Pressure drop determination

A useful device to have installed in a stirred autoclave is a liquid sampling tube by which liquid samples are withdrawn under pressure through a filter attached to the lower end of the tube. This device is especially useful for analysis of reaction progress and supplements information obtained from pressure-drop determinations. It is much easier to improve a less than satisfactory yield, if it can be determined what is going wrong and when. For academically orientated persons, a study of the rise and decline of various reaction products, as a function of reaction parameters and catalyst, can be a fertile source of useful publications. 

Calculate wet tray pressure drop, determine effective head from Figure 8-130. 

Downcomer pressure loss. Qearance between bottom of downcomer and plate = 1-in. max. Underflow area = (9.5 in.) (1 in.)/144 = 0.065 ft. Because this is less than the downflow area (of 0.334 ft ), it must be used for pressure drop determination. No inlet weir used on this design. 

An iron foundry has four workstations that are connected to a single duct. Each workstation has a hood that transports 3000 acfin of air flow. The duct length is 400 ft, and the pressure loss at the hood entrance is 0.5 in. of water. There is also a cyclone air cleaner that creates 3.5 in. H2O pressure drop. Determine the diameter of the duct to ensure adequate transport of the dust. Also determine the power required for a combined blower/motor efficiency of 40%. 

Curvature of the vapor-liquid interface is reliant on the vapor-liquid pressure drop determined for each steady state mode as the entire hydraulic resistance of LHP or CPL. The value of curvature remains constant within single elementary cell of circumferential channel (Fig. 2, mode 2). 

The kinetics of the reaction and the properties of the catalyst, especially the thermal stability, will further narrow the range of possible reaction conditions and define a "window" of possible operating parameters. Process optimization, energy efficiency, and safety aspects will then determine at what conditions within the "window" the reactor should operate to give the optimum result. And then mathematical models are used to determine how big the reactor must be to obtain the performance (conversion and pressure drop) determined by the process optimization. Instrumentation is then considered, proper materials of construction are selected, catalyst loading and unloading is considered, possible transport limitations are determined, workshop manufacture is considered, and at last the design of the reactor is completed. The procedure is, of course, iterative since the reactor cost is one of the parameters in the economical optimization, but, as mentioned above, often a factor of minor importance for the overall result. 

Figure 4-7 shows a comparison of pressure drops determined for the Chari data with the model given by Eq. 4-20. For high gas velocities where Darcy s law is not valid, the data of Albright et al. (1951) and Marcus and Vogel (1979) show the pressure drop per unit length to be proportional to Ug - Up) with a factor of proportionality, the permeability, equal to 6.59 X 10-4(it/s/K/ )3-15 )0.357 -0.84... 

Figure 4 -7 Comparison of experimental and calculated pressure drops determined using the permeability concept for Chari s data.

Due to the change in vapor density with absolute pressure, the pressure drop should be calculated separately for each packed bed. Total column pressure drop is the summation of the pressure drops through the packed beds plus the pressure drops through the tower internals. Overall column pressure drop determined this way must be compared with the pressure drop originally assumed. This procedure should be repeated by varying column diameter or packing size until the assumed and calculated pressure drops agree. 

The system pressure drop is defined as the sum of the individual component fiactional pressure drops. The component fractional pressure drop is defined as the actual pressure loss divided by the absolute working pressure of the component. This system fiactional pressure drop determines how much of the turbine output is absorbed as parasitic pressure loss. A reasonable and realistic value of 5% is chosen here, where 1 % is budgeted for the core heat transfer fins and 4% for the remainder of the closed Brayton cycle. To keep the system as imcomplicated as possible, die compressor will not be intercooled. 

Oil viscosity is an important parameter required in predicting the fluid flow, both in the reservoir and in surface facilities, since the viscosity is a determinant of the velocity with which the fluid will flow under a given pressure drop. Oil viscosity is significantly greater than that of gas (typically 0.2 to 50 cP compared to 0.01 to 0.05 cP under reservoir conditions). 

The first term (AQ) is the pressure drop due to laminar flow, and the FQ term is the pressure drop due to turbulent flow. The A and F factors can be determined by well testing, or from the fluid and reservoir properties, if known. 

The end of field life is often determined by the lowest reservoir pressure which can still overcome all the pressure drops described and provide production to the stock tank. As the reservoir pressure approaches this level, the abandonment conditions may be postponed by reducing some of the pressure drops, either by changing the choke and separator pressure drops as mentioned, or by introducing some form of artificial lift mechanism, as discussed in Section 9.7. 

