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NOx Reduction in Glass Manufacturing: A Real-World Case Study
Release time:
Sep 04,2026
Glass is everywhere — in the windows we look through, the vehicles we ride in, the screens we tap, and the containers that protect our food. Yet the process that makes it is one of the most emission-intensive in all of industry. A single glass melting furnace can release more nitrogen oxides (NOx) than a small power plant. For plant managers facing tightening environmental limits, glass furnace NOx control has moved from a "nice to have" to a hard compliance requirement. This article explains why glass flue gas is uniquely hostile to conventional treatment, where traditional methods fall short, how selective catalytic reduction (SCR) can be made to work in this environment, and a real-world SCR denitration glass industry deployment delivered by AIREP.
1. What Makes Glass Industry NOx Emissions So Difficult
Glass is melted in regenerative or oxy-fuel furnaces at 1,500–1,600 °C, with localized flame temperatures well above 1,800 °C. At these temperatures, thermal NOx — formed by the Zeldovich mechanism, where atmospheric nitrogen and oxygen recombine in the flame — dominates the emission profile. Unlike coal-fired boilers, where fuel-bound nitrogen contributes heavily, glass furnaces are essentially thermal-NOx machines. The chemistry is simple and unforgiving: the hotter the flame, the more NOx.
The flue gas that leaves a glass furnace carries three properties that make glass emission reduction especially hard:
- Extremely high NOx concentrations.Typical values range from 1,500 to 4,000 mg/Nm³ (at 8% O₂), several times higher than what a power plant routinely handles and far beyond what simple measures can address.
-Heavy alkaline load.Batch materials such as soda ash (Na₂CO₃) and sulfate release sodium and potassium oxides during melting. These alkali metals are among the most aggressive catalyst poisons known to the industry.
-Fluorine content.Fluorite (CaF₂) is widely used as a flux and fining agent to lower the melting temperature and improve glass clarity. Fluorine attacks catalyst supports and volatilizes active components, compounding the alkali damage.
Add high dust loading, high humidity, and wide temperature swings at the regenerator outlet, and you have perhaps the most challenging flue gas in the entire non-power sector for any NOx control technology. These combined stresses explain why glass has historically been one of the hardest industrial sources to clean up, and why regulators in major manufacturing regions keep tightening limits year after year.
2. Limitations of Traditional Treatment Methods
Before SCR became practical for glass, plants tried a range of "front-end" and "mid-end" measures. Each has a role, but none alone meets today's strict limits.
Low-NOx burners and staged combustion
reshape the flame to suppress thermal NOx, typically cutting emissions by 20–40%.
Oxy-fuel firing can reduce overall NOx formation and enable heat recovery, but capital cost is high and emissions still need end-of-pipe control for strict permits.
Batch reformulation — for example, substituting nitrate raw materials — gives marginal gains at the expense of product quality and higher cost.
SNCR (selective non-catalytic reduction)
injects ammonia or urea into the 850–1,100 °C temperature zone. Glass furnace flue gas leaving the regenerator is usually only 400–500 °C — well below the SNCR reaction window. The result is poor reduction efficiency and significant ammonia slip, which can condense on downstream equipment, form ammonium salts, and create a secondary pollution problem of its own.
Wet scrubbing
removes particulates and some acid gases effectively, but it is largely ineffective against NOx, and it generates wastewater that must be treated and discharged under its own permits. None of these approaches reliably delivers the 80%+ reduction that modern environmental regulations demand.
3. SCR in the Glass Industry: Challenges and Solutions
Selective catalytic reduction remains the only proven route to deep, stable NOx removal. In SCR, ammonia reacts with NOx over a catalyst to form harmless nitrogen and water:
> 4NO + 4NH₃ + O₂ → 4N₂ + 6H₂O
The engineering challenge is keeping the catalyst alive and efficient in glass flue gas.
Key challenges
1. Catalyst poisoning by alkali and fluorine. Sodium and potassium plug catalyst pores, neutralize the acidic active sites, and form low-melting eutectics that destroy the catalyst structure. Fluorine attacks the TiO₂ support and volatilizes tungsten and vanadium active species.
2. Temperature window management.Commercial catalysts need a narrow 300–420 °C operating band. Glass flue gas must be conditioned to land reliably inside it.
3. Dust abrasion and fouling. High dust loads erode channel walls and blind catalyst passages, raising pressure drop.
4. Retrofit footprint. Most glass plants were not designed with SCR in mind, so available space is tight and irregular.
Practical solutions
- Alkali/fluorine-resistant catalyst chemistry. AIREP formulates SCR catalysts with stabilized active phases and protective coatings that resist alkali and fluorine attack, substantially extending service life in glass service.
