Mills that make their own power: energy, water and the recovery boiler

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Metsa Group says its Kemi pulp mill in Finland generates 2.5 times the renewable electricity it consumes in a year ¹. The fuel is the dissolved wood in the cooking liquor, called black liquor. This post follows that fuel through the recovery boiler, and also looks at water, mill by mill, and at the first trials to capture carbon from the stack.

Published October 27, 2026 · Facts as of October 27, 2026 · 10 min read · Sources listed at the end

Facts as of October 27, 2026. This page states the facts as they stood on that date. Figures, rules and company plans may have changed since publication. We review this guide every six months and update the pages.

250%Electricity self-sufficiency stated by Metsa for its Kemi mill in Finland, which started in September 2023 ¹

7,000 tonsDry solids a day that the recovery boiler at Suzano's Imperatriz mill in Brazil can burn, per Valmet ²

Over 100 to 10Cubic meters of water per ton of pulp: Metsa's figure for mills before the 1970s, and its design value for Kemi ³

66%Share of fuels used by the whole European pulp and paper industry that came from biomass in 2024, per Cepi ⁴

The 60-second version

What is it?

In the kraft process, wood chips are cooked in a chemical solution. The liquid that remains holds the dissolved wood and the cooking chemicals, and mills call it black liquor. The recovery boiler burns it and returns the chemicals for reuse ^5,6.

Why does it matter?

The burning gives steam for the mill and for turbines that make electricity. Some mills sell the surplus to the grid, so a pulp mill can earn from two products ^7,8.

How does it work?

Steam goes to cooking, drying and evaporation. Turbines turn the rest into power. Water is reused in loops, which cut use from over 100 cubic meters per ton of pulp before the 1970s to a design value of 10 at Kemi, per Metsa ³.

Myth or fact?

"A pulp mill is a heavy user of fossil fuel and grid power."

See the answer

Mostly myth. Modern kraft mills burn the wood residue they make themselves. Metsa states 240% electricity self-sufficiency for Aanekoski and 250% for Kemi ^9,1. UPM reports 92% biogenic fuels at Fray Bentos in 2024 ¹⁰. Older and smaller mills can differ, and the figures are company statements.

In this post

1. How does a kraft mill make its own energy?
2. How much of a pulp industry's energy comes from wood?
3. Which mills sell power to the grid?
4. How much water does a pulp mill use?
5. Why does the recovery boiler matter so much to a mill?
6. Can a mill capture the carbon from its stack?

01How does a kraft mill make its own energy?

A kraft mill cooks wood chips in white liquor, a water solution of sodium sulfide and sodium hydroxide. The cooking frees the fibers. The spent liquor, mixed with wash water, is weak black liquor. Evaporators remove water from it, and the strong black liquor is fired in a recovery furnace ⁵. This is the loop described in how a kraft mill works.

Burning the organic part of the liquor gives heat for process steam. It also converts sodium sulfate to sodium sulfide ⁵. The inorganic chemicals collect as molten smelt at the bottom of the furnace. The smelt is dissolved in water to make green liquor, and lime turns the green liquor back into white liquor ⁵.

Babcock and Wilcox says it developed the first kraft recovery boiler with G. H. Tomlinson in 1929 ⁶. Tomlinson's US patent was filed in 1932 and granted in 1937 ⁶. Carl F. Dahl had patented the sulfate process itself in 1884 ¹¹. The boiler does two jobs at once: it recovers the cooking chemicals, and it turns the leftover wood into steam ⁵.

1. Chips and cookingChips are cooked in white liquor, sodium sulfide plus sodium hydroxide. The fibers come free ⁵.
2. Black liquorThe spent liquor holds the dissolved wood. Evaporators take out water ⁵.
3. Recovery boilerStrong black liquor is fired. Organics burn. Chemicals collect as molten smelt ⁵.
4. Steam and powerHigh pressure steam runs the mill and turbines. The surplus can go to the grid ^2,8.
5. Chemicals backSmelt becomes green liquor, then white liquor again. A lime kiln regenerates the lime ⁵.

02How much of a pulp industry's energy comes from wood?

