VOC control is an important topic in coating factories.

VOC stands for volatile organic compounds.
These can be understood as organic solvents in coating materials and thinners that evaporate into the air.

VOCs arise from coating booths, drying ovens, mixing areas, cleaning areas, and other locations.
They also affect environmental measures, odor control, the working environment, and customer audits.

VOC control includes reducing generation at the source through measures such as switching to low-VOC coatings, waterborne coatings, or powder coating, improving transfer efficiency, and reducing cleaning thinner consumption.
If VOCs in the exhaust still require treatment, exhaust treatment equipment is considered.

An RTO is one such option.

RTO stands for Regenerative Thermal Oxidizer.
It is a regenerative thermal treatment system.

Simply put, it decomposes VOCs by combustion at high temperature while recovering and reusing the heat.

An RTO is a strong option for considering VOC control and energy conservation together.
However, it is not suitable for every coating factory.

Exhaust airflow volume.
VOC concentration.
Exhaust temperature.
Operating hours.
Tar.
Dust.
Installation space.
Maintenance arrangements.
Installation and running costs.

These must be checked before deciding whether it is truly suitable.

1. An RTO treats VOCs by combustion while recovering heat

The basic role of an RTO is to decompose VOCs in exhaust at high temperature.

Exhaust from the coating process is sent into the equipment and heated to a specified temperature.
At that high temperature, VOCs are oxidized and decomposed into comparatively harmless forms before discharge.

This is the basic operation of thermal treatment equipment.

The distinctive feature of an RTO is its heat recovery mechanism.

An RTO contains heat-storing components called regenerative media.
When hot treated exhaust passes through them, they retain its heat.
The next incoming stream of cooler exhaust is preheated as it passes through those media.

The system therefore uses heat already generated to warm the next exhaust stream rather than discarding it.

This heat recovery may reduce fuel consumption.

2. VOC treatment is not as simple as burning the exhaust

VOCs can sometimes be treated through combustion.

However, burning them does not simply solve everything.

Thermal VOC treatment requires heating exhaust to a certain temperature.
When exhaust airflow volume is large, substantial energy is needed to heat that air.

If VOC concentration is low, combustion of the VOCs themselves supplies little heat, potentially requiring substantial supplementary fuel.

VOC treatment therefore requires examining the following balance.

• What airflow volume is to be treated?
• What is the VOC concentration?
• How much heat can the VOCs themselves provide?
• How much supplementary fuel is required?
• How much energy can heat recovery save?
• How many operating hours are there per year?

An RTO may improve energy efficiency through heat recovery.
However, unsuitable exhaust conditions may prevent the expected energy savings.

3. Conditions under which an RTO is likely to be effective

An RTO is more likely to be effective when a certain volume of VOC exhaust is treated continuously.

For example, it is worth considering under the following conditions.

• Drying oven exhaust contains VOCs.
• Exhaust volume is reasonably stable.
• Operating hours are long.
• VOC concentration is above a certain level.
• Odor control and VOC control are needed together.
• The aim is to limit exhaust treatment running costs.
• Energy savings through heat recovery can be expected.
• Customer audits or environmental regulations must be addressed.

Drying oven exhaust, in particular, contains volatile components released from the film and may also be hot.
It is therefore one exhaust stream whose compatibility with an RTO can readily be considered.

However, it may contain tar or dust.
In that case, pretreatment and duct cleanability are also important.

4. An RTO may be unsuitable in some cases

An RTO is a strong VOC treatment option, but it is not universal.

Careful consideration is needed under the following conditions.

• VOC concentration is extremely low.
• Exhaust airflow volume is too large.
• Operating hours are short.
• Production is intermittent and stops frequently.
• Tar content is high.
• Dust or mist content is high.
• Exhaust composition is unstable.
• Installation space is insufficient.
• Maintenance arrangements are weak.
• Operating benefits are small relative to installation cost.

For low-concentration, high-volume exhaust in particular, treatment by an RTO alone may require large equipment and increase fuel costs.

In such cases, combining it with a VOC concentrator or first reducing VOCs at the source must be considered.

5. Greater exhaust airflow requires a larger RTO installation

Exhaust airflow volume is one of the first items to check when considering an RTO.

