Masoneilan 84003 Series SteamForm Installation Guide | 17
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Process Control
Controlling temperature at or near saturation is difficult
due to the performance limitations of temperature
sensing technology. If the steam passing the sensor is
“wet”, the sensor recognizes water and signals that the
steam is already sufficiently cooled. Wet steam is difficult
to accurately measure and creates instability and large
swings of process variability.
When reducing steam temperature to saturation, large
quantities of water are injected. Large percentages of
water over steam can result in flooding in the pipeline,
and possible severe water fallout. The longer the distance
that the water travels, the greater the risk becomes of
water fallout and flooding. To limit this occurrence, close
coupling of the SteamForm with a back-pressure dump
tube is recommended. This closecoupled scenario forces
the unvaporized water through the pressure reducing
dump tube and assists in mixing by creating a low-
pressure region that causes the water to instantly flash
into steam. This process requires the use of feedforward
control to maintain a stable and accurate downstream
temperature set point.
Back-Pressure Dump Tubes
The back-pressure dump tube is an essential piece of
equipment for the design of this bypass system. The
pressure drop of this device must be strategically split
to manage a balance between equipment size and
cost compared to overall performance of the system.
By properly staging the pressure drop the dump
tube, SteamForm, and adjoining pipe sizes can all be
minimized. This reduces the total cost of the installation.
The size of the dump tube becomes critical when inserted
into the duct of an air-cooled condenser. Large dump
tubes create an obstruction to the cross flow of the steam
that is exhausting from the turbine prior to admission into
the system condenser. The obstruction creates unwanted
back–pressure on the turbine and reduces the overall
efficiency of the turbine and steam plant. However, the
dump tube must reach a certain size in order to space the
holes of the tube and maintain steam jet independence
for minimize noise generation.
Correctly staging the pressure drop in this system is
essential in minimizing the noise generation and the cost
of the installation. For specific design recommendations,
it is essential to involve the bypass valve supplier and
the condenser supplier up-front in the design stage to
ensure the best design is provided for the interaction of
equipment.
System Noise Evaluation
Noise in this system is created from the combination
of multiple sources. The control valve, dump tube,
and condenser duct are all potential sources for noise
generation. Acoustical insulation is recommended
for protecting pipe segments from excessive noise
generation; however, noise insulated within a closed
system propagates downstream until a noise attenuating
device is installed. As noise propagates farther
downstream, it eventually reaches the point where it is
released into the thin walled duct of the condenser. At this
point, the duct acts as a noise amplifier and increases
the decibel level. Whenever possible, Baker Hughes
highly recommends surrounding all thin walled ducts with
acoustical insulation.
A further challenge is presented in a case where multiple
bypass lines are all discharged into a single point of
injection. Jet streams exhausting from the dump tubes
can combine noise sources and create a single source
that generates much higher levels of noise. To reduce
noise levels, these jets must remain independent by
installing large distances between each dump tube.
Noise levels in bypass to condenser applications have
been measured in excess of 110 dBA. For best results,
pre-installation concerns must be thoroughly evaluated
by the design firm and the supplier of the turbine bypass
equipment.
Final Recommendations
Severe service SteamForm applications have several
specific design features that require detailed evaluation
and consideration. Every hour spent in the design
process can save days of downtime and dollars of
maintenance cost. For each of these applications, it is
recommended to contact a Baker Hughes Masoneilan
Certified Technicians to assist in evaluation and to
provide application specific recommendations for long-
term, successful operation.
It is also recommended to request Baker Hughes Field
Service representative at the plant during installation and
commissioning stage. Baker Hughes’s oversight during
this phase can help ensure appropriate valve installation
and reduce downtown time. Contact your regional Baker
Hughes Sales office, Aftermarket center or Channel
Partner for Field Service requests.
