Catalyst slide valve

Figure 4-50. Catalyst slide valve. (Source Enpro Systems, Channelview, Texas.)...

Regenerated Catalyst Slide Valve, AP Spent Catalyst Slide Valve, AP... 

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. 

The spent catalyst slide valve is located at the base of the standpipe. It controls the stripper bed level and regulates the flow of spent catalyst into the regenerator. As with the regenerated catalyst slide valve, the catalyst level in the stripper generates pressure as long as it is fluidized. The pressure differential across the slide valve will be at the expense of consuming a pressure differential in the range of 3 psi to 6 psi (20 kp to 40 kp). 

Reactor dilute phase (dome) pressure Reactor catalyst dilute phase bed level Reactor-stripper catalyst bed level Reactor-stripper catalyst density Spent catalyst standpipe elevation Pressure above the spent catalyst slide valve Spent catalyst slide valve AP ( 55% opening)... 

Pressure above the regenerated catalyst slide valve = 30.5 psig/210.3 K,... 

The pressure below the spent catalyst slide valve is ... 

The reactor or stripper catalyst level controller is controlled with a level controller that regulates the movement of the spent catalyst slide valve. The regenerator level is manually controlled to maintain catalyst inventory. 

Regenerated and Spent Catalyst Slide Valve Low Differential Pressure Override... 

Normally, the reactor temperature and the stripper level controllers regulate he movement of the regenerated and spent catalyst slide valves, le algorithm of these controllers can drive the valves either fully Of [ or fully closed if the controller set-point is unobtainable. It is ext nely important that a positive and stable pressure differential be mail ined across both the regenerated and spent catalyst slide valves. r safety, a low differential pressure controller overrides the tempera re/level controllers should these valves open too much. The shutdov is usually set at 2 psi (14 Kp). 

Sometimes insufficient differential across the regenerated catalyst slide valve is not due to inadequate pressure buildup upstream of the valve, but rather due to an increase in pressure downstream of the slide valve. Possible causes of this increased backpressure are an excessive pressure drop in the Y or J-bend section, riser, reactor cyclones, reactor overhead vapor line, main fractionator, and/or the main fractionator overhead condensing/cooling system. 

Similarly, a negative pressure differential across the spent catalyst slide valve can allow hot flue gas to backflow to the reactor and the main fractionator, severely damaging the mechanical integrity of these vessels. 

Beyond the standpipes, the available delta P across the valve is affected by the pressure drop in other circuits. For the regenerated catalyst slide valve, downstream pressure is affected by ... 

The regenerated catalyst slide valve upstream pressure is increased by ... 

The pressure balance should be examined to determine the normal pressure readings in the reactor, regenerator, air system, flue gas system, and main fractionator and overhead system. These need to be followed on a time basis and plotted against variables such as feed rate, wet gas rate, and dry gas rate to see if and where problems may occur. Adjustments may be possible if the spent or regenerated catalyst slide valve delta P is at a minimum to provide more operating room. 

The above discussion emphasizes an interesting and vital aspect of troubleshooting an FCCU the hydraulic relationship between the wet gas compressor, the combustion air blower, the floe gas slide valve, the spent catalyst slide valve, and the regenerated catalyst slide valve. A schematic... 

Catalyst slide-valve two-phase flow model... 

At a given reactor outlet temperature, lowering the temperature of the feed oil increases cat/oil (the regenerated catalyst slide valve opens up to supply more hot catalyst to the riser to make up for the reduction in enthalpy of the feed). 

Motor Octane Number ( C or clear indicates lead free) Regenerated Catalyst Slide Valve Rare Earth Y zeolite... 

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