Clearing The Air

By Jack Burke10 May 2019

Gas turbines need clean, dry air to produce energy efficiently. Because intake air quality is so important, inlet design and air filtration products are key.

But not all air is the same; some has more moisture, some has more particulates. So it stands to reason that while one filter may work in one application, it might not be the best choice for another, said Mike Roesner, aftermarket manager for the Gas Turbine systems group at Donaldson Co. Nearly every operator should evaluate three air filtration performance factors: efficiency, watertightness, and, in pulse-cleanable applications, pulse recovery rate, he said.

To help operators make the best filter choice, Donaldson now tests and rates its gas turbine inlet filters on all three characteristics. Using these abbreviations, the company assigns 0 to 5 performance scores to each filter on:

Efficiency (Er0 to Er5)

Watertightness (W0 to W5)

Pulse Recovery Rate (S to P5)

This ErWP rating system is designed to help operators select the best filter choice for their specific environment and work cycle.

“All three tests that we’re using, the efficiency testing, the watertightness testing and the pulse recovery rate testing are tests that have existed in some shape or another within the industry for a number of years,” Roesner said. “The whole premise of the ErWP is based on the customer’s needs, not our needs as an engineering or a product manufacturing company, that doesn’t matter,” Roesner said. “It’s really the customer’s environment, the customer’s system, the customer’s application and the customer’s pain points.”

Efficiency: The proportion of inlet air particulates captured by the filter is the most widely recognized performance metric. Because higher-efficiency filters have associated costs, operators need to determine an efficiency rating that delivers a return on investment.

Watertightness: In humid or ocean-front locations, resistance to moisture becomes a high priority. Salts and other dissolved solids carried by water can be highly corrosive and often more detrimental than airborne contaminants. How the filter performs in wet conditions is important.

Pulse Recovery Rate: How readily filters regain peak performance after compressed air pulse-cleaning is a third key factor. High pulse recovery is a top priority in desert or arctic environments, where there is either continual exposure to dust, snow, and ice buildup, or potentially sudden episodes of heavy loading.

Standardization not always best

Although important, air filtration isn’t always given top priority by operators or even turbine manufacturers, Roesner said. And just because you’re using a technology that was delivered with the turbine, whether it’s from an OEM platform or from a company like Donaldson, that doesn’t mean that it’s the answer to optimize performance of your system, Roesner said.

“You know, OEM A and OEM B and OEM C, they’re competing with each other from a CAPEX standpoint, and a lot of times they look to minimize the overall cost of their equipment by standardizing on filtration. I always tell people, whether I’m speaking at a convention or a user group or something like that, I always tell people OEs build great equipment and they offer really great filtration, but it doesn’t necessarily mean that their Number One concern is your operations and maintenance costs to operate the plant.”

Sometimes, operators may have filtration not best suited for the application. For example, Roesner said that although Donaldson is a leader in pulse technology, it’s not the best solution for every application.

“And we’re not telling the customer, hey, pull your pulse system out because you don’t need it,” Roesner said. “Because that would be like removing the windshield wipers from your car. Just because it’s not raining doesn’t mean that you’re not going to need them someday. What it means is that a watertight media might be a better option for them to optimize their turbine health, optimize their run and, and get the highest ROI possible.”

Roesner said the ErWP system makes sense because every industry has different needs. A peaking station that’s producing power to the grid has a very different need than a gas compression station or an exploration company.

On the exploration side, it’s critical to have equipment be available and to minimize downtime—or costs can skyrocket, Roesner said. So having filters that maximize the life between scheduled outages is key and that’s where the ErWP system can help.

“That was actually the conversation that sparked this ErWP within our engineering team—you know, different plants have different needs, different environments have different needs,” Roesner said. “But yet there’s a lot of manufacturers out there including, you know, X, Y and Z, that are just saying, ‘hey, here’s the best filter for all applications.’ We don’t believe that. In fact, we know that’s not the case…There is no one filter.

“Until that product exists, there’s no one silver bullet,” Roesner said

Industry discussions

Donaldson is in discussion with other filter manufacturers about adopting this more-comprehensive rating method as a new industry standard.

Roesner said the conversations are ongoing.

“A lot of people have been asking about it and we’re all very open to it,” Roesner said. “We want a system—we’re hoping that the Donaldson system is the start of a conversation for a system where you can look at all filters across the board and know what they are.

“Donaldson is very open to the fact we’ll test our filters against anybody’s from a pulse recovery standpoint, from an efficiency standpoint, water tightness and just put it out there and this is what it is. And that’s what this rating system is trying to do, but some manufacturers are more open, obviously, than others. When you’re a manufacturer and you only have one technology, it’s hard for you to be very open about a testing methodology that tests it on more parameters than the one technology you’re selling.”

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