Retrofit solution results in 7 times on stream life for HGO filtration 

Understanding the Problem

The client suspected that the problems were associated with an additional feed stream that had a high percentage of wax solids. Detailed particle size and TSS analysis was performed on the feed streams at varying temperatures. This proved that the solid wax component was removed at the process operating temperatures and that the short filter life was down to the dirt holding capacity of the filters installed. 

Process Flow Diagram showing position of filters protecting downstream FCC catalyst beds.  

The existing filtration system consisted of a 2 housings in duty / standby configuration . Each housing containing 36 x 40" metal mesh filters (single cylindrical wrap design). While this is a low cost filter format it has major drawbacks when on stream life and dirt holding capacity are critical. This is due to the low effective surface area of each filter combined with the fact that they use only a single layer of mesh. The total surface area of the 36 filters only provided a filtration surface area of approximately 4.7 sqm. The original installation and filters are shown below.

When the filters reach an operation differential pressure of 1.2 Bar they are removed and cleaned for re-use. The removal and cleaning of 36 filters is and arduous and time consuming task. 

The Solution

Two key areas of improvements were identified. 

• Substantially extending the on stream life of the filter system
• Minimising the maintenance time required for filter change out 

Both of these needed to be achieved with minimum disruption to the process.

A review of the existing housing design revealed that the filter sheet (where the filters are located) was a bolted on feature. This provided the opportunity to change to a more efficient filter format without the need to replace the filter housing itself.  A new assembly was designed which could be simply lowered and installed into the existing housing. This featuring only 4 off SupaMesh HighFlow cartridges to replace the 36 originals. 

The SupaMesh HighFlow filters utilise a pleated construction maximising the available filtration surface area per filter. These 4 filters cartridges provided a 30% increase in surface area compared to the 36 original filters.

They also incorporate multiple filtration layers, unlike the original single layer mesh. This maximises dirt holding and consequently on stream lifetime.

The Results 

The new retrofit basket assembly was lowered into the existing housing on site, followed by the installation of the 4 SupaMesh HighFlows. 

The new filter operated along side the original filters in the duty / standby configuration. Over a 6 month evaluation period the new SupaMesh installation has consistently delivered up to 7 times the operational life of the originals.  

The retrofit solution delivered a clear operational improvement, using the same vessel and without changing the broader process conditions.  

• Reduced cleaning frequency from as often as twice per day to around once every seven days. 
• The change out and cleaning time for the 4 filters was substantially lower than with 36. The consequence is a freeing up of maintenance resource to concentrate on value added projects.
• Retained the existing vessel shell through a retrofit approach (eliminating capital spend and reducing engineering and installation time)
• Improved operational reliability for heavy gas oil filtration
• Lowered maintenance intervention requirements for the site team