CA1168031A - Production of concrete articles utilizing heat- reclaiming system - Google Patents
Production of concrete articles utilizing heat- reclaiming systemInfo
- Publication number
- CA1168031A CA1168031A CA000374898A CA374898A CA1168031A CA 1168031 A CA1168031 A CA 1168031A CA 000374898 A CA000374898 A CA 000374898A CA 374898 A CA374898 A CA 374898A CA 1168031 A CA1168031 A CA 1168031A
- Authority
- CA
- Canada
- Prior art keywords
- kiln
- heat
- concrete articles
- heat energy
- water
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B28—WORKING CEMENT, CLAY, OR STONE
- B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
- B28B11/00—Apparatus or processes for treating or working the shaped or preshaped articles
- B28B11/24—Apparatus or processes for treating or working the shaped or preshaped articles for curing, setting or hardening
- B28B11/245—Curing concrete articles
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B40/00—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability
- C04B40/0082—Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability making use of a rise in temperature, e.g. caused by an exothermic reaction
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
- F26B21/02—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure
- F26B21/04—Circulating air or gases in closed cycles, e.g. wholly within the drying enclosure partly outside the drying enclosure
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B23/00—Heating arrangements
- F26B23/001—Heating arrangements using waste heat
- F26B23/002—Heating arrangements using waste heat recovered from dryer exhaust gases
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Sustainable Development (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Devices For Post-Treatments, Processing, Supply, Discharge, And Other Processes (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
- Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
Abstract
Production of Concrete Articles Utilizing Heat-Reclaiming System Abstract of the Disclosure A method of producing concrete articles comprises reclaiming a portion of the heat energy from the kiln atmosphere during the curing of the concrete articles, and then utilizing the reclaimed heat energy to pre-heat mixing water used to form other concrete articles, or to add to boiler feed water used to generate low pressure steam, or both. In the case where two or more kilns are operated simultaneously at staggered curing cycles, the high temperature kiln atmosphere from the kiln undergoing cool down is intermixed with the low temperature kiln atmosphere from the kiln undergoing heat up thereby reclaiming heat energy from one kiln and using it in the other kiln thereby reducing the total energy consumption required for curing.
Description
I I J 6803~ .
l Field of Invention I
The present invention relates generally to the production of concxete articles, and more particularly to a method of recovering and utilizing heat energy used during the curing of the concrete articles so as to reduce the total energy !
consumption required to cure other concrete articles.
. Background of Invention In the production o~ concrete articles, concrete . aggregates and mixing water are mixed togethex to form concrete from which is manufactured concrete articles~ After manufacture,l the concrete articles must be cured and as well known in the art, !
the term curing refers to the ~ime during which hydration or hardening of the cement takes place through chemical reaction between the cement and water and during which the newly formed (green) concrete articles acquire their strength. Many types . of curing techniques have been developed and at present, in the concrete block industry, the most widespread technique is low pressure steam curingO Xn the low pressure steam system, the green concrete articles are loaded into a kiln after which a sufficient quantity of steam is injected directly into the kiln .to heat the internal kiln atmosphexe to the desired temperature while, at the same time, maintaining a high degree of saturation thereby providing the combination of heat and moisture which accelerates the hy~ration and hardening of the.cement.
One drawback of the low pressure steam system is that . considerable energy is required to generate the steam which, in most low pressure steam systems, is maintained at a temperature ..., I .1 6803 1 ,-on the order of 160-200F. It has been found that considerable heat energy is consumed in heating up the kiln surfaces (walls, roofs, floors, etc.), in heating up the steel pallets on which the blocX is stacked, and in heating up the steel racks which, 1, if used, support the pallets in the kiln. In addition, heat energy is lost to the outside air due to conduction through the kiln walls and roof. Also, heat energy is required to heat up the volume of air within the kiln itself. In view of the continually escalating cost of fuel, careful consideration is being given to ways in which to conserve energy in not only the curing phase but in the entire process of concrete block production.
.
Summary of Invention It is, therefore, a primary object of the present invention to provide a method of production of concrete articles which requires less energy consumption than the methods presently¦
being used.
It is another object of the invention to provide a heat-reclaiming system for reclaiming heat energy used during the curing of concrete articles and utilizing the reclaimed heat energy in the production of other concrete articles thereby lowèring the total energy consumption required to produce concrete articles.
Another object of the invention is to provide a method of producing concrete articles in which, during the cool-down phase of curing, the high temperature kiln atmosphere is -~recirculated through a heat exchanger to remove therefrom heat energy which is utilized in the subsequent production of other 1 ~ 68~3~
concrete articles.
A still further object of the invention is to provide a method of producing concrete articles utilizing two or more kilns for curing and in whlch the high temperature kiln atmosphere from one kiln is recirculated and intermixed with the low temperature kiln atmosphere of another kiln thereby reclaiming heat energy from the kiln being cooled down and utiliæing the reclaimed heat energy in the kiln being heated up.
The above and other objects are achieved in accordance with the invention by reclaiming a portion of the heat energy from the kiln atmosphere during the curing of the concrete articles, and then utilizing the reclaimed heat energy to pre heat mixing water used to form other concrete articles or to add to boiler Eeed water used to generate low pressure steam, or both. In the case where two or more kilns are operated simultaneously at staggered curing cycles, the high temperature kiln atmosphere from the kiln undergoing cool down is intermixed with the low temperature kiln atmosphere from the kiln undergoing heat up thereby reclaiming heat energy from one kiln and using it in ~he other kiln thereby reducing the total energy consumption required for curing.
