Valve unit fixed

Figure 6.4 Types of valve units, (a) An uncaged, mind valve unit. (6) A caged, round valve unit, (c) A caged, round valve unit featuring contoured orifice, fd) A rectangular valve unit it) A futed, round valve unit, if) A fixed, triangular v hre unit, (forts a and e courtesy of Gtiisch Inej parts b, c and f courtesy of Koch Engineering Company, Inc. pari d courtesy of Nutter Engineering.)...

Step 6. We have only two choices, DIB column base valve or purge column distillate valve, for fixing a flow in the recycle loop. Either of these would work. The rationale for picking one is based upon avoiding disturbances to the unit downstream of the fixed flow" location. Since the purge column is not critical from the viewpoint of product quality we elect to fix the flow upstream of reactor (purge column distillate flow") so that we minimize disturbances in reactor temperature and pressure. 

The Aromax process was developed in the early 1970s by Toray Industries, Inc. in Japan (95—98). The adsorption column consists of a horizontal series of independent chambers containing fixed beds of adsorbent. Instead of a rotary valve, a sequence of specially designed on—off valves under computer control is used to move inlet and withdrawal ports around the bed. Adsorption is carried out in the Hquid phase at 140°C, 785—980 kPA, and 5—13 L/h. PX yields per pass is reported to exceed 90% with a typical purity of 99.5%. The first Aromax unit was installed at Toray s Kawasaki plant in March 1973. In 1994, IFP introduced the Eluxyl adsorption process (59,99). The proprietary adsorbent used is designated SPX 3000. Individual on-off valves controlled by a microprocessor are used. Raman spectroscopy to used to measure concentration profiles in the column. A 10,000 t/yr demonstration plant was started and successfully operated at Chevron s Pascagoula plant from 1995—96. IFP has Hcensed two hybrid units. 

Figure 6-31 illustrates control schemes for the single stage unit which allow greater stability in performance. As the load changes for a fixed suction pressure, the process fluid is replaced by an artificial load (usually air Figure 6-31, item 1) to maintain constant ejector operation. An artificial pressure drop can be imposed by valve (2), although this is not a preferred scheme. Wlten the addi-... 

In some situations it is very important to be able to increase the flow rate above the design conditions (for example, the cooling water to an exothermic reactor may have to be doubled or tripled to handle dynamic upsets). In other cases this is not as important (for example, the feed flow rate to a unit). Therefore it is logical to base the design of the control valve and the pump on having a process that can attain both the maximum and the minimum flow conditions. The design flow conditions are only used to get the pressure drop over the heat exchanger (or fixed resistance part of the process). 

These same notions can be extended to an entire plant in which several unit operations are connected together. The HDA process for hydrodealkylation of toluene to form benzene is a good example of where an eigenstructure can be found that provides a more easily and simply controlled plant. See Fig. 8.15. Assuming that the toluene feed rate to the unit is fixed, this plant has 22 valves that must be set. There are 11 inventory loops (levels and pressures), so they require 11 valves. One possible conventional control structure is shown in Fig. 8.15. 

Existing compatibility with fixed water systems can be modified to allow for the injection of foam from a mobile foam unit by providing hose connection downstream of the system s alarm check valve. A check valve should be provided in the foam injection line as part of this modification. 

Here is a problem that came up on a sulfur recovery facility in Punto Fijo, Venezuela. The combustion air blower, shown in Fig. 28.8, was a fixed-speed, motor-driven centrifugal machine. The air intake filters were severely fouled. They had a pressure drop of about 8 in H/). The atmospheric vent valve, used to control the discharge pressure at a constant 12 psig, was 50 percent open. The unit engineer had been asked to calculate the incentive in electrical power savings that would result from cleaning the filters. 

The pilot plant scale experimental unit, Fig. 2, described in previous papers [2,3] is provided with a blower that supplies a maximum air flowrate of 300Nm3/h at a pressure of 1500 mm of water column. The flow measurement is carried out with two rotameters, used in the ranges from 2.5 to 30 and from 30 to 250 Nm3/h. In the range from 0 to 4 Nm3/h a gas volume meter provided with paddles is used. A system of valves allows for choosing the suitable rotameter for the desired flowrate. This flowrate is fixed by closing or opening a butterfly valve. 

Because the body A/B dimensions of the valve itself are fixed by API, all API 526 valves are interchangeable as a complete unit. However, as we will see, the individual components are never interchangeable. It is very important that original manufacturers parts are used for replacement and maintenance purposes. 

Although the use of membrane reactors for the retention of the enzyme is mostly applied in continuous processes, some authors used a membrane batch reactor in order to reuse the enzyme in consecutive cycles [11, 74]. Flock et al. used a membrane unit coupled to the reactor with recycling of both permeate and retentate streams to the reactor vessel. A valve at the outlet of the membrane maintained pressure within the range fixed by the manufacturer [74]. Pasta et al. operated a reactor with the membrane inside, emptied the reactor content at scheduled times, and thereafter, replenished it with fresh solution of the substrate and the oxidizing system [11]. 

Once we have fixed a flow in each recycle loop, we then determine what valve should be used to control each inventory variable. This is the material balance step in the Buckley procedure. Inventories include all liquid levels (except for surge volume in certain liquid recycle streams) and gas pressures. An inventory variable should typically be controlled with the manipulated variable that has the largest effect on it within that unit (Richardson rule). Because we have fixed a flow in each recycle loop, our choice of available valves has been reduced for inventory control in some units. Sometimes this actually eliminates the obvious choice for inventory control for that unit. This constraint forces us to look outside the immediate vicinity of the holdup we are considering. 

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