Chemical and Biomolecular Engineering

Official blog of the Lehigh University Chemical Engineers

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Going Digital

One of the Unit Operations Labs that my partner and I did was the Data Acquisition Lab. The goal of this experiment was to help us understand how data collecting method work by analyzing signal voltages measured with a computer inserted Analog/Digital data acquisition (DAS) board from a pressure transducer and thermocouples under various conditions and signal variations. Data acquisition systems convert analog signals from specific measurement sensors to digital signals and store them as readable data on a connected computer. The sensors used here are thermocouples and pressure transducers, which convert the physical phenomena of temperature and pressure to measurable voltages with respect to time.

When an analog signal is converted to a digital signal, the voltage is discretized into steps which contain a certain amount of discrete place holders for data. These points are bits, and vary depending on the software.  For example, a 4-bit system will store 4 units of information per step.  The number of steps of an n-bit system can be found by the formula: “2n= steps” The smallest step size, or resolution, of an analog to digital conversion (ADC) can be determined by dividing the reference voltage by the number of steps.

Now here’s something more interesting for those of you music lovers like me. If you wonder how to convert your vinyl collections into digital format, keep reading.  It is actually not that complicated so bear with me. Basically, you first output your analog signal from your vinyl records before you boost it with a preamp. It then passes through a receiver and computer-audio interface that converts analog signal to digital. And then Audacity can record it for you and it’s free. And there you have it! However, if your turntable is analog-line level, you can hook it up directly into the computer audio-interface and then into the computer. Even better, if your turntable output signal at Line level and has a digital output, feel free to connect the turntable directly to the computer.

It’s really useful because now you can bring your digitized music with you to wherever you go. Well unless you are a hipster who prefers to carry turntables around that’s cool too. 

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Controls Problem in Drug Infusion System

In my latest controls homework, we were asked to find a interesting controls problem and assess a case study. It was to learn how multi-variable controls were used to control the system and the techniques that were used. I chose to learn about the Drug Infusion System because understanding how the human body functions is the most relatable subject and it’s interesting to learn how one person sustains himself.

In the first paper that I read, “Issues in the Design of a Multirate Model-Based Controller for a Nonlinear Drug Infusion System”, the Model Predictive Control (MPC) design is used. A model of the process in parallel with the plant to compute the predicted output over a certain number of future sample interval is implemented. The following body parameters were used, Heart rate, Maximum elastance, unstressed venous volume in terms of resistance, systemic resistance, and critical closing pressure. The MPC algorithm consists of two steps. In the prediction step, the model of the process is propagated over the prediction horizon. The unknowns in this propagation are the future values of the manipulated variables. Optimization iterations are required for this part. Nonlinear model is propagated over the prediction horizon prior to optimization, and the linear model is then added on and computed. The multirate nature of the system is then taken care of through correcting disturbances and step by step optimization. A diagram is shown here.

Drug Infusion SystemFor the second paper that I had read, a multi-variable model reference adaptive control (MRAC) algorithm is developed using a two-input, two-output patient model. The patient hemodynamic model is defined by the linear small-signal first-order transfer function matrix. The control signal (up(t)) that presents the drug infusion rate is formulated as a linear combination of the error feedback (Ke(t) * e) and of the two feed forwards reference model output (Ky(t) * ym(t)) and reference model input (Ku(t) × um(t)). The adaptive control law combines the values of the tracking error “e”, the reference model output “ym” and the reference model input “um” with appropriate adaptive gains (Ky, Ku and Ke). A diagram is shown here.body

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Optimizing a Reactor

For part of my Senior Design Project, I have to optimize a plug flow reactor (PFR). In this reactor, ethylene goes through partial combustion with oxygen to produce ethylene oxide. For more details about this project, please see here. Here I’ll go through with you in details how my group and I designed the reactor.

