During gas turbine operation, the pressure drop in the intake filtration system is like body temperature—the most direct indicator of system health. Under normal operation, the pressure drop slowly increases with the filter element’s dust holding capacity; when the pressure drop abnormally spikes, it often indicates an underlying fault.
For every 100 Pa increase in pressure drop, the gas turbine’s output power may decrease by approximately 0.5%-1%. More seriously, if the pressure drop exceeds the design limit, it can lead to filter element rupture, unfiltered air bypassing the compressor, causing blade wear, scaling, and even breakage. Therefore, quickly and accurately diagnosing the cause of pressure drop surges is crucial for ensuring the safe and economical operation of gas turbines.
I. Filter Media Clogging: The Most Classic Fault Mode
Fault Mechanism:Filter media clogging is the most common cause of pressure drop surges. As operating time increases, dust particles gradually accumulate on and inside the filter media, narrowing the airflow channels and causing a continuous increase in resistance. When the filter element reaches its dust holding capacity limit, the pressure differential will increase non-linearly and rapidly.
Typical characteristics:
– The pressure differential increases slowly and continuously over time, without significant fluctuations;
– The pressure differential briefly decreases after backflushing, but quickly returns to a high level;
– A uniform dust cake layer is visible on the filter element surface;
Special case: Abnormal pressure differential decreases instead of increases
It is worth noting that a certain factory’s MS109FA gas turbine experienced the abnormal phenomenon of “no increase or even occasional decrease” in pressure differential after 3000 hours of use of the intake filter element. Analysis revealed that this was due to structural damage to the filter media during long-term operation, with some fibers breaking and causing the pore size to increase. Although the pressure decreased, the filtration efficiency had significantly declined. This case suggests that a decrease in pressure does not necessarily indicate a healthy system; a comprehensive judgment based on efficiency monitoring is necessary.
Diagnostic Methods
– Monitor differential pressure trends and calculate differential pressure growth rates;
– Regularly inspect filter cartridge appearance to observe the uniformity of dust cake distribution;
– Employ deep learning-based diagnostic methods, considering the impact of changes in operating parameters such as mass flow rate and specific volume on differential pressure.
II. Ice Bridge Formation: A Seasonal Threat in Cold Regions
Failure Mechanism
When cold temperatures meet high humidity, the intake filtration system faces severe challenges. Supercooled water droplets from snow, freezing rain, or cooling tower plumes can rapidly freeze on the filter media surface, forming “ice bridges” that cover the entire filter surface. Ice crystals block airflow channels, causing a sharp increase in differential pressure. More dangerously, even if the ambient temperature does not reach freezing point, the Venturi effect within the intake system can lead to localized icing—increased airflow velocity causes a temperature drop, leading to water vapor condensation and freezing.
Typical Characteristics
– Seasonal occurrence, associated with low-temperature weather;
– A rapid increase in differential pressure within hours;
– White ice crystals or ice layers are visible on the filter cartridge surface.
Diagnostic Methods
– Combine meteorological data with ambient temperature analysis;
– Check for ice crystal buildup on the filter element surface;
– Monitor the correlation between differential pressure and relative humidity.
Preventive Measures
International practice shows that the most effective solution is intake air heating. Increasing the intake air temperature by approximately 8°C through compressor bleed-backflow or steam coil heating reduces relative humidity to below 68%, fundamentally preventing icing. Anti-icing systems offered by German gas turbine filtration system supplier TrennTech and others can automatically adjust heating power according to environmental conditions, optimizing energy consumption while ensuring operation.
III. Wet Dust Accumulation: The Synergistic Effect of Moisture and Dust
Failure Mechanism
When a high-humidity environment encounters dust, “wet dust accumulation” may form on the filter media surface. Moisture causes capillary forces between dust particles, forming a dense, hard, mud-like layer that adheres tightly to the filter media surface. This accumulated layer is extremely difficult to remove with pulse backflushing, leading to a persistently high differential pressure.
