PTQ Q3 2022 Issue

A step change in feed nozzle design How Shell’s Max Atomisation Feed Nozzle technology can improve FCC unit margins with minimal capital investment, including audited results from three refinery scenarios

Todd Foshee Shell Catalysts & Technologies

I n a climate in which conservative approaches to capi- tal investment are the norm, fluidised catalytic cracking (FCC) unit operators may be seeking low-cost opportu - nities to increase their margins. After all, investing in mar - gin-improvement projects is usually key to maintaining an operator’s competitive position. What would a creative project that could deliver the desired marginal gains look like on the ground? It may be characterised by one or more of these outcomes: • The ability to process cheaper, lower-quality feeds, such as residues and difficult-to-crack materials • A yield increase from reducing the dry gas yield and increasing conversion, which would shift the yield structure to more valuable product slates • Maximisation of the operating severity. If the opera - tor is seeking to realise this scenario, it will be necessary to relieve any constraints imposed by the capacity of the wet gas compressor or the air blower and heat-balance apparatus. Is it possible to invest in a low-cost technology that could deliver these desirable outcomes and increase margins? For an FCC unit, there is a compelling solution. Following a major research and development pro - gramme using new analytical techniques, Shell Catalysts & Technologies has recently developed new feed nozzles that push the boundaries for feed atomisation, thereby enabling refiners around the world to capture substantial margin increases. Upgrading feed nozzles is a low-capital oppor - tunity with a quick payback that boosts margins and adds flexibility to the FCC and catalytic feed hydrotreating units. Rerun or replace? Dispelling the myth Refiners can occasionally be reluctant to replace or upgrade their feed nozzles, instead preferring to get another run out of their existing ones. Indeed, Shell feed nozzles, includ - ing legacy generations, are robust enough to operate for more than one run cycle. This operating strategy can offer a relatively modest reduction in capital cost, but it comes with risk. Although inspecting feed nozzles during a turnaround can determine the amount of erosion or plugging that has occurred during the previous cycle, it cannot predict the nozzles’ ability to complete a second cycle in such a harsh environment. Therefore, it is necessary to consider whether the capital saving is outweighed by the risk of loss in performance dur - ing the second cycle, given that feed nozzle replacement is

low capital cost and small shifts in yield performance can pay for feed nozzles in a short time. In the pursuit of margin improvements, FCC operators must consider the big ques - tion: is there more value in a rerun or in replacing the exist - ing feed nozzles? In most cases, replacing the feed nozzles provides a shift in yields and feed flexibility that unlocks profitability over the duration of the entire run cycle. The payback time for the latest-generation Shell feed nozzles is typically less than one year. In fact, feed nozzle replacement compares favourably against other technology-based solutions that FCC unit operators are likely to consider. In many cases, the capital cost of replacing the feed nozzles is equivalent to the operating expense of trialling a new catalyst but with - out the associated risk. Improving feed atomisation: the benefits When atomised sprays are discharged from feed nozzles, they transition from liquid sheets to non-spherical liga - ments and agglomerations of liquid (globules) and then, ultimately, to droplets (see Figure 1 ). At Shell Technology Center Houston, shadowgraph par - ticle image velocimetry studies have been used to charac - terise the droplets in an FCC facility and have revealed the previously unidentified presence of liquid globules and liga - ments. These are not apparent or quantified when referring to spray Sauter mean diameter, or D32, data. Technology providers frequently quote low D32 values that may be associated with their feed nozzles. Although important, when taken in isolation D32 values do not reveal the whole story about feed atomisation. In fact, two atomised feeds can have very similar D32 values but very different characteristics. Imaging (see Figure 2 ) shows how the troublesome ligament content for one

Droplets

Steam

Sheets

Nozzle

Oil

Ligaments/globules

Figure 1 Typical spray transitions for a feed nozzle

PTQ Q3 2022