CHBE Team 3

Project Description:

Coal power plants emit various pollutants, including sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon dioxide (CO₂), mercury, and others. These pollutants can have disastrous effects on health and the environment, highlighting the need to limit the amount of pollutants entering the atmosphere, which is the focus of this project.

The goal for this design is to remove the aforementioned pollutants from the emissions of a coal power plant. The method of removal will vary depending on the pollutant. The design of this process was performed using Aspen Plus®. The first step in the process is to remove SO₂ via a SO₂ scrubber. The SO₂ is removed in a dry scrubber where SO₂ in the flue gas reacts with solid calcium carbonate (CaCO₃), removing it from the flue gas and creating calcium sulfite (CaSO₃). This is followed by a distillation column to remove SO₂ and the CaSO₃ produced.  Next, NO₂ will be removed from the stream in a catalytic converter modeled by a plug-flow reactor.  NO₂ will dissociate into N₂ and O₂ with the use of a catalyst. Lastly, CO₂ will be removed from the stream via CO₂ scrubbing. CO₂ scrubbing is a process that removes CO₂ from the air or exhaust. It is done by first chilling the gas to a workable temperature. Then, monoethanolamine (MEA) and piperazine (PZ) with water are introduced to adsorb the CO₂. This was modeled utilizing flash drums in series and stripping columns to separate the CO₂ from the flue gas stream. In addition, a recycle stream was set up to re-use any MEA/PZ and H₂O recovered throughout the system.

This process has successfully removed pollutants from the inlet gas stream. SO₂ and NO₂ levels were reduced completely and enough CO₂ was removed such that the clean air stream releases  CO₂ at concentrations below the approximate atmospheric level, 400 ppm. These results show that the process was able to remove an acceptable amount of the pollutants from the exhaust of a coal power plant and would greatly improve the environmental impacts of gas pollutants. Despite the successful results and positive impacts, the associated costs and feasibility of this process make the process unfavorable. The process requires a high capital investment, cost of raw materials, and annual utility cost and has no direct product or output. Thus, it would only be used as a method of pollution control, ultimately lacking financial incentive for such a high investment. While the process design and configuration are feasible and attain the set goal, it is not recommended for implementation due to its high energy and cost demand. 

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