Combustion Phenomena of High Temperature Air Combustion - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 30

during each c ycle is not adequate. The roles of high temperature air to enhance

stability limits and flame spectral emission are not fully understood. The effects on
health of various pollutants emitted from HiTAC have not been examined. This is
particularly important for waste and low-grade fuels which may result in the forma-
tion of dioxins and polycyclic aromatic hydrocarbon (PAH).
In this chapter, issues relating to the regenerative combustion, which provides
a convenient means of obtaining highly preheated air for combustion, are omitted.
The focus is on understanding the characteristics of HiTAC itself. Thus, discussion
is primarily limited to combustion phenomena affected by variations of both tem-
perature and oxygen concentration of combustion air.

2.2 FLAME FEATURES

2.2.1 F S

LAME TABILITY

The comb ustion limits of flame with hydrocarbon fuel were studied using the 1.3

kW scale test rig under various conditions of air preheating temperature and oxygen
concentration. Stable flame with low oxygen concentration was achieved by diluting
the air with either nitrogen or carbon dioxide. Air at desired oxygen concentration
was preheated using the test facility regenerator prior to its entry into the test section.
A schematic diagram of the experimental facility, used for 1.3 kW scale com-
bustion tests, is shown in Figure 2.1 . The facility consists of a hot air generator,
flow control unit for air, fuel and dilution gases, sequence controller, a flue gas
analyzer, and a test section. The combustion air in the model combustor was pre-
heated with the regenerator, which could preheat the air to temperatures greater than
1300˚C. Low oxygen concentration diluted air was supplied to the regenerator. In
the test procedure, a mixture of air and N (or CO ), after passing through the heat

2 2

storage media of the regenerator, was allowed to heat to a temperature of about

Flue gas sampling &
Analyzer (CO, NO x ,O )

2

Sequence
Controller

Computer

Air-enthalpy Intensifier

Exhaust Gas

IDF

Flow
Control
Unit

Air

Flue gas

FDF

Air

Gas for Dilution
LPG for Measurement Burner
13A for Start-up Burner

CO 2 - N 2

LPG CO 2 N 2

13A

FIGURE 2.1 Schematic of the 1.3 kW -scale hot air combustion test rig.