The best published numbers cover the whole European pulp and paper industry, not pulp mills alone. Cepi, the European industry association, reports that in 2024 biomass supplied 66% of the fuels used, and 58.4% of total primary energy ⁴. The industry generated 43,328 GWh of electricity on site and consumed 81,656 GWh ⁴. Our division gives 53.1%, so on-site generation covered about half of the electricity used. Cepi also reports that 95.7% of the on-site electricity came from combined heat and power ⁴. These totals include paper and board mills that use recycled fiber, so they understate what a kraft pulp mill does on its own.

In Brazil, the industry body Ibá says 90% of the energy the sector consumes comes from renewable sources, and credits black liquor ¹². Suzano reports the same 90% for itself in its 2025 sustainability report ¹³. Neither source gives a data year for the Ibá figure, and neither gives a figure for pulp mills alone.

The data show a pattern, and no source we found gives a single world figure for pulp mills.

03Which mills sell power to the grid?

The newest large mills of pulp exporters are built to produce more electricity than they use. Metsa gives Aanekoski, which opened on October 18, 2017, an electricity self-sufficiency rate of 240% ⁹. Kemi is stated at 250% ¹. In plain words, the rate is electricity produced divided by electricity used on site. Metsa gives no definition on its page ⁹.

In Uruguay, UPM's Fray Bentos and Paso de los Toros mills trade power with each other. Since February 2024, Fray Bentos draws from the grid only when Paso de los Toros has no surplus ¹⁰. Andritz, a supplier, reports around 1 TWh a year of surplus electricity from Paso de los Toros ¹⁴.

These are company or supplier statements. No source we found gives power sales as a share of a mill's revenue. A buyer or lender who wants that number has to ask the mill for it.

Named mills

Energy facts for six pulp mills

Company and supplier statements. Figures are not audited sales data; the basis is as each source gives it ^{1,2,7,9,10,14}.

Mill	Country	Energy fact
Aanekoski (Metsa)	Finland	Opened October 18, 2017. Electricity self-sufficiency of 240%. Capacity 1.3 million tons 9.
Kemi (Metsa)	Finland	Started September 20, 2023. Self-sufficiency of 250%. Generates 2 TWh of electricity a year, with no fossil fuels 1,8.
Imperatriz (Suzano)	Brazil	Recovery boiler burns up to 7,000 tons of dry solids a day. Surplus of 2.0 GWh a day, reported in 2015 2.
Cerrado (Suzano)	Brazil	Surplus of about 180 MW to the grid. Andritz equates it to roughly 1.5 TWh 7.
Paso de los Toros (UPM)	Uruguay	Started April 2023. Around 1 TWh a year of surplus. Biogenic fuels were 93% in 2024 14,16.
Fray Bentos (UPM)	Uruguay	Capacity 1.3 million tons. Biogenic fuels were 92% in 2024. Designed to be self-sufficient in electricity 10.

Metsa states that Kemi generates 2.5 times the renewable electricity it consumes in a year ¹.

04How much water does a pulp mill use?

Metsa says that until the 1970s, pulp mills used over 100 cubic meters of water per ton of pulp ³. It gives design values of 15 cubic meters of raw water per ton for Aanekoski and 10 for Kemi, the lowest of its mills ³. Metsa credits closed water circulation, countercurrent washing and the reuse of condensates ³.

The EU sets a limit on a different measure. For bleached kraft mills, the EU best available techniques decision of 2014 gives a waste water flow of 25 to 50 cubic meters per air-dried ton, as a yearly average at the discharge point. For unbleached kraft the range is 15 to 40 ¹⁵. Raw water taken in and waste water discharged are different measures, so the two sets of numbers should not be compared one to one.

For actual mills, UPM reports in its 2024 environmental statements that Fray Bentos took in 30.0 million cubic meters of water and discharged 22.5 million as process waste water ¹⁰. Paso de los Toros took in 46.2 million and discharged 36.5 million ¹⁶. UPM prints no per-ton result for either mill in these reports.

Across Europe, Cepi reports water intake of 3,160 million cubic meters in 2024 for its whole industry. About 90% of the water taken for paper and board was returned to its source after treatment ⁴.

