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PlantBench / Dehydrator energy per pound of water

What does it cost to remove a pound of water in an industrial dehydrator?

Water removed per pound of fresh input is 1 - (1 - Mi) / (1 - Mf), with both moistures on a wet basis. Dollars per pound of water are that result times a specific energy, priced at the EIA 2025 U.S. industrial natural gas price. Each energy figure below keeps the label of the page it came from. This note does not publish a payback.

Quick answer

Water removed per pound of fresh input is 1 - (1 - Mi) / (1 - Mf). Onions, raw, are 89.11 g water per 100 g in USDA SR Legacy. At an example final moisture of 4 g per 100 g, that row removes 0.8866 lb of water per lb of fresh input. The 4% final moisture is an example input, not a standard.

At 100.00 °C the NIST Chemistry WebBook saturation enthalpies differ by 2,256.40 kJ/kg. On the International Table factor of 2.326 kJ/kg per Btu/lb, that is 970.08 Btu/lb. A running dryer also heats the product, the makeup air, and the exhaust, and it runs fans, so its fuel use sits above that floor.

Dollars per pound of water = (Btu per pound of water ÷ 100,000) × dollars per therm. The EIA 2025 U.S. industrial price is $5.23 per thousand cubic feet. At 1,036 Btu per cubic foot, that is 10.36 therms per Mcf and $0.5048 per therm. The cost table uses that price on each source's own figure. It is not a PlantBench average.

How much water leaves a pound of fresh input?

Mi is the water in the fresh product, as a fraction of its weight. Mf is the water left in the dried product, as a fraction of the dried weight. Both are wet basis. Dry solids in one pound of fresh input are 1 - Mi. The dried weight that still holds those solids is (1 - Mi) / (1 - Mf). Water removed per pound of fresh input is 1 - (1 - Mi) / (1 - Mf).

The water column is USDA FoodData Central, SR Legacy, nutrient Water, number 255, grams per 100 grams, publication date April 1, 2019. Onions, raw (NDB 11282, FDC 170000) are 89.11 g. Carrots, raw (NDB 11124, FDC 170393) are 88.29 g. Apples, raw, with skin (NDB 09003, FDC 171688) are 85.56 g. Potatoes, flesh and skin, raw (NDB 11352, FDC 170026) are 79.25 g. The final column is 4 g per 100 g on every row. That 4% is an example input, not a USDA standard and not a dryer setpoint.

Two published descriptions use the same round figure for a finished dry product. Lund and Lienau, in the 1994 onion-dehydration report, describe plants "reducing the moisture from around 83 percent to 4 percent." USDA SR Legacy lists Carrot, dehydrated (NDB 11683, FDC 170500) at 4.0 g water per 100 g. Apple and potato use 4% only so the table has one final moisture. Replace it with the moisture the plant actually dries to. The 83 percent in the onion paper is that paper's fresh-onion description. It is not the USDA onion row.

Wet basis. Final moisture is 4 g per 100 g on every row, an example input, not a standard. Water removed per pound of fresh input is 1 - (1 - Mi) / (1 - Mf).

USDA SR Legacy water and water removed at an example final moisture of 4 grams per 100 grams
ItemNDBWaterExample finalWater removed
Onions, raw1128289.11 g4 g0.8866 lb/lb
Carrots, raw1112488.29 g4 g0.8780 lb/lb
Apples, raw, with skin0900385.56 g4 g0.8496 lb/lb
Potatoes, flesh and skin, raw1135279.25 g4 g0.7839 lb/lb

What is the least heat the water itself requires?

At 100.00 °C and 1.01418 bar, the NIST Chemistry WebBook saturation properties for water, default reference state, list a liquid enthalpy of 419.16616 kJ/kg and a vapor enthalpy of 2,675.5699 kJ/kg. The difference is 2,256.40 kJ/kg. The page's equation of state is the IAPWS Formulation 1995 of Wagner and Pruss. That difference is the latent heat of vaporization at that state. It is the heat to vaporize water that is already at the boiling point. It is not a dryer measurement.

NIST Special Publication 811, Appendix B.9, lists the International Table conversion as 2.326 × 10³ joules per kilogram per Btu per pound. Dividing 2,256.40 kJ/kg by 2.326 gives 970.08 Btu/lb. The cost lines use that Btu, because EIA's therm is 100,000 Btu. The same WebBook state printed in Btu/lbm is 180.32996 Btu/lb liquid and 1,151.06 Btu/lb vapor, a difference of 970.73 Btu/lb. This page does not put 970.73 into the cost table. The two Btu figures are two unit conventions on one enthalpy difference.

A belt dryer uses more fuel than that floor. The July 15, 2016 Food Manufacturing article lists four heat loads: warming up the product, evaporating water from the product, heating the makeup air, and steady-state heat losses. The same article says "the energy required to change liquid water into vapor is about 2,350 kJ/kg of water evaporated (the value varies very slightly with temperature)." That 2,350 kJ/kg is the article's phase-change figure. It is not the NIST difference, and it is not a measured dryer total. Fans are a separate electrical load. The onion paper states them apart from the fuel figure quoted below.