Having in mind the foregoing and other objects, features and advantages of the invention which will be evident from an understanding of this disclosure, the present invention comprises the metho,d of producing concrete articles as illustrated in the presently preferred embodiments whi~h are hereinafter set forth in sufficient detail to enable those persons skilled in the art to clearly understand the function, ~ J ~31 operation and advantages of the invention.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a schematic side elevational view, partly in section, of a kiln equipped with the heat-reclaiming system of the invention;
Fig. 2A, 3A, 4A and 5A are schematic top plan views, partly in section, of the heat-reclaiming system used in con-junction with plural kilns and Figs. 2B, 2C, 3B, 3C, 4B, 4C, 5B and 5C are time-temperature curves of different conditions within the ~lural kilns; and Fig. 6 is an explanatory time-temperature curve use-ful in explaining the energy savings achieved by the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Two embodiments of the invention will be described with reference to the application drawings and for ease of description, the invention will be described with reference to systems having one or two kilns. The principle of the invention can, of course, be carried out with any number of kilns as will be apparent from the following description.
The invention will also be described with reference to curing concrete blocks and it is understood that the invention is not limited to block curing and is applicable to curing all types of concrete articles. In the United States, the majo rity of concrete block curing is done by low pressure steam so that the invention will be described with respect to this curing technique.
t 1 S~03 1 As shown in Fig. 1, a kiln X of conventional construction has a wall portion 10 covered by a roof portion 12 and is dimensio~ed to receive vertical stacks of pallets containing green blocks to be cured. The front of the kiln is provided with a kiln door l4 which, in the embodiment shown, comprises a roll-up canvas door. For sake of clarity, the kiln X has been shown primarily in outline form as the particular kiln construction is immaterial to the present invention.
In order to supply low pressure steam to the kiln, a steam header 20 is connected at one end to a boiler ~not shown). One or more steam lines 21 branch ofE of the steam header 20 and extend along the length of the kiln. The steam lines 21 have a series of spaced apart nozzles for injecting steam into the kiln to heat the internal kiln atmosphere to the desired temperature and to provide the necessary moisture to accelerate hydration and hardening of the cement. The steam is preferably injected into the kiln by bubbling it through a trough of water thereby enabling the steam to pick up additional molsture content from the water to help maintain the internal kiln atmosphere at a relative humidity of between 90~-100%. The bubbling of the steam through water also avoids ~reation of a superheated steam condition which is disadvantageous in that superheated steam could cause a moisture or hydration reduction state within the green blocks. In order to regulate the injection of steam-into the kiln, a valve 22 is inserted in the steam llne 21.
In accordance with the invention, a heat-reclaiming system is provided for reclaiming some of the heat energy r I l 68031 expended during curing of the block and the reclaimed heat energy is then us~d in the ne~t curing cycle, either in the saSme ~ ~J~ h Ot~g kiln or in ~ ~ kiln, thereby lowering the total consumption of energy needed for curing the block. The heat-reclaiming system comprises an exhaust duct 30 connected to a series of branch exhaust ducts 31 which extend through the kiln roof and open into the kiln interior. The exhaust duct 30 is connected to a header 33 which is connected to the inlet side of a recirculating fan 35. The outlet side of the fan is connected by ductwork to both a fan outlet header 36 and a heat exchanger 37. The header 36 is connected through ducts 38 and 39 to the interior of the kiln to enable recycling of the kiln atmosphere through the loop forrned by the branch exhaust ducts 31, the exhaust duct 30, the recycling fan 35, the header 36 and the ductwork 38 and 39. The heat exchanger 37 is of conventional type and includes tubes 40 for circulating water from a water storage tank (not shown) in heat-exchange relationship with the kiln atmosphere exhausted by the fan 35. The inlet side of the heat exchanger 37 is connected through ductwork to the outlet side of the fan 35 and the outlet side of the heat exchanger is connected through a heat exchanger header 42 to a duct 43 which communicates with the duct 39. By such a construction, the heated and moisture-laden kiln atmosphere which is exhausted by the recirculating fan 35 can pass throùgh the heat e~changer 37 wherein heat energy is given up to the water flowing through the !
tubing 40 and the cooled kiln atmosphere then flows through the header 42 and duct 43 into the duct 39 fQr reentry into the kiln.
In addition, some of the moisture conta~ned in the kiln atmosphere condenses on the tubing 40 and is collected and fed to the boiler feed water tan~ as hot water for use as boiler water make-up. 7 .. .
.,.~ , , !
~'''''. . '.
3 6~031 A set of dampers are provided within the ductwork of the heat-reclaiming system for controlling the manner of flow of the kiln atmosphere during operation of the kiln. A damper 45 is disposed in the exhaust duct 30 and a similar damper 47 is mounted in the duct 39, and both dampers are adjustably movable between op~n and closed positions to regulate flow through their respective ducts. Another damper 48 is pivotably mounted at the intersection of the duct 43 with the duct 39 for regulating the flow of the exhausted kiln atmosphere through the heat-reclaiming system and back into the kiln thxough the duct 39. The damper 48 is movable between one position wherein the damper closes the duct ~3 thereby communicating the ducts 38 and 39 and another position wherein the damper closes the duct 38 thereby communicating the ducts 39 and 43; Though not shown in the drawings, the set of dampers can be mechanically interconnected for common operation.
