Universal filter for ultra-cleaning of reactor streams

Magnetically induced filter removes solid particles to protect catalyst active pore openings from plugging.

Fu-Ming Lee, Mark Zih-Yao Shen, Chi-Yao Chen, Maw-Tien Lee, Yin-Hsien Chen, John Lee and Stephen Yen
Shin-Chuang Technology Co., Ltd.
Kao-chih Ricky, Hsu International Innotech, Inc.

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Article Summary

A magnetically induced filter has been developed and commercially implemented to remove essentially all types of solid particles of any size (down to 7 nm or less) with substantially reduced costs and simpler operations. The impact of nanometer particles removal from liquid streams to the reactor is huge since it protects (or minimises) catalyst active pore openings from plugging, thereby greatly prolonging the catalyst life.

Minimising solid particles
Pipelines and equipment seen in refineries and petrochemical plants are generally made with carbon steel, which is subject to corrosion by hydrogen sulphide (H2S), organic sulphur compounds, and other acidic compounds in crude oil and in-plant petroleum or petrochemical streams. Corrosion of carbon steel equipment generates iron sulphide (FeS), iron oxides (FeO/Fe2O3), and other metal-containing solid particles in the process streams, which may cause severe plugging problems in fixed-bed reactors, lines, valves, and pumps.

The solid particles are removed from liquid streams mainly by filtration. The following methods are currently used to minimise the solid particles in the feed stream before entering the reactor:
Å’ Conventional filter cartridges and/or filtering screens are normally used to remove only large solid particles (larger than 25-50 microns) from process streams. They are easily plugged by the solid particles and require frequent cleaning or costly cartridge replacement, disrupting process operations at significant costs. Furthermore, frequent cleaning and filter cartridge replacement increase the chance of air (oxygen) getting into the filter and reactor, promoting polymerisation of dienes and olefins in the reactor, which causes even more severe pressure drop and plugging problems. To remove additional particles from the liquid stream and provide a better fluid distribution, macropore solids are also packed into the top of the reactor.

In recent years, reticulated top bed materials have been packed in the top of the reactor to improve solid particles removal and fluid distribution into the catalyst bed, thereby minimising pressure drop and promoting reactor performance. Depending on the types of reticulated top bed materials, additional solid particles with sizes larger than 1.0 micron are removed from the liquid stream before reaching the active catalyst bed.

It should be noted that the conventional methods are designed to remove micron-size (10-6 m) solid particles only and are incapable of removing ultra-small nanometer (10-9 m) particles from the process streams. For example, the reticulated top bed technology can only remove solid particles from 1-1,500 microns in size. Unremoved ultra-small particles in the liquid stream tend to plug the pore opening of the catalyst active sites in the downstream reactor.

Pore size distribution (PSD) of commercial hydrodesulphurisation (HDS) catalysts for treating petroleum or coal tar liquids is in nanometer ranges. Two examples are listed as follows:
Å’ For HDS of FCC gasoline, a CoMoS/Al2O3 catalyst was prepared with the alumina having tri-modal pore distribution at approximately 5-8 nm, 15-20 nm, and 90-100 nm.1

For HDS of vacuum resid, a high activity catalyst having a unimodal with maximum pore volume in the medium mesopore range (within 10-25 nm diameter) was prepared.2
Therefore, it is highly desirable to develop a filter capable of effectively removing solid particles of all sizes from the reactor streams, including the ultra-small nanometer-size particles, to protect the catalyst pores from plugging at reduced costs.

Filter performance
Shin-Chuang Technology (SCT) Co.’s magnetically induced Universal Filter removes all types of solid particles down to 7 nm or less at substantially reduced cost and simpler operation. This filtration system achieves a near-total prevention of solid particles in the liquid stream from entering the reactor.

Furthermore, the need for expendable macropore filtration packings in the reactor and filter cartridges at reactor feed entry is substantially eliminated (or minimised) to save material and operational costs, which include loading/unloading and disposal of the spendable materials. The only requirement is that the solids in the liquid stream contain certain amounts of ferromagnetic (FM) substances, such as FeO, FeS, Fe2O3, Ni, NiO, Co, and CoO.

In fact, solid particles in liquid streams feeding to HDS reactors for treating light coal tar from steel mills and FCC gasoline, straight-run naphtha, diesel, and kerosene fuels from refineries or petrochemical plants meet these FM requirements. So far, all commercial applications are successful, as shown in the ensuing discussions.

Treatment of a light coal tar feed stream to HDS reactor
As shown in Figure 1, approximately 52,000 MT/Y of light coal tar from a steel mill is fed to first chamber C1 and secondly to chamber C2 (of the Universal Filter) through valve V1 for removing the solid particles from the liquid stream. The filtered liquid is then transferred to an HDS reactor via valve V2. During the regeneration cycle, water through valves V6 and V7 is used to flush out the solid sludges in both chambers and discharged via valve V5, while valves V1 and V2 in the process side are closed.

To test filter performance, the filter was on-stream continuously for 45 days, treating 6,529.6 metric tons (145.1 MT/D) of light coal tar liquid without regeneration (backwashing). Liquid coal tar samples containing 92% benzene, 5% toluene, and other C6-C7 naphthas were collected from inlet and outlet streams of the filter. A sample of solid slurry accumulated in the filter during the operation was also collected simultaneously for testing and analysis.

Å’ Percent and types of solid removal from process fluid by Universal Filter:
From analysis of the filter inlet and outlet liquid samples, it was determined that as high as 97.6 wt% of the solids were removed by the filter, based on the following measurements:
Weight of total solids collected from 13 litres inlet liquid sample: 0.5877g
Weight of total solids collected from 13 litres outlet liquid sample: 0.0144g
Wt% of solid removal by Universal Filter:  1 - (0.0144/0.5877) = 97.6 wt%

XRF analysis in Table 1 shows that the filter can effectively remove all types of solids, including FM and diamagnetic (DM)/paramagnetic solids, through induced magnetism with the FM inducing agents under an external magnetic field in the filter. Surprisingly, removals of Fe, S, Mn, Mo, and Cu were almost complete (100%), Al and Cr were around 90%, and Ni and Cl were 60-70%.

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