Chemical Engineering April 2020 - 40

Martin Engineering
FIGURE 8. A hatch over the tail pulley allows plant
staff to easily detect entrapped material
tape, but they were some of the longest,
most unpleasant minutes the
men had ever experienced.
By the time he returned and resealed
the breach, every square
inch of the transfer house was covered
in a 1/16-in. film of black powder.
It looked like every surface had
been painted black. To make matters
worse, the air in the room was
filled with a cloud of dust so thick
that it was difficult to see, much
less breathe. Coal particles covered
ears, noses, hair, safety glasses and
clothes, as well as tools and electronics.
The group quickly made an
exit, but they knew they would be
tasting coal dust for days afterward.
Given the physical properties of the
dust, the technicians also knew that
they had just a day or two before it
would begin to self-ignite. The supervisor
was so concerned that he didn't
even order a cleanup crew to address
the problem. Instead, the transfer
house was evacuated, and he turned
on the fire sprinklers. The entire mess
was gone in about ten minutes, avoiding
a potential fire or explosion.
A simple cost-saving decision
made years ago to save a few dollars
resulted in a series of events that
could have resulted in a catastrophe.
What could have been done instead?
There are well-engineered
access doors designed for exactly
this scenario, which would have allowed
a quick inspection and immediate
re-sealing of the opening
simply by closing and latching the
door. Even this modestly priced solution
couldn't compete with a dollar's
worth of duct tape, but reviewing
the events revealed that the cost
savings were an illusion. There were
five people on the inspection team,
40
including the supervisor, all of whom
lost productive time dealing with
the mess. When they realized that
the situation had gone beyond any
hope of manual cleanup, the transfer
house had to cease operation for half
an hour while the sprinklers washed
down the area, forcing three more
workers to evacuate until the dust
was gone. That doesn't include the
cost of the washdown. That dollar's
worth of duct tape turned out to be
an expensive " solution " after all.
Example 2: Equipment failures. A
coal plant in Eastern China had belt
damage, spillage and dust issues
at two conveyor transfer points with
outdated and inadequate equipment
in the loading zones. Raw coal ore
was loaded onto the 40 in.- (1,000
mm) wide belts traveling 500 ft/min
(2.56 m/s). The first chute had a 16.5ft
(5-m) high drop chute that loaded
into a 40-ft (12-m) long loading/stilling
zone. The second chute had a similar
drop, discharging into an 85-ft (26-m)
long loading/stilling zone.
Like many facilities, new demands
began to exceed the system's design
capabilities, which were originally intended
for less tonnage and slower
speeds. The belts were supported
by impact idlers and a troughed
roller system, neither of which were
equipped to cope with new production
demands. Equipment failures
happened regularly, and without
proper accessibility for routine maintenance,
long periods of downtime
were common. Belt sag created gaps
between the belt and rollers, causing
fugitive dust emissions throughout
the facility. Inadequate impact control
led to spillage becoming entrapped
between the belt and tail pulley, damaging
them both. Excessive downtime,
costs for cleanup and equipment
replacement seriously impacted
plant production. Managers sought
a solution that better protected the
belt, sealed the chute from dust and
spillage, and offered easier inspection
and ongoing maintenance.
Technicians from an international
service provider were invited to perform
an on-site assessment and
suggest an affordable solution. After
offering a detailed proposal, the team
installed modern equipment that addressed
the issues on both conveyors
even though they were of different
lengths. The first chute was equipped
with a track-mounted impact cradle
to improve loading and protect the
belt and tail pulley (Figures 6 and 8).
In
addition,
slider
cradles
for
smoother centering were installed,
along with a full-length apron seal
to prevent dust and spillage from
escaping. A comparable solution
was installed in the longer chute,
with added cradle support down the
entire length. Both chutes featured
non-powered dust bag systems to
collect emissions (Figure 7).
Since installation, spillage around
the loading zones is under control.
Dust emissions have been drastically
reduced at the facility, measured at
less than 3.5 mg/m3 within the immediate
area surrounding the transfer
points, and total dust is down
to 10 mg/m3 throughout the facility.
Operators report that a considerable
drop in equipment failure rates has
resulted in a substantial increase in
plant productivity. Contributing to the
success was workers' ability to easily
inspect and service components by
sliding them out and servicing them
outside of the conveyor. Managers
say that workplace safety and the
overall work environment have improved
significantly.
n
Edited by Scott Jenkins
Reference
1. Conveyor Equipment Manufacturers Association, Belt
Conveyors for Bulk Materials, 7th ed., CEMA, 2014,
pp. 43-46.
Author
Daniel Marshall is a product engineer
at Martin Engineering (One
Martin Place, Neponset, IL 61345;
Phone:
309-852-2384; Email:
Marshall
info@martin-eng.com; Website:
www.martin-eng.com).
has been working in the bulk solids
industry for his entire career.
A self-described " numbers guy, "
Marshall joined Martin Engineering
in 2000 as a research and development engineer,
and has since moved into a product engineering role
specializing in conveyor components and finally to a
quality assurance position. Marshall has been instrumental
in the design and development of transfer point
accessories, conveyor components and safety products.
He now ensures that Martin products are manufactured
to the rigorous standards required by the demanding
applications in bulk solids handling. Marshall
has authored 36 published articles, presented at 17
different industry conferences and contributed to more
than 100 press releases. He holds a B.S.M.E. from
Northern Arizona University.
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Chemical Engineering April 2020

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