Atch 7 Drawing Typical Flash Tank Connections.pdf

Typical Flash Tank connec�ons

Proper Flash Tank Piping & Installation Vertical 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. The tangential inlet of the flash tank forces the incoming condensate into a funnel type motion forcing the denser entrained water to the outside of the flash tank to collect on the walls and fall to drain. This leaves dry low-pressure steam in the center of the flash tank to rise and exit the flash tank through the vent.

1. 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.

1. 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. 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.

1. 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.

1. 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.

1. 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 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.

• 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.