Prior to the combustion of coal, it is dried to remove moisture. The moisture content in coal varies widely. For this problem consider a coal that contains 20 wt% moisture. A dryer is to be designed to dry the 1 tonne of dry coal per hour. In order to accomplish this, dry air at 120 C is introduced in a countercurrent fashion into a dryer. The exit air stream is at 30 C and can be considered to be fully saturated. The coal which enters the drier at 20 C is required to exit the dryer with a moisture content of 10 wt%. The specific heat of coal can be approximated to 1 kJ/kgk. a. Why do we dry coal before we burn it? b. What is the flow rate of 'wet' coal into the system? c. Show an energy balance around the entire drier d. How much should the airflow be in SCMH (standard cubic meter per hour) if standard conditions are 1 atm and 25 C? e. What is the temperature at which the coal leaves the unit?