For a Kochi seafood freezer, does an absorption machine fired on biomass briquettes or on liquefied natural gas (LNG) pay back faster, at 50 and 150 tonnes of refrigeration (TR)?

In four Bureau of Energy Efficiency (BEE) Kochi reports, a biomass-fired absorption freezer costs rupees (Rs) 79.11 lakh at 50 TR and Rs 155.83 lakh at 150 TR and pays back in 3.14 and 3.26 years. The LNG versions take 3.86 and 4.21 years, and their printed carbon dioxide savings do not hold up.

The four reports side by side

• 50 TR on biomass briquettes: cost Rs 79.11 lakh, saving Rs 25.22 lakh a year, payback 3.14 years. Electricity falls from 1,039,500 to 81,648 kilowatt hours (kWh) a year; briquettes burnt 785 tonnes. Printed carbon dioxide (CO2) saving 776 tonnes.
• 50 TR on LNG: cost Rs 80.28 lakh, saving Rs 20.82 lakh, payback 3.86 years. Same electricity. LNG 14,508 million British thermal units (MMBTU). Printed CO2 saving 509 tonnes.
• 150 TR on biomass: cost Rs 155.83 lakh, saving Rs 47.83 lakh, payback 3.26 years. Electricity 2,463,300 to 142,800 kWh; briquettes 2,280 tonnes. Printed CO2 saving 1,879 tonnes.
• 150 TR on LNG: cost Rs 147.59 lakh, saving Rs 35.04 lakh, payback 4.21 years. LNG 42,160 MMBTU. Printed CO2 saving 1,103 tonnes.
• All four price power at Rs 5.50 a kWh and briquettes at Rs 3,500 a tonne with a heat value of 4,660 kilocalories (kcal) a kilogram. LNG is Rs 220 a MMBTU in the 50 TR report and Rs 219.60 in the 150 TR report. Each says 21 days of down time.

Why biomass wins on rupees

Both versions need the same heat. At 50 TR it is 3,656,016,000 kcal a year, and at 150 TR 10,624,320,000. The briquette bill is Rs 27.46 lakh against an LNG bill of Rs 31.86 lakh at 50 TR, and Rs 79.80 lakh against Rs 92.58 lakh at 150 TR. Capital cost differs little (Rs 79.11 and Rs 80.28 lakh at 50 TR; Rs 155.83 and Rs 147.59 lakh at 150 TR), so the gap in payback comes mostly from fuel price.

Where the reports differ from themselves

• 50 TR LNG: the summary says Rs 20.82 lakh and 3.86 years, the body Rs 20.76 lakh and 3.87 years. The gap is Rs 0.06 lakh in the LNG bill. The report prints Rs 220 a MMBTU, and 14,508 x 220 is Rs 31.92 lakh, which reproduces the body's Rs 20.76 lakh (57.17 minus 31.92 minus 4.49). The annexure prints the bill as Rs 31.86 lakh, which gives the summary's Rs 20.82 lakh. The body's own table prints both a proposed energy cost of Rs 36.35 lakh and a benefit of Rs 20.76 lakh, and 57.17 minus 36.35 is 20.82. Rs 80.28 lakh over Rs 20.76 lakh is 3.87 years.
• Both LNG reports say in their text that the CO2 saving is around 502 tonnes, but their tables print 509 and 1,103.
• The text of the 150 TR LNG report says the annual saving is Rs 25.99 lakh, while its table, payback and cash flow use Rs 35.04 lakh. It also prints the cost as Rs 147.59 lakh in the summary and Rs 147.69 lakh in Annexure 3.

The LNG carbon figure does not hold at the standard gas factor

The LNG tables print three numbers in tonnes of carbon dioxide equivalent: the electricity the old compressors used, the project's LNG plus electricity, and the difference. The electricity line is the kWh times 0.81 kilograms per kWh (842 / 1,039,500 = 0.81). Taking the electricity the new machine still uses off the project line leaves 267 tonnes for 14,508 MMBTU at 50 TR and 776 tonnes for 42,160 at 150 TR. Both are 18.4 kilograms per MMBTU. The reports do not print the gas factor, so we cannot say where 18.4 comes from.

The Intergovernmental Panel on Climate Change (IPCC) default for natural gas is 56,100 kilograms of CO2 per terajoule (TJ) on a net calorific basis. Indian gas is billed in MMBTU on a gross basis, where the live page on LNG invoices uses 53.3 kilograms of CO2 per MMBTU; on a net basis it is 59.2. If the reports' 14,508 MMBTU are gross, that is 773 tonnes, and if net, 859 tonnes (14,508 x 59.2). Either is 2.9 to 3.2 times the 267.

At 50 TR the project then emits 839 to 925 tonnes against 842 before, so it saves about nothing or adds up to about 83 tonnes a year at the report's grid factor, not the 509 printed. At 150 TR, 42,160 MMBTU gives 2,247 to 2,495 tonnes, so the project emits 2,363 to 2,611 against 1,995, about 368 to 616 tonnes more. The increase stands on either basis. This is our arithmetic, treating LNG as natural gas; ask the report's authors which factor and basis they used.

The biomass figures are the electricity saved times 0.81 (957,852 kWh gives 776 tonnes), so the briquette boiler is counted as zero. Today's grid factors on this site are lower than 0.81, so the electricity side of all four savings would also be smaller now.

The 50 TR LNG report, checked line by line

• Steam 780 kilograms an hour at 90 percent loading is 702. Each kilogram adds 658 minus 100 = 558 kcal. Boiler efficiency 90 percent
• Heat in: 702 x 558 / 0.9 = 435,240 kcal an hour. Over 8,400 hours: 3,656,016,000 kcal. Divided by 252,000 = 14,508 MMBTU
• LNG bill: 14,508 x 220 = Rs 31.92 lakh (the annexure prints Rs 31.86 lakh). Power for the new machine: 81,648 x 5.50 = Rs 4.49 lakh. Old power: 1,039,500 x 5.50 = Rs 57.17 lakh
• Saving: 57.17 minus 31.92 minus 4.49 = Rs 20.76 lakh (the summary, using 31.86, says 20.82). Payback: 80.28 / 20.76 = 3.87 years
• CO2: 14,508 x 53.3 = 773 tonnes on a gross basis, or 14,508 x 59.2 = 859 tonnes on a net basis, against the 267 implied by the report

All figures except the last line are the report's own. 53.3 and 59.2 are the gross and net factors on the live LNG invoice page. The gas check treats LNG as natural gas and is our arithmetic.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so a year of power and fuel bills before a change can be compared once uploaded. Bills show site electricity, not the freezer's alone, so a freezer sub-meter is needed to see its own saving.

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Sources: BEE, Detailed project report: 50 TR vapour absorption on biomass, Kochi seafood cluster (SAMEEEKSHA), BEE, Detailed project report: 50 TR vapour absorption on LNG, Kochi seafood cluster (SAMEEEKSHA), BEE, Detailed project report: 150 TR vapour absorption on biomass, Kochi seafood cluster (SAMEEEKSHA), BEE, Detailed project report: 150 TR vapour absorption on LNG, Kochi seafood cluster (SAMEEEKSHA), IPCC 2006 Guidelines, Volume 2 chapter 2: Stationary Combustion (Table 2.3, natural gas)

Last reviewed 2026-11-05. Report figures are from BEE's Small and Medium Enterprises (SME) programme project reports, at the report year's prices. Check today's briquette and gas prices, a current quote and the current grid factor before you rely on the payback or the carbon saving.