HRSGs and boilers |
also offers models to accommodate high cycling operation as well as a variety of firing solutions including supplementary or fresh-air firing. In addition, it can integrate SCR and CO systems and provide feedwater and condensate heaters for maximum heat recovery.
For example, it provided the HRSG for a combined heat and power (CHP) facility in Florida in conjunction with Chesapeake Utilities Corp, its Florida Public Utilities (FPU) subsidiary, and Rayonier Advanced Materials Inc (RYAM). The HRSG operates along with a Solar Titan 250 gas turbine.
Operating as Eight Flags Energy, the facility sits on RYAM land in Fernandina Beach on Florida’s Amelia Island. RYAM receives low-cost steam and hot water to the adjacent RYAM cellulose products manufacturing facility and 20 MW or so of electricity to FPU, which meets roughly 50% of Amelia Island’s energy needs.
The Rentech HRSG feeds steam to RYAM at 160 psi and 420°F. The HRSG recovers around 70-75 000 pounds of steam per hour and has the capability to increase that amount using duct burners that add 125 000 pounds per hour of process steam for a grand total of 200 000 pounds per hour if needed.
Demineralised water provided by RYAM is channeled through a hot water economiser in the Rentech HRSG to increase the water temperature by 70°F. This hot water is sent back to RYAM for use in production processes. According to Mark Cutshaw, Manager, Electric Operations at FPU, heating the demineralised water saves RYAM from having to generate its own power to heat the water. It also keeps emissions low. In addition, exhaust heat is harnessed to raise overall efficiency by heating the feedwater before it is sent into the HRSG. Most of the time, the Rentech HRSG runs at 75 000 lb per hour. However, the boiler was intentionally oversized to enable the facility to run at 200 000 lb per hour when needed by turning on its duct burners. The modularised HRSG was built and assembled in Texas. It was shipped to Eight Flags in a couple of large sections. Much of the waste heat is used in the HRSG for steam production. The remainder of the waste heat is used to help an economiser to heat feedwater for the boiler and demineralised water for RYAM. Effective use of waste heat raises overall efficiency at Eight Flags to about 80%. “The key to smooth HRSG operation is to have a good HRSG from a reliable vendor and then make sure that water treatment is done well so water quality remains very high,” said Cutshaw. “It is best to oversize the HRSG as you run into fewer maintenance issues and have the option of adding more steam if you need it.”
HRSGs with a vertical design NEM Energy Group is another HRSG vendor, headquartered in the Netherlands. As well as traditional horizontal flow HRSG designs, it offers vertical options. Its vertical once-through steam generator (OTSG) design, for example, offers fast start-up and shutdown capabilities in a small footprint that makes it suitable for onshore and offshore applications. It can cope with lower fuel
The Beni Suef power plant in Egypt features Siemens H-class turbines and NEM Energy vertical exhaust gas flow HRSGs. Photo: Siemens Energy
quality and in the industrial gas turbine range it can be designed with an internal bypass. The gas turbine continues operation and can be shut down later at any given moment. Alternatively, its vertical drum type steam generator comes with standardised pressure part modules to shorten lead time and lower installation costs. NEM Energy Group has delivered dozens of these modular units for industrial gas turbines. “A vertical HRSG makes sense from a physics perspective as exhaust heats wants to go up,” said Niels Veldkamp, Chief Operating Officer of NEM Energy. “Vertical HRSGs in the past utilised forced circulation using feedwater pumps. We have feedwater at the start but otherwise use natural circulation.”
A vertical type of HRSG is often used in areas on land or at sea where space is tight. Through the use of a diverter, operational flexibility is provided to the power plant. However, when switching from open-cycle to combined-cycle mode, the HRSG must handle the exhaust heat of H-class gas turbines, which can reach temperatures of nearly 700°C. Consequently, the HRSGs and associated equipment must be designed to ensure reliable and flexible operation under these thermal conditions. For example, NEM Energy delivered 24 vertical flow HRSGs to three combined cycle plants in Egypt (each 4.8 GW). Built in just over two years, these facilities almost doubled the nation’s electricity capacity when they were brought online. The Beni Suef plant, for example, is situated in an industrial and agricultural zone about 100 km south of Cairo. This area had a weak grid that inhibited production and expansion. It comprises eight SGT5-8000H advance class gas turbines and four SST-5000 steam turbines from Siemens Energy, as well as eight NEM vertical HRSGs.
16 | March 2026 |
www.modernpowersystems.com
The facility is more than 61% efficient. Each of the H-class turbines provides 400 MW. The inlet air flow is 820 kg/s and gas consumption is 22 kg/s per GT. The combustion temperature is 1550°C and the outlet temperature is 650°C. The Nile provides water for once through cooling. A Siemens SPPA-T3000 control system is used to run the plant. Emissions are below 25 ppm NOx
. Tailored HRSGs
The power generation market is evolving today at a rapid pace. The HRSG is responding with a range of options to suit changing needs and the HRSG vendor community reflects this shift. Companies like Rentech are focused squarely on custom units of 50 MW and below as a way to differentiate themselves in the marketplace. By focusing on this sector, they can hone their expertise around specific turbine types and plant configurations.
Others, like NEM, are adding vertical options in addition to their horizontal units to provide market alternatives. In some markets, a vertical solution may make sense. Veldkamp noted that this usually does not include the US as most sites have ample space and many sites specify duct burners as they get money for capacity payments.
Further, OEMs are developing HRSG designs that can better cope with heavy cycling operation and with the ever-hotter exhaust gas from advanced class turbines. Older HRSGs designed for baseload operation can struggle when forced to deal with rapid starts and stops. And traditional designs may not pair well with the latest generation of turbines. Thus, the HRSG market continues to evolve to meet the changing needs of a diverse power generation landscape.
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