Studies on an energy efficient process with Solar Heating System for Multi-end Silk Reeling
Dr. Subrata Das, Textile/Apparel Product Safety & Factory Compliance in Bengaluru, Karnataka, India is the guest author of this feature and TextileFuture is proud to present it to you
The paper was presented on September 17,2016 at the National Conference Conference on Energy & Environment, organized by IIT Madras and Codissia (September 16-17, 2016) at Codissia Trade Fair Complex, Coimbatore, India by the author and his co-author D. Saravanan and is entitled “Studies on an energy efficient process with Solar Water Heating System for Multi-end Silk Reeling”
Solar energy is a silver lining that helps to reduce the greenhouse effect thereby helping restore ecological balance in our ecosystem. The application of solar energy in energy intensive silk industry has a huge potential. A new energy efficient process has been developed with solar water heating system for multi-end silk reeling, and the energy consumption for cooking and reeling operations is calculated and compared with conventional process. It is found that in conventional process, on an average 570 litres and 1000 litres of water is consumed for cocoon cooking and reeling basins respectively for the production of 10 kg raw silk in 10 basin multi-end reeling unit; hence, a huge amount of firewood is required to produce heat energy for processing. The new energy efficient process with solar water heating system yields a saving of 77.97% firewood consumption compared to conventional process.
Solar energy is vital form of renewable energy that can provide practical solutions mitigating many of the energy related risks to our economy1. India has an abundant solar resource with more than 300 days of sunshine every year. This is equal to over 5000 trillion kWh/year1.
Solar energy is a silver lining that helps to reduce the greenhouse effect thereby helping restore ecological balance in our ecosystem2. The application of solar energy in energy intensive silk industry has a huge potential3,4. Being cottage industry located mostly in villages and towns, the industry depends on firewood and different forms of agriculture residues for energy needs5,
causing serious ecological implications and depriving the soil of valuable nutrients and organic conditioning material6.
It is found that about 20 kg of firewood is consumed for the production of 1 kg raw silk. It is estimated that 145,000 MT/year of fuel wood and 170,000 MT/year of other biomass are consumed for the production of raw silk in India due to the limitation in price and availability of commercial fuels such as coal and LPG7, adding pollution into the ecosystem. The level of energy consumption is very high and energy efficiency is low (~10%)6.
In order to prevent deforestation by reducing the consumption of firewood by multi-end silk reeling activity, in this study an attempt has been made to develop a new energy efficient management process with solar heating system.
Materials and methods
Process of Energy Management
The energy management in the conventional type of multi-end silk reeling unit consists of 100 kg boiler for 10 basins multi-end reeling unit 8,9. The firewood is used to fire the boiler to supply steam for all the activities of reeling, namely to heat water in reeling basin, to bring boiling water temperature for cocoon cooking and to heat air in re-reeling machine. Around 200 kg firewood (mainly tamarind wood) is used to fire the boiler for 10 basin unit, producing 10 kg raw silk per day. Since tamarind wood has greater calorific value of 4000 kcal and above, its demand is more in silk reeling clusters.
It is found that about 570 L and 1000 L of water is consumed respectively for cooking and reeling to produce 10 kg raw silk in 10 basin multi-end reeling unit. The specific heat of water is taken as 1 kcal and ambient temperature is recorded as 25°C.
Steam is used to bring the water temperature of open pan cooking vessels to 80-85°C. Four vessels containing 9 L of water in each vessel are used for the production of 10 kg raw silk in a day. The cooking water of vessels is replaced 3-4 times in a day with fresh water to avoid the effect of turbidity on cooking performance. The energy consumption by 4 cocoon cooking vessels in conventional process is ascertained by allowing boiling water at 90C to cool naturally. The temperature of cooling water was recorded after every 2 min by digital thermometer. It is found that boiling water loses energy by natural cooling at the rate of 5 kcal/L/min. Around 54 L of boiling water gets wasted in normal working hours.
Better reeling takes place in hot water having 40-45°C temperature. The volume of each basin contains around 40 L of water at 40-45°C during reeling. Ten basins require 400 L of water. The steam energy is required to bring entire water of reeling basins to reeling temperature and maintain it during reeling. The natural cooling of hot water takes place in all the basins and steam is used to augment the effect of cooling. It is recorded that the cooling of hot water at 45°C occurs by losing 0.07 kcal/L/min heat energy. By continuous reeling of cocoons, the concentration of dissolved sericin becomes more in basin water, affecting the colour of the raw silk produced. To avoid this effect of turbidity, it is practiced that in a day, 2 times fresh water is filled in basins. It is found that total 1000 L of water is consumed by 10 basins and reeling temperature is maintained at 45°C for 8 h in a day.
The energy consumed by 10 basin multi-end reeling unit for the production of 10 kg raw silk per day in conventional process is ascertained (Table 1).
New Energy Efficient Management Process
To use energy efficiently in combination of renewable solar and fossil energy, a new process model is evolved. The schematic line diagram of energy efficient management layout plan addressing the energy needs of cocoon cooking and reeling basin hot water is shown in Fig. 1.
