【Q&A Question 275】2017.10.03

Answer: Catalyst carbon deposition is mainly caused by fluctuations in operating conditions and changes in raw materials. In particular, an imbalance in the water-to-carbon ratio can easily lead to carbon deposition, which may also result from long-term accumulation under harsh operating conditions. The main manifestations are mottling and red tubes on the furnace tubes. In most cases, these phenomena are not widespread, but occur in certain areas of the furnace chamber or on specific furnace tubes. The second main characteristic of catalyst fouling is the increase in pressure drop across the catalyst bed. When minor carbon deposition on the catalyst causes mottling in a few furnace tubes, the deactivation of the catalyst is not very noticeable. Methods for dealing with carbon deposits generally include stopping the feed of hydrocarbons, steam detoxification, and carbon burning. That is, it is operated under pure steam at the specified operating temperature for several hours or even days, in order to achieve detoxification and carbonization. Measures to prevent catalyst carbon deposition include preventing fluctuations in process parameters such as the water-to-carbon ratio, space velocity, pressure, and temperature ； Maintain stability in the feed composition, strictly prevent mixing of light oil feedstock with other oils, and ensure that the storage, transportation, and delivery systems for light oil feedstock are dedicated. Strictly follow the operating procedures for the converter in the event of an emergency shutdown caused by a sudden power outage or equipment failure.

Reason: 1. Imbalance in the water-carbon ratio. 2. Fluctuations in raw material composition or quantity. Phenomenon: 1. The bed pressure drop increases. 2. Catalyst deactivation. Treatment method: 1. Stop feeding. 2. Steam detoxification. 3. Burning charcoal.

Reasons: 1) The actual water-to-carbon ratio is too low, leading to thermodynamic coking. 2) The catalyst is not evenly packed or has been crushed. 3) The new catalyst is fed into the system before it has been fully reduced, resulting in low catalyst activity. 4) The conversion catalyst has poor resistance to coking, and there is significant loss of potassium. 5) The catalyst has become severely deactivated or poisoned by sulfur. 6) The amount of hydrogen supplied is too low or fluctuates excessively. 7) The operating temperature or pressure fluctuates greatly or exceeds the specified limits.
Symptoms: 1) An increase in the pressure difference at the inlet and outlet of the furnace tubes. 2) An increase in the surface temperature of the furnace tubes, resulting in hot spots or mottling. 3) An increase in the methane content at the output of the conversion unit. 4) The furnace temperature remains normal, but the temperature at the outlet of the conversion tubes is high.
Solutions: 1) Reduce the load, increase the amount of hydrogen supplied and the water-to-carbon ratio, so that the conversion catalyst can operate under reduced conditions for several hours. 2) Identify the root cause of coking in the catalyst and take targeted measures. 3) Reduce the load at the PSA unit as well; stop hydrogen supply if necessary

A. Too low water-to-carbon ratio or sudden interruption of steam. B. Sudden changes in the properties of the raw materials, with operations failing to keep up in a timely manner. C. Catalyst poisoning D. Introduction of feed gas before startup steam supply, resulting in catalyst carbon deposition. Treatment method: A. If carbon deposition is not severe or only mild, the flow rate of the feed gas can be reduced, while the flow rate of water vapor should be increased to raise the water-to-carbon ratio; this facilitates the gasification reaction between water vapor and carbon, thereby removing the carbon. B. When carbon deposition is severe, that is, when the furnace tubes turn red or bright red, the feed gas should be stopped and steam should be introduced to remove the carbon. During this time, the operating temperature must be maintained. Once the color of the furnace tubes returns to normal, the feed gas can be resumed and normal production can proceed

Phenomena and Solutions 1) The actual water-carbon ratio is too low, resulting in thermodynamic coking. 2) The catalyst is not evenly packed or has been crushed. 3) New catalyst is fed without sufficient reduction, leading to low catalyst activity. 4) The conversion catalyst has poor coking resistance and suffers from severe potassium loss. 5) The catalyst has been severely deactivated or poisoned by sulfur. 6) The hydrogen supply amount is too low or fluctuates. 7) The operating temperature or pressure fluctuates significantly or exceeds the specified limits. 1) An increase in the pressure difference at the inlet and outlet of the furnace tubes. 2) An increase in the surface temperature of the furnace tubes, resulting in hot spots or mottling. 3) An increase in the methane content at the exit of the conversion unit. 4) The furnace temperature is normal, but the temperature at the exit of the conversion tubes is high. 1) Reduce the load, increase the hydrogen supply amount and water-carbon ratio appropriately, and operate the conversion catalyst under reduced conditions for several hours. 2) Identify the root cause of catalyst coking and take targeted measures. 3) Reduce the load at the PSA unit as well; stop hydrogen supply if necessary

