Q&A

(2012) Question 72: What are Best Practices for steam rates in cokers, heater velocity steam, valve purge steam, and drum steam out? Do newer, double-fired heater designs use less steam?

Sim Romero with KBC, who is sitting in the audience, will be conducting Coking 101 and will cover these topics. Since I am repeating Sim’s responses, I will summarize the answers.

(2012) Question 73: What is your experience with coke bed instability?

We have seen coke beds collapse during the beginning stages of the quench water addition. We have had operational problems because we were not able to get the quench water into the coke bed. We even tried alternating back and forth between the stripping steam and the quench water, but we were not able to penetrate the coke bed with the quench water.

(2012) Question 74: We have experienced leak issues around gaskets in cyclical and hot temperature services. What solutions have you developed to eliminate these issues?

At one of our two cokers, we use ring joint flanges from the coker heater outlet to the coke drum inlet and have had no leak issues. At the other coker, we have a short section of piping at the coke drum feed inlet that had raised face (RF) with spiral wound gasket drum (SPWD) that would occasionally leak.

(2012) Question 75: Please describe your best turnaround practice for cleaning and inspecting heat exchanger bundles versus replacement.

KBC is a nonoperating company, so we do not operate any equipment or conduct turnarounds. However, we do know that the bundle must be cleaned for inspection. We are accustomed to seeing hydrolancing or chemical cleaning for less severe services.

(2012) Question 29: How many refiners are using Layers of Protection Analysis (LOPA) in their Process Hazard Analysis (PHA) studies? How do they quantify the frequency and consequences of initiating events?

Phillips 66 has used LOPA since 2006 when we do our PHA studies. We apply it to the most severe events and use a scale of 1 to 5 for severity. So, if there is a Consequence 4 or 5, then we will apply LOPA to that event. Generally, those are the scenarios with a loss of containment component.

(2012) Question 30: How are water drains routed in alkylation units; for instance, in waterwash or propane drying services? What options exist for separation of the water and entrained light hydrocarbons? How can enclosed systems be monitored?

In many units, including both HF (hydrogen fluoride) and sulfuric acid alkylation units, there may be opportunity to drain water from vessels that contain hydrocarbon.

(2012) Question 31: What is the panel’s experience with temperature excursions (regeneration and otherwise) leading to the catalyst or equipment damage in reforming and isomerization units?

In a refinery where I used to work, our moving-bed reformer experienced a severe temperature excursion in the chlorination zone of the regenerator. After a prolonged outage on the regenerator, the unit was put back into white burns sooner than would have been recommended.

(2012) Question 32: What are the impacts of the presence of acetone in the alkylation unit feed? How is this formed in the FCC? Comment on both HF and sulfuric units.

In both HF and sulfuric acid units, acetone will consume acid, resulting in a reduced acid strength. Regarding sulfuric acid units, some documentation that I got from DuPont STRATCO indicated that one pound of acetone will consume about 10.5 pounds of acid.

(2012) Question 33: Increased feed sulfur increases acid consumption. How does it affect alkylate yield and/or alkylate properties?

In HF units, when sulfur is in the feed, it produces acid-soluble oil (ASO), organic fluorides, and polymers, which then have to be removed through the regeneration process. The light ends that are contained in this ASO can put more pressure on the regeneration system and lead to the higher acid losses. So that is the mechanism there.

(2012) Question 34: Fresh sulfuric acid fed to an alkylation unit can contain niter (nitrosylsulfuric acid) which may lead to excessive corrosion. What is niter; what does it do; can we test for it; and how can we reduce the levels in our fresh acid?

“Niter” is actually a common term referring to the amount of NOx (nitrogen oxide) or nitrates in the sulfuric acid. It is actually generated in the sulfuric acid regeneration process. One of the first steps you go through in acid regeneration is a combustion furnace. In that combustion furnace, you can generate NOx, which is really a function of your peak flame temperature and excess oxygen: the normal NOx contributors.

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