FGD and DeNOx
NEWSLETTER
March 2019
No. 491
Dry
Scrubbing Discussions at the Cement Conference in St. Louis
The
61st Annual IEEE-IAS/PCA Cement Industry Technical Conference will be held in
the St, Louis Convention Center, April 28-May 2, 2019. This is the largest
conference in the cement industry and will include presentations of the latest
technology covering a variety of topics important to the industry. There will
also be Tutorials, Professional Training sessions, a
state-of-the-industry-report and much more. There will be 150 exhibitors
McIlvaine has interviewed exhibitors in the past and posted this coverage plus
other cement industry analyses and articles in a free site. These articles and
interviews can be viewed at
There
is lots of dry scrubbing activity in the cement industry. For applications where
Hg control is either intermittent or low injection rates are needed, a blended
hydrated lime (HL) and powdered activated carbon (PAC) sorbent allows for a
single feed system to be used. For example, Lhoist North America’s blended
HL-PAC product enables concurrent acid gas and Hg control, using a single
sorbent injection system (instead of installing and maintaining two nearly
identical systems), to inject the sorbents simultaneously as a pre-blended,
homogeneous product. Lhoist North America produces customized enhanced hydrated
lime blends (branded Sorbacal® SP and SPS) with brominated PAC. These
are produced either in bag or bulk, in 5 percent PAC (weight by weight) blend
increments up to 30 percent.
Over
the past twenty years, calcium-based sorbents have evolved, driven by the need
to improve acid gas capture efficiencies. Realization of the importance of
physical properties, such as particle size distribution, pore volume, and
surface area, led to the development of enhanced hydrated lime sorbents (EHLSs)
by engineering these properties to create more reactive hydrated lime sorbents.
Sorbent physical properties directly impact material handling properties and
acid gas removal performance, ultimately dictating annual operating
expenditures.
Lhoist’s EHLS products are branded Sorbacal®. The second generation
product is Sorbacal® SP and third generation is Sorbacal®
SPS. Sorbacal® SPS is a chemically-activated formulation of Sorbacal®
SP, specifically designed to provide best-in-class acid gas capture performance.
Surface area and pore volume are the key performance drivers for acid gas
capture.
Sorbent particle size dictates material handling properties and removal
efficiencies in electrostatic precipitators (ESPs) and BH filters. Empirical
data from the field, as well as laboratory flow testing, has demonstrated that
larger median particle diameters (i.e., D50) are recommended for
optimum handling. Specifically, a 32% improvement in flow properties was
demonstrated between particles with D50 = 2 µm and particles with D50
= 11 µm.7,8 This is likely due to small particle-sized hydrated lime
sorbents being more cohesive than larger particles; small particles can
facilitate pluggage in the conveying system.
Additionally, fine particle-sized hydrated lime can become irreversibly lodged
in BH filter bags and bin vents (this is called ‘blinding’), and can result in
premature wear and poor bag cleaning efficiencies. Users should refer to their
manufacturer’s design information regarding particle size and carefully weigh
the impacts of introducing particles outside of the design range. Likewise, ESP
particulate capture efficiencies decrease below approximately 6 µm and can
result in increased particulate emissions.
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