Liquid dump valves

The gas, condensate, and free water are then discharged from the ncs scl through backpressure and liquid dump valves. The gas leaving the separator is saturated with water vapor at the temperature and pressure of the top of the low temperature separator. If this temperature is low enough, the gas may be sufficiently dehydrated to meet sales specifications. Dehydration is discussed in greater detail in Chapter 8. 

Note Liquid dump valves are normally fail closed to prevent giis blowby. That means that in ca.se of loss of instrument gas or air pressure, the spring will drive the valve to the closed position. However, the valve can mechanically fail because the level controller malfunctions or the seat cuts out due to solids erosion, which would cause it to fail in an open configuration. 

Vertical separator. Fig. 2 is a schematic of a vertical separator. In this configuration inlet flow enters the vessel through the side. As in the horizontal separator, the inlet diverter does the initial gross separation. Liquid flows down to the liquid collection section of the vessel, then down to the liquid outlet. As liquid reaches equilibrium, gas bubbles flow counter to the direction of liquid flow and eventually migrate to the vapor space. The level controller and liquid dump valve operate in the same manner as in a horizontal separator. 

Variations 1n liquid level resulting 1n liquid dump valve hunting1. 

Operator exposure Charge liquids and solids materials by means of a to fumes or inerts. closed system (e.g., hard piping, hopper and rotary airlock, screw feeder, double-dump valve system, etc.) Provide local ventilation Use proper personnel protective equipment (PPE) ACGIH 1986 CCPS G-22 CCPS G-23 CCPS G-29... 

In applying FMEA, a mechanical flow diagram must first be developed.. As an example, consider the check valve on a liquid dump line. It can fail... 

An alternate configuration (Fig. 3), the "bucket and weir" design, eliminates the need for a liquid interface controller. Both oil and water flow over weirs where level control is accomplished by a simple displacer float. Oil overflows the oil weir into an oil bucket where its level is controlled by a level controller operating the oil dump valve. Water flows under the oil bucket and then over a water weir. The level downstream of this weir is controlled by a level controller operating the water dump valve. 

A once-throu thermosiphon reboiler could not be started up because tray weeping at startup starved the reboiler of liquid. A valved dump line cotmect-ing rdxriler liquid and bottom sump was added and solved problem. 

Liquids that enter a compressor cylinder will break the valve plates. For this reason, liquid knock-out drums called scrubbers are always placed on the suction side of reciprocating compressors. Accumulated liquid is drained under level control from the scrubbers through a dump valve. 

These valves are prone to leaking through, which results in gas being lost. Such a leak is identified by comparing the scrubber temperature with the temperature of the scrubber-liquid dump line downstream of the level-control dump valve. Any noticeable temperature drop across this valve is indicative of a significant loss of gas. 

Valves. Valves are key components in reactor systems, since they arc the means by which process gas and liquid streams are controlled [48,49]. In the HRE-2 system, which has no control rods, temperature and reactivity arc controlled by valves that control the concentration of the fuel solution, and the power is controlled by valves that control the rate of steam removal from the heat exchangers. "Dump valves perform an emergency scram and normal drain function by controlling the flow of fuel solution to low-pressure storage tanks. Other valves perform pressure-control functions, allotv noncondensablc ga.ses to be bled from the system, or ai ( used to isolate equipment. 

A proper sizing criteria Is to determine the liquid volume that could be dumped before the ESD system shuts in the relief valve source of overpressure. Thus, a dynamic liquid holdup determines the size of the relief drum. It will generally be smaller with the liquid holdup sizing criteria than a comparable horizontal API sized vessel. 

All types of valve and sieve trays are always suffering from lost tray efficiency, as a result of both flooding and dumping. Such trays always have some entrained droplets of liquid, lifted by the flowing vapors, to the trays above. This tends to blow butane up into the lighter propane... 

As shown in Fig. 2.4, a minimum vapor rate exists below which liquid may weep or dump through tray perforations or risers instead of flowing completely across the active area and into the downcomer to the tray below. Below this minimum, the degree of contacting of liquid with vapor is reduced, causing tray efficiency to decline. The ratio of the vapor rate at flooding to the minimum vapor rate is the turndown ratio, which is approximately 10 for bubble cap and valve trays but only about 3 for sieve trays. 

Each sump must have its own drainage facilities. This is best achieved by installing an external valved dump line at a low point to interconnect the liquid outlet lines from each siunp (see Fig. 15.4a). Alternatively, a number of holes can be drilled at the bottom of the baffle, but this gives slow drainage rates and susceptibility to plugging and is therefore not recommended. The author is familiar with cases when it took over a day to drain the reboiler sump via such holes. 

Installing a valved dump line connecting the column bottom outlet line with the reboiler inlet line (Fig. 15.4a). This technique is only needed when the column reboiler sump is separated from the column bottom sump by a baffle or when the reboiler liquid comes from a trapout pan. The valve remains shut during normal operation, but is opened during startup to lower the level and inspire thermosiphon action during startup. One case where this technique was successfully used has been described (237) the author has had several similar experiences. 

One drawback of this system is that the distillate control valve may at times dump liquid out of the reflux drum faster than the reboiler can produce vapor to make up for this (234). Using a reflux drum low-level override which cuts back distillate or reflux flow was advocated (234) as a guard against draining the reflux drum. Another drawback of this system is a possible interaction between the pressure and temperature controllers. 

Filling of the test vessel was accomplished through 2-in. vacuum-jacketed transfer lines. Liquid nitrogen used for precooling and check-out was supplied from a 600-gal dewar liquid hydrogen was supplied from a 1500-gal dewar. Three valves provided control of liquid fill and dump and throttling during outflow. 

---