Process Engineering Fundamentals Continuous Assessment Coursework

Task

This document outlines the continuous assessment coursework for Process Engineering Fundamentals. This
assessment makes up 30% of the overall assessment for the module and is due by the deadline of Wednesday 8th December 14:00. A penalty will be applied for late submission. In order to successfully complete the continuous assessment you’ll need to engage fully with the course, including the discussion board (see the “Case Study – Continuous Assessment” forum) and the drop-in sessions (Thursdays 16:30, C76, The Mill).

Note that no email queries regarding the case study will be replied to as all students must have access to the
same information, use the discussion board to ask any questions. You can provide your solution in any (electronic) form you like e.g. handwritten, word processed etc. The purpose of this assessment is to provide an opportunity to demonstrate competency with material balance calculations on multistage, reactive processes and to show application of the problem solving approach developed during the course. As such you are encouraged to present your answers clearly, logically and ensure that your submission is legible. The use of process simulation software is prohibited. Ensure that you read the whole of this document carefully and note the useful information and data that are given after the question.

Dimethyl ether (DME) is produced by the catalytic dehydration of methanol using an acid zeolite catalyst;
2CH3OH ® (CH3)2O + H2O

The fresh feed supplied to the process contains 99.15 mol% methanol and 0.85 mol% water. The feed is mixed with a recycle stream before being fed to the reactor. This mixed reactor feed contains 98.40 mol% CH3OH, 1.14 mol% H2O and 0.46 mol% (CH3)2O. The methanol conversion per pass is 79.91%. The reactor outlet stream is subsequently fed to a series of two separators. The first separator recovers the dry DME product at a purity of 99.50%, with the bottoms, which is 66.92 mol% water, being fed to the second separation unit. In the second separator waste water, contaminated with 0.53% methanol, is recovered and the remaining unreacted methanol is recycled along with all of the DME present in the bottoms from the first separator, giving a recycle stream which contains 2.11 mol% DME.

i) Draw a block diagram of the DME process and select a suitable basis for your calculation. [4 marks]
ii) Determine the composition and flow rates of all streams in the process, presenting your answer as a stream table. [20 marks]
iii) Determine the recycle ratio and the overall methanol conversion. [2 marks]
iv) If the annual production target is 60,000 tonnes of DME (99.5% purity) calculate the hourly DME production and fresh feed rates in kmol/h, assuming an operating factor of 0.97 (fractional plant availability).