Jackets pressure drop

Chapter 7, Reactor Design, discusses continuous and batch stirred-tank reactors and die packed-bed catalytic reactor, which are frequently used. Heat exchangers for stirred-tank reactors described are the simple jacket, simple jacket with a spiral baffle, simple jacket with agitation nozzles, partial pipe-coil jacket, dimple jacket, and the internal pipe coil. The amount of heat removed or added determines what jacket is selected. Other topics discussed are jacket pressure drop and mechanical considerations. Chapter 7 also describes methods for removing or adding heat in packed-bed catalytic reactors. Also considered are flow distribution methods to approach plug flow in packed beds. 

Consider a single-zone jacket where there is an increase in the jacket flow, and a corresponding increase in the outside film coefficient because hj =f(Njjg, G). Therefore, a two-fold increase in the jacket flow results in an increase in hjj by 2 h . The overall heat transfer coefficient U = l/[FpoL + 1/hj], and a larger outside coefficient subsequently increases the overall heat transfer coefficient. The overall heat flux will increase due to the combined effects of the increased flow and lower jacket outlet temperature. The net result is an increase in the pressure drop. 

To reduce the pressure drop, a batch reactor with a half-pipe jacket of length L and flowrate W can be partitioned into a two-zone jacket, each with a length L/2 and each supplied with W jacket flowrate. This doubles the jacket flow at a lower pressure drop in each zone. The flow in each zone can then be increased to increase the outside and overall heat transfer coefficients, which is similar to those of the single-zone jacket. 

The manufacturer can furnish complete data on temperatures for the particular design together with the quantity of water circulated and the pressure drop through the jackets. 

Applying these factors to the 5= 128 scaleup in Example 5.10 gives a tube that is nominally 125 = 101 ft long and 1.0495 = 4.1 inches in diameter. The length-to-diameter ratio increases to 298. The Reynolds number increases to 85005 = 278,000. The pressure drop would increase by a factor of 0.86 j jjg temperature driving force would remain constant at 7°C so that the jacket temperature would remain 55°C. 

Estimate the heat transfer coefficient at the outside wall of the reactor and the pressure drop through the jacket. 

The span of the temperature transmitter is 100-200°F. Control valves have linear trim and constant pressure drop, and are half open under normal conditions. Normal condenser flow is 30 gpm. Normal jacket flow is 20 gpm. A temperature measurement lag of 12 seconds is introduced into the system by the thermowell. 

VENDOR SHALL STATE THE REQUIREO FLOWS. PRESSURE DROPS AND DESIGN DUTIES FOR EACH JACKET. STILL CONDENSER, AND FREEZEOUTTRAP. 

Use equation 12.18 for estimating the pressure drop, taking the friction factor from Figure 12.24. As the hydraulic mean diameter will be large compared to the roughness of the jacket surface, the relative roughness will be comparable with that for heat exchanger... 

VENDOR SHALLSTATETHE required flows, pressure drops ano design DUTIES for each jacket, still CONDENSER, AND freezeouttrap. 

The most satisfactory columns are usually the ones with a low pressure drop, since they are much less prone to flood. The spinning-band column appears to be one of the best for this purpose, and a concentric-tube column, except for the slow take-off rate, is also fairly satisfactory. A glass-helix-packed column is usually unsatisfactory because of a great tendency toward flooding. Metal packing is more desirable in this respect. With most columns, it is advisable to hold the jacket at a somewhat higher temperature (5 to 10°) than the vapor temperature because of this increased tendency toward flooding. 

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