Question

Problem 7.32 Heating Ethane with Steam Saturated steam at a gauge pressure of 3.00 bar is to be used to heat a stream of ethane. The ethane enters a heat exchanger at 16°C and 1.5 bar gauge pressure at a rate of 895 m3/min and is heated at constant pressure to 93°C. The steam condenses and leaves the exchanger as a liquid at 20.0°C. The specific enthalpy of ethane at the given pressure is 941 kJ/kg at 16°C and 1073 kJ/kg at 93°C. You may take the compressibility factor for ethane to be 0.970 at the Inlet conditions. Physical Property Tables Power You can calculate the specific enthalpy change by subtraction Use ideal-gas behavior to calculate the mass of ethane. Carry sufficient significant figures throughout calculation. How much power must be transferred to the ethane to heat it from 16°C to 93°C? X 3801.7 kW the tolerance is +/-2%

Answer 1

II 11 289.15 K 366.15 K For Ethane: Inlet Temp (T1) 16 C = (16 + 273.15) K Outlet Temp (T2) 93 c = (93 + 273.15) K Volumetric Flowrate(V) 895 m/min Pressure (P) 1.5 Bar gauge Compressibility Factor for ethane at Inlet (21) 0.97 We need to convert Gauge pressure to absolute pressure Absolute Pressure Gauge Pressure = + Atmospheric pressure Thus, P(absolute) + 1 atm 1.01325 Bar 1.5 Bar 1.5 Bar 2.51325 Bar 251.325 Kpa = (1 Bar = 100 Kpa) Using Ideal gas law for ethane at inlet, with compressibility factor, P: V1 Z. *n* RT1 = ni PV Z, RT 251.325. 895 0.97 8.314. 289.15 11 96.4614 Kmol/min 96.4614 60 (1 min = 60 secods) = 1.6077 Kmol/s Mass flowrate of ethane = Molar flowrate * Mol. Wt of ethane 1.6077 * 30 48.231 Kg/sec = Specific Enthalpy of ethane at inlet (Hz) Specific Enthalpy of ethane at outlet (H2) 941 kJ/kg 1073 kJ/kg = Power required to heat ethane Mass flowrate of Ethane * (H2-Ha) = 48.231 * (1073 - 941) kJ/s = 6366.492 kb/s 11 6366.492 kW (1 kJ/s = 1 kW)