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(2012) Question 66: Some refiners are considering substituting potassium hydroxide for sodium hydroxide as a desalted crude treatment to lower overhead chlorides. What is the impact of this change on coker operation and other downstream units? What are the advantages and disadvantages?

They are both alkali metals. Potassium hydroxide should, in theory, act like sodium hydroxide. The effect should be similar with regard to reducing the overhead chlorides in the desalted crude or, similarly, in metal-catalyzed fouling.
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(2012) Question 67: We have an atmospheric overhead system with inadequate waterwashing,and we experience fouling and corrosion issues in the bundle. What might be the pros and cons of making a bundle modification or installing direct water spray into the shell side of the atmospheric tower overhead condenser in terms of underdeposit corrosion and bundle life?

We would not recommend direct water sprays into the shell, regardless of whether this is the first overhead condenser, because direct sprays can cause many problems, including erosion.
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(2012) Question 68: After the operating temperature of the crude column overhead has been raised, corrosion rates in trim coolers’ inlets have increased greatly. Ultrasonic thickness (UT) measurement has indicated some increase in local thinning, but not to the degree of actual damage. What are new trends for monitoring corrosion in distillation columns and overhead condensing systems?

When we talked about this on the panel, we had some very interesting discussions. Generally speaking, increasing temperatures tends to help with most overhead corrosion issues as it moves you away from salt and dew point consideration. What we think is going on here is that if you increase the temperature, you may shift your dew point downstream of where you are designed to handle it.
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(2014) Question 67: What is your experience with toxicity issues at the Water Treatment Plant as related to naphthenic acid content in desalter brine water? What strategies are you employing employed to mitigate this issue?

Some naphthenic acids will not partition into the water phase and normally do not create a wastewater issue. In case of washwater and brine pH’s above 8.5 the naphthenic acids can form a soap, and this can cause severe emulsion formation and oil carry-under to the WTP.
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(2014) Question 69: What is your experience with using thermal scans or other methods to monitor tube wall temperature furnaces?

This is a common practice in furnaces that have severe operation (VBU, Coker, etc.). All VBU’s have multiple fixed TMT measurements on all coils. Thermal imaging is used in furnaces that have specific TMT issues, it does require expertise and specialized thermal imaging cameras in order to get useful data. Thermal imaging will not work on tubes that have external fouling.
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(2014) Question 70: Please discuss the merits and detriments of using low-base strength or high-base strength neutralizers for corrosion control in atmospheric column overhead.

We do not recommend the use of low base strength neutralizers that have a pkb lower than Ammonia for the obvious reason that these are not able to compete with Ammonia in the chloride salt formation. We prefer higher base strength neutralizers but that is only part of the selection criteria, other important criteria are vapor/liquid partitioning, chloride salt properties, oil/water distribution in OVHD and desalter, volatility, toxicity and cost/performance.
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(2014) Question 73: There is increasing economic incentive to operate crude units to yield maximum middle distillate volume. What targets are you using to quantify the degree of separation between naphtha and kerosene and between diesel and gas oil? What amount of distillation curve overlap do you consider good practice? What guidance are you given to achieve the target separation?

Middle distillates are maximized within the constraints of D86, flash point and density specifications. There is some optimizations play between the pump around heat recovery, which is specific to a unit, and maximum distillate recovery.
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