Question

Question 1 25 Marks A fuel consisting of carbon, hydrogen, sulphur, oxygen and non-combustible is burnt under excess air conditions. A bomb calorimeter test gives the fuel energy content of 38.5 MJ/kg and after combustion the mass of ash is 5% of the original mass of fuel burnt. The percentage analysis of the exhaust gas yields (by basis) mass CO2 H20 N2 SO2 14.2% 15% 69.5% 0.3% O2 1% For this combustion calculation, assume 23% O2 and 77% N2 in air by mass. Determine; (a) the air-fuel ratio (5 marks) (5 marks) (5 marks) (b) the % composition of the fuel (c) the stoichiometric air-fuel ratio (d) the mass of fuel required per hour to a continuous energy input of 1 MW (5 marks) (5 marks) (e) the mass of ash produced per hour.

Answer 1

Solution combustion Equation for the O2tN2) C H S +0 + Non-Combustible + Air > C02 H20 N2+ SO2 +02 t Ash 4.2y.) 69-5) 3) Let the mass cexhaust as is JDo Now, fox C 0 CO2 44 32y CO2 14.2 214. 2 JD 33 44 Mass of 02 equired 1equired 124.2 387 44 Mass of For, 2H20 2H202 36 32 4 H20 Fox 4 iguied Mass of02 equire -67 13 33 H2 36XIS = Mass 32 x1S 36 For S SD2 S 02 64 3 2 32 03 of Mass of S Mass of02 euire SD2 3203 PAST O 32x0.3 64

From combustion eaction from air 69.5 kaof N2 comes In air, 02 77 k N2 is mixed uith 23 23 -x 69 S 695 of O 2 20.76 тедайер Mass fair 69.St 20.76 . =90.26 for combustion yeachion Mass balance mf 57 JOO ma of exhaist gas mass mf t 90-26 fuel is raquiee 0.25 Air fuel yahio 90.26 10. 25 Ang = 8.8 oO2 Tequiredfor comhustien Total mass exhaustgas Or) JD 33 13 33 0.15 J 24.S1 Mass ooxygen in air fuel 20.76 24.8)- 20 76 4.05 of 02 in 4.05 Mass ful (by mas) Сompositon Tedet mas5 3.87 C. 37.75 0.3775 0.25 67 10.25 = 16.29y. H OI629 146 S /o.2.5 4.OS 39. 50y 0-25 Non- Combusthble

Focomplete combustium ef 02 eguire SSbuL 23.8J 02 equired from air 4. 0S 23.8) 19.76 cavraperding to 19 76 f ofAir . Mass of air 19.76 100 9.76 23 Stoichiometic air fuel Tatio Ans 8S-S1 8.38 0.25 Given that Calonific Value of fuel x CV Power 38 MA IMW 0. 02.5974 s 38.5 二93.5 ash produced per hour 4-675h Mass f