Chart

Water used per ton of pulp: before the 1970s and today's design values

Cubic meters of raw water per ton of pulp. Source: Metsa, Every drop counts, January 20, 2025 ³. The first bar is plotted at 100 and is a floor, because Metsa says over 100. The other two are Metsa's design values, not measured results.

05Why does the recovery boiler matter so much to a mill?

The boiler is the center of the plant, so its size and age shape what the mill can do. Valmet says the recovery boiler at Suzano's Imperatriz mill can burn 7,000 tons of dry solids a day, and the mill generates its own power plus a surplus of 2.0 GWh a day ². A Suzano manager said the mill had been exporting an average of 80 MW ². At 80 MW, 24 hours a day gives 1.92 GWh, which matches the 2.0 GWh figure in round terms.

The EU best available techniques decision says new recovery boilers can run at a pressure of at least 100 bar and a temperature of 510 degrees C. Higher black liquor dry solids content raises boiler efficiency, steam generation and so electricity generation ¹⁵. A recovery boiler is also a large item of capital goods, so its age and size matter to anyone who finances the mill. It is a limit on output too. Valmet says a lignin extraction plant relieves the recovery boiler, so that more pulp can be made ¹⁷. For the scale of new mills, see why new pulp mills are so big.

Age is part of the picture. TAPPI reported in 2018 that 52% of North American recovery boilers were built in or before 1978 ¹⁸. The data show an old fleet there. For why some northern mills close, in the companies' own words, see the post on mill closures.

Bark, sludge and spare liquor also have uses. Metsa gasifies bark at Kemi to replace heavy fuel oil in the lime kiln ¹. Other by-products of the loop are covered in the biorefinery post.

06Can a mill capture the carbon from its stack?

A recovery boiler gives off biogenic carbon dioxide, from wood. An IEA Bioenergy workshop presentation in January 2026 said about two thirds of the large biogenic emission point sources in Sweden are in the pulp and paper industry ¹⁹. The same presentation names two Swedish projects that had state support, and neither is a pulp mill ¹⁹.

The trials at pulp mills are small and recent. Every one we found is a pilot or a plan. The figure below lists the pilots. Two further items are plans and carry no stage label: Metsa's planned capture plant at Rauma would capture 100,000 tons of CO2 a year, has EUR 21 million in aid, and could reach a final investment decision at the beginning of 2027 at the earliest ²⁰. Svante is running a feasibility study with an unnamed US packaging company, for more than 500,000 tons a year at a paper mill in the Southeast ²¹.

No source we found shows a pulp mill capturing carbon at commercial scale today.

How real is it?

Carbon capture at pulp mills: pilots only

• Pilot
  Stora Enso Skutskar, Sweden ²²Capture equipment installed on a recovery boiler unit in April 2024. Target of about two tons a day of captured carbon, run on low-temperature waste heat. Storage and use are not part of the project.
• Pilot
  Metsa Rauma, Finland ²³Captures about one ton of CO2 a day from pulp mill flue gases. Online since June 2025. Metsa said a demo plant would have a capacity of 30,000 to 100,000 tons a year.
• Pilot
  Mercer Peace River, Canada ²⁴A demonstration unit using Svante solid sorbent on recovery boiler flue gas started on December 31, 2025. The planned trial was about six months. No capacity or result has been published in the sources we found.

Stage labels: In production (commercial plants running), Being built, Planned (announced, not yet built), Pilot (test plant), Lab (research only), Stopped (closed or cancelled). Evidence for each item is in the cited source. Planned projects are described in the text above and are not listed here.

What this means for traders

• Ask a mill for its electricity self-sufficiency rate and its basis. Metsa's 240% and 250% are company statements.
• Check the age and size of the recovery boiler when you assess a mill. It sets how much pulp and power the mill can make ^2,17.
• Treat carbon capture as a pilot stage. Fund no volume on it until a source shows commercial operation. Power sales and pulp stock both affect working capital and inventory finance. See financing industrial goods trade and working capital and trade finance.

Questions traders ask

What is black liquor?

