UNIVERSITY OF NEW HAVEN
TAGLIATELA COLLEGE OF ENGINEERING
EASC2211 Introduction to Modeling of Engineering Systems Spring 2015
TO: EASC2211 Students - Section 03
FROM:
RE: Project 1 – Consulting on the Operation of a Solids Separation Process
Date: March 2nd, 2015
You are working as a consulting engineer and have been hired by a small manufacturing plant. The plant engineer asks your advice on a solids-separation process, requiring that you develop a model to predict the mass accumulation behavior over time for a transient process. The results of your work should be presented in a technical memo, with calculations attached. The memo should include data tables and plots as needed to explain and justify your recommendations. The delivery date for your work is Wednesday, March 25th, 2015. Preliminary results will be required a week earlier to assure that progress is being made.
Solids Separation Process
The separation process is operated in semi-batch mode with solids accumulating in a settling tank and the cleaner liquid product accumulating in a storage tank. The feed stream, containing solid particles in liquid, flows continuously to the settling tank. The liquid moves slowly upward through the tank, allowing the solid particles to settle toward the bottom. The product stream leaving the tank contains a smaller fraction of solids than the feed stream. However, as solids accumulate in the settling tank the fraction of solids in the exit stream increases over time. The exit stream flows to a collection vessel where it accumulates. At some point the feed must be stopped so that the solids can be removed from the settling tank to restart the process.
Some preliminary laboratory work provides the following information:
· The ratio of the mass fraction (y kg solids/kg) of solids in the product stream (leaving the settling tank) to the mass fraction (x kg solids/kg) of solids in the settling tank remains constant at 0.080. (ie. y = 0.08x).
· A maximum solids fraction of 0.25 can be reached before the process must be stopped for solids removal
· The specific gravity of the solution can be estimated by the relationship 2/(2-x), where x is the fraction of solids. This relationship applies to all mixtures in streams or vessels
· A maximum solids concentration of 1.0% (by mass) can be accepted in the product collection tank. Note that this concentration is the value for the accumulated product, but the instantaneous value leaving the separator may be higher.
The stream to be processed has 6.00 mass % solids and flows at a rate of 8.0 kg/min. Assume that the total mass in the settling tank remains constant, but the concentration, density and volume change with time. Initially the settling tank contains 80 liters of pure water, with no solids. The product collection tank is empty at the start of the process.
Simulation Model
Complete the required work in three phases:
1. Develop the simulation model
2. Generate relevant data and establish a recommended operation time for the process
3. Complete a technical memo that contains required information and data displays
Your model will be based on the transient mass balances for the settling tank and the collection tank. Set up total mass and solids balances in rate form for the tanks. Since the total mass in the settling tank is constant, the accumulation rate of total mass is zero, but the solids balance will have a non-zero accumulation rate. Numerical integration will be needed for tracking the solids concentration in each tank. As part of your work you must determine the appropriate time step to produce results that are accurate to three significant figures. Accuracy of numerical integration can be controlled by comparing the results at a specific time (e.g., mass fraction solids in settling tank at 12 minutes) for two runs made with different step sizes. Pick a time step size and then re-run the integration with the time step cut in half. Repeat until you see no difference in the third significant figure. You will need to explain your time step choice in your memo using an appropriate table to justify the accuracy of your model to the client.
Once you have developed your model provide a recommended time for running the process before stopping to remove the solids from the settling tank. The information given above from the laboratory work provides your design constraints. The operators will observe the volume in the settling tank as a simple way to monitor the process, so you will need to indicate the final volume at which they should stop the process. Since the operation requires some flexibility it will be important to provide plots of solids concentration in the settling and collection vessels as a function of time, as well as plots of volumes vs time. This will enable the plant engineer to make adjustments to your recommended operating time when necessary.
Report your results to Mr. Ian T. Graytor, Senior Plant Engineer, in a technical memo, no longer than 3 pages. Appropriate data tables and plots should appear in the memo along with your explanation of your work and your recommendations. Briefly discuss the basis for your model (basic mass balance equations used) and the mathematical techniques employed. A portion of your spreadsheet should be attached as an appendix to the technical memo. Do not include the full table of numerical integration results (it will likely be hundreds of lines), but do include a diagram of the process with variables, equations and enough of the results to allow the client to understand and possibly reproduce your work.
Students may work in pairs to develop the models, but each student must write and submit his or her own memo. A copy of your spreadsheet showing preliminary results (just a page or 2) should be submitted by Wednesday March 11th to assure that progress is being made. Identify both team members in the heading of the spreadsheet. The technical memo with appendix is due Wednesday, March 25th, 2015. Note that this is a PITCH project in which technical communications is a major focus. The project grade will depend on the quality of communications in the memo and spreadsheet as well as the technical merit of the work.