Flashing steam condensate

For the frequent case of flashing steam-condensate lines, Ruskan supplies the handy graph shown above. 

Figure 2-54. Sarco flashing steam condensate line sizing flow chart. By permission, Spirax-Sarco, Inc., Allentown, Pa. [59].

Because flashing steam-condensate lines represent two-phase flow, with the quantity of liquid phase depending on die system conditions, these can be designed following the previously described two-phase flow methods. An alternate by Ruskin [28] uses the concept but assumes a single homogeneous phase of fine liquid droplets dispersed in the flashed vapor. Pressure drop was calculated by the Darcy equation ... 

Rgure 2-55. Flashing steam condensate line sizing chart. By permission, Ruskin, R. R, Calculating Line Sizes for Flashing Steam Condensate, Chem. Eng., Aug. 18,1985,... 

Ruskan, R. P, Sizing Lines For Flashing Steam-Condensate, Chemical Engineering, November 24, 1975, p. 88. 

Sizing of flashing steam condensate return lines requires techniques that calculate pressure drop of two-phase flow correlations. Many correlations have been presented in the literature [15,16,19,23]. Most flow patterns for steam condensate headers fall within the annular or dispersed region on the Baker map. Sometimes, they can fall within the slug flow region however, the flashed steam in steam condensate lines is less than 30% by weight. 

Input Data and Computer Output for Flashing Steam Condensate... 

THIS PROGRAM CALCULATES LINE SIZES FOR FLASHING STEAM CONDENSATE. THE PROGRAM WILL COMPUTE THE FOLLOWING ... 

FORMAT (///, 15X, LINE SIZING FOR FLASHING STEAM CONDENSATE, /, 78(1H ))... 

Where Water Hammer Occurs. Water hammer can occur in any water supply line, hot or cold. Its effects can be even more pronounced in heterogeneous or biphase systems. Biphase systems carry water in two states, as a liquid and as a gas. Such a condition exists in a steam system where condensate coexists with live or flash steam in heat exchangers, tracer lines, steam mains, condensate return lines and, in some cases, pump discharge lines. 

Condensate normally flows at the bottom of a return line. It flows because of the pitch in the pipe and also because of the higher velocity flash steam above it, dragging it along. The flash steam moves at a higher velocity because it moves by differential pressure. 

In our glass pipe demonstrator, cold water is used to simulate condensate and air pressure is applied to simulate the flash steam in the top portion of the pipe (Fig. 2). 

C 0.35 Recovery of low level waste heat f space heating, district heating syste Absorption cooling. Recovery of steam condensate and flash steam. Heat pump for evaporation, drying, etc. 3r m. 

Often in plant operations condensate at high pressures are let down to lower pressures. In such situations some low-pressure flash steam is produced, and the low-pressure condensate is either sent to a power plant or is cascaded to a lower pressure level. The following analysis solves the mass and heat balances that describe such a system, and can be used as an approximate calculation procedure. Refer to Figure 2 for a simplified view of the system and the basis for developing the mass and energy balances. We consider the condensate to be at pressure Pj and temperature tj, from whence it is let down to pressure 2. The saturation temperature at pressure Pj is tj. The vapor flow is defined as V Ibs/hr, and the condensate quality is defined as L Ibs/hr. The mass balance derived from Figure 2 is ... 

Steam condensate systems often are used to generate lower pressure steam by flashing to a lower pressure. Tien this occurs, some steam is formed and some condensate remains, Tvith the relative quantities depending upon the pressure conditions. Figure 2-53 is a typical situation. 

If the mixture is separated by a continuous flash process and the components are considered insoluble in water (check references) and the feed enters at the flash chamber at 20°C, calculate the mols of steam condensed, the total mols steam required per 100 mols of feed, and... 

Condensate from the low-pressure coil together with that from the flash vessel will then drain to a collecting tank, or direct to a condensate pump, for return to the boiler plant. If the pressure of the flash steam is left to find its own level it will often be sub-atmospheric. As the condensate must then drain by gravity through the steam traps these also must be sufficiently below the condensate drain points to provide an appropriate hydraulic head, and a vacuum breaker fitted above the coil. The alternatives are to allow the condensate to drain directly to a condensate pump, or to supply additional low-pressure steam through a pressure-reducing valve, to maintain a positive pressure in the coil and flash vessel. 

Somewhat similar arrangements can be used when radiant panels or unit heaters heat large areas. Some 10-15 per cent of the heaters are separated from the high-pressure steam supply and supplied instead with low-pressure steam flashed off the high-pressure condensate. The heating demands of the whole area remain in step, so supply and demand for the flash steam are balanced. 

In other cases, flash steam is utilized on equipment, which is completely separated from the high-pressure source. Often the low-pressure demand does not at all times match the availability of the flash steam. A pressure-reducing station is often needed to make up any deficit and a surplus valve is required to vent any flash steam in excess of the amount being condensed. 

The pressure drop needed to carry the condensate and any flash steam along the line. 

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