A description will now be given of the mode of ~
operation o~ the heat-reclaiming system with respect to one curing cycle carried out in the kiln X. Initially, the kiln is empty, and green concrete blocks to be cured are charged into the ; kiln. In the event cured blocks were previously unloaded from the kiln, the kiln interior surfaces may be at a temperature in the range o~ 120-140F and when empty, the kiln would normally have a low humidity condition on the order of 50%-60% relative humidity. After loading of the green blocks into the kiln, which would take from 45 minutes to two hours, the kiln door 14 is closed thereby sealing the kiln interior. - -As well known in the art, different types of cement require different pre-set periods before high temperature can be applied to accelerate the hydration or curing of the cement.
During the pre-set period, high humidity low pressure steam is injected lnto the kiln by opening the steam valve 22 and permitting steam to flow through the steam line 21 from which it l S bubbled through a water trough into the kiln. During this period, the dampers 45 and 47 are closed and the recirculating ~an 35 is off. Throughout the pre-set period, the humidity condition throughout the kiln is maintained in the range of 90~-100% relative humidity. After the pre-set period, the steam input is controlled to raise the kiln at~osphere to an accelerated temperature of about 160-200F at a rate of about 30F/hour and again, the steam is bubbled through water to assure that the kiln atmosphere maintains 90%-100% relative humidity during this portion of the curin~ cycle. After the final accelerated curing temperature is reached, the supply of steam is terminated to allow the kiln to soak for a period of some six-ten hours.
Following the soaking period, the recirculating fan 35 is turned on, the dampers 45 and 47 are opened, and the damper 48 is positioned to close the duct 38 thereby permitting withdrawal of the kiln atmosphere through the exhaust ducts 30, 31,and the withdrawn kiln atmosphere passes through the heat exchanger 37 where it undergoes a reduction in temperature and humidity level and then the cooler and dryer kiln atmosphere is re-introduced back into the kiln through the ducts 43 and 39.
The heat and water which are removed from the kiln atmosphere are stored in the watex for use as boiler feed water for the next .' . _9_ (~ ~
t 3 ~3~31 curing cycle and as mix~gwater for themanufacture of the next batch of concrete blocks. During this heat-reclaiming period, the total kiln temperature (block, pallets, kiln surfaces, etc.j is reduced to a level of 120-140F and the kiln atmosphere is reduced to a low humidity whereby the kiln door 14 can be opened and the kiln unloaded by conventional manual means or automated fork lift truck. The reclaimed heat energy is used in the next curing cycle resulting in a lower total consumption of energy for curing concrete block. -Thus the total curing process allows for controlledpre-setting of the concrete block before accelerating the temperature to the ~inal curing temperature. The curing process utilizes a final curing temperature on the order of 160-200F
which is advantageous from the standpolnt of achieving early hig~ compressive strengths as well as allowing for the inclusion of fly ash (Pozzolan) as part of the cementacious material resulting in a lower per unit material cost. Further, the process reclaims much of the energy required for an accelerated ultimate high temperature level and supplies this reclaimed hea~t energy to the subsequent concrete block to be cured as either hot mixing water or to the boiler feed water supply to reduce the energy needed to ge~erate the steam. Thus the heat-reclaiming system achieves energy conservation since the subsequent concrete blocks are preheated by the reclaimed heat energy extracted by the heat exchanger~37. In this embodiment, the extracted heat energy is in the nature of heated water which can be used as hot mixing water for the next batch of concrete block or as boiler feed water, or both, thereby reducing the amount of heat ` i . l' I l B8031 energy needed for the next curing cycle. Alternatively, the extracted heat energy can be used to furnish heat to the manufacturing building.
The heat-reclaiming system of the invention can also be used with two or more kilns to obtain even greater energy conservation. Figs. 2-S show the system being used in connection with two kilns X and Y and in each figure, the corresponding temperature-time curve is shown alongside its respective kiln.
The representations in Figs, 2A, 3A, 4A and 5A are diagrammatic and are in the nature of top plan views as opposed to Fig. 1 which is in the nature of a side elevational view.
With reference to Fig. 2, and assuming the initial conditions that kiln X is in hour 12 of its curing cycle and kiln Y is just beginning its curing cycle (hour 0), a description will be given as to the manner of operating the he~t-reclaiming system using t~o ~ilns. I~ kiln X, the kiln atmosphere is maintained at 190F and a relative humidity between 90~-100% by modulating on and off the steam valve 22 and with thei dampers 45 and 47 closed and the damper 48 in the position shown.
In ~iln Y, the green b~ock has just been charged into the kiln which has a kiln atmosphere of about 70F and a low relative humidity on the order of 50%-60%. The dampers 45a and 47a are closed and the damper 48a is in the position shown. After the block has been loaded in kiln Y, the relative humidity of the ki~
atmosphere is quickly raised to 90%-100% by injecting a controlled amount of steam through the water trough. Figs. 2B and 2C show j/ - ~esp ~c~y ~ ~ ~ the temperature conditions within the ~cp~ccti ~ kilns at this point in time.