Ethylene Oxide Reactor

In the ethylene oxide production process, a plug flow reactor was used due to its proficiency in handling vapor phase reactions. In modeling with ASPEN Plus, it is assumed that, inside a PFR, the gas flows consistently and there is no radial variation in velocity, concentration, temperature, or reaction rate. The kinetics for the reactions proved difficult to model correctly in ASPEN, however they were eventually correctly implemented. The partial pressure of the reacting gas is the driving force for the reaction. The coefficients for the driving force were converted from the given kinetics and catalyst weight was selected as the rate basis.

Since the exothermic reaction requires constant cooling from a thermal fluid to prevent a runaway reaction, boiler feed water was chosen to control the reaction and generate high pressure steam. Hence, 0.28 is the correct overall heat transfer coefficient. The reactor pressure is chosen to be 26 bar from a range of values between 25 bar and 35 bar because the highest amount of ethylene oxide was achieved at that pressure.

Once the operating pressure was fixed, the reaction temperature was determined. Based on the sensitivity results, the optimal reaction temperature was found to be 240oC due to the fact that the most ethylene oxide is produced at that temperature. The reactor length and diameter dictate residence time, conversion, and capital cost. The dimensions need to be carefully selected so that the reactor has enough volume for the reaction to run its course. Any excess volume is wasteful as it increases both capital and catalyst costs. It would be optimal to maximize reactor surface area while minimizing volume. A conversion of 57.5% and a residence time of 73 seconds was reached based on the specifications I had just said.

There’s obviously more details that go along with this such as number of kinetics. But basically, that’s been the approach in designing this reactor. It’s difficult to optimize four parameter at once, so that’s the most logical approach that I could come up with.

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My Fall 2014 Final Exams

Hello all. I only have three final exams this semester, so it’s not all exciting. But they are all going to happen really soon. I have Physical Chemistry tomorrow, Process Control on Saturday, and Polymer Science on Monday. So basically that’s three exams in four days, which is not bad. Some might argue that it’s too compact of a schedule, and others may say that it’s better to get everything over with quickly. To me I think it’s pretty fair. At least I don’t have to stay here till the last day of finals. One of my friends had three exams in two days, and that’s what I would call too much to handle.

So far I’ve been spending most of my time studying for PChem because that’s the first one coming up. Although I’m going to do a bit of Controls tonight just to balance it out. The thing is that these two exams are almost back to back. PChem is tomorrow from 4-7pm, and Controls is Saturday from 8-11am. My mind would be decently fried coming out of the PChem exam. And historically I would need a bit of a break after the exam before I start studying more for Controls. I heard that study breaks are good for you. There’s also a fair chance of me pulling an almost-all-nighter the night before Controls exam. The reason that it’s an almost-all-nighter is that I just pulled a 30-hour-all nighter on Monday to complete my design project, and it didn’t feel all that great afterwards. So you can say that I’m somewhat prepared and warmed up for my next all nighter. But I would try not to do so again since study suggests that you need some sleep before.

Aside from that I have a Biotech take home exam that I have already finished. I appreciate the way how my exam is all going to come down quickly within the next 4 days. Every time I step into the library I get a flashback. Let’s keep it up comrades. Lastly, I want to share with you this amazing view of sunrise from the Mountaintop tower. No instagram filter was used.IMG_0129

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Chemical Engineering and Standard Heats of Reaction

The final section in ChemE 31 is balancing systems of reactive process. For systems like this a large heat transfer be it cooling or heating. The change in enthalpy for a chemical reaction is defined as the heat of reaction (delta Hr). The heat of reaction can be found using a compounds heat of formation. Heat of formation is the change in enthalpy for the formation of a compound. For example Benzene (C6H6) has a heat of formation of 48.66 kJ/mol. The heat of formation comes from the chemical reaction to get benzene 6C(s) + 3H2(g). The heats of formation is found from the tables in the textbook. The heats of reaction can be found by subtracting the heats of formation of products by the heats of formation of the products. For some substances such as O2 and H2 the heat of formation is 0 this is because both are elementary species and are found that way naturally. One other method to finding the heat of reaction is to use the heats of combustion (delta Hc) is the heat produced of that substance when reacted with oxygen. These values are also found in the textbook. However the Hr found by using heat of combustion is that it is reactant minus products and not the other way around.