Greater airflow means more air must be treated.
The equipment becomes larger, requiring greater fan capacity, larger ducts, combustion chambers and regenerative media, and more installation space.

The larger volume of air to be heated also affects fuel and electricity costs.

Coating booth exhaust may require large airflow for working environment and mist control.
However, its VOC concentration may be relatively low.

Treating such exhaust directly with an RTO may require substantial equipment investment and operating costs.

Before considering an RTO, it is important to establish exhaust airflow volume accurately.

6. Low VOC concentration may increase fuel costs

An RTO treats VOCs by combustion at high temperature.

If VOC concentration is above a certain level, the VOCs themselves release heat during combustion.
Using this heat can limit supplementary fuel.

If concentration is low, however, supplementary fuel is needed to maintain the high exhaust temperature.

Lower VOC concentration therefore tends to increase fuel costs.

VOC concentration and fuel costs must be examined together when selecting exhaust treatment equipment.

Looking only at installation cost leads to poor decisions.
Fuel costs may become a major long-term burden.

7. Regenerative heat recovery efficiency determines RTO energy performance

An RTO’s distinctive feature is heat recovery through regenerative media.

If this recovery works well, fuel required to heat the exhaust can be reduced.

If recovery efficiency is poor, however, energy savings are small.

The following factors affect regenerative heat recovery efficiency.

• Regenerative media performance
• Exhaust temperature
• Exhaust airflow volume
• VOC concentration
• Operating hours
• Operating stability
• Equipment insulation performance
• Changeover valve condition
• Contamination of regenerative media

An RTO achieves greater energy savings only when heat recovery works effectively.

At introduction, heat recovery efficiency and fuel consumption must be checked alongside treatment efficiency.

8. Consider heat use in conjunction with the drying oven

When introducing an RTO, heat use in conjunction with the drying oven may be possible.

Treat drying oven exhaust with the RTO and recover its heat.
Use the recovered heat to preheat oven supply air or provide process heating.
This is the approach.

It is, of course, not necessarily possible in every factory.

Duct distance.
Exhaust temperature.
Available heat.
Equipment layout.
Control method.
Safety.
Risk of odors returning.
Equipment investment.

These must be checked.

However, drying ovens consume substantial energy.
Viewing the RTO and oven together as a heat flow, rather than separately, may reveal opportunities for energy savings.

9. Address tar and dust in RTO pretreatment

Drying oven exhaust may contain tar or dust.

If these enter the RTO, they may contaminate its interior, clog regenerative media, reduce treatment efficiency, and increase the maintenance burden.

Exhaust pretreatment is therefore important when considering an RTO.

Check the following items.

• Does the exhaust contain coating mist?
• Does it contain dust?
• Is tar generated?
• Is exhaust temperature appropriate?
• Could condensation occur inside ducts?
• Are filters or mist separators necessary?
• Are duct cleaning access openings available?
• Are measures in place against regenerative media contamination?

An RTO is high-performing equipment, but contaminated exhaust should not simply be fed directly into it.

The system may need to be designed to clean the exhaust before treatment.

10. Pay attention to startup energy in intermittent operation

Factory production is not always continuous.

High-mix, low-volume production.
Daytime-only operation.
Production volume varying by week.
Baking performed only for certain products.
Frequent changeovers.

In these situations, an RTO may start and stop frequently.

An RTO operates at high temperature.
It therefore needs a certain amount of energy at startup.

When operating hours are short, startup energy may impose a greater burden than the benefit of heat recovery.

When considering an RTO, check annual operating hours, daily operating hours, and the number of starts and stops.

Determine whether continuous operation is the appropriate use or whether intermittent operation also provides benefits.

11. Check installation space and surrounding equipment for an RTO

An RTO can be comparatively large equipment.

Checking installation space is therefore important.

Space is required not only for the main equipment but also for the following.

• Exhaust ducts
• Fans
• Inspection access
• Maintenance access
• Regenerative media replacement
• Fuel supply equipment
• Electrical control panels
• Safety clearances
• Delivery access
• Future replacement

A poor installation location may require long ducts, increasing pressure losses and heat losses.
Installing the equipment where maintenance is difficult also makes long-term operation management difficult.

RTO positioning must be considered within the entire factory layout rather than for the equipment alone.