Fig. 3 shows ~he conditions two hours later when the soaking period in kiln X has ~een completed and when the pre-set period of the block in kiln Y has been completed. At this time, ¦
the heat-reclaiming system is activated. The recycling fan 35 is turned on in conjunction with the opening of the dampers 45 ,. 1~ . ~.
1 3 ~S~031 and 47 leading to kiln X and the opening of the dampers 45a and 47a leading to kiln Y. The fan withdraws the high temperature and high humidity atmosphere from kiln X and withdraws the low temperature and lo~ humidity atmosphere from kiln Y and the two kiln atmospheres are intermixed in the fan outlet header 36 and recycled back to both kilns. In this fashion, some of the heat energy from the atmosphere in kiln X is transferred to the atmosphere in kiln Y.
The heat-reclaiming system continues this mode of operation for several hours during which time the kiln X undergoec a cooling down as its kiln atmosphere is mixed with the cooler kiln atmosphere from kiln Y. Kiln Y, on the other hand, undergoes a heating up as its relatively cooler atmosphere is mixed with the hotter atmosphere from kiln X. This condition is shown in Fig. 4 which shows in Figs. 4B and 4C the respective temperatures in kilns X and Y at a time two and one-half hours later than that~
shown in Fig. 3. This mode of operation is continued until the two kilns substantially reach temperature equilibrium, or as close thereto as possible, after which no further heat conservation can be obtained in this mode of operation.
As shown in Fig. 5, when the kiln atmosphere in both kilns X and Y reaches approximately 130F,the heat-reclaiming system undergoes a second mode of operation. In this second mode, the dampers 45 and 47 remain open; however, the damper 48 is moved into the p~sition shown so as to close the duct 38 thereby communicating the duct 43 with the duct 39 so that the atmosphere exhausted from the kiln X passes through the heat exchanger 37 and is then re-introduced into kiln X. In this I 1 ~031 manner, the atmosphere exhausted from kiln X will be cooled and dried in the heat exchanger 37 before being returned to kiln X 1`
thereby lowering the temperature and humidity within kiln X
before the kiln door is open to unload the kiln. At the same time, the dampers 45a and 47a are closed while the damper 48a remains in the position shown,and the steam valve 22a is opened to permit low pressure steam to bubble through the water trough ir._-the kiln Y so that the kiln reaches its final accelerated curing temperature of 190F. Thus, when kiln Y has gained all of the possible heat recovery available from klln X, additional heat energy is supplied by the low pressure steam. In the meantime, the heated water obtained from the heat exchanger 37 is conserved and used as pre-heated mixing~ater for subsequent concrete block to be manufactured or as boiler feed water for subsequent steam generation.
The heat energy saving achieved by the heat-reclaiming system can be seen from the time-temperature curve of Fig 6.
During operation of kilns X and Y, the heat energy added in zone l is reclaimed in zone 2 and added to the adjacent kiln ,during its heat-up in zone 3. It is understood that more than two kilns can be operated in this manner and the showing of two kilns was done for ease of description.
While the invention has been described with reference to two preferred embodiments, it is understood that many modifications thereof and changes thereto will become apparent to those ordinarily skilled in the art and the present invention is intended to cover all such obvious modifications ~nd changes which fall within the spirit and scope of the invention as defined in the appended claims.
. -13-. ~ I
l Field of Invention I
The present invention relates generally to the production of concxete articles, and more particularly to a method of recovering and utilizing heat energy used during the curing of the concrete articles so as to reduce the total energy !
consumption required to cure other concrete articles.
. Background of Invention In the production o~ concrete articles, concrete . aggregates and mixing water are mixed togethex to form concrete from which is manufactured concrete articles~ After manufacture,l the concrete articles must be cured and as well known in the art, !
the term curing refers to the ~ime during which hydration or hardening of the cement takes place through chemical reaction between the cement and water and during which the newly formed (green) concrete articles acquire their strength. Many types . of curing techniques have been developed and at present, in the concrete block industry, the most widespread technique is low pressure steam curingO Xn the low pressure steam system, the green concrete articles are loaded into a kiln after which a sufficient quantity of steam is injected directly into the kiln .to heat the internal kiln atmosphexe to the desired temperature while, at the same time, maintaining a high degree of saturation thereby providing the combination of heat and moisture which accelerates the hy~ration and hardening of the.cement.
One drawback of the low pressure steam system is that . considerable energy is required to generate the steam which, in most low pressure steam systems, is maintained at a temperature ..., I .1 6803 1 ,-on the order of 160-200F. It has been found that considerable heat energy is consumed in heating up the kiln surfaces (walls, roofs, floors, etc.), in heating up the steel pallets on which the blocX is stacked, and in heating up the steel racks which, 1, if used, support the pallets in the kiln. In addition, heat energy is lost to the outside air due to conduction through the kiln walls and roof. Also, heat energy is required to heat up the volume of air within the kiln itself. In view of the continually escalating cost of fuel, careful consideration is being given to ways in which to conserve energy in not only the curing phase but in the entire process of concrete block production.
.
Summary of Invention It is, therefore, a primary object of the present invention to provide a method of production of concrete articles which requires less energy consumption than the methods presently¦
being used.
It is another object of the invention to provide a heat-reclaiming system for reclaiming heat energy used during the curing of concrete articles and utilizing the reclaimed heat energy in the production of other concrete articles thereby lowèring the total energy consumption required to produce concrete articles.
