INTRODUCTION
The thermal power plant’s condition underpins every aspect, from safety, risk management, flexible operation, performance upgrades, life extension, spare parts optimization, investment, and due diligence. Performance testing verifies that the plant can achieve its guaranteed parameters and function as intended. A performance test helps maximize plant efficiency, reduce plant emissions, and minimize operating costs by identifying any shortfalls in the efficiency and capacity of the plant and providing recommendations for recovery and performance improvement.
Cold Air Velocity Test (CAVT)
Generally, in the boiler, the flue gas flow pattern in the second pass may not be uniform due to combustion behavior, fouling tendency, and configuration (ex: Gooseneck). This non-uniformity will lead to uneven heat transfer in the tube bundles and high-velocity zones, including erosion of pressure parts. To assess the flue gas flow pattern, velocity mapping shall be carried out by conducting CAVT (as per the ICAC-EP-7 standard). The non-uniformity shall be ascertained by the co-efficient of variation (COV) in velocity across the cross-section in various planes.
Clean Air Flow Test (CAFT)
CAFT (as per ASME-PTC 4.2 standard) is conducted using clean air during mill standby or shutdown. It is carried out in mill systems to check whether the velocity variation of the pulverized coal pipes is within the allowable limit of ±5%. Further, checking is also done to ensure that the correct size orifices are installed in the coal pipes for equalizing the air flow and that there is no foreign material entry inside the pulverized coal pipes.
Dirty Air Flow Test (DAFT) And Iso Kinetic Sampling
DAFT (as per the ASME-PTC 4.2 standard) is conducted in plant running condition. It is carried out in pulverizers to check for velocity variation among the coal pipes of a pulverizer, ensure the correct size orifices are installed in the coal pipes, and establish equal flow in all the coal pipes of the pulverizer. The standard deviation of velocity among the coal pipes is ensured within the acceptable limit of ±10%. Further, coal fineness is systematically analysed using Iso Kinetic Sampling.
Air And Gas Flow Testing
Air and gas flow testing is performed to verify the flow and velocity profiles in various streams of the boiler’s air and gas circuits and other systems up to the ID fan inlet. This evaluation will indicate the present condition of the flow like velocity profiles, the pressure drop at various locations, and the need for any corrections to be applied by conducting CFD analysis to equalize the flow and improve the performance of the system.
Gas Distribution (GD) Test
The GD test (as per the ICAC-EP-7 standard) is carried out in an electrostatic precipitator (ESP) to verify and achieve uniform flow distribution across the cross-section of the ESP. Due to the longer duration of operating the boiler, the guide vanes, flow splitters, etc. might be disturbed or eroded, resulting in non-uniform flow distribution and increased emissions. The acceptable limit of the coefficient of variation (COV) in velocity should be below 20% to ensure effective collection.
Air Pre Heater (APH) Performance Testing
APH performance testing (as per the ASME-PTC 4.3 standard) is carried out to check the leakage, pressure drop, temperature rise in the air, and temperature drop in the flue gas. This test will indicate the present condition of APH, including choking, seal surface clearances, and the effectiveness of the sealing system.
Flue Gas Analysis Test (Or) Nox & Sox Testing
The combustion of coal converts the nitrogen and sulphur bound in coal to products such as oxides of nitrogen (NOx) and oxides of sulphur (SOx). This test shall be conducted to evaluate whether the NOx and SOx emission levels are within the emission norms or not.