Use of Exhaust Gas as an Oxidant
(including boiler systems)
General
Combustion reactions are highly exothermic. However,
their reactants (fuel and oxidant) continuously absorb considerable
energy to reach proper combustion temperatures. Exhaust gases from
a prime mover, particularly from a gas turbine (because of its high
oxygen content), provide an excellent preheated oxidant.
These gases can be considered as an oxidant source
for combustion of fossil fuels used in most heating applications including
steam generators or boilers.
Processes Uses
Applications for using exhaust gases as an oxidant
include:
- Central boiler systems
- Waste VOC incineration systems
- Kilns
- Calciners
- Large ovens
- Large heat treating operations
- Large furnaces
- Forging operations
- Tempering operations
- Annealing operations
- Cupolas.
Integration of Cogeneration Systems
Many engineering techniques addressing the principle
of preheating the combustion reactant feed (especially the oxidant,
because its volume generally dominates the reactant mixture) are in
practice.
Three categories represent a majority of these
techniques:
- Using the stack exhaust to indirectly (e.g., with
a shell and tube exchanger) heat the air/oxidant feed line
- Burner tip techniques that often incorporate ceramics
to maintain the final mixing chamber at extremely high temperature,
thereby heating the reactants immediately prior to ignition
- Using high temperature, high oxygen content, waste-heat
streams as a combustion reactant/oxidant (as the DG cogeneration
system would offer)
In general the cogeneration based oxidant system
is highly competitive for these options when:
- The process operation is operated such that its
own exhaust is either low in temperature or low in excess oxygen
- The process operation uses coal (or other fuels
releasing soot and sulfur in the exhaust) as a fuel. In such cases
cogeneration offers both a relatively clean preheated feed (so
as not to foul the burner equipment) and also reduces the amount
of sulfur and particulate released (by reducing the amount of
coal needed)
If a system's burner was initially designed for low temperature air
feeds, more heat durable components may be needed to handle a hot
oxidant. The difference in oxygen content also needs careful consideration
to properly engineer the combustion system.
For more information on each application: