US3730265A - Shut-down system for heat storage exchange apparatus - Google Patents

Abstract

A rapidly corrodible metal drain plug disposed in the condensate return line of a heat storage-exchange system effectively evacuates alkaline heat transfer fluid, thereby preventing the transfer of heat from an alkaline heat storage composition when leakage between the storage composition and heat transfer fluid has occurred. The corrodible plug may be disposed in a condensate return line, condensate reservoir or the condensate pump and may be made of aluminum, zinc, tin, titanium or tantalum. A pressure regulating sub-system is provided upstream of the corrodable metal drain plug to adjust the pressure in the condensate return line to substantially atmospheric pressure, thereby eliminating the reduced pressure always found at the exhaust side of the condenser and thus permitting rapid and positive evacuation of the system.

Description

United States Patent 1 1 1111 3,730,265 Lawrence May 1, 1973 SHUT-DOWN SYSTEM FOR HEAT 3,080,119 3/1963 Shutl-tufski. ..237/66 X STORAGE EXCHANGE APPARATUS 2,583,332 13/1325 iaken ..l22/534 1 33 l 1 5 k 22 4 [75] Inventor: Willis Thompson Lawrence, a a

' Winchester, Mass. Primary Examiner-Edward J. Michael Assi Hooker Chemical Cor ration Attorney-Peter F. Casella, Donald C. Studley and gn Niagara Falls N Y p0 Richard K. Jackson [22] Filed: Oct. 15, 1970 57 ABSTRACT PPl- NOJ 81,124 A rapidly corrodible metal drain plug disposed in the RelatedUs Application Data condensate return line of a heat storage-exchange system effectively evacuates alkaline heat transfer Continuation of 822,117, y 6, 1969, fluid, thereby preventing the transfer of heat from an abandoned' alkaline heat storage composition when leakage between the storage composition and heat transfer [52] US. Cl. ..165/l34, 122/504, 1652/5348, fluid has occurred. The corrodible plug may be [51] I t Cl Fzgf disposed in a condensate return line, condensate 58] z 22/504. reservoir or the condensate pump and may be made of 66 236/58 aluminum, zinc, tin, titanium or tantalum, A pressure regulating sub-system is provided upstream of the cor- 56] References Cited rodable metal drain plug to adjust the pressure in the condensate return line to substantially atmospheric pressure, thereby eliminating the reduced pressure al- 1,875,898 9/1932 Thompson ..236/58 Ways f i the xhaust the condfmser and 2,051,147 8/1936 Murphy ..236/6l thus Permmmg rapld and pvsmve evawatwn of the 2,078,802 4/1937 Lum ..237/9 System- 2,3l5,54l 4/1943 ()sterkorn ..237/68 2,434,574 1/1948 Marshall ..237/9 x 6 3 Draw 2,479,664 8/1949 Ayers ..237/9 Patented May 1, 1973 V 3,730,265

SHUT-DOWN SYSTEM FOR HEAT STORAGE EXCHANGE APPARATUS I This application is a continuation application of application Ser. No. 822,117 filed May 6, 1969, now abandoned.

This invention relates to a heat storage heat exchange apparatus and more particularly to an apparatus for withdrawing heat stored in a heat storage apparatus at a desired rate and the conversion of withdrawn heat to its end use at a fixed temperature.

Recent developments in the heat storage art have provided methods, compositions, and apparatuses for the storage of relatively large amounts of heat in a relatively small area. However, for the stored heat to serve a useful purpose, it must be capable of being withdrawn on demand and in the quantity desired when needed. To obtain the most beneficial results from the use of the heat storage system, it is particularly desirable to have a means for withdrawing heat at a rate and quantity which, in many instances, is substantially greater than the rate of heat input into the heat storage medium. Exemplary of such heat storage uses are the domestic, commercial and industrial heating of water particularly wherein the demand for heated water is extremely high during certain periods of the day. Previous methods of providing such heated water require extremely large storage tanks for heated water to maintain the desired adequate supply of hot water. However using a heat storage medium, an equal amount of heat can be stored in a volume up to about 1/ th or less than that required to store the heated water.

