2. H2O is used to scrub HCHO (formaldehyde) from a waste gas stream in an absorption column. The waste gas contains 500 kgh - HCHO and 1900 kgh - N2 and is at 60C. The ratio of water to waste gas flow rates is 4:1. The waste gas is fed into the bottom of the absorption column and meets a counter current stream of H20 entering the top of the column at 20C. The scrubbed N2 leaves the top of the column at 20C. (i) What is the flow rate of the H20-HCHO solution leaving the base of the column? Assume that all the HCHO is scrubbed from the waste gas and dissolves in the water. (ii) What is the temperature of the H2O-HCHO solution which leaves the base of the column? Hints: (1) Assume datum/reference temperature (To) as 0C, (2) Energy in = Energy out + Accumulation, (3) Energy = Stream flow rate x Specific heat x Change in temperature (T-TD) Where accumulation could be a heat of reaction or heat of solution Data Specific heat of N2 (gas) Specific heat of HCHO (gas) Specific heat of H20 (liquid) Specific heat of H2O-HCHO solution 11 11 11 11 1.04 kJkg K-1 1.18 kJkg K-1 4.187 kJkg K-1 4.187 kJkg K-1 = Heat of solution of formaldehyde in water II -87.9 kJmol-1