This article is written to have a detailed understanding of power plants in terms of circulation systems and heat rate reduction. Heat rate is the single most important factor to gauge the performance of power plants and how to reduce it is described in detail in this article.
A typical boiler water circulation system says AFBC, let’s break it down step-by-step:
1. Feed pump: The process begins with a feed pump, which supplies water to the boiler. The pump’s primary function is to increase the water pressure to a level suitable for the boiler operation.
2. High pressure (HP) heater: The water from the feed pump enters the HP heater, where it is heated using steam extracted from the turbines. This process helps to increase the water temperature before it enters the boiler.
3. Economizer: The water then passes through an economizer, which is a heat exchanger located in the flue gas path. The economizer extracts heat from the flue gases and transfers it to the water, further raising its temperature.
4. Drum: The water flows from the economizer into the drum of the boiler. The drum acts as a storage vessel for water and steam. In this portion of the circulation, the movement of water is driven by natural convection due to density differences.
5. Water wall and bed coil: From the drum, the water moves through the water wall tubes and bed coil tubes. These tubes are surrounded by hot combustion gases, which transfer heat to the water, causing it to convert into steam.
6. Drum (return): The steam generated in the water wall and bed coil tubes returns to the drum for separation from water. The separated steam will be further superheated.
7. Superheaters: The separated steam flows through superheaters, which are additional heat exchangers that raise the temperature of the steam to the desired level.
8. Steam turbine: The superheated steam then enters a steam turbine, expanding and producing mechanical work to drive a generator, generating electricity.
9. Condenser: After passing through the turbine, the steam enters a condenser, where it is cooled and condensed back into water using a coolant, typically circulating water from a cooling tower.
10. Condensate extraction pump (CEP): The condensed water is then pumped by a condensate extraction pump to increase its pressure and send it to the deaerator.
11. Deaerator: In the deaerator, the water is heated and its oxygen content is reduced to prevent corrosion in the boiler system. The deaerator also removes other gases and impurities from the water.
12. Low pressure (LP) heater: The deaerated water passes through an LP heater, where it is further heated using steam extracted from the turbines. This process helps to increase the water temperature before it returns to the feed pump.
13. Feed pump (return): Finally, the water is pumped back to the boiler by the feed pumps, completing the circulation loop.
The purpose of the circulation loop is to maintain a continuous flow of water and steam, allowing for efficient heat transfer and power generation. Let us see the image of a pulverised fuel-fired PFFB thermal power plant. Basically, the concept is the same for steam boilers.
How to reduce heat rate in the existing set-up;
1. Insulation improvement: Enhance insulation on steam lines, valves, and equipment to minimize heat losses and improve overall thermal efficiency.
2. Economizer optimization: Regular inspection and maintenance of economisers to ensure effective heat recovery from flue gases and preheating of boiler feedwater.
3. Variable frequency drives (VFDs): Implement VFDs on fans, pumps, and other rotating equipment.
4. Air preheater maintenance: Regular cleaning and maintenance of air preheaters to ensure efficient heat exchange between the flue gas and combustion air, thereby improving boiler efficiency.
5. Boiler feedwater heater upgrade: Upgrade feedwater heaters to increase the temperature of the water entering the boiler, reducing the fuel needed to reach operating conditions.
6. Intelligent soot-blowing systems: Sonic horn -Implement smart soot-blowing systems that optimize cleaning schedules and minimize excessive boiler tube fouling thereby improving heat transfer efficiency.
7. Advanced control strategies: Implement advanced control algorithms and strategies to optimize combustion, steam temperature, and pressure, as well as coordinate the operation of various plant systems for improved efficiency.
8. Performance monitoring and benchmarking: Regularly monitor and benchmark the plant’s heat rate performance against industry standards and best practices to identify areas for improvement and track progress.
9. Turbine blade coating: Application of advanced coatings on turbine blades to improve aerodynamics and reduce losses, enhancing turbine efficiency and overall heat rate.
10. Waste heat utilization: Explore opportunities to utilize waste heat for on-site processes, such as drying, preheating, or space heating, to maximize energy utilization and reduce overall heat rate.
11. Pump and motor efficiency
12. Steam system leak reduction: Identify and repair steam leaks in the distribution system to minimize energy losses and improve overall plant efficiency.
13. Air intake optimization: Regularly cleaning and maintaining air intake filters and systems.
14. Coal quality management: Implement strict quality control measures for coal procurement and handling to ensure consistent fuel properties and optimal combustion conditions.
15. Heat recovery steam generator (HRSG/WHRB) optimization: Optimize the operation and maintenance of HRSGs to maximize heat recovery from exhaust gases and improve overall cycle efficiency.
16. Cogeneration opportunities
17. Energy-efficient lighting and HVAC: Upgrade lighting and HVAC systems across the plant to more energy-efficient alternatives, reducing auxiliary power consumption.
18. Fan and compressor efficiency
19. Continuous improvement culture: Foster a culture of continuous improvement by encouraging employees to identify and implement small-scale efficiency measures that collectively contribute to heat rate reduction.
20. Condenser cleaning and acc foam cleaning. You may go for online surface condenser cleaning with Rubber Ball, an innovative Israeli technology.
20. Lifecycle analysis
Mr. Ashwini Mishra
Vice President-Power. Mtech, BOE, EM,EA,CE,AIE