Flashing condensate

One pound of steam at Opsig occupies 1,600 times the volume of a pound of water at atmospheric conditions. This ratio drops proportionately as the pressure increases. When the steam collapses, water is accelerated into the resulting vacuum from all directions. This happens when a steam trap discharges relatively high-pressure flashing condensate into a pump discharge line. 

Two-phase flow is beyond the scope of this pocket guide. One word of advice Be careful when designing low pressure and/or flashing condensate lines. These deserve special care. Ruskin10 has a quick method for condensate line sizing. 

A computer algorithm has been developed for making multi-component mixture calculations to predict (a) thermodynamic properties of liquid and vapor phases (b) bubble point, dew point, and flash conditions (c) multiple flashes, condensations, compression, and expansion operations and (d) separations by distillation and absorption. 

To be useful, this type of simulator must calculate the thermodynamic properties of multicomponent mixtures in both liquid and vapor phases while predicting bubble and dew points or partial vaporizations or condensations. Using this basic information, the simulator must then make calculations for other processes, such as gas cooling by expansion, gas compression, multiple flashes condensations, and separations by absorption... 

The least problematic stream is the flash condensate obtained when depressurizing the digesters to 1 ATM. Stemming from a vapor, this stream is, of course, free of pentose as the latter is nonvolatile, and for the same reason it is free of calcium sulfate. Consequently, this small stream containing some furfural is readily submitted to distillation to recover the furfural. 

The following equations are used to determine the pressure drop for flashed condensate mixture [20]. 

The computer program PROG37 evaluates the pressure drop of any given condensate header. The program also determines whether the velocity of the flashed condensate mixture would cause deterioration in the header line. Table 3-15 illustrates the results for the 4-, 6-, and 8-inch headers. Table 3-16 shows a typical input data and computer output for the 4-inch (Schedule 40) pipe. The computed results show that the 4-inch pipe gives the velocity of the flashed condensate mixture to be 7055 ft/ min. This indicates a possible deterioration in the pipe. For the 6- and 8-inch pipes, the velocities are 3109 ft/min, and 1795 ft/min respectively, indicating that the condensate pipe lines will not deteriorate. 

FLASHED CONDENSATE MIXTURE VELOCITY IS GREATER THAN 5000 ft./min. DETERIORATION OF THE LINE IS POSSIBLE... 

PRESSURE DROP OF FLASHED CONDENSATE MIXTURE, psi/iooft. 

FLASHED CONDENSATE LIQUID DENSITY, lb/ft 3. DENSITY OF MIXTURE (FLASHED CONDENSATE/STEAM) lb/ft"3. 

STEAM CONDENSATE PRESSURE BEFORE FLASHING, psia. FLASHED CONDENSATE HEADER PRESSURE, psia. TEMPERATURE OF FLASHED CONDENSATE, OF. 

VELOCITY OF FLASHED CONDENSATE MIXTURE, ft/min. TOTAL FLOW OF MIXTURE IN CONDENSATE HEADER, Ib/h. WEIGHT FRACTION OF CONDENSATE FLASHED TO VAPOR. FLASHED STEAM FLOWRATE, Ib/h. 

FORMAT (lOX, FLASHED CONDENSATE MIXTURE VELOCITY IS GREATER, ) WRITE (1, 210)... 

For most flashing-condensate services, a standard stainless steel control valve will provide long reliable life. Special trims and seats are available for high-pressure service. The control valve should always be sized for flashing service. In many instances, this wiil require a large valve-body with reduced trim to maintain valve-position control, because the flash steam causes high back pressure in the small valve-bodies. 

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