Some issues regarding the heating furnace in delayed coking units
Thread Content
The unit has been in operation for over a month now, and there have been some issues with the furnace. I would like to ask for your advice: 1. The flame is light blue and combustion is thorough, but several nozzles located near the main air ducts (that is, at the beginning of each branch duct) keep going out on their own. Increasing the air intake valve of the burner helps to alleviate this problem. What approach should be followed for adjustment? 2. The feed from one line has indicated coking in the furnace tube, and the pressure at that branch is very close to the outlet pressure of the radial feed pump. Is it possible that the coking in this furnace tube is quite severe? Does that mean there’s no passage in the middle? What should be done after shutting down operations in such a situation? Is high-pressure water jet cleaning suitable for removing coke?
In my opinion: 1. It seems that your stove is experiencing some backfire; you might consider increasing the valves controlling the gas and air supply slightly to ensure sufficient pressure, while also regulating the combustion process to prevent backfire. 2. Observe on-site whether the color of the furnace tube is normal; at the same time, check whether there are any significant changes in the temperature of this branch compared to the flow rates and temperatures of the other branches. If everything is normal, it is necessary to verify whether the pressure gauge is malfunctioning. If coking is detected, the furnace must be shut down to burn off the coke, and prompt action must be taken.
1. Check whether the pressure behind the gas pressure control valve is around 0.1 MP – is this normal? Verify whether the air duct pressure is normal and there is no significant pressure imbalance, and ensure that the negative pressure distribution within the furnace is even; check if all burners in the same area exhibit the same conditions. Clean the burners or replace them, then observe the combustion status and the color of the flame after opening the air valves, in order to assess the condition of the burner flames and take appropriate action. 2. It is possible to make a comprehensive assessment of whether the system is functioning properly by considering factors such as branch flow rates, the flow rates of water or steam injected into the branches, pressures at various points along the branches, gas volume in the branches, temperature distribution within the furnace, the color of the furnace tubes, and tube wall temperatures. If the pressure at the radiation inlet is roughly equal to the pump pressure, it’s likely that the system is not functioning properly. 3. For treatment, try first using 3.5MP steam injection at multiple points for purging, in both forward and reverse directions; if that doesn’t work, high-pressure water can be used to remove coke, but this requires cutting the furnace tubes, which is troublesome. It’s better if there is a elbow box available.
The burner dampers can be appropriately adjusted using mechanical coke cleaning
During shutdown, coking can be removed by burning or mechanical methods; using high-pressure water for this purpose is not appropriate. Can’t you just cut the pipes to remove the coke? I just finished mechanical coking of a set of coking units here, and the results were quite good
With the same opening degree of the air duct dampers, the pressure at the beginning of the air duct is at its lowest! The wind pressure is highest at the end, and it increases gradually from the beginning to the end. The opening degree of the air duct doors can be gradually reduced from the beginning to the end to ensure uniform wind pressure!
I strongly disagree with the person above. I suggest gradually increasing the opening of the air valves from the start to the end of the system. I agree with the second-floor suggestion; it’s possible that the gas valve is opened too wide, resulting in a loss of combustion. Check the burner nozzles – swapping the central burner with those at the beginning of the system can help rule out nozzle blockages
Reply to 1# Refinery Operator: Answering your second question: 1. It’s impossible for the furnace tubes to be strong; if they were, the wall temperature of the furnace would rise sharply. 2. Mechanical coking is possible; generally, the smallest balls are around 50 in size. They enter through the convection inlet and exit through the radiation outlet, which makes it quite simple.
If coking is confirmed, online coking removal can be employed.
1. There is a high likelihood of an issue with the air duct structure; it seems that the burner’s branch air duct is connected at a right angle to the main air duct, which results in the highest air flow velocity and thus insufficient air supply to the burner.
During adjustment, the burner dampers at the back can be reduced while those at the front can be increased; this will only help to improve the situation. It is best to make some modifications to the air duct structure during the maintenance period.