In the air separation unit, the steam turbine serves as the power source for the air compressor, and its operational safety performance is crucial.
When the main steam temperature increases, the total enthalpy drop, relative internal efficiency, and cycle thermal efficiency of the thermal system inside the turbine will all be improved, resulting in a decrease in heat consumption and an increase in operational economic benefits. However, if the temperature exceeds the allowable value, it will pose a threat to equipment safety. The increase in main steam temperature will increase the enthalpy drop of the regulating stage, which may cause overloading of the regulating stage blades under constant load. Excessive main steam temperature can reduce the mechanical strength of high-temperature metal components such as main steam pipelines, automatic main steam valves, speed regulating steam valves, cylinders, and regulating stage inlet chambers, accelerate creep rates, and may lead to equipment damage or shortened service life. Excessive steam temperature can cause thermal deformation and expansion of various heated metal components. If the expansion is obstructed, the unit may experience vibration.
The decrease in main steam temperature will lead to a reduction in the total enthalpy drop inside the turbine. In order to maintain the rated load, it is necessary to increase the intake of main steam, thereby increasing steam consumption and reducing the unit's economy. After the main steam temperature decreases, in order to maintain the rated load unchanged, the main steam flow rate needs to increase, the enthalpy drop of the last stage increases, and the last stage blades may be in an overloaded state. It will increase the steam humidity of the last few stages of blades, intensify the water droplet erosion of the last few stages of moving blades, and shorten the service life of the blades. It will increase the reaction degree at all levels, resulting in a significant increase in the axial thrust of the rotor, an increase in the temperature of the thrust pad, and a decrease in the safety and reliability of the unit operation.
If the main steam temperature drops rapidly and significantly, the inner wall temperature of high-temperature components such as automatic main steam valve housings, regulating stages, cylinders, etc. will drop sharply, resulting in significant thermal stress and deformation. In severe cases, it may cause cracks or wear accidents in metal components. When the main steam temperature drops sharply by more than 50 ℃, it is often a precursor to water shock accidents, posing a serious threat to the safety of the unit.
