Understanding HRSG, Auxiliary Boiler, and More

Hello Power Engineers
This video is about the industrial or #Boilers used in Captive Power Plants (CPP).
Heat Recovery Steam Generators ( #HRSG ) and utility boilers are both types of steam-generating equipment used in #powerplant and industrial settings, but they have distinct differences in terms of their design, operation, and applications. Here's a detailed comparison:
1. Purpose and Application:
HRSG:
Purpose: HRSGs are designed to recover waste heat from the exhaust gases of gas turbines or other industrial processes. The primary purpose is to enhance overall plant efficiency by utilizing otherwise wasted heat.
Application: Commonly used in combined cycle power plants (CCPPs), where they are paired with gas turbines to form a combined cycle power plant. They can also be used in cogeneration plants where both electricity and useful heat are produced.
Utility Boiler:
Purpose: Utility boilers are designed to generate steam for power generation, industrial processes, or district heating. They burn various fuels (coal, natural gas, oil, biomass) to generate heat.
Application: Widely used in standalone power plants (thermal power plants) where the primary purpose is to generate electricity. They can also be found in large industrial facilities requiring significant amounts of steam and power.
2. Heat Source:
HRSG:
Heat Source: Utilizes waste heat from the exhaust of gas turbines or other industrial processes. It does not have its own fuel combustion system.
Utility Boiler:
Heat Source: Burns fuel directly to generate heat. It has its own combustion system to burn coal, natural gas, oil, or biomass.
3. Design and Structure:
HRSG:
Design: Comprises multiple sections (economizer, evaporator, superheater) to maximize heat recovery from exhaust gases. Typically has multiple pressure levels (high, intermediate, and low pressure) to improve efficiency.
Structure: Usually designed as modular units, can be vertical or horizontal, and tailored to match the exhaust flow of the gas turbine.
Utility Boiler:
Design: Includes components like a furnace, economizer, superheater, reheater, and air preheater. Typically operates at high pressures and temperatures to maximize efficiency.
Structure: Usually a large, standalone structure with a tall furnace section to facilitate efficient combustion and heat transfer.
4. Efficiency:
HRSG:
Efficiency: High overall plant efficiency when combined with a gas turbine in a combined cycle configuration. The efficiency of the HRSG itself depends on the temperature and flow rate of the exhaust gases.
Utility Boiler:
Efficiency: Standalone efficiency depends on the type of fuel and the design of the boiler. Modern utility boilers can achieve high efficiencies through advanced combustion technologies and better heat recovery systems.
5. Startup and Operation:
HRSG:
Startup: Typically quicker startup times because they do not have to ignite and ramp up a combustion process.
Operation: Depends on the operation of the gas turbine or the primary industrial process. Load following can be challenging as it is tied to the primary process.
Utility Boiler:
Startup: Generally longer startup times due to the need to ignite fuel and gradually ramp up to operating conditions.
Operation: More flexible in terms of operation as it is an independent unit. Can be adjusted based on steam demand and power requirements.
6. Environmental Impact:
HRSG:
Environmental Impact: Generally lower environmental impact as it uses waste heat and doesn’t directly burn additional fuel. However, overall impact depends on the primary process (e.g., gas turbine emissions).
Utility Boiler:
Environmental Impact: Depends on the type of fuel used and the efficiency of the combustion and emission control systems. Burning fossil fuels can lead to significant emissions unless mitigated by advanced technologies like flue gas desulfurization and selective catalytic reduction.
In summary, HRSGs are primarily used to recover waste heat from gas turbines in combined cycle plants, enhancing overall efficiency without direct combustion, while utility boilers are standalone units that burn fuel to generate steam for power generation and industrial applications.

[@Ankit_Tarpara]

Thank you sir for describing very basic differences between HRSG & Auxiliary boiler.