Side-stream valves

Fig. 4.2-7. In-line safety- and side-stream valve (PN 2500, DN 60/32, adopted from BOHLER). 1, Tubular reactor train 2, In-line valve 3, Hydraulic actuator 4, Side outlet (inlet).

Figure 9.39 Temperature at each stage when side stream valve is closed at time = 5 h.

The exposure of sensors in a by-pass stream (which can be valved off), is an alternative way of collecting monitoring data although correlation is required between the main-stream and the by-pass The use of a side-stream taken either side of a choke in the main-stream can provide a useful monitoring point. Traps where product streams can be condensed can offer alternative sampling systems. 

Assuming a perfect material balance with no extraneous losses, the input of new monomer should match the output of polymeric product. To accomplish this and maintain essentially constant polymer solids in the reactor, the solids content should be measured and used to control the displacement of monomer-polymer solution with monomer. A satisfactory method is to use a torque tube viscometer (J) in a side stream of monomer-polymer and use a viscosity recorder-controller to control a valve forwarding monomer-polymer to the devolatilizer. Reactor pressure is used to control monomer input, replacing the monomer-polymer solution forwarded to the devolatilizer. 

A side-stream accumulator was lifted off its foundation by a pressure surge at startup. During hot oil recirculation, back flush of the spare pump was being attempted. The pump discharge valve was cracked open before the suction valve was closed. A pocket (rf water in the pump or its piping was sucked into the hot oil, causing the surge. 

The basic components of a plate distillation column include a feed line, feed tray, rectifying or enriching section, stripping section, downcomer, reflux line, energy-balance system, overhead cooling system, condenser, preheater, reboiler, accumulator, feed tank, product tanks, bottom line, top line, side stream, and an advanced instrument control system. Plate columns hold trays that may be bubble-cap, valve, or sieve. Figure 6-19 shows the basic components of a plate distillation column. 

The symbol used on a diagram for a plate column should indicate the type of tray used in the system bubble-cap, valve, or sieve. The first distillation column was invented in 1917. Today, a number of modifications allow modern process technicians to operate much more efficiently. The design, however, still includes the original still-on-top-of-a-still approach. The basic components of a plate distillation column are a feed line feed tray stripping section below the feed line enriching or rectifying section above the feed line overhead vapor outlet, side-stream outlet, and bottom outlet reboiler instrumentation for level, temperature, flow, pressure, and composition control outer shell and a top reflux line. 

I found that the instrument air tubing connection to the kerosene-draw control valve was loose. That valve controls the flow of kerosene from the crude tower to the side-stream stripper. The control valve simply wasn t getting enough air to open fully. I tightened the connection, and kerosene production rose to the normal rate. 

The homogeneous mixture of LDPE + ethylene that leaves the reactor is expanded through a pressure control valve, from reaction conditions down to 200-400 bar, where the molten polymer precipitates from the supercritical ethylene. Due to a reverse J oule-Thomson effect, the expansion of ethylene at these conditions leads to a temperature increase, which requires a proper cooling system before the first separation is carried out. Most of the available manufacturing processes provide a product cooler to reduce the mixture temperature down to 250-300 °C. Alternatively, a direct gas ethylene side stream coming from the hypercompressor is used to cool down the mixture. 

One must take care in determining the number of steady-state and dynamic degrees of freedom for more complex columns. Tyreus [4] describes the determination of the degrees of freedom for an extractive distillation system and for an azeotropic column with an entrainer. In the case of an extractive distillation system, recycle streams reduce the dynamic degrees of freedom through an increase in the steady-state degrees of freedom if the recycle contains a component that neither enters nor leaves the process. Also, if it is important to control the inventory of a trapped component, such as an entrainer for azeotropic distillation, then it is necessary to provide extra control valves to account for the loss of degrees of freedom. The loss comes from the addition of a side stream. 

Dry inlet gas that has been dehydrated by molecular sieves (qv) or alumina beds to less than 0.1 ppm water is spHt into two streams by a three-way control valve. Approximately 60% of the inlet gas is cooled by heat exchange with the low pressure residue gas from the demethanizer and by external refrigeration. The remainder of the inlet gas is cooled by heat exchange with the demethanized bottoms product, the reboiler, and the side heater. A significant amount of low level refrigera tion from the demethanizer Hquids and the cold residue gas stream is recovered in the inlet gas stream. 

The tank in Problem 66 is 6 in. in diameter and contains water at a depth of 3 ft. On the side of the tank near the bottom is a 1.5 in. ID outlet to which is attached a ball valve, which has a loss coefficient of 1.2. When the valve is opened, the water flows out in a horizontal stream. Calculate ... 

After an activation period of 4 h, the conversion showed a maximum of 40% followed by a steady decrease in conversion (Figure 4.38). Overnight, the pressure was decreased to 6 MPa and the needle valve on the permeate side was closed. This shutdown procedure caused the catalyst to precipitate and no reaction occurred anymore. The precipitated catalyst can be used for a new cycle by pressurization of the membrane reactor, redissolving the catalyst. At the end of the third run the conversion had dropped to 33%. A TON of 1.2xl05 in 32 h (t 62 min) was obtained. ICP-AAS analysis of the permeate stream indicated complete retention of the catalyst. The authors propose possible traces of oxygen as the cause of the decrease in activity of the catalyst. 

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. 

The raffinate and extract streams leave the UOP Parex unit adsorption section via the UOP rotary valve and are respectively routed to the raffinate and extract columns for separation of the mixed xylene components from the PDEB as shown in Figure 7.4. Because the desorbent has a higher boiling point than the mixed xylenes, the desorbent exits the bottom of the distillation column and is pumped back to the adsorbent chamber section. The mixed xylene raffinate stream is taken as a side cut from the raffinate column to remove water. The extract p-xylene stream is taken from the top of the extract column and routed to a finishing column where any toluene that was in the Parex feed is removed. The p-xylene product exits the bottom of the finishing column. The adsorbent has some selectivity for toluene as well as p-xylene. 

---