Channel head pass partition baffle

This improved heat-transfer rate, promoted by low velocity, applies not only for condensing steam but also for condensing other pure-component vapors. And since condensation rates are favored by low velocity, this permits the engineer to design the steam side of reboilers and condensers in general, for low-pressure drops. For example, if we measured the pressure above the channel head pass partition baffle shown in Fig. 8.1, we would observe a pressure of 100 psig. The pressure below the channel head pass partition baffle would typically be 99 psig. 

One important feature of Fig. 8.6 is the condensate drum balance line. Note, that this line is connected below the channel head pass partition baffle. This ensures that the pressure in the channel head, below the pass partition baffle, and the pressure in the condensate drum, are the same. If these two pressures are not identical, then the level in the condensate drum cannot represent the level in the channel head. For this reason, never connect the condensate drum vapor space to either the steam supply line or the top vent of the reboiler s channel head. 

Steam produced from demineralized water is free of carbonates. Steam produced from lime-softened water will be contaminated with carbonates that decompose in the boiler to carbon dioxide. As the steam condenses in a reboiler, the C02 accumulates as a noncondensable gas. This gas will be trapped mainly below the channel head pass partition baffle shown in Fig. 8.6. As the concentration of C02 increases, the C02 will be forced to dissolve in the water ... 

The center channel head pass partition baffle is cut out. 

Two off-center channel head pass partition baffles are welded in place, so that 25 percent of the tubes are above the upper baffle and 25 percent of the tubes are below the lower baffle. 

Accupfiulations of non-condensables in the channel head will also retard the condensation rate of steam and lead to a loss in reboiler duty. Typically, CO2 contained in the steam supply collects below the bottom channel head-pass partition baffle. If left to accumulate, the CO2 will dissolve in the steam condensate and form corrosive carbonic acid. 

Excessive tube-side pressure drop due to fouling can cause the channel head pass partition baffle to fail. (Consult the TEMA data book for exchanger details. ) This pass partition baffle prevents the crude from bypassing the tube bundle. However, as the tube-side AP rises, this baffle will eventually fail and lead to a sudden loss in the preheat exchanger duty. The maximum allowable pressure difference across this baffle should be listed on the exchanger data sheet. 

Most of my experience with this subject is a loss in reboiler duty (over one day) due to a tube leak, or the more gradual loss of reboiler duty (over one month) due to CO accumulation in the channel head. Regardless, to alleviate the loss of reboiler duty, vent the channel head just belozv the bottom channel head pass partition baffle. 

I see this frequently when tube bundles are extracted from the shell during a unit turnaround. The distorted tubes interfere with the proper fluid flow through the shell side of the exchanger and likely promote both shell-side fouling and shell-side bypassing. Also, as the tubes plug off, tube-side AP increases. If half the tubes plug, then the differential pressure across the channel head pass partition baffle will increase by a factor of four and may result in the failure of the channel head pass partition baffle. 

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