【Q&A Question 100】April 10, 2017

1. Insufficient amount of new hydrogen, resulting in a decrease in system pressure； 2. Low reaction depth, high hydrogen purity ； 3. The reverse flight motion line has an excessive opening degree ； 4. Excessive amount of cold hydrogen used.

1. Issues related to the cycle hydrogen compressor itself, such as faults in the gas flow control system, or fluctuations in the flow rate of the cycle hydrogen compressor caused by variations in steam pressure in the drive machinery, particularly the turbine； 2. A sudden drop in the amount of fresh hydrogen supplied; an accident occurring in the hydrogen supply unit or the fresh hydrogen generator leads to a reduction in the flow rate of fresh hydrogen, or there is a failure in the fresh hydrogen return valve ； 3. Failure of the cold hydrogen control valve caused a large amount of hydrogen to flow directly into the reactor bypassing the flow meter ； 4. The operation of the circulating hydrogen desulfurization system experiences significant fluctuations, resulting in variations in flow rate ； 5. There are areas where high voltage leaks into low voltage ； 6. The internal leakage of the emergency pressure relief valve is significant, resulting in a drop in system pressure and a decrease in the flow rate of circulating hydrogen. 7. Fault in the flow monitoring instrument

If the feed rate and hydrogen purity remain unchanged, and only the amount of recycled hydrogen changes, this actually results in a change in the hydrogen-to-oil ratio; the volume ratio of hydrogen to oil at the reactor inlet can be controlled by adjusting the flow rate of the recycled hydrogen. Generally, a higher hydrogen-to-oil ratio needs to be maintained. Using a higher hydrogen-to-oil ratio has the following advantages: 1 it enables the operating temperature of the reactor bed to remain stable. A large amount of circulating gas can promptly remove the heat of reaction from the system, allowing the reactor temperature to be easily maintained at a stable level. 2 can maintain an adequate hydrogen partial pressure in the system, facilitating the hydrogenation reaction. 3 A lower hydrogen-to-oil ratio can reduce the reaction hydrogen partial pressure. When the pressure is insufficient, thermodynamic equilibrium often plays a role, causing the polycyclic aromatic hydrocarbons in the feedstock to undergo a certain degree of condensation reaction. This leads to carbon deposition on the surface of the catalyst, resulting in its deactivation and a reduced service life. Excess hydrogen can act as a protective layer for the catalyst surface, preventing the oil from condensing and coking on its surface within a certain range. However, increasing the hydrogen volume also brings a series of disadvantages: thicker high-pressure pipelines, increased energy consumption, and greater system pressure drop. An increased hydrogen volume further shortens the contact time between the oil product and the catalyst, resulting in a decrease in the degree of reaction. Factors affecting the hydrogen-to-oil ratio: feed oil volume, fresh hydrogen volume and recycled hydrogen volume, hydrogen purity.

Insufficient new hydrogen supply, too many impurities, high discharge volume

1. Issues related to the circulating hydrogen compressor itself; 2. Check the hydrogen production system to see its operating condition； 3. Check the process system to see if there are any leaks ； 4. Check the flow monitoring instrument.

Answer: The main reasons for the decrease in the amount of recycled hydrogen, based on personal analysis, are as follows: 1. Issues with the recycled hydrogen compressor itself, such as faults in the gas flow control system, or fluctuations in the flow rate of the recycled hydrogen compressor caused by variations in steam pressure in the drive machinery, particularly the turbine； 2. A sudden drop in the amount of fresh hydrogen supplied; an accident occurring in the hydrogen supply unit or the fresh hydrogen generator leads to a reduction in the flow rate of fresh hydrogen, or there is a failure in the fresh hydrogen return valve ； 3. Failure of the cold hydrogen control valve caused a large amount of hydrogen to flow directly into the reactor bypassing the flow meter ； 4. The operation of the circulating hydrogen desulfurization system experiences significant fluctuations, resulting in variations in flow rate ； 5. There are areas where high voltage leaks into low voltage ； 6. The internal leakage of the emergency pressure relief valve is significant, resulting in a drop in system pressure and a decrease in the flow rate of circulating hydrogen. 7. Fault in the flow monitoring instrument

