Problem:
60 tons per day of oil-sand (25 mass % oil and 75 mass % sand) is to be
extracted with 40 tons per day of naphtha in a counter-current
extraction battery. The final extract from the battery is to contain 40
mass % oil and 60 mass % naphtha and the underflow from each unit is
expected to consist of 35 mass % solution and 65 mass % sand. If the
overall efficiency of the battery is 50%, how many stages will be
required?
