power study of motor, replacement of motors consuming high no load power
  • Investigation of exact burning reason, rewinding as per original technical data

Motors convert electrical energy into mechanical energy to drive machinery. During this conversion, some energy is lost.

Current motors feature improved designs and incorporate the latest developments in materials technology. The most efficient of these motors are termed High Efficiency Motors (HEMs).

Other advantages of HEMs besides energy savings are:

  • Higher power factor
  • Longer lifespan and fewer breakdowns
  • Run cooler and less susceptible to voltage and load fluctuations
  • Produce less waste heat and noise

Displayed below are the estimated savings according to motor capacities.

2. Thermal Energy
Apart from electrical energy, the wet processing department of a textile mill requires substantial quantities of thermal energy in the form of steam as a source of heating. The various ways and means by which a substantial portion of huge quantities of thermal energy consumed during textile wet processing can be saved include the following.

Since most of the thermal energy is wasted in removal of water, different attempts have been made to reduce the energy as follows:

  • Efficient removal of water using heavy squeezing enables 15-20 per cent reduction in energy requirement for drying
  • Vacuum impregnation squeezes out the air from the cloth 'and provides better dye or chemical impregnation and more uniform application and this process enables 60-65 per cent fuel saving compared to conventional system
  • Vacuum roll extractor enables 70-75 per cent saving in energy

Some developments relating to increase in efficiency of drying and setting units:

  • The heating up time on conventional stenters and hot flue driers are 10-20 sec. and 40-60 sec. respectively. But by employing sieve drum drier which reduces the time of heat up to 1.3 sees. and gives almost 60-70 per cent energy saving.
  • Radio frequency is used for uniform heating throughout the mass of the material which gives 60 per cent saving in energy.
  • Use of heat transfer fluids (thermos pack) like hydrocarbon of enabling temperatures up to 300o C. This process gives 80 per cent savings in energy.

Some developments relating to techniques based on reduced liquor- to- material ratio in the operations:

  • Foam application technique gives almost. 50- 60 per cent savings in energy for low wet pick-up applications.
  • Use of low M. L. R. jet dyeing machines saves 40-60 per cent fuel.
  • Azeotropic / emulsion-based system of processing saves 60-70 per cent fuel considerably because of significantly low water content of the system.

Some developments relating to process developments and lor process modifications:

  • Reduction in pressure kier time by kier modification from 6-8 hrs.
  • It enables 60-65 per cent energy saving.
  • By using reducing agents like Anthraquinone the scouring time can be reduced to 3-4 hrs from 6-8 hrs. This process enables 40- 50 per cent savings in energy.
  • By solvent scouring process 60-80 per cent energy can be saved.
  • Cold bleaching by activating sodium chloride by hypochlorite use no thermal energy and hence 80- 90 per cent energy saving is possible. e: Hot mercerisation enables the combining of scouring and mercerisation and saves energy around 30-40 per cent.
  • Mather and Platts vaporIac bleaching process is a continuous so curing and bleaching under pressure which can be completed in 3-7 minutes and this process saves around 40-50 per cent energy.
  • Dupont’s two minutes bleaching uses hydrogen peroxide at very high pH value with a special formulation to prevent undue decomposition of peroxide and damage to the fabric. An energy saving around 80-85 per cent is possible with this process.
  • Combined one step hypochlorite bleaching and scouring at R. T. enables almost 100 per cent energy saving.
  • Combined one step de-sizing, scouring and bleaching by redox system reduces almost 60 per cent energy requirement.
  • Use of solar energy for de-sizing and scouring enables almost 40-50 per cent energy saving.
  • Cold pad batch method for reactive dyeing by sodium silicate for fixation of the dyestuff gives 100 per cent energy saving.
  • Rapidogen development by dry heat fixation with compounds like urea uses no acid ager and hence saves 40 per cent energy.
  • Low temperature curing of pigment prints by using highly active catalysts.
  • Like ammonium chloride, ammonium sulphate etc. saves 30-40 per cent energy.
  • Use of flash agers for reactive colour printed and dried goods the printed and dried cloth is padded with alkaline solution of high electrolyte content and steamed for about 30-60 minutes. This method saves almost 50 per cent steam.
  • Dyeing cum sizing of denim warps enables almost 40 per cent saving in energy.

Novel Concepts of Energy Conservation
Higher energy consumptions involved in textile operations make pathway to innovations in various operations involved in the chemical processing of textile materials.

Supercritical Dyeing Technique
Supercritical dyeing technique is an innovation to conserve the thermal energy as the fabric is in the dried state because at the end of process CO2 is released in gaseous state. This is a new technique of using supercritical carbon dioxide as a dyeing medium. Dyeing is performed in a high-pressure vessel called an autoclave. Carbon dioxide exists as a supercritical fluid at temperature at about 31°C and pressures above 72 bars. The anhydrous process offers number of ecological and economic advantages such as, no preparation of processing water and low energy consumption for heating up liquor.

Ultrasonic Assisted Wet Processing
Ultrasonic assisted process is an alternative to conventional high temperature processing of the textile materials. Ultrasound equipment installed in the existing machines offer improved performance in fabric preparation and dyeing without impairing the properties of the processed materials. The influence of ultrasound intensifies the mass transfer in the wet processing of textile materials. The advantages of ultrasonic in textile wet processing include energy saving by reduced processing temperature, time and lower consumptions of auxiliary chemicals and further processing enhancement by control of overall costs. Therefore, the areas that demand higher energy consumption can be benefited using ultrasound techniques.

Foam Technology
The application of foam processing leads to considerable savings in the energy required for heating, drying, thermo-fixing, and steaming and so on because the water content is very low. The foam processes bring down the liquor ratios required for pretreatment, dyeing and finishing by producing uniform foam with the required characteristics in terms of viscosity, stability, and blow ratio. De-sizing, bleaching and finishing as well as fluorescent brightening of goods can be done using a foam technique. It offers potential savings in materials and energy.

Energy Conservation through Software Approach
NITRA has developed a user-friendly approach which performs energy balance on any machine in a textile mill, stores the data along with information on the actual cost and theoretical cost of the performed operation along with the gradation of quality obtained. Records stored by this operation can be recalled later to review weekly/monthly/yearly performance of machine. The software is also helpful in comparing the energy demands between machines processing the same production and shade. This can help in the selection of a machine required for a particular quality where the cost benefit will be more.

Non-Conventional Sources of Energy
The different alternative renewable sources 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 are their origin to these energy sources. India's geographical location favours unlimited and uninterrupted supply of solar energy and hence it must be effectively utilised. Solar energy is widely utilised in the heating up of water. Solar water heaters are available that are used to mostly save thermal energy. The bagasse and biogas is used as fuel in the boilers which is readily available. 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.