Help: Causes of coking in catalytic oil and gas pipelines

General view: One aspect is the velocity of oil and gas flow; in the past, it was only around ten meters per second, but nowadays it is generally above thirty meters per second； Additionally, external insulation for large oil and gas pipelines is also important; otherwise, high-boiling-point substances tend to condense on the pipe walls, leading to coking. Some also believe that introducing a quenching medium at the upper part of the riser helps to prevent coking.

The problem of coking in oil and gas pipelines has a long history, and the generally accepted solution is to improve insulation to reduce oil and gas condensation, increase pipeline flow rates to shorten residence time, and thereby make it more difficult for coke deposits to form. Generally, with the external insulation design for hot-wall systems, it is difficult to meet the design requirements during construction, resulting in numerous local cold spots. In contrast, the lining of cold-wall oil and gas pipelines can be made more uniform, providing better insulation effects. The use of insulating coatings on the flanges at the inlet of distillation towers also helps to reduce heat loss. However, with a double-layer lining of turtle shell mesh, since the insulation nails are connected to one end to the pipe wall and to the other end to the turtle shell mesh, local cold spots may still occur, leading to the condensation of oil and gas. Theoretically, a single-layer lining should provide better insulation with virtually no local cold spots. However, the strength of single-layer linings is currently somewhat low, which makes it easy for the lining to be damaged during the removal of coke layers. Therefore, there is still much work to be done in terms of lining design. Increasing the line speed will lead to an increase in system pressure drop, which needs to be considered carefully. It is generally recommended to keep the speed at no more than 35 meters per second, and a layer of coking material formed inside the oil and gas pipelines provides better insulation effects. Furthermore, in terms of the layout and route of the reaction oil and gas pipelines, detailed calculations should also be carried out to minimize the residence time of oil and gas.

Additionally, the properties of the raw materials need to be considered, such as the blending ratio； Catalyst type, catalyst conversion capacity, fine powder loss, centrifuge efficiency; selection of reaction temperature ； Selection of reaction time ； Nozzle atomization efficiency, etc.

Guidelines for Preventing Coking in Catalytic Cracking Units (Trial) China National Petroleum Corporation Chapter 1 General Provisions 1.1 Purpose To reduce unplanned shutdowns of catalytic cracking units caused by coking, the company has prepared these \"Guidelines for Preventing Coking in Catalytic Cracking Units\" (hereinafter referred to as the \"Guidelines\”), with the aim of providing guidance for design, production, and technical management departments during the renovation and operation of catalytic cracking units in the future. Chapter 3: Measures to Prevent Coking in Catalytic Cracking Units 3.1 Raw Material Management 3.2 Catalysts 3.3 Engineering Design 3.3.11 The reaction oil and gas pipelines shall be designed as cold-wall type, with a temperature drop of no more than 5°C. 3.3.12 It is recommended that the gas flow velocity for large oil and gas pipelines be 35–45 m/s. 3.3.13 The horizontal section at the inlet of the distillation tower should have an appropriate slope to allow the condensed liquid to flow automatically into the tower. 3.3.14 For large oil and gas pipelines, the number of elbows should be minimized, their length should be kept as short as possible, and the pressure drop should be as low as possible (not exceeding 15 KPa). 3.3.15 For large oil and gas pipelines, elbows with a large radius of curvature are used at the reactor outlet, while elbows with a small radius of curvature are used at the distillation tower inlet (determined by the design team based on calculations of thermal stress and pressure drop), ensuring that the distance between the elbow and the distillation tower inlet is as short as possible. 3.4 Operating Conditions 3.5 Maintenance Work 3.5.2 Enhance the insulation of the large oil and gas pipelines; after maintenance, promptly insulate the exposed areas at the oil and gas inlets of the distillation tower as well as the manholes used for coking removal, ensuring that the temperature drop in these large oil and gas pipelines does not exceed 5°C. 3.5.5 The **lanes before the oil and gas enter the distillation tower should be equipped with rain protection facilities. 3.6 Production Operations 3.6.1 Ensure the stable operation of the unit, minimize the number of times reaction feed is interrupted and catalyst fluidization is halted, and avoid significant fluctuations in the temperature of the settler. 3.7 Equipment Operation

There are many reasons for coking in oil and gas pipelines, and the mechanisms of coking vary as well. An important reason is that our raw materials have become heavier in quality.

It would be great to have a machine or device that can quickly remove the blind flange; when coking occurs, it’s very difficult to remove the blind ring.