FCC Slurry Oil Filtration with Mott HyPulse® LSI Filters

Since 1990, Mott has delivered HyPulse® LSI Filters and Systems to many refinery sites located in the US, Europe, and China. Systems operate reliably over multiple cycles with consistent cycle lengths and long filter element lifetime. Operating systems continue to utilize filter elements originally provided with the system.

HyPulse® LSI Filter Description

Mott's HyPulse® LSI filters are backwashable metal filters that contain tubular porous metal elements installed in a tubesheet at the bottom of a vessel. During operation, the feed slurry containing suspended solids is introduced to the filter below the tubesheet and flows through the inside of the filter elements. Solids collect on inside surface of the elements as filtrate passes through the elements to the outside surface.

Mott HyPulse LSI Filter

The accumulation of solids on the inside surface of the filter elements is followed by backflushing to remove the solids as highly concentrated slurry. This process is as simple as flushing a slurry through a pipe.

The benefits of this configuration and operation are many:

Materials of Construction

Mott's standard filter elements are constructed entirely of 316L stainless steel. Other alloys are available for severe process conditions. For refinery FCC slurry oil, carbon steel is typically used as the filter vessel material for operating temperatures up to 600 Degrees Fahrenheit or 315 Degrees Celcius.

Mott Precision Filter Media

There are many types of backwashable filters in the commercial marketplace in a variety of mechanical configurations. What truly distinguishes one from the other is the filter media used in the filter. Media selection It is the key parameter for achieving the desired separation and for ensuring long operating life. Mott precision porous metal filter media has controlled porosity and pore size that maximizes efficiency. For backwash filters to be successful over time, the media must provide the particle retention efficiency required and backwash clean cycle after cycle. Typical Mott filter cycle performance is shown below:

Mott HyPulse LSI Filter Element Graph

Mott media, with its tightly controlled pore size, offers exceptional particle removal efficiency with minimal particle penetration into the media. The tightly controlled pore size and backwash operation of HyPulse® LSI filters enable long operating periods between cleanings. Keeping the solids on the surface results in efficient backwashing and long filter element life. Several HyPulse® LSI filters in slurry oil service have been operating with their original elements, contributing to low operating costs.

Previous FCC Slurry Oil Filter Installations

Mott has designed and installed slurry oil filtration systems with 24, 36, 42, and 66 inch HyPulse® LSI filters. These include single vessel installations operating on a continuous basis with an interruptible flow, and duplex or triplex filter system operating on a continuous basis. One filter operates online, one is on standby, and one is a spare used during maintenance periods. These filters operate on a simple cycle of filtration and backwash with an occasional flush with Light Cycle Oil. They have operated reliably and effectively since 1993.

Recent Advancements

When a major refinery approached Mott with a requirement for a high flow, high efficiency filter for FCC slurry oil, the scalability of the Mott HyPulse® LSI filter provided the obvious choice. The high flow requirement was satisfied by selecting a filter of sufficient size to contain the required number of filter elements. The high efficiency particle removal requirement was met with the proven Mott precision porous stainless steel media. Pilot filter testing confirmed all operating parameters. The required filter was 66 inches in diameter and is capable of processing in excess of 10,000 BPD slurry.

The requirement for a continuously operating process was satisfied by a Mott triplex filtration system, which included a backwash receiver. The normal operating mode has one filter on line, one on standby, and one as a spare. Given the reliability of Mott filters, extended cycle times were obtained by running two filters simultaneously, but staggered in cycle time, with the third filter being on standby for utilisation when one of the online filters requires backwashing. All three filters are employed in the filtration cycle to make maximum utilization of the available surface area.

For maximum operating efficiency, product oil is purged from the filter housing and is replaced with LCO for backwashing. This is completed without loss of solids during the fluid exchange, one of the features of the HyPulse® LSI design.

This filter installation represents a major enhancement of HyPulse® filter technology in both the scale of design and operating efficiency. The system operation takes advantage of every design feature of the HyPulse® LSI filter, resulting in maximum economic benefit to the refinery. As noted earlier, Mott's customer realized the benefits of the HyPulse® LSI design and promptly selected an identical system for a second refinery.

A review of the system's process conditions, filtration requirements, design specifications, and operating results is summarized below:

Process Fluid : FCC Slurry Oil
Gravity, API : -1.0
Process Rate : More than 10,000 BPD
Slurry Solids Concentration : 1,000 ppm
Product Solids Concentration : Not to exceed 50 ppm
Operating Temperature : 450-550 Degrees F / 232-288 Degrees C
Operating Pressure : 50-130 Psi / 3.5-8.9 Bar
Minimum Cycle Time (Interval between Backwashes) : 2 Hour
Filter Backflush Liquid : Light Cycle Oil
Operation : Continuous with maximum interchangeability between the filter vessels. Backwash solids to a receiver tank with LCO.

Operating Results

Filtrate Quality - The filter system has consistently delivered product solids concentration well below the required maximum.

Filter Cycle Time - With low viscosity resulting from high slurry temperatures, and high cycle pressure drop of 60 psi, filter cycles between backwashes exceeded 4 hours with one filter online at full flow rates, and more than 16 hours with two filters online.

Process Efficiency - With long cycle times, the efficiency of recovered product as a percentage of feed slurry exceeds 99.8%. For every 1000 barrels of filtered product slurry, only 2 barrels are lost to the backwash. Cycle time is affected by the oil viscosity, operating filtration flux rate, and rate of solids to the filter. Since the filter loads to a certain solids level under prescribed conditions, the filtration cycle can change with these variables.

Filter Pressure Drop - Clean pressure drop (i.e. pressure drop seen after a backwash) has been very stable at under 3 Psi / 0.2 Bar, indicating that the filter media is being cleaned effectively by the backwash. The dirty filter pressure drop is program adjustable up to the design limit of 100 Psi / 6.9 Bar. The typical cycle pressure drop is set for 60 Psi / 4.1 Bar for routine operation to reduce wear and tear on the equipment.

The unique HyPulse® LSI design provides for high pressure drop capability that significantly extends the filter cycle time. The precision pore size filter media is designed to work at these pressures without plugging due to particle penetration. In actual operation, inadvertent pressure drop excursions as much as 40% above desired operating limits have had no affect on the filter, the media, or subsequent filter cycle performance.

Conclusions

The Mott HyPulse® LSI has performed from startup beyond the requirements and expectations of the customer. The mechanics of the system have functioned very well with few corrections required. This latest installation is one of a series of successful HyPulse® LSI applications that continue to demonstrate state of the art filtration with Mott filters.

Registered Address - Venturi Jet Pumps Ltd, Venturi House, Edensor Road, Longton, Stoke on Trent, Staffordshire, ST3 2QE, United Kingdom
Tel. : +44 (0) 1782 599800, Fax. : +44 (0) 1782 599009
Company Registration Number - GB 3654492