Operational flexibility is critical to ensuring that a gas power plant generates reliable electricity while maintaining profitability. Taking advantage of fuel flex capabilities can play a pivotal role in helping strike this balance by maintaining efficient operation when a primary fuel is not available. In addition to being seen as a resource to help improve energy stability and security to the grid, plant owners/operators facing cost constraint can save millions in annual operating costs by shifting to a lower-cost alternative.
The economics of alternative fuels
Across the industry, the prices of many fuels – particularly natural gas and liquefied natural gas (LNG) – have fallen dramatically over the last 10 years. For example, LNG spot prices in Japan have dropped from $18 per million BTU ($/MMBTU) in 2014 to less than $6/MMBTU. Today, global spot LNG prices are less than $6/MMBTU, with prices below $5/MMBTU in Europe and the U.S. While this shift has driven up demand for these fuels, power producers must weigh additional factors when making business decisions, such as operating expenses associated with increases in fuel flexibility.
Fuel is typically the largest operating cost for a gas plant. Therefore, even small cost changes can have a big impact on plant economics. For example, an F-class gas turbine (1×1 multi-shaft configuration) operating 8,000 hours per year on fuel costing $5/MMBTU will incur an annual fuel expense of ~$100 million. This represents roughly 75% of the plant’s annual operating expenses. If the plant can switch to a fuel that only costs $4/MMBTU, this $1 shift in cost reduces the plant’s annual fuel expense by ~$20 million.
Impact of fuel price on annual operating expenses
The ability to operate on a wide range of fuels – including lower-cost alternatives – can be crucial to a plant’s economics. Consider the industry’s trending interest in propane and liquefied petroleum gas (LPG). The rapid development of shale gas in the U.S. has reduced the prices of these fuels over the last few years. Although prices have risen in recent months, propane spot prices at Mt. Belvieu are still less than $1 per gallon, which translates to $11.50/MMBTU. Even though this costs more than LNG in many places, it is lower than the price of diesel in many parts of Asia, South America, and Africa. Given the impact of even small changes in fuel pricing, propane is being studied as an alternative to diesel and heavy fuel oil (HFO) in areas where natural gas and LNG are not available.
Preparing the total plant
The ability to operate on alternative fuels can require modifications beyond the gas turbine. Some fuels require pre-combustion treatments that may include increased filtering, injection of additives, removal of salts or fuel heating. There may also be special requirements for fuel storage and tank configurations.
For example, some alternative fuels differ so greatly from natural gas and diesel that they cannot be operated in a Dry Low NOx (DLN) combustion system. Gaseous fuels with heating values significantly lower than natural gas (syngas, steel mill gases, high hydrogen), as well as ash-bearing liquid fuels (residual oil, heavy fuel oil) all fit into the category of needing a diffusion (non-DLN) combustor. These combustion systems are well proven, with more than 3.5 million operating hours.
Depending on the specific fuel and local emission regulations, post-combustion emissions controls may also be required. This could include a selective catalytic reduction (SCR) system for NOx emissions or a catalyst bed to reduce CO emissions.
In addition, the higher sulfur levels of some gas and liquid fuels can create potential corrosion problems in both the fuel accessory systems and the heat recovery steam generator (HRSG) of a combined-cycle plant. Configuration changes may be required in these systems to avoid corrosion due to the formation of sulfuric acid.
The good news is that many of these fuel-related modifications do not require any changes to the gas turbine compressor or hot gas path. When required, many of the configuration changes are relatively simple to implement, providing enhanced flexibility even for gas turbines that have been operating for many years.
Although these plant configuration modifications will add to a power plant’s capital expenditures, the reduced operational costs associated with using a lower cost fuel can create a positive return on investment in a short period of time.
GE’s fuel flexibility solutions
GE has partnered with customers in developing solutions for a variety of alternative fuel challenges worldwide over the past decade.
Refinery gases and flare to power – Many industrial customers have waste gases used for internal processes that would otherwise have to be flared. In cases where there is an onsite gas turbine, these gases could be used to power the existing asset(s). This approach reduces unwanted emissions, increases the efficiency of the overall plant/process, cuts down on annual fuel and operating costs. This was the case at a Compañía Española de Petróleos (CEPSA) site in Spain, where GE provided an upgraded DLN 1 combustion system that allowed the existing 6B gas turbine to operate more efficiently on a refinery gas. This solution increased plant efficiency, reduced the plant’s NOx emissions by up to 90%, and reduced maintenance costs. To date this site has over 21,000 fired hours with this new configuration.
Riyadh PP11 Combined cycle power plant
Use of crude oil in F-class gas turbines – Due to the impact of fuel availability and economics, many new gas turbine power plants in Saudi Arabia are required to use Arabian Super Light (ASL) crude oil as a backup fuel instead of diesel. Unlike other crude oils, ASL has very low vanadium content, making operation on higher firing temperature gas turbines possible. After a detailed examination of ASL, including dedicated combustion testing, GE validated the operation of this crude oil on a 7F gas turbine at the Riyadh PP11 combined-cycle power plant in Saudi Arabia. To date, GE has commissioned 15 F-class gas turbines on this fuel, with more expected in 2018.
Randolph Harley Power Station, St. Thomas, USVI
Propane fuel conversion – Due to shifts in regulations, the U.S. Virgin Islands (USVI) Power and Water Authority decided to convert the Richmond and Randolph Harley Power Stations to operation on propane after running the plants on diesel for many years. GE provided the required modifications to the control systems and the gas turbine enclosures of seven gas turbines – five Frame 5 gas turbines, and a single 6B.03 gas turbine. After the new fuel system was constructed, the turbines were commissioned on propane.
LM2500 gas turbine steel mill installation
Use of steel mill gases in aeroderivative gas turbines – Like heavy-duty gas turbines, aeroderivative turbines are capable of operating on a wide range of fuels. In addition to natural gas, LNG, LPG, distillate and kerosene (i.e. jet fuel), these turbines can operate on process and waste fuels. For example, GE installed five turbines into two steel mill plants in China capable of operating on a coke oven gas with 60% hydrogen (by volume).
Into the future
Many countries around the world that are aiming to reduce their carbon emissions view low-carbon electricity generation as an important step in this process. Due to the important role of gas turbines in ensuring electric grid stability, there is continued focus on preserving the role of gas generation in the global energy mix. One option in this low-carbon paradigm could be to convert natural gas into hydrogen (using renewable power), which could then be used to generate reliable electricity without carbon emissions.
GE high H2 fleet leader
Fortunately, there are technical solutions available today to support this option. With multiple heavy-duty gas turbines operating on fuels with more than 50% hydrogen for more than 20 years, and more than 100,000 hours on fuels with up to 95% H2, GE has the demonstrated expertise to put high H2 fuels to work in reliable power generation.
Whether driven by logistics, economics or environmental regulations. The ability of gas turbines to operate on a wide range of gas and liquid fuels provides operational flexibility and a path to stable, lower-cost power generation.
To learn more about the fuel flex capabilities of GE’s gas turbines, try the online fuel explorer tool.