Combustion Characteristics of 0.5 MW Class Oxy-Fuel FGR (Flue Gas Recirculation) Boiler for CO2 Capture

Joon Ahn,Hyouck-Ju Kim

doi:10.3390/en14144333

Abstract

A 0.5 MW class oxy-fuel boiler was developed to capture CO2 from exhaust gas. We adopted natural gas as the fuel for industrial boilers and identified characteristics different from those of pulverized coal, which has been studied for power plants. We also examined oxy-fuel combustion without flue gas recirculation (FGR), which is not commonly adopted in power plant boilers. Oxy-fuel combustion involves a stretched flame that uniformly heats the combustion chamber. In oxy-natural-gas FGR combustion, water vapor was included in the recirculated gas and the flame was stabilized when the oxygen concentration of the oxidizer was 32% or more. While flame delay was observed at a partial load for oxy-natural-gas FGR combustion, it was not observed for other combustion modes. In oxy-fuel combustion, the flow rate and flame fullness decrease but, except for the upstream region, the temperature near the wall is distributed not lower than that for air combustion because of the effect of gas radiation. For this combustion, while the heat flux is lower than other modes in the upstream region, it is more than 60% larger in the downstream region. When oxy-fuel and FGR combustion were employed in industrial boilers, more than 90% of CO2 was obtained, enabling capture, sequestration, and boiler performance while satisfying exhaust gas regulations.

Highlights

Increasing atmospheric CO2 emissions from burning fossil fuels are a major barrier to greenhouse gas reduction and global warming control
The use of fossil fuels warrants the incorporation of carbon capture and sequestration (CCS) technologies—which include oxy-fuel combustion and pre- and postcombustion carbon capture technologies—into power plants
While oxy-pulverized coal (PC) burners of the coaxial (Air Liquide [16], Alstom Power [17]), eccentric duct (Hitachi [18]), and tangential (Doosan Babcock [19]) types have been used as an air and oxy-fuel flue gas recirculation (FGR) convertible burner, the coaxial type has been the most widely used [9]

Summary

Introduction

Increasing atmospheric CO2 emissions from burning fossil fuels are a major barrier to greenhouse gas reduction and global warming control. Since the heat transfer characteristics of the combustion chamber and heat exchanger are different, a system that recycles CO2 present in the exhaust gas has been frequently attempted. When When oxy-fuel combustion is usedis used in large-volume boilers, measures are required to stretch the flame and protect the burner from high-temperature flames. A 0.5 MW class industrial boiler system employing oxy-fuel combustion was constructed. Previous research on oxy-fuel boilers has been focused on boilers for coal-fired power generation [9]. Natural gas generates a large amount of water vapor in the combustion process; its combustion and heat transfer characteristics are different. FGR (flue gas recirculation) combustion, which was Previous researchstudy on oxy-fuel boilers has been focused on boilersnatufor was constructed.

Experimental

Oxy-Fuel

Results and Discussion

Emissions

Conclusions