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AIREP SCR Systems Meet UL Certification Requirements — Fully Compliant with U.S. EPA Emission Standards
Release time:
Jul 26,2026
When industrial facilities in the United States need to reduce nitrogen oxide (NOx) emissions, two questions inevitably arise: Does the SCR system meet UL certification requirements? and Will it satisfy EPA emission regulations? At AIREP, the answer to both is yes — and here's how we make it happen.
Why UL Certification Matters for SCR Systems
Underwriters Laboratories (UL) standards are not optional for equipment installed in U.S. industrial facilities — they are the baseline for safety compliance, insurance approval, and regulatory acceptance. For an SCR (Selective Catalytic Reduction) denitrification system, several UL standards apply simultaneously:
UL 508A — Industrial Control Panels
Every SCR system relies on a PLC-based control cabinet to manage ammonia injection, temperature regulation, and emission monitoring. UL 508A is the governing standard for these industrial control panels. Compliance means:
- All components inside the panel must be UL-listed
- Wiring, spacing, and enclosure ratings must meet UL specifications
- The panel must carry a UL 508A nameplate upon certification
AIREP designs and builds our control panels to UL 508A requirements from the outset, selecting UL-listed components for breakers, contactors, relays, and terminal blocks — so there are no surprises during the NRTL (Nationally Recognized Testing Laboratory) inspection.
UL 2200 3rd Edition — Stationary Engine Generator SCR
This is the one everyone is talking about. The third edition of UL 2200, effective March 31, 2026, introduces explicit requirements for SCR aftertreatment systems connected to stationary generators — particularly those serving Life Safety applications. The key provisions include:
- SCR fault must not cause generator shutdown — The SCR system must fail safe without taking the generator offline
- Watchdog timer — Continuous monitoring of the SCR controller; automatic alarm on communication loss
- Pressure and temperature alarms — High exhaust back-pressure and over-temperature must trigger alarms and protective actions
- Emergency stop (E-stop) — A dedicated hardware E-stop circuit independent of software control
- Pressure testing — The SCR housing must pass documented hydrostatic or pneumatic pressure testing
These requirements reflect a fundamental shift: the SCR system is no longer treated as peripheral equipment. It is now part of the safety-critical chain for emergency power generation.
Additional UL Standards in SCR Applications
| Standard | Scope |
| UL 499 | Electric heaters (ammonia vaporizer heating) |
| UL 515 | Electrical heat tracing (pipe and vessel frost protection) |
| UL 61010| CEMS analyzers and emission monitoring instruments |
Explosion-Proof Requirements for Ammonia Areas
Ammonia storage and vaporization zones fall under NEC Article 505 (Class I, Division 1/2) or NEC Article 500 (Class I, Zone 1/2) in the U.S. All electrical equipment — lighting, junction boxes, sensors, solenoid valves — in these areas must carry appropriate explosion-proof certifications. AIREP specifies Zone/Division-rated components and explosion-proof enclosures for all ammonia-area equipment, aligned with both NEC and IECEx frameworks.
EPA Emission Standards — Where SCR Delivers
The U.S. Environmental Protection Agency (EPA) enforces some of the world's most stringent NOx limits. Key regulatory frameworks include:
- 40 CFR Part 60 (NSPS) — New Source Performance Standards for stationary combustion sources
- 40 CFR Part 63 (NESHAP / MATS) — National Emission Standards for Hazardous Air Pollutants, including the Mercury and Air Toxics Standards
- CSAPR — Cross-State Air Pollution Rule, which sets state-level NOx and SO₂ budget allowances
- Tier 4 Final — Off-road and stationary engine emission limits (as low as 0.30 g/kWh NOx)
IRA Section 45V and the ≤35 mg/Nm³ Threshold
The Inflation Reduction Act's Section 45V clean hydrogen production tax credit introduces a new performance gate: to qualify for the highest credit tier, hydrogen production facilities must demonstrate low lifecycle emissions. For co-located or upstream NOx sources, this effectively means NOx emissions ≤ 35 mg/Nm³ (at reference O₂) — a level that requires precisely engineered SCR systems with high-activity catalysts.
AIREP's catalyst formulations and system designs consistently achieve “NOx reduction efficiencies above 90%”, delivering outlet concentrations well below 35 mg/Nm³ — even in challenging conditions such as high sulfur, high dust, or variable-load operation.
EPA Verified Technologies List
The EPA maintains a Verified Technologies List for NOx control. SCR technology is recognized as a proven, verified approach for stationary source NOx reduction. AIREP systems are designed to align with the performance parameters established in EPA-verified test protocols, facilitating smoother permitting and compliance demonstrations for our clients.
The AIREP Advantage: From Inlet to Outlet
What sets AIREP apart is not just that we make catalysts — it's that we engineer the entire SCR system as an integrated solution.
1,500+ Projects, Real-World Complexity
With over 1,500 SCR project references worldwide, AIREP has tackled the tough cases: high-temperature exhaust from gas turbines (including CNOOC and AECC projects above 500°C), high-sulfur flue gas from sulfuric acid plants, and variable-load applications from distributed generation. This experience means we don't just design to the standard — we design for the reality.
Catalyst + System Integration
AIREP supplies the complete SCR package:
- Honeycomb/catalyst elements — manufactured in-house, tailored to your flue gas conditions
- Reactor and housing — designed to UL 2200 pressure test requirements
- Ammonia injection and vaporization system — with UL 499-compliant electric vaporizers
- Control system (PLC + HMI) — built to UL 508A, with watchdog timers and E-stop per UL 2200
- CEMS and analyzers — UL 61010-rated continuous emission monitoring
This single-source approach eliminates interface gaps between catalyst and equipment — the most common source of performance shortfalls in multi-vendor SCR projects.
Fast Estimation with Our Calculator Tool
Need a quick estimate of catalyst volume and NOx reduction for your project? Try our [SCR Catalyst Calculator](https://www.aireptech.com/calculator.html) — input your flue gas parameters and get an instant sizing result.
NRTL Certification Support
We don't just build to spec and walk away. AIREP works with your team and your chosen NRTL to facilitate the UL certification process — providing documentation, supporting factory witness testing, and coordinating any design modifications required for certification closure.
Moving Forward
Whether you're upgrading an existing SCR system for UL 2200 3rd Edition compliance, building a new installation that must meet EPA NOx limits, or pursuing IRA 45V qualification, AIREP has the experience and the integrated capability to deliver.
ext steps:
- Estimate your catalyst needs: [SCR Calculator](https://www.aireptech.com/calculator.html)
- Discuss your project: [Contact AIREP](https://www.aireptech.com/contact.html)
Shandong AIREP Environmental Protection Technology Co., Ltd. — 1,500+ SCR projects worldwide. UL-ready. EPA-compliant.
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Last Updated: March 27, 2026
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