Poor flow distribution

Distributors in industrial units typically have large numbers of injection points of quite diverse design characteristics, some of which are depicted in Eigure 16 for fluidized-bed appHcations. Flow variations through these parallel paths can lead to poor flow distributions within a reactor, thus reducing product yields and selectivity. In some circumstances, undesirable side products can foul portions of the distributor and further upset flow patterns. Where this is important, or where the possibiHties and consequences are insufficiently understood and independent means caimot be employed to assure adequate distribution, the pilot plant must be sized to accommodate such a distributor. Spacing should be comparable to those distributors that are anticipated to be... 

Poor flow distributions may result in localized dry hotspots which, absent control of the temperature fluctuations, may cause rapid overheating. Temperature and pressure fluctuations, and poor flow distribution, are the main problems that accompany the use of two-phase micro-channels. 

It can be seen that poor flow distribution causes the efficiency to decrease. With much larger systems, this effect can end up being significant and may cause the baghouse to be out of compliance. 

Flow reversal is more likely to occur in parallel-flow systems that are subject to poor flow distribution. 

The maintenance of uniform flow distribution in fixed bed reactors is frequently a problem. Undesirable flow patterns lead to excessive spreads in the distribution of residence times with adverse effects on the reactor performance, particularly when consecutive reactions are involved. Poor flow distributions may aggravate problems of hot-spot formation and lead to regions of the reactor where undesired reactions predominate. Disintegration or attrition of the catalyst may lead to or may aggravate flow distribution problems. 

Low Initial Catalyst Activity Due to Poor Flow Distribution During Presulfiding. 

One manifestation of hydrotreater malfunctioning is low conversion. This is usually noted on the basis of past history on the feedstock or from scaleup correlations from pilot plant data. Poor presulfiding, as mentioned above, can cause low catalyst activity. However, not only process malfunctions can cause problems in activity but also poor flow distribution during presulfiding. 

Air-cooled reactor effluent coolers of hydrocracking and hydrotreating units are also prone to impingement-type corrosion. Poor flow distribution through large banks of parallel air coolers can result in excessive flow velocities in some coolers, usually those in the center. The resulting low flow velocities in the outer coolers can canse deposition of ammonium sulfide and/or chloride in these coolers this blocks the tubes and further increases velocities in the remaining air coolers. 

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