ENERGY SAVING IN TEXTILE PROCESSINGNandish Mehta (Technical Director) Harish Enterprise Pvt. Ltd. Introduction: Cost of energy in Textile processing is a major factor, next only to the chemical cost and hence every processing unit strives to adopt ways and means best known to them to minimise the energy cost. An attempt is made here to provide practical tips and a ready reckoner for making investment decisions related to energy saving. 1.0 Basic Fuels Energy is consumed in processing units either in the form of fuel or in the form of electric power. Several fuels can be used like, furnace oil, cost, husk, natural gas or compressed natural gas stored in bullets. Electric power can be bought directly from electricity Board or self generated through DG Sets or turbines. Table A below compares the cost per kilo calorie of each fuel. [Figures are based on actual situation in Tarapur, Surat and Mumbai]. Table A Fuel Furnace Oil Coal Natural Gas Unit Lit Kg M3
Kcal/Unit 9300 4500 8600 860
Boiler Eff. 85% 70% 90% 100%
Price/Unit (Rs.) 15.00 2.20 8.00 5.00
Cost per 1 Lac kilo Cal (Rs.) 189.75 69.84 103.36 581.40
Electric power kWh
Coal is undoubtedly the cheapest fuel available for steam boiler or a thermic fluid boiler even after taking into account extra electric power consumed for larger sized ID fan. As for maintaining precise temperature on a Coal fired thermic fluid boiler, it poses no problem with modern fluidised bed boiler with mechanized coal handling and coal charging equipment available. In Mumbai region where coal is not being permitted, the obvious choice is Natural Gas over furnace oil. In Surat region all the three fuels are available. Coal is the obvious choice for steam Boiler. However there are heated arguments about using a Coal fired thermic boiler or using natural gas directly for stenter and dryers. It would be worth while analyzing the economics of Coal fired thermic fluid boiler Vs. Direct Gas firing in Stenter and Dryers.
2.0 Coal fired Thermic fluid Boiler Vs Direct Gas firing in Stenter / Dryer: Energy Consumed in Stenter: For all practical purpose the average drying capacity in a stenter is 100 kg of water/hr/chamber i. e. 100,000 K. Cal/Hr/Chamber. (This figure is 80 kg of water/hr/chamber and 80,000 kcal/hr/chamber respectively for fine fabric like sari being processed in Surat). Let us consider 2 stenters each of 5-chambers, which is generally the case in most processing units either both using direct firing systems or both catered by a 1 million kcal/hr Coal fired thermic fluid boiler. Case I Direct fired system using natural gas Natural Gas Consumption = 100,000 K.Cal/Hr/Chamber x chambers 8600 x 0.95 (eff) = 122.40 M /Hr. Cost of Natural Gas Electric power Consumed is = Rs. 8 x 122.40 = Rs. 979.20 /hr. = 120 Amps/m/c x 2 m/c x 0.415 x 3 = 172.3 kWh. = 172,3 x 5 = Rs. 861. 54/h. = Rs. 1840.74/h.3
Cost of power Total cost of energy
Case II Coal fired Thermic Fuel system with Oil radiators in stenter Coal Consumption = 100,000 K.Cal/hr/Chamber x 10 Chambers 4500 x 0.70 (eff) x 0.98 (pipe line loss) = 323.93 kgs coal/hr. Cost of Coal Consumed =329.39 x 2.2 = Rs. 712.66 /hr
Power consumption in this system is sum total of power consumed by Thermic Fluid Boiler and power consumed by Stenters. Power consumed by Thermic Fluid Boiler is ID fan Circulation Pump Total Power consumed by Stenter: = 20 HP = 20 HP = 40 HP i.e.30 kWh i.e. Rs 150/ hr. = 140 amp/m/c x 2 m/c x 0.415 x 3 = 201.026 kWh. = 201.026 x 5 = Rs. 1005. 13 /hr = Rs. 712.66 + Rs. 150 .00 + 1005.13 = Rs. 1867.79 /hr. (Power consumed by stenter with Thermic Fluid system is higher compared to direct gas fired system due to Oil radiators offering resistance in Blower Air Circuit. Ideally the Blowers have to be larger in case of Oil radiators in comparison to direct gas fired system for identical drying capacity.).
