The plant manager asks the maintenance manager to set a target for the stack temperature at 350 degrees F (and to save money).  Your job is to propose any changes that can perhaps meet the target and then determine what savings in gas and dollars might result

A plant has a 10.5 MMBtu natural gas boiler that produces steam for process requirements. A combustion analysis test performed on the boiler showed that the oxygen content in the stack is around 7%.  The boiler’s feed water temperature is 185 degree F, and the stack temperature is around 650 degree F.  The boiler is an older boiler, which has been operating in the plant for quite a few years, without a great deal of maintenance. The plant maintenance manager estimates the boiler load factor at 0.7. The boiler operates ten hours per day for four days a week; and the natural gas cost is $4.80/MMBtu.

The plant manager asks the maintenance manager to set a target for the stack temperature at 350 degrees F (and to save money).  Your job is to propose any changes that can perhaps meet the target and then determine what savings in gas and dollars might result.  For example, state your changes and then perform your calculations.  Clearly state any references or assumptions made in the calculations.