Pressure separation

Figure A2.1.5. Irreversible changes. Two gases at different pressures separated by a diathemiic wall, a piston that can be released by removing a stop (pin).

The two portions of the feed stream recombine and flow into the high pressure separator where the Hquid is separated from the vapor and is fed into an intermediate section of the demethanizer with Hquid level control. The decrease in pressure across the level-control valve causes some of the Hquid to flash which results in a decrease in the stream temperature. The pressure of the vapor stream is decreased by the way of a turboexpander to recover... 

Recycle and Polymer Collection. Due to the incomplete conversion of monomer to polymer, it is necessary to incorporate a system for the recovery and recycling of the unreacted monomer. Both tubular and autoclave reactors have similar recycle systems (Fig. 1). The high pressure separator partitions most of the polymers from the unreacted monomer. The separator overhead stream, composed of monomer and a trace of low molecular weight polymer, enters a series of coolers and separators where both the reaction heat and waxy polymers are removed. Subsequendy, this stream is combined with fresh as well as recycled monomers from the low pressure separator together they supply feed to the secondary compressor. 

Hollow-fiber membranes may be run with shell-side or tube-side feed, cocurrent, countercurrent or in the case of shell-side feed and two end permeate collection, co- and countercurrent. Not shown is the scheme for feed inside the fiber, common practice in lower-pressure separations such as air. 

The heated oil is flashed into the VPS flash zone where vapor and liquid separate. Split between distillate and bottoms depends on flash zone temperature and pressure. Separation of vapor and liquid in the flash zone is incomplete, since some lower boiliug sidestream components are present in the liquid while bottoms components are entrained in the vapor. The liquid from the flash zone is steam stripped in the bottom section of the VPS to remove the lower boiling components. 

Depending on the number of stages, the gas that flashes in the lowci pressure separators can be compres.sed and then recombined with the gas from the high-pressure separator. Both reciprocating and centrifugal compressors are commonly used. In low-horsepower installations, especially lor compressing gas from stock tanks (vapor recovery), rotary aiuf vane type compressors are common. 

The simplest form of condensate stabilization is to install a low-pressure separator downstream of an initial high-pressure separator. Unless the gas well produces at low pressure (less than 500 psi) and the gas contains very little condensate (less than 100 bpd), the additional expend -... 

It should be clear from the description of LTX units in Chapter 5 that the lower pressure separator in an LTX unit is a simple form of cold-feed condensate stabilizer. In the cold, upper portion of the separator some of the intermediate hydrocarbon components condense. In the hot, lower portion some of the lighter components flash. 

Suction throttle valves are common in gas-lift service to minimi/c the action of the flare valve. Flow from gas-lift wells decreases with increased back-pressure. If there were no suction valve, the flare valve may have to be set at a low pressure to protect the compressor. With a suction valve it may be possible to set the flare valve at a much higher pressure slightly below the working pressure of the low-pressure separator. The difference between the suction valve set pressure and the flare valve set pressure provides a surge volume for gas and helps even the flow to the compressor. 

A vessel may be subject to more than one condition under different failure scenarios. For example, a low pressure separator may be subject to blocked discharge, gas blowby from the high pressure separator, and fire. Only one of these failures is assumed to happen at any time. The relief valve size needs to be calculated for each pertinent relieving rate... 

Production Separators I est Separators 1 ow Pressure Separators < iij col Contact Tower nil Treater... 

Hesitation method of applying pressure is applicable to both high and low-pressure squeeze cementing operations. This method of applying pressure (and thus volume) appears to be more effective than continuous pressure application. The hesitation method is the intermittent application of pressure, separated by a period of pressure leakoff caused by the loss of filtrate into the formation. The leakoff periods are short at the beginning of an operation but get longer as the operation progresses. 

In the two-stage operation, the feed is hydrodesulfurized in the first reactor with partial hydrocracking. Reactor effluent goes to a high-pressure separator to separate the hydrogen-rich gas, which is recycled and mixed with the fresh feed. The liquid portion from the separator is fractionated, and the bottoms of the fractionator are sent to the second stage reactor. 

Figure 10-11. The Institut Francais du Petiole process for the hydrogenation of benzene to cyclohexane " (1) liquid-phase reactor, (2) heat exchanger, (3) catalytic pot (acts as a finishing reactor when conversion of the main reactor drops below the required level), (4) high-pressure separator, (5) stabilizer.

In a two-stage system, the vapors from the compressor s first stage discharge are partially condensed and flashed in an interstage drum. The liquid hydrocarbon is pumped forward to the gas plant, either to the high pressure separator (HPS) or directly to the stripper. 

Inject a Dehazer Additive into the High Pressure Separator (HPS)... 

Pure sodium chloride, like pure water, has a definite melting (freezing) temperature (at a given pressure). Separating operations—such as distilling or freezing—do not separate the salt into components. The composition of the salt, whether expressed in relative numbers of sodium and chlorine atoms or in the relative weights of these atoms, is fixed and is represented by the formula NaCl. Sodium chloride, like water, is an example of a pure substance. 

One of the major trends to be anticipated is greater availability of instrumentation that can be used to perform multidimensional separations at ultrahigh pressures. Some instrument makers have recently introduced LC pumps capable of operating at pressures up to 15,000 psi. As time progresses, ultrahigh pressure separations are likely to become more routine and the pressure limit of commercial instruments is likely to increase... 

Early design and simulation of large-diameter, melt-fed extruders were described by Fenner [17]. A numerical simulation of the axial pressure and temperature fora screw similar to that shown in Fig. 15.8 is shown in Fig. 15.10. This simulation was performed using a three-dimensional method using a finite difference approach. The process starts with an LDPE resin (2 dg/min, 2.16 kg, 190 °C) in the low-pressure separator at a pressure of 0.04 MPa (gauge) and a temperature of 230 °C. 

The conditions in the low-pressure separator are typically in the range of 0.04 to 0.14 MPa absolute pressure and at a temperature near 250 °C [11, 12]. At these conditions, the LDPE resin in the low-pressure separator is expected to contain about 750 ppm of dissolved ethylene at equilibrium. Another 250 to 750 ppm of ethylene can also be entrained as a gas or at a supersaturated condition in the LDPE. As the resin flows from the low-pressure separator into the first diameter of the extruder, the pressure is expected to be nearly the same since the flow pipes are not restrictive. If the temperature of the inside wall of the feed casing of the extruder is less than 250 °C, then the ethylene will remain in solution, foaming... 

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