Since the commercial operation of the world’s first industrial gas turbine, in Neuchâtel, Switzerland, in 1939, GE Vernova and its predecessor companies have developed and deployed several generations of gas turbines (GTs), steam turbines (STs), generators, and heat recovery steam generators (HRSGs). GE Vernova is a supplier of all major equipment within a gas fired power plant and builds on know-how across GT, ST & HRSG as well as plant controls to provide optimal solutions.
HRSG technology has evolved over time together with the evolution of GT technology and is a critical component that makes the mighty combined cycle power plant (CCPP) possible, as the connective tissue between the gas turbine and the steam turbine. HRSG designs were derived from fired boiler design (utility boiler) experience and know-how and the first generation HRSGs were mostly vertical gas flow, horizontal tube forced circulation designs, both with and without supplemental firing.
In the 90s, HRSGs saw various product changes and improvements as a new fleet of large frame gas turbines, the F-Class, entered the marketplace. The higher exhaust temperature and flow of these GTs enabled higher combined cycle efficiency and triple pressure with reheat HRSGs became the standard, while going to horizontal gas flow and transitioning from bottom to top supported pressure parts to accommodate the larger thermal expansions that came with the higher GT exhaust gas energies. Water–steam cycle parameters through much of the 1990s were below 540°C/120 bar; however, by the late 1990s the 565°C/165 bar water steam cycle became standard in the industry. This required the application of advanced materials such as 9% chromium alloys previously used in utility boilers. During this time GE Vernova’s Once Through (OT) HRSG technology was developed and introduced to the marketplace, with 33 units installed across the US and Mexico behind GT24 gas turbines.
The 2000s started out with the “gas-bubble” and very low natural gas prices in the US driving the build out of many CCPPs powered by mostly F-Class GTs. The horizontal gas flow HRSG with natural circulation, established in the late 90s and early part of 2000s, became the technology of choice moving forward for most applications in both 50 Hz and 60 Hz markets. Supplementary firing capability was introduced in the USA to capitalise on high electricity prices and to this day most combined cycle power plants in the USA have supplemental firing. Also, during this time US regulatory requirements led to the introduction of emission control equipment in HRSGs for NOx and CO, which have become standard for most advanced combined cycle power plants.
In the early 2000s HRSGs were engineered with limited capability for cycling as the plants were intended to be base loaded. However, with the increase in gas prices in the mid 2000s there was a change of operating regime to more cycling operation as daily starts and stops became more the norm. This is where GE Vernova’s innovative single row harp arrangement originated and today all of our HRSGs, regardless of the operating profile specified in RFQs, utilise single row harps in the front end. This configuration provides more flexibility to support reliable high-cycling duty and produces three times less stress than conventional multi-row harps, while capable of fast starts, high ramp rates and enhanced operational flexibility.
Also, during this period in the USA, constructability of HRSGs became a big driver and consequently GE Vernova started to offer various constructability options, from loose harps to pressure part modules, C-frame, supermodules, and fully assembled HRSGs delivered by boat, enabling customers to choose the degree of prefabrication that best fits the site-specific project requirements and logistics constraints.
Today, GE Vernova’s advanced combined cycle power plants with OT HRSGs for high fuel hour regions represent a new era of high efficiency combined cycle power plant where the OT HRSG technology is a key enabler. These HRSGs are paired with GE Vernova’s highly efficient H-class GTs, which have pushed exhaust gas temperatures beyond 650°C. GE Vernova’s OT HRSG technology has more than 2.5 million operating hours and enables:
- higher operating steam pressures resulting in higher thermal efficiencies at base load;
- superior off design and part load performance due to the ability to vary feedwater flow, resulting in increased thermal efficiencies;
- stable operation from low load to baseload with excellent cyclic operation;
- faster startup due to continuous flow and less water inventory, which allow rapid heating;
- highly flexible operation as the OT HRSG can efficiently handle varying loads and quick changes;
- implementation of an integrated water chemistry concept, allowing better impurity control and eliminating the need for a 50% condensate polisher, decreasing total plant cost; and
- the required steam turbine admission conditions to be consistently achieved
more swiftly.
GE Vernova has booked and executed more than 20 OT HRSGs downstream of its H-class GTs for both 50 Hz and 60 Hz applications with the first plant being Track 4A in Malaysia, which entered commercial operation in January 2021.
With the energy sector undergoing a transformative shift, driven by the growing need for more sustainable, flexible, and more efficient generation technologies, gas-fired power plants remain essential in ensuring grid reliability. In this evolving landscape, HRSG technology plays a critical role, particularly in combined cycle power plants that demand high efficiency and operational flexibility.
As a result, start-up times have become more aggressive over time. In the 2000s a typical hot start duration was 70 minutes with all plant components brought online in unison. In 2010s we saw a shift towards unrestricted start-up of the GT, with start-up time around 30 minutes. Today we see unrestricted GT ramp rates and start-up times of less than 20 minutes with the water steam cycle decoupled and brought online separately.
The need for flexibility coupled with more elevated steam conditions – from the past 565°C/165 bar to 600°C/185 bar – due to demands for higher plant efficiencies, has introduced a need for austenitic stainless steel for some HRSG components, leading to the necessity of dissimilar metal welds (DMW) transitioning from austenitic stainless steel to 9% chromium alloys (ferritic steel).
We produce these in-house developed DMWs within our own factories to meet the stringent fabrication requirements and install them at strategic locations in the HRSG. With a manufacturing facility in Changwon, South Korea, and another one in Dung Quat, Vietnam, GE Vernova’s in-house capability to manufacture pressure part modules together with a well established supply chain helps us to deliver highly reliable HRSGs with increased quality assurance while directly navigating supply constraints.
HRSGs integrated with carbon capture
GE Vernova is also executing strategies for reducing the amount of CO2 emitted per unit of electricity generated in a combined cycle power plant. This involves implementing measures such as enhancing plant efficiency, reducing carbon content in fuel by using lower carbon alternatives like hydrogen, and adopting carbon capture and storage/utilisation technologies.
The landmark Net Zero Teesside Power project in the UK, the world’s first combined
cycle power plant with integrated CCS plant under execution, exemplifies the integration of 9HA power island equipment with CCS and exhaust gas recirculation (EGR) technology, with the HRSG an integral part engineered to enable the elimination of CCS flue gas blowers.
This plant, which is expected to generate over 740 MW, capture up to 2 million tons of CO2 annually and transport it via pipeline to secure offshore sequestration, demonstrates a combination of innovation, efficiency, and sustainability, helping to drive the energy transition forward.
