Hydrogen combustion is increasingly viewed as a pathway to decarbonize high-temperature industrial processes, particularly in steel, glass, and cement manufacturing. Unlike fossil fuels, hydrogen burns without emitting carbon dioxide, though nitrogen oxide (NOx) emissions remain a concern due to high flame temperatures. Understanding emission benchmarks, retrofit challenges, and monitoring practices is critical for industries transitioning to hydrogen-based systems.
### Emission Benchmarks
**Steel Industry**
Traditional blast furnaces emit approximately 1.8 to 2.2 tons of CO2 per ton of steel produced. Hydrogen-based direct reduction iron (DRI) processes can reduce emissions to 0.5 to 0.8 tons of CO2 per ton of steel when using green hydrogen. Pilot projects have demonstrated NOx emissions ranging from 50 to 150 mg/Nm³, depending on combustion conditions and burner design.
**Glass Industry**
Conventional natural gas-fired glass furnaces emit 0.5 to 0.7 tons of CO2 per ton of glass. Hydrogen combustion can eliminate CO2 emissions, but NOx levels may increase to 100 to 300 mg/Nm³ without mitigation measures. Trials with hydrogen-natural gas blends (20-30% H2) show NOx reductions of 10-15% compared to pure hydrogen.
**Cement Industry**
Cement kilns typically produce 0.8 to 1.0 tons of CO2 per ton of clinker. Hydrogen substitution in precalciner burners can reduce CO2 emissions by 30-40%, but full decarbonization requires addressing process emissions from limestone calcination. NOx emissions with hydrogen combustion range from 200 to 400 mg/Nm³, necessitating selective catalytic reduction (SCR) systems.
### Retrofitting Challenges
**Steel Furnaces**
Existing blast furnaces cannot operate on pure hydrogen due to material constraints and process chemistry. Retrofitting requires shifting to DRI-electric arc furnace (EAF) routes, which demand new infrastructure. Challenges include hydrogen embrittlement of pipelines, storage safety, and the need for high-purity hydrogen to avoid contamination.
**Glass Furnaces**
Glass furnaces face refractory degradation under hydrogen atmospheres, as hydrogen can react with silica-based linings. Burner modifications are necessary to accommodate hydrogen’s high flame speed and wider flammability range. Temperature uniformity is harder to maintain, impacting glass quality.
**Cement Kilns**
Cement kilns require burner redesign to prevent flame instability and localized overheating. Hydrogen’s low density necessitates higher volumetric flow rates, complicating fuel handling. Process emissions from raw materials remain a barrier, requiring supplementary carbon capture or alternative binders.
### Best Practices for Emission Monitoring
Continuous emission monitoring systems (CEMS) must be adapted for hydrogen applications. Key considerations include:
- **NOx Measurement:** Laser-based analyzers or chemiluminescence detectors provide accurate real-time data.
- **Hydrogen Leak Detection:** Catalytic bead sensors or infrared detectors should be installed near storage and piping.
- **Combustion Control:** Advanced process control systems optimize air-fuel ratios to minimize NOx while maintaining efficiency.
### Case Studies
**Steel: HYBRIT Project (Sweden)**
The HYBRIT initiative successfully replaced coking coal with hydrogen in a pilot DRI plant, achieving a 90% CO2 reduction. Emissions were monitored using integrated CEMS, with NOx controlled via staged combustion. The project highlighted the need for scalable hydrogen storage to buffer supply fluctuations.
**Glass: Pilkington UK Trials**
Pilkington tested a 20% hydrogen blend in a float glass furnace, reducing CO2 emissions by 12%. NOx levels remained within regulatory limits due to flue gas recirculation. The trial identified refractory wear as a long-term concern, prompting material upgrades.
**Cement: HeidelbergCement Germany**
HeidelbergCement demonstrated hydrogen use in a precalciner burner, cutting CO2 emissions by 35%. SCR systems kept NOx below 200 mg/Nm³. The project revealed challenges in hydrogen supply consistency, emphasizing the need for onsite electrolysis or storage buffers.
### Conclusion
Hydrogen offers a viable route to cut emissions in heavy industries, but technical and economic hurdles persist. Retrofitting demands careful material selection, burner redesign, and robust emission monitoring. Pilot projects provide valuable insights, though scaling requires policy support and infrastructure investment. The steel, glass, and cement sectors must collaborate on standardization and best practices to accelerate adoption.