No natural gas infrastructure? LPG cleans up heavy-fuel power generation
You might know liquefied petroleum gas (LPG) in the form of propane or butane from your camping stove. But did you know it has the potential to replace fuel oils (such as diesel and HFO) in industrial power generation in order to provide a secure, reliable source of electricity with reduced carbon emissions? Operating on LPG is just one of the benefits of fuel-flexible gas turbines, explains Michael Welch, Industry Marketing Manager at Siemens Industrial Turbomachinery Limited, in this interview.
By Ben Suter
What are the big trends you are witnessing at the moment?
Michael Welch: All around the world, the need to reduce greenhouse gas emissions is driving the transition to lower carbon-content fuels. We clearly need the fossil fuel mix to change. And gas turbines have an important role to play in facilitating this transition. For instance, where natural gas is readily available and affordable, we have seen – and are still seeing – coal plant retirements and replacement of these assets with natural gas-fired power plants.
While much attention is focused on reducing CO2 emissions, utilizing natural gas also produces lower emissions of combustion pollutants such as NOx and volatile organic compounds. We have already achieved low levels of these emissions through the use of dry low emissions (DLE) technology, but we are working to reduce these emissions still further. Thus, the main advancements in gas turbine technology focus on burning a wider range of fuels and on burning them more cleanly than previously possible.
And how does this progress translate into furthering the effort of decarbonization?
Welch: The environmental benefits are clear – no matter where in the world you are, more environmentally friendly fuels can be used to produce the energy needed for economic growth. The reduction in “local” pollutants such as NOx and particulate matter also has a positive impact on human health by improving local air quality.
For instance, the expansion of our DLE fuel capabilities on smaller gas turbines has enabled lower-carbon fuels such as LPG to be used. You see, in developing areas with no or insufficient natural gas infrastructure, distributed power generation used to rely on fuel oils like diesel and HFO, because they could be easily transported to remote regions by truck.
However, LPG can easily fill the role played by fuel oils. It’s a clean-burning fuel with far lower emissions of all types than fuel oils, especially HFO, and it’s also readily available in many countries because there is already an LPG infrastructure to serve domestic and commercial demand.
LPG is a good fuel for gas turbines: It can be burned as a gas or a liquid. Gas turbine performance and emissions are similar to that of natural gas, making LPG and natural gas interchangeable. LPG is also much easier to store than HFO or diesel, it requires no heating and has no shelf life, which means that LPG can serve as an excellent back-up fuel.
" LPG can easily fill the role played by heavy fuel oils. It’s a clean-burning fuel with far lower emissions and it’s also readily available in many countries. "
Liquid or gaseous – how important is fuel flexibility in generator technology?
Welch: While expanding the fuel capabilities of our gas turbines, we always have to bear in mind that our customers may want to switch between different fuels for security of supply purposes, or may have a fuel source that is inherently variable in composition.
We’ve been working on not only expanding the types of fuel we can combust, but the range of fuels that can be accepted in a single burner design as well. We now have DLE burner designs on some of our small and medium gas turbines that can run on natural gas, a biogas with a high CO2 content, which is considered a “lean” gas, and “rich” gases such as LPG, and switch between them automatically on load without needing to stop the turbine or modify any hardware.
Looking forward, improved fuel flex technology may act as an enabler for other technologies, such as those that produce bio-methane, bio-LPG or bio-hydrogen, to help meet the deep decarbonization targets that governments aspire to.
What are some of those “new” fuels that are now being used in lower carbon-content power generation?
Welch: A number of industries are using their process off-gas to generate the power (and heat) needed to produce their end product. Amongst the many units we’ve installed to operate on “nonstandard” fuels, we have units in refineries that run on high hydrogen process off-gases, or in the petrochemical industries such as propane dehydrogenation (PDH) that work on propane and butane-rich waste gases, and in the ethanol industry that run on the biogas byproduct from the fermentation process.
Burning fuels containing hydrogen is of course another huge trend. Hydrogen is a zero-carbon fuel, so there are no carbon emissions when it’s combusted. Therefore, there is a lot of interest in burning pure hydrogen, or hydrogen/natural gas blends to reduce the carbon footprint of energy production.
Lower carbon content is already great but zero carbon sounds very enticing – what percentage of hydrogen admixture can Siemens Energy currently offer in commercial gas turbine operation?
Welch: Recent advancements in burner technology and manufacture are now enabling us to offer DLE systems with up to 60 percent hydrogen by volume blended into natural gas and 100 percent hydrogen in non-DLE combustors on some gas turbine models. We’re currently implementing an electric and steam cogeneration plant for Braskem Chemicals in Brazil where two SGT-600 turbines will feature third-generation DLE technology and run on residue gas with high concentrations of hydrogen.
But along with other turbine manufacturers we have signed a pledge to offer 100 percent hydrogen-burning capability by 2030 and are concentrating our R&D efforts on delivering this goal. Until then, we will continue to lower carbon, NOx and other emissions by offering fuel-flexible systems that can run on the most environmentally friendly fuel available.
Mr. Welch, thank you for sharing these fuel and technology trends.
Jan 12, 2020
Ben Suter is an independent journalist based in Switzerland.
Combined picture credits: Siemens Energy
Liquefied petroleum gas includes various mixes of mostly propane (C3H8) and butane (C4H10) and other hydrocarbons in small concentrations. It is a suitable fuel for power plants where natural gas for various reasons is not available.
Several Siemens Energy industrial gas turbines can already burn 100 percent propane in standard natural-gas DLE combustors, and recent combustion tests on the SGT-300 have shown that even butane-rich LPGs can be considered for the standard combustors.
There are a number of reasons for the increasing popularity of LPG for power generation:
· LPG is a cleaner fuel than heavy fuel oil (HFO) or diesel
· LPG is traded as a commodity worldwide
· Transportation is easy by sea, rail or truck, regardless of batch size
· Storage of LPG is relatively simple and does not require cryogenic storage tanks
· Storage and distribution infrastructure for LPG is readily available in many countries as it is used for transportation, in
industry and also small-scale heating and cooking.