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The concept of the proposed concrete evaporator structure design includes use of prestressed and pretensioned sections to permit use of thinner walls capable of withstanding the differential pressures to the atmosphere and between stages. Additionally, the use of stressed concrete will minimize cracking and leakage. Flexible seals embedded in the concrete at section joints provide for thermal expansion while pretenting in-leakage of air. Each stage has been established with a length of 40 ft. in the direction of flow. In order to provide adequate brine surface for release of vapors, the stages are 260 ft. wide. Brine flows across the floor at about 5 ft. per second and about 1-1/4 ft. deep. Distillate collected from troughs under each condenser bundle flows in a separate central channel along the floor. It increases in width through the stages. The flowing streams take their pressure drops through under flow" weirs in the barrier walls with orifices properly sized for each stage. The last of the recycling stages has extra length to contain large piping manifolds. At this point, the heat rejection water leaves the condenser streams and recycle brine enters. The concrete floor and portions of walls exposed to flowing water are lined with bonded neoprene materials as suited for the various temperature levels. Suppliers of the materials give assurance of good service life for the exposure conditions encountered. The arched roofs of each stage are arranged in sections for removal in case condenser bundles are replaced. Rails in each valley carry a gentry crane which spans the arch and carries its load to either -8-19-Epson Perfection 4870 Photo, 400 dpi, 8 bit, 14,204,928 byte