LPG price is becoming costlier day by day. PCRA has been propagating energy efficient cooking at different forums – ladies clubs, industrial workshops, different fairs organized by local bodies, yet mass awareness is far from reality. Availability of non ISI stoves is the real cause of collosal gas wastage. To prevent it immediate banning of these non-ISI stoves is required.
Problem identification: A large section of housewives use ISI make two or three burner type cooking range – where burners are designed for blue flame having high flame temperature and CO content. PCRA message for efficient gas uses are:
- Cut all vegetables, fish etc., before starting cooking.
- Reduce the gas flow to minimum when boiling starts.
- Use always pressure cooker/pressure pan for cooking.
- Try to eat at a time with all family members to save gas.
- Soak rice with water for one hour prior to cooking.
- Use solar hot water for bath and cooking.
Many households adopt above techniques in their daily life, but one disadvantage of the above system is that processing time gets longer and longer. That is why in modern households the cooking assistants employed by the owners or housewives shorten the time by increasing gas flow. The reason is their attitude for quick completion. There efficiency is sacrificed.
In the street corner, the restaurants or road side food joint waste gas because of their non-ISI large size burners with reducing flame shape – and that is why thermal efficiency drops to even 20%. The picture shows the flame of one street food joint.
BIS marked stove
The BIS marked stoves have high thermal efficiency of 72% and more as per the specification, but in household it is not maintained.
Structure of flame: The size and shape of flame depend on type, namely, premixed and diffusion, laminar and turbulent and also on the basis of burner dimension.
The burner has a nozzle diameter ‘d’. The distance covered by initial boundary of flame is ‘Li’ and may be called the zone of complete combustion. In case of laminar flame the inflammation zone is sharply pointed and that has a thin surface (flame front), under turbulent condition the flame front is is wide as shown ‘б’. The distance between visible front and flare tip ‘Ls’ represents boundary of complete combustion .The most intense combustion takes place in flame front while the process is much slower in the zone ‘Ls’ where diffusion of some air from atmosphere is involved .Thus the total flame length is Lf= Li + б +Ls , Lf increases with gas velocity, and nozzle diameter.
Kitchen LPG oven: In ‘kitchen LPG OVEN’ simple laminar diffusion flame is shown, fuel gas and air flow separately but at the linear velocity through two concentric tubes, the inner tube supply the fuel jet. The mixing between fuel and air is possible by molecular diffusion or eddy diffusion. When air is excess, gas and air diffusion continues. A novel flame has a shape of (a) or over ventilated, this flame turns to bell shape when fuel in excess.
The roti and vegetable making process is highly inefficient, there is no flame management.
The basic problem lies in this area where due to public demand gas burner efficiency is sacrificed.
Solution: The new generation gas burner
Japan has developed new gas burner to prevent gas wastage. The picture of the burner is shown hereafter.
- Thermal efficiency approx. 56% (new Japanese burner)
- Thermal efficiency approx. 46% (old household burner)
- The high efficiency burner inward-facing flame in the inner burner quickly and efficiently heats the entire pot.
- The flame shape of domestic LPG burner is shown in following photo.
This flame is radiating heat to outside, as a result efficiency drops. Normally flat surface ‘kadai’ is suitable. Here excess air % is high.
Impact of Japan make high efficiency burner to Indian economy
The predicted rise of thermal efficiency and phase wise replacement of low thermal efficiency non-BIS county make stoves will cut gas consumption to a value of 10% from existing 26.33 million metric ton.
Dr. Shivaji Biswas is the Ex -Director of National Productivity Council, Kolkata. He is also the Proprietor of DS Cube Energy and Enviro Consultants.