What do the published dryer figures actually say?

Lund and Lienau, Onion Dehydration (Geo-Heat Center technical report, July 1, 1994), describe continuous belt dryers on onions. One sentence states: "These plants produce 2.25 million kg of dry product per year using from 35 - 46 MJ/dry kg produced (+14 MJ/kg of electrical energy), or 9.3 MJ/kg of water evaporated." A later paragraph, about the single-line dryer the paper names, states about 530 GJ/day "using approximately 35 MJ/kg of dry products" and "This is estimated to cost 11 cents per kg of finished product." The 11 cents is the paper's estimate for finished product. This page does not use 11 cents as today's price. The same section says dryer-motor electricity "amounts to 2.30 MJ/kg of finished product and increases to about 14 MJ/kg when all electrical requirements are considered." Those electrical figures are per kilogram of product. This page does not divide them into kilowatt-hours per pound of water.

The Food Manufacturing article of July 15, 2016 says: "Typically, dryers will use between 3,000 kJ/kg and 4,500 kJ/kg of water evaporated. A poorly-operated or poorly-designed dryer might even use much more." The article is about an extruded product. The byline identifies the author as process development manager at Bühler Aeroglide. The 3,000 and 4,500 are that article's band. They are not a fruit or vegetable belt-dryer survey, and this page does not average them with the onion paper.

Masanet, Worrell, Graus, and Galitsky, LBNL-59289-Revision (March 2008), an ENERGY STAR guide, report a British Sugar beet factory in Wissington: "Each screw press had specific energy use of 23 kilojoules (kJ)/kg of water removed, compared to a specific energy use of 2,907 kJ/kg for the rotary dryer." The 2,907 is that rotary dryer, on beet pulp, as the guide reports it. The 23 is the screw press, which is mechanical dewatering, not a dryer. Neither number is an onion belt dryer.

The same guide's Table 4.7 is in Btu per pound of product output, not per pound of water. It lists drum drying of dehydrated mashed potato flakes at 6,000 Btu of steam, 350 Btu of electricity, and 6,350 Btu total, and the prose says the drum drying process "consumes an estimated 6,000 Btu of steam per pound of dehydrated mashed potatoes." The guide also says drying intensities range "from around 1,500 Btu per pound of water in the product to over 28,000 Btu per pound of water in the product (Sikirica et al. 2003)." "Water in the product" is the guide's wording. It is not the same basis as water removed, so those two spans are not in the cost table. The guide says its process tables "might not be representative of operating conditions at any single facility."

The LBNL guide describes heat-pump dehumidifying dryers and does not state a kilowatt-hour per kilogram of water. This page has no sourced electric intensity on a water-removed basis, so it does not add an electric or heat-pump price.

What does a pound of water cost at the 2025 industrial gas price?

The EIA Natural Gas Industrial Price, annual series N3035US3, is $5.23 per thousand cubic feet for the United States in 2025. The release date on that table is September 30, 2026. The EIA heat-content table for gas delivered to consumers is 1,036 Btu per cubic foot for the United States in 2025, same release date. One thousand cubic feet at 1,036 Btu per cubic foot is 1,036,000 Btu, which is 10.36 therms, because a therm is 100,000 Btu. $5.23 divided by 10.36 is $0.5048 per therm.

EIA's FAQ on this conversion says that in 2025 the heat content delivered to end-use sectors "averaged about 1,037 Btu/cf" and that dollars per Mcf divided by 10.37 equals dollars per therm. The worksheet uses that 10.37 divisor when a state is selected. This page's worked price uses the 1,036 Btu per cubic foot series instead, and says so. With no state selected, the worksheet gas price is $0.95 per therm. That $0.95 is a planning rate. It is not $5.23 per Mcf and not $0.5048 per therm.

Dollars per pound of water = (Btu per pound of water ÷ 100,000) × $0.5048 per therm. Btu per pound is the source's kJ/kg divided by 2.326. Each row is that source's figure at this gas price. Reading across the rows is a sensitivity table. It is not a range this site measured.

Each row is that source's figure. Dollars per pound of water = (Btu per pound ÷ 100,000) × $0.5048 per therm. Btu per pound is kJ/kg divided by 2.326. $0.5048 per therm is $5.23 per Mcf divided by 10.36.

Specific energy and gas cost per pound of water at the EIA 2025 industrial price
FigurekJ/kg waterBtu/lb water$/lb water
Latent heat at 100.00 °CEnthalpy of vaporization. Not a dryer.2,256.40970.08$0.0049
Beet-pulp rotary dryer2,907 kJ/kg of water removed at British Sugar, Wissington. Not a fruit or vegetable belt dryer.2,9071,249.79$0.0063
Extruded-product dryer, low endThe article's low end: 3,000 kJ/kg of water evaporated. An extruded product, not a stated fruit or vegetable belt dryer.3,0001,289.77$0.0065
Extruded-product dryer, high endThe article's high end: 4,500 kJ/kg of water evaporated. Same article and product as the low end.4,5001,934.65$0.0098
Onion belt-dryer water figureThe paper's figure: 9.3 MJ/kg of water evaporated. Not an average with the other rows.9,3003,998.28$0.0202

How do you enter it on the dehydrator worksheet?