Reasons: 1) The actual water-to-carbon ratio is too low, leading to thermodynamic coking. 2) The catalyst is not evenly packed or has been crushed. 3) The new catalyst is fed into the system before it has been fully reduced, resulting in low catalyst activity. 4) The conversion catalyst has poor resistance to coking, and there is significant loss of potassium. 5) The catalyst has become severely deactivated or poisoned by sulfur. 6) The amount of hydrogen supplied is too low or fluctuates excessively. 7) The operating temperature or pressure fluctuates greatly or exceeds the specified limits.
Symptoms: 1) An increase in the pressure difference at the inlet and outlet of the furnace tubes. 2) An increase in the surface temperature of the furnace tubes, resulting in hot spots or mottling. 3) An increase in the methane content at the output of the conversion unit. 4) The furnace temperature remains normal, but the temperature at the outlet of the conversion tubes is high.
Solutions: 1) Reduce the load, increase the amount of hydrogen supplied and the water-to-carbon ratio, so that the conversion catalyst can operate under reduced conditions for several hours. 2) Identify the root cause of coking in the catalyst and take targeted measures. 3) Reduce the load at the PSA unit as well; stop hydrogen supply if necessary

Treatment for mild coking of conversion catalyst: Causes, Symptoms, and Solutions 1) The actual water-to-carbon ratio is too low, leading to thermodynamic coking. 2) The catalyst is not evenly packed or has been crushed. 3) New catalysts are fed into the system without being fully reduced, resulting in low catalyst activity. 4) The conversion catalyst has poor resistance to coking, with severe potassium loss. 5) The catalyst has become severely deactivated or poisoned by sulfur. 6) The hydrogen supply is insufficient or unstable. 7) Significant fluctuations or excess levels in operating temperature or pressure. 1) An increase in pressure difference at the inlet and outlet of the furnace tubes. 2) An increase in the surface temperature of the furnace tubes, leading to the formation of hot spots or mottling. 3) An increase in methane content at the exit of the conversion unit. 4) The furnace temperature remains normal, but the temperature at the exit of the conversion tubes is high. 1) Reduce the load, increase the hydrogen supply and water-to-carbon ratio appropriately, and allow the conversion catalyst to operate under reduced conditions for several hours. 2) Identify the root cause of coking in the catalyst and take targeted measures. 3) Reduce the load at the PSA unit as well; stop hydrogen supply if necessary

1) The fresh catalyst is fed in without being fully reduced. (2) An excessively low water-to-carbon ratio leads to thermodynamic carbon deposition. (3) The catalyst has been severely deactivated, or its activity has decreased due to poisoning. (4) Severe potassium loss in the upper catalyst section. (5) Large fluctuations in operation.

Reasons: 1) The actual water-to-carbon ratio is too low, leading to thermodynamic coking. 2) The catalyst is not evenly packed or has been crushed. 3) The new catalyst is fed into the system before it has been fully reduced, resulting in low catalyst activity. 4) The conversion catalyst has poor resistance to coking, and there is significant loss of potassium. 5) The catalyst has become severely deactivated or poisoned by sulfur. 6) The amount of hydrogen supplied is too low or fluctuates excessively. 7) The operating temperature or pressure fluctuates greatly or exceeds the specified limits.
Symptoms: 1) An increase in the pressure difference at the inlet and outlet of the furnace tubes. 2) An increase in the surface temperature of the furnace tubes, resulting in hot spots or mottling. 3) An increase in the methane content at the output of the conversion unit. 4) The furnace temperature remains normal, but the temperature at the outlet of the conversion tubes is high.
Solutions: 1) Reduce the load, increase the amount of hydrogen supplied and the water-to-carbon ratio, so that the conversion catalyst can operate under reduced conditions for several hours. 2) Identify the root cause of coking in the catalyst and take targeted measures. 3) Reduce the load at the PSA unit as well; stop hydrogen supply if necessary

The most obvious sign of catalyst coking is the formation of knots in the converter tubes, along with localized hot spots. The pressure difference in the converter tubes increases. The hydrocarbon conversion rate decreases.