Typical Characteristics
– Occurs during the rainy season, in coastal areas, or in high-humidity regions;
– Rapid pressure differential increase, poor backflushing effect;
– Visible mud-like deposits on the filter element surface;
Diagnostic Methods
– Check if the deposits on the filter element surface are mud-like and difficult to peel off;
– Assess the pressure differential recovery rate before and after backflushing;
– Analyze in conjunction with environmental humidity data;
Solutions
Experience from international filtration companies indicates that solving wet dust caking requires a two-pronged approach: first, using hydrophobic filter media to reduce moisture adhesion; second, optimizing backflushing parameters to improve cleaning intensity. A gas-fired power plant successfully solved the problem of rapid pressure differential increase in the filter screen by improving the coarse filtration accuracy and upgrading the fine filtration media.
IV. Salt Spray Penetration: The Invisible Killer of Coastal Power Plants
Fault Mechanism
Suspended salt spray in the air in coastal areas poses a unique threat to filtration systems. Salt particles are hygroscopic, transforming from solid crystals into liquid droplets when the relative humidity exceeds 70%. Liquid salt spray has strong penetrability, reaching deep into the filter media, evaporating and condensing under high-temperature conditions to form corrosive deposits.
Typical Characteristics
– Occurs on coastal or offshore platforms;
– Increased differential pressure accompanied by decreased efficiency;
– Salt crystals are visible deep within the filter media;
Engineering Hazards
Salt spray not only clogs the filter media, but more seriously, it corrodes downstream components. Salt buildup on compressor blades alters the blade profile, reducing compressor efficiency; salt entering the combustion zone can trigger sulfide corrosion, damaging the protective layer of hot-end components.
Diagnostic Methods
– Analyze for salt accumulation deep within the filter media
– Monitor intake air salt spray concentration (highlighted for offshore platforms)
– Check downstream compressor blades for signs of salt buildup
V. Backflush Failure: The “Strike” of the Self-Cleaning System
Failure Mechanism
For gas turbines equipped with pulse backflush systems, backflush failure is a major cause of soaring differential pressure. When the electromagnetic pulse valve malfunctions, compressed air pressure is insufficient, the control system fails, or cleaning parameters are improperly set, dust on the filter element surface cannot be effectively removed, and the differential pressure will continue to rise.
Typical Characteristics
– Continuously rising differential pressure with no significant decrease after backflushing;
– No pulse valve activation sound or abnormal sound during backflushing;
– Compressed air pressure lower than the set value;
– Excessively thick and unevenly distributed dust cake on the filter element surface;
Diagnostic Methods
– Check if the compressed air pressure is within the range of 0.76-0.83 MPa;
– Listen to whether the pulse valve operates normally;
– Assess the differential pressure recovery rate before and after backflushing;
– Check if the dust cake on the filter element surface is evenly shed;
Common Causes of Backflushing Failure
1. Pulse valve failure: diaphragm damage, solenoid coil burnout;
2. Compressed air problems: insufficient pressure, oil or water content;
3. Control system malfunction: differential pressure sensor failure, logic error;
4. Improper parameter settings: pulse width too short, interval too long;
5. Venturi tube[19] blockage or damage.
VI. From Fault Diagnosis to Predictive Maintenance
Differential pressure spikes each have their unique physical mechanisms and performance characteristics. Accurately identifying the root cause of a fault is a prerequisite for taking effective countermeasures. With advancements in sensor technology, big data analytics, and artificial intelligence, intake system fault diagnosis is shifting from “post-event analysis” to “real-time early warning,” and from “experience-based judgment” to “quantitative diagnosis.” At the Hannover Messe industrial trade fair[20] in Germany, an increasing number of filtration companies are showcasing their latest technological achievements in integrated intelligent monitoring.
For the daily operation of gas turbines, a deep understanding of the underlying mechanisms of various faults, combined with comprehensive analysis of operational data and environmental information, is the fundamental prerequisite for ensuring the intake system is always in optimal working condition and safeguarding every smooth “breath.”