Industrial case study: Retrofit of a multi-stage VOC removal and deodorization system on a 1,200 kg/h post-consumer r-HDPE bottle recycling line, achieving 96.8% VOC removal efficiency.
The situation
A project is read from the conditions it began with — the profile, the background and the constraints are the customer's, and the result only means something beside them.
Capture and treat 100% of fugitive emissions from extruder degassing ports and the pelletizer shroud; achieve Non-Methane Hydrocarbon (NMHC) emissions < 20 mg/m³ at the exhaust stack, and reduce workshop odor concentration to ≤ 30 OU (Odor Units) without causing backpressure on the extruder vacuum pumps.
An established post-consumer plastic recycling enterprise in East China operating three multi-stage extrusion pelletizing lines with a combined annual capacity of 25,000 tons of high-grade recycled HDPE (r-HDPE) granules for industrial containers and drainage pipes.
Post-consumer HDPE bottle flakes frequently carry stubborn residues of laundry detergents, cooking oils, fragrance surfactants, and printing inks. When melted at 200°C–230°C in an extruder barrel, these contaminants undergo severe thermal desorption and partial cracking, releasing volatile short-chain hydrocarbons, acrolein, fatty acids, and noxious organic odors that violate environmental discharge standards.
The existing 1,200 kg/h r-HDPE single-screw recycling line operated with an open water ring pelletizer and two vacuum degassing ports venting directly into the workshop atmosphere. Workshop ambient VOC concentration exceeded 85 mg/m³, with dense oil mist accumulation on roof steel structures and recurring complaints from surrounding industrial park facilities.
The system had to be retrofitted without altering the existing extruder’s vacuum degassing efficiency (-0.095 MPa), and outdoor installation footprint was restricted to an 8.5 m x 3.5 m equipment corridor beside the plant perimeter wall.
Delivery
The scope below is what this project actually received; the configuration snapshot is the one agreed for this delivery, not a current product sheet.
A multi-stage mechanical demisting + electrostatic precipitation (ESP) + deep-bed carbon system was chosen over direct thermal oxidation (RTO) because the exhaust volume (15,000 m³/h) carried significant sub-micron oil droplets that would clog RTO ceramic media, while carbon adsorption provides low operational energy cost and rapid ROI for intermittent recycling loads.
Custom SUS304 capture hoods were designed with gas-tight silicone seals contoured exactly to the extruder vacuum ports and pelletizer chute, equipped with counterweighted manual balance dampers to prevent air infiltration from overloading the system.
Main industrial exhaust abatement skid treating all vacuum vent and pelletizing exhaust streams.
Fully skidded unit mounted outdoors adjacent to extrusion bay, wired to master PLC.
Captures 98%+ of fugitive vapors directly at the twin degassing vents and water-ring cutting hood.
Included 45 meters of SUS304 ductwork with condensate drain traps.
Ionizes and collects sub-micron oily aerosols and plasticizer droplets to prevent carbon bed fouling.
Automatic spark quench and high-voltage power regulation cabinet included.
Air balance calibration, electrical hookup, and emission compliance sign-off.
Included operator maintenance training for ESP plate cleaning and carbon replacement.
Verification
A stage is written down only when there is evidence for it; a project that is running says so, and a project still in the factory does not claim more.
Factory Tested
The complete VOC treatment skid underwent factory dry-run testing before dispatch: fan dynamic balance verification, ESP high-voltage dielectric breakdown test at 75 kV, and air tightness pressure testing on the carbon vessel housing.
Shipped
The treatment skid and pre-fabricated stainless ducting were transported via two 13.5-meter flatbed logistics trucks with all components weather-wrapped and crated.
Installed
The outdoor skid was positioned on a concrete pad adjacent to the plant wall. Stainless steel ducting was routed through high-level penetrations down to the extruder ports over a scheduled 36-hour planned maintenance shutdown, causing zero unplanned production downtime.
Commissioned
The system was commissioned over three consecutive 8-hour production shifts with the customer’s r-HDPE recycling line running at full 1,200 kg/h capacity. Gas sampling probes measured inlet and outlet NMHC concentrations, ESP current stability, and air pressure drop across the activated carbon bed.
In Operation Verified
The system has operated continuously for over 14 months on a 24/7 basis. Routine maintenance consists of monthly ESP collector plate high-pressure hot water washing and annual activated carbon replacement.
Results
Every result names its evidence. A number without the method and conditions behind it would not be a result worth quoting.
580 18.5
mg/m³
Stack Non-Methane Hydrocarbon (NMHC) emissions dropped from 580 mg/m³ to 18.5 mg/m³, achieving 96.8% VOC removal efficiency and easily satisfying local environmental standards (< 50 mg/m³).
Evidence Customer Confirmation
1500 30
OU (dimensionless)
Exhaust odor concentration was reduced from over 1,500 OU to ≤ 30 OU, completely eliminating acrid plastic fumes and pungent perfume odors from surrounding industrial receptors.
Evidence Commissioning Record
The integrated negative-pressure draft control prevented any oily mist buildup inside the extruder vacuum lines, maintaining steady vacuum degassing without a single emission-related plant shutdown in over a year.
Evidence Customer Confirmation
Evidence
Only material the customer has cleared for publication is shown here.
Details
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