Paper mills spend large amounts of energy creating heat.

At Koehler Paper’s Kehl mill in Germany, part of that heat was leaving the process through the exhaust system of an offline coating machine.

Now, some of it is coming back as steam.

Koehler and Voith have installed a SteamBooster system on coating machine SM 8, where exhaust air from non-contact dryers can reach temperatures of around 300°C.

Instead of allowing much of that thermal energy to leave the production process, the system transfers the heat through a heat exchanger and uses it to generate steam from condensate.

Voith says the installation produces approximately one tonne of process steam per hour, reducing boiler demand and associated energy costs.

The project forms part of a wider three-stage heat-recovery system that has been operating since June 2025.

According to Voith, the complete system can reduce annual CO₂ emissions by up to 1,500 tonnes.

For the pulp and paper industry, the important point is not simply the carbon figure.

It is the energy logic behind it:

before producing more steam, ask how much usable heat is already leaving the mill.

A 300°C Exhaust Stream Is an Energy Asset

The SteamBooster is installed in the production line for machine-glazed specialty papers at Kehl.

The offline coating operation uses Voith MCB non-contact dryers.

These dryers generate hot exhaust air reaching temperatures of up to 300°C.

That temperature matters.

Not every warm exhaust stream contains enough useful energy to economically produce process steam.

Low-temperature heat may still be valuable for applications such as:

water heating;

building heating;

dryer-air preheating;

or heat-pump systems.

But high-temperature exhaust creates more options.

At Kehl, the temperature is high enough for Voith’s heat-recovery arrangement to take condensate and generate steam that can be returned to the production process.

Instead of treating exhaust air only as something that needs to be discharged, the mill is treating it as a secondary energy source.

That is a useful change in how paper mills can approach decarbonization.

Why One Tonne of Steam per Hour Matters

One tonne per hour may sound small compared with the scale of an industrial paper mill.

It should not be viewed in isolation.

Steam is used continuously across papermaking and coating operations.

Every tonne of useful steam recovered from waste heat is one tonne that does not need to be generated in exactly the same way by the existing boiler system.

Voith says this reduces boiler load.

At Kehl, that point is particularly relevant because Koehler already operates biomass combined heat and power plants that supply the mill’s base-load heat requirements, while natural-gas-fired in-house steam generators cover peak demand.

This helps explain why another heat-recovery project still has value at a mill that has already invested heavily in renewable energy.

Koehler is not starting from an entirely fossil-fuel-based steam system.

It has already reduced that dependence.

The next improvements are therefore likely to come from finding smaller remaining sources of gas consumption and reducing them where technically possible.

Recovered steam can contribute to that process.

Decarbonization Becomes Harder After the First Big Projects

This is an issue the European paper industry is increasingly confronting.

The first phase of industrial decarbonization can include relatively clear interventions:

replace coal;

switch electricity supply;

install biomass;

improve heat recovery;

upgrade motors;

or increase process efficiency.

Once those projects are completed, the next tonne of CO₂ can become more difficult and expensive to remove.

Koehler already has substantial renewable-energy infrastructure at Kehl.

Its biomass CHP plants have supplied process steam for years, while Production Line 8 has used renewable electricity since 2021. Koehler said that electricity switch alone was calculated to avoid around 45,000 tonnes of CO₂ annually.

That makes the SteamBooster project interesting in context.

It represents a more incremental stage of decarbonization.

Rather than replacing an entire energy source, it tries to extract more useful work from energy already inside the process.

For mature European mills, that type of project may become increasingly important.

Waste Heat Recovery Can Come Before Electrification

Industrial heat electrification is receiving increasing attention across Europe.

Heat pumps, electric boilers and other technologies can reduce direct fossil-fuel use when suitable low-carbon electricity is available.

But there is a basic efficiency question that should come first.

Why generate replacement heat if recoverable heat is already available?

Heat recovery and electrification are not competing strategies.

They can work in sequence.

A mill can first:

recover the highest-temperature process heat;

reuse steam and condensate efficiently;

reduce unnecessary thermal losses;

and lower the total heat demand.

Then it can evaluate what remaining heat load needs electrification, biomass, renewable gas or other energy sources.

This matters economically.

A smaller residual heat demand can mean smaller replacement-energy equipment and lower operating requirements.

In practical mill terms:

the cheapest megawatt of new heat capacity may be the megawatt the plant no longer needs to generate.

