Most of a paper machine’s energy vanishes as hot, wet air. Mills that wring out water in the press, upgrade vacuum systems, and mine the dryer exhaust for heat are reporting double‑digit savings — with short paybacks.
Paper machines are extremely energy‑intensive: roughly 5–7 GJ thermal (~1.4–1.9 GJ steam) and 600–1000 kWh electric are needed per tonne of paper (sunnea.fi). Steam by itself is ~70% of total energy (sunnea.fi), and about 76% of that steam is consumed in the dryer section (sunnea.fi).
In practice most heat leaves with the hot, humid exhaust air (sunnea.fi) (sunnea.fi), making pre‑evaporation of moisture and heat recovery critical targets.
Press‑section dewatering optimization
Since >¾ of steam is used to boil water off the sheet, maximizing mechanical dewatering in the press saves significant energy. After the forming section, the web (the wet paper sheet) is typically around ~20% solids; roll presses can raise web solids to ~50% after pressing, as shown in a tissue machine case study (mdpi.com). A 1%‑point increase in press dryness cuts dryer steam needs by ~4–5% (mdpi.com).
Runtech (a vacuum/press specialist) reports that improving press dewatering by 1–3% — via better nip pressing, doctoring, felt design, etc. — yielded roughly 4–12% less dryer steam (paper360.tappi.org). In practice this means each dry‑solids point shaved in the press can cut steam use by several tenths of a GJ per tonne (roughly 5–10 kg steam/tonne per %-point of dryness gained). Advanced press technologies — extended‑nip “shoe” presses (a press with a longer nip contact to increase dewatering pressure/time) or multiple press nips (the nip is the pressure zone between rolls) — can routinely achieve higher solids (50–60%) before drying; studies estimate shoe presses can reduce drying energy by 10–15% vs. conventional nip presses (iipinetwork.org).
High‑efficiency vacuum systems
Vacuum pumps (for wire and press section dewatering) are often the largest electrical loads after motors and drives. Many paper machines run oversized or outdated vacuum systems, so right‑sizing and upgrading can yield dramatic savings. In one tissue mill retrofit, replacing five liquid‑ring vacuum pumps with two high‑speed turbo blowers (EP600 turbos) dropped vacuum‑system power from 1250 kW to 400 kW — a 68% reduction (paper360.tappi.org).
Industry sources report optimized vacuum systems cutting electrical vacuum loads by 30–70% (paper360.tappi.org). Audits of multiple machines found on the order of megawatts of savings: one study of 14 machines showed ~3.5 MW could be saved through vacuum‑system tuning (iipinetwork.org).
Key measures include installing variable‑speed, water‑free turbo blowers (instead of fixed‑speed liquid‑ring pumps), installing separate blowers for different vacuum levels, and using online dewatering measurements to avoid over‑pumping. For instance, controlling suction‑box levels to match felt conditions avoids “double compression” losses that can increase air flow by 30–50% and thus energy (paper360.tappi.org) (paper360.tappi.org). Implementing these yields very quick payback: saving 1.5 MW in vacuum saves ~4,000 tCO₂/yr (paper360.tappi.org), and typical examples show 30–50% or more electrical savings in the vacuum plant (paper360.tappi.org) (paper360.tappi.org). Many mills can remove low‑use vacuum consumers entirely (e.g., vacuum couch rolls — the couch is the roll at the end of the forming section) — cited savings of ~225 kW each (iipinetwork.org).
Dryer exhaust heat recovery
Since the dryer hood exhaust (the hood encloses the dryer section to capture hot, moist air) carries most of the dryer’s energy, capturing it can offset steam usage. The humid exhaust air (often 100–180 °C) has a heat content many times higher than the intake air (sunnea.fi), so it is an excellent heat source.
Modern machines use multi‑stage air‑to‑air and air‑to‑water heat exchangers on the hoods: recovered heat is used to preheat the dry‑air supply, warm building ventilation or shower/process water, and recirculate heat in closed loops (sunnea.fi) (sunnea.fi). With well‑balanced airflow and efficient exchangers, documented recovery rates are very high — on the order of 55–80% of exhaust heat can be reclaimed (sunnea.fi).
In practice this yields double‑digit percentage reductions in steam demand. For example, one mill installed cross‑flow heat exchangers on its dryer exhaust and used the recovered heat for facility heating; this saved ~$1 million/year and paid back in ~1.5 years (iipinetwork.org). Even without new technology, repairing/optimizing old hood systems can cut losses; consultants note that adding or refurbishing ventilation heat‑recovery typically pays for itself within a year (sunnea.fi). More advanced options (flue‑gas condensing, multi‑stage hoods, mechanical vapor recompression — MVR, which compresses water vapor to a higher temperature so its heat can be reused — etc.) can drive even greater savings (e.g., MVR can cut ~50% of steam use at the expense of added electricity) (iipinetwork.org).
When recovered heat is routed to shower/process water or returned through condensate circuits, mills typically interface it with standard utility skids; examples include supporting equipment for water treatment (water-treatment ancillaries) and polishing of steam condensate after heat exchange cooling (condensate polisher).
Implementation costs and policy signals
All of the above measures have been quantified in practice and yield strong ROI. Installing a shoe press may cost on the order of $30–40/t of annual capacity (then save ~15% of drying energy) (iipinetwork.org). Vacuum system retrofits often have negligible extra infrastructure cost but save 100’s of kW (worth tens of thousands USD/yr in energy) (paper360.tappi.org) (paper360.tappi.org). Heat‑exchanger installs (around ~$1–2 million for a large machine) often pay back in 1–2 years (iipinetwork.org) (sunnea.fi).
Energy‑efficiency policies reinforce these technical measures: Indonesia’s Green Industry regulations set per‑ton energy targets for pulp & paper (Reg. 51/2015, requiring low steam and electricity use) (iea.org). In summary, data from studies and mill case histories show that investing in high‑efficiency vacuum blowers, maximizing press dryness, and installing dryer‑hood heat recovery are “best available techniques” that cut energy use by tens of percent, with measurable savings and short payback.
Sources: Industry studies and case reports of paper‑machine upgrades (mdpi.com) (paper360.tappi.org); papermaking best‑practice guides and audits (paper360.tappi.org) (sunnea.fi); peer‑reviewed and technical papers on press/dryer performance (sunnea.fi) (iipinetwork.org); Indonesian industry regulations (iea.org) (see metadata).
