【Q&A Question No. 090】2018.03.31
Thread Content
【Q&A Question 090】March 31, 2018: Briefly explain why preheating is necessary before starting a hot oil pump The main reason is to reduce the temperature difference between the pump body and the medium, thereby facilitating the startup of the pump and preventing damage to it due to an excessive temperature difference. Generally, the pre-heating valve at the outlet of the standby pump is slightly opened. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) Due to the limitations on the number of posts in the “One Question per Day” section, “One Image per Day” has been moved to the registered devices section; you can access it through the directory I posted. For management purposes, if you need to access content from a few days ago, please go to the summary post below to enter the “My Registration Season” event – (Note: This event is currently underway in the Chemical Engineering section). https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=18978 For the daily questions section related to chemical engineering technology training in 2018: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1888971 For the daily image summary section related to registered equipment in 2018: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1888970 For the Q&A section related to hydrogen production and hydrogenation technologies in 2018: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1888968 For the daily questions section related to LNG technology in 2018: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1888973 For the Q&A section from 2017 (updates have started): https://bbs.hcbbs.com/thread-1657793-1-1.html For the daily questions summary section from 2017 (updates have started): https://bbs.hcbbs.com/thread-1657794-1-1.html For the daily image summary section from 2017: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1875160 For the list of daily questions related to LNG in 2017: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1804162 For the Q&A section from 2016 (updates are complete): https://bbs.hcbbs.com/thread-1597792-1-1.html
Hot oil entering a cold pump body causes severe temperature differences within the pump, leading to leaks and damage to components. The medium transported by hot oil pumps has high viscosity; it solidifies at low temperatures, which prevents the pump from starting to deliver fluid properly, and can also cause vibration and noise in the pump
(1) High temperature. If not preheated, hot oil entering a cold pump body will cause severe temperature fluctuations in the pump, leading to leaks and damage to components. (2) High viscosity. The medium transported by hot oil pumps has high viscosity; it solidifies at low temperatures, which prevents the pump from starting to deliver fluid properly, and can also cause vibration and noise in the pump.
(1) High temperature. If not preheated, hot oil entering a cold pump body will cause severe temperature fluctuations in the pump, leading to leaks and damage to components. (2) High viscosity. The medium transported by hot oil pumps has high viscosity; it solidifies at low temperatures, which prevents the pump from starting to deliver fluid properly, and can also cause vibration and noise in the pump.
If a hot oil pump is started without preheating, the hot oil will quickly enter the cold pump body, causing uneven heating of the pump. The upper part of the pump expands more due to heat while the lower part expands less, which can lead to the shaft bending or cause the sealing rings on the pump body and the rotor to get stuck； Forcing it to start can cause wear, shaft binding, and shaft breakage. If high-viscosity oils are not preheated, they will condense inside the pump, resulting in no flow after startup, or the electromechanical system may trip due to the high starting torque. Due to insufficient preheating, uneven thermal expansion occurs throughout the pump, leading to leaks at the static seal points. Issues such as leaks at the outlet and inlet flanges, the flange on the pump’s cover, and the balance pipes can lead to serious accidents like fires and explosions
If a hot oil pump is started without preheating, the hot oil will quickly enter the cold pump body, causing uneven heating of the pump. The upper part of the pump expands more due to heat while the lower part expands less, which can lead to the bending of the pump shaft or jamming of the seal rings on the pump body and those on the rotor； Forcing it to start can cause wear, shaft binding, and shaft breakage. If high-viscosity oils are not preheated, they will congeal inside the pump, resulting in no flow after startup, or the motor may trip due to the high starting torque. Due to insufficient preheating, uneven thermal expansion occurs throughout the pump, leading to leaks at the static seal points. Issues such as leaks at the outlet and inlet flanges, the flange on the pump’s cover, or the balance pipes can even lead to serious accidents like fires and explosions.
The main reason is to reduce the temperature difference between the pump body and the medium, thereby facilitating the startup of the pump and preventing damage to it due to an excessive temperature difference. Generally, the pre-heating valve at the outlet of the standby pump is slightly opened.
If a hot oil pump is started without preheating, the hot oil will quickly enter the cold pump body, causing uneven heating of the pump. The upper part of the pump expands more due to heat while the lower part expands less, which can lead to the shaft bending or cause the sealing rings on the pump body and the rotor to get stuck； Forcing it to start can cause wear, shaft binding, and shaft breakage.
Different parts of the pump are made of different materials, which results in varying degrees of thermal deformation; preheating to the designed operating temperature helps to prevent deformation and leakage
If the cold oil or condensate inside the pump is not preheated before it mixes with hot oil at temperatures of 200–350°C, vaporization will occur, leading to the pump becoming evacuated. When hot oil enters the pump body, uneven heating of different parts of the pump leads to uneven expansion, resulting in leaks and cracks. It can also cause the shaft arch waist phenomenon, leading to vibrations. The medium transported by hot oil pumps has a high viscosity; it has poor flow properties at normal and low temperatures, and may even solidify, which prevents the pump from starting or results in a prolonged startup time that leads to tripping.