(Daily Question) Coal-to-Oil and Olefins Forum, April 26, 2018

①When the vacuum in the condenser is too high, the rotor encounters less resistance; less steam is required for impulse, making it more difficult to control the speed； ②As the rotation speed increases, the steam consumption rises accordingly; however, due to the low exhaust pressure, the amount of steam remains low, failing to achieve the desired warming effect ； ③When the vacuum level is too low, the resistance to the impulse rotor is high; the static time of the rotor during the impulse process is prolonged, which can easily lead to rotor bending ； ④Too low a vacuum and high exhaust temperature can lead to poor expansion in the low-pressure cylinder, affecting the rotor’s centering.

If the vacuum level is too high, the opening degree of the speed control valve is too small, making it difficult to control; if the vacuum level is too low, it becomes hard for the unit to draw in air, preventing it from starting properly.

①When the vacuum in the condenser is too high, the rotor encounters less resistance; less steam is required for impulse, making it more difficult to control the speed； ②As the rotational speed increases, the steam consumption rises accordingly; however, due to the low exhaust pressure, the amount of steam remains low, failing to achieve the desired warming effect ； ③When the vacuum level is too low, the resistance to the impulse rotor is high, the static time of the rotor during the impulse process is long, and rotor bending is likely to occur ； ④Too low a vacuum and high exhaust temperature can lead to poor expansion in the low-pressure cylinder, affecting the rotor’s center alignment.

(1) When the vacuum level inside the condenser is too high, the resistance to rotation of the rotor is low; as a result, less steam is required for starting up. Slight fluctuations in the control system can cause significant changes in speed, making it difficult to maintain stability； (2) As the warming-up speed increases, the steam flow rate consumed by the turbine should increase accordingly; however, due to the excessively low exhaust pressure, the amount of steam supplied is relatively low, failing to achieve the desired warming-up effect ； (3) The vacuum level inside the condenser is too low, resulting in high resistance when the rotor starts rotating ； (4) If the vacuum is too low, the exhaust temperature of the turbine increases. An excessively high exhaust temperature can lead to poor expansion in the low-pressure cylinder, affect the alignment of the rotor, and even cause friction between the moving and stationary components, resulting in damage to the rotor assembly.

①When the vacuum in the condenser is too high, the rotor encounters less resistance, less steam is consumed during impulse operation, and it is more difficult to control the rotor speed； ②As the speed increases, the steam consumption rises accordingly; however, due to the low exhaust pressure, the amount of steam remains low, failing to achieve the desired warming effect ； ③When the vacuum level is too low, the resistance to the impulse rotor is higher, the static time of the rotor during the impulse process is longer, and rotor bending is likely to occur ； ④Too low a vacuum and high exhaust temperature can lead to poor expansion in the low-pressure cylinder, affecting the rotor’s center alignment.

Answer: ① When the vacuum inside the condenser is too high, the rotor encounters less resistance; therefore, less steam is required for impulse, and it is more difficult to control the speed； ②As the rotation speed increases, the steam consumption rises accordingly; however, due to the low exhaust pressure, the amount of steam remains low, failing to achieve the desired warming effect ； ③When the vacuum level is too low, the resistance to the impulse rotor is high; the static time of the rotor during the impulse process is prolonged, which can easily lead to rotor bending ； ④Too low a vacuum and high exhaust temperature can lead to poor expansion in the low-pressure cylinder, affecting the rotor’s centering.

Why is it necessary to maintain an appropriate vacuum in the condenser during the startup of the turbine unit? Answer: Operational experience shows that, when starting a turbine-compressor unit, maintaining an appropriate vacuum in the condenser not only facilitates a smooth start-up of the unit but also contributes to the safety of the equipment. 1. If the vacuum level is too high, the rotor resistance is low; as a result, less steam is required to generate thrust. This leads to large fluctuations in the speed of turbines that use control valves, which hinders speed stability and results in poor warm-up performance. 2. If the vacuum level is too low, the rotor encounters high resistance; when warming up while the rotor is at rest, thermal bending of the rotor can occur, requiring continuous rotation of the rotor. The high exhaust temperature leads to poor expansion in the low-pressure cylinder, causing the rotor center to shift downward; this can even result in collisions and moderate damage to the rotor. 3. Each unit has an appropriate vacuum level. The control principle is as follows: during startup, the vacuum level can be slightly lower, as long as it remains above the alarm threshold; as the speed increases, the vacuum level should be raised gradually, and at the rated speed, it should reach the designed value.

When the turbine-compressor unit is started with rotor impulse, maintaining an appropriate vacuum in the condenser not only facilitates smooth startup of the unit but also contributes to the safety of the equipment.

①When the vacuum in the condenser is too high, the rotor encounters less resistance, less steam is consumed during impulse operation, and it is more difficult to control the rotor speed； ②As the speed increases, the steam consumption rises accordingly; however, due to the low exhaust pressure, the amount of steam remains low, failing to achieve the desired warming effect ； ③When the vacuum level is too low, the resistance to the impulse rotor is higher, the static time of the rotor during the impulse process is longer, and rotor bending is likely to occur ； ④Too low a vacuum and high exhaust temperature can lead to poor expansion in the low-pressure cylinder, affecting the rotor’s center alignment

When the turbine-compressor unit is started with rotor impulse, maintaining an appropriate vacuum in the condenser not only facilitates smooth startup of the unit but also contributes to the safety of the equipment. ①When the vacuum in the condenser is too high, the rotor resistance is low, and less steam is consumed during impulsion, a phenomenon that is particularly evident during individual tests of the turbine. For units started using a regulating valve, when the opening degree of this valve is very small and there are slight fluctuations in the regulating system, the speed experiences significant variations, making it difficult to maintain stability. As the warm-up speed increases, the steam flow rate consumed by the turbine should increase accordingly; however, due to the excessively low exhaust pressure, the steam supply is relatively low, failing to achieve the desired warm-up effect. ②The vacuum level inside the condenser is too low; as a result, there is high resistance when the rotor is started, causing the rotor to warm up while it is at rest. A similar situation occurs in units that use the main steam valve for startup and control valves for startup; sometimes, there is even suspicion that the rotor has seized, leading to a false alarm. If the rotor is not turned manually at this time, thermal bending of the rotor is likely to occur, which is very dangerous. Furthermore, if the vacuum level is too low, the exhaust temperature of the industrial steam turbine increases. An excessively high exhaust temperature can lead to poor expansion in the low-pressure cylinder, affect the alignment of the rotor, and even cause friction between the moving and stationary components, thereby damaging the alignment between the rotors. Therefore, industrial steam turbines are equipped with alarms for exhaust pressure and temperature; the unit is not allowed to start operating when the exhaust pressure exceeds the set alarm value. ③Each unit has a starting vacuum value suitable for its own characteristics; a vacuum level of 67–80 kPa is considered appropriate. The general principle is that the vacuum value can be kept slightly lower during startup, but it should not fall below the alarm threshold. As the speed increases during warm-up, the vacuum level should be increased gradually, until the speed reaches the rated value, at which point the vacuum level can be raised to the design value.