Pressure equalizing line

Water tube boilers have a pressure gauge, vent cock, and drum safety valve on the top of the steam drum. Where superheaters are fitted, the steam takeoff line leads to the superheater, which is followed by a superheater safety valve, automatic nonreturn valve, and stop valve with a pressure-equalizing line and valve. 

Automatic NRVs act like check valves and cut out the boiler if its pressure falls below the main steam-header pressure. The installation of an automatic NRV may require the provision of a bypass pressure equalizing line and a pressure equalizing valve. 

A pressure-equalizing line must be provided. This is a small line (often 1 in diameter) connecting the top of the reboiler with the top of the condensate pot. Without this line, it will be impossible to maintain a steady pressure and level in the condensate pot. 

Pressure-equalizing lines should be sized for negligible pressure drop. One designer (77) found that an equalizing line with at least 20 percent of the cross-sectional area of the column overhead vapor line is adequate. 

This control method should not be used unless a pressure-equalizing line is included (77, 164). Without this line, pressure in the reflux accumulator will be unsteady. A smaller equalizing line is required when the subcooled liquid is introduced below the drum liquid level. 

Figure 17.5/ shows a flooded condenser scheme similar to that of Fig. 17.5a, but with the control valve located at the condenser inlet. This method is inferior compared to Fig. 17.5a (77). It requires a larger control valve, is more difficult to understand, and it affects condensation at a lower temperature. The condenser outlet line must enter the reflux drum well below the liquid level. A pressure-equalizing line as in the method shown in Fig. 17.5a is also required.

The van der Waals p., p. isothenns, calculated using equation (A2.5.3), are shown in figure A2.5.8. It is innnediately obvious that these are much more nearly antisynnnettic around the critical point than are the conespondingp, F isothenns in figure A2.5.6 (of course, this is mainly due to the finite range of p from 0 to 3). The synnnetry is not exact, however, as a carefiil examination of the figure will show. This choice of variables also satisfies the equal-area condition for coexistent phases here the horizontal tie-line makes the chemical potentials equal and the equal-area constniction makes the pressures equal. 

The lower chip contains the micro-channel test section with inlet and exit plenums, eight static pressure tap lines intersecting the micro-channel at equally spaced intervals, and one tap line per plenum. The tap line to the micro-channel... 

A more quantitative gas bubble history than that of Fig 1 is shown in Fig 4 (from Ref 1). The dashed horizontal line is the bubble radius at which the bubble pressure equals the hydrostatic pressure of the water. Note that, over most of the first bubble cycle in this example, the gas pressure in the bubble is below the surrounding hydrostatic pressure. The maximum velocity of the bubble surface is about 200ft/sec... 

A cone bottom (sometimes provided with sand jets) may be used to help solids pass through vertical vessels. The cone is normally at an angle to the horizontal of between 45° and 60°. Produced sand may have a tendency to stick to steel at 45°. If a cone is installed, it may be part of the pressure containing walls of the vessel, or for structural reasons, it could be installed internal to the vessel cylinder. In such a case, a gas equalizing line must be installed to assure that the vapor behind the cone is always in pressure equilibrium with the vapor space. 

The gas is pushed out into the discharge line, at a pressure equal to the discharge-line pressure. 

We saw in Section 10.5 that the vapor pressure of a liquid rises with increasing temperature and that the liquid boils when its vapor pressure equals atmospheric pressure. Because a solution of a nonvolatile solute has a lower vapor pressure than a pure solvent has at a given temperature, the solution must be heated to a higher temperature to cause it to boil. Furthermore, the lower vapor pressure of the solution means that the liquid /vapor phase transition line on a phase diagram is always lower for the solution than for the pure solvent. As a result, the triplepoint temperature Tt is lower for the solution, the solid/liquid phase transition line is shifted to a lower temperature for the solution, and the solution must be cooled to a lower temperature to freeze. Figure 11.12 shows the situation. 

Figure 8.22. Equilibrium curves for the reaction CaC03 + SiC>2 —> CaSiC>3 + Si02 at a CO2 pressure of 1 atm and at a CO2 pressure equal to total pressure on the system. At P-T values between the two CO2 pressure extremes, caicite and quartz are stable. Heavy solid line is experimentally determined and dashed lines are extrapolated or theoretical. (After Barth, 1962.)...

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