Analysis of the causes of excessive non-condensable gas in the stabilization system of the delayed coking unit and optimization plan for on-site disposal

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In the production and operation system of the delayed coking unit, the stabilization system assumes the core functions of distillation separation of liquefied gas and stable gasoline and product quality control, and the stabilization tower is the key equipment to maintain the separation efficiency of the system. The non-condensable gas at the top of the tower is mostly composed of C₂ light components. The precise control of its emissions directly determines the liquefied gas product yield and the overall energy consumption of the device. It is also an important link to ensure stable system pressure and eliminate safety risks. In actual production, an increase in the instantaneous release of non-condensable gas is a frequent process abnormality. If the on-site treatment is not timely and the operation logic is unreasonable, it will not only cause the escape loss of light hydrocarbon components and increase processing costs, but also cause production hazards such as violent fluctuations in tower top pressure, pressure suppression in the condensation system, and tripping of safety accessories, which directly affects the long-term smooth operation of the device. Combining the on-site practical experience of the coking unit and the principles of the distillation and separation process, we comprehensively sorted out the core causes of excess non-condensable gas, formulated a three-level practical plan for emergency rapid control, root cause rectification, and long-term management and control, optimized the operating process, and refined the key points of control to provide front-line operators with implementable, low-risk problem solutions, and effectively solve outstanding problems in production operations. 1. Core incentives: Three key factors influencing the excessive production of non-condensable gas. Non-condensable gas in the stabilizing tower is light hydrocarbons that cannot be liquefied and recovered after the gas phase at the top of the tower is processed by the condensation unit. The abnormal increase in production is not caused by a single equipment or parameter, but is the result of the synergistic imbalance of the condensation unit, desorption unit, and tower operation. The main incentives are concentrated in the following three aspects.: The heat exchange efficiency of the tower top condensation unit is insufficient. The tower top condenser is the core equipment for realizing the liquefaction recovery of light components. The heat exchange effect directly determines the scale of non-condensable gas generation. The temperature of the liquefied gas after cooling is the core indicator for judging the condensation capacity. When the temperature after cooling exceeds the process control range, the saturated vapor pressure of the light hydrocarbon component increases rapidly. The gas-liquid phase change cannot be completed under the current working conditions, and the uncondensed gas phase directly accumulates into non-condensable gas. The main reason for the decrease in condensation efficiency: In high temperature seasons, the ambient temperature rises and the cooling capacity of circulating water decreases. ； The effective heat exchange area is reduced due to scaling and material accumulation in the condenser tube bundle. ； The circulating water flow is low, the water supply temperature exceeds the standard, and the system bypass leaks ； The condenser equipment fails and problems such as gas phase short circuit and internal leakage occur. The separation accuracy of the desorption tower is not up to standard. The core function of the desorption tower is to remove the C₂ light components in the deethanized gasoline and prevent the light components from entering the stabilization tower and increasing the separation load. If the desorption unit operates abnormally and the C₂ component is not completely removed, it will directly enter the stabilizing tower with the feed, greatly increasing the concentration of light components at the top of the tower, exceeding the processing capacity of the condensation system, and ultimately causing the amount of non-condensable gas to exceed the standard. Factors causing poor desorption effect: The temperature control at the bottom of the tower is too low, the heat supply of the reboiler is insufficient, and the desorption of light components is insufficient. ； Failure of tower internal parts, clogging of trays, and reduced gas-liquid contact efficiency ； The absorption tower is over-operated, the amount of absorbent is too large, and the absorption temperature is too low, resulting in the enrichment of light components in deethanized gasoline. Stabilizer tower process operating parameters match unbalanced stabilization tower operating pressure and the condensation effect of light components are positively correlated. Properly increasing the tower pressure can increase the bubble point temperature of light hydrocarbons, strengthen the condensation effect, and reduce the generation of non-condensable gas. However, in actual production, parameter control is prone to coupling conflicts.: Simply increasing the tower pressure without synchronizing the heat load of the reboiler will lead to a decrease in the separation effect at the bottom of the tower, and the stable gasoline vapor pressure will exceed the standard. ； The heat source supply fluctuates, the flow rate is insufficient, and the heat load cannot meet the needs of distillation. ； Unreasonable control of the reflux ratio and feed volume further aggravates the imbalance of the gas phase components