The Coating Section Is an Interesting Place to Look

Paper-machine drying receives a great deal of attention because evaporation requires substantial energy.

Coating operations create another heat-recovery opportunity.

After coating is applied, additional energy is needed to remove water and dry the coated surface.

Non-contact hot-air dryers can therefore create significant exhaust streams.

At Kehl, the coating-machine exhaust provided a stream hot enough to support steam generation.

This illustrates why mills should not evaluate energy use only at the boiler house.

Potential recovery points can exist throughout the process:

paper-machine dryer exhaust;

tissue hoods;

coating dryers;

vacuum systems;

compressors;

condensate systems;

and other thermal processes.

The challenge is identifying which streams provide the right combination of:

temperature;

volume;

operating hours;

location;

and proximity to a useful heat demand.

A technically recoverable heat stream is not automatically an economically useful one.

SteamBooster Started in Tissue

Voith originally developed and patented the SteamBooster concept for heat recovery from tissue-machine hoods.

The supplier says it has since adapted the technology for broader paper-machine applications.

According to Voith, the concept can generally be considered where exhaust-air temperatures exceed approximately 100°C, including sources such as hot-air dryers and vacuum blowers.

That does not mean every exhaust stream above 100°C will justify an installation.

Actual feasibility will depend on the site.

The amount of available heat matters.

Operating hours matter.

Steam pressure and demand matter.

Pipe routing matters.

Existing condensate and boiler systems matter.

Energy prices matter.

Installation cost matters.

Those variables will determine whether the business case works.

This is why site-specific energy mapping becomes important.

Voith Claims One to Five Tonnes of Steam per Hour

For a typical paper mill configuration, Voith says SteamBooster installations can generate between one and five tonnes of steam per hour, depending on available conditions.

Kehl sits at the lower end of that stated range with around one tonne per hour.

The supplier also says average installations can achieve a payback period of less than two years.

That claim should be treated carefully.

Voith is the equipment supplier, and it has not published the detailed Kehl investment cost, annual energy savings or site-specific payback calculation.

Therefore, it would be inaccurate to say that Koehler’s own installation has already demonstrated a payback below two years.

The defensible wording is:

Voith says its experience across multiple installations indicates an average payback of under two years.

The actual financial return at any mill will depend heavily on local steam and fuel costs.

Natural Gas Price Changes the Equation

The economics of heat recovery are closely linked to what type of energy it displaces.

At a mill using low-cost waste biomass, the financial value of another unit of recovered heat may be different from a mill where steam is generated predominantly from natural gas.

At Kehl, biomass CHP covers the base heat load, while natural gas is used for peak process-steam requirements.

That creates a potentially attractive target.

If recovered process heat reduces periods when gas-fired steam generation is required, its economic and carbon value can be greater than if it merely displaces already-renewable base-load heat.

Voith specifically describes the three-stage project as being designed to lower natural gas consumption at the mill.

However, neither Voith nor Koehler has disclosed how many cubic metres or MWh of natural gas are saved annually.

That number would be useful for evaluating the project’s full operating economics.

Until then, the confirmed result should remain stated in terms of steam generation, boiler-load reduction and the reported CO₂ saving for the overall heat-recovery system.

1,500 Tonnes of CO₂ Is the System Figure

This distinction is particularly important when discussing the carbon result.

Voith says the three-stage heat-recovery concept, which includes the SteamBooster, saves up to 1,500 tonnes of CO₂ per year.

It does not state that the SteamBooster alone delivers all 1,500 tonnes.

The difference matters.

Industrial technology case studies frequently combine several measures into one reported performance figure.

Separating component performance from system performance protects the technical credibility of the article.

What we know is:

the SteamBooster contributes around one tonne of recovered steam per hour;

it reduces boiler load;

and it is one element of the wider system responsible for the reported annual CO₂ reduction.

Anything more specific would require additional data.

Retrofitability Could Be More Important Than the Technology Itself

Voith says the system can be retrofitted during regular maintenance shutdowns as well as incorporated into new installations.

For Europe’s paper industry, that characteristic could be particularly valuable.

The continent contains hundreds of existing pulp and paper mills.

Many machines have operated for decades while being continuously rebuilt and modernized.

Complete replacement is rarely economically realistic.

That means decarbonization technologies have a much larger addressable market if they can integrate with existing assets.

