Italian turbine maker Ansaldo Energia and carbon capture specialist Equinor are collaborating on the validation of a 100% hydrogen gas turbine combustor.
Under an agreement announced on Oct. 24, Equinor (formerly Statoil) will co-fund tests that could show Ansaldo’s GT36 H-class gas turbine combustor can be operated purely with hydrogen.
“The purpose of this collaboration is to advance the hydrogen combustion technology with full-scale, full-pressure combustor validation tests. To this regard the main goals are the optimization for ultra-low [nitrogen oxide (NOx)] emissions, operational flexibility and minimization of engine derating at very high hydrogenc contents,” the companies said in a statement.
Like all its major competitors in the heavy-duty gas turbine market—including GE Power, Siemens, and Mitsubishi Hitachi Power Systems—Ansaldo has stepped up efforts to “future-proof” operational flexibility of its H-class line to help it compete in a changing marketplace, where low prices, subsidies, and regulatory mandates have introduced a surge of renewables. Like GE Power, which earlier this month rolled out a new fuel-flexible H-class model, Ansaldo is betting that renewable intermittency will continue to be a challenge in the long run.” That’s “why existing gas-fired plants are still bound to play a major role in the energy market as guarantors of grid reliability,” it said.
(Read more about how and why gas turbine manufacturing heavyweights are developing gas turbines that can operate on high-hydrogen-volume fuel in “High-Volume Hydrogen Gas Turbines Take Shape,” in POWER’s May 2019 issue.)
“Among all combustible gases, hydrogen stands out as an almost perfect combination of storability for long periods and reliability,” Ansaldo said. “Being able to burn hydrogen alone or in combination with other natural gases, and to do it safely and efficiently, could therefore make all the difference.”
The company noted that its product portfolio of lean premix technologies for advanced gas turbine combustion systems has been developed with fuel flexibility as a “prime consideration.” Its latest models, the GT26 F-Class and GT36 H-Class gas turbines, for example, are based on its Sequential Environmental (SEV) combustion system platform, which allow it to burn a large range of natural gas and hydrogen blended fuel mixes. And while the GT36 H-Class turbine can already be operated with a volumetric hydrogen content of 0% to 50% (and the GT26, up to 30%), recent full-scale high-pressure tests showed the “the feasibility of operating up to 70% hydrogen without power or efficiency derating and the possibility to burn up to 100%,” it said.
SEV, it noted, also allows it to overcome a key drawback faced by other turbine makers: “Compared to natural gas, the main challenge of hydrogen combustion is its increased reactivity resulting in a decrease of engine performance for conventional premix combustion systems,” Ansaldo explained.
“In a traditional premix gas turbine combustor, a change in fuel reactivity implies a change in flame location. In particular, higher fuel reactivity forces the flame to move upstream, increasing NOx emissions, and potentially overheating the burner, while lower fuel reactivity results in the opposite and pushes the flame downstream, increasing [carbon monoxide (CO)] and unburned hydrocarbons emissions due to the insufficient burnout time,” it said.
Sequential combustion essentially entails two combustion stages: a conventional stage and an an auto-ignited second stage. It comprises two short combustion chambers to enable rapid mixing, so post-flame residence times are low enough to keep detrimental NOx emissions below limits. In the GT26, the two stages are separated by a high pressure turbine, whereas in the GT36, no high-pressure turbine is implemented. For more reactive fuels like those with a high hydrogen volume, sequential combustion systems help flames avoid moving too close to the burner exit by dropping the first-stage flame temperature, which then also causes a drop in the second-stage inlet temperature (or mixer exit temperature [MET]), where dilution air mixes with first-stage flue gases.
“Since the sequential burner flame is mainly auto-ignition stabilised, its flame position is driven by its inlet temperature and not its exit temperature, in contrast to the case of propagation stabilised flames,” Ansaldo said. “Therefore a drop of MET compensates the higher fuel reactivity, maintaining the optimal flame location and the original desired flame temperature without compromising engine performance. This also allows the turbine inlet temperature to be held constant.”
As part of its efforts to demonstrate a 100% hydrogen gas turbine, Ansaldo has joined several prominent European and international projects. These include EncapCo, a project to develop premix combustors for hydrogen-rich combustion; DECARBIT, which is developing reheat combustors for 100% hydrogen; and BigH2, which is studying fuel injector fundamentals.
The company has also developed and commercially offers a “retrofit combustor,” which it calls “FlameSheet,” that it claims “can burn up to 10 times more hydrogen than ultra-low emission (DLE) combustors” from other OEMs “without the need for costly diluent injection.”
—Sonal Patel is a POWER senior associate editor (@sonalcpatel, @POWERmagazine)