Another object of the invention is to provide a method of producing concrete articles in which, during the cool-down phase of curing, the high temperature kiln atmosphere is -~recirculated through a heat exchanger to remove therefrom heat energy which is utilized in the subsequent production of other 1 ~ 68~3~
concrete articles.
A still further object of the invention is to provide a method of producing concrete articles utilizing two or more kilns for curing and in whlch the high temperature kiln atmosphere from one kiln is recirculated and intermixed with the low temperature kiln atmosphere of another kiln thereby reclaiming heat energy from the kiln being cooled down and utiliæing the reclaimed heat energy in the kiln being heated up.
The above and other objects are achieved in accordance with the invention by reclaiming a portion of the heat energy from the kiln atmosphere during the curing of the concrete articles, and then utilizing the reclaimed heat energy to pre heat mixing water used to form other concrete articles or to add to boiler Eeed water used to generate low pressure steam, or both. In the case where two or more kilns are operated simultaneously at staggered curing cycles, the high temperature kiln atmosphere from the kiln undergoing cool down is intermixed with the low temperature kiln atmosphere from the kiln undergoing heat up thereby reclaiming heat energy from one kiln and using it in ~he other kiln thereby reducing the total energy consumption required for curing.
Having in mind the foregoing and other objects, features and advantages of the invention which will be evident from an understanding of this disclosure, the present invention comprises the metho,d of producing concrete articles as illustrated in the presently preferred embodiments whi~h are hereinafter set forth in sufficient detail to enable those persons skilled in the art to clearly understand the function, ~ J ~31 operation and advantages of the invention.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a schematic side elevational view, partly in section, of a kiln equipped with the heat-reclaiming system of the invention;
Fig. 2A, 3A, 4A and 5A are schematic top plan views, partly in section, of the heat-reclaiming system used in con-junction with plural kilns and Figs. 2B, 2C, 3B, 3C, 4B, 4C, 5B and 5C are time-temperature curves of different conditions within the ~lural kilns; and Fig. 6 is an explanatory time-temperature curve use-ful in explaining the energy savings achieved by the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Two embodiments of the invention will be described with reference to the application drawings and for ease of description, the invention will be described with reference to systems having one or two kilns. The principle of the invention can, of course, be carried out with any number of kilns as will be apparent from the following description.
The invention will also be described with reference to curing concrete blocks and it is understood that the invention is not limited to block curing and is applicable to curing all types of concrete articles. In the United States, the majo rity of concrete block curing is done by low pressure steam so that the invention will be described with respect to this curing technique.
t 1 S~03 1 As shown in Fig. 1, a kiln X of conventional construction has a wall portion 10 covered by a roof portion 12 and is dimensio~ed to receive vertical stacks of pallets containing green blocks to be cured. The front of the kiln is provided with a kiln door l4 which, in the embodiment shown, comprises a roll-up canvas door. For sake of clarity, the kiln X has been shown primarily in outline form as the particular kiln construction is immaterial to the present invention.
In order to supply low pressure steam to the kiln, a steam header 20 is connected at one end to a boiler ~not shown). One or more steam lines 21 branch ofE of the steam header 20 and extend along the length of the kiln. The steam lines 21 have a series of spaced apart nozzles for injecting steam into the kiln to heat the internal kiln atmosphere to the desired temperature and to provide the necessary moisture to accelerate hydration and hardening of the cement. The steam is preferably injected into the kiln by bubbling it through a trough of water thereby enabling the steam to pick up additional molsture content from the water to help maintain the internal kiln atmosphere at a relative humidity of between 90~-100%. The bubbling of the steam through water also avoids ~reation of a superheated steam condition which is disadvantageous in that superheated steam could cause a moisture or hydration reduction state within the green blocks. In order to regulate the injection of steam-into the kiln, a valve 22 is inserted in the steam llne 21.
In accordance with the invention, a heat-reclaiming system is provided for reclaiming some of the heat energy r I l 68031 expended during curing of the block and the reclaimed heat energy is then us~d in the ne~t curing cycle, either in the saSme ~ ~J~ h Ot~g kiln or in ~ ~ kiln, thereby lowering the total consumption of energy needed for curing the block. The heat-reclaiming system comprises an exhaust duct 30 connected to a series of branch exhaust ducts 31 which extend through the kiln roof and open into the kiln interior. The exhaust duct 30 is connected to a header 33 which is connected to the inlet side of a recirculating fan 35. The outlet side of the fan is connected by ductwork to both a fan outlet header 36 and a heat exchanger 37. The header 36 is connected through ducts 38 and 39 to the interior of the kiln to enable recycling of the kiln atmosphere through the loop forrned by the branch exhaust ducts 31, the exhaust duct 30, the recycling fan 35, the header 36 and the ductwork 38 and 39. The heat exchanger 37 is of conventional type and includes tubes 40 for circulating water from a water storage tank (not shown) in heat-exchange relationship with the kiln atmosphere exhausted by the fan 35. The inlet side of the heat exchanger 37 is connected through ductwork to the outlet side of the fan 35 and the outlet side of the heat exchanger is connected through a heat exchanger header 42 to a duct 43 which communicates with the duct 39. By such a construction, the heated and moisture-laden kiln atmosphere which is exhausted by the recirculating fan 35 can pass throùgh the heat e~changer 37 wherein heat energy is given up to the water flowing through the !
tubing 40 and the cooled kiln atmosphere then flows through the header 42 and duct 43 into the duct 39 fQr reentry into the kiln.
