Figure 1.
Polyethylene Tellerettes are a recent addition to commercially available packing materials
AARON J. TELLER' Fenn College, Cleveland, Ohio HARRY E. FORD The Harshaw Chemical Co., Cleveland, Ohio
Packed Column Performance of Carbon DioxideMonoethanolamine System Flow pattern effects due to packing geometry, as well as inherent packing surface, make a significant contribution to mass transfer efficiency
CARBON
dioxide is generally removed from industrial gas streamb by absorption in alkaline solution. Finding wide commercial application today are aqueous solutions of weak organic bases known as the ethanolamines. Monoethanolamine (MEA), because of its high absorption capacity, is one of the most widely used. I n industrial installations the absorbing solution is circulated continuously in a closed circuit, first through an absorption tower countercurrent to the gas from which the carbon dioxide is removed. then through a stripping column where the amine carbonate is decomposed by heat, thus liberating the carbon dioxide. Excessive shipping costs for liquid and
Present address, University of Florida, Gainesville, Fla.
solid carbon dioxide have made it advisable to construct plants of relatively small size; in fact, portable units are enjoying popularity. Many commercial installations, relatively small, utilize packed columns. For a unit as compact as possible and requiring a minimum of investment and operating costs, good process design necessitates adequate information on the effect of flow rates and packing geometry on performance. Although the performance characteristics of a commercial tray column for this system have been presented by Kohl (3), published information on packed column operation a t atmospheric pressure is very limited. T h e data of Schneerson and Leibush (7), although thorough, were obtained with a unit 1 inch in diameter and cannot be extrapolated to large column design. Gregory and Scharmann (2) used a commercial
sized tower (11.75 inches diameter) but limited carbon dioxide removal to that from hydrogen a t 200 p.s.i.g. T h e authors have compared three 1inch nominal sized packings for use in the carbon dioxide-monoethanolamine system (see table on next page). Ceramic Berl saddles and steel Raschig -rings have long been used in absorption processes and have received considerable attention in the literature. Polyethylene Tellerettes (formerly called Rosettes) are a recent addition to the list of commerically available packing materials (Figure 1). Experimental Procedure The pilot plant unit (Figure 2) consisted of an absorption column for determining comparative packing performance and a stripping column for therVOL. 50, NO. 8
AUGUST 1958
1201
Figure 2. The experimental unit consisted of an absorption column and a stripping column '
mally dissociating the amine carbonate formed during carbon dioxide absorption by the monoethanolamine solution. The absorption tower, 8 inches in inside diameter, was fabricated of glass sections and had a packed height of 5.67 feet The column was lined with polyethylene nonwetting wall liner, 1 / 1 6 inch thick ( 9 ) . This construction decreased the channeling tendency of the liquid along the column wall. Uniform irrigation of the packing was afforded by a multiple weir 8 inches above the packed bed. The weir-type overflow distributing tubes extended through a woven wire mesh located above the bed and below the gas outlet to decrease carry-over of entrained liquid. The atmospheric pressure regeneration unit consisted of a glass stripping column 8 inches in inside diameter containing seven bubble trays. A 150gallon reboiler supplied vapor to the feed plate of the stripper. A small overhead water-cooled condenser returned condensable vapors to the stripper while the liberated carbon dioxide was discharged to outside atmosphere. Four 55-gallon storage tanks acted as reservoirs for the regenerated amine solution.
Solution storage \
