Masoneilan 84003 Series SteamForm Installation Guide | 7
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Spray Water System Requirements
When selecting a spray water source the impact on both
system turndown and operation cost must always be
considered. Tradeoffs exist, especially when debating
the added expense of a water pump verses using low-
pressure spray water. The pressure differential between
the water and the outlet steam dictates the operating
range of the nozzle. The low pressure water source
severely limits the turndown and performance of a
steam conditioning system, regardless of the upstream
equipment supplied. The design goal is to provide a
water source that achieves the required turndown of the
system, while minimizing the cost of operation. Some
guidelines are provided in the following sections.
Water Pressure
When evaluating performance of a spray water source,
it is important to remember that water passes through
two stages of pressure drops. The first stage is the spray
water control valve. This valve controls the amount of
water that is injected into the steam flow. The second
stage is the spray nozzle. At this point, the spray water
is broken down into a fine aerosol spray mist and
introduced into the steam.
The availability of water pressure is paramount in the
selection of the appropriate spray nozzles. This is
because each nozzle design has a critical point where
the pressure differential becomes too low and yields large
slugs of water as opposed to the desired aerosol effect.
Large slugs of water are ineffective in cooling the steam
because their mass exceeds the limit of what the steam
flow is capable of suspending. This results in poor cooling
of the steam and severe water fallout.
Other types of nozzles, such as variable orifice nozzles,
require a minimum differential pressure that must be
present to overcome the force on the nozzle and allow
the flow passage to open.
When the minimum pressure limitations are satisfied the
spray nozzle becomes effective in injecting a fine aerosol
of water into the steam. When the minimum pressure
limitations are surpassed, the nozzle is able to supply a
larger capacity of spray water and supplies a larger range
of turndown. The amount of available pressure differential
above the minimum limit dictates the turndown range
of the spray nozzle. This is explained in the following
example application. In the example below, assume
the use of a spray nozzle with C
v
= 1.0. Also assume
the specific gravity of the water is 1.0. This example
compares two operating scenarios, the first uses a water
source with an available pressure differential of 400 PSI,
and the second uses a water source with an available
pressure differential of 100 PSI. In both scenarios,
assume the minimum effective pressure differential of the
nozzle is 25 PSI.
The equation to calculate the C
v
of an incompressible
fluid such as water is:
This can be rearranged to calculate the volume flow rate, Q (GPM):
Scenario 1: 4:1 Turndown Application
