Chemical Engineering July 2015 - 41

Additional utilities
A few utilities outside of the fermenter are
required to complete the temperature regulation
part of the process. First, natural gas
used to generate the steam that sterilizes
the tank is sent through small pipes operated
by fire-safe ball valves. These valves will
close in case of a fire or gas leak. If the valve
material burns, there is a secondary metal
backup that will prevent gas from escaping
and further fueling the fire. The gas is also
fed through larger pipes (more than 4-in. diameter)
using fire-safe butterfly valves actuated
by rotary actuators.
Steam. As noted above, natural gas is used
to fuel a boiler to heat the water into steam.
To feed water into the boiler, a globe-style
control valve is used specifically to negate
flashing or cavitation that often occurs when
dealing with heated water. globe-style control
valves are available with an anti-cavitation
trim that consists of staged holes that prevent
the fluid from flashing or cavitating. This trim is
not exclusively available in globe-style valves,
but these valves offer the most robust design
for severe-service applications.
As steam comes out of the boiler, a steamisolation
valve is used to shut down the sysCIC-10307
halfp page ad.qxd 3/25/07 6:19 PM Page 1
tem. The purpose of this valve is to shut off the
steam when the boiler is not in use. This does
not occur on a regular basis, so a gate valve is
used, due to its durable metal-seated design
and full flow path, which does not reduce the
pressure or create differential pressure that
affects the quality of the steam. gate valves
have a sliding disc (gate) that reciprocates into
and out of the valve port. This makes them
an ideal isolation valve for high-pressure-drop
and high-temperature applications where operation
is infrequent. Multi-turn electric actuators
are typically required to automate gate
valves; however long-stroke pneumatic and
electro-hydraulic actuators are also available.
In this case, the valve is actuated by a multiturn
actuator, which is not easy to automate
or control but is still advantageous in this case
because of the valve properties.
downstream from the boiler, the steam
branches off to different locations at junctions,
or steam headers, each of which uses
an isolation valve and a control valve. The
isolation valve is used to turn the steam on
or off to a particular location, while the control
valve is used to modulate the flow and
amount of steam needed for the particular
location. Both the isolation and control valve
PLASTIC CONTROL VALVES FOR
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Collins plastic control valves are
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designed for use with corrosive
media and/or corrosive atmospheres.
Collins
valves feature all-plastic
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Valves may be furnished without
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Tel. (979) 849-8266 * www.collinsinst.com
Circle 8 on p. 62 or go to adlinks.chemengonline.com/56199-08
ChemiCal engineering www.Chemengonline.Com july 2015
41
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Chemical Engineering July 2015

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