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I. Overview Generally, drainage is divided into two main categories: drainage from the turbine itself and system drainage. The steam turbine’s own drain systems include the cylinder drains, as well as the drains for various pipes that are directly connected to the cylinder. These include those located after the high and medium pressure main steam valves, in front of the valves on the various extraction pipes that are in direct connection with the cylinder, in front of the check valve for the exhaust gas from the high-pressure cylinder, and those related to the shaft seal system. The other types of condensate are classified as system condensate, such as the first-stage cylinder of the small turbine, high-pressure steam conduits, internal steam seal condensate, and so on. The drain system designed for the unit, when operating under various conditions, should be able to prevent potential water ingress into the turbine from the outside as well as abnormal water accumulation within the turbine itself, and it should also meet the requirements for warming up the system and maintaining it in a hot standby state. During startup, shutdown, and load variation conditions in large steam turbine units, steam comes into contact with the turbine itself and the steam pipes, and the steam is generally cooled. When the steam temperature is lower than the saturation temperature corresponding to the steam pressure, the steam condenses into water. If this condensed water is not removed in time, it will accumulate in certain pipe sections and cylinders. During operation, due to the differences in density and flow rate of steam and water, the resistance exerted by the pipes on them also varies; these accumulated waters can cause water hammer in the pipes, which may lead to pipe vibration and generate noise that pollutes the environment ； In severe cases, it can cause cracks in the pipes, or even lead to their rupture. Worse still, once some of the water accumulates in the turbine, it can cause the stationary and rotating blades to be damaged or broken due to the impact of the water, leading to permanent deformation of the metal components as a result of rapid cooling, and even causing the main shaft to bend. In addition, the drain system of the turbine itself should have a sufficient capacity, so that steam can be discharged immediately when the unit trips, thereby preventing the turbine from speeding up or overheating. To effectively prevent the turbine from encountering such adverse operating conditions, it is necessary to promptly remove the condensed water accumulated in the cylinders and steam pipes to ensure the safe operation of the unit. At the same time, hydrophobes of qualified quality should be recovered as much as possible to improve the economic efficiency of the unit. To this end, steam turbines are equipped with a drain system that includes drain pipes for steam leakage from in front of and behind the high- and medium-pressure main steam valves of the turbine, as well as from in front of and behind the various main and medium-pressure control valves; it also includes steam extraction pipes, main pipes for supplying steam to the shaft seals, and so on. In addition, the auxiliary steam system of the turbine, the small turbine itself, as well as the steam inlet pipes before and after the high and low pressure main steam valves, the deaerator heating system and the high and low pressure feedwater heaters all have their own drain systems. These hydrocarbons are either directly discharged into the hydrocarbon expansion tank and then recovered to the condenser, or directly discharged into the drain. The drainage water from steam turbines consists mainly of the following components: drainage water from low points on the main steam and reheat steam pipelines, drainage water from the turbine casing, the main steam control valves, and the high-pressure steam conduits; drainage water from the extraction steam pipelines; drainage water from the steam supply pipelines for the feedwater pumps; drainage water from auxiliary steam and deaerator heating pipelines; drainage water from the shaft seal system and leaks from the valve stems; as well as drainage water from other auxiliary systems. II. Operation of the hydrophobic system 1. The hydrophobic steam turbines consist of high-pressure and low-pressure hydrophobic systems, and automatic control of the hydrophobic flow is achieved through DEH. All drain valves shall be opened before the unit is started, and the drain valve on the high-pressure section shall be automatically closed when the unit load reaches 20% of the rated load ； When the load reaches 25% of the rated load, the low-pressure section body drain valve closes automatically. During shutdown, when the unit load reaches 25% and 20% of the rated load, the low-pressure section and high-pressure section body drain valves are automatically activated in sequence. When automatic failure occurs, manual intervention should be carried out promptly to adjust the status of the body’s steam trap. Additionally, when the unit is shut down, it is necessary to ensure that all steam from the cylinders has been drained before closing the cylinder drain valves, in order to prevent a large temperature difference between the upper and lower cylinders from causing dynamic and static friction. Furthermore, in the event of a severe accident that causes a vacuum loss and triggers an emergency shutdown, the condenser protection will activate, and it is necessary to prevent the opening of high-pressure drains to avoid damaging the equipment. The main reheat steam pipeline drains and the cylinder body drains should both be turned on before the unit is started, in order to ensure thorough drainage and prevent water from entering the turbine or accumulating there. During shutdown, when the load drops to a certain value, verify that the drain valve on the main reheat steam pipeline is open. 2. For the drains of auxiliary systems such as the drain system of the auxiliary steam turbines, the auxiliary steam drain system, the deaerator heating system, and the shaft seal drainage system, these drains should be turned on before the respective systems are put into operation, in order to allow proper drainage and to warm up the pipes. This prevents steam-water shock from occurring, which could lead to pipe vibration and other accidents. Turn it off after the pipe warming is complete. These hydrophobic valves are available in both automatic and manual versions. During operation, the relevant provisions of the operating procedures and safety regulations must be strictly followed. 