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What is the most effective way to capture particulates in FCC flue gas?

Apr-2021

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Tomasz Jozwik, Multiconsult Polska, tomasz.jozwik@multiconsult.com.pl

I cannot say anything new if I say that most effective way to capture solid particulates is electrostatic filter charged to a voltage of upto13 kV at any plant.

Aug-2021
Todd Foshee, Shell, todd.foshee@shell.com

Effective particulate matter (PM) capture starts in the regenerator, where a typical two-stage regenerator cyclone system can remove the majority of the catalyst from the flue gas, leaving the exiting flue gas cleaned of particulates down to levels around 200-400 mg/Nm3, depending on regenerator and hardware conditions. If particulate levels are much higher than those levels, troubleshooting around the regenerator should be done to see if there is an attrition source or if there is cyclone damage. Shell Catalysts & Technologies has FCC cyclone technology that can provide a high separation efficiency with high reliability and a long life of operation.

Assuming that particulate levels exiting the regenerator are normal, the next consideration is the environmental regulatory requirements for PM emissions for your unit. This will determine the PM removal technology required at the FCCU stack. Many locations require PM emissions at the FCC stack to be 50 mg/Nm3 for which Shell Catalysts & Technologies has Third Stage Separator (TSS) and Fourth Stage Separator (FSS) technology that provide such levels or lower. Shell’s TSS and FSS technology are driven by Shell’s swirltube internals which offer an industry leading separation efficiency and d50 cutpoint amongst other TSS offerings.

If the PM emissions at the stack are required to be well below 50 mg/Nm3, say in the 20-30 mg/Nm3 range, then a wet gas scrubber (WGS) or electrostatic precipitator (ESP) would be required for those much lower PM levels at the stack. If SOx reduction is also required, a WGS is typically chosen.

As a final note, if there is an expander in the flue gas system, then the expander will need to be protected from particulates regardless of the final PM removal technology at the stack as the expander can’t handle the dust load and particulate sizes in the flue gas exiting the regenerator with two-stage cyclones alone. For expander protection, a TSS is the technology of choice, and Shell’s TSS removes practically all dust particles that are 10 microns and larger, which is essential for expander reliability. If the stack emissions are not overly stringent, then the TSS for expander protection can be coupled with an FSS to also provide stack PM reduction for stack emissions. If the stack PM emissions are well below 50 mg/Nm3, then the TSS will be only for expander protection (no FSS) with the TSS underflow re-joining the flue gas stream downstream of the expander, and either a WGS or ESP providing particulate removal for stack emissions.

Jul-2021
Jeff Pollard, Filtroglobal LLC, jeffp@filtroglobal.com

Typically, the solution FiltroGlobal LLC and our partners at Dahlman Filtration Technology have offered in the past is a TSS cyclone system, with the underflow then directed to our FSS particulate filter. To date, this has met emissions requirements in Europe and around the world. This is accomplished with sintered metal filter media due to the temperature of this stream.

More recently, we have been successful installing a "Full Flow Filter" downstream of WHB, and installed a blowback system that filters the entire flue gas stream. Our original system has been in operation for over 5 years now, and was on-line for the entire time, from turnaround to turnaround.

May-2021
King Yen Yung, Petrogenium, kingyen.yung@petrogenium.com

Before deciding on the most effective option, one should consider what the specifications are for the reduction of particulates in the FCC flue gas being ultimately released to the atmosphere.

Standard FCC units are equipped with two stage cyclones in the regenerator. Nowadays many countries prescribe that dust emissions be reduced to a level below 50 mg/Nm³ which requires additional catalyst fines capturing capacity. The most cost effective and simple way to achieve this is the installation of third and fourth stage separators (for instance, TSS and FSS from Shell licensed through Dupont).

The TSS/FSS system enables separation of virtually all erosive particles and hence protects the power recovery expander and is fully contained in a single vessel of proven mechanically sturdy construction.

Only when a TSS/FSS system is not able to meet the dust emissions limit should someone consider the installation of a far more expensive and operationally cumbersome electrostatic precipitator or wet gas scrubbing system.

Apr-2021
Mel Larson, Becht, mlarson@becht.com

The industry has two basic systems that maximise particulate removal from the FCC flue gas. In the US the EPA expanded the definition of particulate from catalyst by adding condensable particulates. This answer will concentrate on the catalyst element. The systems can be divided into wet and dry. A wet system is a flue gas scrubber where the flue is passed through a venturi chamber that has a solution which will trap catalyst, react with SOx, and make a slurry solution that can be used for other purposes. Scrubber systems often have a third stage catalyst separation system before the scrubber to assist recovery of catalyst.

A dry system is most often but not always a two stage system of third stage multiple cyclone separation followed by a electrostatic precipitator (ESP). The most effective system will be a function of location. In arid locations where water is a scare resource, using water may not be desired, even if the mass of loss is lower than in an ESP. ESPs have a narrower operating temperature range, allowing for some energy inefficiencies. Optimally, regardless of flue clean-up, always consider the most efficient means to extra value from the FCC flue gas, be it steam generation, power generation from pressure letdown, and or a combination of both to maximise the energy recovery.

Apr-2021
Raj Singh, Technip Energies, Raj.singh@technipenergies.com

Today, refiners are taking a number of steps to reduce emissions across their operations to lower the environmental impact. FCC regenerators are the largest single source of particulate emissions in refineries. Capturing catalyst particles from flue gas is accomplished through a combination of equipment. The primary equipment utilised are regenerator cyclones. The catalyst losses from a FCC regenerator are generally in a range of 250- 450 mg/Nm³.

The selection of equipment downstream of the regenerator depends on additional objectives besides the capture of catalyst fines. Typically, a third stage separator (TSS) provides a further reduction of catalyst in the flue gas. This is critical for units that include a turboexpander for power recovery. Depending on the underflow capture device, the TSS system can bring the catalyst loading to less than 150 mg/Nm³ for a underflow cyclone, or 100 mg/Nm³ for an underflow filter.

To get below 50 mg/Nm³, either an electrostatic precipitator (ESP) or a flue gas scrubber is used. A flue gas scrubber (FGS) can also reduce SOx emissions. However, scrubbers require water, which can be a challenge for certain locations, although they do alleviate the safety concerns that have been associated with ESP use during transient operation.

An alternative to the ESP and FGS is a full flow barrier filter. These are offered by a couple of suppliers and have demonstrated the capability to reduce particulates to less than 5 mg/Nm³. There are not many installations, but at least one has been in operation for over 15 years.

The barrier filter has demonstrated to obtain the lowest particle emissions (see Table 1). But, to properly answer the question of what is the “most effective”, requires an examination of other parameters such as:

- What are the target emissions?
- What other contaminants need to be removed?
- What utilities are available?
- What is the available plot space?
- What is the importance of capital cost versus operating costs?

Apr-2021