Fig. 1—Energy efficient process layout Plan for 10 basin multi-end reeling unit
1–Overhead water tank, 2–Insulated solar water tank (1000 LPD), 3–Solar collectors (each 2m2), 4–Insulated hot water additional tank (500L), 5–Chimney to escape smoke, 6–Heat recovery unit (HRU), 7–Insulated 50 kg mini-boiler, 8–Water pump, 9–Ten basin multi-end reeling machine, 10–Insulated cocoon cooling bench, 11–Firewood burning window, 12–Cold water supply, 13–Water supply to solar collectors, 14–Solar hot water supply, 15–Solar hot water supply, 16–Hot water supply to HRU for further heating, 17–Heated water supply from HRU, 18–Hot water supply from additional tank, 19–Hot water supply to insulated bench, 20–Pre- heated water supply to boiler, 21–Hot water supply to reeling basins, and 22–Steam supply to insulated cooking bench]
In this study, smaller type of firewood mini-boiler of 50 kg capacity is used which is fully insulated along with a solar water heating system (SWHS) having 10 Solar collectors of 2 m2 each, heat recovery unit (HRU) and fully insulated cocoon cooking bench.
Results and Discussions
As shown in Fig. 1, the overhead tank supplies cold water to 1000 LPD water tank and by gravitational circulation of water through solar collectors, water gets heated ~65-85C in one full day sunshine in insulated solar tank (1000 LDP). The incidence of solar radiation on each solar panel is 4-6 kW/m2/day2. More number of panels may also be added for better performance of the system. The hot water in solar tank is drawn to additional insulated tank of 500 LPD (or 1000 LPD) in morning or afternoon before starting reeling in order to avoid mixing of cold water in 1000 LPD solar tank during water consumption for reeling. 500 LPD insulated additional tank is connected to inlet and outlet point of a heat recovery unit (HRU), developed by Tata Energy Research Institute (TERI) for further heating through HRU. The HRU is chimney like attachment mounted on the 50 kg capacity mini- boiler’s chimney and it is fully insulated to avoid heat loss that takes place by natural cooling. The HRU recovers energy that is being escaped through the mini- boiler chimney while burning firewood in the boiler. The firewood burning process involves around 55% of energy for generating steam in the mini- boiler and remaining 45% of energy derived gets lost by emitting gases into the atmosphere, viz. carbon dioxide, carbon monoxide, etc.4 HRU helps to recover the energy that is being wasted otherwise. Such recovered energy helps further heating of the water drawn in the additional insulated tank as shown in Fig.1 and this hot water is used for 10 reeling basins and as pre- heated water for boiler and cooking vessels.
The detail of energy consumption in this new energy efficient management process layout plan is shown in Table 2.
Tables 1 and 2 show comparison in terms of energy and firewood consumptions between conventional process and new energy efficient management process. In the conventional process, 113.48 kg of firewood is burnt for cooking and reeling activity for the production of 10 kg raw silk in 10 basin multi-end reeling unit and for similar production under new energy efficient management layout plan it reduces to 25 kg, resulting a saving of 77.97% in firewood consumption. Thus, the new energy efficient management process plan reduces the pollution significantly by reduction in carbon dioxide and other gases emission into the atmosphere, helping to reduce global warming.
The economical benefit, which can be derived by promoting energy efficient management process, is studied. It is corroborated from the data that the total expenditure incurred in the new process, which includes installation of solar water heating system
(Rs 1,20,000), heat recovery unit (Rs 7000), 50 kg mini-boiler (Rs 40,000) and insulated cooking bench (Rs. 17,000), is Rs 1,84,000. The savings from firewood consumption due to use of new energy management process per annum is Rs 79,632.32, which is 77.97% of 113.48 kg firewood @ Rs.3/kg for 300 working days. Thus, the recovery period works out to be 2.31 years by considering the total investment in the new energy management process with respect to the amount saved in the consumption of firewood.
India produces 16,000 MT of raw silk per annum by using conventional energy sources, estimated 1,45,000 MT/year of fuel wood and 1,70,000 MT/year of other biomass. The new energy efficient management process reduces around 70 % CO2 emission into atmosphere. The installation of solar water heating system with heat recovery unit for mini-boiler and fully insulated cocoon cooking bench in the multi-end silk reeling sector is advised to protect our globe from environmental imbalance.
1. Subramanya K, Business Standard (Tata BP Solar India Ltd), June 2008, 3.
2. Brown Eri W, An Introduction to Solar Energy, http://www.ccs.neu.edu/home/feneric/solar.html, 1988.
3. Kumar V J F, Indian Silk, January (1997) 25.
4. Rama Kumar B, Raghu K, Anjaneyulu K S R & Sujatha P, Non-conventional energy for silk industry-Rays of hope, Indian Silk, May (2008) 14.
5. Somashekar T H & Kawakami K, Manual on Bivoltine Silk Reeling technology, JICA, PPP, BST Project (Central Silk Board, India), 2002, 42.
6. Kumar Atul & Kumar Vivek, Energy, Industries and Commerce (The Energy and Resource Institute, New Delhi), 2005, 8.
7. Dhingra Sunil, A Case Study of Silk Industry (The Energy and Resources Institute, New Delhi), 1998, 1.
8. Sonwalkar Tammanna N, Hand Book of Silk Technology (Wiley Eastern Limited, New Delhi), 1991.
9. Kim B H, Raw Silk Reeling (Associated Business Centre Limited, Colombo), 1989.
Authors are thankful to Mr. Iyaz Pasha, Owner, a Multi-end Reeling Unit, Siddlaghatta, Karnataka, India for extending support to conduct trials. Thanks are also due to TATA BP Solar India Ltd., Bangalore, for helping to install the solar water heating system and to M/s. Hitze Equipments (India) Pvt. Ltd, Bangalore, India for providing insulated 50 kg mini-boiler and developing an insulated cocoon cooking bench.