In addition, some of the moisture conta~ned in the kiln atmosphere condenses on the tubing 40 and is collected and fed to the boiler feed water tan~ as hot water for use as boiler water make-up. 7 .. .
.,.~ , , !
~'''''. . '.
3 6~031 A set of dampers are provided within the ductwork of the heat-reclaiming system for controlling the manner of flow of the kiln atmosphere during operation of the kiln. A damper 45 is disposed in the exhaust duct 30 and a similar damper 47 is mounted in the duct 39, and both dampers are adjustably movable between op~n and closed positions to regulate flow through their respective ducts. Another damper 48 is pivotably mounted at the intersection of the duct 43 with the duct 39 for regulating the flow of the exhausted kiln atmosphere through the heat-reclaiming system and back into the kiln thxough the duct 39. The damper 48 is movable between one position wherein the damper closes the duct ~3 thereby communicating the ducts 38 and 39 and another position wherein the damper closes the duct 38 thereby communicating the ducts 39 and 43; Though not shown in the drawings, the set of dampers can be mechanically interconnected for common operation.
A description will now be given of the mode of ~
operation o~ the heat-reclaiming system with respect to one curing cycle carried out in the kiln X. Initially, the kiln is empty, and green concrete blocks to be cured are charged into the ; kiln. In the event cured blocks were previously unloaded from the kiln, the kiln interior surfaces may be at a temperature in the range o~ 120-140F and when empty, the kiln would normally have a low humidity condition on the order of 50%-60% relative humidity. After loading of the green blocks into the kiln, which would take from 45 minutes to two hours, the kiln door 14 is closed thereby sealing the kiln interior. - -As well known in the art, different types of cement require different pre-set periods before high temperature can be applied to accelerate the hydration or curing of the cement.
During the pre-set period, high humidity low pressure steam is injected lnto the kiln by opening the steam valve 22 and permitting steam to flow through the steam line 21 from which it l S bubbled through a water trough into the kiln. During this period, the dampers 45 and 47 are closed and the recirculating ~an 35 is off. Throughout the pre-set period, the humidity condition throughout the kiln is maintained in the range of 90~-100% relative humidity. After the pre-set period, the steam input is controlled to raise the kiln at~osphere to an accelerated temperature of about 160-200F at a rate of about 30F/hour and again, the steam is bubbled through water to assure that the kiln atmosphere maintains 90%-100% relative humidity during this portion of the curin~ cycle. After the final accelerated curing temperature is reached, the supply of steam is terminated to allow the kiln to soak for a period of some six-ten hours.
Following the soaking period, the recirculating fan 35 is turned on, the dampers 45 and 47 are opened, and the damper 48 is positioned to close the duct 38 thereby permitting withdrawal of the kiln atmosphere through the exhaust ducts 30, 31,and the withdrawn kiln atmosphere passes through the heat exchanger 37 where it undergoes a reduction in temperature and humidity level and then the cooler and dryer kiln atmosphere is re-introduced back into the kiln through the ducts 43 and 39.
The heat and water which are removed from the kiln atmosphere are stored in the watex for use as boiler feed water for the next .' . _9_ (~ ~
t 3 ~3~31 curing cycle and as mix~gwater for themanufacture of the next batch of concrete blocks. During this heat-reclaiming period, the total kiln temperature (block, pallets, kiln surfaces, etc.j is reduced to a level of 120-140F and the kiln atmosphere is reduced to a low humidity whereby the kiln door 14 can be opened and the kiln unloaded by conventional manual means or automated fork lift truck. The reclaimed heat energy is used in the next curing cycle resulting in a lower total consumption of energy for curing concrete block. -Thus the total curing process allows for controlledpre-setting of the concrete block before accelerating the temperature to the ~inal curing temperature. The curing process utilizes a final curing temperature on the order of 160-200F
which is advantageous from the standpolnt of achieving early hig~ compressive strengths as well as allowing for the inclusion of fly ash (Pozzolan) as part of the cementacious material resulting in a lower per unit material cost. Further, the process reclaims much of the energy required for an accelerated ultimate high temperature level and supplies this reclaimed hea~t energy to the subsequent concrete block to be cured as either hot mixing water or to the boiler feed water supply to reduce the energy needed to ge~erate the steam. Thus the heat-reclaiming system achieves energy conservation since the subsequent concrete blocks are preheated by the reclaimed heat energy extracted by the heat exchanger~37. In this embodiment, the extracted heat energy is in the nature of heated water which can be used as hot mixing water for the next batch of concrete block or as boiler feed water, or both, thereby reducing the amount of heat ` i . l' I l B8031 energy needed for the next curing cycle. Alternatively, the extracted heat energy can be used to furnish heat to the manufacturing building.
The heat-reclaiming system of the invention can also be used with two or more kilns to obtain even greater energy conservation. Figs. 2-S show the system being used in connection with two kilns X and Y and in each figure, the corresponding temperature-time curve is shown alongside its respective kiln.
The representations in Figs, 2A, 3A, 4A and 5A are diagrammatic and are in the nature of top plan views as opposed to Fig. 1 which is in the nature of a side elevational view.
