Mix-valve pressure drop

Mix valve pressure drop should be about 10 psi for good mixing. On our caustic wash facility, we had a static mixer. This meant no adjustment could be made. Usually, one should increase mix-valve pressure drop when inadequate treating is reported. 

On the rare cold days we had in Texas, high mix-valve pressure drop would reappear. Caustic would stick to the cold metal walls of the mix valve. Steam tracing the mix valve corrected this difficulty. 

If substantial increases in caustic circulation and mix-valve pressure drop do not improve treating, the operating engineer must assume he is faced with an extraction equilibrium problem. 

Inadequate circulation rate ol wash liquid Mechanical damage to circulation pump Low mix-valve pressure drop Mix valve plugged Quality of fresh make-up wash liquid... 

High settler interlace level Excessive mix-valve pressure drop... 

How does one know if a salt drum or a calcium chloride dryer has anything left in it Is caustic carry-over from a settler normal, or is it a sign of excessive mix-valve pressure drop ... 

The causes of carry-over can be related to high settler interface level, excessive mix-valve pressure drop, inadequate settler residence time, dirt, settler internal mechanical damage, or all of the above. 

Figure 19-14 Optimizing mixing valve pressure drop in desalting.

A mixing valve in the form of a conventional globe valve is simple and economical. A typical service iavolves caustic washing of gas oil and water—oil mixing upstream of a desalter. The valve is normally specified to handle a pressure drop ia the range of 20—350 kPa (0.2—3.5 atm). 

Mixing Valve This type of mixing device is normally a manually operated globe valve operated at 20 to 350 kPa pressure drop. Common use of this device in refinery operations is for water and crude oil mixing before a desalter and in caustic scrubbing operations. 

Finally, a proper investigation about the effect, on axial mixing, pressure drop and heat transfer coefficient, of the end pulsing valve is missing. 

Due to the lack of published data on the special flow field generated in the LDPE tubular reactor by the end pulsing valve, the development of the mathematical model was preceded by a fluiddynamic study, with the aim of evidencing the influence, if any, of the pulsed motion on the axial mixing, the heat transfer coefficient and the pressure drop in the reactor. 

A first model is used to compute the flowrates allowing to perform the separation with the greatest productivity. Then, the "mixed cell in series" model takes into account thermodynamic, hydrodynamic and kinetic properties of the system and compute the concentration profile inside the columns [14], In this model, we make the assumptions that the pressure drop inside the column is negligible compared to the pressure drop realized and controlled with the analogical valves, and we model the true moving bed assuming that the performance of SMB and TMB are equivalent. A mass balance equation is written for each stage and a classical Newton Raphson numerical method is used to solve the permanent state of the process [14],... 

The power requirecT to accomplish mixing in a motionless mixer is provided by the pump used to force the fluid through the mixer. The pressure drop through a motionless mixer is usually expressed as a multiplier K of the open pipe loss or as a valve coefficient Cy- The value of the multiplier is strongly dependent on the detail geometry of the mixer, but is usually available through information from the supplier. Fluid properties are taken into account by the value of the Reynolds... 

The mass-transfer devices may be sieves (holes), fixed valves, moveable valves, or bubble caps. Fig. 2 shows a selection of mass-transfer devices. The purpose of the device is intimate mixing of the vapor and liquid on the tray deck. An ideal device has high capacity, high flexibility, low leakage, low pressure drop, and low cost. 

Argon or helium at a pressure of 100 Torr is bubbled through JP-10, generating a reactant flow that is 5% JP-10. The reactant mix is metered into the flow-tube through a leak valve where the pressure drops to a few tori-celli. The flow properties of the reactor have been discussed in detail previously. Briefly, the total pressure in the heated zone of the flow-tube varies from 3 to 1.2 Torr over the temperature range from 300 to 1700 K, while the residence time drops from 4.5 to 1.5 ms. The flow-tube exhaust is dumped into a temperature-stabilized ( 200 °C) ionization source where the pressure is 1 Torr. The analyte molecules can be ionized either by EI or by methane Cl. The ions are then mass analyzed by the tandem guided ion-beam quadrupole mass spectrometer described in the above-referenced publications. 

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