Barometric leg

The jet barometric legs should go in a straight line to the seal tank. A 60°-90° slope from horizontal is best. 

One or more filter pumps (either receiver mounted or connected to the seal tank of a barometric leg)... 

Low-head jet units without a barometric leg use a pump to withdraw the water from the barometric condenser. This pump must be carefully selected as it must operate under vacuum suction conditions. 

Flash Tank Cerr. Allow Barometric Leg Corr. Allow ... 

The hot well is the sump where the barometric leg is sealed. It must be designed to give adequate cross-section below the seal leg and for upward and horizontal flow over a seal dam or weir. At sea level the hot well must be a minimum of 34.0 ft below the base of the barometric condenser. For safety to avoid air in-leakage, a value of 35-36 ft is used. For an altitude corresponding to a 26-in. Hg. barometer, the theoretical seal height is 29.5 ft actual practice still uses about 34 ft. 

When laying out the diagram, it is only necessary to show the relative elevation of the process connections to the equipment where these affect the process operation for example, the net positive suction head (NPSH) of pumps, barometric legs, syphons and the operation of thermosyphon reboilers. 

Other pieces may have to be elevated to enable the system to operate. A steam jet ejector with an intercondenser that is used to produce a vacuum must be located above a 34 ft (10 m) barometric leg. Condensate receivers and holding tanks frequently must be located high enough to provide an adequate net positive suction head (NPSH) for the pump below. For many pumps an NPSH of at least 14 ft (4.2 m) H2O is desirable. Others can operate when the NPSH is only 6 ft (2 m) H2O. See Chapter 8 for a method of calculating NPSH. 

Kraft pulp Deep sub. drum or Disc 1.5 0.05 90 Barometric leg ... 

The water is then conveniently discharged at atmospheric pressure, without the aid of a pump, by allowing it to flow down a vertical pipe, known as a barometric leg, of sufficient length for the pressure at the bottom to be slightly in excess of atmospheric pressure. For a jet condenser with a barometric leg, a chart for determining the water requirement has been prepared by Arrowsmith(49), and this is shown in Figure 14.27. 

The original steam condensers were barometric condensers, which were used to increase the efficiency of the steam-driven reciprocating beam engines by a factor of 10. The barometric condenser was invented by James Watt (the steam engine was invented by Thomas Newcomen). Exhaust steam is mixed directly with cold water. As this creates a vacuum, the barometric condenser must be elevated about 30 ft above grade. The mixed condensate and cooling water drains through a pipe called a barometric leg—hence the name barometric condenser. 

Two problems arose with the use of the barometric condenser. First, if the condenser operated at subatmospheric pressure, how can the water be drained out of the condenser That is easy. Set the condenser on a hill 34 ft high. Then drain the water down, through a barometric leg, to a seal pot. The pressure which a column of water 34 ft high exerts is equal to one atmosphere, or one bar. Hence the term, barometric leg. ... 

Air-displacement systems air lifts, acid eggs or blow cases, jet pumps, barometric legs... 

Barometric-leg pumps are used for assisting in maintaining a vacuum when condensable vapors are involved. Auxiliary pumps are necessary to remove any fixed gases that may accumulate in the leg. For water condensation, the leg usually empties into an open well, and the vertical length of the leg must be longer than 34 ft. 

Owens Corning manufactures a similar extruded polystyrene foam under the trade name FoamulaR. A single-screw tandem extrusion line is used to produce foam boardstock in a vacuum chamber connected to a barometric leg that acts as a vacuum seal [78]. Owens Corning also licenses their process to a number of international parties. 

B). If downstream pressure is greater, then a barometric leg may be used to maintain a seal, as shown in Figure 3.5(C). The overflow line shown must be adequately sized to self-vent otherwise, it may begin to siphon. 

Back-mix reactor design, 721, 728 Baffles in heat exchangers, 595, 610-612 pressure drop over, 599-602, 605-606 Bailee s liahihty, 263 Balance sheet, 140-142 Barometric-leg pumps, 523 Batch operation versus continuous, 35-36 Batch-reactor design, 721-727 Battery-limit additions, definition of, 167 Berl saddles, 688-690 cost of 710... 

Simonson-Mantius evaporator, which is supplied with saturated steam at 400 kPa gauge to lead coils submerged in the acid, and the condensate leaves at the saturation temperature. A vacuum is maintained at 4.0 kPa by means of a barometric leg. The acid is concentrated to 80% H2SO4 the boiling point at 4.0 kPa is 121°C. How many kilograms of acid can be concentrated per 1000 kg of steam condensed ... 

FIGURE 10.4 Details of operation of a slurry vacuum cooler, In which a small water jet exhauster maintains the vacuum, largely produced by direct steam condensation and the barometric leg of the barometic condenser. (From Slack [55], page 275 by permission, Marcel Dekker Inc.)... 

In the design shown in Fig. 15.10, part of the cooling water is sprayed into the vapor stream near the vapor inlet, and the remainder is directed into a discharge throat to complete the condensation. When a shell-and-tube condenser is operated under vacuum, the condensate is usually pumped out, but it may be removed by a barometric leg. This is a vertical tube about 10 m (34 ft) long, sealed at the bottom by a condensate-receiving tank. In operation the level of liquid in the leg automatically adjusts itself so that the difference in head between levels in leg and tank corresponds to the difference in pressure between the atmosphere and the vapor space in the condenser. Then the liquid flows down the leg as fast as it is condensed without breaking the vacuum. In a direct-contact condenser the pressure regain in the downstream cone of the venturi is often sufficient to eliminate the need for a barometric leg. 

The barometric leg represents one way to prevent process material from flowing back into the vaporizer. The height of the leg should suit the density of the process fluid. When the process operates under pressure or when chlorine enters the process against a substantial head of process fluid, a barometric leg may be impractical. Other devices used include low-pressure shutdown systems, power-operated control valves, backpressure regulators, and vacuum breakers. Check valves are another possibility, but they are not widely recommended and must be used with discretion and with some assurance that they provide positive shutoff. A variation is the use of an automatic value that shuts when the differential pressure between two points in the transfer line reverses, indicating the potential for backflow. 

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