Cost of power in Stenter Total Energy Cost
Direct Gas fired stenters work out marginally better compared to thermic fluid system for the parameters assumed in above calculation. However, of late imported coal having calorific value of 6000 k cal/kg is available in the market in the same price range. This will change the equation in favour of coal-fired system. Reliability of gas supply too is in question an many units in Surat are experiencing frequent stoppage of gas supplies. 3.0 Means of Energy Saving on Dryer & Stenter The most energy consuming equipments. Drying of Wet fabric consumes the highest energy compared to any other process in textile processing. The known means of extracting water from fabric and the resultant remained water (expression in % is shown in Table B below. Table B Type of Equipment Mangle (Ebonite/Rubber) Mangle (Rubber/ Rubber) Open width Continuous Mangle (Ebonite + + Roberto Roll) Open width Continuous Centrifuge (Hydro Extractor) Rope Batch
Fabric Condition Operation Expression for 100 % Polyester 100% Cotton 65% Poly 35% Viscose
Open width Continuous
65% 70% 60%
55% 60% 52% 1.45 kwh
25% 55% 40% 1.45 kwh
25% 50% 35% 6 kwh
Electric Power Consumed 1.25 kwh For 1000 mets 65/35 suiting 300 gm/i.m. (300 kgs/1000 mts) at 40m/min speed. Cost of Electric power/1000 mts Rs. 6.25
Let us examine the cost of energy on a Cylinder Drying Range for all the above cases. Thermal Energy 300kgx0.6. 900kcal required for 1000 mtrs (300kg) fabric = 16,2000 kcal = 51.4 kg 300kg/0.25x 900 300kgx0.40x 900 300x0.35x 900
Equivalent coal consumption Cost of coal/1000 mtr Total Power & energy cost/1000 mtr
=140,400 kcal = 44.57 kg
= 108,000 kcal =94,500kcal = 34.28 kg =30.00 kg
=Rs.113.05 = Rs.119.33
=Rs. 98.05 =Rs. 105.30
=Rs.75.43 =Rs. 82.68
General tendency of buyers is to pay least attention to a Mangle while buying Cylinder Drying Range. From the table above, one can realise that a good mangle (10 Ton capacity) compared to ordinary (2T) will pay back in less than a years time. It is also worth while to have a hydroextractor if the previous process is in rope form.
Drying on Stenter vs. Drying on Cylinder Drying Range Drying on stenter not only needs thermic energy for heating but also needs electrical energy for blowing hot air on the fabric. This makes the stenter drying the costliest process, Table C below shows comparison between Cylinder Drying and Stenter considering coal as the fuel for Boiler/Thermic boiler together with Electric Power. Table C Cylinder Dryer (16 cyl) Drying speed of 65% poly 35% viscose Suiting with 52% mangle expression (300 gm/lmt) using a Rubber+Rubber Mangle Production in kgs/hr Production in kgs/hr Water to be evaporated Coal Consumption 40 m/min Stenter (5-Chamber) 40 m/min
2400 mts 720-kgs/hr 0.52 x 720 = 374.40 kgs/h 374.40 x 900 4500 x 0.7 = 106. 97 kg
2400 mts. 720 kgs/hr. 374.40 kgs/h 374.40 x 1000 4500 x 0.7 =118.86 kg Rs.261.49 100 kWh x 5 = Rs.500 Rs. 761.49
Cost of /hr Cost of power /hr Total Energy cost/hr
= Rs. 235.33 = 5 kWh x Rs. 5 = Rs. 25.00 = Rs. 260.33
It is obvious form the above cost analysis that it is atrocious to use stenter or any convection dryer for simply drying the fabric. Stenter however is an essential equipment for heat setting and equalising the width. Most processors also use Stenter for final finishing of fabric. Ideally even for finishing the fabric one should pad-dry on Mangle + Drying Range and then only bring on stenter for curing/width equalising and controlling the shrinkage. The cost of this process will work out cheaper as the stenter speed can be increased to 50 m/min for the fabric mentioned in the above example. The exact cost comparison is given in table D below.
Table D (Energy Cost of Finishing Process on 65/35 300-gm/lm suiting). Mangle + Drying Range + stenter Drying speed on Cylinder Dryer Cost of Energy + Power (from Table-C) Speed on Stenter Energy required in one hr. Energy required for 2400 mts. 40 m/min Rs. 260.33 /hr. or Rs.260.33 / 2400 mts 50 m/min 15000 Kcal/ch x 5 =75000 K.Cal =75000 x 2400 ------50 x 60 = 60,000 K.Cal Coal Consumption = 60,000 --------= 19.04 kg 4500 x 0.7 = Rs. 41.89 = 100 Kw x 2400 ------50 x 60 = 80 Kwh. Cost of Power for 2400 mts. Total Energy Cost for 2400 mts. = Rs. 400.00 = Rs. 441.89 33 m/min. 35 x 60 x 0.3 x 100 =630,000 K.Cal. = 630,000 x 2400 ------35 x 60 =7,75,384 K Cal. = 775384 ------ = 246.15 kg 4500 x 0.7 =Rs. 541.54 100 Kw x 2400 -------35 x 60 =114.29 Kwh. =Rs.571 .45 =Rs. 1112.99. Mangle + Stenter NA
Cost of coal / 2400 mts. Power consumption for 2400 mts.
The cost saving is unbelievable and technicians must try to establish finishing process on Cylinder Drying o Range. On cylinder dryer the fabric temperature never reaches above 130 C which is far below the o required temperature of 170 C for polyester t be affected in any way. It is therefore only a myth that o polyester blended fabric will get harsh and shiny when dried on cylinder drying range. Below are some practical measures one may take to minimise energy consumption on Cylinder Drying Range and Stenter. Cylinder Drying Range Precautions on a Cylinder Drying Range to run it efficiently are:
No steam leakages in the pipe line. Good functional steam traps properly maintained, preferably independent steam trap for each cylinder. Recovery of condensate for Boiler feed. Proper tension in the fabric so as to have intimate contact between fabric and cylinder. Uneven tension will form creases as well as reduce drying efficiency. Maintain clean surface of cylinders teflon coated cylinders are recommended.
Stenter: Precautions on a Stenter to run it efficiently are:
Sealing of chambers with proper asbestos rope packing and tightening top, bo