FUNCTIONAL DESIGN OF PROCESSING VESSELS
Besides ordinary storage of bulk solids, silos can also act as processing vessels in which materials are dried, purged of VOCs, heated, cooled, cured, conditioned, or tempered. To facilitate processing, the vessels are equipped with heat exchangers or are modified to permit gas injection. Examples of processing vessels for bulk solids include:
- Purge columns for polyolefins
- Sugar conditioning silo
- Hopper dryers for removing moisture from biomass
- Moving bed reactors
- Grain dryers and/or wheat tempering vessels
At Jenike & Johanson, we use a scientific method to design processing vessels based on measured kinetic, thermal, and flow properties of the bulk solids. Using our proprietary two-phase flow models, we are able to calculate solids stress and gas profiles, which allows us to design systems providing efficient processing while preventing flow problems such as plugging, erratic flow, and segregation.
From our tests and analyses, we are able to recommend::
- Outlet dimensions that prevent flow obstructions
- Hopper angles that ensure mass flow
- Dryer or purge column residence time
- Maximum gas injection rates
- Anti-channeling gas distribution systems (J-Purge™)
Jenike & Johanson can also provide complete design engineering services and supply equipment based on our functional design recommendations. We also are able to perform structural and load calculations using our unique proprietary methods in addition to commercial software.
Solids Processing Vessel Improves Product Quality at BP
Problem
A polypropylene (PP) unit at INEOS’ Geel, Belgium facility included a purge column in the design downstream of the reactors to remove trace volatiles and neutralize the catalyst. The column design did not originally perform adequately because of the poor performance of the inverted cone gas distribution design.
In spite of the benefits of purge vessels, problems can occur that limit their effectiveness. Incomplete purging can be caused by localized fluidization, non-uniform gas distribution, and non-uniform solids velocity profiles and result in off-grade product, fire/explosion risks, environmental compliance issues, or downstream handling problems. Other problems include excess purge gas usage and product cross-contamination during grade changeovers.
 Poor purging due to solids stagnation in silo |
Solution
The first steps were to define the process requirements and to determine the flow properties of the solids and the gas usage requirements. Based on the flow properties measured for the polypropylene, we developed the functional design for the purge column. It was designed to deliver a robust residence time distribution of the PP, based on the material’s internal and wall friction. Purge gas was introduced just above the top of the conical hopper section using our patented J-Purge™ technology. The design provided a uniform distribution of the purge gas, with no adverse effects on the flowing solids.
 Calculated purge profiles |
Success in the field
The purge column has been in operation now for over a decade and has performed very well, meeting the design basis. According to Jim Lee, Research Associate and lead on the project, “the performance of the purge column has exceeded our expectations. In fact, it did not require any modification when the rest of the PP unit was debottlenecked by 40%.” This technology has been incorporated into subsequent plants which use the INEOS gas phase process.
 Installed purge column |
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 Construction of purge vessel
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 Example of purge column internals
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 Conditioning silo configuration
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