Solvent scavenger for a desolventizer toaster using a vapor recovery system
An improved desolventizer-toaster (DT) unit is used for removing traces of a hydrocarbon solvent from a mass of vegetable particles of oil. A conventional DT unit has within a housing, a set of solvent removal trays and a main ejector transporting solvent vapor and steam from below the tray set to between a pair of the trays in the set. The improved DT unit has a further scavenger tray between an inlet of the main ejector and the housing floor. A scavenger ejector transports solvent vapor from between the scavenger tray and the housing floor before it exits from the unit, to the space between the tray set and the scavenger tray.
1. A desolventizer-toaster (DT) unit for removing liquid solvent from a mass of vegetable meal, the DT unit comprising:
a floor, and above the floor, a series of permeable intermediate trays and a bottom tray, each intermediate tray receiving steam for heating and permeating the mass of vegetable meal, and through which cascades downward, through ports therein, the mass of vegetable meal to a bottom tray, and through which upwardly flows a mixture of the steam and vaporized solvent, the bottom tray and the floor of the DT unit each having a transport device for passing the mass of vegetable meal to a space below while resisting passage of vapors;
a main ejector with an inlet in the space below the bottom tray and an outlet between adjacent trays above the bottom tray,
a scavenger tray between the main ejector inlet and the floor; and,
a first scavenger ejector having an inlet in the space between the scavenger tray and the floor and an outlet in the space between the scavenger tray and the bottom tray.
2. The DT unit of claim 1 , wherein the first scavenger ejector outlet is located adjacent to the main ejector inlet.
3. The DT unit of claim 2 , including a second scavenger ejector spaced from the first scavenger ejector and having an inlet in the space between the scavenger tray and the floor and an outlet in the space between the scavenger tray and the bottom tray.
4. The DT unit of claim 3 , wherein the inlet comprises an opening generally facing along a line tangent to the housing wall in the vicinity of the inlet.
5. The DT unit of claim 4 , including a stirring arm moving circularly around the upper surface of the scavenger tray, and wherein the inlet opening faces opposite the direction of stirring arm movement.
6. The DT unit of claim 5 , wherein the inlet opening is bell-shaped.
7. The DT unit of claim 1 , wherein the inlet comprises an opening generally facing along a line tangent to the housing wall in the vicinity of the inlet.
8. The DT unit of claim 1 , wherein the main ejector and first scavenger ejector are each configured to provide momentum transfer between a steam jet and solvent vapor.
9. The DT unit of claim 1 , wherein the transport device is a rotary valve.