Regenerator pressure drop

An example is shown in Figure 4-84, whieh represents the regenerator pressure following a malfunetion of the expander bypass valve. The bypass valve trips open in 1 see while the expander inlet valve maintains eontrol. Tlie regenerator pressure drops approximately 2.0 psi before starting to reeover. The inlet valve stroking time was 10 see and the eontroller settings were 5% proportional band and 30 see reset. 

The regenerator pressure fell by 28 mbar. This value was within the eontraetually agreed limits. Nevertheless, two further tests were performed with modified parameters. Five hours after beginning the optimization proeess, a test was performed in whieh the regenerator pressure dropped by just 8 mbar. This value is within the normal operating spread of the regenerator output pressure. 

The cyclones are typically designed with diameters of 100—160 cm for ease of maintenance. Cyclone inlet velocities are usually restricted to 18—21 m /s in the first stage and to 20—26 m/s in the second stage to achieve satisfactory pressure drop and erosion characteristics (62). The number of sets of two-stage cyclones thus depends on the total gas flow. Finding room to house all the necessary cyclones within the regenerator frequently requires considerable ingenuity (62). 

The expansion turbine converts the dynamic energy of the flue gas into mechanical energy. The recoverable energy is determined by the pressure drop through the expander, the expander inlet temperature, and the mass flow of gas (66). This power is then typically used to drive the regenerator air blower. 

Dyna Sand Filter. A filter that avoids batch backwashing for cleaning, the Dyna Sand Filter is available from Parkson Corporation. The bed is continuously cleaned and regenerated by recycling solids internally through an air-lift pipe and a sand washer. Thus a constant pressure drop is maintained across the bed, and the need for parallel fdters to low continued on-stream operation, as with conventional designs, is avoided. 

In the design of reactors for fluids in the presence of granular catalysts, account must be taken of heat transfer, pressure drop and contacting of the phases, and, in many cases, of provision for periodic or continuous regeneration of deteriorated catalyst. Several different lands of vessel configurations for continuous processing are in commercial use. Some reaciors with sohd catalysts are represented in Figs. 23-18 and 23-24. 

The regenerator (Figure 4-80) is represented by a simplified model that ineludes the total volume and mass balanee ealeulation. The regenerator exit temperature is assumed eonstant for the duration of the transient. The third-stage separator is handled as a fixed volume and assoeiated pressure drop. Blow-down (bypass) flow is subtraeted from the input flow. 

In the dynamic simulation run, the pressures and flowrates at the input and output of each module are known. It is, therefore, possible to perform non-linear correction of the control mode, such that the changes in regenerator pressure in the event of load shedding are minimized. In a test performed with a correspondingly corrected controller structure, the pressure drop after load shedding was reduced from 46 mbar to 19 mbar. The subsequent pressure rise of 27 mbar is just below the specified threshold. 

These trimming faetors ean, for instanee, be used to reduee the bypass valve step in eomparison to that ealeulated. Opening the bypass valve too mueh ean eause the regenerator pressure to drop, eausing eatalyst to enter the expander and exit the staek. This should be avoided, whieh ean be aehieved by the trimming faetors. 

Inereasing the effeetiveness of a regenerator ealls for more heat transfer surfaee area, whieh inereases the eost, the pressure drop, and the spaee requirements of the unit. 

Figure 2-5 shows the improvement in eyele effieieney beeause of heat recovery with respect to a simple open-cycle gas turbine of 4.33.T ratio pressure and 1,200°F inlet temperature. Cycle efficiency drops with an increasing pressure drop in the regenerator. 

The process consists of a reactor section, continuous catalyst regeneration unit (CCR), and product recovery section. Stacked radial-flow reactors are used to minimize pressure drop and to facilitate catalyst recirculation to and from the CCR. The reactor feed consists solely of LPG plus the recycle of unconverted feed components no hydrogen is recycled. The liquid product contains about 92 wt% benzene, toluene, and xylenes (BTX) (Figure 6-7), with a balance of Cg aromatics and a low nonaromatic content. Therefore, the product could be used directly for the recovery of benzene by fractional distillation (without the extraction step needed in catalytic reforming). 

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. 

Higher catalyst circulation usually requires opening the regenerated and spent catalyst slide (or plug) valves. Higher circulation increases the pressure drop in the riser and in the reactor cyclones, lowering the differential pressure across the slide valves. This causes the valves to open further, until the unit finds a new balance. 

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. 

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 ... 

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