Q&A

(2018) Question 19: What considerations do you use for designing a hydrocracking reactor? What criteria do you use to determine number of beds, diameter, and beds’ lengths?

Hydrocracking reactor design is a proprietary technology with each licensor having their own specific design practice based on operating experience, catalyst technology, and engineering expertise. It is not the purpose of this forum to reveal proprietary technology, but to improve refiners’ operations through shared experience.

(2018) Question 20: What considerations do you give to co-processing or block mode operations with renewables in an existing hydroprocessing unit?

In all scenarios, a refiner must consider their RFS obligations, potential biodiesel tax incentives, biodiesel merchant market, refiner’s existing hydrotreating units’ utilization rates, capabilities, and designs, renewable feedstock types, availability, price, and pre-treatment requirements, and product specifications and storage constraints.

(2018) Question 21: What are your important considerations for water washing with respect to: 1) Intermittent injection a. Process temperature of injection b. Duration of injection c. Frequency - triggers to begin d. How frequently before making it continuously? 2) Water Quality: a. pH range b. Oxygen c. Total Suspended solids d. Total dissolved solids e. Recirculation vs. make-up f. Other

Hotter temperatures typically will increase in the need for better designed injection systems. The injection mix point needs to be designed to contact and scrub the vapor well, with adequate dilution of water, with metallurgy at the injection point selected to handle the lower pH of the droplets.

(2018) Question 22: Can you elaborate on the benefits, drawbacks, and trade-offs of liquid phase vs. gas phase catalyst activation in a hydrocracking unit? Is there an activity or yield difference of liquid phase or gas phase activation of 2nd stage catalyst in a 2-stage hydrocracking unit? Consider both catalyst formulation and operational factors (MPT, excursion risk, etc.)

Activation (or sulfiding) of hydrotreating and hydrocracking catalysts can be done either ex-situ or in-situ. In both methods, the objective is to convert all the catalyst’s metal oxide sites to active metal sulfides.

(2018) Question 23: What are the sources of silicon that can impact a hydrotreater? How does silicon affect hydrotreater operations? What are your best practices for managing / mitigating silicon poisoning?

One source of silicon is antifoam chemistries. These may be introduced into HDS feeds via use in the Coker process within the refinery or via use in production upstream of the refinery.

(2018) Question 24: How many refiners import and/or purchase gasoil feed for a hydroprocessing unit? What are common issues associated with imported or purchased gasoil feeds? Are there specific characteristics to target and / or avoid? Are there best practices for minimizing negative impacts to unit operations / reliability? How are supply limitations managed?

Key characteristics of imported feed like end point, sulfur, nitrogen, chlorides and carbon residue can be controlled by establishing allowed specifications. But other characteristics may be hard to control.

(2018) Question 36: How do you manage the potential negative impacts of H2S Scavengers in imported coker feed?

How do you manage the potential negative impacts of H2S Scavengers in imported coker feed?

(2018) Question 37: Do you extend the time between de-coking the furnace by cutting coil outlet temperature or cutting furnace charge? How often are spallings done in coker furnaces? What is the temperature recovery after spalling?

Heater fouling is dependent on several variables that include the process film temperature, residence time at temperature and coke precursor concentration. I like to target a coke drum outlet temperature of 825°F before quench injection, which normally requires a Coker heater outlet temperature of 925°F.

(2018) Question 38: How does coke morphology vary with changes in feed quality? What feed tests do you require to quantify the impact on coke quality?

Predicting coke morphology from feed properties has not been 100% successful as the Coker operating conditions can make a difference if the feed is close to the shot coke vs. sponge coke threshold. The traditional approach uses the asphaltene content of the feed divided by the concarbon value of the feed.

(2018) Question 39: What operating conditions increase the generation of coke fines? What reliability issues do you associate with increased fines production?

Coke fine generation is really a function of the coke cutting process. Feed stock and coke drum operations during the actual drum fill cycle have very little to nothing to do with the generation of coke fines.

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

Q&A