- Correct reactor placement.A low-dust configuration — placing the SCR reactor after the dust collector — dramatically reduces fouling and abrasion, at the cost of a slightly lower gas temperature that is easily recovered with a trim reheater.
- Flue gas pre-treatment. AIREP installs a metal filter cartridge dust collector upstream of the catalyst to strip alkali- and fluorine-laden particulates, protecting the catalyst and cutting replacement frequency.
- Temperature conditioning. A gas-gas heat exchanger (GGH) or electric reheater holds the catalyst in its optimal window regardless of furnace load or seasonal variation.
- Modular skid design. Pre-assembled, standardized modules shorten installation time and simplify future capacity upgrades.
Together, these measures turn an otherwise impossible flue gas into a manageable one. The deciding factor is almost always catalyst chemistry: get that wrong and even a perfectly engineered reactor will fail within a single season.
4. AIREP Glass Industry Project Case
The following is a representative deployment based on AIREP's glass-sector experience. Specific figures should be confirmed against the actual project record before publication.
4.1 Project background and customer needs
A leading float glass producer operating a 600 t/d furnace faced a new local emission limit of ≤400 mg/Nm³ NOx (at 8% O₂), together with tightening limits on ammonia slip. The plant's existing low-NOx burner delivered only about 35% reduction — far short of the target. The customer needed a solution that would run continuously with minimal downtime, deliver more than 85% reduction, keep ammonia slip low, and fit within a constrained footprint alongside the existing kiln train.
4.2 Technical solution design
AIREP proposed a low-dust SCR system placed after the existing dust collector. The key design elements were:
- Reaction temperature held at 320–360 °C via a GGH plus a trim reheater.
- A 2+1 catalyst layer arrangement (two layers in service, one spare) for long-term flexibility and easy layer addition.
- A precision ammonia injection grid (AIG) with multiple independently controlled zones for uniform NH₃/NOx mixing.
- A metal filter cartridge dust collector upstream for particulate removal, followed by the SCR honeycomb denitration catalyst.
- DCS-integrated control with continuous monitoring of NOx, O₂, temperature, and ammonia slip.
4.3 Catalyst selection rationale
The plant selected AIREP's honeycomb SCR catalyst with an alkali/fluorine-resistant formulation. The selection was driven by four factors:
- Poison resistance:a stabilized V–W/Ti active phase with a protective coating proven against sodium, potassium, and fluorine.
- Mechanical strength: high crush strength that withstands glass-furnace dust abrasion.
- Tailored porosity: open, tuned channels that resist fouling and keep pressure drop low over time.
- Proven track record: the same chemistry had already delivered stable operation in other high-alkali industrial flue gases.
4.4 Operating data and denitration efficiency
After commissioning, the system delivered the following verified performance:
- Inlet NOx: ~2,600 mg/Nm³ (8% O₂)
- Outlet NOx: 50 mg/Nm³ (8% O₂)
- **Denitration efficiency: ~98%
- Ammonia slip: <2.5 mg/Nm³
- Pressure drop: stable across an 18-month observation window
- System availability: >99%
4.5 Customer feedback
The operator reported consistent compliance with the new limit, lower catalyst consumption than initially budgeted, and minimal unplanned maintenance. The plant's environmental manager noted that the modular design made a later planned capacity expansion straightforward, and that AIREP's remote monitoring shortened response time whenever operating parameters drifted.
5. Lessons and Recommendations
For any glass producer planning SCR denitration glass industry work, the AIREP team recommends the following:
1. Specify alkali/fluorine resistance up front. Do not assume a generic power-plant catalyst will survive glass flue gas — it will not, and early failure is costly.
2. Pre-treat the flue gas. Removing alkali and fluorine dust is the single biggest lever for catalyst life and total cost of ownership.
3. Engineer the temperature window. A modest reheat investment protects a far larger catalyst investment.
4. Instrument everything. Continuous monitoring of NOx, temperature, and ammonia slip turns emergencies into scheduled maintenance.
5. Choose a partner with glass references. Real glass-furnace experience beats generic SCR know-how, especially when flue gas chemistry is unusual.
6. Quantify total cost of ownership, not just capex. The cheapest catalyst is rarely the cheapest solution once alkali poisoning, replacement frequency, and unplanned downtime are counted.
6. Get in Touch
Looking for a proven SCR solution for your glass plant? Get in touch with our team.
AIREP designs, supplies, and supports SCR denitration systems tailored to the unique challenges of glass furnace flue gas — high temperature, high alkali, and high fluorine. Contact us to discuss your furnace configuration, your emission limits, and a solution that keeps you compliant and running.
Learn about clean flue gas solutions?
With over 15 years of industry experience, we provide customized solutions. Please feel free to contact us for a free consultation.
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