Refining Community Logo

Emergency Procedure

Home Forums Coking Technical Heaters & Furnaces Emergency Procedure

This topic contains 6 replies, has 2 voices, and was last updated by  Mike Kimbrell 2 years, 6 months ago.

  • Author
    Posts
  • #28845

    Hedewandro Lucredi
    Participant

    What would be the emergency procedure related mainly with the heaters and drums in case of utilities shutdown or even in case of simultaneously utilities shutdown ? In case of steam shutdown what would be the procedure ? In our case once we inject fire water in the drums, but in the case of the heaters, we had inject condensate water because we have in the heaters. But if we do not have ? What can we do ? Or even in the case of utilities shutdown simultaneously like; steam, instrument air and so on ? What can we do ?

  • #28848

    Mike Kimbrell
    Participant

    The problem of both an electrical power failure coupled with a steam system failure is a very difficult emergency to address. The steam system will decrease in pressure over time. If possible, the remaining steam should be used to purge hydrocarbons from the heater coils. At the emergency steam rate only two minutes are needed to purge enough hydrocarbons from the heater to prevent plugging the coil completely. You will likely not have enough steam to steam out the coke drums, so there will be unconverted oil in the drum that will drain backwards into the heater transfer line and back into the heater coils if the switch valve stays lined up to the drum that was coking. Move the switch valve to the bypass position to prevent the unconverted oil from draining back into the heater as it will coke off the heater coils completely if that occurs.

    When power or steam or both are restored, you will need to try to steam out the coke drum. It is possible that the feed line is plugged off and you will need to add water to the top of the coke drum to quench the drum. If you can get steam or water or both into the coke drum by the normal methods, that is best. You can try to use electric resistance coils to heat up the feed line and the inlet area of the coke drum in an attempt to get steam and water back into the drum. If not, use top water to quench the coke bed. Monitor the water level as the energy stored in the coke will boil the water off and the level will decrease.

    Once the coke bed is quench with water as well as can be done, then attempt to drain the drum. Again, if the feed line is plugged, you may have to try to open the bottom head to drain the water. Depending on the type of bottom head this can be extremely dangerous. An exclusion zone should be set up around the coke pit and the bottom deck of the Coker to ensure personnel are not anywhere near the bottom head when attempting this task. P66 gave a good presentation on this very issue in the 2016 Galveston Coking.com meeting. There are lots of details that have to be considered and opening the drum should not be done without a thorough Management of Change process and the use of personnel external to the site to ensure all potential hazards are considered.

    The fractionator and the blowdown system should be pumped out as soon as it is possible. During the initial shutdown, the distillates should be routed to the bottom of the fractionator to dilute and thin out the liquid in the bottom of the tower. The feed line will need to be purged as well. Again, electric resistance coils may be necessary to unplug the lines.

    As I stated, this is a very difficult and potentially dangerous emergency so extreme care needs to be exercised if you are in this condition.

  • #28858

    Hedewandro Lucredi
    Participant

    Mr Kimbrell. Thanks for the answer. You help me a lot.

  • #28909

    Hedewandro Lucredi
    Participant

    Another related question. If we do not have utilities (steam, electric, instrument air), but we have FLO (Flushing oil) from a off site pump. Can we use FLO to inject in the heaters after the shutdown ? Are there any problem related with flange leaking, heater coking and so on ? We have in our heaters a smal pipe (1 1/2 in) that inject FLO in the furnace header. We can inject in each heater pass because I think the flowrate is not enough for the overall heater pass, or is better to inject in all pass equaly. The FLO temperature is +/- 30 Celsius.

  • #28913

    Mike Kimbrell
    Participant

    Yes, in a situation where you have lost power and steam having a source of flushing oil to purge the heater so that the coils do not coke off completely would be an advantage. It seems like the flow rate is low, so purging each coil individually makes sense. Purging the line long enough to ensure that the transfer line up to the switch valve remains clear would also be beneficial.

    Purging the heater with a light flushing oil from off-site will result in the level in the fractionator increasing. Getting light oil in the fractionator could be helpful to thin out the oil in the fractionator which will facilitate pumping the tower out once you get some of your utilities back. It would be good to use a local pressure gauge to measure the suction pressure on the heater feed pumps as a method to monitor the liquid level in the fractionator. This pressure should be monitored regularly while the flushing oil is being used to clear the heater and the transfer line.

  • #28915

    Hedewandro Lucredi
    Participant

    If I inject the FLO (flushing oil) that is cold immediately after the heater shutdown and the heaters are still hot is there any risk of leaking in some flange, mule ears, etc because the temperature ?

  • #28918

    Mike Kimbrell
    Participant

    Yes, anytime a bolted or threaded joint is thermally cycled there is a potential for leakage. The heater is normally on-line spalled so that significant thermal cycles are already experienced in this equipment without leaking, typically. The emergency steam that should purge the heater coil is colder than the process temperature and will cause a thermal cycle that the heater experiences without incident, typically. It is true that the heat capacity of steam is much lower than the flushing oil so the potential of a large thermal cycle exists. You indicated that the flow rate of this flushing oil is low, which helps in limiting the magnitude of the thermal cycle.

    The alternative to not purging the heater in your example is for the heater to coke up completely. The return bends will have to be cut off so the heater can be hydroblasted to clear the heater coil. The transfer line from the heater to the coke drums is also at risk of significant coking if there is no purge of the heavy hydrocarbons in that piping. My preference in this case is to purge slowly with the cold flushing oil.

You must be logged in to reply to this topic.

Refining Community