Heavy black liquor heaters provide indirect heating of kraft black liquor prior to
combustion in the recovery boiler. By using indirect heating rather than direct addition
of steam, steam usage is reduced in the concentrator and greater steam generation is
possible in the recovery boiler.
The Lundberg heavy liquor heating system uses one or two shell and tube heaters
installed in parallel. This allows cleaning of one shell while operating the other. Heaters
may be switched without any interruption of the liquor flow to the burner. Flowsheet
CL-990801 shows how these heaters are arranged. Instead of a second parallel heater,
a direct steam heater may be used during wash.
Because of the necessary safety precautions for recovery boilers, the piping for Lundberg
liquor heaters is arranged so that the heating surfaces may be washed without risk of
diluting the heavy black liquor. This is accomplished by use of movable pipe spools
rather than valves for connecting flush liquor to the heaters. After cleaning a heater, it
must be drained and the pipe spool must be physically moved to connect the unit to the
heavy liquor lines. Labor required for this change-over may be minimized by the use of
quick disconnects and swivel joints.
The liquor heaters themselves have features that provide good performance, ease in
cleaning, and safety.
Good performance is obtained by placing liquor in the tube side of the heaters. This
gives a high heat transfer rate with minimal pressure drop.
For cleaning, the heater normally need only be flushed out on a regular basis.
Heavy Black Liquor Systems
SB-1034-A