Introduction

In textile industry, electricity consumption and power cost is in increasing trend due to modernised machines and continuous usage of the machines in inefficient operating parameters. Apart from the power cost, man power is also shortage in textile mills due to dusty environment inside the mill and heavy noise from the textile machines. Due to these reasons workers are not showing interest in working at textile mills, which compel mill management to deploy more automated machines. Hence, textile machinery manufacturers are integrating automation in the machines, indirectly requirement of power of the machines is increased.

The main objective of the textile mill is to produce yarn (thread) from the raw cotton which requires six stages of process. These are discussed briefly for readers understanding. The textile mill can be split into three systems namely, card sliver, combed sliver and ring spinning system.

The card sliver system consists of blowroom and carding machine, which does the function of removing the foreign particle from the raw cotton and convert the same into thick yarn (sliver).

The combed sliver system consists of draw frame and comber machines, the draw frame machine ensures the uniformity in thickness of the sliver and comber machine removes the unwanted short fibre in the sliver.

Ring spinning system consists of Speed frame and Ring frame machine, which does the conversion of sliver (thick thread) into yarn (thin thread). Ring frame is the final product of the spinning mill.

Energy Distribution in Textile Mill

Energy audit had been conducted in one of the leading textile mill, which is located in Southern part of Tamil nadu. Installed power of the mill had been gathered from the mills and plotted in Table 1 department-wise. From the Table 1, Figs. 1 and 2, the major power govern area had been recognized to adopt energy saving concepts.

Table 1 Power distribution in textile mills including productive and non productive machines
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Fig. 1
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Power distribution in textile mills including productive and non productive machines

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Fig. 2
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Productive and non-productive machines power (kWh) consumption per hour

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From the above data it was found that the major power saving regions are preparatory process, Ring frame, humidification plant and compressor. Apart from the above, cable loss and power factor also plays a major task in textile mills to conserve the energy. It was observed that the power factor is changing from 0.8 to 0.96 at load end of the machines. Also, the voltage fluctuates from 395 VAC to 430 VAC at load side of the machines.

As a preliminary audit, actual data of units consumed and actual yarn production had been collected from the mills for a complete year in month-wise. From the data, for producing 1 kg of yarn, on an average 8.45 units of electricity are consumed during the year of 2010.

Energy Saving in Blowroom Department

The blowroom department is the first department where the mixings or materials from the bales are opened to smaller tufts and cleaned from external impurities like seed coats etc. The cleaning is achieved by means of a combination of revolving beaters either positioned vertically or horizontally and grid bars are suitably arranged. The following machines are arranged in an order (lines 1, 2, 3) and material from one machine is conveyed to the next machine by means of air suction created by fans for removing the waste. The machines will be running depending upon the production requirement. (Table 2)

Table 2 Units consumed per kilogram in the textile mill before conducting energy audit
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From Table 3, 54 induction motors are employed to eliminate the impurities from the raw cotton. Out of 54, 15 motors are underutilized while conducting power study by using Hioki make (type no: PW3198) power analyser. Selective motor data has been tabulated in Table 4 before and after changing appropriate motor power with respect to load. Also, motor connection changed from delta to star.

Table 3 Name of the machines with motor power in blowroom department
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Table 4 Units saved after changing a new motor and wiring connection changed from delta to star
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In Table 4, the motor runs with abnormality have been mentioned and the same are running for 24 h in the plant. As a result, a unit saved per hour is 2.15 kWh, so 51.6 units per day would be saved, in turn 1,548 units per month would be saved by adopting the above technique.

In the mills, the blowroom line is running continuously irrespective of requirement of material (cotton) request from the subsequent other machine (carding machine). Hence, start stop ratio of blowroom line has been tuned as 95:5 ratio. By doing so, 37.46 kWh per day has been saved during power audit. This is not only improving the opening and cleaning efficiency of blow room machines, but it also saves power. Thus, 1,123.9 kWh would be saved per month (Table 5).

Table 5 Power saved after increasing start stop ratio of blowroom line
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In blowroom department, to collect the wastes from the above mentioned machines, a centralised waste collection system is installed. The waste collection system consists of three fan motors connected with pipeline of individual machines according to the suction pressure requirement. By reducing the pressure from 1,000 Pa to 700 Pa in the waste collection system, energy has been saved around 102 kWh per day. The power study data has been pointed out in the Table 6.

