### Understanding Boiler Efficiency in 210 MW BHEL Units
A 210 MW BHEL boiler is typically a coal-fired, subcritical unit common in thermal power stations, where efficiency (often around 80-85% on a higher heating value basis) is influenced by combustion, heat transfer, and auxiliary losses. Improving it can reduce fuel consumption, emissions, and operational costs. Based on thermal audits and BHEL-specific practices, here are proven methods, categorized for clarity. These draw from operational optimizations, retrofits, and maintenance strategies.
### 1. **Optimize Combustion and Flue Gas Management**
- **Reduce excess air levels**: Maintain low excess air (typically 15-20%) across all loads to minimize dry flue gas losses and fan power. This can save significant fuel; tune burners regularly and use oxygen trim controls.
- **Lower stack temperature**: Aim for 120-140°C by cleaning heat transfer surfaces (e.g., economizer, superheater) to recover more heat. Install or optimize air preheaters for better combustion air heating.
- **Minimize unburnt carbon and moisture losses**: Optimize coal fineness (via ball mills) and use blended or washed coal to reduce hydrogen combustion and moisture in fuel. Target <0.5% unburnt carbon in fly ash.
### 2. **Enhance Heat Recovery and Steam Cycle**
- **Install or upgrade economizers and regenerative feed heating**: Increase feedwater temperature (e.g., via high-pressure heaters) to reduce boiler heat input. For 210 MW units, adopting enhanced regenerative cycles can lower heat rate by 50-100 kCal/kWh.
- **Operate in sliding pressure mode**: At part loads (<80%), reduce main steam pressure before turbine valves to improve cycle efficiency by 1-2%.
- **Preheat combustion air and recover blowdown heat**: Use waste heat from flue gas or blowdown to preheat air, potentially boosting efficiency by 1-3%.
### 3. **Reduce Auxiliary and Leakage Losses**
- **Minimize air and flue gas leakages**: Seal leaks in air preheaters and ducting (use thermovision for detection); this cuts ID/FD fan power by 5-10%.
- **Install variable frequency drives (VFDs)**: On fans, pumps (e.g., boiler feed pumps in three-element mode), and mills to match load demands, saving up to 20% auxiliary power.
- **Optimize condensate return and blowdown**: Return 90%+ of condensate to the boiler and control blowdown rate to <1% of feedwater flow, recovering heat from blowdown.
### 4. **Maintenance and Water/ Ash Handling Improvements**
- **Improve water chemistry and tube cleaning**: Maintain low dissolved oxygen and pH to prevent tube failures; clean waterside regularly to avoid scaling, which can drop efficiency by 2-5%.
- **Reduce clinkering and ash handling losses**: Use smart wall-blowing systems (e.g., automated soot blowers) to minimize steam usage and ash buildup, saving ~Rs 62 lakhs/year per unit in makeup water and steam.
- **Switch to dry ash evacuation**: From wet systems to reduce water and power use in ash handling.
### 5. **Advanced Retrofits for Long-Term Gains**
- **Increase steam parameters**: Retrofit to higher MS pressure (e.g., 170 bar) and temperatures (540°C) for 1-2% efficiency gain, though this requires turbine upgrades.
- **Adopt low-NOx burners and emission controls**: While primarily for compliance, they improve combustion uniformity and reduce excess air needs.
- **Conduct regular thermal audits**: Analyze losses in air/flue gas, steam, fuel/ash, and cooling cycles to identify site-specific fixes, like impeller coatings or compressor upgrades.
Implementing these can yield 2-5% overall efficiency gains in a 210 MW BHEL boiler, depending on baseline conditions. Start with low-cost operations (e.g., tuning) before capital retrofits. Consult BHEL or a site audit for tailored advice.
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