Vaporizers constant vapor outlet temperature

Why, at constant heater outlet temperature, does the coke drum vapor outlet run hotter when shot coke is produced compared to when needle coke is produced ... 

Constant vapor outlet temperature. The hookup illustrated in Fig. V-35 shows an alternate arrangement that is sometimes used to give a fairly constant vapor outlet temperature. It may be combined with a constant pressure arrangement through use of pumps and reducing valves if the pressime must also be controlled to obtain constant gas density for the requirements of mixing valves. 

For partial condenser systems, the pressure can be controlled by manipulating vapor product or a noncondensible vent stream. This gives excellent pressure control. To have a constant top vapor product composition, the condenser outlet temperature also needs to be controlled. For a total condenser system, a butterfly valve in the column overhead vapor line to the condenser has been used. Varying the condenser cooling by various means such as manipulation of coolant flow is also common. 

A hydrocarbon vapor stream is cooled in a heat exchanger where the outlet pressure is 100 kPa. What is the required outlet temperature that would result in 75% mole condensation of the stream The feed stream composition and the components Antoine Equation 2.19 constants (p° in kPa, T in K) are given below. Raoult s law may be assumed valid at the problem conditions. 

The above swii can be eliminated by controlling the preheater heat duty or, better still, the preheater heat duty per unit feed flow (362), instead of the preheater outlet temperature. For steam (or condensing vapor) preheaters, the duly per unit feed flow equals the ratio of the measured steam (or vapor) flow to the measured feed flow times a constant, the constant being the steam latent heat. For a sensible-heated preheater, the above ratio is multiplied by the measured hot-side temperature difference, and the constant is the average hot-fluid heat capacity. For two or more feed preheaters, it is best to compute their total heat duty on-line and ratio it to the feed (68, 259). The computation can be readily performed using conventional analog instrumentation. Similar techniques cured the above-cited swing problems (239,259). 

Because this type of operation essentially involves the Nusselt theory with enhanced liquid flow, a heat transfer coefficient approach is used for calculative purposes, rather than transfer units. Temperature differences are calculated as if a surface condenser were being used. If a single-component vapor is condensing at a constant pressure, the temperature difference at the liquid coolant inlet is T — q. Similarly, the temperature difference at the liquid coolant outlet is Ti — to- This is true because the vapor temperature remains constant from the first drop of condensate to the last drop. Thus, the logarithmic mean temperature driving force is ... 

Solvent mixtures that contain heat-sensitive compounds, are viscous, or have high boihng points can be separated using wiped-film evaporators (WFE) [57, 58]. A WFE operates by receiving a liquid feed into a column that contains several wiper blades. The walls of the WFE are heated at a constant temperature in order to vaporize the solvent film. As the solvent vapors migrate to the center of the WFE, they come into contact with a coohng unit that condenses the vapors, allowing them to flow down the condenser to the outlet receiver. The thin solvent film and reduced system pressure (in the case of vacuum operation) allows the solvents to be separated slowly at lower temperatures [57-59]. 

In this table, A, B, and C are Antoine equation constants, al, av, and bv are the coefficients of the given heat capacity formulas Tbp(°C) and DHv(kJ/mol) (A v) are the normal boiling point and heat of vaporization, xF(mol pentane/mol) is the mole fraction of pentane in the feed. TfCC) is the feed temperature, P(mm Hg) is the system pressure. HAF (Haf) and HBF (Hbf) are the specific enthalpies of pentane and hexane in the feed stream, pA is the vapor pressure of n-pentane (to be determined using the Antoine equation), x and nL x and l) are the mole fraction of pentane in the liquid product stream and the molar flow rate of that stream, respectively, y and nV are the corresponding properties of the vapor product stream. HAL is the specific enthalpy of pentane in the liquid product stream, and DH (A//) is the expression given in Equation 5 for the change in total enthalpy from inlet to outlet. 

The starting conditions of a given hydrocarbon stream are 38°C and 690 kPa. The stream is heated in an exchanger where 23,200 kJ/kmol are transferred to the stream. Calculate the temperature, vapor fraction, and vapor and liquid compositions at the exchanger outlet. Assume the pressure remains constant at 690 psia. Stream composition ... 

The modified Utzir er tube h, the lower part of which is flattened to increase the vaporization surface as much as possible (see cross section), is surrovinded Iqr a heatii jacket and carries a separatory funnel t and a 500-ml. flask r. The attached condenser and the spiral condenser h (which is identical to that used in trisulfane purification and has a toroidal expansion and an outlet to the receiver y) are provided with separate constant-temperature circulating systems. Again, condenser A3 is connected to trap /, which is immersed in a Dry Ice-methanol mixture. Trap f adjoins double trap Z, cooled with liquid nitrc en, which is connected to a high-vacuum pump. The connectii sections of the condensers are covered with asbestos insulationandig. 

Multieffect evaporator [5]. In an evaporation process, the fluid is heated to its saturation temperature, and then additional energy is applied to start the liquid evaporation. Evaporation occurs at constant temperature and requires a large amount of energy so that the molecules in the liquid state pass to the vapor state. Unlike dryers, what is achieved in the evaporator is concentration, where normally a diluted "juice" with 5-10 % solids is concentrated to 30-50 % solids. Indeed, evaporation is a concentration process and not a dehydration process. Tomato juice will be concentrated in a three-stage multieffect evaporator (Fig. 7.46). 1,000 kg/h of tomato juice are fed to the system with an initial concentration of 6 % solids (w/w). The object of the operation is to obtain a commercial concentrate of 31 % solids (w/w). The outlet solid concentration of stages 1-3 are 13, 21, and 31 % (w/w), respectively, (a) How much water was removed in each stage of the system (b) What is the flow rate of the concentrate at the outlet in kg/h ... 

Vapor concentration depends on several factors such as the size of the dispersion bottle, the temperature of the liquid, and the carrier gas flow rate. It can be expected that the carrier gas at a higher flow rate may not be vapor saturated at the outlet since it is constantly passing through the liquid without sufficient residence time to reach liquid — vapor equilibrium. Increasing the volume above the liquid or decreasing the flow rate of the dilution gas prolongs residence time and increases the saturation level of the generated vapor at the outlet. If equilibrium can be established. 

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