Filtration upgrades and carbon cuts for advanced gas turbines

(Source: GE Vernova.)

By Tim Nicholas, Global Powergen Market Manager, Gas Turbine Filtration Division, Parker Hannifin

Carbon is the key to sustained success in many businesses nowadays. According to the Ember climate organization, Europe’s gas-fired power stations emitted some 236 million [metric tons] of emissions in 2020. Currently, emissions allowance prices in the EU are hovering around the EUR80/[metric ton] mark suggesting an overhead of nearly a quarter of a billion euros every year in Europe alone.

Furthermore, similar emissions schemes also operate or are under development in Canada, China, Japan, New Zealand, South Korea, Switzerland and the United States. But not only is there a financial cost to emissions, there are shareholder and customer expectations to consider too. Today there are countless examples of shareholder resolutions that hold company boards to account on climate action, while increasingly companies are looking right down the supply chain for carbon savings too.

For the owners and operators of gas turbine-based power plants, under these circumstances, any measures that can save carbon emissions are clearly to be welcomed. Apart from anything else, a reduction in carbon emissions is typically also translated as an improvement in system efficiency. This is a factor that will often dwarf the cost of emissions allowance purchases, even while those are a significant cost burden.

Getting the best out of gas

Modern advanced gas turbines are of course a marvel of optimization and overall system efficiency can exceed 60% in combined cycle. However, other such assets may still be operating after many decades and as such many do not necessarily benefit from the latest technology advances. An example comes from the air inlet filtration system.

Turbines can be located in heavily polluted industrial or urban areas but even in more rural districts agricultural processes can result in a substantial loading of airborne materials.

These materials and contaminants within the air stream include dust and other particulates, water, salts, hydrocarbons or even insects, and can have a surprisingly big impact on turbine efficiency. If such materials enter the turbine, they impinge on the compressor section or possibly deeper internals where they can be deposited on the blades or even cause erosion. This has a dramatic and negative effect on aerodynamic efficiency, which is directly recorded in the turbine’s output. Avoiding this outcome is the primary role of the air inlet filtration system.

Even so, some of these airborne materials inevitably do find their way through into the machine, especially smaller particulates. Given this normal outcome of running the machine, it is typical for operators to conduct periodic off-line washes of the compressor section. Such service washes allow operators to clean the surface and restore aerodynamic performance. Of course, this mode of operation does result in downtime and lost production as the washing process is executed but is also characterized by a drop-off in compressor performance in between washdown cycles. Any performance reduction is associated with increased fuel production and lower output and therefore a fouled compressor is equivalent to an increase in the specific mass of CO₂ produced per MWh of output.

For older machines with less efficient filtration systems, materials build up on the blades far more quickly when compared with more advanced filtration systems. This in turn means that the anticipated performance drop-off occurs more frequently than might be expected for the modern generation of machines. The reasons behind this difference are simply related to the design of the filtration system.

Older filtration technology typically delivers efficiency levels of around M6/F7, which will filter out particulates from about 1.0µm up to 3.0µm in diameter. However, the earlier M6/F7 rated filters have long been superseded and the latest generation of filtration units have efficiency ratings as high as E10-12. Such systems filter out particles down to 0.3µm without impacting other performance parameters such as the pressure loss through the filter house. In addition to advancements in filtration efficiency, technological of media, such as hydrophobic/oleophobic treatments, offer additional gains that would not have been possible during earlier iterations of filtration media. This big step up in filtration efficiency and media technology essentially leaves compressor blades cleaner for much longer and thus aerodynamic performance is sustained for extended periods compared with earlier filter designs. This then reduces the frequency of offline wash treatments and supports higher efficiency of the overall system.

While older M6/F7 rated filters might be considered to deliver a medium level of protection by modern standards, even a step up to F8-9 rated filters, which can remove particles between 0.3µm and 1.0µm, or the addition of hydrophobic/oleophobic treatments will result in a noticeable uptick in performance. For a 350 MW machine that is running for 8,000 hours or more every year even a few percentage points gained in efficiency can represent a significant reduction in emissions. 

Retrofitting uprated filtration systems

While some gas turbine units have been installed for many years and are not currently benefiting from the advances in filtration technology that can improve performance, upgrades are possible. Indeed, switching to a higher efficiency filtration has been proven to dramatically arrest the rate at which performance declines. With sufficient care, such systems can typically be retrofitted to existing installations.

Parker Hannifin’s clearcurrent® gas turbine inlet systems have been tailored for specific environmental conditions, such as damp coastal regions, or dry and dusty deserts. They are also more suitable to maintain performance in the face of the growing challenges of climate change.

A recent example, from spring 2023, was found in North America where extensive forest fires in Canada resulted in a big increase in airborne particulates from the smoke that blew south into the United States. One utility with multiple generations of gas turbine technology operated a range of filtration technologies. Operators noticed that at various older plants, they lost 5-8 MW of output during this event due to compressor fouling. The older plants were using traditional non-hydrophobic nano-fiber filtration that has been on the market for 20+ years. The end result was additional downtime to perform an offline water wash, but this was after an extensive period of time running below optimal performance until the forest fires subsided. Overall, the result was multiple penalties both in terms of a dollar cost and CO₂ emissions to the atmosphere.

Within the same fleet the utility had a newer 1,500 MW plant using advanced gas turbines which fared much better. This plant was using a modern filtration technology with a higher efficiency and hydrophobic/oleophobic treatment. The utility noted this plant was untouched from the smoke of the fires and compressor cleanliness was great.  Even a small loss on a 1,500 MW plant would have a big impact and recognizing this the utility is now investigating a filtration upgrade for its other plants. In spring 2024, a plant with 600 MW capacity will make an upgrade to the modern filtration standard which is a great win for the cleaner more efficient world of gas power.

The future of frontline filtration

By offering better protection from compressor fouling, machines have better efficiency and increased power. This all adds up to lower carbon emissions, as well as lower operations and maintenance costs, with fewer wash cycles, for example.

The U.S. Energy Information Administration (EIA) reports that in 2021, power generation from natural gas resulted in 1.6 million [metric tons] of CO₂ emissions across the nation. Improving this by even a few percentage points would add up to a substantial contribution to net-zero targets. An upgraded filtration system has been proven to result in up to a 0.7% improvement in CO₂ emissions on an annual basis.

Then, there are financial impacts given the scale of the opportunity, but perhaps more important are the shareholder and customer expectations of robust action on climate damaging emissions. For the owners and operators of gas turbines, this is a growing risk – the pressure is on for better climate performance where possible.

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