How much energy does each leather drying method use per kilogram of water, and what does a heat pump change?
The European tanning reference document lists drying energy in megajoules (MJ) per kilogram of water evaporated: toggling 8.17, vacuum 7.20, chamber 5.83 and through-feed 5.22, against a theoretical minimum of 2.48. With a heat pump, the same table gives 1.62 for chamber and 1.12 for through-feed.
The table, MJ per kilogram of water evaporated
- Theoretical minimum: 2.48
- Toggling: 8.17. Pasting: 6.37. High-frequency drying: 6.84 (no heat pump figure).
- Chamber drying: 5.83 without a heat pump, 1.62 with one.
- Vacuum drying: 7.20 without, 1.37 with.
- Through-feed drying: 5.22 without, 1.12 with.
- The document takes these from a 1986 German-language paper, so treat them as old.
Which energy is it?
Without a heat pump the document says the energy is mainly thermal. The exception is high-frequency drying, which uses electricity only. For the heat pump columns it does not say which energy is counted.
My reading: the heat pump figures sit below the 2.48 theoretical minimum, which is possible when they count only what the heat pump draws, because a heat pump delivers more heat than the electricity it uses. If so, a heat pump moves energy from a fuel invoice to the electricity bill. Confirm with the maker before you plan the Scope 1 and Scope 2 change.
When the document says a heat pump pays
It says generating heat with heat pumps is normally only economical when the price of a gigajoule (GJ) of electricity is less than 2 to 2.5 times the price of a GJ of heat from fuel. Work that ratio out from your own bills before you ask for quotes.
Cheaper steps the document names first
- Squeezing out more water in samming before drying can save 0.5 to 1 GJ per tonne of raw hide in drying.
- Up to 75% of the waste heat from drying may be recovered with heat exchangers.
- Clean cooling water from a vacuum dryer, fed into the hot water supply, may recover 10 to 20% of the vacuum drying energy.
- Natural drying uses the least energy, but needs time and a favourable climate.
Example: 1,000 kilograms of water evaporated in a chamber dryer
- Without a heat pump: 5.83 x 1,000 = 5,830 MJ
- With a heat pump: 1.62 x 1,000 = 1,620 MJ, which is 4,210 MJ less, or 72.2%
- Vacuum: (7.20 minus 1.37) / 7.20 = 81.0% less. Through-feed: (5.22 minus 1.12) / 5.22 = 78.5% less
- If the 1,620 MJ were all electricity (an assumption): 1,620 / 3.6 = 450 kilowatt hours (kWh) x 0.675 kilograms of carbon dioxide (CO2) per kWh for financial year (FY) 2025-26 = 303.8 kilograms (kg)
Table values are the document's, from 1986 literature. Your dryer, leather and load will differ; measure your own fuel and kWh per month before and after.
What Senseible does here
Senseible reads fuel invoices and electricity bills into records by billing period, so a before and after comparison of fuel and kWh is on file. It does not meter a dryer or measure water evaporated.
Sources: European Commission, Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Tanning of Hides and Skins, February 2003 edition (filed by the publisher as superseded), CEA, CO2 Baseline Database for the Indian Power Sector, version 22.0
Last reviewed 2026-11-06. Figures are from the February 2003 edition of the European tanning reference document, which the publisher files as superseded; its energy and effluent tables rest on European tanneries and on older studies. Check the current edition and your own records before you quote a number to a buyer.