- October 3, 2026
- Posted by: Aceget
- Category: RECD & Emission Control Devices
Stand next to a hydraulic injection moulding machine and watch its ammeter. The needle climbs as the screw drives melt into the mould, eases during hold, rises again while the screw recovers, and drops almost to nothing while the part cools. Then the clamp opens, the part falls, and the whole pattern repeats every twenty or thirty seconds, around the clock.
Now picture twenty of those machines, a few extruders, a blow moulding line, chillers, dryers and a granulator that roars into life whenever someone feeds it a tray of runners. That is the load a plastics plant hands its DG set during a grid failure. It is busy, restless and very different from the smooth load of a pump house or office block.
When you plan an RECD for plastic manufacturing units, the cyclic nature of that load is the thing to understand first. It affects how hot the exhaust runs, how much soot the engine produces at each load step, and whether the generator was sized sensibly in the first place. This guide breaks the load down machine by machine, shows a worked averaging method you can repeat with your own numbers, and ends with a set of checks to agree with your vendor.
Where Plastics Units Stand on DG Emission Rules
Plastics processing clusters sit in and around the National Capital Region in large numbers: Bawana, Narela and Mundka in Delhi, the industrial areas of Noida, Ghaziabad, Sahibabad, Faridabad, Bahadurgarh, Sonipat and Kundli. Many are MSMEs with one DG set. Larger moulders supplying the automotive and appliance sectors often run two or three.
The NCR framework that most of these units work under comes from CAQM Direction No. 76 of September 2023. In short: generators between 19 and 125 kW were to convert to dual fuel; those between 125 and 800 kW could choose dual fuel or a retrofit emission control device; and those above 800 kW were to fit an RECD. Earlier, CAQM had also said that DG sets up to 800 kW could be permitted for industrial and commercial use subject to dual fuel conversion where gas infrastructure existed. Directions get revised, so check the latest CAQM order and your SPCB before deciding. Our GRAP rules for DG sets in Delhi NCR post explains the seasonal restrictions on top of these rules.
Many plastics units have a choice between the two routes. A good load assessment is one of the best tools for making that choice, because the two technologies respond differently to the load pattern. Our comparison of RECD vs dual fuel kit covers the broader trade-offs.
Why Cyclic Loads Matter to an RECD
An RECD combines a diesel oxidation catalyst with a diesel particulate filter. The filter traps soot and then needs to burn it off. The cleanest way for that to happen is passive regeneration during normal running, which depends on the exhaust staying hot. Hotter exhaust comes from higher engine load. If you are new to the device, our article on what a diesel particulate filter is and how it helps is a good primer.
A cyclic load raises three separate questions:
- What is the average load? This decides the general exhaust temperature and therefore how well the filter regenerates.
- How large and how fast are the load steps? These decide how much extra soot the engine produces in brief bursts, and how hard the governor and voltage regulator have to work.
- How often does the plant drop to near idle? Mould changes, material changeovers and break times can leave a big set running almost empty.
Plastics plants are interesting because the answers to those three questions are often in tension. A plant can have a healthy average load, sharp steps that create smoke puffs, and long idle spells on certain days. You need to look at all three.
Thermal mass smooths the seconds, not the hours
This point surprises many plant engineers. An exhaust manifold, a run of steel pipe and a ceramic filter block together hold a lot of heat. When the load on the engine jumps for three seconds during injection and falls for ten seconds during cooling, the temperature inside the filter does not follow every jump. It settles somewhere close to what the average load would produce.
That means a machine cycle measured in seconds does not, by itself, starve the filter of heat. What matters for regeneration is the load averaged over minutes and hours. A plant whose average is high will regenerate well even with a jagged load trace. A plant whose average is low will struggle even if the trace contains frequent peaks.
The seconds still matter for a different reason, which we cover under transient soot below.
Anatomy of the Loads in a Plastics Plant
Different processes produce very different load shapes. Here is what each one typically looks like from the generator’s side.
