Date of Graduation

2015

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Ismail B Celik

Committee Co-Chair

John M Kuhlman

Committee Member

Hailin Li

Committee Member

Matthew Targett

Committee Member

John W Zondlo

Abstract

Oxy-coal combustion with recirculating flue gas is a promising technology in CO2 capture. This technology is intended to reduce emissions of CO2 and other pollutants, such as NOx and SO2. Since the CO2 concentration in flue gas is higher than in conventional air operation, CO2 capture is easier. Other unique applications of oxy-coal combustion are now possible due to the very high temperatures (circa 2000-2500°C) that can be generated with char/ O2 /CO 2 mixtures which in turn can be used to activate chemical reactions which can lead to high valued chemical products. This for example can be an economical alternative to the energy intensive electric arc furnace process for calcium carbide (CaC2) production. At present, research towards developing an oxy-coal combustion process for production of CaC2 from char and calcium oxide (CaO) is being conducted by the U.S.-China Clean Energy Research Center (CERC). In this process, CaC2 is produced in the molten slag layer flowing along the walls of an oxy-coal combustion reactor. A model capable of predicting the performance of oxy-coal reactors for CaC2 production will be a useful tool to support this effort. Nonetheless, previous work in the field of slag modeling in coal-fired systems has been focused on analyzing its effect on the wall heat transfer and the combustion process. This alone is not sufficient to support the design of a carbide producing reactor.;In the present work, a physics-based computational model has been developed to predict the performance of oxy-coal combustion reactors for CaC2 production. The approach is based on a computational framework that utilizes the computational fluid dynamics (CFD) method to model both the oxy-coal combustion process and the slag flow. The slag flow model (SFM) describes the slag behavior including the chemical reactions occurring during the synthesis of CaC 2, as well as the liquid and solid layer thickness, average velocity and bulk temperature of the slag layer.;The model developed was applied to the design of two different types of reactors, namely, a vertical down-fired reactor, known as very high temperature entrained flow reactor (VHTER) and a horizontal reactor referred to as CTC reactor. It was found that the minimum temperatures required to activate the CaC2 formation in the VHTER were obtained for oxy-coal combustion cases with 35% molar oxygen concentrations; CO2 the balance gas. The results for the slag flow model showed that although the VHTER reactor is able to attain the high temperatures required for the production of CaC 2, the viscosities obtained can be so small that the residence time of the slag is insufficient to attain a considerable formation of CaC 2 in the slag.;The simulation results for the CTC reactor indicated that the operation conditions evaluated in current tests were not suitable for CaC2 production. Nonetheless, it was possible to obtain suitable temperatures for production of CaC2 in the CTC reactor by modifying the operation conditions. The modifications included increasing the amount of natural gas, as well as replacing a portion of the air entering the reactor with pure O2.

Download

Share

COinS