Seeking solutions to coking at the outlet end of large oil and gas pipelines

1. Water in the anti-coking steam at the top of the tower can cause coking; it is necessary to ensure the quality of the superheated steam. 2. If the residence time of oil and gas is too long, and if there is a large temperature difference between the steam at the top of the tower and the oil temperature in the distillation tower, it is likely due to problems with the oil and gas pipelines; otherwise, it is probably related to the design or operation of the distillation tower.

Generally, this section is a horizontal pipe, and expansion joints should be present; desulfurization steam is supplied at these two expansion joints, which yields good results

First, minimize the length of the oil and gas lines to the distillation tower. Second, ensure proper insulation of the oil and gas lines (hot walls and cold walls). Thirdly, the elbows on the oil and gas lines are mostly 90-degree right-angled elbows, which can be replaced with 45-degree elbows to reduce the residence time of oil and gas. Fourth, a superheated steam line is added at the large blind flange on the oil and gas line of the fractionation tower as anti-coking steam.

1. Nowadays, most are hot-wall types, so heat insulation is very important； 2. If the line speed is low or the pipe diameter is too large, the amount of steam can be increased appropriately to raise the line speed ； 3. It is also feasible to add anti-coking steam at the large blind flange.

　　In my opinion, first, due to the combined effect of oil and gas pipelines and large-scale valves, the linear velocity of the oil and gas is high in the middle section while it is low near the pipe walls； Secondly, due to the temperature drop at the outlet, the heavy components in the oil and gas condense and adhere to the wall, resulting in a laminar flow phenomenon. 　　The reaction oil and gas contain large amounts of olefins and dienes; through aromatization reactions, large-molecule polycyclic aromatic hydrocarbons are formed, which are then polymerized, dehydrogenated, and condensed to produce coke. At the same time, the heavier components in oil and gas condense and easily adhere to the pipe wall surface to form \"coke nuclei,\" which gradually grow and carbonize to form coke. 　　

If it is in operation, a sledgehammer can be used to gently tap the junction part of the distillation tower, causing the coked masses to fall into the tower; this method is very effective and yields quick results. But do not use too much force to prevent damaging the equipment. You can give it a try. We’ve been doing this all along, knocking once every couple of weeks.

I haven’t heard that device doesn’t suffer from coking in that area! As the oil and gas emerge from the pipelines and enter the distillation tower, their partial pressure drops rapidly; the heavier components precipitate out. Additionally, the liquid phase flowing down along the tower walls is much colder than the oil and gas, causing them to cool down quickly – which inevitably leads to coking! It’s solely based on the processing load of the device – that is, the issue of the length of coking time here! We have carried out modifications here by adding annular tubes around the oil and gas pipelines, inserting them into the pipelines at a 45-degree angle (toward the distillation tower) – just 4 short tubes are sufficient – and injecting steam to increase the flow rate in this area! During the shutdown for inspection, coking did occur, but it was significantly reduced, so there was no need to force repeated reductions in production volume! Of course, heat retention is also very important! Hitting with a sledgehammer is also an emergency solution, but be careful! In short, it’s still crucial to control the line speed properly and enhance insulation here!

Increase the steam usage; both stripping steam and anti-coking steam can be increased, which is very beneficial for preventing coking.