Hydraulic injection moulding machines
A conventional hydraulic machine runs an electric motor driving a hydraulic pump. Older machines use fixed-displacement pumps, which keep the motor running at substantial power even when little oil is needed, with excess flow dumped over a relief valve. The cycle phases look roughly like this:
| Cycle phase | What the machine is doing | Motor demand (relative) |
|---|---|---|
| Clamp close | Platen moves, mould locks | Moderate to high |
| Injection | Screw pushes melt into the cavity | Highest |
| Hold or pack | Pressure held while the part freezes off | Moderate |
| Screw recovery | Screw rotates to plasticise the next shot | High |
| Cooling | Part cools in the mould | Low |
| Open and eject | Platen opens, ejectors push the part | Moderate |
On top of the motor, barrel heater bands switch on and off under temperature control. During steady production they might run at a third to a half of their rated power on average, but at start-up they are on continuously.
Servo-hydraulic and all-electric machines
Servo-driven pumps only spin as fast as the cycle needs, and all-electric machines use servo motors for each axis. Both cut average power substantially compared with fixed-pump hydraulics. Independent studies such as the ACEEE paper on all-electric injection moulding machines reported large energy savings, and work at NIST on profiling energy consumption in injection moulding showed how power varies through the cycle. For DG planning, the practical effect is that a plant which has replaced old hydraulic machines with servo or electric ones may now be running a generator sized for a load that no longer exists.
Extruders
Pipe, profile, film and sheet extruders are the steady performers of a plastics plant. The main motor runs continuously at a fairly constant load once the line is up to speed, and barrel and die heaters cycle gently. Extrusion lines are friendly to a DPF: high, steady load and a hot exhaust.
Blow moulding
Extrusion blow moulding combines a continuous extruder with a cyclic clamp, blow and cut sequence. Accumulator-head machines for large containers add a pronounced step when the accumulator pushes out the parison. Stretch blow moulding for PET bottles often adds a high-pressure air compressor, itself a large cyclic load.
Thermoforming
Heater banks warm the sheet, the form station operates, and the cycle repeats. Heater loads can be large and switch in blocks.
Granulators and shredders
These are the troublemakers. A granulator spins up from rest with a high starting current, and when a large sprue or a lump of purging is fed in, the motor can see a sudden shock load. On a small DG set this can cause a visible voltage and frequency dip.
Auxiliaries
Chillers, mould temperature controllers, hopper dryers and dehumidifying dryers, vacuum loaders, air compressors and cooling towers make up a large share of the total. Chillers and compressors cycle on their own control logic, not in step with the machines.
Our load calculation basics before buying a generator shows how to list connected loads. In a plastics plant, that list is only the start, because the shape of each load matters as much as its size.
The Averaging Worksheet: A Worked Example
The method below estimates the average load your DG carries in each operating mode. You can do it with a spreadsheet and some readings from a clamp meter or the machines’ own energy displays. The figures are illustrative.
Step 1: Build a cycle profile for one representative machine
Take a 250 tonne hydraulic machine with a fixed-displacement pump, running a 30 second cycle. Measure or estimate motor power in each phase:
| Phase | Duration (s) | Motor kW | kW x s |
|---|---|---|---|
| Injection | 3 | 40 | 120 |
| Hold | 5 | 25 | 125 |
| Screw recovery | 8 | 35 | 280 |
| Cooling | 10 | 10 | 100 |
| Open, eject, close | 4 | 30 | 120 |
| Total | 30 | 745 |
Average motor power = 745 / 30 = about 25 kW.
Add heaters. With 20 kW of heater bands running at roughly 40% duty in steady production, that is 8 kW. The machine’s average draw is therefore about 33 kW, while its instantaneous peak is around 60 kW when injection and heaters coincide. The ratio of peak to average is close to 1.8.
