14 | Baker Hughes
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These proactive measures require additional system
costs; however they extend the active life of the steam
conditioning valve and the surrounding system.
The design of this system can be flexible to meet the
constraints of the plant. A Baker Hughes representative
can be contacted for an in depth evaluation of
various design options and warm-up steam quantity
recommendations. For general preheating guidelines
assuming 1000°F steam temperature, Baker Hughes
recommends following:
ṁ
(kg/s) =
0.0104 x D(m) x L(m)
ṁ
(pph) =
0.052 x D(in) x L(in)
Where:
D = O.D. of upstream pipe
L = Pipe length up to the header upstream
of the valve
Insulation
All SteamForm valves should be surrounded with thermal
insulation. The SteamForm bonnet and spray nozzle
flanges must be accessible through the insulation for
routine maintenance reasons.
Accessibility
Larger SteamForm valves require two or more
maintenance personnel to service the installation. To
properly service and maintain the valve, adequate space
must be provided. If the valve is not accessible from the
ground level, a working platform must be provided around
the valve as a safe workable area for maintenance
engineers. A safe route must be carefully planned out
in advance to satisfy the needs of a proper start-up and
routine maintenance.
Temperature Control Methods
The SteamForm must always be designed around
the most critical operating scenario. This can include
intermittent operations such as plant start-up and load
rejection scenarios or may be a steady-state operation
such as a continuous application of a process plant.
Regardless of the operating technique, the SteamForm
temperature control methods must be considered along
with the design of the valve for best control performance.
The spray water control valve must not be opened before
steam conditioning valve is opened. Temperature set
point for the spray water control valve to be provided by
OTHER.
Temperature – Feedback Control
Temperature feedback control is the most common
method for controlling the amount of spray water that is
injected into the steam flow. This method requires the use
of a downstream temperature sensor that relays a signal
to a separate water control valve, to adjust the amount of
water injected and achieve the desired downstream set
temperature.
When using the feedback control method, it is essential
that the temperature sensor is located downstream
at a distance greater than or equal to the minimum
required distance that is specified by the factory for
the application. For more information on the proper
location of the temperature sensor, please refer to
the temperature sensor location section under the
downstream pipe recommendations of this document.
Temperature – Feedforward Control
The temperature sensor is a proven method of control,
but this method requires a longer lag time as a signal
must travel from a sensor to the control valve and
must also allow for response time. Feedback control
also requires a significant length of downstream pipe
to ensure spray water is vaporized and has achieved
an evenly distributed temperature profile. These
requirements are not available for all SteamForm
installations. For these instances, a feedforward control
method is suggested.
The feedforward control method is achieved with a
control algorithm and inherent steam tables that are
programmed into the Distributed Control System (DCS).
This algorithm is a heat balance calculation used to
calculate the required amount of spray water based on
upstream conditions and a specific downstream set point.
The algorithm is programmed directly into the DCS to
provide fast response temperature control. Baker Hughes
customizes an algorithm to the Masoneilan SteamForm
valve flow characteristics for each application requiring
this control technology.
Warning:
Noise insulated within a system remains
within a system and propagates downstream. To
reduce the effects of downstream noise, sufficient
downstream attenuating equipment must be
designed within the system.
Warning:
Failure to provide adequate downstream
pipe length prior to the temperature sensor will result
in instability and inability to control temperature.