A retrofit project that fits into an annual shutdown has a very different operational risk profile from one requiring a lengthy standalone outage.

Koehler’s Innovation Manager Energy, Mario Vollmer, specifically highlighted the speed and ease of installation in commenting on the Kehl project.

That may ultimately be one of the stronger commercial arguments for heat recovery.

Not every mill can approve a new energy plant.

Many can investigate whether an existing exhaust stream is worth recovering.

But Retrofitting Still Requires Good Heat Integration

“Easy to install” should not be interpreted as plug-and-play.

Industrial heat recovery is highly site-specific.

The equipment needs to be located where hot exhaust can be captured.

Condensate has to reach the system.

Generated steam needs a useful destination.

Control systems have to coordinate with existing steam pressure and demand.

And the heat exchanger must perform reliably under the contamination and operating conditions of the exhaust stream.

A technically successful retrofit therefore requires more than placing a heat exchanger in the duct.

The complete mill heat balance matters.

This is one reason Voith describes its approach as beginning with a site concept study covering available heat sources and appropriate electrification or recovery systems.

For paper producers, that is the right starting point.

Do not begin by selecting the equipment.

Begin by mapping the heat.

The Larger Opportunity Is Hidden in the Mill Heat Balance

The Kehl project points toward a broader question for paper producers.

How much energy is currently leaving a mill at a temperature that could still be useful?

Not every stream will justify recovery.

But the energy audit should identify:

temperature;

mass flow;

operating hours;

seasonality;

distance from a heat user;

and the value of the energy source being displaced.

Then rank the opportunities.

A 250°C exhaust stream operating continuously may deserve attention before a large low-temperature stream that is difficult to reuse.

Likewise, recovered heat that displaces natural gas may offer a different business case from heat that displaces low-cost biomass.

This is where decarbonization becomes an engineering prioritization problem rather than a list of technologies.

Specialty Paper Also Makes Reliability Important

Koehler’s SM 8 coating machine forms part of a specialty paper operation.

That means energy efficiency cannot be improved at the expense of coating quality or production stability.

Drying is closely connected with:

coating uniformity;

moisture;

web stability;

surface quality;

and production speed.

A heat-recovery project therefore has to capture exhaust energy without compromising the operating conditions required by the coating process.

Voith and Koehler have not reported adverse impacts on production performance from the installation.

The system has been operating as part of the wider heat-recovery arrangement since June 2025.

That operating period is relevant.

The technology is no longer being described only as a newly commissioned trial.

It has now passed more than a year in operation before Voith’s September 2026 public case study.

What Should Paper Mills Look at First?

For pulp, paper and board mills trying to reduce fossil-energy consumption, the Kehl case suggests a practical sequence.

Start with the exhaust systems.

Identify every significant stream above 100°C.

Then ask:

How many hours per year is the heat actually available?

Is there a nearby process that needs steam or hot water during the same operating period?

Which fuel would the recovered energy replace?

Can condensate and steam be integrated without major changes to the existing network?

Can the installation fit into a scheduled shutdown?

What is the true annual saving after pumps, maintenance and other auxiliary energy are included?

Only after answering those questions should a mill calculate the payback period.

The result may not always justify investment.

That is fine.

The objective is to identify which thermal losses are large enough and valuable enough to recover.

Before Buying More Energy, Measure What Leaves the Stack

For mill managers, energy engineers and decarbonization teams planning the next capital budget, one of the most useful exercises may be simpler than another technology review.

Map the temperature and flow of the major exhaust streams across the mill.

Then put their energy value beside your current:

natural gas use;

steam demand;

boiler loading;

electricity consumption;

and planned decarbonization investments.

Ask one question:

Are we planning to buy or generate energy that is already leaving another part of the plant?

At Koehler’s Kehl mill, the answer was partly yes.

The coating line was producing exhaust air at up to 300°C.

Today, part of that energy returns to the process as approximately one tonne of steam every hour.

The full three-stage recovery system saves up to 1,500 tonnes of CO₂ annually, according to Voith.

It is not the largest decarbonization project Koehler has undertaken.

That may be exactly why it matters.

As mills remove the biggest fossil-energy sources, future progress will increasingly depend on finding smaller losses throughout existing operations.

Paper mills do not only need cleaner energy. They also need to stop throwing useful energy away.

Last Updated on 04/09/2026 by Jota Machinery