Flow reversals

A stable pressure differential must be maintained across the slide valves. The direction of catalyst flow must always be fix m the regenerator 

Cavitation and/or toss of Main Column Bottoms Pumps 

Fouling and loss of Heat Transfer in Bottoms Exchanger 

Higher pressure drop across the Reactor Overhead vapor line 

Changes in Operating Conditions Changes in Catalyst Properties Changes in feedstock Properties Changes in Mechanical Conditions of the Equipment 

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Rheology is the science of the deformation and flow of matter. It is concerned with the response of materials to appHed stress. That response may be irreversible viscous flow, reversible elastic deformation, or a combination of the two. Control of rheology is essential for the manufacture and handling of numerous materials and products, eg, foods, cosmetics, mbber, plastics, paints, inks, and drilling muds. Before control can be achieved, there must be an understanding of rheology and an ability to measure rheological properties. 

Other modes of operation, including recycle and flow reversal schemes and continuous chromatography, are discussed in Ganetsos and Barker (Preparative and Production Scale Chromatography, Marcel Dekker, New York, 1993). 

No flow Reverse flow Less flow More temperature Less temperature Composition change Sampling Corrosion/erosion... 

When we translate these observations into Lagrangian wave speed, the data would look like that shown in the lower diagram of Fig. 7.11. The points e and q represent volume strains at whieh elastie-perfeetly-plastie release (e) and quasi-elastie release (q) would undergo transition to large-seale, reverse plastie flow (reverse yield point). The question is the following What is responsible for quasi-elastie release from the shoeked state, and what do release-wave data tell us about the mieromeehanieal response in the shoeked state ... 

The flow in the diffuser is usually assumed to be of a steady nature to obtain the overall geometric configuration of the diffuser. In a channel-type diffuser the viscous shearing forces create a boundary layer with reduced kinetic energy. If the kinetic energy is reduced below a certain limit, the flow in this layer becomes stagnant and then reverses. This flow reversal causes... 

In all static surge-detection devices, the actual plienonemon of flow reversal (surge) is not directly monitored. What is monitored are other conditions related to surge. Control limits are set from past experience and a study of compressor characteristics. 

Continuous flow With continuous flow operations consider (e.g. using a HAZOP procedure) the effects of No flow Reduced flow Reverse flow Increased flow Contaminated flow Flow of a substituted material, etc. 

Cowl A roof-mounted device designed to provide airflow out of a building with the minimum of flow reversal. 

Flow reversal The backflow that occurs when a fluid changes its flow direction due to an imposed pressure gradient. 

Wind stop A flat plate or a cone fitted over an outlet or inlet duct in order to reduce the possibility of flow reversal due to wind pressure. 

Does not have a tendency to slam shut on flow reversal. 

When the Imer is rotated past the no flow" point, the volume above the rotor exceeds that below, and net flow reverses direction even though pump speed and rotation have not changed (Limited to approx 30 cof lull forward How on all models)... 

The purpose of the regenerated catalyst slide valve is threefold to regulate the flow of regenerated catalyst to the riser, to maintain pressure head in the standpipe, and to protect the regenerator from a flow reversal. Associated with this control and protection is usually a 1 psi to 8 psi (7 Kp to 55 Kp) pressure drop across the valve. 

To protect the reactor and the regenerator against a flow reversal, pressure differential controllers are used to monitor and control the differential pressures across the slide valves. If the differential pressure falls below a minimum set-point, the pressure differential controller (PDIC) overrides the process controller and closes the valve. Only after the PDIC is satisfied will the control of the slide valve return to the process. 

Catalyst Circulation Catalyst Loss Coking/Fouling Flow Reversal... 

Steam scrubbers These use flow reversal in conjunction with a large contact surface area to remove BW mist from steam. 

Pressure drop on the tube-side of a shell and tube exchanger is made up of the friction loss in the tubes and losses due to sudden contractions and expansions and flow reversals experienced by the tube-side fluid. The friction loss may be estimated by the methods outlined in Section 3.4.3 from which the basic equation for isothermal flow is given by equation 3.18 which can be written as ... 

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