12. Consider reducing generation at the source before introducing an RTO

An RTO is effective for VOC treatment, but source reduction should also be considered before installing treatment equipment.

This is because reducing VOC generation reduces the load on the treatment equipment.

Source reduction methods include the following.

• Improve transfer efficiency.
• Reduce overspray.
• Reduce thinner consumption.
• Reduce cleaning thinner consumption.
• Reduce the time containers remain open.
• Consider low-VOC coatings.
• Consider waterborne coatings.
• Consider powder coating.
• Optimize drying conditions.
• Reduce unnecessary exhaust.

Reducing VOCs at the source may limit RTO size, fuel costs, and maintenance burdens.

VOC control should first examine what can be reduced in the process before considering treatment equipment.

13. Basic items for deciding whether to introduce an RTO

Check the following items when deciding whether to introduce an RTO.

1. Sources

Identify which processes generate VOCs.

2. Exhaust airflow volume

Establish the airflow volume to be treated.

3. VOC concentration

Check the concentration and whether it varies greatly.

4. VOC composition

Check whether the components are suitable for thermal oxidation and identify the odor components.

5. Exhaust temperature

Check whether the exhaust is from a drying oven or at ambient temperature.

6. Tar and dust

Check whether pretreatment is necessary.

7. Operating hours

Check whether operation is continuous or intermittent.

8. Heat recovery

Check whether recovered heat can be used.

9. Installation space

Check space for the main equipment, ducts, and inspection access.

10. Running costs

Check fuel, electricity, maintenance, and consumable costs.

14. Common challenges in RTO assessment in Vietnamese factories

Vietnamese factories often face the following challenges when considering an RTO.

Beginning equipment assessment without measuring VOC concentration.
Not knowing exhaust airflow volume accurately.
Treating oven and booth exhaust in the same way.
Overlooking tar and dust pretreatment.
Judging solely by installation cost.
Not considering fuel and electricity costs over the long term.
Assuming continuous operation despite short operating hours.
Not examining opportunities to use recovered heat.
Insufficient installation or maintenance space.
Trying to respond solely through treatment equipment without considering source reduction.

An RTO is advanced environmental equipment.
This makes organizing conditions before introduction particularly important.

15. The value CoatureVietnam sees in RTO assessment

CoatureVietnam does not regard an RTO simply as environmental control equipment.

Under suitable conditions, an RTO can potentially combine VOC control and energy conservation.
Under unsuitable conditions, however, both installation and operating costs become substantial burdens.

CoatureVietnam therefore first examines the entire coating process when considering an RTO.

Which coating materials are used?
How much thinner is used?
Which processes generate VOCs?
Can transfer efficiency be improved?
What are the temperature and VOC concentration of drying oven exhaust?
Are tar or dust present?
Can heat recovery be used?
Is there potential to switch to low-VOC or powder coatings?

Materials, equipment, operation, and energy are examined together in this way.

This puts into practice the principle CoatureVietnam values:
“Coating the Future with Science and Care”.

Science means checking VOC concentration, exhaust airflow volume, exhaust temperature, operating hours, and heat recovery effects numerically to make an investment decision.
Care means creating conditions in which the factory can operate confidently over the long term without burdening operators or the surrounding environment.

Conclusion

An RTO is a strong treatment option for considering VOC control and energy conservation together.

It aims to limit energy consumption by treating VOCs through high-temperature combustion while recovering heat through regenerative media.

However, an RTO is not universal.

Exhaust airflow volume.
VOC concentration.
VOC composition.
Exhaust temperature.
Tar.
Dust.
Operating hours.
Installation space.
Maintainability.
Potential to use recovered heat.
Running costs.

An appropriate decision cannot be made without checking these items.

Source reduction should also be considered before introducing an RTO.

Improve transfer efficiency.
Reduce cleaning thinner consumption.
Consider low-VOC coatings.
Examine the potential to switch to powder coating.
Optimize drying oven conditions.

VOC control is not completed through treatment equipment alone.
Coating materials, equipment, operation, and energy must be considered together.

CoatureVietnam treats VOC control, including RTOs, as a topic linking energy conservation, quality, working conditions, and long-term investment decisions as well as environmental measures, and proposes practical approaches suited to Vietnamese factories.