Table 6 Units saved after optimising waste collection pressure in carding waste collection system
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Re-engineering of filter plant i.e., reducing the suction pipe length between the machines, by using solenoid valves suction flap can be opened and closed for a period of set time for individual machines to save the power. By resizing of motors based on the power drawn saves the power at mills. However, in this mill, there is no scope in doing energy saving by re-engineering of the filter plant.

Energy Saving in Ring Spinning

In accordance with Fig. 1, ring spinning region is contributing around 50 % of total installed power. Combination of Speed frame and Ring frame is called as ring spinning region, which reduces the thickness of sliver and mainpart twist which is required for winding. During power audit more concentration was given on Ring frame machines to conserve the energy in this mill. On observation, the Ring frame machines were running with lesser efficiency (91.5 %) on main motor. Hence, replaced higher efficiency motor (94.5 %) in one machine as trial basis and study had been conducted with same process and machine parameters, which gave good energy saving on Ring frame machine. The gists of results are tabulated below Table 7. As per European Directive, EuP Directive 2005/32/EC nominal minimum efficiency level for IE3 motor for 30 kW with 4 pole motor is 93.6.

Table 7 Power saved after installing energy efficiency motor in Ring frame machines
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Number of spindles

960

Count processed, K

30’s

Max spindle speed, rpm

18,000

Ring dia, mm

38

Based on the study result, the payback period was calculated as mentioned below and submitted to the mill management.

Investment in Rs/motor/machine, Rs.

90,000 (approx)

Unit saved/day/machine

51

Unit saved/month/22 machines

1,122

Amount saved per year (Rs. 4.45/unit), Rs.

82,837

Payback period, months

13

Next extensive scope in Ring frame machine is the optimisation of speed curve pattern. In Ring frame machine, the speed of the machine can be set (spindle speed) with respect to length of the yarn produced from the machine. By setting the speed curve such a way that the maximum speed will be reached before 25 % of the final length of the yarn to be produced. By doing so, there is a considerable power saving in the machine. This method is very easy as there is no speculation for doing this exercise. The same has been done and subsequent are the results.

Avg spindle speed, rpm

18,000

Total run time, min

145

Yarn breakage/100 spl/h

4.65

Average load, A

35.94

Average load, kW

24.46

Units/doff/machine, kWh

59.02

Total production, kg

46.9

UKG/doff

1.259

Units saved/day/machine, kWh

11

Units saved/day/22 machine, kWh

242

Figures 3 and 4 explains about the power against speed of the machine for the whole doff (final yarn length) of the machine. From the Figs. 3 and 4, it is clear that by optimising the speed curve, peak load of the motor power can be decreased and utilisation of the motor can be enhanced.

Fig. 3
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Measured power consumption during hole doff with respect to speed and power. (after optimisation of speed curve)

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Fig. 4
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Measured power consumption during hole doff with respect to speed and power. (before optimisation of speed curve)

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For every Ring frame and Speed frame machines, there is an over head travel cleaning device (OHTC) installed to blow and suck the cotton flies sediment throughout the machine, which travels from one end to other end of the machine. Instead of continuous running of OHTC from one end to other end of the Ring frame and Speed frame machine, every reversal at end of the machine, OHTC is stopped for 1 min to 5 min. This has given good energy saving without any investment. The detailed study report is mentioned in the Table 8.

Table 8 Power saved after changing power save mode in OHTC of Ring frame machine
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The above referred optimisation technique has been incorporated in all the 22 Ring frame machines. Thus, the energy saved per day for 22 machines is 313.5 kWh.

Alike, this concept has been incorporated in the speed frame machine also. In the Speed frame machine, energy saving per day per machine is 5.4 kWh. Total number of machines available in this mill is 5. Hence, total energy saving per day per 5 machines is 27 kWh.

The Ring frame machine has fan motor, which is used to suck the broken thread while machine is running. Power study has been conducted in fan motor of Ring frame machine by installing energy efficient excel fans (less weight) instead of conventional aluminium fans. (Fig. 5)

Fig. 5
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Energy efficient fan motor vanes installed in Ring frame machine

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Power of the motor, kW

4.0

Conventional fan units/h, kWh

3.6

Energy efficient fan units/h, kWh

2.75

Energy saving/day/machine, kWh

20.4

Energy saving/day/22 machines, kWh

448.8

It was noticed in the mills that the empty cops and spindles were old one for ten of the machines. The empty spool (generally it is called as cops. This is the plastic component, where the thread wound over it while machine is running) and spindles (this is the mechanical component which is coupled through the belt drive from the motor shaft for spinning the yarn) are the resulting components of Ring frame machines, which are used to spin the yarn. By replacing less weight spindles and empty spool will give the energy savings in Ring frame machines. However, the same had not been tried in this mill.