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To Be Elle Woods Doesn’t Mean Being Blonde

Based on some of my other blogs, you can assume I am a firm believer in female empowerment. During all this stress with finals, I decided to take a study break and watch one of my favorite movies: Legally Blonde. I had this gigantic epiphany that my sole aspiration for college is to be the Elle Woods of chemical engineering. Aside from the fact she is beautiful and intelligent, she is a strong, independent woman that sets goals and achieves them. As I pondered this, I realized everyone should aspire to be like Elle because there are a lot of empowering moments in the seemingly comedic movie.

Her boyfriend breaks up with her, so instead of letting her life come crashing down, she decides she’s going to win him back and ends up getting in to Harvard Law school. Is this realistic? I mean, no, probably not. Even still, how often do we let things like relationships, insecurities, and other people keep us from achieving our goals? We need to learn to be flexible and to use the things that happen to us as reasons to move forward, not things to hold us back.

23 Times Elle Woods Empowered You As A Woman

Not only does she get into Harvard, but she becomes the top of her class, gets a competitive internship, and finds a boyfriend. Whoever said you can’t have it all is seriously disturbed. All throughout her time there, she is dealing with constant adversity where people assume she’s too stupid and too blonde to succeed, but she knows her self-worth and didn’t let anyone bring her down.

23 Times Elle Woods Empowered You As A Woman

Honestly, she is girly, bubbly, and a killer lawyer. Without her unique knowledge of hair care, Brook would have gone to jail for killing her husband. Her perspective makes her unique, and gives her a competitive edge over other people. We should embrace the things that make us different because those differences can be our most valuable asset.

And finally, as her class-elected speaker, she left the Harvard Class of 2004 and all of us with a very important lesson:

23 Times Elle Woods Empowered You As A Woman

You might read this and think this is a silly comparison, but if you think about it, it’s really not. Everyone should constantly be working to achieve their goals, surround themselves with people who support them, prove to others, but more importantly themselves that you can do whatever you set your mind to, and you can be a genuine, nice person while doing it. Go ahead and mock her if you want, but Elle is a role model, and I would be thrilled to be that influential!

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Final Stages of Senior Design Project I

As we enter the last hump day of the Fall 2014 regular season, things are closing out quickly. It is especially true for our senior design project; the due day for the final design projects is 4pm on Monday, Dec. 8th. There’s going to be a lot of cramming happening in the next 5 days, and a lot of all-nighters going to be pulled. At the final stages of this project, there’s a few things to need to do. One of the biggest things is CO2 removal.

First of all, we need to come up with goals. We need to implement a CO2 removal system into our EO production plant. There’s 3 options (really there’s 2). The first option is using a magical separation column in Aspen which magically removes CO2 from the system and recycles ethylene feed. It’ll allow us to close the recycle loop easily and simultaneously have the rest of the flowsheet converge. However, This option is technically crossed out because it’s not a real thing we can in real life (Come on keep it real guys).

This leads to option 2. Option 2 involves actually implementing a CO2 absorption column; usually an MEA column is used for this purpose. However, we’ve tried and realized that ethylene and CO2 behave similarly in separation and it’s difficult to separate one from another. We’re currently looking into other possibilities such as a different solvents or different methods of separation.

The last option is to add a splitter in the recycle stream to reduce the amount of CO2 in the stream returning to the feed. The way some of the ethylene is recycled, but some of ethylene is wasted. The fuel gas containing CO2 and ethylene can be burnt and sold for money. A price tag is going to be put on that.

After evaluating our options, we’ve decided that option 3 is our base case. It’s certainly not the most ideal case, but it can be our last resort at the moment. The reach goal would be to implement a CO2 removal system that removes CO2 and returns clean ethylene to the feed stream. Right now we’re looking into solutions, and let’s make things work.


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