Black liquor is the liquid left after wood chips are cooked in the kraft process. It holds the dissolved wood and the cooking chemicals. Mills concentrate it in evaporators and burn it in the recovery boiler.

What does a recovery boiler do?

It burns strong black liquor to make high pressure steam. The inorganic chemicals collect as molten smelt and are turned back into white liquor for reuse. Babcock and Wilcox says it developed the first kraft recovery boiler in 1929, with G. H. Tomlinson.

What does 240% electricity self-sufficiency mean?

In plain words, it means the mill produces 2.4 times the electricity it uses on site. Metsa states 240% for Aanekoski and 250% for Kemi. The company gives no definition on its page, so this is the common reading.

How much water does a pulp mill use?

Metsa says mills used over 100 cubic meters of water per ton of pulp until the 1970s. It gives design values of 15 for Aanekoski and 10 for Kemi. These are design values from the company, not measured results.

Do pulp mills capture their carbon dioxide?

Only in pilots so far, in the sources we found. Stora Enso in Sweden, Metsa in Finland and Mercer in Canada have run small capture trials. Metsa plans a larger plant at Rauma, and no final investment decision had been made.

Read next

• Inside the millHow a kraft mill works: the chemical loop that made modern pulp
• Inside the millWhy new pulp mills are so big
• InnovationMore than paper: the biorefinery
• Inside the millWhy northern mills close: the companies' own reasons
• Inside the millThe tree race: 7 years in Brazil, 60 to 80 in Finland
• Money and rulesFinancing a mega mill
• Ossiano Trade Finance GuideHow each trade finance instrument works
• GlossaryTrade finance terms in plain English

Financing a mill, its stock or its pulp sales? Ossiano Capital works on trade finance for pulp and paper trades.