An improved heat transfer system is one provided with a thermally stable heat storage medium capable of storing heat at widely varying temperatures, a thermally stable heat transfer fluid, a vaporizing passage designed for the conveyance of heat transfer. fluid through said heat storage medium, a heat exchange condensing means exterior to said heat storage medium, and a conduit for the passage of said heat transfer fluid from said vaporizing passage to said heat exchange condensing means, then to a condensate.

reservoir and from said reservoir to said vaporizing passage in said heat storage medium.

Such an apparatus provides a means for extracting heat at a rapid rate from the heat storage medium thereby making available larger amounts of heat on demand. The present apparatus also makes practical use of relatively slow heating means for the heating of large amounts of fluids in relatively short periods of time. In particular, normal household line voltages and current supplies can be used to heat the heat storage medium over an extended period of time thereby providing sustained or periodic heat withdrawal for a relatively shorter period of time. In addition to providing a means for the rapid heating of water, the present apparatus is also particularly useful for providing heated air for other fluids such as non-freezing, snow and ice melting, fluids. Numerous domestic, commercial, and industrial applications will become readily apparent to those skilled in the art from the description of the invention. It will become immediately apparent that the present system can be used whenever heating temperatures of about 100 to 400 F. are used.

The most preferred heat transfer fluid is water. Other fluids such as various organic and inorganic thermally stable liquids volatilizing within the given range can The preferred heat storage medium is an inorganic, substantially anhydrous composition. Various heat storage compositions are well known in the art having varying heat storage capacities and temperatures of operation. The most preferred compositions are alkali metal hydroxide compositions, such as those containing sodium hydroxide, potassium hydroxide, lithium hydroxide and the like. Such compositions are particularly desirable because of the thermal stability and large heat storage capacity over extremely large ranges.

One major problem attending the uses of substantially anhydrous alkali metal hydroxide heat storage composition occurs upon failure of the vaporizing passage within the heat storage medium. When an opening develops between the body of heat storage material and the fluid in the heat transfer conduit within the heat storage vessel, the molten alkali metal hydroxide composition seeps into the heat transfer conduit. This condition not only presents a problem of rapid dissipation of heat of solution but it also affords an alkaline heat transfer fluid which is highly corrosive toward other metallic components of the heat transfer system. In order to avoid damage to the heat storage heat exchange apparatus, it is desirable, to rapidly shut down the entire system when the heat transfer fluid has becomealkaline due to a leak in the vaporizing passage within the heat storage vessel.

In accordance with this invention, an automatic safety device is provided for a heat storage exchange apparatus, which comprises a rapidly corrodible alkaline soluble metallic plug disposed in the heat transfer medium conduit. The corrodible plug is situated to close the entrance of a drain and is adapted to open said drain upon contact with an alkaline material, thereby emptying the heat transfer conduit of fluid.

The safety device of this invention may embody one of several devices. For example, the safety plug may be disposed in the condensate reservoir of the heat transfer system at a point below the level of the condensate return line to the heat storage vessel. Likewise, the safety plug may actually be a section of the condensate return line or, in analogous manner, either a section of the pump housing or a part of the dynamic pump mechanism may be converted to a safety plug device.

The corrodible safety plug may be constructed of aluminum, zinc, tin, tantalum or titanium. Although various materials may be employed which are rapidly corroded by an aqueous alkaline medium, it is preferred to employ aluminum or zinc as the corrodible plug material. It is understood that various alloys of the recited metals may be employed as long as they exhibit the characteristics of rapid dissolution is aqueous alkaline medium.

It is to be understood that the corrodible plug may be used in conjunction with an electrically controlled switch which will open the circuit for an electrical heater within the heat storage material. Although an electrically activated pH meter device for preventing introduction of heat into the heat storage material may be used in conjunction with the corrodible plug of the instant invention, the use of a corrodible plug is itself superior to a device which will deactivate the heat elements within the heat storage material because the corrodible plug almost instantaneously closes down the entire heat transfer system.

If the substantially anhydrous alkali metal hydroxide heat storage composition is in the molten state at the time a leak occurs in the vaporizing passage through the heat storage material, when heat transfer fluid is not passing through the passage, the liquid heat storage material passes into the vaporizing passage where it later contacts the heat transfer fluid producing an alkaline state. The alkaline heat transfer medium rapidly corrodes the safety plug, draining the heat transfer conduit. After the heat transfer conduit, has been drained, the heat storage material will continue to pass into the vaporizing passage. When it reaches the colder parts of the heat transfer conduit is solidifies preventing further leakage.

