RECD for Printing Facilities: Exhaust Routes Near Process Ventilation

Look at the roof of a busy printing plant and you will see a small forest of ducts. Dryer exhausts from flexo and gravure presses, extraction from the ink kitchen, fans pulling solvent vapour from the press hall, make-up air units pushing fresh air back in, perhaps a thermal oxidiser or a solvent recovery unit, and somewhere among them, the exhaust stack of the DG set.

When a plant decides to fit a retrofit emission control device to that generator, the device itself is the easy part. The harder question is where the exhaust goes, and what it passes on the way. In a printing facility, the DG exhaust route crosses or runs near process ventilation that carries flammable vapour, draws in fresh air for the pressroom, or holds the building at a carefully set pressure. A route that looked fine for twenty years can become a problem the day the line is opened, rerouted and lengthened to fit an RECD.

This guide is written as a route review. It walks the exhaust from the engine to the outlet in five segments, and for each one asks how it interacts with the plant’s process ventilation. It then looks at building pressure, gives a simple airflow balance method, and ends with a sign-off checklist for the drawing.

Why Printing Plants Need a Route Review

Printing processes vary widely, and so does their ventilation.

• Flexographic and gravure printing for flexible packaging often uses solvent-based inks with ethyl acetate, ethanol, n-propanol, isopropanol and similar solvents. Presses have powerful dryers and extraction, and many plants run solvent recovery or a thermal oxidiser.
• Heatset web offset runs hot-air dryers that drive off ink oils, often followed by an oxidiser.
• Sheetfed offset usually has lighter extraction, though fountain solution additives and wash-up solvents still produce vapour.
• Lamination, coating and adhesive lines in packaging plants add their own solvent loads.
• Digital and screen printing range from minimal to significant extraction depending on ink chemistry.

Insurers take these hazards seriously. FM’s loss prevention guidance on printing plants (Data Sheet 7-96) covers the fire and explosion risks of inks, solvents, dryers and exhaust systems. The European solvents industry’s flammability safety guide for industrial solvents is a clear introduction to vapour, flash point and ignition sources.

A diesel exhaust line is a long, hot surface. In a plant where flammable vapour may be present, its route deserves the same scrutiny as any other potential ignition source.

The regulatory reason for the retrofit

Many printing and packaging plants sit in Okhla, Noida, Greater Noida, Faridabad, Gurugram and Sahibabad. In NCR, CAQM Direction No. 76 set out the route by generator size: 19 to 125 kW towards dual fuel, 125 to 800 kW with a choice of dual fuel or RECD, and above 800 kW with an RECD. Confirm current requirements with CAQM and your SPCB before deciding. Our DG set emission regulations page summarises the position, and how to get a pollution NOC for a DG set covers the consent side.

Two Systems That Must Never Be Mixed

Before the route review, one principle. The DG exhaust and the plant’s process exhaust are separate systems with separate jobs.

• The RECD treats diesel engine exhaust. Its oxidation catalyst acts on carbon monoxide and hydrocarbons from combustion, and its particulate filter traps diesel soot. It is not designed to treat press solvent vapour.
• The process ventilation removes solvent vapour from the press hall and dryers, sometimes sending it to an oxidiser or recovery unit.

It can be tempting, when space on the roof is short, to run the DG exhaust into an existing stack or duct. Do not. Connecting a hot, pressurised diesel exhaust to a duct carrying solvent vapour creates an ignition and backflow risk, upsets the process fan system, and complicates compliance for both. Every DG should have its own exhaust line and outlet. If you are unsure what an RECD can and cannot do, our explainer on exhaust after-treatment systems sets out the basics.

The Five-Segment Route Review

Lay the existing exhaust drawing, the proposed RECD layout and the plant’s ventilation drawing side by side. If you do not have a ventilation drawing, walk the roof and sketch one. Then review the DG exhaust in five segments.

Segment 1: Engine outlet to the flexible bellows

This short section runs from the turbocharger outlet to the flexible connection. It is the hottest part of the system, with surface temperatures at full load that can be several hundred degrees Celsius.

Questions to ask:

• Is the DG room separated from the press hall, ink kitchen and solvent store by a proper wall?
• Could solvent vapour reach the DG room through shared doors, trenches or ventilation?
• Is the turbo outlet and manifold area clean of oil and ink residues?

