Consultation on potential hazards such as explosions and deformation associated with nitrogen sealing of VOCs containers in coking flue gas
Thread Content
VOCs exhaust gases are recovered under negative pressure through nitrogen sealing. The following issues were observed during operation: (1) Media such as tar and crude benzene in the tank can easily clog the breather valve, leading to its failure； (2) The pipes of the negative pressure system remain in a negative pressure state for an extended period, resulting in high gas consumption for nitrogen sealing ； (3) The nitrogen supply and discharge control valves have poor sensitivity, a long response time, and high nitrogen supply pressure ； If nitrogen is removed slowly, and the amount of nitrogen supplied exceeds the rate at which it is removed as well as the amount discharged by the vent valve, it can lead to overpressure in the tank and an explosion. (4) Similarly, if the medium in the tank is emptied in a short period of time, a slow opening of the nitrogen supply valve will create negative pressure inside the tank, causing it to be \"squashed\". Have any of you encountered this issue? How can it be resolved?
This post was last edited by sdwfsgyykai on 2020-4-30 at 14:57. (1) Media such as tar and crude benzene in the tank can easily clog the breather valve, leading to its failure； Personal advice: Replace the breathing valve with an appropriate one depending on the medium ； (2) The pipes of the negative pressure system remain in a negative pressure state for an extended period, resulting in high gas consumption for nitrogen sealing ； As a personal suggestion, based on what the original poster has described – since this is a system that allows passage in just one go – it is recommended to replenish an appropriate amount of the flue gas generated after oil and gas recovery, using it as nitrogen in order to maintain pressure balance within the recovery system ； (3) The nitrogen supply and discharge control valves have poor sensitivity, a long response time, and high nitrogen supply pressure ； If nitrogen is removed slowly, and the amount of nitrogen supplied exceeds the rate at which it is removed as well as the amount discharged by the vent valve, it can lead to overpressure in the tank and an explosion. (4) Similarly, if the medium in the tank is emptied in a short period of time, a slow opening of the nitrogen supply valve will create negative pressure inside the tank, causing it to be \"squashed\". Have any of you encountered this issue? How can it be resolved? Personally, regarding points 3 and 4, replacing the control system with a more sensitive one and installing safety valves to prevent overpressure or underpressure in the system will help maintain its stable operation, which is the best way to reduce costs
Notice on the Issuance of the \"Provisional Safety Technical Requirements for Oil and Gas Connection at the Tops of Storage and Transportation Tanks in Petrochemical Enterprises\"
Media such as tar tend to cause clogging, so the breathing valve should be of the insulated jacket type to prevent blockage and failure. If the nitrogen sealing system is not sensitive, it’s also possible that the control valve has stuck over time, resulting in an actual start-up pressure that is higher than the set pressure; this in turn leads to insufficient nitrogen supply or pressure relief. In this case, to recalculate the nitrogen seal, choose a nitrogen seal valve with a larger diameter and provide insulation for the entire pipeline system using jackets.
The use of a breather valve is not recommended; instead, a nitrogen seal combined with a safety water seal tank and a positive-pressure water seal tank is advised, with the tanks maintained at a slight positive pressure
I think the flattening is due to corrosion, which reduces the thickness of the material and lowers its mechanical strength; our 1041 material could be considered for anti-corrosion protection on the inner wall
If there is a slight positive pressure, won’t it be impossible to collect waste gas? This could lead to wastewater leakage
Are there any other control valves that are more sensitive?
Even the best valves will see a decrease in sensitivity over time due to the erosion by coal tar and benzene； The best approach is to clean it regularly or wash it online.