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B91DW Coursework Assignment Chemical Engineering

Instructions:

* In answering these questions, you may need to find data online. Cite any source you use; you don’t need to cite learning materials.

* Briefly describe your steps and thinking behind your calculations

* Provide calculations, either written out or attach Excel workbooks used in finding the answers

Question:

1. Calculate the bubble point of an ideal mixture of 40 mol% butane and 60% hexane at atmospheric pressure. Show all steps of your calculation; a literature value, result from an online calculator or reading off a diagram is not permitted.

2. A continuous still fitted with a partial reboiler is fed with 200 kmol/h of an ethanol/water mixture containing 15 mol% ethanol. The feed is a liquid at bubble point. The vapour that leaves the column at 106.8 kmol/h is completely condensed, but not sub-cooled. A reflux ratio of 2 is used, and the bottom product contains 2 mol% ethanol.

2a. Find the composition of the distillate product.

2b. Find the temperature of the vapour leaving the reboiler.

2c. Find the composition of the liquid running down from the 3^rd theoretical plate in the column.

2d. Calculate the heat load of the condenser in W.

3. For the distillation described in question 2, the distiller is considering to reduce the reflux ratio to 1 and install additional plates (at £1,000 each) as she is concerned about the increasing gas prices. Advise the distiller if this is a good idea, by calculating the saving/loss over the next 10 years, assuming that over this period the gas price will average £0.10/kWh. Plates can be considered 100% efficient (i.e. theoretical plates) and net present values can be ignored (i.e. assume an interest rate of 0%). The column is operated 24 hours per day for 340 days per year.

Marking scheme