US3581514A

US3581514A - Breather system for sealed storage structure

Info

Publication number: US3581514A
Application number: US817776A
Authority: US
Inventors: Frank D Hamerski; Vern D Overbye
Original assignee: AO Smith Corp
Current assignee: AO Smith Corp
Priority date: 1969-04-21
Filing date: 1969-04-21
Publication date: 1971-06-01
Anticipated expiration: 1988-06-01

Abstract

A sealed storage structure such as a silo having a breather system including a flexible breather bag or equivalent pressurebalancing member. To increase the pressure-balancing capacity of the breather system, a gas cooler assembly is provided. Conduit members connect the cooler assembly to the interior of the silo and to a blower unit to provide a closed gas recirculation path. The cooler and blower are controlled by a thermostat switch within the silo, which switch is set to initiate the recirculation operation at a predetermined maximum temperature and to similarly terminate operation at a predetermined minimum temperature.

Description

3,426,669 2/1969 Peterschmidt................

Inventors Frank D. Hamerski;

Vern D. Overbye, both of Milwaukee. Wis. 817,776

FOREIGN PATENTS 9/1958 Great Britain...

Primary Examiner-William J. Wye

[22] Filed Apr. 21,1969

[45] Patented June 1,1971

[73] A i A. 0. s i h Corporation Att0mey-Andrus, Sceales, Starke & Sawall Milwaukee, Wis.

ABSTRACT: A sealed storage structure such as a silo having a breather system including a flexiblebreather bag or equivalent pressure-balancing member. To increase the pressure-balanc- 3 N 2 E 6 G A R O T S D E L A E S R 0 n T m w S M u w m Ru E flT m TCmL nmc s BS4U 4 U U 5 .m e m m d m a e a m V w m w D.

ing capacity of the breather system, a gas c provided. Conduit members connect the cooler assembl the interior of the silo and to a blower unit to gas recirculation path. The cooler and blower are controlled by a thermostat switch within the silo, which switch is set to initiate the recirculation operation at a predetermined max- UNlTED STATES PATENTS imum temperature and to similarly terminate operation at a 2,643,602 6/1953 Martin............ 6.

98/54 predetermined minimum temperatur PATENTED JUN 1 I97! Jmm'lors v9. filamersh ddbmqys BREATH-HER SYSTEM FOR SEALED STORAGE STRUCTURE This invention relates to generally sealed storage structures and particularly to breathing means for such structures.

Storage structures such as silos are often constructed to be generally airtight because of spoilage caused by air coming in contact with the stored materials. Sealed silos, however, experience problems with pressure differentials arising between the interior of such structures and the ambient. These pressure differentials arise because of gases being generated by the stored material, variations due to ambient temperature, normal atmospheric pressure changes, and absorption of solar heat energy by the silo with the resultant heat transfer to gases within the silo. The situation is undesirable, since too great a pressure differential across the walls of a silo can cause destructive stresses in the walls. At the same time it is prohibitively expensive to construct structures with wall thickness capable of withstanding the more extreme stresses which could possibly arise.

What is generally done, therefore, is to provide the sealed silo with a relief valve which operates to allow passage of gas from the high pressure side of the wall to the low pressure side when predetermined maximum differentials are reached. This method of pressure balancing will at times allow air into the silo and thus detract from the airtight nature of the unit. Because of the above considerations, the relief valve is set to provide a measure of pressure balancing only when the more extreme pressure differentials occur.

To provide a sealed silo with pressure-balancing means, which is operable within the maximum limits determined by the pressure relief valve, breather systems have been developed. The breather system may take the form of a breather bag installed within the space at the top of the silo. The bag has its interior exposed to atmospheric pressure while the bags exterior surface is exposed to the pressure in the silo. By expanding and contracting in response to differences in the two pressures, the bag tends to erase the pressure differential and the pressure balancing is accomplished without allowing extraneous air into contact with the stored material.

It has been found that the conventional breather bag and relief valve are capable of balancing pressures under all but extreme conditions. Greater breathing capacity to balance extreme pressure differentials can be derived by increasing the size or number of breather bags but this method of increasing the capacity of the breather system will correspondingly reduce the volume available for storage.

In experimenting with silos having breather systems of given capacity, it has been found that extreme pressure differentials can occur. One major cause of extreme differentials was found to be the absorption of solar energy by the roof and walls of a silo. It was determined that the gas within the silo reached considerably higher temperatures than the outside air when being warmed by the sunlight.

