Learn about Heat Recovery Steam Generators (HRSG), their types, and applications in power generation and industrial processes.
Understanding Heat Recovery Steam Generators (HRSG)
Heat Recovery Steam Generators (HRSGs) are critical components in the power generation and industrial processes, where they capture heat from hot gas streams, often from gas turbine exhaust, to generate steam efficiently. This steam is typically used for additional power generation in turbines, or for various industrial processes. Depending on their configuration and the specific requirements of the application, HRSGs come in different types, each with unique features and advantages. Here, we explore seven common types of HRSGs.
1. Horizontal Drum Units
Horizontal drum HRSGs feature drums that are placed horizontally. This design is commonly used in smaller units where space constraints are not a significant issue. They are simpler in design and generally cost less than other types. The natural circulation of water and steam flow helps in reducing pump requirements, which lowers operating costs.
2. Vertical Drum Units
In contrast to horizontal units, vertical drum HRSGs have drums that are oriented vertically. This configuration is beneficial in tight spaces where the footprint needs to be minimized. Vertical drum HRSGs are preferred in applications involving high-pressure and temperature steam. They facilitate better steam quality and reduce the risk of steam carryover.
3. Once-Through Units
Once-Through HRSGs (OTSG) do not use drums. Instead, they operate by feeding water directly through the boiler tubes, which turns into steam as it absorbs heat from the hot gases. An advantage of OTSGs is their ability to rapidly adjust to changes in steam demand, making them suitable for applications with highly variable loads. They are often used in combined cycle power plants.
4. Modular HRSGs
Modular HRSGs consist of several pre-assembled modules that can be easily transported and installed at the site. This pre-fabrication means the construction time at the actual location is significantly reduced. Modular HRSGs are especially useful in projects with limited site fabrication facilities or in remote locations.
5. Reheat Units
Reheat HRSGs have additional capabilities to reheat the steam after it expands through the high-pressure stage of a steam turbine. This reheating process increases the thermal efficiency of the cycle by allowing the steam to expand through additional stages of the turbine. Reheat HRSGs are particularly advantageous in high-efficiency power stations.
6. Cogeneration HRSGs
Cogeneration HRSGs are designed to maximize the production of both electricity and useful thermal energy from the same energy source. These are typically used in industries where both power and heat are required for processes. The configuration can vary depending on the precise thermal and power needs of the application.
7. Fresh Air Fired HRSGs
These HRSGs are unique in that they can operate even when the gas turbine is shut down. They have an integrated burner that can heat clean air to generate steam. Especially useful during maintenance periods of gas turbines, or when additional steam is needed, fresh air fired HRSGs provide high flexibility in operations.
Each type of HRSG is tailored for specific operational needs, whether it’s for power generation, industrial use, or both. By understanding the differences and applications of these HRSGs, one can better optimize their process or power generation capabilities, contributing to overall efficiency and sustainability.