A Step-Change In Feed Nozzle Design

Absolutely. Shell has experience with replacing other licensors’ feed nozzles. In those instances, Shell typically replaces the feed cone section of the riser to include the shrouds within the riser that protect the feed nozzles (keeping feed nozzle performance sustained throughout the FCC unit full run length).

We have been able to make the performance improvements with Shell Max Atomisation Feed Nozzles using similar nozzle pressure drop and atomisation steam percentage as before.

For VGO feeds, Shell Max Atomisation Feed Nozzles typically use 1–1.5% steam.

Typical feed nozzle pressure drop for Shell Max Atomisation Feed Nozzles is between 3 and 5 bar.

Shell Max Atomisation Feed Nozzles are designed to minimise oil vaporisation within the feed nozzle. This is done by not mixing the steam and oil within the nozzle, but rather, using the steam to shear the oil into droplets at the nozzle tip.

We advise using separate feed nozzle(s) for any bio-oils that contain polar compounds that do not mix well with traditional fossil feedstocks.

Shell is currently working on a proprietary feed nozzle for the injection of certain pyrolysis oils that are susceptible to degradation.

There has been much debate about the best feed injection point for non-traditional feedstocks, and this is an area that we continue to research.

Shell has correlations for feed nozzle pressure drop that it uses during design.

Feed temperature has an impact on feed viscosity which can impact feed nozzle performance (Shell has experience designing feed nozzles for heavy, viscous residue feeds as well as lighter feeds).

Typical steam/oil ratios are around 1.5 for VGO and up to 3 for residue.

Our typical control of feed and steam to each feed nozzle is done by restriction orifice with ball valves on each feed nozzle feed line in case it is needed for trim control.

We have a feed nozzle design tool for process design of the feed nozzle, the kinetic effects are simulated in Shell’s FCC kinetic model (SHARC), and we have a feed nozzle testing unit for correlating different process parameters to feed nozzle performance.

More complete atomisation means less feed coke and less vaporisation time in the riser, which translates into higher conversion and typically higher margin.

The basic feed nozzle design does not change for higher temperatures. Shell uses 304 stainless steel for most designs (similar to regenerator internals).

The benefits of the Shell Max Atomisation Feed Nozzle outlined in the webcast include improved flexibility in operation through better and more complete atomisation leading to higher severity/conversion with better, more selective yields (i.e., more desirable yields with less feed coke and less dry gas), or higher throughput, or more regenerator capacity through lower temperatures or more air capacity, or some combination thereof.

Shell Max Atomisation Feed Nozzles can be retrofitted to any FCC unit (not just Shell units). This is most effectively done by replacing the riser cone to install the Shell feed nozzle shrouds that are sized for the new nozzles and provide high feed nozzle reliability.

Shell typically has a control valve on the main feed line and the main steam line to the respective ring headers. Individual feed and steam flow control to each feed nozzle is done through restriction orifices.

Shell also has a pressure indicator on the feed and steam ring header, and individual ones on the feed lines to each feed nozzle. This allows the operator to see if there are erosion or plugging issues with an individual feed nozzle.

Shell’s feed nozzle designs provide local pressure indicators on each feed line to the individual feed nozzles. Plugging or erosion can be seen by differences in pressure in these pressure indicators.

Shell Max Atomisation Feed Nozzles are designed for full flow and turndown flow. Typical turndown is 50–60%.

Typical nozzle sizes are 6 or 8 in. NPS (nominal pipe size), but we have produced other sizes for customers.

Shell has a range for feed rate per nozzle that is used as a guideline to ensure that you get good feed distribution and penetration into the riser without too high a pressure drop. We prefer to use an even number of nozzles to maintain good distribution. All these factors go into nozzle sizing.

This is not typically a concern. The goal is to produce feed droplets of a similar size or order of magnitude to the catalyst.

The data on temperature profile shifts due to Shell Max Atomisation Feed Nozzles was shared in the presentation.