1. Issues related to the cycle hydrogen compressor itself. 2. A sudden decrease in the amount of fresh hydrogen supplied; an accident in the hydrogen supply unit or the fresh hydrogen generator leads to a reduction in the flow rate of fresh hydrogen, or there is a malfunction in the fresh hydrogen return valve

1. Issues related to the cycle hydrogen compressor itself, such as faults in the gas flow control system, or fluctuations in the flow rate of the cycle hydrogen compressor caused by variations in steam pressure in the drive machinery, particularly the turbine； 2. A sudden drop in the amount of fresh hydrogen supplied; an accident occurring in the hydrogen supply unit or the fresh hydrogen generator leads to a reduction in the flow rate of fresh hydrogen, or there is a failure in the fresh hydrogen return valve ； 3. Failure of the cold hydrogen control valve caused a large amount of hydrogen to flow directly into the reactor bypassing the flow meter ； 4. The operation of the circulating hydrogen desulfurization system experiences significant fluctuations, resulting in variations in flow rate ； 5. There are areas where high voltage leaks into low voltage ； 6. The internal leakage of the emergency pressure relief valve is significant, resulting in a drop in system pressure and a decrease in the flow rate of circulating hydrogen. 7. Fault in the flow monitoring instrument

1. Issues related to the cycle hydrogen compressor itself, such as faults in the gas flow control system, or fluctuations in the flow rate of the cycle hydrogen compressor caused by variations in steam pressure in the drive machinery, particularly the turbine； 2. A sudden drop in the amount of fresh hydrogen supplied; an accident occurring in the hydrogen supply unit or the fresh hydrogen generator leads to a reduction in the flow rate of fresh hydrogen, or there is a failure in the fresh hydrogen return valve ； 3. Failure of the cold hydrogen control valve caused a large amount of hydrogen to flow directly into the reactor bypassing the flow meter ； 4. The operation of the circulating hydrogen desulfurization system experiences significant fluctuations, resulting in variations in flow rate ； 5. There are areas where high voltage leaks into low voltage ； 6. The internal leakage of the emergency pressure relief valve is significant, resulting in a drop in system pressure and a decrease in the flow rate of circulating hydrogen. 7. Fault in the flow monitoring instrument

If the feed rate and hydrogen purity remain unchanged, and only the amount of recycled hydrogen changes, this actually results in a change in the hydrogen-to-oil ratio; the volume ratio of hydrogen to oil at the reactor inlet can be controlled by adjusting the flow rate of the recycled hydrogen. Generally, a higher hydrogen-to-oil ratio needs to be maintained. Using a higher hydrogen-to-oil ratio has the following advantages: 1 it enables the operating temperature of the reactor bed to remain stable. A large amount of circulating gas can promptly remove the heat of reaction from the system, allowing the reactor temperature to be easily maintained at a stable level. 2 can maintain an adequate hydrogen partial pressure in the system, facilitating the hydrogenation reaction. 3 A lower hydrogen-to-oil ratio can reduce the reaction hydrogen partial pressure. When the pressure is insufficient, thermodynamic equilibrium often plays a role, causing the polycyclic aromatic hydrocarbons in the feedstock to undergo a certain degree of condensation reaction. This leads to carbon deposition on the surface of the catalyst, resulting in its deactivation and a reduced service life. Excess hydrogen can act as a protective layer for the catalyst surface, preventing the oil from condensing and coking on its surface within a certain range. However, increasing the hydrogen volume also brings a series of disadvantages: thicker high-pressure pipelines, increased energy consumption, and greater system pressure drop. An increased hydrogen volume further shortens the contact time between the oil product and the catalyst, resulting in a decrease in the degree of reaction. Factors affecting the hydrogen-to-oil ratio: feed oil volume, fresh hydrogen volume and recycled hydrogen volume, hydrogen purity.