Question

1. In the production of alternative and natural sweeteners from Stevia, the cleaned leaves at a rate of 875 kg/h are first passed through a mechanical sorter. 23.0% of the fresh feed are small leaves and can go straight to the drier. They are dried to 8.00% moisture, from the original 46.7% moisture. After drying, they are ground to a fine powder. The remaining large leaves are first fed to a grinder where the leaves are ground to a pulp. They are then fed to an extractor where hexane is also added to extract steviol glycosides, the “sweet component” of the stevia leaves. Fresh hexane at 27.2 kg/h is added to a recycled condensed hexane stream and is then fed to the extractor at 2.75 kg hexane per kg of ground stevia leaves. The exit stream of the extractor then passes through a filter where the filter cake (predominantly containing pulp) is separated from the liquid part of the stream (filtrate). The filtrate is then fed to a decanter where the hexane stream is separated from the aqueous stream. The aqueous stream is virtually pure water. The hexane stream is fed to an evaporator where all of the hexane is evaporated, leaving pure steviol glycosides. The evaporated hexane is then condensed and recycled back to the extractor. Given below are useful information for the composition of some streams and materials:
   1. Fresh Stevia leaves contain 46.7% moisture, 3.80% steviol glycosides, and the remainder is pulp.
   2. The filter cake is 92.4% pulp, the remainder is a mixture of hexane and steviol glycoside.
   3. Two final products are produced in the process: dried ground Stevia leaves and pure steviol glycoside.

Calculate the following:

1. Rate of production of the two final products in tons/year (assume that 1 year of operation is equal to 300 days of continuous operation)
2. Rate of hexane recycle (kg/h) and recycle ratio (recycled hexane/fresh hexane)

Answer 1