Step 2: Repeat for each machine type
Do the same for each family of machines, then group them:
| Load group | Quantity | Average kW each | Group average kW |
|---|---|---|---|
| 250 T hydraulic moulders | 8 | 33 | 264 |
| 150 T servo moulders | 4 | 12 | 48 |
| Chillers and mould controllers | 45 | ||
| Dryers and loaders | 20 | ||
| Air compressor | 22 | ||
| Granulators (average across the shift) | 2 | 5 | |
| Lighting, office, cooling tower | 15 | ||
| Plant average, full production | 419 |
Step 3: Compare with the DG rating
Suppose the plant runs one 750 kVA set, which at 0.8 power factor gives about 600 kW. At full production the average load is 419 / 600, roughly 70%. That is a comfortable place for passive regeneration. Our explainer on how to read a generator’s kVA and kW rating covers the conversion.
Step 4: Repeat for every operating mode
Now the important part. A plant does not run at full production all the time. List each mode and estimate it:
| Operating mode | Typical average kW | % of 600 kW | Comment |
|---|---|---|---|
| Full production, all machines | 419 | 70% | Good regeneration |
| Night shift, half the machines | 226 | 38% | Borderline |
| Start-up after a stop (heaters all on) | 330 | 55% | Short but helpful |
| Mould change or maintenance day | 60 | 10% | Very light; soot builds |
| Lunch or shift change (machines on standby) | 120 | 20% | Light |
The picture is clearer now. The set regenerates well during day production but spends meaningful time in light modes. Whether that is a problem depends on how many DG hours fall in each mode, which is why step 5 matters.
Step 5: Weight by DG running hours
Look at your outage pattern. If the grid in your area fails mostly during the day, most DG hours will fall in full production. If outages cluster at night or on Sundays when only toolroom and maintenance work is happening, the set may spend more of its life at light load. Weight each mode by the share of DG hours it represents. Our guide on understanding generator load factor and duty cycle explains the idea in more detail.
Diversity: Why Twenty Machines Behave Better Than Three
In a plant with many machines running unsynchronised cycles, their peaks rarely line up. One machine is injecting while another is cooling and a third is ejecting. Add them together and the aggregate load trace is much smoother than any single machine’s, typically swinging only a modest amount around the average.
A small unit with two or three large machines is a different story. With so few machines, their injection phases coincide often, and the aggregate swings widely.
Consider an illustrative small moulder with three 150 tonne hydraulic machines, a chiller and some auxiliaries on a 160 kVA set (about 128 kW). Average load is around 90 kW, a healthy 70%. But when all three machines inject together while heaters are on and the chiller compressor cuts in, the instantaneous demand can approach or briefly exceed the set’s rating. The operator sees the lights dip and the DG note change.
For this kind of plant, the average looks fine for the RECD, yet the transient behaviour needs attention. That leads to the next two topics.
Transient Soot: The Puff on Every Step
When a diesel engine meets a sudden increase in load, the governor opens the fuel rack straight away. The turbocharger, however, takes a moment to spool up and deliver extra air. For that brief interval, the engine burns more fuel than its air supply can fully oxidise, and a puff of dark smoke leaves the stack. Our article on why a generator emits black smoke describes the same mechanism in a fault-finding context.
On a set feeding a plastics plant, these steps happen many times an hour: granulator starts, chiller compressor cut-ins, accumulator shots and coincident injections. Each puff sends a little extra soot into the DPF. A filter that would comfortably handle the soot from steady running may load faster on a plant with frequent large steps.
What reduces transient soot:
- Smaller steps. Soft starters or VFDs on granulators, compressors and chiller compressors limit the size of each jump.
- Staggered starts. Bring machines and auxiliaries online one at a time after the DG takes over, instead of letting everything restart together.
- A healthy engine. Worn injectors, a sticky turbo or a restricted air filter make transient smoke much worse.
- A good base load. An engine already running at moderate load handles a step better than one starting from near idle.