With reference to Fig. 2, and assuming the initial conditions that kiln X is in hour 12 of its curing cycle and kiln Y is just beginning its curing cycle (hour 0), a description will be given as to the manner of operating the he~t-reclaiming system using t~o ~ilns. I~ kiln X, the kiln atmosphere is maintained at 190F and a relative humidity between 90~-100% by modulating on and off the steam valve 22 and with thei dampers 45 and 47 closed and the damper 48 in the position shown.
In ~iln Y, the green b~ock has just been charged into the kiln which has a kiln atmosphere of about 70F and a low relative humidity on the order of 50%-60%. The dampers 45a and 47a are closed and the damper 48a is in the position shown. After the block has been loaded in kiln Y, the relative humidity of the ki~
atmosphere is quickly raised to 90%-100% by injecting a controlled amount of steam through the water trough. Figs. 2B and 2C show j/ - ~esp ~c~y ~ ~ ~ the temperature conditions within the ~cp~ccti ~ kilns at this point in time.
Fig. 3 shows ~he conditions two hours later when the soaking period in kiln X has ~een completed and when the pre-set period of the block in kiln Y has been completed. At this time, ¦
the heat-reclaiming system is activated. The recycling fan 35 is turned on in conjunction with the opening of the dampers 45 ,. 1~ . ~.
1 3 ~S~031 and 47 leading to kiln X and the opening of the dampers 45a and 47a leading to kiln Y. The fan withdraws the high temperature and high humidity atmosphere from kiln X and withdraws the low temperature and lo~ humidity atmosphere from kiln Y and the two kiln atmospheres are intermixed in the fan outlet header 36 and recycled back to both kilns. In this fashion, some of the heat energy from the atmosphere in kiln X is transferred to the atmosphere in kiln Y.
The heat-reclaiming system continues this mode of operation for several hours during which time the kiln X undergoec a cooling down as its kiln atmosphere is mixed with the cooler kiln atmosphere from kiln Y. Kiln Y, on the other hand, undergoes a heating up as its relatively cooler atmosphere is mixed with the hotter atmosphere from kiln X. This condition is shown in Fig. 4 which shows in Figs. 4B and 4C the respective temperatures in kilns X and Y at a time two and one-half hours later than that~
shown in Fig. 3. This mode of operation is continued until the two kilns substantially reach temperature equilibrium, or as close thereto as possible, after which no further heat conservation can be obtained in this mode of operation.
As shown in Fig. 5, when the kiln atmosphere in both kilns X and Y reaches approximately 130F,the heat-reclaiming system undergoes a second mode of operation. In this second mode, the dampers 45 and 47 remain open; however, the damper 48 is moved into the p~sition shown so as to close the duct 38 thereby communicating the duct 43 with the duct 39 so that the atmosphere exhausted from the kiln X passes through the heat exchanger 37 and is then re-introduced into kiln X. In this I 1 ~031 manner, the atmosphere exhausted from kiln X will be cooled and dried in the heat exchanger 37 before being returned to kiln X 1`
thereby lowering the temperature and humidity within kiln X
before the kiln door is open to unload the kiln. At the same time, the dampers 45a and 47a are closed while the damper 48a remains in the position shown,and the steam valve 22a is opened to permit low pressure steam to bubble through the water trough ir._-the kiln Y so that the kiln reaches its final accelerated curing temperature of 190F. Thus, when kiln Y has gained all of the possible heat recovery available from klln X, additional heat energy is supplied by the low pressure steam. In the meantime, the heated water obtained from the heat exchanger 37 is conserved and used as pre-heated mixing~ater for subsequent concrete block to be manufactured or as boiler feed water for subsequent steam generation.
The heat energy saving achieved by the heat-reclaiming system can be seen from the time-temperature curve of Fig 6.
During operation of kilns X and Y, the heat energy added in zone l is reclaimed in zone 2 and added to the adjacent kiln ,during its heat-up in zone 3. It is understood that more than two kilns can be operated in this manner and the showing of two kilns was done for ease of description.
While the invention has been described with reference to two preferred embodiments, it is understood that many modifications thereof and changes thereto will become apparent to those ordinarily skilled in the art and the present invention is intended to cover all such obvious modifications ~nd changes which fall within the spirit and scope of the invention as defined in the appended claims.
. -13-. ~ I
Claims (3)
PRIVILEGE OR PROPERTY IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of reclaiming heat energy in the produc-tion of concrete articles produced by the steps of mixing together concrete aggregates and mixing water to form con-crete; manufacturing concrete articles from the concrete;
and curing the concrete articles in a kiln by allowing the concrete articles to pre-set during a pre-set period, heating up the pre-set concrete articles while maintaining the kiln atmosphere in a high humidity condition, maintaining the heated-up concrete articles at elevated temperature and high humidity during a soaking period, and then cooling down the heated and soaked concrete articles, the improvement com-prising; reclaiming a portion of the heat energy from the kiln atmospshere by extracting heat energy therefrom after the concrete articles reach their maximum curing temperature by recirculating the kiln atmosphere in heat-exchange relation-ship with water so that the high temperature and high humid-ity kiln atmosphere gives up some of its heat energy to the water, thereby heating up the water, and utilizing the reclaimed heat energy contained in the thusly heated water in the subsequent production of other concrete articles thereby lowering the total energy consumption required to cure the subsequently produced other concrete articles.
