Question

A bituminous coal is burned with air in a boiler furnace. The coal is fed at a rate of 40000 kg/h and has an ultimate analysis of 76wt% C, 5wt% H, 8wt% O, negligible amounts of N and S, and 11wt% non-combustible ash. Air enters a preheater at 30 °C and 1 atm with a relative humidity of 30%, exchanges heat with the hot flue gas leaving the furnace and air enters the furnace at temperature Ta (°C). The flue gas contains 7.8 mole% CO2, 1.2 mole% CO, 11.4mole% O2 and 79.6 mole% N2 on a dry basis. It emerges from the furnace at 260 °C and is cooled to 150 °C in the heater. Non-combustible residue (slag) leaves the furnace at 450 °C and has a heat capacity of 0.97kJ/(kg. °C).

Steam H20a) Flue gas 260 C 0,000 kg coal/h Air 25 C FURNACE Ar 30 C Slag 450 C a) Calculate the rate of cooling required to cool the flue gas from 260 °C to 150 °C and the temperature to which the air is preheated. b) If 25700 kJ/kg energy is generate from the combustion of coal and 60% of the heat transferred from the furnace goes into producing saturated steam at 30 bar from liquid boiler feed water at 50 °C, at what rate (kg/h) is steam generated?

Answer 1

Solutions Gwen the data Coal feed at 40000 talh ulkmati 16 C,5. H, 840 x I1" Ash C+02 CO2 2H2+02 =H0. Imole c need Imole o2 Here, 12 ka c Needs 32 Kq o 32 Kg02 kg c needs 12 tgc 813 2 Hz+o2 t20 2 mol needs mol o2 32 kg0 23%. 02 On mass batis), ( Stnce afr ts hau?ng Theorikcal n Yeuement 00 x40,000 23 ma 40,000 Sxo.+6 x8x o 05- O.23 (30.0 h afr ma 408115 wtRH 3o7 atm Ar enterk 30c and of coaltaiy -ash wil mm Total mat con served, So mas rmain in ue gas

ofue game mas ot ofqmas of-total coal-man ah Total maas arsume ash leaue furnace 408115.9+40 ,000-40,000 Xo-1 atth bottom gegln JHEhh Juw Specific heat o flue gas tA Cf = ik5|eg.k Co) Ra o Coolfnq reaured to cool flue qaa rom 260'c to mf pp C260-150o) F 44371.9 1x C260 -150) 48 80875Y Khr heat qatned b air entercat 30c Heat lo stby ftue gat macpalT-30 hst8o38h 408115.9x1x-30) T144.590c Pre heatd AR to Isbc atA PH exest. 25100 kkg energy t generatd fom cool. 60- o t anferred to produce steam 30 aud oater enters at 50% Supply by ol gained by watev Heat Heat

25700x 40,000 xo.6 mw H2 En talpy ot Seam 2903-2K5tg 30 mcp lso-0)- Enlhalpy of water @soc HI [ ms 2803 26-4.186 x so 25100 x 40000X o6- 2317 83. 16kg hy mu Sleamproctt onrate 30 bar Salu sahon 231.383 Toh