The breather bag, being located within the silo, itself absorbs some of the solar energy. Thus, the gas within the bag will also tend to be at a higher temperature than the outside atmosphere and the bag will tend to contract more slowly than normal, thereby reducing its capacity to balance the pressure.

Also it was found that a breather bag system has reduced effectiveness to balance pressure differentials which occur beyond a certain temperature within the silo. Further experimentation has shown that this certain silo temperature could be predicted on the basis of daily temperature variations which are common to a geographical region. This temperature was found to be somewhat dependent on the region in which the silo was situated and the pattern of temperature variations over the period of a day which are commonly experienced in that region. Of course, the solar absorption characteristics of the silo structure were found to affect the determinations as well.

Other conditions of the atmosphere also tend to create situations which reduce the effectiveness of the breather system. For instance, when on a hot, sunny day a sudden rainstorm would occur, initially the temperature of the silo would rise will above the ambient temperature and would remain high until falling rain rapidly cools the silo surfaces and surrounding ambient. The pressure differentials resulting from such a cooldown could be of a high magnitude.

The present invention is directed to a structure for increasing the pressurebalancing capacity of the breather system of a sealed storage structure or silo. According to the invention, chilled gas is supplied to the silo at times when the tempera ture would be expected to create an extreme pressure differential. The system operates to maintain the conditions within the silo within the range of proper operation of conventional breather systems. Thus, the pressure balancing is provided by the conventional breather assembly and the invention provides the assurance that extreme conditions will be avoided.

More specifically, the apparatus of the invention includes a cooling unit for cooling gases which are supplied from the storage structure by a conduit and returned to the structure by a second conduit. A blower unit is connected in one of the conduits and serves to circulate the gas within the closed system.

The recirculation-cooling assembly does not operate except at times when the certain predetermined temperature is reached. A control unit is programmed to actuate the recirculation-cooling unit when a given maximum temperature is reached in the storage structure. This given maximum temperature is determined on the basis of experience with conditions in the geographical region as they effect a storage structure having given solar energy absorption characteristics. The recirculation-cooling system is programmed to shut off at a silo temperature at which it could be expected the extreme conditions will no longer occur.

By cooling the gas in the storage structure after the given maximum temperature has been reached, extreme pressure differentials which are beyond the capacity of the breather system are avoided and the pressure differentials are maintained within the range of proper operation of the breather system. This permits a smaller sized breather bag to be employed and thus increases the volume available for storage in the silo.

Other objects and advantages will occur in the course of the following description:

The drawing illustrates the embodiment of the invention storage most preferred by the inventors: diarammatically.

The FIGURE is a side view of the storage structure with part broken away and portions of the structure shown diagrammatically.

The drawings illustrate a sealed storage structure or silo 1, which is adapted to contain a stored material 2. The silo 1 is supported on a foundation 3 and includes a generally cylindrical wall 4 having an open top which is enclosed by roof 5. An unloader unit 6 is located in the bottom of the silo and is of a type commonly used, such as that disclosed in Tiedmann U.S. Pat. No. 2,635,770. Unloader unit 6 serves to dislodge the stored material 2 and to convey the materially to a radially extending trough 7 formed in the foundation 3. The material is conveyed through the trough by a conveying unit 8 and is discharged to the exterior through a door formed in the end of the housing 9 which forms an extension of trough 7.

The drawings show a conventional breather assembly associated with the silo 1 which includes a breather bag 10 suspended from the roof 5 and adapted to expand and contract in the usual manner within the headspace ll of the silo. The interior of the bag 10 is exposed to the atmosphere through the neck 12' secured within an opening in the roof 5, while the exterior of the bag is exposed to the pressure of the gas within the silo. The bag 10 will expand in headspace 11 in response to a negative pressure differential between the interior of the silo and the atmosphere, and conversely, it will contract in response to positive silo pressure, thereby serving to equalize silo and ambient pressures.

The breather system also includes a relief valve 13 connected in an opening in the roof 5. Valve 13 is set to allow air to flow into headspace 11 when the ambient pressure exceeds the silo pressure by a predetermined value, and conversely, allows gas to flow outwardly when the silo pressure exceeds the pressure of the ambient by a predetermined value. The relief valve 13 thus acts to supplement the operation ofthe breather bag 10 when more rapid pressure balancing is required.

