Armstrong Horizontal Flash Tank (HAFT)

Armstrong Horizontal Flash Tank (HAFT)
Armstrong Horizontal Flash Tank
Installation and Maintenance
This bulletin should be used by experienced personnel as a guide to the installation and maintenance of the Armstrong Horizontal
Flash Tank. Selection or installation of equipment should always be accompanied by competent technical assistance. We
encourage you to contact Armstrong or your local representative if further information is required.
The maximum operating pressure for the Armstrong Horizontal Flash Tank is 150 psig (10.3 bar). The maximum
design pressure for the Armstrong Flash Tank is 150 psig @ 500°F (10.3 bar @ 260°C). Armstrong Horizontal Flash
Tanks vary in weight:
R-4 = 42 lbs (19 kg)
R-6 = 46 lbs (20 kg)
R-8 = 50 lbs (22 kg)
R-10 = 55 lbs (24 kg)
R-12 = 92 lbs (41 kg)
R-16 = 135 lbs (60 kg)
R-2448 = 231 lbs (103 kg)
R-2472 = 560 lbs (252 kg)
R-30 = 960 lbs (432 kg)
Horizontal Flash Tank Operation
1. Condensate from various points of operation enters the flash tank at
relatively high pressure. As the condensate enters the low pressure
flash tank, part of the condensate flashes into steam.
2. The flash steam exits through the vent at the top of the tank and is
either vented to atmosphere or piped to a low pressure line for use in
low pressure steam applications.
3. The condensate is discharged through the bottom of the flash tank.
When piping flash steam into a low pressure steam line and
discharging condensate directly to a return line, it is important that
the condensate has enough of a pressure differential to overcome
any back pressure from the return line. Additionally, the placement of
a steam trap after the flash tank would be necessary to prevent blow
through of steam. If a steam trap is necessary, an inverted bucket (IB) trap is suggested (F&T can be substituted).
The trap should be sized with a 3:1 safety factor. If back pressure exceeds tank pressure, the use of a reservoir
and pumping trap may be necessary to ensure proper drainage.
If the flash tank is held at atmospheric pressure, the use of a steam trap on the discharge line would not be
necessary since the flash steam is being vented to atmosphere. The condensate, in this case, would be drained
by gravity to a vented receiver which would be placed below the level of the flash tank.
Suggested Installation and Application
1. A flash tank, like a pumping trap or reservoir, should be located below any equipment or steam lines being
drained. Condensate return lines should be pitched toward the flash tank. It is important that the flash tank be
securely bolted to the surface on which it sits. Accordingly, inlet and outlet piping should be properly supported.
IMPORTANT: The flash tank is not designed to be the sole supporting structure for piping.
2. When multiple return lines are fed into the flash tank, check valves should be fitted to each line to prevent a
reversal flow of condensate and resultant flash steam.
3. It is suggested that the condensate lines, the flash tank and the low pressure steam line be insulated to prevent
waste of flash through radiation.
4. If the flash steam will be piped to a low pressure steam line for use in other applications within a plant, such as
use in low pressure heating equipment, the flash tank pressure must be controlled accurately.
A. A back pressure regulator (BPR) should be connected into the low pressure steam line. This will relieve excess
pressure in the system when steam demand is less than the amount of flash steam produced. The BPR should
be sized to relieve the entire project load. CAUTION: Do not use a BPR as a safety relief valve.
B. A pressure reducing valve (PRV) should be connected into the high pressure steam line for make up steam.
This will supplement the flash steam when the steam demand is greater than the amount of flash steam
produced. The PRV should be sized to provide the entire low pressure steam demand.
IMPORTANT: A properly sized safety relief valve should be installed on the flash tank. It should be set for
the flash tanks maximum allowable working pressure (MAWP) or the MAWP of equipment being supplied by
the low pressure steam.
Flash Tank Sizing
Makeup Steam
Reducing Valve
(if required)
Selecting the proper flash tank depends upon the
condensate load entering the vessel and the
corresponding amount of flash steam that is
generated. See the sizing example below.
The percentage of flash steam generated inside
a vessel is calculated by the following formula:
% of flash steam = SH - SL x 100
Low Pressure
SH = Sensible heat in the condensate at the higher
pressure before discharge.
SL = Sensible heat in the condensate at the lower
pressure to which the discharge takes place.
High Pressure
High Pressure
Condensate Inlets
Back Pressure
(if required)
Latent heat in the steam at the lower pressure
to which the condensate had been discharged.
Note: Exact temperatures can be located in the
steam table.
Steam Trap
Let’s say for example that we have 300°F (149°C)
condensate flowing at 10,000 lb/hr @ 125 psig into a
flash tank held at 15 psig. Calculate the amount of
flash steam generated at these parameters.
% flash steam = 324.82 - 218.82 x 100
% flash steam = .112 or 11.2%
To find the amount of flash steam in lb/hr we would need to multiply our condensate load by the percent of flash
steam produced. In this case we would have the following:
.112 x 10,000 lb/hr = 1,120 lb/hr flash steam produced
According to this example, you will neeed a flash tank that can handle 1120 lb/hr flash steam. This would be
Armstrong’s model R-2448. For further sizing questions, please see Armstrong’s All Product Catalog 326 or call
the factory.
Flash Tank Vibrates Excessively
Possibly water hammer. Condensate lines and/or
flash vessel may be undersized. Vessel not secured.
Contact Factory
Excessive Flash Steam
Need to adjust pressure reducing valve or back
pressure regulator
If too much flash steam is being produced, set your
back pressure regulator to reduce excess steam
pressure or reduce make-up steam through PRV
Back Pressure Regulator
Vents Often
Differential settings between BPR and PRV
Set PRV on make-up steam a few psi below
desired low steam pressure and set the BPR a
few psi above desired low steam pressure
Steam trap may have failed
Replace trap.
Steam trap or pump trap on discharge line may have
failed. Discharge check valve may have failed.
Isolate and check traps and check valves
Set point on valve too low.
Set valve for maximum pressure rating of vessel or
the maximum operating pressure of equipment
downstream. Replace if it blows.
Blowing Steam Into Return Line,
Pressurizing Return Line
Flash Tank Floods and/or
Upstream Equipment Floods
Saferty Relief Valve Blows
Armstrong Condensate Management Group, 221 Armstrong Blvd., Three Rivers, MI 49093 – USA Phone: (269) 279-3601 Fax: (269) 279-3150
Bulletin IB-116
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