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Thanks for the information. Where is your coker located? capacity? age?
In regard to draining:
The first key point is to not expose personnel to the open top head during the initial stages of draining (coke beds can shift as the water drains past, exposing 800F coke to the water, resulting in an explosion of 180 – 200F water out the drum top). Automatic, remote top deheading can allow this operation during the early stage of draining.
The second key point is to insure that sufficient water has drained so that it is safe to remove the bottom head from the coke drum prior to removing the bottom head.
=> Leaving residual water in the coke drum (a short or inadequate drain) is the primary cause of coke fallouts during deheading.
Methods to insure a proper drain:
(1) Verify that a proper drain has occurred using three independent methods
+ Visually verify drain rate several times during drain
+ Verify level probes are dropping and the rate at which they are dropping (see Rick Enlow Calculation below)
+ Measure drain water recovery in tank and compare to expected amount for a “good” drain (this is only possible if water is not being drawn down for quench/cutting and if make-up water is not being added)
+ Verify drain time is normal
+ Add top water at end to visually verify water drains through the coke bed to exit point (“proof the drain”)
(2) Maintain good steam purge during switch to avoid leaving resid in feed line, which would then crystallize and restrict the path to the drain line.
(3) Avoid a high initial quench water rate when switching from steam to water. The high water rate can break coke, which then falls into the drain line and obstructs the drain. It is recommended to stay < 200 gpm at the start.
If drain was slow or abnormal in any way, the following procedures can be considered after reviewing and addressing all safety risk issues:
+ Blowback the drain line with a high rate of steam to possibly break-up or remove obstructions that may be acting like a check valve in the drain path (using this blowback method as part of the normal procedure is NOT recommended since it can pulverize the coke, causing it to partially collapse and worsen the drain)
+ Do a “Pressure Drain”, closing the top head and vent and carefully allowing pressurization of the top head to push the water with more force.
One of our sites blows the bottom utility header after warm-up to insure clear lines. In addition, if the drain is slow, they close the drain line blocks to the tank and maze and use a pressure gauge on the drain manifold to see how much water head there is. This pressure also reads out in the TDC for the console. The gauge is used to help verify that steam blowing worked to free the drain.
Another site has a TDC alarm that sounds if the time from start of drain until the water level drops below the highest level detector takes too long and also a TDC alarm that sounds if the time for the water level to drop between the highest and next highest level detectors (both above the normal coke outage level) is too long.
They also have a vacuum gauge on 1 coker to indicate if there is vent pluggage or closure, preventing excessive vacuum from damaging the coke drum.
Best regards – Mitch Moloney
29-jan-2011 Thanks for posted questions on bird cage inisulation. We are in the process of advancing a project with bird cage design and removable panels. Your concern on build up of hydrocarbon in the air gap between the coke drums and panels due to a leak is something we have not considered. The insulation panel system is not air tight, so gas will dissipate. However, it ultimately comes down to (A) the size of the leak and (B) the rate gas can escape. If A is greater than B, it will accumulate in the air gap, possibly creating an LEL risk. Mitigations that come to my mind are to provide a way (I have no exact idea at this point) for leaks to pass through the insulation system (tell tale vents), eliminating the risk; have a rigorous inspection program for the circ welds that allows cracks to be found and monitored (expensive solution). We are going to do further analysis of this risk and get back to the forum.
