Q&A

(2017) Question 36: What are your primary indicators that a coker furnace spall is complete? What steps do you take to optimize the efficiency of spalling?

Delayed coker furnace spalls are performed to remove the buildup of coke on the inner walls of the furnace tubes in order to improve furnace heat transfer and maintain unit throughput and efficiency. As furnace spalls require coker and sometimes refinery crude rate reductions, they should be planned and communicated effectively to the refinery’s Planning Department to ensure that crude and product inventories are managed appropriately.

(2017) Question 37: What programs have you implemented to improve reliability and life of the coke drums including inspection and maintenance?

The refining industry is continuously experiencing coke drum problems and failures due to low cycle fatigue. The two main problems caused by the cyclical operation of coke drums are shell bulging and shell/skirt circumferential weld-seam cracking.

(2017) Question 38: How do you monitor coke drum overhead lines to determine when cleaning is required? What cleaning techniques are effective and which are ineffective?

Higher pressure drop reduces gasoil yields in the coker fractionator and profitability for the refinery. Establish graphs that demonstrate the relationship between pressure drop and yield loss and make them visible to the organization.

(2017) Question 39: What procedures and techniques are you currently using to monitor and control cyanide corrosion on coker overhead circuit and light ends units?

Cyanide corrosion is a hydrogen permeation phenomenon on steel that tends to cause cracking, commonly at high stress zones, and possible blistering on “dirty” base steel. Finding cyanide in an overhead circuit does not mean there is a problem.

(2017) Question 40: What crude properties and process conditions are you monitoring as part of a crude slate change?

Crude quality should be compared against similar crudes already approved for processing at the refinery. Obtain crude samples, when possible, to confirm the properties listed in the assay. Ensure that sufficient sample volume (three to five quarts is recommended) to pre-test for crude compatibility with other crudes in your tank farm.

(2017) Question 41: What are some of your operating practices used to mitigate incursion of water slugs in crude feed from tankage? Are there any early warning devices or procedures currently being used successfully?

Plugs of water are problematic, in terms of causing desalting and crude column upsets. Pockets of water can form in the tank due to the characteristics of the crude. The primary defense is to minimize water in crude oil; but with current upstream practices, we know water will enter in with the crude. Having systems in place to reduce, mitigate, and handle water intrusion is important to maintain stable crude unit operations.

(2017) Question 42: What water sources are you using for desalter waterwash, and what are the advantages and disadvantages of each? What role does desalter waterwash source and injection location play in desalter performance?

Over the years, we have established several Best Practices concerning desalter wash water rates, quality, injection locations, and sources that – when utilized – help ensure optimum crude oil desalting.

(2010) Question 51: In your experience, what are the implications on coker heater run length and coke drum operations with the following feedstock quality: Contaminants (Na, Ca), low saturates or high asphaltenes, crude compatibility, solvent deasphalt (SDA) pitch, low asphaltenes and high saturates?

There are at least three main mechanisms under which the heater tubes become fouled: •Inorganic material deposition or precipitation, •Rapid asphaltene precipitation, •Coke formation

(2010) Question 54: What is the current best practice for number of feed nozzles, angle, and location on coke drums considering the use of slide valves for the bottom unheading device?

There is not a one-size-fits-all answer to this question. However, we believe that an arrangement that closely matches the conventional bottom center upflow arrangement will provide more uniform thermal stresses on the drum and minimize operational impact.

(2010) Question 55: What is considered the best-in-class design for coker main fractionator wash zones? Have refiners seen good performance and target run lengths using grids in this service?

Cokers today are normally designed to operate to maximize liquid yield from the unit. This will require the coker to operate at as low a recycle as possible while still maintaining the required product specifications for the heavy coker gas oil (carbon content, metals, asphaltenes, etc.). For a low recycle operation a spray chamber is the best-in-class.

Find the answer to your technical question in AFPM's extensive Q&A database.

Q&A