Some common press solvents have autoignition temperatures in the range of roughly 360 to 480°C. Unlagged exhaust components can exceed that. The DG room should not be a place where solvent vapour can collect.

Segment 2: Run inside the DG room or building

This is where the RECD often sits in an indoor layout, and where the route may pass along internal walls or through ceiling voids.

Questions to ask:

• Does the route pass through or above any area classified as a hazardous area for flammable vapour, such as the ink kitchen, solvent store or press hall near the dryers?
• Is the line clad and insulated along its full length, with a measured outer surface temperature?
• Is there enough clearance from cable trays, paper stock and combustible building materials?

Plants that handle solvent-based inks often have a hazardous area classification drawing prepared to standards such as IS/IEC 60079-10-1. If the DG exhaust route crosses or runs next to a classified zone, stop and redesign. A hot exhaust line has no place in a zone where flammable vapour is expected.

Segment 3: The wall or roof penetration

The point where the exhaust leaves the building is often overlooked.

Questions to ask:

• Is the sleeve fire-stopped with suitable high-temperature material?
• Is the penetration close to a louvre, window, door or make-up air intake?
• Is the gap around the pipe sealed so that the building’s pressure cannot pull exhaust back in?

A poorly sealed sleeve in a building held under negative pressure will draw exhaust gas inward every time the DG runs.

Segment 4: The outdoor run and the RECD location

In many printing plants, the RECD is mounted outdoors, on the roof or a wall platform, because indoor space near the press is scarce and hot equipment indoors is unwelcome.

Questions to ask:

• Is the RECD placed away from the outlets of dryer exhausts, oxidiser stacks and extraction fans?
• Is it clear of rooftop make-up air units and their intakes?
• Can it be reached safely for inspection without walking among process ducts?
• Is the roof structure rated for the device’s weight plus supports?

Remember that each extra metre and bend adds resistance. The vendor must confirm the total backpressure stays within the engine maker’s limit. Our post on how exhaust backpressure affects a DG set explains why.

Segment 5: The stack outlet

The outlet decides where the plume goes after it leaves the pipe.

Questions to ask:

• Is the outlet higher than nearby roof equipment and the eaves of adjacent buildings?
• Does it discharge vertically, without a cap that pushes the plume down?
• How far is it from the nearest make-up air intake, and is that intake downwind under common wind directions?
• Is it far enough from oxidiser and dryer stacks that plumes do not combine near intakes?
• Does it carry a sampling port in a position that meets your SPCB’s stack monitoring requirements?

Our article on whether increasing chimney height can replace an RECD explains why height is not a compliance route by itself, but height still matters for dispersion. If the existing silencer is being moved or replaced at the same time, see whether an RECD can replace a generator’s exhaust silencer.

Building Pressure: The Hidden Route

A printing plant’s process ventilation does not only remove vapour. It also sets the pressure inside the building. If the exhaust fans pull out more air than the make-up air units push in, the building runs under negative pressure. Air then enters through every gap: doors, dock shutters, louvres, cable openings and the sleeve around the DG exhaust.

In a plant running under negative pressure, diesel exhaust released anywhere near the building can be drawn into the pressroom. The symptoms are familiar to many plant managers: a diesel smell in the press hall during power cuts, soot marks around doors, complaints from operators on night shift.

A simple airflow balance

You can estimate building pressure with a rough balance. Figures below are illustrative.

Airflow item	Flow (m³/h)
Press 1 dryer and hood exhaust	18,000
Press 2 dryer and hood exhaust	15,000
Laminator exhaust	8,000
Ink kitchen extraction	3,000
General hall extraction fans	10,000
Total exhaust	54,000
Make-up air unit 1	25,000
Make-up air unit 2	20,000
Total supply	45,000
Imbalance	9,000 m³/h drawn in through gaps

In this example, about 9,000 cubic metres of air every hour enters the building through unplanned openings. If the DG exhaust outlet or its wall sleeve is near any of those openings, exhaust will be part of that air.