Examples include Shell Energy and Chemicals Park Singapore’s (formerly Pulau Bukom refinery) drop in riser temperature profile by 15°C while increasing conversion by almost 3 wt%; also, Puget Sound refinery’s drop in regenerator bed temperature by 22°C while increasing conversion 0.6 wt%.

There is a range of droplet sizes produced that is in the same order of magnitude as catalyst particles (somewhere around a few hundred microns is typical).

 For nozzles that do not atomise well, liquid globules and strands are much larger (size of these globules and strands is in the order of millimeters).

Having been active in sulphur recovery for about 50 years, Shell has built up extensive expertise in this area. We have developed our own dedicated software design tool that incorporates extensive commercial plant and research data to ensure very accurate performance predictions.

We can support our customers in the catalyst decision-making process. We can advise which of our tail gas catalysts will best fit their situation for maximising performance and catalyst cycle life.

The main issue is actually the unatomised parts of the liquid feed. These go directly to coke, which limits conversion and regenerator capacity.

Shell uses the momentum force of steam at the nozzle head exit to shear the liquid into tiny droplets, so there is no substantial mixing of hydrocarbon and steam in the nozzle body.

In general, feed nozzles are one of the hardware items that can give you the biggest return on investment in terms of margin as they have an impact on both reactor and regenerator operation, as well as yield performance.

The webcast demonstrated that Shell Max Atomisation Feed Nozzles provide the right mix of higher performance and reliability to dramatically improve conversion and yield performance, and can have a payback of less than 1 year, making them budget friendly.

Feed nozzle performance is usually tracked by periodic mass balances and calculation of yields.

We use the Shell proprietary FCC kinetic model SHARC to model performance including thermal and catalytic cracking reactions.

Dry gas is caused through thermal reactions due to high catalyst temperature in the feed mix zone. Shell Max Atomisation Feed Nozzles provide better catalyst quenching to reduce mix zone temperature and dry gas.

Feed quality can have a dramatic effect on feed nozzle performance. The heavier the feed (as would be the case with higher CCR and metals feeds), the harder it is to atomise the feed into sufficiently small droplets. Since aromatics don't crack in the FCC, and heavier feeds typically have higher quantities of aromatics, the already difficult to crack feed is made worse by lack of proper atomisation.

In other words, more of the crackable hydrocarbons are not sufficiently atomised and turn into coke (not vaporised within the riser) and add onto the coke pre-cursors in the feed (CCR and poly ring aromatics) to make more coke, and less naphtha and lighter products.

Shell Max Atomisation feed nozzles are designed to maximise the atomisation of more difficult, heavy feeds which allows a higher proportion of crackable heavy components to convert to more valuable products.

Shell Max Atomisation Feed Nozzles can be used for many different types of feeds from VGO to residue to deasphalted oil (DAO) and hydrowax. They can also be used for naphtha recycle, depending on the desired injection location and quantity of naphtha.

Shell Max Atomisation Feed Nozzles can be designed to handle a wide variety of feeds, from naphtha recycle to VGO to heavy residues and more. If there are feeds that are truly incompatible when mixed in a feed tank (i.e., separate into different liquid phases or precipitate), we would most likely design a separate feed system for those feeds.

For heavy, viscous feeds, we would typically try to increase feed temperature (within reason) and likely use slightly higher steam (~3% for heaviest hydrocarbon feeds).

Yes, the Shell Max Atomisation Feed Nozzle can be used to feed light naphtha to the riser.

Shell accommodates different feed rates for different FCC units through the number of feed nozzles provided and, to a lesser extent, by the size of the feed nozzles. We design our feed nozzles for the full range of flowrates from design to turndown. In our experience, pressure drop for feed nozzles ranges from 2.5–5.5 bar.

Shell has feed nozzle design experience with heavy residue feeds with high viscosity. Higher viscosity feeds are usually handled through a combination of higher feed temperature and a slight increase in atomisation steam (up to 3%).

This depends on the quantity of naphtha that is to be recycled, temperature of the feed to the feed nozzle and the preferred location for naphtha injection. It is possible to recycle naphtha to the riser through the normal feed nozzles if the recycle rate is low and the temperature is conducive (to limit naphtha vaporisation).