The present invention is operated utilizing a thermally stable heat transfer fluid and a thermally stable heat storage composition. The expression, thermally stable, is used to describe a composition which does not decompose on heating or cooling within the desired heat storage temperature range. As such, the heat storage medium is normally a solid or liquid state within the heat storage temperature ranges. The heat transfer fluid is a liquid which preferably is volatilized at the heat storage temperature and condensed at the heat transfer temperature. Thus, a thermally stable liquid having an atmospheric, sub-atmospheric, or super atmospheric boiling point in the range of about 100 to 800 F. and more preferably about 150 to 350 F. can be used. Preferably, a liquid with an atmospheric boiling point in the given range is used. Using a vaporization-condensation cycle, a high heat transfer rate is effected with a smaller flow of heat transfer fluid because the latent heat of vaporization and condensation is used in withdrawing the heat from the heat storage medium. Therefore, the most preferred heat transfer fluids are those having high latent heats.

The invention may best be understood by reference to the drawings in which:

FIG. 1 represents a diagramatic view of a heat storage vessel and a hot water holding tank, illustrating the heat transfer conduit, a condensate reservoir and pump.

FIG. 2 is a diagrammatic representation of the corrodible plug of the instant invention as it may be disposed in the condensate reservoir or a section of the pump housing.

FIG. 3 represents a diagrammatic view of the corrodible plug of the instant invention as it may be disposed in the condensate return line.

The heat transfer system is operated by passing heat transfer fluid (condensate) 24 through a heat storage apparatus containing a heat storage medium 11 heated to a temperature of about 300 to l200 F The heat transfer fluid is passed in heat exchange relationship to the heat storage medium 11, such as by means of vaporizing passage 12. The heat transfer fluid is vaporized in passing through the heat storage medium 11. The vapor is withdrawn from the heat storage apparatus l0 and passed to heat exchange means 14 which is in contact with a fluid to be heated. The heat exchange contact with the fluid to be heated effects the condensation of the volatilized heat transfer fluid. The condensed heat transfer fluid is subsequently withdrawn to condensate reservoir 16. The fluid to be heated may be a liquid or a gas such as air. When air is a fluid to be heated, heat exchange means 14 can be located in a room, conduit or other enclosure to be heated by the sensible heat liberated in the condensation of the vaporized fluid.

In the preferred embodiment, the present system is used to heat water or other liquid such as a non-freezing ethylene glycol solution or the like used for the melting of ice and snow. Similarly, other liquids can be heated for other purposes in the same manner. When a liquid is the fluid to be heated, heat exchange means 14 is positioned in container 14 having a fluid inlet 20, which feeds container 15 with replenishing amounts of fluid, and a fluid outlet means 22 for the withdrawal of the heated fluid. Condensed heat transfer fluid 24 is withdrawn from heat exchange means 14, and retained in the heat transfer fluid reservoir 16 for eventual recycle to the heat storage apparatus. In communication with the heat transfer fluid within reservoir 16 is a corrodible plug 26 disposed in a sidewall of said reservoir at a point below the level of the condensate return line. Heat transfer fluid is withdrawn from the fluid reservoir 16 via pump 18 for recycle to the storage apparatus 10 on demand for heat. Suitable thermostat monitors may be employed within the fluid to be heated or alternatively, the air temperature in the area of the heat exchange means 14 may be monitored to signal a call for additional heat. The heat transfer fluid in reservoir 16 may be circulated by means of pump 18 or by a gravity feed device. A pressure regulating means 1 is disposed in the top wall of heat transfer fluid reservoir 16 said means containing safety regulator valves 2, and 3, which are set for about plus and minus one pound per square inch pressure respectively and an expansion bag 4 which has a capacity of about one cubic foot. This pressure regulating system is thus adjusted to permit the system to operate at about atmospheric pressure.

The corrodible plug 26 may be conveniently assembled in the side-wall of reservoir 16 in the manner depicted in FIG. 2. A wafer of corrodible metal 30 is firmly seated between two hallow insert nuts 32 within the wall 28 of the condensate reservoir 16. A drain pipe 34 is conveniently attached to the outlet to carry condensate to a drain (not shown).

