How do the 63 kilovolt-ampere (kVA) and 100 kVA coal gasifier and generator projects for a tea factory compare on coal, diesel, power and payback?

The larger coal gasifier set in the Bureau of Energy Efficiency (BEE) Jorhat reports, 100 kVA, makes 288,000 kilowatt hours a year and saves 205 tonnes of coal, against 181,440 and 137 tonnes for the 63 kVA set. It also burns about 50% more diesel for each kilowatt hour made.

What the project is, in plain words

A gasifier heats coal with very little air, so the coal gives off a burnable gas instead of burning outright. The gas feeds a diesel generator that has been changed to run on gas and diesel together (dual fuel), so it needs less diesel. A kVA is the size rating of a generator, like the engine size on a car.

Two more things happen in the reports. The hot exhaust of the generator warms the drying air, and the coke left after gasification is burnt in the dryer's air heater instead of coal. So the factory gets power and saves coal from one plant.

The two sizes side by side

• 63 kVA set: coal use falls from 238 to 200 kilograms an hour, 38 saved, which is 136,800 kilograms over 3,600 hours. Power made 50.4 kilowatts (kW), 181,440 kilowatt hours (kWh) a year. Extra diesel 2.5 litres an hour, 9,000 litres a year. Net benefit 16.25 lakh rupees (Rs) a year, where a lakh is 100,000. Cost Rs 18.72 lakh, payback 1.15 years.
• 100 kVA set: coal falls from 374 to 317 kilograms an hour, 57 saved, 205,200 kilograms a year (the coal table prints 205,000, while the money and carbon dioxide lines use 205,200). Power made 80 kW, 288,000 kWh a year. Extra diesel 6 litres an hour, 21,600 litres a year. Net benefit Rs 22.48 lakh a year. Cost Rs 23.08 lakh, payback 1.03 years.
• Both assume the set runs 3,600 hours a year, the same hours as the dryer, with power valued at Rs 7.45 a kWh, coal at Rs 4.50 a kilogram and diesel at Rs 38 a litre.
• Coal saved is 16% of the coal burnt for the 63 kVA set (38 / 238) and 15% for the 100 kVA set (57 / 374). The bigger set does not save a bigger share, only more tonnes.

Diesel per unit of power is not the same

The 63 kVA set burns 2.5 litres for 50.4 kW, which is 0.050 litres for each kWh. The 100 kVA set burns 6 litres for 80 kW, 0.075 litres for each kWh, about 50% more. The reports do not explain the difference, so ask the supplier what diesel share you should expect at your load.

Diesel takes 17% of the gross benefit in the 63 kVA case (Rs 3.42 lakh of Rs 19.67 lakh) and 27% in the 100 kVA case (Rs 8.21 lakh of Rs 30.69 lakh). The bigger set still pays back faster, because cost rises 23% (23.08 / 18.72) and net benefit rises 38% (22.48 / 16.25).

Where the reports do not match themselves

• 63 kVA: the summary table gives the project cost as Rs 17.85 lakh. The cost table and the payback use Rs 18.72 lakh. 18.72 / 16.25 = 1.15 years, which is the payback printed. 17.85 would give 1.10.
• 100 kVA: the summary and the cost table give Rs 23.08 lakh, but the benefit table shows Rs 22.05 lakh as the capital cost. The printed payback of 1.03 years fits 23.08 / 22.48. 22.05 would give 0.98.
• The 63 kVA carbon dioxide (CO2) table prints the coal factor as 95.81 kilograms per kilojoule. It only works as 95.81 per gigajoule: 246.94 tonnes / 95.81 = 2,577 gigajoules, or 18.8 gigajoules a tonne of coal.
• The 63 kVA text also says 180,000 kWh a year, while its table gives 181,440. The 100 kVA file also carries a copy of the 63 kVA report ahead of its own, so check which set of figures you are reading.

The carbon dioxide line

• The reports show 410.42 tonnes of CO2 saved for 63 kVA and 610.89 for 100 kVA. They count 1.03 kilograms per kWh for the power made, coal at 95.81 kilograms per gigajoule and diesel at 2.6 kilograms per litre.
• At the factors Senseible uses now, 1.76 kilograms per kilogram of Indian coal, 0.675 per kWh of grid power for financial year (FY) 2025-26 and 2.645 per litre of diesel, the net saving is 339 tonnes for 63 kVA and 498 tonnes for 100 kVA. That reading counts every kWh made as grid power replaced.
• If part of your power already comes from a diesel generator, the power made replaces a dirtier source, so the true saving is higher. If you cannot say which, report the grid reading and say so.

The 100 kVA project, line by line

• Power: 100 kVA x 0.8 power factor = 80 kW x 3,600 hours = 288,000 kWh. 288,000 x Rs 7.45 = Rs 21.46 lakh
• Coal: 57 kg x 3,600 = 205,200 kg x Rs 4.50 = Rs 9.23 lakh
• Diesel: 6 litres x 3,600 = 21,600 litres x Rs 38 = Rs 8.21 lakh
• Net: 21.46 + 9.23 minus 8.21 = Rs 22.48 lakh a year. 23.08 / 22.48 = 1.03 years
• CO2 at today's factors: coal 205.2 x 1.76 = 361.2 tonnes; grid power 288,000 x 0.675 = 194.4 tonnes; diesel 21,600 x 2.645 = 57.1 tonnes added. 361.2 + 194.4 minus 57.1 = 498.5 tonnes

These are the reports' printed figures with our own arithmetic on top. Prices are the reports' 2010 prices. The CO2 line is our reading at current factors, not a figure either report prints.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the drop in bought coal and grid power after a gasifier shows on your own bills. Meters for the gasifier's gas output and the generator's hours can be added as a custom service, on request. Meanwhile keep those logs yourself.

• Coal gasification and captive power in a tea factory: the 63 kVA case
• Tea dryer: coal to biomass gasifier and CO2
• Jorhat tea factories: coal, gas and CO2
• Green loan readiness check

Sources: BEE and SAMEEEKSHA detailed project report: coal gasification for thermal and 100 kVA captive generation, Jorhat tea cluster, BEE and SAMEEEKSHA detailed project report: coal gasification for thermal and 63 kVA captive generation, Jorhat tea cluster, CEA CO2 Baseline Database for the Indian Power Sector, version 22.0 (FY 2025-26 grid factor)

Last reviewed 2026-11-07. Costs and paybacks are at the reports' 2010 prices. The diesel per kWh figures and the CO2 reading at current factors are our own arithmetic on the reports' printed numbers. Ask suppliers for a written guarantee of coal, diesel and power at your load.