1-feb-2011 We have determined that the installation of “chimney stop” baffles (every 8 – 12 ft in elevation) within the bird cage will prevent the accumulation of hydrocarbon gas within the air gap volume. Leaks will then be detectable through seams in the insulation system. Ignition of leaks, and damage to the insulation, is always a possibility with all insulation systems, but we view this as a low, manageable risk. Prevention of large coke drum cracks and leaks requires an effective inspection/maintenance/repair strategy. Every owner/operator will need to make their own risk-based analysis of the scenario. Best regards – Mitch
It is common practice to use stripped sour water for coker water system make-up. Levels of H2S and NH3 in such water are typically below 10 wppm and 75 wppm respectively. Regular monitoring and controls are needed to ensure safe levels are maintained. Best regards
Marc – I recommend steaming the drum for at least 12 hours with big steam, then cool with water. Given 45 minutes of feed and a long steam out, you will only need about 15% of your normal water total (since feed that entered is likely less than 10% of normal total; coke yield will be high since coking temperatures are low for first 45 minutes). Concern will be a plugged drain after water cooling- hopefully the extended steaming will reduce or eliminate risk of uncoked resid plugging the inlet distributor or drain line. Worst case you would have to partially open the bottom head (using remote unheading techniques) to drain the water. Hopefully that will not be needed and you will drain via your normal line-up.
Of course, you should not unhead if you cannot get water into the coke drum. In that case you need to try to get steam in and then add water simultaneously. There may be water-hammer issues, but that is acceptable if it allows water to enter the drum. Another option is to add water via the top water line, assuming you have such a connection. Cooling can be validated by determining if steam is being generated as water enters from the top (a rise, even a modest one, in top oulet temperature should be apparent).
We have had success with this technique at our Beaumont and Chalmette-2 Cokers. Best regards – Mitch Moloney
November 1, 2010 at 4:18 pm in reply to: Chainless Bike Business Boooms @ US Refineries Application #5431
Very cool idea relative more relaible safer bicycles. I’m intrigued. One point of consideration is the human factor. Our refineries have had issues with people hurting themselves on bikes in the refinery because they did not have the physical skills to handle them, or were not attired properly, and were hurt in falls. As a result, many sites do not allow their use; others have changed policy back and forth over the years. In the latest policy at some sites, extensive training and qualification is required to become a “licensed and qualified” rider, IF you meet the usage need requirements (frequency, location, job type, etc).
Best regards – Mitch Moloney
Is the temperature real on that pass? Loose Thermocouple Connection?
I would strongly recommend not installing the radar gauge on the tank manway containing hot resid and in the presence of nitrogen. The risks are high due to the possiblity of resid ignition on loss of nitrogen flow or intrusion of air. In addition, the nitrogen poses a suffocation risk to workers.
A more prudent path would be to consider installing a gamma level detection device, which can be done without shutting down the feed surge tank or opening it while in service.
Best regards – Mitch Moloney
You stated that you have a 2-drum coker, F-W design. Cycle of 20 hours. Before the earthquake (27-feb-2010), one drum was in pressure test and the other was in 12 hour of run, prior to injection of antifoam. The unit hasn’t utilities (steam, electricity, etc), but this situation will change this week.
My response in Spanish, the English:
Hay que tener cuidado con el tambor de coque que alimentaba brea durante 12 horas. Las buenas noticias es que el tambor tiene un lecho bien formado. Las malas es que seguirn calientes porciones grandes del lecho de coque, aun despus de 25 das de sentarse radiando calor (el coque sirve de aislamiento el cual impide emisin de calor del lecho).
Fue posible desplazar los tubos de horno y la lnea de alimentacin con vapor de agua antes de apagar la unidad? Si no, tendr mucho trabajo adelante para sacar la brea coquificada / solidificada de esos equipos. Despojamiento con vapor y enfriamiento con agua se necesita antes de abrir las tapas del tambor de coque. Hay que enfocar esfuerzos en la introduccin de vapor y/o agua de suficiente presin (ojo los limites de bridas de tubera) a la lnea de alimentacin, para permitir enfriamiento del lecho por procedimientos normales. Podra requerir equipos y procedimientos especiales. Si no se puede abrir un camino de flujo despus de una semana de intentos, una segunda opcin es introducir agua de enfriamiento a la parte superior del lecho, vigilando la presin de tambor de coque, la temperatura de salida, la cantidad de agua aadida, y los indicadores de nivel el tambor de coque. Un riesgo es que el agua no penetra el lecho de coque. Paciencia y tiempo debera permitir que entre el agua al lecho. Se puede hacer clculos para determinar cuando una cantidad suficiente de calor hubiera sido extrado por el agua, dado que ustedes hayan verificado que el agua entra al lecho por un aumento de temperatura en la salida de tambor y el comportamiento de los indicadores de nivel.