Similarly representative of the instant invention, is the corrodible plug assembly depicted in FIG. 3, in which plug 30 is held by ring nut 32 against a shoulder 40 of sleeve 38 which is attached to a section of heat transfer conduit 36. When corrodible plug wafer 30 is consumed or opened by attack of the heat transfer fluid within conduit 36, the heat transfer fluid drains from the system thereby preventing damage to corrodible metal parts of the apparatus.

The heat storage medium in the heat storage apparatus is maintained at a temperature above the boiling temperature of the heat transfer fluid. Normally, the temperature is in the range of about 250 to 1200 F. and more preferably in the range of about 300 to 900 F. The heat in the heat storage apparatus may be replenished by means of any conventional heating device such as a resistance heater, gas burner, or solar energy. Utilizing the heat storage ability of the heat storage medium the heat replenishment can be effected with normal line voltages, when employing a resistance heater, over an extended period of time.

Hence, large quantities of heat are made available for rapid withdrawal over a shorter period of time than could be provided with an electrical heater alone. Although electrical energy is conveniently used in the present apparatus, other sources of heat can be used to replenish the heat storage medium as indicated above.

The following examples illustrate the present invention. Unless otherwise indicated, all parts and percentages used in the examples and claims are by weight and all temperatures are in degrees Fahrenheit.

EXAMPLE 1 perature of about 900 F. This corresponds to a heat storage capacity of about 400 btu per pound of heat storage composition or about 43,400 btu per cubic foot. Based on a 70 temperature rise, the, storage capacity of the composition is about ten times that of water.

The heat storage material is retained in a mild steel container having a coiled. vaporizer passage therein with an inlet means at the bottom and an outlet means to the top thereof. Also contained in the heat storage container is a resistance heater drawing 19.5 kilowatts of power. This power source is rated capable of heating 80 gallons of water per hour through a 100 F. rise. The heat storage container is insulated to reduce the heat loss to the atmosphere.

Connected to the outlet of the vaporizer passage within the heat storage composition is a conduit passing to a second container for water. The conduit is connected to a coil condenser within the water container. The condenser drains to a reservoir for the heat exchange fluid. A conduit joins the heat exchange fluid reservoir with the inlet end of the vaporizer passage within the heat storage composition. An electrical, thermostatically actuated pump supplies the vaporizer vpassage within the heat storage medium with heat transfer fluid. ln communication with the heat exchange fluid reservoir, a pressure regulating system may be employed adjusted to operate at about at- I mospheric pressure with safety regulator valves set for about plus or minus one pound per square inch of pressure. An expansion bag having a gaseous capacity of about 1 cubic foot may be used in the pressure regulating system which provides the capacity for two changes in the gas volume of the reservoir without changing the pressure more than plus or minus one pound per square inch. Water is used as the heat exchange fluid.

In the sidewall of the reservoir holding condensed heat transfer fluid a drain orifice is installed. A waferthin plug of aluminum, graded 99.95 aluminum, is inserted by means of two threaded hollow insert nuts;

The system is operated by passing water at a temperature of about F. from the heat transferreservoir to the heat storage apparatus having an initial heat storage temperature of about 900 F. Water is vaporized to super heated steani at a temperature approaching that of the heat storage composition while passing through the heat storage apparatus. The super heated steam is then passed to the to the condenser and the water container, wherein it is condensed, giving up its latent heat of vaporization, thereby heating the water in the water container. The condensed water is withdrawn from the condenser and passed to the heat transfer fluid reservoir for recycle to the heat storage apparatus. On continued use, the temperature of the heat storage composition decreases as heat is withdrawn at a rate in excess of heat input.

After an extended operation, an opening is made through the wall of the vaporizer passage in the heat storage container thereby permitting alkaline heat storage material to escape into the heat transfer fluid. The alkaline material is carried over by the vaporized heat transfer fluid to the water holding tankand eventually finds its way into the condensate reservoir. The alkaline material in the condensate reservoir rapidly corrodes and dissolves the aluminum plug in the wall of the condensate reservoir completely draining the heat transfer fluid from the'system. Heat withdrawal from the heat storage vessel is no longer possible.

While there has been described a specific embodiment involving the use of a corrodible plug in the condensate reservoir of a heat transfer system, it is understood that the corrodible plug may be positioned in the condensate return line to the heat storage vessel or as a moveable or a fixed part (the housing) of the pump which circulates the heat transfer fluid to the heat storage material.

