Date of Award

2018

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Mechanical Engineering (MS)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Jeffrey D. Naber

Advisor 2

Alexander K. Voice

Committee Member 1

Tom Tzanetakis

Abstract

The transportation sector accounts for the second largest source of CO2 emissions after power generation. New Corporate Average Fuel Economy (CAFE) regulations are focusing on improving energy through reduced fuel consumption and greenhouse gas emissions. This work investigates the potential of a CO2 capture system downstream of an aftertreatment system for a heavy-duty engine application. Amine absorption has been described as one of the most effective ways to capture CO2 from the exhaust for point sources. Therefore, using thermal-swing absorption process with potassium carbonate (K2CO3) as the absorbent liquid, a process was analyzed for onboard CO2 capture with a 15-liter heavy-duty truck engine. The CO2 capture system comprises of a CO2 absorber that separates CO2 from the exhaust; a CO2 stripper or regenerator that regenerates the absorbent liquid; heat exchangers and coolers for maintaining the required temperature of the system; and a compressor for compressing the CO2 for storage. The operating parameters of the CO2 capture system, including liquid flow rates, lean/rich loading were estimated by assuming a driving force for the mass transfer. The regenerator pressure was determined from the vapor-liquid equilibrium data as a function of temperature and lean CO2 loading. The components of the system were designed and simulated individually in GT-Suite at a 60% CO2 capture rate and this allowed for the determination of liquid flow rates, outlet temperature and the heat transfer across the system for a mid-speed, mid-load operating condition. The components are then integrated in GT-Suite to form a CO2 capture system model downstream of the aftertreatment system. The system performance was then determined for different exhaust gas conditions representative of the Supplemental Emissions Test (SET) operating conditions from idle to full load. The CO2 capture requires both heat and power for the absorption as well as the separation process which can utilize the energy extracted from waste heat recovery system (WHRS). The exhaust heat would be used to heat the solvent and desorb the CO2 in the stripper. Unlike point sources, the onboard CO2 capture system has challenges such as space limitations and availability of processes and cooling water. However, exhaust heat also provides a low-cost source of waste heat not typically available at stationary power plants. This work aims to determine the heat duty, cooling duty, and compression work required for capturing CO2 at different engine operating conditions.

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