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At the bottom of the cooler is a liqucr reservoir Jư This serves as a storage tank for the circulating liquor and as a decanter for separating the tar which is drawn off through the pipe O which extends to the bottom of the reservoir. As the quantity of liquor is constantly increased by condensation of vapor, a constant level overflow N is provided through which liquor, equal in volume to the condensate, flows continuously to the liquor reservoir in the secondary cooler. K is a baffle over which the liquor dropping from the grids flows to the side of the reservoir opposite the tar and liquor outlet pipes. The circulating liquor is drawn off through the suction pipe P to the centrifugal pump R which delivers it to the cooling coils S, whence it flows through the pipe L to the distributing pipes M which enter the top of the cooler and discharge the cooled liquor over the grids through suitable sprinkling nozzles.

The circulation of liquor in the secondary washer-cooler is similar to that in the primary. As the heat transferred however, is much less, a lower rate of flow and less cooling capacity are required. Through the constant level overflow N1 in the secondary cooler a quantity of liquor, equal to that condensed plus that fed to the apparatus from the primary cooler, flows to a weak liquor collecting tank.

Two types of cooler, single pipe and double pipe, are used to cool the circulating liquor. These are clearly shown in the illustration Fig. 3. The single pipe coolers are stacks of 2 inch galvanized iron pipe, eleven pipes high. The hot liquor enters the bottom pipe, through which it flows, then through a return bend to the pipe above, etc., through the stack. Cooling water properly distributed by a gutter, flows down over the outside surface of the pipes. The double pipe coolers are made up of stacks of eight 2 inch pipes enclosed in 3 inch pipes; the two inch pipes in each stack being connected together in series by return bends. Special fittings are provided which connect in series the annular spaces between the different 2 inch and 3 inch pipes. The hot liquor enters the annular space at the bottom, flows through it, then to the one above, etc. Cooling water flows through the 2 inch pipe in the opposite direction. During the summer, cooling

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FIG. 3. THE PRIMARY WASHER COOLERS AND PART OF THE COOLING COILS

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