Air leakage noticed in most of the machines during power audit. Air leakage observed in the machines, wherever the air hoses had been connected for machine application in particular for automatic doffer and top arm for individual spindles. By replacing the new hose and joints, air leakage inside the machines will reduce the compressor ON time, which saves compressor energy (Fig. 6).

Fig. 6
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Compressor hot air duct is near to Speed frame machine

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Energy Saving in Humidification Plant

In the mills humidification plant is installed for maintaining the RH (relative humidity) and temperature for processing the yarn. As the numbers of motors are more, there is a towering of scope in energy saving in this zone. Individual motor study had been conducted in humidification plant and found that the motors were loaded greater than rated power. Also, the power factor of the individual motor looks as to be poor in humidification plant.

In this mill, there were four plants to maintain the relative humidity in the spinning mill. The power study had been conducted for individual motors in all the four plants. Tables 9, 10 and 11 exemplify the motor load pattern in humidification plants. The load pattern of the motor was considered as 92 % maximum. During the power study if the load percentage of the motor load increased to greater than 92 %, the same were marked as over loaded. The power study had been taken for complete mill plant.

Table 9 Actual power consumption of the humidification plant motors (plant A): this plant for preparatory section
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Table 10 Actual power consumption of the humidification plant motors (plant B): this plant for combed sliver system
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Table 11 Actual power consumption of the humidification plant motors (plant C): this plant for Ringspinnig system and autoconer section
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By servicing and optimising the motors which are marked as over loaded, considerable power saving will be achieved. The same are illustrated below.

Plant A, kWh/h

4

Plant B, kWh/h

4.14

Plant C, kWh/h

6.01

Plant D, kWh/h

0.07

Total units saved/day, kWh/day

341.28

Put together, 341 units per day can be saved.

Energy Saving in Compressor

In this mill, reciprocating compressor of 500 cfm is used for operating the machine. Following are the compressor details.

Motor power, kW

93

Compressor cooling motor, kW

5.5

Chiller fan motor, kW

1.6

Compressor loading time, s

62

Compressor unloading time, s

19

Power study had been conducted before tuning of ON and OFF time in the compressor. While conducting power study on the cooling motor, it overloaded by 1.36 kW (considered 92 % is the maximum load).

Compressor power, kWh

76.56

Cooling motor, kWh

6.42

Fan motor, kWh

1.1.4

After tuning compressor ON and OFF time (6 and 7 bar, respectively) by correcting the air leakage inside the plant and machines, following are the power savings obtained. As well, the overloaded motor bearing had been changed, as the drive end bearing failed.

Compressor power, kWh

71.56

Consequently, 6.36 kWh/h had been saved by doing the above exercise. Hence, 152.64 kWh would be saved per day.

Heating Lamp Removal

In the speed frame machine, to avoid over lapping of the sliver (thick yarn), heating lamps are used for increasing the temperature. 8 incandescent lamps were used for a machine (power 1 kW/lamp). Total numbers of speed frame machines available in the mills are 6. On an average, the heating lamp would be switched on about 3 h/day when the RH % is worst.

kWh consumed for heating lamp/machine/3 h

24

kWh consumed for heating lamp/6 mc/3 h

144

Through circulating hot exhaust air of the compressor, heating lamp has been switched off. Hence, 144 units had been saved per day.

Summary of the Study

The energy study had been conducted in the textile mill for productive and non-productive machines. After conducting power audit, total energy saving per month in textile mill is as given in Table 12.

Table 12 Total energy savings/month
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In accordance with the above table, 56,053 kWh is saved per month. Considering unit cost of Rs. 4.50, total amount Rs. 2,52,239 had been saved during month.

Conclusion

In India, there are many textile industries. Hence, by incorporating the above technique in all the textile mills, ample energy can be saved. In general, most of the mills have not included renewable energy techniques in productive and non-productive machines. By means of adopting these techniques, significant energy saving can be realised.