What changes during a power cut

Here is a twist that many plants miss. During a grid failure, the DG often powers some fans but not others. If process exhaust fans restart on DG but make-up air units are left off to save capacity, the building becomes more negative just when the DG is running. That is exactly when diesel exhaust is most likely to be pulled in.

Review your DG load schedule. If make-up air units are not on DG, consider whether they should be, or whether some exhaust fans should also be held off during outages when presses are stopped.

Practical fixes

• Seal the DG exhaust sleeve and any gaps near the outlet
• Move the outlet away from doors, shutters and louvres that act as inlets
• Rebalance supply and exhaust so the building runs close to neutral or slightly positive in the press hall
• Include make-up air units in the DG load schedule if presses or extraction will run during outages

An RECD sharply reduces soot and is designed to cut hydrocarbons and carbon monoxide. Many users notice less diesel smell after fitment, as covered in can an RECD reduce diesel exhaust odour. But it is not a substitute for keeping the exhaust out of the building in the first place.

Does the Load Profile Suit the Filter?

Route questions dominate in a printing plant, but the load pattern still matters. The particulate filter in an RECD burns off trapped soot during normal running when the exhaust is hot enough, and that depends on how hard the engine works.

Printing plants fall into two broad groups:

• Plants that print on DG. Packaging converters with tight delivery schedules often keep presses, dryers, extraction and make-up air running through an outage. Dryer heaters and large fans give the set a substantial, steady load, which suits passive regeneration.
• Plants that only hold on DG. Smaller commercial printers may stop presses during a grid failure and run only lighting, servers, prepress and a few fans. A large set carrying that load spends its outage hours lightly loaded, and soot accumulates faster than it burns.

If your plant is in the second group, look at whether some loads could sensibly run on DG, and plan periodic runs at a meaningful load. Our guide on understanding generator load factor and duty cycle explains how to measure your pattern, and the post on whether an RECD suits a DG set that runs only occasionally discusses the options for low-duty sets.

There is a neat link back to the route review here. If you decide to put make-up air units on the DG to fix building pressure, you also add a steady load that helps the filter.

Hot Work in a Printing Plant

The retrofit involves cutting and welding the exhaust line. In a plant with solvent inks, paper stock and film rolls, this needs careful control.

1. Check the hazardous area drawing. No hot work in or near a classified zone without a specific safe system of work.
2. Stop solvent operations nearby. If the route passes near the ink kitchen or solvent store, schedule the work for a time when these areas are closed and vapour-free. Use a gas detector to confirm before issuing the permit.
3. Clear combustibles. Paper reels, film rolls, cartons and waste bins within a safe radius should be moved or covered with fire blankets.
4. Hot work permit and fire watch. Keep extinguishers at the work point and maintain the watch after the work ends.
5. Protect process ducts. Sparks entering an extraction duct can travel to a dryer or filter. Cover nearby duct openings during cutting.

Flanged connections can reduce on-site hot work. See can an RECD be installed without cutting the existing exhaust pipe.

Timing Around Print Jobs

Printing plants run to customer deadlines, often with short notice. Packaging converters may run three shifts. Commercial printers see seasonal peaks around festivals, the financial year end and academic calendars.

• Choose a slow week, such as the weeks after a festival rush.
• Avoid days when solvent-heavy jobs are scheduled on presses near the route.
• Check the grid. If the plant must keep presses running during fitment, have a rental set on standby.

Fitment usually needs a day or two of downtime per set, after survey and fabrication are complete. Our RECD installation process guide explains the sequence.

Commissioning Checks for the Route

Beyond the vendor’s standard commissioning tests, add these route-specific checks:

• Surface temperatures of the cladding along the route, especially near any wall, ceiling or classified zone boundary
• Backpressure measured at the highest available load, compared with the engine maker’s limit
• Smoke or tracer test at the outlet with the process exhaust fans running, to see where the plume travels
• Odour check in the press hall, ink kitchen and near make-up air intakes while the DG runs on load
• Building pressure check, using a simple differential pressure gauge or tissue test at doors, with DG loads as they would run during a real outage
• Sampling port location confirmed for stack monitoring

Keep the results in your DG file. If an inspector visits, our note on what happens during a pollution control board inspection shows which records they tend to request.

