Final answer:
To calculate the concentration of CO in ppm, we find the moles of CO produced from the partial combustion of methane, account for the total moles in the stack gas including products and excess air, and then use the ratio of CO to total moles, multiplied by 10^6, to get the concentration.
Step-by-step explanation:
The question asks us to calculate the concentration of CO (ppm) in the stack gas after a mixture of methane and hydrogen is burned with excess air, given certain conversion rates and reaction specifics. To solve this, we need to use stoichiometry to determine the amount of CO produced and then relate it to the total amount of gases present after combustion to find the concentration in parts per million (ppm).
Initially, we have 75 mole% methane and 25 mole% hydrogen. With an 85% conversion rate of hydrogen and a 90% conversion rate of methane where 95% of the reacted methane forms CO2 and the remaining 5% forms CO, we calculate the moles of CO formed.
Next, we account for the excess air (which is 25% more than the theoretical amount needed for complete combustion). We then find the total number of moles in the stack gas by adding together the moles of nitrogen (from the excess air), unreacted methane, unreacted hydrogen, products of combustion (CO2, CO, water vapor), and the leftover oxygen.
Finally, the concentration of CO is calculated using the formula:
Concentration of CO (ppm) = (moles of CO / total moles of stack gas) x 106
We can then calculate and express the CO concentration in the stack gases in ppm.