(c) A power plant operates with 1150 ppm NOx in the fue gas. The flue gas fow ra
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(c) A power plant operates with 1150 ppm NOx in the fue gas. The flue gas fow rate is 6 x 101m' min1 at 300°C and 1 atm. Afier passing through an SCR unit (vohume 6,000 litres) the NOx content of the gas is reduced to the required 200 ppm Calculate NOx conversion (1 mark) (i) Space velocity (2 marks) i)the stoichiometric amount of ammonia required in kg hr to reduce the NOx content from 1150 ppm to 200 ppm. (4 marks) part (c) falls dramatically due to poisoning deactivation. Suggest possible causes of this poisoning/deactivation and briefly outline characterisation methods which may be used to verify your suggestions. (5 marks)Explanation / Answer
1.Initial concentration of NOx= 1150 ppm, concentration of NOX after passing through SCR= 200ppm
% conversion =100*( initial concentration of NOx- final concentration of NOX)/ initial concentration of NOX
=100*(1150-200)/1150 =82.61%
2. volume of ractor = 6000L, 1000L= 1m3, 6000L= 6 M3 and flow rate = 6*104 m3/min
space time = volume of SCR/Volumatric flow rate = 6/(6*104) min=1/104 min
space velocity = 1/space time = 104/min
3. the reaction is NO + NO2 + 2NH3 2N2 + 3H2O
2 mole of NO and NO2 requires 2 moles of ammonia
moles of flue gas can be calculated from ideal gas equation, n= PV/RT
P=1atm ,T = 300 deg.c= 300+273= 573K, V= 6*104m3/min, 1 m3= 1000L, V= 6*104*1000 L/min, R= 0.0821 L.atm/mole.K, n = 1* 6*107/(0.0821*573)=1275421 moles =1.275*106 moles /min
there is 1150 moles per 106 moles of flue gas
1.275*106 moles will have 1.275*1150 moles/min =1466.25 moles/min of NOX.
NOX contains NO and NO2 and the mixture of NO and NO2 as per the reaction requires 1466.25 moles/min of NH3
1466.25*60 moles/hr of NH3= 87975 moles/hr
molar mass of NH3= 17 g/mole, mass of NH3= 87975*17 g/hr =1495575 g/hr= 1495.775 kg/hr
SCR catalyst contain a carrier like TIO2 and base metal of either vanadium,molybdenium etc.
The SCR is sensitive to contamination due to variation of composition of flue gas and also plugging. The untreated gas plugs the pores of the catalyst present in the catalyst.
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