Chemical Engineering Thermodynamics Assignment - Applied Thermodynamics

Question 1 - By considering the flows into and out of a general control volume, derive a 'steady flow entropy equation' which describes the Second Law in a flowing system.

Consider a heat exchanger which raises steam at 1 bar. You may assume the feed enters as saturated liquid at 1 bar and leaves as saturated vapour. The steam is to be raised by condensing steam at a higher pressure. You may assume that this steam enters as saturated vapour, and leaves as saturated liquid. There is no pressure drop on either side of the exchanger.

By using the equation derived above, or otherwise, plot the entropy generated in this exchanger (per kg of steam raised), against the temperature driving force for heat transfer.

Comment on the plot, and other considerations that must be made when designing a heat exchanger.

Question 2 - A stream of a perfect gas is to be compressed from an initial pressure P₁, to a final pressure P₄ in a three stage compressor. Between each stage is an intercooler. It may be assumed that there is no pressure drop across the intercoolers. Each intercooler reduces the temperature of the gas to its initial temperature T₁. Each stage of the compressor has an isentropic efficiency η. Derive expressions for the optimal inter stage pressures that would result in the minimum power being supplied to the compressor. What fraction of the total work is done by each stage?

Question 3 - The export compressor on a North Sea oil rig takes gas from the low pressure separator, and pressurises it such that it can be piped to the shore. The gas is to be piped to shore at a rate of 5 kg/s, and the pressure at which it must enter the pipeline is (100 + URN-5) bara. It can be assumed that the low pressure separator operates at 1 bara and a temperature of 25^oC. The compressor is to be designed to operate for ten years. Design an appropriate multi-stage compressor (i.e. devise a strategy to find the optimal number of stages) with intercooling to perform this task. It may be assumed that the gas is pure methane, which can be treated as a perfect gas with C_P = 3256 J/kg K. You may assume that each stage of the compressor has an isentropic efficiency of 80%, and that the intercoolers use cooling water.

Please provide a brief description of design methodology, and detailed calculations. If a spreadsheet is used, please ensure that the logic can be followed, rather than just presenting a table of numbers.

What additional factors must be considered when designing the compressor for this application?

In these questions URN-5 is the last two figures of your URN.

Attachment:- Assignment File.rar