7.Gas Absorption

DAY 2: CHEMICAL ENGINEERING – Gas Absorption

GAS ABSORPTION Review Questions 1. For a.) b.) c.) d.)

absorbing a sparingly soluble gas in a liquid, the gas side coefficient should be increased liquid side coefficient should be increased gas side coefficient should be decreased liquid side coefficient should be decreased

2. For a.) b.) c.) d.)

contacting a highly soluble gas with a liquid bubble the gas through liquid spray the liquid on gas stream either a or b will suffice none of these

3. Wetted wall tower experiment determines a.) molal diffusivity b.) volumetric coefficient c.) mass transfer coefficient d.) none of these 4. Stacked packing compared to dumped packing a.) provides poorer contact between the fluids b.) gives lower pressure drop c.) both (a) and (b) d.) gives higher drop 5. Channeling is most severe a.) in towers packed with stacked packing b.) in towers packed randomly with crushed solids c.) in dumped packing of regular units d.) at very high liquid flow rate 6. Flooding results in a.) High tray efficiency b.) Low tray efficiency c.) High gas velocity d.) Good contact between the fluids 7. Operating velocity in a packed tower is usually a.) half the flooding velocity b.) twice the flooding velocity c.) equal to flooding velocity d.) more than the flooding velocity 8. At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid a.) is greater than that in dry packed b.) is lower than that in drying packing c.) is same as that in drying packing d.) cannot be predicted as data are insufficient 9. Berl saddle made of carbon cannot be used a.) for alkalis b.) for SO2 c.) for H2SO4 d.) in oxidizing atmosphere

DAY 2: CHEMICAL ENGINEERING – Gas Absorption

10. Flooding in a column results due to a.) high pressure drop b.) low pressure drop c.) low velocity of the liquid d.) high temperature 11. The operating line for an absorbed is curved when plotted in terms of a.) mole fractions b.) mole ratios c.) partial pressure d.) mass fractions 12. In case of an absorber, the operating a.) line always lies above the equilibrium curve b.) line always lies below the equilibrium curve c.) line can be either above or below the equilibrium curve d.) velocity is more than the loading velocity 13. For a.) b.) c.) d.)

an absorber, both equilibrium and operating line will be straight for concentrated solution and non-isothermal operation dilute solution and non-isothermal operation dilute solution and isothermal operation concentrated solution and isothermal operation

14. In case of desorber (stipper) a.) the operating line always lies above the equilibrium curve b.) the operating line always lies below the equilibrium line c.) temperature remains unaffected d.) temperature always increases 15. The minimum liquid rate to be used in an absorber corresponds to an operating line a.) of slope = 1 b.) of slope = '1 c.) tangential to the equilibrium curve d.) none of these 16. Absorption factor is defined as a.) slope of the equilibrium curve slope of the operating line b.) slope of the operating line slope of the equilibrium curve c.) slope of the operating line - slope of the equilibrium curve d.) slope of the operating linexslope of the equilibrium curve 17. H2S present in naphtha reformed gas is removed by absorbing with a.) ethanolamine b.) K2CO2 c.) HCL d.) vacuum gas soil 18. If G = insoluble gas in gas stream and L = non-volatile solvent in liquid stream, then the slope of the operating line for the absorber is a.) L/G b.) G/L c.) always < 1 d.) none of these 19. Raschig ring made of porcelain cannot be used for treating a.) concentrated hydrochloric acid b.) concentrated nitric acid c.) alkalis d.) concentrated sulfuric acid 20. For absorbers, high pressure drop results in a.) increased efficiency b.) decreased efficiency c.) high operating cost d.) better gas liquid contact

DAY 2: CHEMICAL ENGINEERING – Gas Absorption

21. Which of the following is an undesirable property for an absorbing solvent? a.) low vapour pressure b.) low velocity c.) low freezing point d.) none of these 22. Out of the following properties of a solvent for absorption, which combination of properties provides a good solvent? I. high viscosity II. Low viscosity III. high vapour pressure IV. Low vapour pressure V. high gas solubility VI. High freezing point VII. low freezing point Choose from the following combinations: a.) II,IV,V,VII c.) II,IV,V,VI

b.) I,IV,V,VI d.) I,IV,V,VII

23. When both the fluids flow concurrently in an absorber, the slope of the operating line is a.) negative b.) positive c.) 1 d.) -1 24. Ammonia present in the coke oven gas is removed by washing with a.) caustic solution b.) dilute ammoniacal liquor c.) dilute HCl d.) ethanolamine 25. Which of the following is not fixed by process requirements in the design of absorbers? a.) flow rate of the entering gas b.) composition of the entering liquid c.) terminal concentration of gas stream d.) none of these 26. In an absorber, HETP does not vary with a.) flow rate of liquid c.) type and size of packing

b.) flow rate of gas d.) none of these

27. Which of the following is an undesirable property in a low-packing a.) large surface per unit volume b.) large free cross-section c.) low weight per unit volume d.) large weight of liquid retained 28. Very tall packed towers are divided into series of beds to a.) reduce the over-all pressure drop b.) avoid channeling c.) reduce liquid hold-up d.) avoid flooding 29. For the same system, if the same liquid used in an absorber is decreased, the tower height will a.) increase b.) decrease c.) remain unaffected d.) decrease or increase depends on the type of liquid 30. HETP is numerically equal to HTU only when operating line a.) lies below the equilibrium line b.) lies above the equilibrium line c.) and equilibrium lines are parallel d.) is far from the equilibrium line

DAY 2: CHEMICAL ENGINEERING – Gas Absorption

31. Desirable value of absorption factor in an absorber is a.) 1 b.) 1 d.) 0.5 32. Absorption accompanied by heat evolution results in a.) increased capacity of the absorber b.) increase in equilibrium solubility c.) decrease in equilibrium solubility d.) none of these 33. Co-current absorbers are usually used when the gas to be dissolved in the liquid is a.) sparingly soluble b.) highly soluble c.) a pure substance d.) a mixture 34. Channeling in a packed tower results from a.) high pressure drop c.) non-uniformity of packing

b.) maldistribution of liquid d.) both b and c

35. Diameter of raschig rings used in packed tower in industry is normally around a.) 2" b.) 8" c.) 12" d.) 18"