Riser pressure drop

Riser pressure drop (1) Reversal Area Greater than Riser Area... 

The riser pressure drop is related mainly to the catalyst circulation rate and the slip factor. Catalyst circulation rate is largely a function of the oil feed rate, the reactor temperature, and the feed temperature. Increasing the feed rate, reactor temperature, or lowering the feed temperature will increase the pressure drop across the riser. 

The vapor-line riser pressure drop, including the vapor outlet nozzle loss. 

Another operational limit in the CFB system involves gas suppliers. Three types of gas suppliers, i.e., a reciprocating compressor, a blower with throttle valve, and a compressor, are commonly used in the CFB system. For blower operation, as the gas flow rate decreases, the pressure head of the blower increases. For compressor operation, the pressure head of the compressor can be maintained constant with variable gas flow rates. The interactive behavior between a CFB system and a blower can be illustrated in Fig. 10.9, where dashed curves refer to the blower characteristics and solid curves refer to the riser pressure drop. At point A, the pressure drop across the riser matches the pressure head provided by a blower thus, a stable operation can be established. Since the pressure drop across the riser in fast fluidization increases with a decrease in the gas flow rate at a given solids circulation rate, a reduction in the gas flow rate causes the pressure drop to move upward on the curve in the figure to point B with an increase in the pressure drop of Spr. In the case shown in Fig. 10.9(a), with the same reduction in the gas flow rate, i.e., SQ, the increase in the pressure drop, Spr, from point A to point B is greater than that which can be provided by... 

Riser pressure drop, reversal area greater than riser area. 

Chimney trays equipped with rectangular risers that stretch from one end of the tray to another often use open-top gutters ("rainwater conduits ) rather than hats (see Fig. 8.66 later). The gutters can be V-shaped or U-shaped, are mounted above the risers, and slope toward the short edges of the rectangles. Compared to hats, these reduce riser pressure drop and eliminate the downward velocity component of vapor leaving the chimneys, but at the expense of allowing some liquid to rain into the risers. This makes them less suitable for total drawoffs. 

For the KE and Ktf Reactors, No. 1 Safety Circuit trip results if process water riser pressure drops more than 60 psi below noiml. This trip setting Is optional, and may have substituted for It the trip setting of the flow detection device for individual process channels eis noted In Footnote 6. 

Riser pressure drop and densities can be calculated by a number of different methods e.g., Jazayeri (1991). Typically feed risers have an average density of 5 Lb/FF 10 Lb/Ft" at the bottom, 1 Lb/FF at the top. Including entrance and exit (separator) effects, riser pressure drop is usually in the 4 psi range. For optimum conversion, riser residence times are designed to be about 1.8 to 2.4 seconds based on outlet moles (i.e., the volume of the riser divided by the volume of hydrocarbon and steam exiting the riser). Most state-of-art risers are 100+ Ft long with an L/D ratio of over 20. 

The orifice-riser distributor is designed to lay the hquid carefully onto the bed, with a minimum of contact with gas during the process. It can be designed to provide a large number of liquid streams, with the limit of sufficient liquid head to provide uniform liquid flow through the orifices. The gas risers must oe designed to accommodate the expected variations in flow rate, often with a minimum of pressure drop. For veiy distribution-sensitive packings, it is necessaiy to include pour points in the vicinity of the column wall (to within 25 mm). 

The gas risers must have a sufficient flow area to avoid a high gas-phase pressure drop. In addition, these gas risers must be uniformly positioned to maintain proper gas distribution. The gas risers should be equipped w ith covers to deflect the liquid raining onto this collector plate and prevent it from entering the gas risers where the high gas velocity could cause entrainment. These gas riser covers must be kept a sufficient distance below the next packed bed to allow the gas phase to come to a uniform flow rate per square foot of column cross-sectional area before entering the next bed. 

Solve for the combined riser, reversal, annulus, and slot pressure drop by ... 

Cap assembly partial pressure drop, including drop through riser, reversal, annulus, slots, in. liquid Pressure drop through risers, in. liquid Pressure drop through reversal and annulus, in. liquid... 

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. 

The solid circulation rate (Gs, kgm-2s-1) can be controlled by aeration gas in the loop-seal to adjust pressure balance in the CFB loop. Solid circulation rate is a unique operating variable in the CFB system as a function of pressure drop across loop-seal of a CFB photoractor [10] and directly related to solid holdup in the riser where the photodegradation of TCE occurs. 

Solid holdup (es), the volume fraction of solids, and A/JriScr, pressure drop in the riser are defined as... 

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