A. H. Lundberg Associates, Inc.'s preferred concentrator technology is flooded forced circulation. This technology utilizes forced liquor circulation through the tube side of a heater with the liquor under a backpressure to prevent boiling. The superheated liquor is discharged into a flash tank (vaporhead) where it is allowed to expand and equalize at a lower temperature. The change in temperature results in evaporation of water from the liquor.

This process is particularly suited to liquors with a high scaling tendency since there is no change in composition of the liquor within the tubes. Further, because the liquor is forced through the tubes, the tube bundle is flooded and there is no concern about liquor distribution.

The concentrator system can be a single or multiple effect system and the vapor from the concentrator can either be sent to a condenser or back to the multiple effect evaporator system to maximize economy.

The flooded forced circulation technology utilizes separate vessels for the vaporhead and heater. This permits easy access to the heater tubing through the two channel covers if mechanical cleaning is required. A heater may be mounted vertically or horizontally depending upon space constraints.

The benefit of reduced scaling tendencies does come at the cost of horsepower. The horsepower requirement is mitigated by the addition of flow enhancers within the tubes. These enhancers induce a swirl to the liquor thereby causing turbulence. This turbulence improves the heat transfer coefficient and makes it possible to reduce the liquor velocity and flow within the tubes resulting in a significant horsepower savings.

The vaporhead provides for the separation of the vapor from the liquor. The vapor passes through a chevron type entrainment separator for removal of liquor droplets on its exit from the effect. Equally as important is the liquor residence time the vaporhead provides. First, it provides a constant source of liquor for the recirculation pump to insure a steady liquor flow through the heater. Second, since there is no liquor concentration change within the heater, the residence time in the vaporhead provides time for crystal growth and liquor concentration change.

While flooded forced circulation is most associated with concentrator technology, it is quite suited to any liquor or fluid of lower solids that shows high scaling tendencies upon evaporation. This includes sulfite pulping liquors, spent liquors from tropical hardwood pulp mills and non-woody mill spent liquors.