Improving Auxiliary Power Consumption in Coal-Based Thermal Power Plants: A Path to Tariff Reduction

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Introduction

Coal-based thermal power plants (TPPs) remain a cornerstone of electricity generation in India and many other countries. Despite the global push toward renewables, coal continues to account for over 50% of India’s installed capacity. However, one of the persistent challenges in coal-fired TPPs is Auxiliary Power Consumption (APC), the energy consumed by internal systems to keep the plant operational. Typically ranging from 7% to 10% of gross generation, high APC directly impacts the net power available for sale and, consequently, the tariff.

Reducing APC is not only a technical necessity but also a strategic imperative to improve plant economics, reduce emissions, and remain competitive in the evolving energy market.

Understanding Auxiliary Power Consumption

Auxiliary power refers to the electricity consumed by various subsystems within the plant, including:

  • Boiler Feed Pumps (BFP)
  • Induced Draft (ID) Fans
  • Forced Draft (FD) Fans
  • Primary Air (PA) Fans
  • Coal Handling Systems
  • Ash Handling Systems
  • Cooling Water Pumps
  • Lighting and HVAC

The Central Electricity Authority (CEA) recommends APC norms between 5.75% and 11%, depending on plant size and configuration

Key Factors Contributing to High APC

  1. Outdated Equipment: Legacy systems with low efficiency.
  2. Poor Maintenance: Leakages, wear and tear, and fouling.
  3. Oversized Machinery: Operating below optimal load.
  4. Coal Quality: High moisture and ash content increase fan and pump loads.
  5. Partial Load Operation: Plants running below rated capacity consume more auxiliary power per unit of output.

Strategies to Reduce Auxiliary Power Consumption

1. Equipment Optimization and Upgrades

  • Variable Frequency Drives (VFDs): Installing VFDs on BFPs, ID, FD, and PA fans allows speed modulation based on load, saving up to 40% power in some cases.
  • Impeller Trimming and De-Staging: Reduces pump power consumption by matching capacity to actual demand.
  • High-Efficiency Motors: Replacing old motors with IE3/IE4-rated motors improves efficiency.

2. Maintenance and Housekeeping

  • Cleaning Air Preheater (APH) Baskets: Reduces pressure drop and fan loading.
  • Duct and Filter Cleaning: Prevents blockages and improves airflow.
  • Leakage Detection and Repair: Thermographic inspections help identify steam and water leaks.

3. Operational Optimization

  • Full Load Operation: APC is lower at full load; scheduling generation to match peak demand improves efficiency.
  • Combustion Optimization: Adjusting air-fuel ratios and oxygen levels in flue gas reduces fan power.
  • Coal Blending: Using higher-grade coal or blending improves combustion and reduces fan and mill loads.

4. Design Improvements

  • Right-Sizing Equipment: Oversized fans and pumps consume more power; design optimization is crucial.
  • Steam-Driven BFPs: In subcritical units, switching from electric to steam-driven BFPs can save 2.25% APC.

Technological Innovations

  • Digital Twin and AI-Based Monitoring: Predictive analytics for equipment health and performance.
  • Smart Sensors and IoT: Real-time monitoring of energy consumption and fault detection.
  • Advanced Control Systems: Automated control of combustion, feedwater, and draft systems.

Tariff Reduction Through APC Optimization

Reducing APC directly increases the net exportable power, improving revenue and reducing the per-unit cost of generation. Here's how:

1. Increased Revenue

  • More power available for sale at the same fuel input.
  • Better plant load factor (PLF) improves financial metrics.

2. Lower Fuel Cost per Unit

  • Efficient operation reduces coal consumption per MWh.
  • Less wear and tear on equipment reduces maintenance costs.

3. Compliance and Incentives

  • Meeting CEA norms avoids penalties.
  • Eligible for performance-based incentives under regulatory frameworks.

Case Study Highlights

  • 500 MW Unit with VFD on ID Fan: Reduced power input from 1436.9 kW to 867.15 kW with increased flue gas flow
  • Steam vs. Electric BFP: Steam-driven BFPs showed a 2.25% reduction in APC compared to electric motor-driven ones.

Conclusion

Reducing auxiliary power consumption in coal-based thermal power plants is a multi-dimensional challenge that requires a blend of technological upgrades, operational excellence, and strategic planning. With rising fuel costs and competitive tariffs, optimizing APC is no longer optional—it is essential for survival and growth.

By adopting best practices and investing in energy-efficient technologies, TPPs can significantly reduce their cost of generation, improve profitability, and contribute to a cleaner energy future.

Location: India

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