Cocurrent packed towers

Wankat ° has a description of the design method for cocurrent packed towers. The procedure to determine the tower height using the HTU method follows that for countercurrent flow. 

A 27 ft/sec cocurrent packed tower can achieve 90 percent SO2 removal with less energy input than a countercurrent spray tower. 

After the SO converter has stabilized, the 6—7% SO gas stream can be further diluted with dry air, I, to provide the SO reaction gas at a prescribed concentration, ca 4 vol % for LAB sulfonation and ca 2.5% for alcohol ethoxylate sulfation. The molten sulfur is accurately measured and controlled by mass flow meters. The organic feedstock is also accurately controlled by mass flow meters and a variable speed-driven gear pump. The high velocity SO reaction gas and organic feedstock are introduced into the top of the sulfonation reactor,, in cocurrent downward flow where the reaction product and gas are separated in a cyclone separator, K, then pumped to a cooler, L, and circulated back into a quench cooling reservoir at the base of the reactor, unique to Chemithon concentric reactor systems. The gas stream from the cyclone separator, M, is sent to an electrostatic precipitator (ESP), N, which removes entrained acidic organics, and then sent to the packed tower, H, where SO2 and any SO traces are adsorbed in a dilute NaOH solution and finally vented, O. Even a 99% conversion of SO2 to SO contributes ca 500 ppm SO2 to the effluent gas. 

Packed-bed scrubbers m be construc ted for either vertical or horizontal gas flow. Vertical-flow units (packed towers) commonly use countercurrent flow of gas and liquid, although cocurrent flow is sometimes used. Packed scrubbers using horizontal gas flow usually employ cross-flow of liquid. 

For dilute mixtures and when Henry s law applies, prove that the number of overall transfer units for cocurrent gas absorption in packed towers is given by... 

Packed towers, used for continuous contact of liquid and gas in both counter-current and cocurrent flow, are vertical columns which have been filled with packing or devices of large surface, as in Fig. 6.27. The liquid is distributed over, and trickles down through, the packed bed, exposing a large surface to contact the gas. 

Absorption can take place in a countercurrent, cocurrent, or cross-flow device. Vertical countercurrent towers are either built with a metal, plastic, or ceramic packing or constructed as plate towers with various types of plates. This chapter will discuss the solvents used to carry out absorption and the various types of absorption equipment. 

It shoiild be pointed out that in most liquefaction processes, the flow of the reactants is cocurrent i q)ward. In cocurrent operation, there is no flooding limit, and greater throu put is attained compared with co mterc irrent column of similar size. Moreover, for the same values of gas and liquid flow rates, interfacial area, liqiaid mass transfer coefficient and pressure drop values in a cocurrent upward packed column are always higher than those obtained in downflow towers (l 3). Upflow operations also give a better performance due to larger liqioid holdup and better liq iid distribution throu out the catalyst bed jlkk). 

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