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Sources and notes

1. Metsa, Kemi bioproduct mill brochure (undated; mill started September 20, 2023): 250% electricity self-sufficiency, bark gasification. https://metsagroup.com/globalassets/metsa-fibre/attachments/brochures/metsa-fibre-kemi-bioproduct-mill-en-lowress.pdf
2. Valmet, Suzano sets new standards for green energy in Brazil, July 30, 2015. https://www.valmet.com/insights/articles/all-articles/suzano-sets-new-standards-for-green-energy-in-brazil/
3. Metsa, Every drop counts, January 20, 2025. https://www.metsagroup.com/metsafibre/news-and-publications/news-and-releases/stories/2025/every-drop-counts/
4. Cepi, Cepi Key Statistics 2025, European pulp & paper industry (energy section pp. 30 to 31, water section p. 32). Data cover the whole European pulp and paper industry, 2024. https://www.gzs.si/Portals/Panoga-Papirna-Industrija/Cepi-Key-Statistics-2025-FINAL.pdf
5. US EPA, AP-42 Chapter 10.2, Chemical Wood Pulping, September 1990 (reformatted January 1995). https://www.epa.gov/sites/default/files/2020-10/documents/c10s02.pdf
6. Babcock and Wilcox, Process Recovery Boilers brochure E101-3194, 2021; US Patent 2,070,632, G. H. Tomlinson, granted February 16, 1937. https://www.babcock.com/assets/PDF-Downloads/Steam-Generation/E101-3194-PR-Boilers-Babcock-Wilcox.pdf
7. Andritz, Spectrum 46, Ramp up in style (Suzano Ribas do Rio Pardo), undated: 180 MW surplus, about 1.5 TWh. https://www.andritz.com/resource/blob/720710/3f255b37e5dfe45c3d37525bab867f03/pp-spectrum46-en-ramp-up-in-style-suzano-ribas-do-rio-pardo-data.pdf
8. PaperAge, Metsa Group Starts Up Kemi Bioproduct Mill, September 20, 2023. https://paperage.com/2023news/09-20-2023metsa-group-starts-up-kemi-mill.html
9. Metsa, Aanekoski bioproduct mill page (undated); Pulpapernews, Metsa Group inaugurates new Aanekoski pulp and bioproducts mill (inauguration October 18, 2017). https://www.metsagroup.com/metsafibre/about-metsafibre/pulp-production/aanekoski-bioproduct-mill/
10. UPM, UPM Fray Bentos Environmental and Societal Responsibility 2024 (EMAS statement), published September 2025. https://www.upm.com/siteassets/reporting-hub/emas-reports/emas-report-2024---upm-fray-bentos-mill-english.pdf
11. United States Patent Office, US Patent 296,935, C. F. Dahl, Process of Manufacturing Cellulose from Wood, granted April 15, 1884. https://patents.google.com/patent/US296935A/en
12. Ibá, Manual do setor 2026, p. 17, Autossuficiencia energetica. https://iba.org/wp-content/uploads/2026/07/IBA2026_Manual_do_setor-v2-1.pdf
13. Suzano, Relatorio de Sustentabilidade 2025, p. 9, March 2026. https://s201.q4cdn.com/761980458/files/doc_downloads/2026/03/RS2025_POR_Vfinal.pdf
14. Andritz, Spectrum magazine, UPM giant pulp mill Uruguay: Passage of the bulls, undated. https://www.andritz.com/spectrum-en/upm-giant-pulp-mill-uruguay-passage-of-the-bulls
15. European Commission, Implementing Decision 2014/687/EU, BAT conclusions for pulp, paper and board, September 26, 2014 (BAT 5, BAT 31, BAT 32). https://aida.ineris.fr/sites/aida/files/documents-bref/CELEX_32014D0687_EN_TXT_0.pdf
16. UPM, UPM Paso de los Toros Environmental and Societal Responsibility 2024 (EMAS statement), 2025. https://www.upm.com/siteassets/reporting-hub/emas-reports/emas-report-2024---upm-paso-de-los-toros-mill-english.pdf
17. Valmet, LignoBoost plants produce large volumes of lignin, case studies (undated). https://www.valmet.com/insights/articles/up-and-running/new-technology/PEERS1stLignoBoostPlants/
18. TAPPI, Paper360, Are North American Kraft Pulp Mills at Risk?, November/December 2018. https://imisrise.tappi.org/TAPPI/Products/18/NOV/18NOVPA42.aspx
19. IEA Bioenergy Task 40 and IETS workshop, CCUS Sweden, January 15, 2026. https://task40.ieabioenergy.com/wp-content/uploads/sites/29/2026/05/IEA-IETS-XXI-WS-Jan-15-2026-CCUS-Sweden.pdf
20. Metsa Group, Carbon dioxide capture plant receives EUR 21 million in aid (2026); Advanced Biofuels USA, Three Finnish Industrial Biogenic Carbon Capture Projects Receive EUR 26.6 Million in Support (decision September 9, 2026). https://www.metsagroup.com/news-and-publications/news/2026/metsa-groups-carbon-dioxide-capture-plant-receives-eur-21-million-in-aid/
21. Svante Technologies via Business Wire, feasibility study for biogenic CO2 capture at a Southeast US paper mill, March 10, 2026. https://www.businesswire.com/news/home/20260310319382/en
22. Stora Enso, Capturing carbon at Stora Enso Skutskar Mill, April 29, 2024. https://www.storaenso.com/en/newsroom/news/2024/4/capturing-carbon-skutskar-mill
23. Metsa Group, Metsa Group's carbon capture pilot underway, investigation of a demo plant beginning, September 4, 2025. https://www.metsagroup.com/news-and-publications/news/2025/metsa-groups-carbon-capture-pilot-underway--investigation-of-a-demo-plant-beginning/
24. PaperAge, Mercer's Peace River Pulp Mill Starts-up CO2 Capture Demonstration Unit, December 31, 2025. https://www.paperage.com/2025news/12-31-2025mercer-peace-river-pulp-starts-up-co2-capture-demonstration-unit.html

Trade figures come from UN Comtrade (2015 to 2025, as reported by 10 countries) and FAOSTAT (1961 to 2024), checked and recalculated by us; each chart names whose data it uses. All tons are metric tons. All facts on this page are as of October 27, 2026, the date of publication, and may have changed since. For rules and tariffs, check the pulp watch before you act.

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