what are the effects of increasing length of air filters on output of gas turbine ?

 

Turbine efficiency is not just a function of filter type, size, media, configuration. It's a function of both filtration and axial compressor cleanliness, and filters can only remove certain types of contaminants (primarily particulates).

Increasing the length would increase the filter surface area. Increasing the filter surface area may somewhat reduce the differential pressure, or it may actually increase it if the wrong filter media is selected.

Filters don't generally have much of an effect on gas turbine output; it's the cleanliness of the filters that has the effect. That's a qualified statement, qualified by saying that if the proper filters are used for the expected flow-rates and types of contaminants. In other words, in general the turbine manufacturer's recommended filter type. I'm not saying it's necessary to use only the manufacturer's filters, but one should certainly choose a filter type that's similar to or the same as the ones recommended for the best performance in the long run.

Gas turbines are mass flow machines. The more mass (air) they can flow the more power they can make. Simply increasing filter area, without considering the change in air flow and filter media may not result in the desired result.

It's best to work with filter suppliers and/or filter manufacturer's representatives. Develop a dialog with them, explaining your current situation, and what you hope to achieve with a new filter or filter system.

There have been improvements in filter systems in the last few years. It might be wise to have a review of your filter system to see if you can achieve some efficiencies.

The biggest efficiency most people strive for is filter longevity. They're expensive to replace, and so the "self-cleaning" systems were developed.

There are pre-filters which can be installed without too much of an adverse affect on air (mass) flow, and which can be changed at a higher frequency and lower cost that the "main" filter elements they cover.

Again, you need to work with one or two or three various filter vendors, explaining your current situation, and what it is you hope to achieve. Filters can only remove some contaminants; others (hydrocarbon vapors, salt air, diesel exhaust and certain dusts (cement, for example)) can still get past some filters and so compressor washing is very important. Any humidity or "gaseous" vapors which can cause dust and other contaminants to adhere to axial compressor components cannot be removed by filters, and it's a combination of filtration and compressor cleanliness that really affects overall turbine performance. Most filters really only remove particulates above the size they are designed for from the air stream.

Ambient conditions have a lot to do with filter efficiency and life span. Sometimes, a change is warranted, after a proper analysis is performed.

Be aware that performance improvements due to filtration changes are very difficult to quantify and verify. To do so would require extensive "before and after" testing, and would likely require testing with a new and clean set of the current filters in use along with a clean axial compressor, and then a re-test with the new filter system and a clean axial compressor. Lots of work, over some period of time. And apples need to be compared to apples, meaning that like data has to be obtained and compared to like data; new and clean filters and dp over time, versus new and clean filters and dp over time. Very difficult to measure and quantify; sometimes these things are a calculated leap of faith based on some data and some salesmanship.

 

It depends on the type of filter. For example a longer Vbank filter will always outperform a shorter Vbank filter (assuming same design criteria and surface area per m of length).