Keeping the Route Under Review After Commissioning

Printing plants change. A new press arrives, an extra laminator is squeezed in, a solvent recovery unit is added or a make-up air unit is moved to free up roof space. Each of these can undo a good route review without anyone noticing, because the people planning the new equipment rarely look at the DG drawing.

Build a simple rule into your management of change procedure: any new or modified process exhaust, supply air unit or solvent area must be checked against the DG exhaust route and outlet before installation. Add the DG outlet and RECD location to the plant’s master ventilation drawing so it appears on every future layout discussion.

On the maintenance side, inspect cladding for damage after any roof work, keep the area around the RECD free of stored materials, and review IoT backpressure and temperature trends monthly. The RECD maintenance guide sets out routine checks.

The Route Review Sign-off Checklist

Before approving the vendor’s drawing, the plant engineer, the EHS lead and the person responsible for process ventilation should sign off on each item.

Item	Check	Signed
Separation from solvent areas	No part of the exhaust route in or near a hazardous area zone
Cladding and surface temperature	Full-length cladding; target surface temperature agreed
Penetrations	Fire-stopped and sealed; away from inlets
RECD location	Clear of process stacks, fans and make-up air intakes
Outlet	Height, direction and distance from intakes reviewed
No shared ducts	DG exhaust not connected to any process duct or stack
Backpressure	Calculated value within engine maker’s limit
Building pressure	Supply and exhaust balance reviewed; DG load schedule checked
Hot work plan	Permit, gas test, combustible clearance, duct protection
Access	Safe route for inspection and maintenance
Sampling port	Location meets SPCB requirements

Illustrative Plant Profiles

These composite examples are for illustration only.

Flexible packaging converter, Noida, 625 kVA

Two solvent-based rotogravure presses, a solventless laminator and a slitting section. The DG exhaust runs along the inside wall of the press hall to a roof outlet three metres from a make-up air unit. Operators report diesel smell during outages.

Review outcome: The RECD is mounted on a roof platform at the opposite end of the building, with a new external route that avoids the press hall wall entirely. The outlet is raised above the make-up air unit and moved well away from it. The make-up air units are added to the DG load schedule. The 625 kVA DG set RECD is the reference size.

Commercial offset printer, Okhla, 250 kVA

Sheetfed offset presses, a perfect binder and a guillotine section. Ventilation is light, but a wash-up solvent store sits beside the DG room.

Review outcome: The solvent store is relocated away from the DG room wall. The RECD is fitted inside the DG room, with full cladding and a sealed sleeve. The outlet is checked against the press hall windows. The 250 kVA DG set RECD is the reference model.

Frequently Asked Questions

Can the DG exhaust share a stack with the press dryer exhaust?

No. Keep the DG exhaust completely separate from any process duct or stack. Mixing them creates ignition and backflow risks and complicates compliance for both systems.

Will the RECD treat solvent vapour from the presses?

No. The RECD treats diesel engine exhaust only. Solvent vapour is handled by the plant’s process ventilation, oxidiser or recovery system.

Why does our pressroom smell of diesel during power cuts?

Usually because the building is under negative pressure and the DG outlet or sleeve is near an opening. During outages, if exhaust fans run on DG but make-up air does not, the effect gets worse. Seal gaps, move the outlet and rebalance airflows.

Is the exhaust surface hot enough to ignite solvent vapour?

Some parts can be, especially near the engine. That is why the route must stay clear of hazardous area zones and be fully clad.

Where should the RECD go in a printing plant?

Often outdoors, on a roof or wall platform, clear of process stacks and make-up air intakes, with safe access. The final choice depends on space, backpressure and your ventilation layout.

Do we need a hazardous area drawing before the retrofit?

If you use solvent-based inks, adhesives or coatings, you should already have one. Use it to review the exhaust route. If it does not exist, commission one.

Get the Route Right, Then Fit the Device

In a printing facility, the success of an RECD project depends on where its exhaust line runs and how that route sits among dryers, solvent areas and make-up air. A careful five-segment review, a quick airflow balance and a signed checklist will catch most problems before any metal is cut. Aceget supplies CPCB type-approved RECDs for DG sets from 25 kVA to 2500 kVA and can review your exhaust route during the site survey. Send us your DG details or explore the full retrofit emission control device range.