Automatic valve closure improves chlorine gas safety at Petrolia water treatment plant
By Terry Blackmore, P.Eng,Wendy Trottier and Vlad Petran, P.Eng.
Sign located at the Petrolia WTP with
the original spelling of the town
name.
Installation of two 68-kg chlorine gas
cylinders, each with a yellow automatic
valve closure devise installed.
The Petrolia Water Treatment
Plant, located in the neighbouring
town of Brights Grove,
Ontario, was established in
1896. Following failed attempts to drill
deep wells in neighbouring townships,
the town voted in favour of spending
$172,000 to build an 11 mile (18 km)
long cast iron pipeline from Lake Huron
to Petrolia and 14 miles (23 km) of a distribution
network in town for the supply
of the much needed fresh, clean water.
The original pump house was located at
the present day Water Treatment Plant.
The Ontario Government began to
set minimum water quality standards
and in 1929 the department of health
recommended chlorine disinfection,
which the Petrolia WTP complied with
in 1930 with the installation of a gas
chlorination system. Coagulation
using aluminum sulphate (alum) followed,
with filtration using anthracite,
sand, gravel, and stone coming online
much later in the 1980s.
In 2002, KMK Consultants Limited,
Brampton, Ontario, was selected by the
Town of Petrolia to design and manage
the construction of an upgrade to the
Water Treatment Plant to be able to
produce up to 8 MLD, serving a population
of 9,000 people. The major scope
of the project included upgrades to the
low lift pump station, installation of a
membrane microfiltration system (Pall
Corporation), installation of an emulsion
polymer makedown unit (USFilter
Stranco Products) as part of the residue
management system upgrade, installation
of liquid chemical feed systems
(LMI-Milton Roy), and modifications
to the existing chlorine contact tank.
Another major aspect of the project
involved the upgrade of the chlorination
system including a new chlorine
gas feed and control system and integration
of the two existing chlorinators
(USFilter Wallace & Tiernan). TheTown of Petrolia preferred the use of
chlorine gas to sodium hypochlorite
but understood the safety concerns of
operations staff as well as the residential
community, which has encroached
on the Water Treatment Plant over the
many decades the plant has been in
operation. The Petrolia WTP uses two
68 kg chlorine gas cylinders and three
chlorinators for pre-chlorination, postchlorination,
and trim. The objective is
to produce potable water with a chlorine
residual of 2.0 mg/L before making
the 11 mile (18 km) trek to the
Mandaumin in-ground storage reservoir
and finally to Petrolia for storage
in the water tower.
In order to address the safety concerns,
the Town of Petrolia and KMK
agreed to investigate the use of automatic
valve closure systems to provide
added safety to the chlorine gas system.
Automatic valve closure systems
are actuators that mount directly onto
the cylinder valve stem system (CGA
Connection 820 yoke and adapter). An
automatic valve closure system is
designed to provide 40-50 ft-lb of closing
torque to the valve stem upon
receipt of an emergency shutdown signal,
stopping any leakage that may be
occurring.
The advantage of an automatic valve
closure device is that the source of the
leak can be isolated, stopping the leak
before it becomes a reportable incident.
In some cases, with adequate subsequent
ventilation, the operator is able to
enter the chlorine room without the need
for a self-contained breathing apparatus
and protective clothing to troubleshoot
and find the source of the leak. Without
the ability to close the valve stem, the
entire contents of the container would
empty without operator intervention, the
plant’s emergency protocol would have
to be initiated (i.e. contacting the local
HAZMAT organization), the incident
would have to be reported and instrumentation
within the chlorine room
could be severely damaged due to chlorine
gas exposure.
Both the International and the
Uniform Fire Codes in the United
States, as an alternative to treatment systems
for 68-kg and 1-tonne toxic gas
containers, such as chlorine, sulfur dioxide,
and ammonia, recognize automatic valve closure systems. The Chlorine
Institute (CI) recognizes these devices
and publishes “Recommendations for
Emergency Closure Devices for
Chlorine Institute Standard Cylinder
and Ton Container Valves”.
The British Columbia Occupational
Health and Safety Regulation discusses
toxic gases and states that “in the
event of an emergency or accidental
release, the employer must ensure that
… the gas supply can be shut down
manually from a remote location or by
the alarm system so as to isolate the
reserve supply within the system and
stop the generation or flow of the
gas…”.
Halogen Valve Systems of Irvine,
California, was selected as the basis of
design. The Terminator Emergency
Shutoff System, designed specifically
for 150-lb gas cylinders, is an electrically
driven actuator that acts directly
on the cylinder valve stem.
The actuator mounts on the cylinder
valve stem by means of a drive bushing
and two parallel rods that straddle the
gas valve nozzle making it easy to
remove during cylinder changes. The
actuator is designed to apply 40 ft-lb of
closing torque to the valve stem after
receiving an emergency shut down signal
from any number of sources such
as a chlorine gas detector. The actuator
is designed as an emergency closure
device and therefore is powered only in
the closing direction. The duty operator
must always accomplish opening of
the valve manually. The electronic circuit
board within the Gemini control
panel, designed to operate two actuators,
contains a microprocessor programmed
to precisely control the valve
closing cycle time and apply the
required torque to the valve stem. An
uninterruptible 12 VDC battery power
supply ensures operation even during
loss of plant power. In the event of a
sustained loss of charging power (up to
seven days), the microprocessor will
initiate actuator closure while sufficient
power remains to apply the specified
torque to the valve stem.
At the Petrolia WTP, the actuators
are installed on two 68-kg chlorine gas
cylinders designed for automatic
switchover. The actuator is tied into the
chlorine gas detector installed within
the chlorine gas building as well as the
Emergency Shutdown Button and plant
SCADA. Plant operators utilize the
actuators to close the valves during
change out of the cylinders. As well, the
actuators are tested again when
installed on the new cylinders, which
ensures that the actuators are operating
according to design specification.
Since installation of the Halogen
automatic valve closure system, there
have not been any incidents with respect
to chlorine gas leakage. However, operators
at the Petrolia WTP are confident
that the actuators are in position and
ready to use should the situation warrant,
which will minimize chlorine leaks
and any risk to themselves and to the
community.
Halogen Valve Systems is represented
in Eastern Canada by Indachem Inc.,
Toronto, Ontario.
