Liquid-to-gas ratio

Calculation of Liquid-to-Gas Ratio The minimum possible liquid rate is readily calculated from the composition of the entering gas and the solubility of the solute in the exit liquor, saturation being assumed. It may be necessaiy to estimate the temperature of the exit liquid based on the heat of solution of the solute gas. Values of latent and specific heats and values of heats of solution (at infinite dilution) are given in Sec. 2. 

The actual liquid-to-gas ratio (solvent-circulation rate) normally will be greater than the minimum by as much as 25 to 100 percent and may be arrived at by economic considerations as well as by judgment and experience. For example, in some packed-tower applications involving veiy soluble gases or vacuum operation, the minimum quantity of solvent needed to dissolve the solute may be insufficient to keep the packing surface thoroughly wet, leading to poor distribution of the liquid stream. 

Optimization of the liquid-to-gas ratio in terms of total annual costs often suggests that the molar fiquid-to-gas ratio Lm/G should be about 1.2 to 1.5 times the theoretical minimum corresponding to equilibrium at the rich end of the tower (infinite height), provided flooding is not a problem. This would be an alternative to assuming that L /G>i, — mlO.7, for example. 

When the exit-liquor temperature rises owing to the heat of absorption of the solute, the value of m changes through the tower, and the liquid-to-gas ratio must be chosen to give reasonable values of miG ilh. and where the subscripts 1 and 2 refer to the bot-... 

Calvert found that reentrainment from the baffles was affected by the gas velocity, the liquid-to-gas ratio, and the orientation of the baffles. Horizontal gas flow past vertical baffles provided the best drainage and lowest reentrainment. Safe operating regions with vertical baffles are shown in Fig. 14-112. Horizontal baffles gave the poorest drainage... 

Limestone is pulverized to 80 to 90 percent through 200 mesh. Shiny concentrations of 5 to 40% have been checked in pilot plants. Liquid to gas ratios are 0.2 to 0.3 gaLMSCF. Flue gas enters at 149°C (300°F) at a velocity of 2.44 m/s (8 ft/s). Utilization of 80 percent of the solid reagent may be approached. Flow is in parallel downward. Residence times are 10 to 12 s. At the outlet the particles are made just diy enough to keep from sticking to the wall, and the gas is within 11 to 28°C (20 to 50°F) of saturation. The fine powder is recovered with fabric filters. 

When liquid content of the feed is high, a condenser and a separator are needed. The liquid-to-gas ratio can be as high, so that even at reaction temperatures a liquid phase is present. The reactor still performs as a CSTR, however the response time for changes will be much longer than for vapor phase alone. Much lower RPM will be needed for liquid-phase studies (or liquid and gas phase experiments) since the density of the pumped fluid is an order-of-magnitude greater than for vapor phase alone. In this case a foamy mixture or a liquid saturated with gas is recirculated. 

Boiling point Critieal temperature Critieal pressure Liquid-to-gas ratio by volume... 

FIG. 17-46 Performance of pilot-plant venturi scrubber on fly ash. Liquid-to-gas ratio, gal/1000 ft3 0,10 A, 15 , 20. (Raben, United States-U.S.S.R. Symposium on Fine-Farticulate Emissions from Industrial Sources, San Francisco, 1974.)... 

Example 9.11 employs this method for finding the number of transfer units as a function of liquid to gas ratio, both with finite and infinite values of km/kh. The computer programs for the solution of this example are short but highly desirable. Graphical methods have been widely used and are described for example by Foust et al. (1980). 

Structure. Foam structure is characterized by the wetness" of the system. Foams with arbitrarily large liquid to gas ratios can be generated by excessive agitation or by intentionally bubbling gas through a fluid. If the liquid content is sufficiently great, the foam consists of well-separated spherical bubbles thal rapidly rise upwards displacing the heavier liquid. Such a system is usually called a froth, nr bubbly liquid, rather than a foam. 

C with a water content of 0.075 kg/kg. Although heat and mass transfer rates were relatively insensitive to the choice of the model, the amount of fog formation was not. The models neglect the effects of condensation within the boundary layer, thus underestimating fog formation by a factor of up to three. The amount of fog formed in flue-gas washing plants increased up to a maximum value with decreasing feed-water temperature over a narrow band of liquid-to-gas ratios. 

Liquid-to-Gas Ratio The L/C ratio can have a significant influence on the development of temperature profiles in gas... 

When no chemical reactions are involved in the absorption of more than one soluble component from an insoluble gas, the design conditions (temperature, pressure, liquid-to-gas ratio) are normally determined by the volatility or physical solubility of the least soluble component for which the recoveiy is specified. 

Example 7 Multicomponent Absorption Dilute Case Air entering a tower contains 1 percent acetaldehyde and 2 percent acetone. The liquid-to-gas ratio for optimum acetone recovery is L /Gm = 3.1 mol/mol when the fresh-solvent temperature is 31.5°C. The value of y°/x for acetaldehyde has been measured as 50 at the boiling point of a dilute solution, 93.5°C. What will the percentage recovery of acetaldehyde be under conditions of optimal acetone recovery ... 

The liquid-to-gas ratio is chosen on the basis of the least soluble component in the feed gas that must be absorbed completely. Each component will then have its own operating line with slope equal to Lm/Gm (i.e., the operating lines for the various components will be parallel). 

A hydrocarbon feed gas is to be treated in an existing four-theoretical-tray absorber to remove butane and heavier components. The recovery specification for the key component, butane, is 75 percent. The composition of the exit gas from the absorber and the required liquid-to-gas ratio are to be estimated. The feed-gas composition and the equilibrium K values for each component at the temperature of the (solute-free) lean oil are presented in the following table ... 

FIG. 14-126 Predicted spray-tower cut diameter as a function of sprayed length and spray droplet size for (a) vertical-countercurrent towers and (b) horizontal-cross-flow towers per Calvert [J. Air Pollut. Control Assoc., 24, 929 (1974)]. Curve 1 is for 200-lJn spray droplets, curve 2 for 500-lJn spray, and curve 3 for 1000-pm spray. QdQc is the volumetric liquid-to-gas ratio, L liquid/m3 gas, and uG is the superficial gas velocity in the tower. To convert liters per cubic meter to cubic feet per cubic foot, multiply by 10 3. 

Bendure indicates 10 ways to increase foam stability (1) increase bulk liquid viscosity, (2) increase surface viscosity, (3) maintain thick walls (higher liquid-to-gas ratio), (4) reduce liquid surface tension, (5) increase surface elasticity, (6) increase surface concentration, (7) reduce surfactant-adsorption rate, (8) prevent liquid evaporation, (9) avoid mechanical stresses, and (10) eliminate foam inhibitors. Obviously, the reverse of each of these actions, when possible, is a way to control and break foam. 

Determine the liquid and gas loadings. The liquid and gas loadings are defined by the liquid-to-gas ratio determined in step 3 and by the stipulation that the tower is to operate at an approach to flooding of 80 percent at constant L/G. For flooding defined at constant L/G, Eq. (11.1) becomes... 

---