Fig. 24. Souders load diagram for capacity limit determination for four stmctured packiags of the Sul2er-MeUapak type. The soHd lines represent the capacity limits of the respective packiags as defiaed by a pressure drop of 1.2 kPa/m (A) 125 Y (B) 250Y (C) 350Y (D) 500 Y. Flooding rates are about...

Capillary Viscometers. Capillary flow measurement is a popular method for measuring viscosity (21,145,146) it is also the oldest. A Hquid drains or is forced through a fine-bore tube, and the viscosity is determined from the measured flow, appHed pressure, and tube dimensions. The basic equation is the Hagen-Poiseuike expression (eq. 17), where Tj is the viscosity, r the radius of the capillary, /S.p the pressure drop through the capillary, IV the volume of hquid that flows in time /, and U the length of the capillary. 

Steady-state, laminar, isothermal flow is assumed. For a given viscometer with similar fluids and a constant pressure drop, the equation reduces to 77 = Kt or, more commonly, v = r /p = Ct where p is the density, V the kinematic viscosity, and C a constant. Therefore, viscosity can be determined by multiplying the efflux time by a suitable constant. 

Piston Cylinder (Extrusion). Pressure-driven piston cylinder capillary viscometers, ie, extmsion rheometers (Fig. 25), are used primarily to measure the melt viscosity of polymers and other viscous materials (21,47,49,50). A reservoir is connected to a capillary tube, and molten polymer or another material is extmded through the capillary by means of a piston to which a constant force is appHed. Viscosity can be determined from the volumetric flow rate and the pressure drop along the capillary. The basic method and test conditions for a number of thermoplastics are described in ASTM D1238. Melt viscoelasticity can influence the results (160). 

The quantity of catalyst used for a given plant capacity is related to the Hquid hourly space velocity (LHSV), ie, the volume of Hquid hydrocarbon feed per hour per volume of catalyst. To determine the optimal LHSV for a given design, several factors are considered ethylene conversion, styrene selectivity, temperature, pressure, pressure drop, SHR, and catalyst life and cost. In most cases, the LHSV is ia the range of 0.4—0.5 h/L. It corresponds to a large quantity of catalyst, approximately 120 m or 120—160 t depending on the density of the catalyst, for a plant of 300,000 t/yr capacity. 

A catalyst manufactured using a shaped support assumes the same general size and shape of the support, and this is an important consideration in the process design, since these properties determine packing density and the pressure drop across the reactor. Depending on the nature of the main reaction and any side reactions, the contact time of the reactants and products with the catalyst must be optimized for maximum overall efficiency. Since this is frequendy accompHshed by altering dow rates, described in terms of space velocity, the size and shape of the catalyst must be selected carehiUy to allow operation within the capabiUties of the hardware. 

The expansion turbine converts the dynamic energy of the flue gas into mechanical energy. The recoverable energy is determined by the pressure drop through the expander, the expander inlet temperature, and the mass flow of gas (66). This power is then typically used to drive the regenerator air blower. 

Sepa.ra.tlon, Sodium carbonate (soda ash) is recovered from a brine by first contacting the brine with carbon dioxide to form sodium bicarbonate. Sodium bicarbonate has a lower solubiUty than sodium carbonate, and it can be readily crystallized. The primary function of crystallization in this process is separation a high percentage of sodium bicarbonate is soHdified in a form that makes subsequent separation of the crystals from the mother hquor economical. With the available pressure drop across filters that separate Hquid and soHd, the capacity of the process is determined by the rate at which hquor flows through the filter cake. That rate is set by the crystal size distribution produced in the crystallizer. 

An equation for use with venturi meters was given by Chisholm [Br Chem. Eng., 12, 454—457 (1967)]. A procedure for determining steam quahty via pressure-drop measurement with upflow through either venturi meters or sharp-edged orifice plates was given By Colhus and Gacesa [J. Basic Eng., 93, 11-21 (1971)]. 

Shirato, Gotoh, Osasa, and Usami [J. Chem. Eng. Japan, 1, 164— 167 (January 1968)] present a method for determining the mass flow rate of suspended sohds in a liqiiid stream wherein the liquid velocity is measured By an electromagnetic flowmeter and the flow of sohds is calculated from the pressure drops across each of two vertical sections of pipe of different diameter through which the suspension flows in series. 

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