It is recognized as useful to be able to store two liquids of different density under conditions which maintain them essentially separate, even when the composition of both liquids is identical. Such separation can be achieved by two independent vessels, a single vessel with internal compartmentalization, a vessel with simple or labyrinthine fixed baffles, a vessel with a movable rigid baffle or a vessel with flexible diaphragm or membrane. Such systems, however, have technical, operational or economic drawbacks.
A more desirable system is to maintain separation of the two different density liquids as separate layers by stratification with the lower density liquid layer above the higher density liquid layer. Even though the density of the two liquids is different, they have the same composition. This can occur because the density of the liquid used increases as its temperature decreases and the density decreases as its temperature increases. Examples of such liquids, at least over some of the most useful temperature ranges, are water, aqueous solutions of organic liquids such as methanol and ethylene glycol, aqueous solutions of inorganic salts such as sodium chloride, carbon dioxide, oil and molten salts. Such liquids are stored in stratified layers as sources of thermal energy for heating and for refrigeration or cooling purposes. See, for example, the U.S. Pat. Nos. 4,449,368 (Haynie); 4,315,404 (Schmitt); and 4,643,212 (Rothrock).
When the lower cold layer is used for refrigeration or cooling, a stream of the cold liquid is withdrawn, used for cooling and then returned warm or hot, and at a lower density, to the top layer while cold liquid is simultaneously removed from the bottom layer. In this way, essentially the entire stored volume can be used for cooling so that the entire liquid content returned to the tank becomes heated. At an appropriate time the warm or hot liquid can be withdrawn from the tank and be cooled and then returned to the tank as a lower stratified cold layer of higher density with a hot layer of lower density on top unless, of course, cooling continues until all of the hot liquid in the tank is withdrawn and returned as cold liquid.
Maintaining the described stratification of the two liquid layers having different densities requires than the liquids be withdrawn and fed to the tank without promoting undue mixing at the tank inlet and outlet and at the interface of the two liquids. The desired result can be achieved by the use of manifolds, usually including a myriad of nozzles, ports, holes, slots, perforations or other openings, but they have been determined to be cumbersome and costly in fabrication, support, erection and maintenance.
Andrepont et al U.S. Pat. No. 4,987,922 discloses a storage tank for two liquids of different density. The tank has a lower liquid distribution plate which controls the distribution of higher density liquid, i.e. cold water, into and from the tank. The tank also has an upper liquid distribution plate which controls the distribution of lower density liquid i.e. hot water into and from the tank. While the apparatus disclosed in that patent is highly useful for the intended purpose it is not particularly adapted for normal maintenance of the tank, particularly at the bottom since it obstructs ready access to portions of the tank that require inspection and painting. Also, the particular apparatus of the patent requires considerable welding and expensive fabrication. Additionally, while the apparatus can be installed in a new tank during construction it is not easily installed in retrofitting an old tank for storing liquids of different densities because many of the pieces cannot pass through a conventional manhole having a 2 to 3 foot diameter. Accordingly, there is a need for improved apparatus for liquid distribution in a tank and for apparatus which can be fed through a tank manhole in retrofitting an old tank for storing two liquids of different density, as well as for providing ease of access for inspection and painting.