Srinivas Shroff - Innovations

Innovating Common cocoon cooking bath

It was say 1998-99, we were finding ways to improve operational convenience of gasifier integrated cocoon cooking oven.

Silk cocoons are immersed in hot water for 30 to 60 seconds in vessel which can hold about 8 to 10 litres of water. About 6 vessels are embedded in an oven. These ovens are biomass fired. The cocoons after processing in hot water, dissolves sericin gum and allows pulling threads in reeling machine. The person ‘cook’ supplies them to the ‘reeler’.

For good performance, silk experts say the temperature should be 90 plus or minus 3 degree Celsius. But with open fired biomass oven it is difficult to maintain the required temperature. We have seen it range from 80 to 97 degree Celsius. If the temperature increases, the threads break that means more joints to be done by the reeler. If the temperature is on lower side, then sericin gum holds the thread tighter, thread breaks, which needs to be joined. 14 parameters reflect quality of silk.

Our gasifier oven had six vessels to mirror the traditional cooking bath, to heat up these vessels, 6 burners. Managing so many burners, air valves was no less than a circus. Even two persons did not seem to be sufficient. Most often we used to have issue with one or the other burner and ended up increased waiting time to the ‘cook’. Though overall time taken and performance was fine, the operators did not feel convenient, and reeler was not confident to depend on only gasifier oven.

Maintaining required temperature has implication on not only reducing wood consumption by 50%, but to our surprise we discovered that it resulted in at least 2 to 3% increase in silk yield, premium on quality by Rs 15 to 25 per kg. Say if a typical reeling unit processed about 100 kg of cocoons, it burnt about 200 to 250 kg of biomass, produced 10 kg of silk and also produced ‘Jute waste’. Jute waste is a raw material for spun silk.

Whenever the gasifier performance was best, all burners are performing well, we could get these results. So Dr Kishore and others said there should be a way to resolve this problem. They asked the team to meet some experts in thermal industry. One team went to meet Kvaerner Powergas a multinational consultancy firm in Mumbai. Myself and Sunil Dhingra were supposed to do the initial scouting. In Coimbatore, we met proprietor of Jaya Boilers. An old man in his late seventies may be. He listened to us, about our work, the structure of oven etc. and the problem. We said the major problem is inconsistency in temperature profile we get.

He asked us why should you have six different vessels? Why can’t you put a large vessel filled up with water and reelers process cocoons in it. Thereby perhaps you can just use one burner. The solution appeared to us and we got back to team and discussed it further.

Then there was brainstorming on common vessel with partition to make it into six, then the bath. Then we analysed work and motion study to understand flow of cocoons, decided on having just 4 partitions. The system worked. We could provide consistent heat with just one burner and cater to the cocoon cooking with four vessels! In fact, just the common cooking bath can provide 50% of the benefits of a gasifier integrated cocoon cooking oven. We applied for patent and received patent to the ‘Gasifier integrated common cocoon cooking oven’. The innovation was also identified as one of the top 50 best renewable energy technologies and given ‘Energy Globe Award’.

2. Innovating improved cookstove to also to generate hot water from chimney flue gases through simple Tube in Tube Heat Exchanger

In most Indian rural houses, there is more than one stove. One stove in kitchen to cook food, one in bathroom to heat up water and one to prepare food for cattle if they have cattle.

Though the quantity of biomass consumed vary, on an average a stove in kitchen burns about 2,000 kg of biomass in a traditional cookstove and a stove in bath room burns about 600 kg of biomass annually.

There were over 100 models of improved biomass cookstoves world over claim to reduce biomass consumed by half at least vis-à-vis conventional cookstoves. They often have two pot facility with a chimney to take the smoke out of kitchen. These chimneys are made of asbestos. A biomass cookstove has an efficiency of just 8% or so. One third of heat is lost to the ground, one third through the fire openings, and another one third is lost through flue gases in Chimney. The improved cookstoves double the efficiency, reduce the biomass burnt by half, but still there is enormous potential to make use of heat.

Scientists across the globe feel efficient biomass stove is more carbon neutral than exhaustible gaseous and other fuels, and aimed at producing user friendly, more efficient stove.

We trialled if we can make use of the chimney flue gases using a tube in tube heat exchanger and heat water, and eventually avoid use of another stove in the bathroom. We succeeded in making few pilots. Spin off of this experiment is its adoption use in cocoon cooking stoves in Siddlaghatta area.