Skip to main content
Engineering LibreTexts

1.5: Process Controls in Everyday Life- Applying process control thinking to everyday situations

  • Page ID
    22363
  • Written By: Andrew Sereno, Randy Tin (FA09)

    5.1 Introduction

    Have you ever wondered if the abstract and arbitrary subject of chemical engineering process controls has any relevance outside of Dow 1013? Below are a few examples of how the concepts learned in process controls can be applied to situations in your everyday life.

    5.2 Examples of Process Control for the Common Man

    5.2.1 Consumption

    Spicing Up Soup

    Pavlo LaBalle just finished scaling up a mixing tank for use in the manufacture of horse glue. Scaling up mixing tanks for horse glue is hard work - enough to make any man crave a hearty bowl of spicy liver soup. Fortunately, Mrs. LaBalle has a batch of liver soup ready for Pavlo's return home. Using his built-in composition sensor, the tongue, Pavlo realizes the liver soup spice concentration is below his specified setpoint - the soup is not spicy enough. Having never spiced his own soup, but not wanting to offend Mrs. LaBalle, Pavlo attempts to increase the spiciness of the soup using his favorite hot sauce, Sriracha. In order to prevent catastrophic overspicing, Pavlo adds a drop of Sriracha (a differential amount) and immediately begins sampling the soup after addition. In this way, Pavlo is able to determine the effect of a small disturbance (the introduction of Sriracha) on the process output (the soup's spiciness). Using his new knowledge of Sriracha's effect on the soup, Pavlo is able to optimize his addition of Sriracha so as to not catastrophically overspice the soup. Pavlo then adds a new amount of Sriracha estimated to bring the soup closer to the spice setpoint and samples the soup shortly after. By tasting the soup after the addition of spice, Pavlo is able to bring the soup closer to his desired spice setpoint through the use of feed backward spice control. By applying his education in chemical engineering process controls, Pavlo has enabled himself to enjoy his spicy liver soup.

    Imbibing Alcohol

    Jimmy Johnson just finished a presentation and a final report for Chemical Engineering 460. Unfortunately, during the presentation, Jimmy's personal record of 80 straight hours without sleep came to an abrupt end as he blacked out mid-line, and he was subsequently criticized for insufficiently displaying the iron resolve befitting of a Michigan engineer. Jimmy decided to drown his sorrows at Good Time Charley's through the careful ingestion of mood-improving fluids. Jimmy planned on drinking until he felt a moderate buzz, then leaving to finish his graduate school application to pursue a masters degree in English.

    Jimmy, inexperienced with the process of satiating his thirst with such beverages, planned to continuously drink until he felt adequately affected. However, Jimmy failed to take into account the dead time inherent in his body's response to alcohol. Jimmy was unable to control his body's response as he had planned, resulting in a vast overshoot into drunken stupor.

    Jimmy woke up with no pants the next morning. Fortunately, by applying his education in chemical engineering, he earned the necessary experience for tuning the amount he should drink in the future.

    Purchasing Food at U-Go's

    Rachel Malta was busy typing her technical report on the design space of a distillation column in a pilot horse glue plant. It was 11:50 p.m., and Rachel was making good progress until she felt the odd sensation of bubbling acids corroding through her stomach wall, at which point she decided to visit U-Go's to find something to eat.

    Confronted with the shop's wide array of processed foods and saturated fats, a difficult problem lay before Rachel. If she purchased too much food, her hunger set point would be reached, but she would be left with bags of uneaten popcorn and sour patch kids. If she purchased too little, she would remain hungry and would be unable to return to purchase more food after the store closed. Rachel needed to make a prediction of how much food her digestion process would require to reach her desired fullness. Based on her previous experiences with U-Go's "food," her predictive control (her memory) decided to purchase a bag of barbecue chips, one apple, and a bagel. By applying her education in chemical engineering, Rachel was able to successfully predict how much food would satisfy her hunger without being forced to find more food.

    5.2.2 Hygiene

    Filling a Bathtub

    Lan Ri has been in the Duderstadt Center for the past 3 nights working on his ChE 487 project. Having not bathed for 60 hours, Mr. Ri decides it is time to wash himself for the sake of his fellow Duderstadt dwellers, however Mr. Ri has forgotten how to stand up (he's been sitting at a computer for 60 hours). The ever creative Mr. Ri decides to take a bath instead of his usual standing shower. At the bath, Mr. Ri finds himself confronted with two flow rate controllers: one "hot water feed" controller and one "cold water feed" controller. Turning the controls, he realizes that they control the flow rate of the bathtub feed streams. Yet Mr. Ri has a problem - the hot water feed temperature, as measured by his built-in temperature sensor (his skin), is far too high. The cold water feed temperature, also measured using his skin-type temperature sensor, is too low for a comfortable bath. Accordingly, Mr. Ri performs a quick energy balance to determine expected ratio of the feeds necessary to achieve a bath temperature close to what his desired setpoint. However, because Mr. Ri has poor control of the actual flow rate of each stream (hot and cold), the actual resulting temperature is still below that which Mr. Ri desires. Mr. Ri then readjusts the hot-to-cold feed ratio by increasing the hot water feed flow rate. As the bathtub fills up, Mr. Ri uses his built-in level sensor (his eyeballs) to turn off the valves controlling the feed stream flow when the bathtub level is at his calculated level. Mr. Ri was able to calculate the level to which the bathtub should be filled by using his knowledge of static fluid systems. By applying his education in chemical engineering process controls, Mr. Ri has enabled himself to wash away the smell of the Duderstadt Center.

    [Can use some diagrams, pictures, and/or equations to describe these problems - RZ].