3. Protection against water ingress in the turbine: 1) The turbine is equipped with protection against water ingress, to prevent accidents such as water hammer caused by water entering the cylinder during operation or shutdown, as well as issues like friction between moving and stationary parts and shaft bending resulting from large temperature differences between the upper and lower cylinders. The metal temperature measurement points on the turbine itself should be properly arranged and give accurate readings. If a large temperature difference is detected between the upper and lower cylinders, the cause should be identified immediately and eliminated completely. 2) Install steam traps in the drain ports of all major steam pipelines (in front of the high-pressure check valves and before the interconnecting pipes). Additional steam traps should be placed at the low-point drain locations on the reheat cold section pipes, and two level sensors should be installed to control the opening and closing of the valves. 3) A cooling water control valve was added to the shaft seal cooling water pipeline. A steam-water separator for shaft seal steam is installed after the temperature reducer, which prevents water from being carried in the shaft seal steam while ensuring the appropriate temperature of the low-pressure shaft seal. 4) All pneumatic valves in the drain system are equipped with local operation handwheels to enable manual control in case of automatic failure, and the status of the drain valves (open or closed) is displayed in the main control room. 5) The turbine extraction pipeline system and the high and low pressure heaters are also equipped with automatic protection against water ingress, including an automatic drain system for the heater housings (including the shut-off valves in the system), electric valves for extraction on the pipelines connecting the turbine to the heaters, as well as electric valves for the inlet and outlet on the water side of the heaters. III. Drain valves 1. The purpose of the turbine drainage system is to prevent water from entering the components of the turbine or accumulating inside it during startup, operation under load, load shedding, or shutdown of the unit. Once water enters a steam turbine, damage to its components is almost inevitable. Water can cause thermal shock and mechanical shock, leading to failures such as damage to the blades and shrouds, damage to the thrust bearings, rotor cracks, cracks in the diaphragm sleeves, permanent bending of the rotor, permanent deformation of the stator section, and wear of the steam seal plates. 2. Operating principles for all steam turbine traps: 1. Keep them open from the time the turbine is shut down until it is cooled down. 2 It must be opened before starting the turbine and supplying steam to the shaft seal. 3 It remains open when the unit’s load increases; the high-pressure steam trap is closed when the load reaches 10% of the rated value, and the medium-pressure steam trap is closed when the load reaches 20% of the rated value. 4 When the unit reduces its load, the medium-pressure steam trap is opened when the load drops to 20% of the rated value, and the high-pressure steam trap is opened when the load drops to 10% of the rated value. 5 Avoid breaking the vacuum before the main drain valve is opened. However, this recommendation is not suitable for situations where it is necessary to break the vacuum immediately in an emergency, nor is it suitable for the steam traps in the user’s main steam pipes. 3. The hydrophobic expansion vessel itself serves to receive various types of condensate from the steam turbine unit, including condensate from main steam, reheat steam, extraction systems, high-pressure heaters in case of accidents, low-pressure heaters during normal operation as well as in case of accidents, small steam turbines, auxiliary steam systems, and deaerator overflow. It expands, reduces the pressure, and lowers the temperature of this condensate in order to recover the working fluid. During operation, it is important to ensure that the steam traps do not overheat or vibrate, as this could damage the equipment and affect the vacuum level of the main unit as well as its operation. Additionally, since there are significant differences in the pressure and temperature of the steam traps, they are classified according to their pressure levels. To prevent interference between steam traps with different pressures, which could lead to accidents and increased stress, those with similar pressures are connected to the same collection pipe. This unit is equipped with high and low pressure drain headers, which are located at the high-pressure condenser. The hydrophobic system includes: automatic or manual control of hydrophobicity ； Thermostat hydrophobicity ； Continuous hydrophobic treatment of throttle orifice plates ； It also includes ventilation and exhaust valves ； Steam leaking from the valve stem is discharged directly into the gutter.