PTQ Q4 2024 Issue

About the Shell TSS

which does not meet regulations in many countries. The Shell TSS, when installed downstream of a two-stage cyclone system, reduces the dust emissions to 50 mg/ Nm3 or below, meeting the maximum emission levels in most developed nations. The Shell TSS consists of multiple axial flow cyclones called swirl tubes, hanging from two tubesheets (see Figure 1 ). The gas enters between the two tubesheets through the central inlet duct, flows into the swirl tube assemblies and then moves downwards. Vanes within the swirl assemblies induce a spin in the gas and solids mixture, creating a high-velocity centrifugal force. This gas-solid mixture impinges on the wall of the separa - tor can, causing the solids to fall by gravity. Meanwhile, the gas makes a 180-degree turn and exits the swirl assembly through the central gas outlet, proceeding to the top section of the Shell TSS. The collected solids descend into the cone region of the Shell TSS vessel. A small percentage of gas (approximately 3% of the total inlet gas), referred to as the underflow, is directed to the bottom to carry the separated solids to the underflow line, thus keep - ing the bottom section free of solids. In FCC catalyst service, the underflow gas quantity is controlled by a critical flow nozzle, but in pyrolysis or hydropyrolysis applications, it would likely be controlled by a flow control valve situated on the fines drum vent down - stream of the Shell TSS. requires that the primary dipleg be connected to the sec - ondary dipleg due to low solids flux in the secondary. This, in turn, requires that a loop seal be installed in the primary dipleg. However, loop seals are not proven in commercial units, and their proper function relies on correct design and aeration, which makes two-stage cyclones with a loop seal more complicated than a primary cyclone with a Shell TSS. • Lower Capex and Opex required for the downstream guard bed (solids trap) than with a two-stage cyclone system, owing to less solids carryover into the downstream equipment. • Higher reliability than a candle filter system. The risk of swirl tubes plugging with coke is lower because the vapours pass through the free space between the vanes, as opposed to mass transfer through pores in the candle filter. Additionally, candle filters represent a more expensive alternative in terms of both Capex and Opex. Shell’s cyclone and TSS technologies have been com- mercially proven over the last 70 years, achieving high per- formance in FCC units. Recent modelling efforts and tests using a cyclone followed by a TSS in biochar service have shown good performance. Developing models for biochar service Shell Catalysts & Technologies has robust models and soft- ware for cyclones used to separate FCC catalyst particles

The Shell TSS is widely used in the refining industry for protecting the expanders as well as for reducing stack particulate emissions. It enhances reliability by eliminat- ing 10 µm and bigger catalyst particles from the flue gas. These particles, carried from the second-stage cyclone outlet, can cause erosion of the expander blades, which can potentially lead to catastrophic failure. The Shell TSS is also widely used to reduce dust emissions in flue gas. A typical regenerator two-stage cyclone system reduces the dust in the flue gas to around 150-350 mg/Nm³,

TSS

Flue gas

Flue gas and catalyst particles

Swirl tube assembly (x44)

Catalyst particles

Feed gas

Figure 1 Shell TSS vessel (right) and swirl tube assem- bly details (left)

particle sizes more readily in the cyclones than FCC catalyst. In addition, proper design of the two-stage cyclone in biochar and ash service is crucial, including a loop seal between the primary and secondary cyclone diplegs to prevent secondary cyclone dipleg issues that could impact system efficiency. A candle filter is an option to replace the two-stage cyclone system, as it has the highest separation efficiency. Such a system can remove almost all the biochar from the vapours. However, it is susceptible to coking, which can lead to reliability issues and higher operational costs com- pared to other methods. Another option is to install a Shell TSS downstream from a single cyclone. In pyrolysis and hydropyrolysis applica- tions, modelling suggests that a single cyclone can separate the bulk of the biochar material. However, having the single cyclone outlet directed to a Shell TSS allows for even better separation efficiency than having a second-stage cyclone since the Shell TSS has a d50 cutpoint of 2 µm. As the Shell TSS and the primary cyclone operate independently of each other, their separation efficiencies are unaffected. The main advantages that the primary cyclone and Shell TSS system have over other options include: • Higher efficiency and less complexity than a two-stage cyclone system. The Shell TSS has a much lower d50 cut- point compared to a secondary cyclone, which allows for better separation efficiency. Also, the two-stage cyclone

PTQ Q4 2024