The RECD itself is designed to trap these puffs, which is one of its main benefits. The aim is not to eliminate them entirely, but to make sure the filter’s regeneration keeps pace.
Voltage and Frequency: Will the RECD Change Anything?
Plant engineers sometimes ask whether adding an RECD will make the DG less able to handle load steps. A correctly sized device keeps exhaust backpressure within the engine maker’s limit, so the engine’s ability to accept load should not change in any meaningful way. Our post on whether an RECD changes a generator’s usable power output covers this.
That said, a filter that is allowed to load up with soot does raise backpressure, and a heavily restricted exhaust can affect transient response. This is one more reason to watch backpressure trends after installation.
If your plant already sees voltage dips and frequency swings on DG, those problems belong to sizing, governor tuning and AVR settings, not to the RECD. It is worth fixing them during the same project. Our guides on diagnosing voltage fluctuations in a generator and on generator frequency problems are useful references. Injection moulding controllers, servo drives and robots are sensitive to poor power quality, and scrap rates often rise during DG running for exactly this reason.
The Opposite Problem: Oversized Sets After a Machine Upgrade
Many plastics units in NCR bought their generator ten or fifteen years ago, when the shop floor was full of fixed-pump hydraulic machines. Since then, they have added servo machines, replaced old chillers with efficient ones and fitted energy-saving drives. Production has gone up, but the electrical load has not.
The result is a DG that was correctly sized for the old plant and is now oversized for the new one. If the averaging worksheet shows the set running below about a third of its rating for most of its hours, regeneration will be slow and soot will accumulate. Engines that run light for long periods also suffer wet stacking, which adds oily deposits to the exhaust.
Options in that situation:
- Consolidate loads onto the DG. Make sure the DG carries everything it reasonably can during outages rather than shedding non-critical loads by default.
- Exercise the set under load. Schedule periodic runs on a resistive load bank or on full production load.
- Right-size at replacement. If the set is near the end of its life, a smaller, compliant new set may be better than retrofitting the old one. Compare with RECD vs new CPCB IV+ genset cost comparison.
- Discuss the duty with the vendor. Some designs suit lighter duty better than others.
The general method in our generator sizing for factories guide helps check whether your set fits your current plant.
Taking Measurements Without Stopping Production
The worksheet works best with real data. Here is a low-disruption way to collect it.
What to measure
- Total kW and kVA at the DG output during at least one real outage, preferably several, using a logging power analyser
- Representative cycle profiles for one machine of each type, using a clamp meter with a fast logging rate
- Heater duty from the machine controller or by logging heater contactor current
- Start current and duration for granulators and compressors
Logging interval
To see the cycle shape, log one machine at one-second intervals or faster. To see the plant average, one-minute intervals at the DG output are enough, because thermal mass smooths faster changes.
When to measure
Capture a full production day, a night shift, a mould change day and a restart after a stop. Exhaust temperature measured at the planned RECD location, during those same periods, is the most direct evidence of what the filter will see.
Pre-Purchase Checks to Agree with the Vendor
Before you order, put these points on paper with your vendor:
| Check | Why it matters for a cyclic load |
|---|---|
| Average load by operating mode | Confirms regeneration conditions over the year |
| Largest single load step and its frequency | Helps estimate transient soot loading |
| Engine condition, especially turbo and injectors | A tired engine makes every step smokier |
| Calculated backpressure at full load | Must sit within the engine maker’s limit |
| Backpressure alarm thresholds | Early warning of soot build-up |
| Strategy for light-load periods | Load bank exercise, schedule or design choice |
| IoT data access for the plant engineer | Lets you compare backpressure trends with production patterns |
| CPCB type approval for the model offered | Basic compliance requirement |
Our page on how to read an RECD test certificate helps you check the approval paperwork.
Scheduling the Fitment in a Moulding Shop
Plastics plants rarely stop. Moulds run against delivery schedules, and customers expect parts every day. A few practical points for the fitment window:
- Use a planned mould change or maintenance day. Most shops plan these anyway. If the grid is stable, the DG can be out of service for the day or two fitment usually needs.
