Vignette Example

Envision the first semester of chem-engineering where students are involved in a semester-long case study of a local coal combustion power plant in need of a sustainable engineering upgrade. The challenge presented to students would be to better serve the socioeconomics of the local residents by engineering the plant to be more sustainable. The chemistry topics and concepts that are covered during this semester include: atomic structure and bonding, intermolecular forces, states of matter, gases and kinetic molecular theory, the first and second laws of thermodynamics and stoichiometry. Learning about each of these topics would be situated in the power plant problem and would emphasize the design challenge to an engineering solution. Nested within the larger case study, students would be challenged to think about engineering solutions for the fate of combustion products based on the design goals of sustain, recycle, re-use, and recover (Figure 1).

coal plant

The industrial-environmental chemical cycle created by the combustion of coal.

Coal contains numerous elements with C, O, H, and N as major components, S, Si, Al, Fe, and Ca as minor components, as well as various metals as trace components (Fig. 1, A). In a coal combustion system, these elements interact with supplied air to form various oxidation products, the major ones in the gas phase being CO2, H2O, SO2 and NO, and the ash mainly contains Al2O3, SiO2, Fe2O3 and CaO (Fig. 1, B). The structures of these compounds, types of bonding and their states vary from one to the other, and they cover a wide spectrum (Fig. 1, C). The amount of air (i.e., oxygen O2) supply needed to yield complete combustion is an excellent example for stoichiometry (Fig. 1, D), while the reaction provides examples of oxidation and reduction. As the goal of burning coal is to produce energy, students can calculate the energy content based on the bond energy and enthalpy to learn the 1st law of thermodynamics (Fig. 1, E). The increased entropy resulting from the combustion process can be used to explain the 2nd law of thermodynamics and why the reverse process is challenging (i.e., CO2 → C). The ideal gas law can be applied to determine the corresponding changes in temperature, pressure and volume of the flue gas to be emitted from the stack to the atmosphere (Fig. 1, F).

The emission of SO2, which is the major cause of acid deposition, is curtailed by an engineering process of injecting lime slurry to scrub SO2 from flue gas that produces gypsum (Fig. 1, G). The amount of lime to be injected and the amount of gypsum produced are two other great examples for stoichiometry calculation. The SO2 scrubbing process is a wonderful example for acids, bases, and neutralization. The deposition of SO2 into water bodies is a well-known environmental issue that students can easily connect with (Fig. 1, H). The change of pH affects the fates of various organic compounds in water bodies, the structure and functional groups of which can be elaborated. This context-first approach is drastically different from the way general/freshman chemistry is typically taught.

At the beginning of the semester, in this large lecture section of 300-students, imagine 30-teams of approximately 10-students each. The teams are constructed so that each team includes students from the broadest range of engineering majors (i.e. biomedical, civil, chemical, electrical, environmental, industrial, mechanical, materials, nuclear) and their work is focused around the four key plant processes: the Boiler Division, Precipitator Division, Scrubber Division, and the Stack Division. All teams in each division are required to understand the chemical composition of coal (the natural mixture, not an assumption of the pure chemical element), the stoichiometric amounts, identities, and states of the possible combustion products. The teams are challenged to deliver a work product based on their plant process in the three work areas and supported in doing so (e.g. scaffolding, coaching).

The learning activities could include mini-design challenges, homework sets, and outside of class assignments that are situated in the chemistry of the case study and are scheduled so as to build knowledge collaboratively related to the design problem. The outside assignments would culminate in an oral group presentation by each member of the project teams. These presentations could occur at the end of the semester in the breakout recitation sessions that are facilitated by graduate student teaching assistants. Peer review from other students could serve as the primary assessment of the presentation. In addition to design elements, this rubric could include a dimension for ethics as well as the components of critical thinking. Each student would submit a Design Documentation Report that details the technical basis for the project plans and specifications. Within each of the main learning activities, the four key syllabus assessment components would be addressed: stoichiometry, energy (enthalpy 1st Law and entropy 2nd Law), structure and bonding of coal itself and the combustion materials, and states of matter.  All of this could be done with an eye to the Florida environment (air, water and waste) and sustainability.

CC BY 4.0 This work is licensed under a Creative Commons Attribution 4.0 International License.


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