Therms per 1,000 lb of fresh input = pounds of water removed per pound of input × 1,000 × Btu per pound of water ÷ 100,000. One labeled case: the onion row, the example final moisture of 4 g per 100 g, and the onion paper's 9.3 MJ/kg of water evaporated. That case is 0.8866 lb of water per lb of input and 35.45 therms per 1,000 lb of input. The 9.3 is the paper's water figure. The 4% is still an example input. A different final moisture or a different row in the cost table changes the therms.

The dehydrator worksheet starts at 2 therms per 1,000 lb on the current case and 14 therms per 1,000 lb on the projected case, and at 12 kWh and 35 kWh per 1,000 lb. Those four intensities are worksheet assumptions, not the mass balance above. Type a therm figure you can label into the gas fields. Leave the kilowatt-hour fields at a measured plant figure. This page does not fill them.

Yield points recovered are saleable pounds you keep, on an input-weight basis. Water driven off is not a yield gain. Drying lowers finished weight. Do not type the water-removed fraction into Yield points recovered. Payback, NPV, and IRR stay blank until equipment cost is entered. This page does not estimate that cost.

Turn water removed into therms on the dehydrator worksheet

  1. 1. Set the two moistures. Read initial water from a plant test or from a USDA SR Legacy row. The table uses 89.11, 88.29, 85.56, and 79.25 g per 100 g for onion, carrot, apple, and potato. Set the final moisture the plant dries to. The 4 g per 100 g column is an example input, not a standard.
  2. 2. Compute the water removed. Water removed per pound of fresh input is 1 - (1 - Mi) / (1 - Mf), with Mi and Mf as wet-basis fractions. Multiply by 1,000 for pounds of water per 1,000 pounds of input.
  3. 3. Keep the specific energy's label. Use a figure you can cite. The cost table includes the NIST latent heat at 100.00 °C (2,256.40 kJ/kg), the LBNL guide's beet-pulp rotary dryer (2,907 kJ/kg of water removed), the Food Manufacturing article's 3,000 and 4,500 kJ/kg of water evaporated, and the onion paper's 9.3 MJ/kg of water evaporated. Do not average them.
  4. 4. Convert to therms per 1,000 pounds. Divide kJ/kg by 2.326 to get Btu per pound of water. Therms per 1,000 lb of input equal water removed per pound times that Btu figure, divided by 100. The onion row at the example 4% final moisture and the onion paper's 9.3 MJ/kg is 35.45 therms per 1,000 lb.
  5. 5. Type therms, and leave yield as saleable pounds. Enter the therms in the dehydrator worksheet's current and projected gas fields. The sheet's 2 and 14 therms per 1,000 lb are worksheet assumptions. Do not type water removed into Yield points recovered. Yield there is saleable pounds. Kilowatt-hours stay a plant measurement. Equipment cost stays blank until you enter it.

Run it on the worksheet

Questions

What does it cost to remove a pound of water in an industrial dehydrator?

It depends which specific energy you use. At the EIA 2025 U.S. industrial gas price of $5.23 per Mcf, converted at 1,036 Btu per cubic foot to $0.5048 per therm, the NIST latent heat at 100.00 °C (2,256.40 kJ/kg, 970.08 Btu/lb) is one row, and the onion paper's 9.3 MJ/kg of water evaporated is another. Those are the sources' figures at one gas price. They are not a PlantBench average and not a payback.

Is 4% the final moisture a dryer should hit?

No. Four grams per 100 grams is an example input on every crop row so the table has one final moisture. The 1994 onion paper describes finished onions around 4 percent, and USDA SR Legacy lists dehydrated carrot at 4.0 g water per 100 g. Apple and potato do not get a final moisture from either source. Type the plant's final moisture.

Why is a real dryer above the latent heat?

The NIST difference at 100.00 °C, 2,256.40 kJ/kg, is only the phase change for water already at the boiling point. The Food Manufacturing article names four heat loads: warming the product, evaporating water, heating makeup air, and steady-state losses. Fans are extra. The article's own phase-change sentence says about 2,350 kJ/kg. That sentence is not the NIST value.

Does the dehydrator worksheet compute energy per pound of water?

No. You type therms and kilowatt-hours per 1,000 pounds. One worked case on this page, the onion row at the example 4% final moisture and the onion paper's 9.3 MJ/kg of water evaporated, is 35.45 therms per 1,000 lb of input. Yield points on that sheet are saleable pounds, not water driven off. The sheet's 2 and 14 therms are worksheet assumptions.

Why is there no electric or heat-pump example?

None of the sources fetched for this page states kilowatt-hours per pound of water removed. The onion paper's electrical figures are 2.30 MJ/kg of finished product for the dryer motors and about 14 MJ/kg of dry product when all electrical requirements are included. The LBNL guide describes heat-pump dehumidifying dryers and does not give a kilowatt-hour per kilogram of water. This page does not invent that conversion.

Sources

Figures retrieved October 21, 2026.