Explosion Isolation Valves incorporate heavy duty knife gate style valves that mate with a round duct Range.
The isolation gate has to be capable of taking both the pressure and the shock load and have an electronic circuitry that transmits on an ultra fast basis to facilitate required operating speeds.
Given duct velocities, the likely source of ignition and the foregoing, a sufficient sensing distance upstream is needed to dose the gate. Pressure and infra red sensing are the most likely followed by heat sensing. Fan shutdown (dependent on location, etc.) may have to be incorporated, for obvious reasons. The construction of the system must be quite rugged. |
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More about Explosion
Isolation Valves: Rarely in the
“real world” of the Process Industry do we find equipment that requires
explosion protection, of some kind, that stands alone. More typically, of
course, it is an integral part of a “system” that is comprised of various
pieces of equipment connected together with ducts etc. Too often, the
overall system has not had a “HAZOP’ (Hazardous Operations) Review done.
Many times, in fact, the dust collector or cyclone in such systems is the
only thing looked at and comes equipped with “explosion protection” – be
it vents, doors, or suppression etc – as provided by the OEM (original
equipment manufacturer) as the purchaser has required “explosion
protection” be supplied as part of the piece of equipment’s supply scope.
And those responsible feel that they have protected their equipment, their
plant and their personnel from the hazards of an explosion.
Unfortunately, the foregoing is only token gesture towards proper
protection though a HAZOP may show the dust collector or baghouse may be
at greatest risk – but possibly from being the generator of a secondary
explosion after the migration of a fireball from upstream in the process
loop, where the actual source of ignition was. So this is the scenario
that can be addressed by explosion isolation valves. As inferred by the
name, their function is to isolate different pieces of equipment from each
other, or to isolate the most likely source of ignition from the balance
of a system – a coal grinder exhaust from the baghouse/dust collection
system. In some cases, to isolate a piece of equipment from the ingress of
any more air flow and to allow suppression systems to disperse their
agents without dilution being a concern.
In order to perform this function, just as
with explosion suppression or spark detection systems, the requirements
for speed are onerous – both for the sensor/electronics as well as the
valve/actuation system. There are those that have attempted to utilize
sensors, components and control panels from the fire protection industry –
only to find out, sometimes the hard way, that their speeds of responses
are nowhere near acceptable – “solid state” or not. So the isolation valve
system must sense the requirement to activate using the same alternatives
as suppression or isolation: heat, pressure, temperature, infra-red etc.
and transfer the signal by way of what is the same control panel and then
the isolation valve must be capable of closing in milliseconds. The valve
must be rugged enough to not only withstand the maximum explosive pressure
that it will see but to absorb the shock loads as well - Aluminum dust is
extremely nasty being in the highest of the explosibility Classes and
capable of generating 180 psig explosive pressures. Given duct velocities,
the likely source of ignition and the foregoing we then need sufficient
sensing distance upstream to get the gate closed. Obviously, fan shutdown
(dependent on location etc.) may have to be incorporated, if fans are in
the system. And you don't want the isolation valve to be the only thing to
survive the explosion! So you have to have a pretty rugged construction of
your system and ducting. Rarely is explosion isolation suitable as stand
alone protection in process systems of any kind in any industry. |