- Avoid peak heat months if possible. North Indian summers bring both heavy grid failures and high chiller loads.
- Keep moulds warm or plan a restart. If a long outage hits while the DG is out of service, heaters cool and restart scrap rises. Have a rental set lined up if your feeder is unreliable.
- Watch hot work near materials. Polymer granules, packaging film and finished goods burn readily. Clear the area, issue a hot work permit and post a fire watch. Our list of common RECD installation mistakes includes several site preparation points.
After Commissioning: Reading the Trends
Once the device is running, compare its data with your production calendar.
- Backpressure falls or holds steady during day production and rises slowly at night or on maintenance days. This shows regeneration is working when load is high.
- Backpressure climbs steadily week after week. Either the average load is lower than estimated, or transient soot is higher. Revisit the worksheet and the engine.
- Sudden jumps in backpressure after granulator or compressor starts suggest large, smoky steps. Consider soft starters.
- Exhaust temperature consistently low in particular shifts confirms where to schedule a loaded exercise run.
Fold these reviews into the plant’s monthly maintenance meeting. The RECD maintenance guide covers inspection routines.
Illustrative Plant Profiles
These are composite examples for illustration, not real customers.
Pipe extrusion plant, 500 kVA
Two PVC pipe lines and one HDPE line run continuously. Average DG load is high and steady. The main risk is a long weekend stop, so the plant schedules a loaded test run before restart. An RECD fits comfortably; the 500 kVA DG set RECD is the reference size.
Mixed moulding shop, 750 kVA
The worked example above. Good day loads, light night and maintenance-day loads. The plant adds a monthly load bank run and moves non-urgent night maintenance to shifts with production running.
Small moulder, 160 kVA
Three hydraulic machines and a granulator. Healthy average, sharp coincident peaks. The owner fits a soft starter on the granulator, staggers machine restarts after changeover, and checks whether the set’s kW rating places it in the dual fuel band. The 160 kVA RECD page and the 160 kVA dual fuel kit page let him compare both routes.
Frequently Asked Questions
Do rapid injection cycles stop the DPF from regenerating?
Not on their own. The exhaust system’s thermal mass smooths second-by-second swings, so regeneration depends mainly on average load over minutes and hours. Check the average load in each operating mode instead of the instantaneous trace.
Will an RECD make my DG struggle with load steps from moulding machines?
A correctly sized RECD keeps backpressure within the engine maker’s limit, so step response should not change meaningfully. Existing dips on DG usually come from sizing, governor or AVR settings.
Why does my generator puff smoke when the granulator starts?
A sudden load step makes the engine burn extra fuel before the turbocharger supplies extra air. The RECD traps this soot, but frequent large steps load the filter faster. Soft starters and staggered starts help.
We replaced hydraulic machines with servo ones. Does that matter?
Yes. Servo and all-electric machines draw much less average power, so your DG may now run light. Recalculate the average load before specifying the RECD and plan for periodic loaded runs if needed.
How long should we log load before choosing an RECD?
Capture at least one full production day, one night shift, one maintenance day and one restart. Several real outage events give the most reliable picture.
Should a plastics unit choose an RECD or dual fuel?
It depends on your set’s kW band under the current CAQM direction, gas availability and your load pattern. Use the averaging worksheet to compare how each option would cope with your plant’s duty.
Start With the Load, Then Choose the Device
The best RECD project in a plastics plant begins on the shop floor, with a clamp meter and a spreadsheet. Once you know your average load in each mode, your largest steps and your light-load hours, choosing and running the right device becomes much simpler. Aceget supplies CPCB type-approved RECDs with IoT monitoring for sets from 25 kVA to 2500 kVA. Share your load data and nameplate details through our contact page, or browse the RECD range to see sizes and specifications.