n a sugar factory operating 24 hrs for 250 days in a year, saturated steam at 250oC is supplied to the evaporation station by a natural gas furnace. The steam is used to remove water from incoming...

n a sugar factory operating 24 hrs for 250 days in a year, saturated steam at 250oC is supplied to the evaporation station by a natural gas furnace. The steam is used to remove water from incoming cane juice thus producing a syrup. The excess saturated steam is blown out into the air. This practise is wasteful as fuel at R16.10/kJ is used to generate the steam in an 85% efficient furnace. In order to save costs, installation of water-steam heat exchanger to preheat the cold water into the boiler by the excess steam is proposed.
A counter flow double pipe heat exchanger is tested for the pre-heating of feed water at 30oC using superheated steam at a temperature of 250oC. The superheated steam experiences a temperature drop of 70oC as it exits the heat exchanger. The water to be heated flows through the heat exchanger tube of negligible thickness at a constant rate of 3.47 kg/s. The convective heat transfer coefficients on the superheated steam and water sides are 850 W/m2·K and 1250 W/m2·K, respectively. To account for fouling due to chemical impurities that might be present in the feed water, use an appropriate fouling factor for the water side. Determine :-
(a) the heat exchanger area required to maintain the exit temperature of the water at a minimum of 70oC,

(for counter current flow).

(b) the mass flowrate of steam into the condenser,

(c) what would be the required heat exchanger area in the case of a parallel flow arrangement?