Assignment Task
Problem statement
Part A
1. Extraction never exists by itself. There is always a solvent recovery separation unit”. Justify this statement.
2. Explain the purpose of using a decanter in the solvent recovery extraction system of partially miscible solvent and diluent?
B. Benzene, toluene and xylene are important precursors in the manufacture of petrochemicals. The feedstock can be reformed naphtha.
You have been contracted to design the distillation column for the recovery of benzene.
You may assume that a constant flow of 150 metric tonnes per hour of feedstock is to be processed.
Typically, a column will have a feed stream pumped at a certain temperature and pressure, a vapour stream that is cooled by an overhead condenser, a reflux stream that is pumped back to the column by a reflux pump, and a reboiler that adds heat to the process.
Temperature and Pressure
You choose, but ensure that these parameters are suitable to comply with the client’s specification. Note that some of the materials may need to be in a liquid state and that the pressure needs to be at a level that will cause the benzene to flash when it enters the column.
Data for Pump and Line Sizing
The base of the feed tank is vertically elevated 3 metres above ground. The pipe descends from the base of the feed tank and, moving left to right, travels a distance of 2 metres laterally before entering the feed pump. The pipe exits the feed pump and travels 4.5 metres laterally before entering the heat exchanger. The pipe then exits the heat exchanger and travels 2 metres laterally to a point below the distillation column, the pipe then vertically ascends 9 metres to a bend, and continues 2 metres laterally from the bend before entering the side of the distillation column. The pipe carrying the distillate exits the side of the distillation column and descends to the discharge pump which is located near the base of the distillation column. The pipe then exits the discharge pump and travels 30 metres laterally to a point below a tank, it then vertically ascends 20 metres to a bend, and continues 2 metres laterally from the bend before entering the side of the tank. Another pipe exits the base of the distillation column and enters the bottoms pump. The pipe then exits the bottoms pump and travels 90 metres laterally to a point below a vessel, it then vertically ascends 8 metres to a bend, and continues 1.5 metres laterally from the bend before entering the side of the vessel. All pumps are at ground level. You may assume that all piping will be Schedule 40 Mild Steel.
Pump sizing
- The pumps need to be carefully designed to suit this process.
- The critical requirement is to ensure that the pumps are designed with sufficient NPSH. Drawing a sketch showing the various vessels, pipes, and discharges may assist you in designing the pumps.
- Ensure you add up the losses and account for vapour pressure.
- Consider if you need sparing of pumps.
- Again, whilst UniSim is useful as a first pass, you need to ensure that the pump sizes in your model are acceptable. It is, therefore, recommended that you create a Microsoft Excel spread sheet or use hand calculations to calculate the various pump sizes.
Drawings
Based on your UniSim model, you may obtain a process flow diagram (PFD) showing the column, feed pump, condenser, reflux pump, distillate pump, reboiler, recycle pump and bottoms pump.
- Using an appropriate software program (such as Microsoft Word’s Autoshapes, Microsoft’s Paint, or other suitable program such as Visio), draw a P&ID of this chemical engineering process.
- Ensure the drawing shows the line sizes and other relevant details.
- Show additional piping as required.
Requirements
Using the UniSim software program, develop a PFD to successfully comply with the client’s specification of designing a distillation column for the recovery of benzene. Once you have completed this simulation furnish the following requirements:
a. Provide a PFD of this chemical engineering process showing the main equipment in this process. Ensure that the PFD includes a shortcut distillation column, main distillation column, feed pump, heat exchangers, reboiler, bottoms pump, and distillate pump.
b. Develop a stream table as a part of the PFD for all the major streams. Remember to go into the Column environment for the overheads and reboiler information.
c. Size the piping and pumps.
Ensure that you include the:1. Feed pump.
2. Distillate discharge pump.
3. Bottoms pump.
Provide the detailed table for each pump. This can be obtained by right-clicking on the pump and selecting “Show Table”.
Also provide a brief summary of your pipe sizing and pump sizing.
d. Draw a P&ID from the feed pump to the discharge streams. This drawing requires you to accurately size the lines and the pumps.
e. Briefly discuss the research methodology and challenges which you adopted for sizing the piping and pumps in your UniSim Model. Ensure that your answer includes a justification for selecting the specific piping and pump sizing in your UniSim model.
f. Briefly discuss about the importance of simulation tool in engineering and how it will help engineers to improve efficiency.
g. Underline the importance of sustainable practices and environmental considerations in chemical processes by providing a detailed discussion of the implications of these in the system which you have designed.