Does an adjustable gas burner save more on a 200 kg an hour tea dryer than on a 150 kg an hour one, and why is the burner only 20% efficient?

An adjustable gas burner saves 27,000 standard cubic metres (scm) of gas a year on a 150 kg an hour tea dryer and 36,000 on a 200 kg dryer in the Bureau of Energy Efficiency (BEE) Jorhat reports. Both cut gas by about 10%, so the bigger dryer pays back sooner: 0.82 years against 0.97.

Why an old burner wastes gas, in plain words

A burner mixes gas with air and burns it to heat the air that dries the tea. If the mix is wrong, extra air carries heat straight up the chimney, like leaving a window open while the heater runs. On the old burners the mix is fixed and nobody can adjust it.

The new burner has its own fan and a knob on the gas line. The operator turns the knob until the flame goes bluish, which the report takes as the sign of a good mix, and leaves it.

The two dryers side by side

• 150 kg of made tea an hour: gas 76.5 scm an hour before (0.51 per kg), 69 after (0.46 per kg). Over 3,600 hours that is 275,400 scm falling to 248,400, a saving of 27,000 scm. At 8.30 rupees (Rs) a scm that is Rs 2.24 lakh a year, where a lakh is 100,000. Cost Rs 2.17 lakh, payback 0.97 years.
• 200 kg an hour: gas 102 scm an hour before, 92 after. 367,200 scm falling to 331,200, a saving of 36,000 scm. Rs 2.99 lakh a year. Cost Rs 2.46 lakh, payback 0.82 years.
• Burner price: Rs 1.87 lakh for the 150 kg dryer and Rs 2.14 lakh for the 200 kg dryer. The saving per kg of tea is the same, 0.05 scm. The bigger dryer simply makes more tea over the same hours, while the burner costs about 14% more.
• Both reports run the dryer 12 hours a day for 300 days, 3,600 hours a year, and take natural gas at 9,400 kilocalories a scm.

Is the burner really only 20% efficient?

Both reports call the 19.82% the operating efficiency of the natural gas burner, and they show the sum. It counts only the heat that dries the leaf, against the heat in the gas. On the report's sum, about one part in five of the gas heat goes into drying the leaf. Taking 1.45 kg of water out of the leaf for each kg of made tea needs about 885 kilocalories. The report rounds that up to 950 kilocalories a kg to be safe. The gas burnt gives 0.51 x 9,400 = 4,794 kilocalories a kg. So 950 / 4,794 = 19.82%: about one part in five of the gas heat does useful drying.

With the new burner it is 950 / (0.46 x 9,400) = 21.97%. The reports call this an improvement of 2.15, and mean percentage points of efficiency. That is 21.97 / 19.82 = 10.8% more useful heat from each scm, which matches the 10% less gas. It does not mean gas use falls by 2.15%.

The rest of the heat still leaves with the exhaust air and through the dryer walls. The burner swap does not touch that.

The carbon dioxide line

• The reports show 59.57 tonnes of carbon dioxide (CO2) a year for the 150 kg dryer and 79.43 tonnes for the 200 kg dryer. Both use 56.06 kilograms per gigajoule.
• At the 2.05 kilograms per scm that Senseible uses for natural gas, the same gas saving is 27,000 x 2.05 = 55.4 tonnes and 36,000 x 2.05 = 73.8 tonnes. The reports' figures are about 8% higher. The reason is the factor: 9,400 kilocalories is 39.35 megajoules, and at 56.06 kilograms per gigajoule that is 2.21 kilograms per scm, against 2.05.
• Which one your buyer accepts depends on the factor the buyer names. State which you used.

How to check it on your own dryer

1. Before fitting, log scm of gas and kg of made tea per dryer for two weeks.
2. After fitting, log the same for two weeks at similar leaf moisture.
3. Compare scm per kg of made tea, not monthly gas totals, which swing with the crop.

Both dryers, line by line

• 150 kg dryer: 0.05 scm x 150 kg x 3,600 hours = 27,000 scm. 27,000 x Rs 8.30 = Rs 224,100. 2.17 / 2.24 = 0.97 years
• 200 kg dryer: 0.05 scm x 200 kg x 3,600 hours = 36,000 scm. 36,000 x Rs 8.30 = Rs 298,800. 2.46 / 2.99 = 0.82 years
• Efficiency now: 142,500 kilocalories an hour needed / 719,100 supplied = 19.82% (150 kg dryer); 190,000 / 958,800 = 19.82% (200 kg dryer)
• Efficiency after: 142,500 / 648,600 = 21.97%; 190,000 / 864,800 = 21.97%
• CO2 at 2.05 kg a scm: 27,000 x 2.05 = 55,350 kg; 36,000 x 2.05 = 73,800 kg

These are the reports' printed figures with simple arithmetic on top. Gas price and costs are the reports' 2010 prices; check today's gas price and a current quote before relying on the payback.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so a drop after the burner change shows in the factory's monthly figure. Production counters can be added as a custom service, on request. Until then keep kg of made tea beside the bills.

• Efficient gas burner on a tea dryer: the 200 kg case
• Jorhat tea factories: coal, gas and CO2
• Tea factory carbon footprint per kg of made tea
• Green loan readiness check

Sources: BEE and SAMEEEKSHA detailed project report: energy efficient natural gas burner for a 150 kg an hour tea drier, Jorhat tea cluster, BEE and SAMEEEKSHA detailed project report: energy efficient gas burner for a 200 kg an hour tea drier, Jorhat tea cluster

Last reviewed 2026-11-07. Costs and paybacks are at the reports' 2010 prices. The 8% gap to the reports' CO2 figures is our own arithmetic; ask your buyer which gas factor they accept.