I claim:

1. In a two-step heat storage heat exchange system comprising a thermally stable alkali metal hydroxide heat storage composition, a primary heat exchange closed loop in heat exchange relationship with said heat storage material through which a thermally .stable vaporizable heat exchange medium is circulated, a secondary heat exchange loop in heat exchange relationship with said primary loop, and a thermal load connected with-said secondary loop, the improvement comprising a primary vaporizing heat exchanger in heat exchange relationship with said heat storage medium, a second condensing heat exchanger means in heat exchange relationship with said secondary loop, delivery conduit means connecting the output side of said vaporizing heat exchanger means to the input side of said second condensing heat exchanger means, exhaust conduit means connecting the output side of said condensing means to a condensate reservoir and recycling conduit means connecting said reservoir to the input side of said vaporizing heat exchanger means thereby forming said primary loop, a heat transfer medium volatilzed at heat storage temperature and condensed at heat transfer temperature adapted to be circulated through said primary loop, a secondary loop in heat exchange relationship with said condensing heat exchanger, protective venting means inserted in said recycling conduit means of said primary loop comprising a dissolvable insert adapted to be consumed by an alkaline contaminate, and pressure regulating means in communication with said condensate reservoir upstream of said protective device whereby the partial vacuum on the exhaust side of said condensing means is adjusted pressure to permit rapid dumping of said heat exchange medium from said primary loop and thereby isolating and disconnecting said secondary loop from said heat exchange system.

2. The heat exchange system of claim 1, in which said heat transfer medium has an atmospheric boiling point within the range of to 800 F.

3. The heat exchange system of claim 1 in which said pressure regulating means is adjusted to operate at substantially atmospheric pressure.

4. The heat exchange system of claim 3 in which safety regulating valves are provided which are set to maintain a pressure range of plus or minus one pound of atmospheric pressure.

5. The heat exchange system of claim 1 in which an expansion bag is connected to said pressure regulating system.

6. The heat exchange system of claim 5 in which said expansion bag provides the capacity for-two changes in the gas volume of the condensate reservoir without changing the pressure of the gas in the condensate reservoir more than plus or minus one pound per square inch.

Claims (6)

1. In a two-step heat storage heat exchange system comprising a thermally stable alkali metal hydroxide heat storage composition, a primary heat exchange closed loop in heat exchange relationship with said heat storage material through which a thermally stable vaporizable heat exchange medium is circulated, a secondary heat exchange loop in heat exchange relationship with said primary loop, and a thermal load connected with said secondary loop, the improvement comprising a primary vaporizing heat exchanger in heat exchange relationship with said heat storage medium, a second condensing heat exchanger means in heat exchange relationship with said secondary loop, delivery conduit means connecting the output side of said vaporizing heat exchanger means to the input side of said second condensing heat exchanger means, exhaust conduit means connecting the output side of said condensing means to a condensate reservoir and recycling conduit means connecting said reservoir to the input side of said vaporizing heat exchanger means thereby forming said primary loop, a heat transfer medium volatilzed at heat storage temperature and condensed at heat transfer temperature adapted to be circulated through said primary loop, a secondary loop in heat exchange relationship with said condensing heat exchanger, protective venting means inserted in said recycling conduit means of said primary loop comprising a dissolvable insert adapted to be consumed by an alkaline contaminate, and pressure regulating means in communication with said condensate reservoir upstream of said protective device whereby the partial vacuum on the exhaust side of said condensing means is adjusted pressure to permit rapid dumping of said heat exchange medium from said primary loop and thereby isolating and disconnecting said secondary loop from said heat exchange system.

2. The heat exchange system of claim 1, in which said heat transfer medium has an atmospheric boiling point within the range of 100* to 800* F.

3. The heat exchange system of claim 1 in which said pressure regulating means is adjusted to operate at substantially atmospheric pressure.

4. The heat exchange system of claim 3 in which safety regulating valves are provided which are set to maintain a pressure range of plus or minus one pound of atmospheric pressure.

5. The heat exchange system of claim 1 in which an expansion bag is connected to said pressure regulating system.

6. The heat exchange system of claim 5 in which said expansion bag provides the capacity for two changes in the gas volume of the condensate reservoir without changing the pressure of the gas in the condensate reservoir more than plus or minus one pound per square inch.

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