at the top of the tower and increases the emission of non-condensable gas. 2. Graded disposal: The full-process on-site operation plan for non-condensable gas exceeding the standard targets the core incentives for non-condensable gas exceeding the standard, and follows the operating principles of controlling risks first, then treating the root causes, and then optimizing operations. It implements precise control in stages to avoid blind operations causing large fluctuations in the system.: (1) Emergency response: Rapid pressure drop to reduce emissions and prevent system risks. The core goal of this stage is to quickly suppress the continued growth of non-condensable gas, stabilize tower top pressure, and prevent overpressure hazards. The three operations can be executed simultaneously.: Quickly restore condensation heat transfer capacity: Check the operating status of the condenser on-site. If there are scaling or clogging problems, immediately put the spare condenser into use or perform online flushing to quickly restore the heat exchange efficiency. ； Simultaneously optimize the circulating water system, open the water supply valve, increase the circulating water flow, stabilize the temperature of the liquefied gas after cooling within the design range, and curb the generation of non-condensable gas from the source. Gradient adjustment tower pressure control index: Under the premise of sufficient heat source supply, gradually increase the operating pressure of the stabilizing tower and control it within the range of 0.8~1.0MPa gauge pressure. It is strictly forbidden to exceed the upper limit of the equipment design. ； The pressure increase amplitude is controlled at 0.05MPa each time, and the gasoline vapor pressure is monitored and stabilized simultaneously to ensure that the product indicators are qualified, taking into account both pressure control and product quality. Standardize the control of non-condensable gas emissions: Through automatic control valve or manual operation, moderately increase the discharge rate of non-condensable gas to avoid excessive accumulation of gas phase at the top of the tower and reflux tank. ； The discharge process strictly controls the rate to prevent sudden pressure drops from triggering massive vaporization of liquefied gas and causing secondary process fluctuations. (2) Root cause management: Targeted rectification, eliminating the core factors that caused the abnormality, and after emergency control and stabilization, targeted solutions to system shortcomings will fundamentally solve the problem of non-condensable gas exceeding the standard.: Strengthen the separation effect of desorption tower: Based on the analysis data of deethanized gasoline components, the temperature at the bottom of the tower should be increased appropriately to ensure that the C₂ component is fully desorbed. ； Check the operating status of tower internal parts, find problems such as blockage and uneven distribution, and arrange maintenance in a timely manner ； Optimize the operation of the absorption tower, rationally adjust the amount of absorbent, increase the absorption temperature, and prevent excessive absorption from bringing light components into the stabilizing tower. Rectify condensation system hardware defects: In response to the problem of insufficient heat exchange capacity, carry out equipment technical transformation assessment, replace high-efficiency heat exchangers, and increase heat exchange area ； Establish a regular blockage cleaning and maintenance mechanism, and regularly carry out offline chemical cleaning to maintain long-term and efficient operation of the condenser. Stable heat source supply for reboiler: Coordinate to ensure stable heat source flow and meet the heat load requirements of the reboiler ； Relying on the device heat integration system, waste heat from the process is recovered to supplement heating. ； If the heat source continues to be insufficient, the processing load of the stabilizing tower can be moderately reduced to avoid deterioration of separation due to shortage of heat load. 3. Operation control: Key risk prevention and control points for on-site disposal: The pressure adjustment of the stabilizing tower must follow the gradient principle. Sudden rise and fall are strictly prohibited to prevent safety risks caused by overpressure in the tower or large amounts of light components vaporizing. ； When raising the bottom temperature of the desorption tower, strictly control the upper temperature limit to avoid excessive desorption causing loss of the C₃ component and reducing the liquefied gas yield. ； Condenser switching and cleaning operations strictly implement equipment isolation procedures and standardize operating procedures to prevent safety accidents caused by media cross-talk. ； If the non-condensable gas continues to exceed the standard, it is necessary to focus on checking the changes in the properties of the raw materials, and adjust the processing plan in a timely manner to adapt to the fluctuations in the raw material components. The control of non-condensable gas in the stabilizing tower is a comprehensive work covering the entire system of condensation, desorption, and distillation. It needs to take into account the coordination and unification of equipment status, process parameters, and operating specifications. Operators need to thoroughly understand the process principles, flexibly regulate the on-site working conditions, maintain the bottom line of safety in emergency response, eliminate operational hazards in root cause management, achieve cost reduction and increase efficiency in long-term optimization, and comprehensively ensure the safe, efficient and long-term operation of the stable system of the coking unit.