By Drew Robb

The HRSG market is healthy! According to McCoy Power Reports, 7,975 individual heat recovery steam generator (HRSG) units were installed between 1980 and 2018 for a combined capacity of 555 GW. Since then, another 40 GW of combined cycle plants have come online and the projections are for a lot more. Analyst firm SkyQuest predicts that the HRSG market will be worth $1.1 billion annually by 2030 with a growth rate per year of 3.5% between now and the end of the decade. SkyQuest reports that this is being fueled by surging interest in clean energy solutions and sustainability. Heat recovery is seen as an obvious way to increase the efficiency of gas turbine plants and reduce their environmental impact. Further, modern HRSG designs can lower emissions and ease the maintenance load.

Those procuring HRSGs, therefore, should engage with manufacturers to ensure they obtain the right design – one that fits current needs and is set up to meet future performance and regulatory demands. That entails design customization. There is no cookie-cutter approach to HRSG design.

“Each plant is different, even within fleets that utilize the same gas turbines and have very similar requirements,” said Kevin Slepicka, Vice President of Heat Recovery Boilers at Rentech Boiler Systems.

Some try to fit the facility to the HRSG which may be a little cheaper by specifying standardized HRSG designs. But that rarely aligns appropriately with the space or the workflows of the facility. The recommended approach is to fit the HRSG to the exact needs of the facility.

“A customized design reduces the amount of work that needs to be conducted onsite,” said Slepicka. “It also reduces disruption during the assembly and installation process.”

Custom HRSG are built, preassembled, and tested in the manufacturer’s facility to ensure they meet the specifications of the plant. Once they have been satisfactorily tested, they can then be shipped in pieces to the site. Sending them in pieces simplifies the transportation and installation process. In the case of large HRSGs, it may not even be possible to transport them unless they are broken down into several parts. Parts and components can also be sent in stages to minimize space requirements during installation. As parts are needed, they arrive at the facility and are assembled. That frees up space for more parts to be delivered and, in turn, assembled. A relatively small amount of work is required to combine the parts at the site.

“Design customization is the best way to circumvent space limitations, while providing the facility with equipment that is more closely suited to its needs,” said Slepicka. “As the HRSG was fully assembled and tested by the manufacturer before being disassembled and shipped, final installation and commissioning are much faster.”

These are some of the reasons why many embrace the customized approach. It often makes financial sense to specify an HRSG that exactly fits site requirements. By matching and integrating the system to the plant layout and the combustion turbines selected, it is possible to maximize the efficiency of the units while containing overall costs. 

Case in point: College engineers contacted Rentech to go over their exact needs on how to couple new HRSGs to existing Solar Titan turbines. Instead of ordering a standard HRSG size and then trying to cobble that together with their turbines, they took the time to work with the manufacturer to precisely size the HRSGs to fit their operating, performance and emissions parameters. This entailed many meetings and design revisions, but the result was the installation of HRSGs tailored to their exact needs.

Design with an eye to the future

Designing the HRSG for current requirement may appear smart. Costs can be contained by allowing little margin in terms of drum size, wall thickness, emissions and overall output. But things rarely stay the same for long. It is quite possible that the plant owners may decide they need higher output, lower emissions or wish to introduce changes at a later point. Slepicka recommends a conservative design approach.

For example, a slightly larger drum size and wall thickness than are strictly necessary will save on maintenance costs over the long term while enhancing the longevity of the unit. A larger steam drum prevents water carrying over into the superheater. How? It allows better separation to remove water from the steam before it arrives at the superheater. If feedwater flow is lost, a bigger drum gives the plant operator more time to correct any water issues before steam levels fall. This is far more desirable than scrambling with only a minute or so before the normal operating level on the steam drum falls enough to result in a low-level trip. That can be a disaster in terms of lost production as it can sometimes leave too little time to correct the situation.

“By sizing and building conservatively, warranty problems can be avoided, and sites typically gain far more reliability,” said Slepicka. “However, those that size HRSGs with little margin may pay a little less but at the risk of overall reliability.”


About the Author: Drew Robb has been working as a full-time freelance writer in engineering and technology for the last 25 years. For more information, contact drew@robbeditorial.com.

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