The design of the FLEX4H2 combustor will be based on Ansaldo’s Constant Pressure Sequential Combustion (CPSC) technology, a second-generation combustion system developed for Ansaldo’s flagship GT36 H-class gas turbine (760-MW in combined cycle) combustors. Sequential combustion evolved from burner technology applied to Ansaldo’s GT26 and GT24 gas turbines. In the GT26, sequential combustion is implemented with two combustion stages separated by a high-pressure turbine: the first stage (EV) operates at pressures greater than 30 bar, while the second stage (SEV) operates at roughly half of the EV pressure. In the GT36, no high-pressure (HP) turbine is implemented, but the sequential combustion concept is maintained.

“Due to the high-burning velocity and high-flame temperature, standard gas turbine combustion technology struggles at high hydrogen content with high [nitrogen oxide (NOx)] emissions and the risk of flashback,” Ansaldo explained. “This usually results in the necessity of power derating to comply with required standards. Based on two successive combustion stages, the GT36 recovers the derating of the first stage by shifting the fuel into the second stage. This allows for full operational flexibility, low NOx, and no derating.” Ansaldo says its GT36 can already combust 70% hydrogen in natural gas blends. “Development to 100% is on the way,” it said.

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