Question

3.3 Electric Heating 8 marks One of the other engineers has suggested that electric immersion heaters would be cheaper for heating the solution instead of the steam heat exchanger. a) If the site supply voltage is 414 V, 3-phase what would be the current required?[2] b) What would be the resistance of the heating element required for this duty? [2] c) Do you consider electric heating would be cheaper over the anticipated plant life of 20 years? You must justify your answer. [4] 3.2 Steam Heating [12 Marks In the above nickel refinery steam is used to heat nickel bearing solution from 90°C to 230°C in a conventional shell and tube heat exchanger prior to oxyhydrolysis, below. The solution does not evaporate owing to its high pressure and the heat loss from the shell is 3% of the heat transferred to the solution as shown Heat loss 3% Steam 90 °C (230 C 4000 kPa) w 40 tonne/hour Fitered Ni solution from Condensate- leaching plant OXYHYDROLYSIS REACTOR hydrogen REDUCTION AUTOCLAVE (200 deg C 2800 kPa) a) If the mean specific heat of the nickel solution between 80 & 250°C is 4.18 kJ/kg °C, calculate the heat exchanger duty in kW. [4] b) Determine the steam pressure and flow rate required. [8 3.3 Electric Heating (8 marks One of the other engineers has suggested that electric immersion heaters would be cheaper for heating the solution instead of the steam heat exchanger. a) If the site supply voltage is 414 V, 3-phase what would be the current required ?12 b) What would be the resistance of the heating element required for this duty? [2] Do you consider electric heating would be cheaper over the anticipated plant life of 20 years? You must justify your answer. c) (4] End of Part A

Answer 1

mard a tua n'ekle per houwr (m) 4.0 tonned 40 X10° K Tetal temperahuhe conge = At = t2-t 230-9o 140'c 4-18 KJ/up'e Specifiu hiat CS) Total heat faguisd mxs xAt =-40 EBX4AF 2 40x10 X4.18x 140 = 2 3 4-08 O 00 KJ 0, 00 4-2 Kwh KJ= kwh= 9 &31 3-6 knh MeanA per hour 9631 36 Kwh s Aaguired pour- 98313 6 kW

(a) 4ppiy vai tage = 414V, 3 element has powerfactor kestiy SO 98313.6 KW=n3 x414x IL* | 1370 47 KA elemert hasistan ee 14V 2 3./VL P 9 &313.6 KW = 3x 414' X R 3 .74 33 m .

weuld be cheaper Euctric HLating to Hne ct e due element ond maintenam yeand omd polluti en 20 Auo i i e of coTrsien