Technical Requirements For High-efficiency Air Filters in The Operation Of Gas Turbines in Thermal Power Plants

Based on the operational characteristics of gas turbines in thermal power plants, a complete system of technical requirements for high-efficiency air filters has been formed, with the latest international standard ISO 29461-1 and domestic standard DL/T 2849-2024 as the core. The core logic is to achieve efficient interception of submicron particles with the lowest pressure drop energy consumption through precise graded filtration in extremely variable intake environments, thereby protecting expensive gas turbine blades and ensuring the safe, efficient, and long-term operation of the unit.
The following are the core technical requirements summarized based on the latest standards and practical engineering applicatio

The final high-efficiency filter is E12 grade, and typical renovation projects require the final fine filter element to meet E12 grade, so that the overall particle permeability is less than 0.5%. This corresponds to ISO 29461-1 standard T12 level, which requires a filtration efficiency of ≥ 99.5% for the most penetrable particle size (MPPS).

• Graded filtering configuration: Two levels of filtering are commonly used, with first level coarse efficiency (G4/M5) and second level high efficiency (F9/E12).
•  Testing standards: Testing and grading shall be conducted in accordance with ISO 29461-1 (for turbo machinery) or EN1822. The Chinese power industry standard DL/T 2849-2024 has also been released. The group standard T/CAQI 248-2022 also proposes comprehensive technical requirements.

•  Low initial pressure difference: At rated air volume, the initial pressure difference of E12 high-efficiency filter cartridge is usually required to be<270Pa.
•  Final Resistance Limit: The operating resistance should be controlled within a reasonable range, and it is usually recommended that the final resistance not exceed 2-3 times the initial resistance, or be replaced according to the system set value (such as ≤ 1000Pa).

• Long service life: High efficiency filter cartridges typically require>12000 operating hours or 36 months of idle operation.
•  Standardized dust holding test: ISO 29461-1 introduces for the first time a standardized dust holding test procedure for sub efficient (EPA) and high-efficiency (HEPA) filters, which is used to more realistically compare the lifespan of filters in actual use.

•  Temperature resistance: It is necessary to withstand the temperature changes of the intake environment during the operation of the gas turbine, especially the instantaneous high temperature impact of 80-120 ℃.
•  Moisture resistance: For foggy, rainy, or high humidity coastal environments, filters need to have good moisture resistance.
•  Mechanical Strength and Sealing: The structural design must meet the requirements of ISO 2941-2943 and other series of standards, and verify the anti rupture, structural integrity, and pressure resistance of the filter element. Under pulse blowback pressure of up to 0.4-0.6MPa, the filter element needs to maintain structural stability.

• Adopting specialized testing standards (ISO 29461-1): General standards (such as ISO 16890, EN1822) cannot accurately simulate actual working conditions such as high flow rate and pulse blowback in turbomachinery. ISO 29461-1, as the first international standard for turbo mechanical intake filters, provides a unified testing and grading method (T1-T13 levels), enabling operators to compare and select products more scientifically.
•  Evaluate the true efficiency after "static elimination": Many filters rely on static fibers to improve initial efficiency. But in the intake environment of gas turbines, static electricity will quickly dissipate. Therefore, the new standard requires evaluating the minimum mechanical efficiency of the filter after static elimination, which is the performance that the filter can truly rely on throughout its entire life cycle.
•  Introducing HEPA dust holding capacity testing: In the past, high-efficiency filters only measured efficiency without measuring dust holding capacity, making it impossible to evaluate their true lifespan. ISO 29461-1 * first specifies the dust holding capacity testing method for EPA/HEPA filters, providing a quantitative basis for long-life design.

A genuine procurement document for a gas-fired power plant clearly demonstrates the practical application of these technical requirements:
Project background: Mitsubishi M701F4 gas turbine, with a low-level layout of the intake system and three sided intake.
Renovation plan:
First level filtration: Upgraded from G4 to M5 grade bag filter, with an initial pressure difference of<170Pa and a lifespan of>2500 hours.
Secondary filtration: Upgraded from F9 to E12 grade high-efficiency filter element (EN1822 standard), with an initial pressure difference of<270Pa and a lifespan of>12000 hours.
Core objective: To achieve an overall particulate matter transmittance of less than 0.5%, delay compressor efficiency degradation, and achieve energy conservation and carbon reduction.