In a surface coating operation, a polymer (plastic) dissolved in liquid acetone is sprayed on a solid surface and a stream of hot air is then blown over the surface, vaporizing the acetone and leaving a residual polymer film of uniform thickness. Because environmental standards do not allow discharging acetone into the atmosphere, a proposal to incinerate the stream is to be evaluated.

The proposed process uses two parallel columns containing beds of solid particles. The air— acetone stream, which contains acetone and oxygen in stoichiometric proportion enters one of the beds at 1500 mm Hg absolute at a rate of 1410 standard cubic meters per minute. The particles in the bed have been preheated and transfer heat to the gas. The mixture ignites when its temperature reaches 562°C, and combustion takes place rapidly and adiabatically. The combustion products then pass through and heat the particles in the second bed, cooling down to 350°C in the process. Periodically the flow is switched so that the heated outlet bed becomes the feed gas pre-heater/combustion reactor and vice versa.

Use the following average values for C_p [kJ/(mol∙°C)1 in solving the problems to be given: 0.126 for C₃H₆O. 0.033 for O₂, 0.032 for N₂, 0.052 for CO₂, and 0.040 for H₂O (v).

(a) If the relative saturation of acetone in the feed stream is 12.2%, what is the stream temperature?

(b) Determine the composition of the gas after combustion, assuming that all of the acetone is converted to CO₂ and H₂O and estimate the temperature of this stream.

(c) Estimate the rates (kW) at which heat are transferred from the inlet bed particles to the feed gas prior to combustion and from the combustion gases to the outlet bed particles. Suggest an alternative to the two-bed feed switching arrangement that would achieve the same purpose.