Gas or Vapor Flow Rates

The upper limit on gas-flow rates is dictated by two factors, excessive liquid entrainment and excessive frothing. Neither of these is necessarily fatal to the operation, but both bring about a serious deterioration in column performance. The upper limit is usually set in terms of the superficial vapor velocity Vg based on the cross-sectional area of the column A, which is given by the relation 

Suppose, now, that the boil-up rate Qg is 0.2 m /s. We can then, by dividing Qg by the permissible upper limit to Vg, obtain an estimate of the minimum column diameter  

An increase in liquid flow, brought about, for example, by an increase in reflux ratio, causes the liquid to back up in the downcomer, ultimately spilling over onto the tray above. The column floods and operation essentially ceases. To avoid this fatal occurrence, an upper limit is usually set on liquid velocity in the downcomer, v, given by 

Mass Transfer and Separation Processes Principles and Applications 

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The situation is similar to class 1, except that the MTT is above Tm4. This means that under heat accumulation conditions, the activity of secondary reactions cannot be neglected, leading to a slow but significant pressure increase, or gas or vapor release. Nevertheless, the situation may become critical only if the reaction mass is left for a longer time at the level MTT. The assessment can be made using the same procedure as for criticality class 1, represented in Figure 10.8. The gas or vapor flow rate is an important parameter for the design of the required protection measures such as condenser, scrubber, or other treatment units. 

Release Source Terms (Gas or Vapor Flow Rates).1441... 

Maximum gas or vapor flow rate in the column section of interest (kmol/h)... 

Faraday number, C/mol gas or vapor flow rate, kg/s or mol/s superficial carrier flow rate, kg/m s heat transfer coefficient, J/m s K height, m... 

G = Gas specific gravity = mol. wt./29 Pi = Valve inlet pressure, psia AP = Pressure drop across valve, psi Q = Gas flow rate, SCFH Qs = Steam or vapor flow rate, Ib/hr T = Absolute temperature of gas at inlet, °R T5I1 = Degrees of superheat, °F... 

The rate of gas or vapor flow throngh a hole in process eqnipment is a fnnction of (in descending order of importance) the diameter of the hole, the pressnre within the eqnipment, the molecular weight of the gas or vapor, the temperature of the gas or vapor within the eqnipment, and the specific-heat ratio. 

The following simplified equation can be used to estimate the rate of gas or vapor flow from the open end of a pipe, for unchoked (sub-sonic) conditions [10] ... 

At higher total flow rates, particularly when the Hquid is prone to foaming, the reactor is a pulsed column. This designation arises from the observation that the pressure drop within the catalyst bed cycles at a constant frequency as a result of Hquid temporarily blocking gas or vapor pathways. The pulsed column is not to be confused with the pulse reactor used to obtain kinetic data ia which a pulse of reactant is introduced into a tube containing a small amount of catalyst. 

Three related methods based on the quasiisostatic method are used to measure permeability. The most commonly used technique allows the permeant gas or vapor to flow continuously through one chamber of the permeability cell. The gas or vapor permeates through the sample and is accumulated in the lower-concentration chamber. At predetermined time intervals, aliquots are withdrawn from the lower cell chamber for analysis. The total quantity of accumulated permeant is then determined and plotted as a function of time. The slope of the linear portion of the transmission-rate profile is related to the sample s permeability. 

MW OAREA PTB Q Qa QAO Qo Qw RHOG RHOL RHOW S molecular weight oil cross-section area, ft2 salt in oil at outlet of desalter unit, lb/1000 bbl total flow of emulsified water and oil actual gas flow rate, ft3/s liquid rate, ft3/s crude oil flow rate, dry basis, bpd production water rate, bpd gas or vapor density, lb/ft3 liquid or oil density, lb/ft3 water-phase density lb/ft3 total salt content in the production water and dilution water, lb/day... 

A continuous-flow calorimeter is used for measuring (CP) (J mol-1 K-1) for liquids, gases, and vapors, and even mixed gases a flow of liquid, gas, or vapor is passed at a known constant flow rate F (mol s ) over an electrical heater with input power W (watts) the temperature is measured just before... 

The combustion train and recording method was developed by R. D. Goodwin (Goodwin, 19), and allows measurements to be made on individual catalyst particles, and quantities of catalyst material of 100 mg. and less. The total amount of CO2 produced at any one time is recorded vs. time on a pen recorder. The total recorder deflection reached supplies the value of initial carbon concentration Cc. The air (or oxygen) flow rate is maintained sufficiently high to provide the known constant oxygen partial pressure Co in the gas stream. The ratio n is found to be close to unity in the case of coke laid down on the porous catalysts by exposure to hydrocarbon vapors at cracking temperatures. The diffusivity is best... 

High ratios of gas (or vapor) to catalyst volumes, and velocities of 15 to 40 ft./second, are used in carrier lines in order to maintain the catalyst in dilute suspension and to prevent accumulation of stagnant catalyst at any point (53). The net flow rates of catalyst and vapors in the carrier lines typically correspond to an aerated bulk density of the order of 5 Ib./cu. ft. (68). However, the actual density is about twice the calculated value because of slip factor (105). 

One of the earliest flow diagrams for horizontal flow was devised by Baker.An example is given in Fig. 12 based on the work of Schicht from Butterworth and Hewitt.The vertical axis is Gx/X and the horizontal axis is (1 — x)hj/jx, where G is the total mass flow rate and x is the quality, i.e., the gas or vapor phase mass flow fraction ... 

A relief device should be installed vertically and preferably on a nozzle at the top of the equipment (for example, vessel) or on a tee connected to a pipeline. When discharging a gas or vapor, the fluid reaches sonic velocity when passing through a relief device. Thus, the gas flow rate or AP can be determined by a method as described in Chapter Three. 

Absorbent rates of 200, 250, or 300 kmol/h are possible. It is required to determine the lowest among these that would meet the butane speci-hcation, and to calculate the product rates and compositions when the column is operated with the selected absorbent rate. Use the modular column section method with stripping factors based on inlet liquid and vapor flow rates. The gas and absorbent streams are defined below. 

The EPA standard states that the total quantity of gas or vapor is to be divided by 10 min, to obtain a rate of flow that could then serve as input to the dispersion tables. 

The total interstage flow rate of heads or tails is a measure of the size of the separation plant. In a distillation plant, for example, the total volume of column internals is proportional to the total interplate vapor flow rate. In a gaseous diffusion plant, the total amount of power expended in pumping gas from one stage to the next is proportional to the total heads flow rate. 

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