Boiler Feedwater Heater

Introduction

This is a 3D model of a Boiler Feedwater Heater.

3D Model Annotations

Feedwater Heater

Feedwater is heated prior to it entering a steam generator or boiler. Extraction steam from the steam turbine(s) is used to heat the feedwater. In a feedwater heater, extraction steam is the shell-side fluid whilst feedwater is the tube-side fluid. As the steam transfers its heat to the feedwater, it condenses, and is drained out of the bottom of the heater; the drained fluid is referred to as ‘drips’. Note that a feedwater heater has a very similar design to a u-tube shell and tube heat exchanger.

Partition Plate

The partition plate separates the upper and lower halves of the heat exchanger. The partition plate ensures the tube-side fluid flows into the lower tubes, then returns to the header via the upper tubes.

Tube-Side Inlet

The tube-side fluid enters the heat exchanger through this connection; the tube-side fluid is feedwater.

Tube-Side Discharge

The tube-side fluid is discharged from the heat exchanger through this connection; the tube-side fluid is feedwater.

Shell-Side Inlet

The shell-side fluid enters the heat exchanger through this connection; the shell-side fluid is extraction steam from the steam turbine(s).

Shell-Side Discharge

The shell-side fluid is discharged from the heat exchanger through this connection; the shell-side fluid is extraction steam from the steam turbine, but it is condensate that is drained from the heater, not steam.

Shell

The shell (housing) contains the shell-side flowing medium and houses the tubes, baffles, tie-bars and tubesheets. It also serves as a strong structural piece upon which other apparatus can be attached. Due to its size, the shell is the largest pressure boundary piece of a shell and tube heat exchanger. For this reason, it is preferred that the lower pressure fluid should flow on the shell side, whilst the higher-pressure fluid should flow through the tubes.

Cover Plate

The cover plate is used to seal one end of the shell. Removing the cover plate gives personnel quick access to the tubes; this is useful for periodic visual inspections.

Gasket

A gasket is placed between two surfaces to eliminate any unintended flow path that may exist. Gaskets are usually constructed from gasket paper or rubber. The gasket on this 3D model is ‘squeezed’ between the two metal surfaces to create a leak-tight seal. The shape of the gasket also prevents leakage form one side of the partition plate to the other.

Tubesheet

The tubesheets sit within the shell and support the ends of the tubes. The weight of the tubes is further supported by the baffles (depending upon the design). The tubes are usually cold-rolled and expanded into the tubesheets.

Baffle

Baffles are used to change the flow direction of the shell-side flowing medium. Changing the direction of flow ensures an even heat distribution throughout the heat exchanger. The turbulent flow created by the baffles increases the heat transfer rate of the heat exchanger and helps to reduce deposits forming on the exterior surfaces of the tubes (deposits reduce the efficiency of the heat exchanger).

Tie Bars

Tie bars are used as guides for the baffles to ensure no rotational or axial movement of the baffles occurs.

Tubes

The tube-side fluid flows through the tubes whilst the shell-side fluid flows around the tubes. Heat is exchanged between the two mediums due to proximity. Turbulators can be installed within the tubes to create turbulent flow (rather than laminar flow), which increases the heat exchanger’s efficiency.

Header

The area where the shell side fluid enters and exits the heat exchanger, is referred to as the 'header'.

De-superheating Section

Exhaust steam from the steam turbine(s) enters the desuperheating area of the feedwater heater. For higher pressure heaters, the desuperheating section may contain metal plates that shield the heater tubes from the incoming steam; the plates reduce the likelihood of damage occurring to the tubes due to the high temperature and pressure of the steam.

Cooling Section

The cooling section is the area of the feedwater heater with the lowest temperature. Cold (relative) feedwater enters the heater through the tubes in this section and is heated as it passes through the heater.

Waterbox / Header

The area where the tube-side fluid enters and exits the heat exchanger, is referred to as the 'waterbox' or 'header'.

Condensate

Cooled steam forms condensate. Condensate accumulates in the lower part of the heater and flows through channels into the cooling section, then through the shell-side outlet.

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