To cooperate with the breather system, and to provide a further margin for more extreme conditions, the invention includes a gas recirculation and cooling system which serves to cool and dehumidify the gas contained within the silo. The recirculation and cooling system includes a gas cooling unit 14, a blower 15, a conduit 16 and a second conduit 17 which in conjunction with the interior of the silo, comprise a closed gas circulation system.

The gas cooling unit 14 may be any commercially available refrigerating unit which is adaptable for cooling gases supplied at moderate to high volume rates. The cooling unit 14 includes a condensate trap drain 18 for collecting and removing condensate from the gas being cooled within the unit 14. The gas returned to the silo 1 through conduit 17 is thus, dried as well as cooled.

The inlet of cooling unit 14 is connected to the lower end of silo l by conduit 16 which extends through the foundation 3 adjacent the trough 7 toward the center of the silo. The inner end of conduit 16 communicates with the central portion of trough 7. A screen 19 is disposed over the open end of conduit 16 is order to keep dislodged stored material 2 from entering the circulation system. If lower power requirements are desired for blower l5, conduit 16 could be connected into the top of the silo, so that the cooled gas would not have to be impelled through the stored material. As well, this system would permit the use of less cooled gas to obtain the same temperature in headspace 11.

Blower 15 is connected in conduit 17 to the exhaust end of cooling unit 14 and can be any commercially available variety which can circulate gas at moderate to high volume rates. conduit 17 is in turn, connected to the headspace 11 of the silo 1. With stored materials, the gas will pass through the stored material 2 from top to bottom at high enough rates so as to make recirculation as described above feasible.

The recirculation-cooling assembly does not operate continuously. To program the system s operation, a control unit is provided and includes a temperature responsive actuator, such as a thermostat 20, disposed in the headspace 11 and connected through a suitable electrical control circuit to the blower l and cooling unit 14. The thermostat 20 is designed to initiate recirculation and cooling at a predetermined maximum silo temperature, and to terminate the operation after the headspace 11 has been cooled to a second predetermined minimum temperature.

The system control may embody a pressure responsive actuator responsive to internal silo pressure, in addition to the previously mentioned thermostat. The function of the presureresponsive actuator would be to override the primary thermostat control and initiate startup of the recirculation-cooling system when preselected high pressure in the silo is exceeded and to prevent operation of the recirculation-cooling system when silo pressure is less than a preselected low pressure setting.

In the manner of the invention, the conventional breather assembly, meaning the bag and the relief valve 13, is continuously operating to equalize pressure differentials in the silo. At a silo temperature corresponding to the value at which the conventional breather assembly approaches its designed capacity, or the predetermined maximum temperature, the contacts of thermostat 20 are closed to close the circuit to the blower and the cooler 14 to start their operation. Gas then begins to circulate from silo 1 through the conduit 16 to the cooling unit where the gas is cooled and excess water vapor is condensed. Blower 15 delivers the cooled and dehumidified gas to the headspace 11 through conduit 17. The operation continues until the thermostat senses the shutoff temperature in the silo and signals the blower 15 and the cooler 14 to terminate operation. In some units, it may be desired to employ more complicated control sequences, such as one which interposes a time delay between the cooler shutoff and blower shutoff.

Although the maximum temperature and shutoff temperature are dependent on such factors as color of the silo roof 5, the amount of stored material 2 contained in the silo l, and the geographical region of use for the system, it has been found that temperature values ranging from to 1 10 F. and preferably from to F. for the maximum temperature give reasonable assurance that the conventional breather system will be operating within its range of capability. The shutoff temperature should be from 20 to 30 F. below the maximum temperature, and preferably from 20 to 25 F. below the maximum temperature, so that the system does not continually fluctuate through on-off cycles.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim:

1. In a storage unit having a generally sealed storage structure for storing a perishable material, the storage structure having a headspace and a breather system operating in fluid communication with the headspace; a gas-cooling system comprising:

a gas-cooling unit;

a first conduit connecting the gas-coolin g unit to the storage structure,

a second conduit connecting the cooling unit to the headspace of the storage structure,

gas-recirculating means for conveying gas through the first conduit means from the structure to the gas-cooling unit and for returning gas discharged from said gas-cooling unit through the second conduit means to the headspace; and

a temperature-responsive control means disposed in the headspace for actuating said gas-cooling unit and gasrecirculating means in response to the temperature in the headspace reaching a first selected value in the range of 90 F. to 1 10 F., and for terminating the operation of said gas-cooling unit and gas-recirculating means in response to a second temperature in the headspace reaching a second selected value in the range of 20 F. to 30 F. less than said first selected value, whereby the operation of the breather system is supplemented in high temperature conditions.

