Success Story
Air Cannons Remove Ash Buildup in Generating Facility SCR
[Neponset, IL]  An innovative
Midwest generation facility has
specified a unique multi- port air
cannon to prevent ash build-up in the
plant’s Selective Catalyst Reduction
(SCR) system, improving NOx
reduction and eliminating the need for
2-3x yearly cleanouts. The company
estimates that in addition to better
system performance, the savings
amount to $200,000-300,000 annually
in contract labor costs.
The facility is a 205 MW coal-fired plant that came online in 1970. Upgrades have been
made throughout its lifespan, including a 1990 conversion to blend low-sulfur coal with
local supplies to comply with new clean air standards. In 2007, the company added a
sophisticated SCR system to further reduce NOx emissions, an investment larger than
the cost to construct the plant originally.
Over time, operations personnel noticed a drop in SCR performance, and during a
scheduled plant outage they inspected the system and discovered that fly ash contained
in the exhaust stream was accumulating in the top layer. “The deposits became so
severe along the front wall that they completely blocked the sonic horns which were in
place to facilitate the ash flow,” recalled Martin Engineering Product Specialist Jeff
Shelton. “At times, the plant would have to reduce the boiler load, due to poor NOx
reduction.”
Martin Engineering ■ One Martin Place ■ Neponset, IL 61345-9766 USA
Ph 800 544 2947 ■ Fax 800 814 1553 ■ info@martin-eng.com ■ www.martin-eng.com
To address the situation, the plant was forced to enlist a contractor to come on-site 2-3
times each year during scheduled plant outages and evacuate the build-up. “The
cleanout was an extensive process,” said one company official. “It required two vacuum
trucks and operating crews for most of a week to remove the accumulated ash.”
In a move designed to implement a more permanent solution, facility engineers met with
representatives from Martin Engineering and inspected the SCR system. Together they
settled on a plan to first rebuild the sonic horns for maximum performance, followed by
installation of a Martin® Multi Port Performance Air Cannon, with fan jet nozzles below
the sonic horns.
The unique air cannon uses a single air reservoir and control unit to replace up to eight
traditional (tank-and-valve) air cannons. With one air tank discharging through stainless
steel hoses into as many as eight ports in the vessel wall, the Multi Port Performance
Air Cannon improves process efficiency, while simplifying installation and maintenance.
“Reducing downtime is one of the key reasons customers specify a multi port air
cannon,” observed Shelton. “Depending on the specific installation and operating
environment, some air cannon designs can require such frequent maintenance that the
production stoppages become a significant problem,” he said. “The multi port air
cannon can be placed at a greater distance from the process, to minimize the effects of
harsh environmental conditions.”
The multi port approach also allows equipment to be positioned for easier access.
Rather than having traditional tank-and-valve air cannons in locations that may be
difficult to service, the multi port air cannon places the air reservoir and control
mechanism in one central location, relaying the energy of the discharged air to the point
of application through flexible steel hoses.
“Any time you can perform maintenance or repairs without subjecting personnel to
potential hazards, that’s a good thing,” commented Shelton. “When you combine that
safety aspect and easier maintenance with the high reliability of the multi port approach,
it delivers some valuable advantages, even beyond improved material flow.”
Martin Engineering ■ One Martin Place ■ Neponset, IL 61345-9766 USA
Ph 800 544 2947 ■ Fax 800 814 1553 ■ info@martin-eng.com ■ www.martin-eng.com
To initiate the firing sequence of a multi port air cannon, a solenoid valve is activated,
allowing compressed air to fill the tank. At the same time, the air cylinder and isolation
disk of the desired discharge port are retracted, opening the port to allow the air blast to
release through it. The master cylinder and tank seal plunger are then retracted,
evacuating the air from the tank through the open discharge port. As the air cannon
resets, all cylinders return to their closed position, sealing off the unit from the process
in preparation for the next firing sequence.
With the improved horn performance and addition of the air cannon, the SCR function
was noticeably improved. Subsequent inspections revealed that over time, however,
some build-up continued to
form small piles in between the
horns. Installing additional fan
jet nozzles at the accumulation
points appears to have
resolved the issue, and the
SCR system is functioning
properly, no longer requiring
manual cleanout.
The customer credits the air
cannon with effectively preventing the build-up, an assessment that was confirmed
when a scheduled shutdown permitted close inspection of the system and revealed very
little accumulation. Eliminating the build-up has also opened up the gas lanes within the
SCR, resulting in better NOx reduction. The performance improvement has allowed the
facility to delay the purchase of replacement catalyst, which carries an estimated cost of
$1,000,000.
“Efficient flow is a critical element of an efficient SCR system, and ash accumulation can
put a strangle hold on a generating plant’s profitability,” Shelton concluded. “Although
many plants still use manual techniques to remove build-up, the cost of labor and
periodic shutdowns has led some producers to investigate more effective methods for
dealing with this common issue.”
Martin Engineering ■ One Martin Place ■ Neponset, IL 61345-9766 USA
Ph 800 544 2947 ■ Fax 800 814 1553 ■ info@martin-eng.com ■ www.martin-eng.com