CHE3166 - Process Design - Material Of Construction In Chemical Plants - Engineering - Report Writing Assessment Answer

CHE3166 - Process Design - Engineering Assessment Answer

Assessment Task:

Special Assignment- Material Selection and Corrosion 

PART A: RUDIMENTARY MASS AND ENERGY BALANCE FOR PFD (30 MARKS) 

Complete the rudimentary mass and energy balance for your Process Flow Diagram (PFD) based on the sketch that is given to you. You are expected to do a rudimentary mass and energy calculation (both manual calculations and aspen plus simulation are acceptable) on all the streams given in the PFD. This project is still at its conceptual design phase hence there is not a lot of information available to you (this includes clearly defined pressure and temperature for each stream), make appropriate assumptions to complete your rudimentary mass and energy balance. Clearly state all the assumptions you have made while performing your rudimentary mass and energy calculation. Tabulate your mass and heat energy balance in your main report. You may use the template given in Table 1 to tabulate the results of your mass and energy balance. 

Hint 1: At this stage, it is acceptable to lump components/chemicals that have similar properties together in order to simplify your calculations (you should justify why you lump certain types of chemicals together in your report). For example, methane, ethane, propane and butane can be lump together to be one pseudo- component and you can rename them as “C1-C4”. The goal of Part A is to work out the types of chemicals that end up in different parts of your plant and not about the accuracy of your mass and heat balance calculations. With the amount of information available to you (at this stage), the accuracy of your mass and heat balance is probably around ±30% from the actual plant condition. You will gradually improve the accuracy of this calculations when more information is available to you (remember that design is an iterative process). Hence, I will not be overly concern about the accuracy of your calculations at this stage. 

Hint 2: This assumption is optional (there are other ways to estimate the Joule-Thomson effect): At this stage, you may assume that the pressure drop across the JT-Valve is approximately 15 bar. Stream 004 has a temperature of 25°C and it is used to cool Stream 003 from 50°C to 38°C. 

SPECIAL ASSIGNMENT – MATERIAL SELECTION AND CORROSION 2 

2019 S2 CHE3166 SPECIAL ASSIGNMENT CHEM ENG DEPT MONASH 

Hint 3: This assumption is optional (in fact this might over specified your system): If you are stuck with mass and energy balance, you may assume that the condensate heater, E-2000 heats the condensate to 110 °C.

Table 1: Template for mass and energy balance table for Part A in Special Assignment  Stream Number* 001 002 003 004 005 Pressure (barg) Temperature (oC) Mass Flow (kg/hr)  Composition* (mol %) H2S Methane Ethane Propane iso - Butane n-Butane iso-Pentane n-Pentane n-Hexane n-Heptane n-Octane n-Nonane n-Decane H2O *Note: You may add, remove or change the stream number or composition of this table as you deem appropriate.

PART B: PRELIMINARY MATERIAL SELECTION (15 MARKS) 

Based on the mass and heat balance calculations/simulation, select materials for all the equipment and major pipelines (pipelines with stream number) shown on the PFD. Discuss why these materials are the most suitable materials for your process equipment and pipelines assuming that material cost is not a concern at this point of time. You need to make your material selection data easy to read (wall of text is not a good way to present your material selection results). Table 2 shows one of the many ways to make your material selection easy to read for the markers. 

PART C: REVISIT THE MATERIAL SELECTION FOR PROCESS PIPELINES (15 MARKS) 

You attended a quarterly meeting with the material specialists from Sustainable HC Pty Ltd (your clients). Your clients told you that the materials you have selected in PART B is too expensive and they want you to review the material selection you have done in PART B. You are instructed to minimize the material cost of your process pipelines without jeopardizing the safety of your plant. You should propose another cheaper materials for your process pipelines (you need to show the price difference). Discuss the types of corrosions you expect to happen when you used these materials as your pipelines. In the event you choose polymer/composite pipes as the alternative material, you need to discuss how frequently you expect to replace the polymer/composite pipelines in your chemical plant. You should also tabulate the corrosion rates/degradation rates of your selected materials (you need to cite your source clearly). Assume that all your pipelines have a size of DN100 (schedule 40) and a length of 1 km at this stage. Note that we have not cover equipment sizing at this stage, so leave your process equipment and instruments (vessels, tank, pumps, valves and heat exchanger) out of this section. 

Hint 1. Polymers degrade over time even though it does not undergo corrosion. 

Hint 2. Corrosion and polymer degradation rates are difficult to predict theoretically. The easiest way is to look for these data in the literature (engineering textbooks, handbooks and journals). If you cannot find these data, it probably means that the material you selected is not suitable for your application. Engineers only pick materials which they know will work (data is readily available). This explains why material selection for chemical plants are mostly limited to a few types of materials which are well studied. 

2019 S2 CHE3166 SPECIAL ASSIGNMENT CHEM ENG DEPT MONASH 

PART D: ECONOMIC ANALYSIS 

You are instructed to perform an economic analysis to investigate which materials are the best (one from PART B and one from PART C) choice for your process pipelines. The process pipelines need to keep a minimum thickness equals to the thickness of schedule 40 pipelines throughout their service in the plant. If you chose a material that undergo corrosion, you will need to add additional thickness (corrosion allowance) to the pipe. You will need to replace your pipes once the thickness of the pipes become lower than a schedule 40 pipes. Factor in the additional corrosion allowance into your purchasing costing and discuss which material is better for a plant with a design life of 30 years. 

Hint 1: You do not need to replace the pipeline(s) if you have literature to support your arguments that the chosen material does not undergo corrosion. 

Hint 2: Assume that pipe installation cost is equal to 10% of its purchase cost. 

Hint 3: You should cap your corrosion allowance at 5mm max. 

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