Si han verificado enfriamiento adecuado del lecho de coque y que no es posible drenar el lecho a travs de la tubera y vlvulas normales, se puede bajar la tapa inferior asegurndose que no hay personas expuestas a riesgo de lesiones.
You should be concerned about the drum that was coking for 12 hours. Good news is that the drum has a well-formed coke bed. Bad news is that it will still be hot large portions of the coke bed, even after 25 days of sitting idle.
Were you able to sweep the furnace and feed line with steam, prior to shutdown? If not, you have a lot of work ahead of you to remove coked / solidified tar from that equipment. Steaming and water quenching of the coke bed is needed before opening the coke drum heads. Efforts should focus on introduction of steam and/or high-pressure water (check feed line flange limits) to the feed line, so that the coke bed can be cooled per normal procedures. This may require special equipment and procedures. If this cannot be achieved after best efforts over a week’s time, a second option is to introduce top water, monitoring the coke drum pressure and outlet temperature, amount of water added and level indicators in the coke drum. A risk is that water does not penetrate the coke bed. Patience and time should allow the water to migrate into the coke bed. Calculations can be done to determine that sufficient heat has been removed with the water, given that you have verified it is entering the coke bed via a rise in outlet temperature and level indicators.
If the coke bed is verified to have been cooled and draining cannot be done via the normal piping and valves, draining may be done by lowering the bottom head with no personnel in harm’s way.
MOV’s are recommended for the cutting water isolation valves located on the cutting deck. Besides the ergonomic operability advantage, the MOV can be reliably interlocked with the winch and jet pump operations.
Causes of coke conveyor fires are usually a bad conveyor belt wheel bearing, causing localized overheating or sparks, which ignites the coke and/or its VCM material. Oily coke can also lead to conveyor belt fires. Autoignition of the coke is an unlikely cause.
June 26, 2009 at 4:05 pm in reply to: Interlocks and Actuator Control Philosophy – Looking for Advice…. #6089
You need to have interlock/PLC signal power and motor operator power separate. We deenergize and lock out the MOV’s at a breaker panel on the structure to protect the open drum from receiving hydrocarbon inadvertently.
I would also recommend not doing a sequence based interlock logic, if that is what you are inferring. I recommend that each valve have a unique relationship with 2 or 3 other valve positions; those valves must be in their proper postion (closed, open, not closed or not open) as a permissive for moving the given valve to the desired position.
Best regards – Mitch
XOM Sarnia has a Fluid Coker. Cause was Hydraulic Oil leak from a slide valve actuator igniting on hot steel. Fire was minor, though localized damage occurred. Based on early reports, cyclones and dip legs are clear following rough shutdown. SU steps in progress. MJ Moloney
You need to perform at least three volume displacements of the coke drum with steam to be in a safe range. Four or five displacements is best.
Due to the fact that the NBS devices are designed to prevent radiation leakage, they hold up very well in fires. Our Baton Rouge East Coker suffered a severe fire in 1993, which destroyed the structure, and the NBS devices were not breached. There was no special fire proofing in place.
What caused your fire? How extensive was the damage on the top deck? Can you identify yourself?
Regards – Mitch Moloney
We typically have 2″ gusseted nozzles on the coke drum, swedged to 1.5″ diameter pipe for the run of carrier and antifoam to each coke drum. You do not need 2″ pipe for the run of carrier oil and antifoam to each coke drum, unless you are injecting a lot of carrier (not recommended). 2″ pipe is less flexible, as well. Still, I cannot overemphasize the need to perform proper process hydraulic calculations and piping flexibility models, that take into account the cold and hot coke drum positions and the cold and warm antifoam piping positions. Best regards – Mitch Moloney