Q&A

(2012) Question 10: Does hydrotreated product recycle count the same as fresh virgin feed for the catalyst break-in period?

Generally, a break-in period is very dependent upon the catalyst type in the intended service; so, it changes a little with each unit. To reiterate again, it is important to have a good relationship with your catalyst vendor. Ask specifically what the vendor wants to see in terms of unit start-up procedures and feed specs.

(2012) Question 11: How do you set your maximum endpoint targets (short residue, coker, and FCC) for a two-stage mixed feed HCU operating in distillate mode? What is the impact on catalyst life?

Catalyst typically deactivates due to an accumulation of contaminants and due to process upset coke formation. It also deactivates due to what I will refer to as routine coke formation.

(2012) Question 12: For units originally designed as naphtha selective HCUs, what are the considerations for shifting selectivity to distillate production?

There have been many inquiries into shifting naphtha hydrocrackers to distillate mode over the last couple of years. The optimal solution is dependent on feed qualities, hydrocracker configuration, distillation, and gas recovery hardware, as well as the value of volume expansion across the hydrocracker.

(2012) Question 13: What equipment size limitations set the maximum capacity for a single-train, high pressure, heavy feed hydro-conversion unit (HCU ebullated-bed resid)? What are the other considerations?

With an ebullating-bed reactor, the primary throughput limit is set by the superficial velocity, which is a function of reactor diameter and throughput. The superficial velocity is what determines the ability to separate gas from liquid going to the recycle pump.

(2012) Question 14: What is cycle life limiting factors in low pressure jet/kero hydrotreaters?

Factors limiting cycle life in low pressure kero/jet hydrotreaters are mainly related to product quality specifications. In particular, specifications related to aromatic saturation such as smoke point and color.

(2012) Question 15: What can be done to mitigate foaming and emulsion formation in our hydrotreater high pressure separator? Is there any favorable experience with injection of antifoam/chemical emulsion breaker?

We are starting to hear about more foaming problems, particularly with some of the unconventional or shale crudes being processed, and there are a few other instances.

(2012) Question 16: What is the commercial experience on the use of H2 membranes in hydrotreaters or hydrocrackers for H2 recovery? What is a reasonable membrane life given the sensitivity to fouling and temperature changes?

At the Denver Refinery, we have a few hydrogen separation membranes. We call them our hydrogen purification unit. Our #3 HDS, which is currently our ULSD unit, was previously a gas oil hydrotreater until we revamped it in 2006. So, the HPUs (hydrogen purification units) were in consistent service from 1990 to 2006.

(2012) Question 17: Now that natural gas prices are low in North America, what options are available to increase refinery volume gain and product quality by exploiting low-cost hydrogen? Is the low hydrogen production cost impacting the economics between the selection of coking or hydrocracking?

There were a number of questions this year that requested information about how to effectively utilize low-cost hydrogen to increase refinery volume yields.

(2012) Question 18: What are the economic incentives to justify upgrading reactor internals? What techniques have been utilized to assess the performance of existing reactor internals?

The primary incentive is catalyst life and the ability to meet turnaround intervals. Gas and liquid distribution improvement results in increased catalyst performance and potentially longer catalyst life. Reactor internal upgrades may consist of quench decks, mixing chambers, and improved liquid distributor trays.

(2012) Question 19: Since API-932 (Waterwash Best Practices) was published, what has been the impact on reactor effluent air cooler washwater system design and reliability? Are there any active or ongoing studies to improve waterwash systems, in addition to API-932?

The question of issues associated with waterwash has been discussed since the API-932 was issued. This first slide gives a little chronology of some of the documents.

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