28 Power Engineering International June 2017 www.PowerEngineeringInt.com
Dry sorbent injection for
SOx emissions control
As many in the
begin to make decisions
on technologies that will
meet the latest regulatory
requirements, dry sorbent
injection is a viable
option to be considered
for SOx emissions control,
argues Connor Cox
The injection of hydrated lime, trona or sodium bicarbonate (SBC) into the fue gas for the removal of SO2 and SO3 is a proven solution and a preferred technology both in Europe and the US.
A dry sorbent injection (DSI) system
enables plants to remain in operation when
the capital cost of a wet or semi-dry fue gas
desulphurization (FGD) system is too high.
Injection of these alkali sorbents can also offer
other benefts to the plant including lower
operating costs, less corrosion and reduced
activated carbon usage for mercury removal
in high SO3 environments.
DSI for SO3 removal typically employs
hydrated lime as a low cost, high-effciency
sorbent. The hydrated lime can be injected
into several locations throughout the fue
gas path, depending on preferred operation.
Performance can vary based on mixing,
injection location, and whether the station
employs an electrostatic precipitator (ESP) or
fabric flter (FF) as their particulate removal
Traditionally, sorbent was injected after
the air pre-heater and before the particulate
collection device. This proved very effective
at eliminating visible plumes at the stack.
However, long-term operation in the US has
proven that injecting upstream of the air pre-heater can provide several additional benefts.
By injecting hydrated lime upstream
of the air heater, utilities have shown an
improvement in air pre-heater performance
through the reduction of H2SO4 corrosion and
ammonium bisulfate (ABS) buildup caused
by SO3 reaction with excess ammonia from
In other instances, this location will be
upstream of an activated carbon injection
(ACI) system, and the reduction in SO3 prior
to interaction with powdered activated
carbon (PAC) will allow for improved sorbent
high effciency system