NCEES 2011 TF Problem 538

[SK82 P.E.]

This is problem 538 in the NCEES 2011 TF practice exam.  

Can someone break down the solution to this problem for slow ones like me.  I have no clue how to approach this problem.  I assuming they couldn't change this problem that much so if they asked for lbm NO2/day, then I would use 7.5xE6 [lbm/day] x .013  x 46 (MW of NO2)/ 14 (MW of N) ?

 

[Audi Driver P.E.]

The approach: the first step is to figure out how much coal is required, based on the heating value of coal, duration, required output, etc.  Once you know how much coal you need, then you have to break that total down into its relevant parts.  The question basically is, if you start with this much carbon, how much CO2 can you end up with?  So you multiply the total coal by the fraction that is carbon (in this case).  Then, to find the amount of CO2 that is produced from the amount of Carbon, you multiply that by the ratio of CO2 to Carbon.  Since it's a one to one ratio, they leave off the multiplying factor in the given solution.  If it was a 2 to 1 ratio, then you would divide by 2 (i.e.  (1* MW CO2)/(2 * MW C) ). Your approach for if the question were NO2 is correct, if all the N is converted to NO2.  If only half of the N is converted to NO2 then you would need to divide by 2.

 

[Audi Driver P.E.]

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