How to Protect your Fixed-bed Reactors from Contamination
February 2, 2012 Leave a comment
How liquid filtration systems protect fixed-bed reactors from contamination, leading to extended catalyst life and longer run lengths.
In the petroleum refining industry, catalysts represent a significant cost, so refineries are chiefly concerned with extending a catalyst’s life as long as possible. The simplest way to do this is to protect the fixed-bed reactor from becoming contaminated with dirt, carbon deposits, and other organic materials. These items can cause the bed to plug, resulting in decreased reaction efficiency, and potentially require the unit to be brought down early. Catalysts must then be regenerated or replaced.
In general, catalyst bed protection requires the filtration of all particles larger than 25 microns from the feedstock stream. Particles that are smaller than 25 microns will pass through the reactor bed without plugging the catalyst.
Three major factors must be taken into consideration when selecting a proper filtration system:
- Flux rate
- Filtration media
- Clean ability
The size of the filtration system is dependent on the flux rate, which is defined s the flow rate per unit of filtration area.
For example, 100 gpm of VGO flowing through a filtration system with 50 ft2 of filtering area represents a flux rate of 2 gpm/ft2. It can be seen from this flux rate formula that an increase in filtration area will lead to a lower flux rate, which will in turn result in a lower velocity of the fluid as it passes through the media.
Lower flow velocity across the filtering media allows the formation of a porous cake on the surface of the media. This leads to longer run times between backwash cycles and increases efficiency in particle removal.
This cake formation also has the added benefit of preventing particles from becoming embedded in the media, allowing for easy removal of particulate during the backwash cleaning cycle.
Filtration Media and Clean ability:
When selecting a feedstock filtration system, another important consideration is media type and its clean ability.
Possible media choices include slotted wedge wire, woven wire mesh, and multi-layered sintered metal. Each one carries its own advantages and disadvantages, but perhaps the most critical consideration when choosing a feedstock filtration system is the ability to completely regenerate the filtration media to its original clean state.
If the media is not sufficiently cleaned, the result is shorter run times and will eventually require the filter to be bypassed for manual cleaning or media replacement.
In summary, feedstock filtration is an important aspect in efficiently refinery operation. Protecting catalyst beds from particulate contamination prevents bed plugging and increases catalyst life. Several factors affect filtration system efficiency and should be carefully considered when selecting a feedstock filtration system.