and curing the concrete articles in a kiln by allowing the concrete articles to pre-set during a pre-set period, heating up the pre-set concrete articles while maintaining the kiln atmosphere in a high humidity condition, maintaining the heated-up concrete articles at elevated temperature and high humidity during a soaking period, and then cooling down the heated and soaked concrete articles, the improvement com-prising; reclaiming a portion of the heat energy from the kiln atmospshere by extracting heat energy therefrom after the concrete articles reach their maximum curing temperature by recirculating the kiln atmosphere in heat-exchange relation-ship with water so that the high temperature and high humid-ity kiln atmosphere gives up some of its heat energy to the water, thereby heating up the water, and utilizing the reclaimed heat energy contained in the thusly heated water in the subsequent production of other concrete articles thereby lowering the total energy consumption required to cure the subsequently produced other concrete articles.
2. A method of reclaiming heat energy according to claim l; wherein the reclaimed heat energy is utilized by applying the heated water to boiler feed water to thereby pre-heat the boiler feed water.
3. A method of reclaiming heat energy according to claim l; wherein the reclaimed heat energy is utilized by applying the heated water to mixing water used to form con-crete to thereby pre-heat the mixing water.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US14968380A | 1980-05-14 | 1980-05-14 | |
| US149,683 | 1980-05-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1168031A true CA1168031A (en) | 1984-05-29 |
Family
ID=22531369
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000374898A Expired CA1168031A (en) | 1980-05-14 | 1981-04-07 | Production of concrete articles utilizing heat- reclaiming system |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5747784A (en) |
| AU (1) | AU544296B2 (en) |
| CA (1) | CA1168031A (en) |
| DE (1) | DE3118046C2 (en) |
| NZ (1) | NZ197078A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102235824A (en) * | 2010-04-29 | 2011-11-09 | 刘毅 | Dynamic thermal efficient energy-saving emission-reducing environmentally-friendly curing and drying kiln equipment |
| CN113146817A (en) * | 2021-03-04 | 2021-07-23 | 贵州迪森元能源科技有限公司 | Automatic control system for residual gas utilization |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6321266A (en) * | 1986-07-10 | 1988-01-28 | 大成プレハブ株式会社 | Latent heat generator |
| FR2627264B1 (en) * | 1988-02-11 | 1991-09-27 | Gerbaud Pierre | PROCESS FOR MINIMIZING THE LOSS OF THERMAL ENERGY ON AIR REJECTED BY THE DRYING PLANTS AND INCREASING THE PRODUCTIVITY OF THESE PLANTS AND PLANTS IMPLEMENTING THIS PROCESS |
| AT399840B (en) * | 1992-06-16 | 1995-07-25 | Wienerberger Ziegelind | METHOD FOR PRODUCING BLOCKS FROM CERAMIC MATERIAL |
| JPH0754317Y2 (en) * | 1992-11-30 | 1995-12-18 | サムエンジニアリング株式会社 | Batch tumbler |
| DE19541866C2 (en) * | 1995-11-09 | 2001-02-22 | Ytong Ag | Process for the hydrothermal hardening and drying of CSH-bound moldings and device for carrying out the process |
| CN105171908B (en) * | 2015-08-21 | 2017-12-15 | 中泰国际高新技术有限公司 | A kind of steam-cured method and device |
| CN111791352B (en) * | 2020-06-03 | 2021-06-08 | 张家港市华诚混凝土构件有限公司 | Intelligent curing means of concrete pipe pile |
| CN113276260B (en) * | 2021-06-09 | 2022-09-13 | 临沂亿利新型材料有限公司 | Method for manufacturing and maintaining lightweight concrete building blocks |
| CN113878699A (en) * | 2021-09-23 | 2022-01-04 | 中国一冶集团有限公司 | Precast beam concrete curing method based on BIM |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1084629B (en) * | 1956-05-26 | 1960-06-30 | Jur Dr Phil Johann Jakob Kindt | Process and machine system for the production of building blocks, in particular shell building blocks, from cement-bound, light or porous building materials |
-
1981
- 1981-04-07 CA CA000374898A patent/CA1168031A/en not_active Expired
- 1981-04-29 AU AU69946/81A patent/AU544296B2/en not_active Ceased
- 1981-05-07 DE DE3118046A patent/DE3118046C2/en not_active Expired
- 1981-05-12 NZ NZ197078A patent/NZ197078A/en unknown
- 1981-05-14 JP JP56072868A patent/JPS5747784A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102235824A (en) * | 2010-04-29 | 2011-11-09 | 刘毅 | Dynamic thermal efficient energy-saving emission-reducing environmentally-friendly curing and drying kiln equipment |
| CN113146817A (en) * | 2021-03-04 | 2021-07-23 | 贵州迪森元能源科技有限公司 | Automatic control system for residual gas utilization |
Also Published As
| Publication number | Publication date |
|---|---|
| NZ197078A (en) | 1986-12-05 |
| DE3118046A1 (en) | 1982-04-08 |
| AU544296B2 (en) | 1985-05-23 |
| AU6994681A (en) | 1981-11-19 |
| DE3118046C2 (en) | 1986-10-30 |
| JPS5747784A (en) | 1982-03-18 |
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