2. A method of balancing the pressure in the interior of a generally sealed storage structure having a headspace and a flexible breather unit operating in fluid communication with the headspace, comprising the steps of:

cooling the headspace when the temperature in the headspace reaches a first selected value in the range of 90 F. to 1 10 F and terminating Terminating the cooling of the headspace when the temperature in the headspace reaches a second selected value in the range of 20 F. to 30 F. less than said first selected value.

3. A method of balancing the pressure differentials between a generally sealed storage structure and the ambient, the storage structure having a headspace containing a gas and an expandible breather member in said headspace; comprising:

continuously operating the expandible breather member to expand and contract such as to generally equalize the pressure in the headspace and the ambient; and

maintaining the temperature in the headspace below a predetermined maximum value at which the expandible breather member experiences decreased effectiveness.

4. The method of claim 3 wherein the temperature is main tained by recirculating and cooling the gas in the headspace when said predetermined maximum value is reached, and terminating the recirculating and cooling when a predetermined lower temperature is reached; said predetermined maximum value being in the range of 90 F. to 1 10 F., and said predetermined lower temperature being in the range of 20 F. to 30 F. less than said predetennined maximum value.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,58l, 5l4 Dated June 1, 1971.

Inventor(s) Frank D. Hammerski and Vern D. Overbye It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 45 cancel "storage" and substitute therefor --presently---, column 2, line 45 cancel "diarammatically" column 4, line 53 cancel "Terminating", second occurrence.

Signed and sealed this th day of January 1972.

( SEAL Attest:

EDWARD M.FLETCHEH, JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Patents FORM PO'1O50UO'59) USCOMM-DC 6D376-P69 9 U 5 GOVERNMENT PRINTING OFFICE: 1969 O355-334

Claims

1. In a storage unit having a generally sealed storage structure for storing a perishable material, the storage structure having a headspace and a breather system operating in fluid communication with the headspace; a gas-cooling system comprising: a gas-cooling unit; a first conduit connecting the gas-cooling unit to the storage structure, a second conduit connecting the cooling unit to the headspace of the storage structure, gas-recirculating means for conveying gas through the first conduit means from the structure to the gas-cooling unit and for returning gas discharged from said gas-cooling unit through the second conduit means to the headspace; and a temperature-responsive control means disposed in the headspace for actuating said gas-cooling unit and gas-recirculating means in response to the temperature in the headspace reaching a first selected value in the range of 90* F. to 110* F., and for terminating the operation of said gas-cooling unit and gasrecirculating means in response to a second temperature in the headspace reaching a second selected value in the range of 20* F. to 30* F. less than said first selected value, whereby the operation of the breather system is supplemented in high temperature conditions.

2. A method of balancing the pressure in the interior of a generally sealed storage structure having a headspace and a flexible breather unit operating in fluid communication with the headspace, comprising the steps of: cooling the headspace when the temperature in the headspace reaches a first selected value in the range of 90* F. to 110* F.; and terminating Terminating the cooling of the headspace when the temperature in the headspace reaches a second selected value in the range of 20* F. to 30* F. less than said first selected value.

3. A method of balancing the pressure differentials between a generally sealed storage structure and the ambient, the storage structure having a headspace containing a gas and an expandible breather member in said headspace; comprising: continuously operating the expandible breather member to expand and contract such as to generally equalize the pressure in the headspace and the ambient; and maintaining the temperature in the headspace below a predetermined maximum value at which the expandible breather member experiences decreased effectiveness.

4. The method of claim 3 wherein the temperature is maintained by recirculating and cooling the gas in the headspace when said predetermined maximum value is reached, and terminating the recirculating and cooling when a predetermined lower temperature is reached; said predetermined maximum value being in the range of 90* F. to 110* F., and said predetermined lower temperature being in the range of 20* F. to 30* F. less than said predetermined maximum value.