Liquid trim

The liquid trim modifies the shape of the huddling chamber so that the full capacity at 10% overpressure can be achieved with a non-compressible fluid. Some manufacturers provide an all media trim which fulfils the requirements for gas and liquid with one single trim others have an interchangeable trim for each fluid. 

It was a positive development when the code insisted on special liquid trim designs besides the fact that the standard gas valve did not reach rated capacity at 10% for liquid, it was also demonstrated that the valve became very unstable during the opening cycle, as can be seen in Figure 5.9. 

Opening and closing curve liquid trim design... 

However, a conservative approach, which has been successful for many years in my personal experience, is to limit the liquid phase to about one-third by volume. Anything above that will need at least a liquid trim for a spring-operated valve or a modulating pilot as a solution to this problem. Oil/gas separators are a typical application where this rule of thumb can be applied. 

The liquid capacity is >30% total (volumetric capacity) If a spring valve is required, it should be a valve with liquid trim. Preferably, however, a modulating pilot-operated valve can be used. The modulating pilot ensures stability of operation whatever the phase and cannot be oversized as it adapts its flow to the need of the system. 

Rohsenow. W. M. A Method of Correlating Heat Transfer Data for Surface Boiling Liquids. Trims. ASME. vol. 74. p. 969, 1952. 

Two sources of absorption oil are normally utilized in this tower. The first is the hydrocarbon liquid from the main fractionator overhead receiver. This stream, often called wild, or unstabilized, naphtha, enters the absorber a few trays below the top tray. The second absorbent is cooled debutanized gasoline, which generally enters on the top tray. It has a lower vapor pressure and can be considered a trim absorbent. The expression lean oil generally refers to the debutanized gasoline plus the unstabilized naphtha from the overhead receiver. 

To 2 mmol of freshly prepared ethereal LiCu(C.H3), are added 154 mg (1 mmol) of ( — )-m-5-melhyl-2-cyclo-hexenyl acetate (3a). [a]25 —2.7 (c = 3, CHC1,), in a centrifuge tube at 0°C. The mixture is kept at 0 °C for 8 h after which 1 mL of water is added. Methane is evolved and a reddish precipitate forms. After centrifuging, the supernatant liquid is decanted and concentrated, and the product trims-4 is isolated by preparative GC. Isolated yields range from 30% and 40%. However, it was reported in a similar reaction that the yields range from 90% and 95% 5. Analysis by capillary GC shows the product to be 99.5% trans-4 and 0.5% t -4. Capillary GC of the starting 3a shows the acetate 3a to be homogeneous except for a trace ( — 1.0%) of the trans-isomers. 

You want to control the flow rate of a liquid in a transfer line at 350 gpm. The pump in the line has the characteristics shown in Fig. 8-2, with an 5 in. impeller. The line contains 150 ft of 3 in. sch 40 pipe, 10 flanged elbows, four gate valves, and a 3 x 3 control valve. The pressure and elevation at the entrance and exit of the line are the same. The valve has an equal percentage trim with the characteristics given in Table 10-3. What should the valve opening be to achieve the desired flow rate (in terms of percent of total stem travel) The fluid has a viscosity of 5cP and a SG of 0.85. 

The basic reason for using different control-valve trims is to keep the stability of the control loop fairly constant over a wide range of flows. Linear-trim valves are used, for example, when the pressure drop over the control valve is fairly constant and a linear relationship exists between the controlled variable and the flow rate of the manipulated variable. Consider the flow of steam from a constant-pressure supply header. The steam flows into the shell side of a heat exchanger. A process liquid stream flows through the tube side and is heated by the steam. There is a linear relationship between the process outlet temperature and steam flow (with constant process flow rate and inlet temperature) since every pound of steam provides a certain amount of heat. 

Fig. 9.4.10 Apparatus for the gas flow-arc plasma method. The apparatus is composed of two components. The upper part is a glass Dewar, which accumulates small particles in a cryogenic matrix on the trim cooled with liquid nitrogen (LN). Sorv, inlet of organic vapor Syr, syringe for transferring produced colloids under anaerobic conditions RP, rotary pump S, target sample. Lower part is for plasma discharge. A BN furnace has gas inlets (G) and is specially designed for Ar gas to flow in screwed stream hence the plasma is emitted in a jet flame due to a plasma pinch effect. The black parts are copper electrodes cooled by water. In order to maintain a constant spacing between the surface of sample and tbe upper electrode, the sample position can move vertically so that the current through the sample to the upper electrode is precisely controlled and constant. This is very important to produce powders with a narrow size distribution.

Trim Cotiler—This unit condenses the last remaining light-end vapors and cools the liquid to the ultimate storage temperature (often about 100 F 38 Cl hy using cooling water. This cooling usually is not conducted in the main condenser because it would reduce column pressure. 

A final alternative for metal patterning is the use of lasers to selectively and accurately etch small metal areas. Lasers are routinely used to trim thin-film resistors (126) they may also be used to repair defects or etch conductor lines by direct ablation in an inert atmosphere (127,129) or by laser-initiated etching in a reactive gas or liquid (128). 

It is important to mention that gas and vapours have different release characteristics than liquids, and that what is being discussed here is typical for gas, vapours and steam. Until 1985, the code allowed for liquid applications to have an overpressure of 25%. Until then, the same valve trim was used for both gases and liquids, resulting in the release characteristics shown in Figure 5.7. 

However, since 1985, the code has also required a maximum overpressure of also 10% on liquid valves. This meant manufacturers had to redesign many trims so that the same valve could be fitted for both gas and liquid. So it is important to know the age of a liquid valve in order to determine whether it will flow full capacity at 10% or at 25%. Also, blowdown on liquid spring-operated valves was and is still rather unstable, and can be as high as 30% depending on the design. The code does not specify a blowdown requirement for liquid valves. 

Opening and closing curve Liquid (Non-compressible) in a gas trim valve... 

Wide range of service temperatures Risk of chattering on liquids, unless special trims are used... 

Normal operation Spring-operated valves can be used but need to be equipped with a trim suitable for liquid service so they can obtain nominal flow at 10% overpressure. When quick opening (and closing) is required, the operation will be unstable and will possibly cause water hammer. Alternatively, a modulating pilot valve can be used, preferably equipped with a filter. The volume of the filter slows the pilot, which may otherwise react too fast, creating instability and water hammer. 

The long, extended bonnet is provided with a plug stem seal to minimize liquid "refluxing" into the bonnet and packing area, thereby minimizing the heat loss due to conduction and convection. Cold boxes are commonly used in hydrogen and in the air separation industry. Valves used in these applications feature bodies with welded extension necks and standard-length bonnets to allow in-place trim maintenance from outside the cold box. On LH2 service these valves are often provided with vacuum jackets for additional... 

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