US1885418A - Process of heat application and equipment therefor - Google Patents

Description

Nov. 1, 1932. w. A. DARRAH 1,835,418

PROCESS OF HEAT APPLICATION AND EQUIPMENT THEREFOR 3 Sheets-Sheet l Inventor.

Filed July 20, '1929 1932- w. A. DARRAH 1,885,418

PROCESS OF HEAT APPL'I CATION AND EQUIPMENT THEREFOR Filed July 20. 1929 s Sheets-Sheet 2 [lei/ea for.

Nov. 1, 1932. w. A. DARRAH 1,885,413

PROCESS OF HEAT APPLICATION AND EQUIPMENT THEREFOR Filed July 20, 1929 3 Sheets-Sheet 3 figure 5:

' ing, heat treatin Patented Nov. 1, 1932 PATENT OFFMIE WILLIAM A. DARE-AH, OF CHICAGO, ILLINOIS PROCESS OF HEAT APPLICATION AND EQUIPMENT THEREFOR Application filed July 20,

This invention relates to methods and apparatus which may be employed for transmitting heat in such operations asdrying, bakand similar operations.

Some of the ob ects of this invention are to provide economical, controllable equipment which will give rapid eflicient, and uniform results.

Other objects of this invention are to devise processes and apparatus which will permit obtaining the maximum production with a given size of equipment. Another object of this invention is'to obtain a highly uniform heat distribution and a highly uniform drying condition in all parts of the equipment.

Other objects of this invention are to control the circulation of the heated gases, to control the amount of exhaust gases and to control the distribution of temperature within the equipment.

Other objects of this invention will be apparent from the specifications, claims and drawings attached hereto. 7

Referring to the drawings:

Figure 1 shows a side elevation of one form. of my equipment; while Figure 2 shows a plan view partly broken away,

Figure 3 shows a cross sectiontaken on Figure 1 on line AA; while Figure 4 shows a cross section of the equipment shown in Figure 1 taken on line BB.

Figure 5 shows a'detail of a portion of the dryer and the air distributing nozzles.

Figure 6 shows a vertical sectional elevation in part of the detail shown in Figure 5.

lln the drawings, 1 represents a housing or enclosure surrounding a roller dryer although the equipment is equally applicable to any other type of drying chamber, or heating device. The dryer consists of a series of live rolls indicated by 2 arranged in horizontal layers and provided with a driving mechanism consisting of a series of sprockets 3 driven by a continuous chain or belt not shown. Partition walls 4 and 5 extend, the length of the dryer and separate the dryer enclosure from parallel ducts 6 and 7. No heating means are supplied within the dryer, heat and circulation being supplied by one or more combustion devices 32 or 33.

1929. Serial No. 379,641.

circulating fans indicated by 8 and 9 respectively. The discharge of the fans is connected to nozzle manifolds 10 and 11 respectively. The nozzle manifold is divided into a series of openings indicated by ll-A and 12 and similar ports which are placed between the rows of live rolls as shown in enlarged section in Figure 6. These nozzle manifolds are provided with a series of deflectors at their extreme. ends. The deflectors are illustrated in Figure 5 as 13, 14, 15 and 16 and can be adjusted to control the spread of the circulating gases as they leave the manifold nozzle. Ad-

justment of the deflectors is provided by means of damper rods 17, 18, 19 and 20.

The air blown into the nozzle manifolds is divided in such a manner as to obtain the desired amount in each of the manifolds by a series of adjustable deflecting vanes indicated as 21, 22, 23, 24. and 25. These are operated from damper rods as indicated by 26 which operates damper 21. Obviously the angular position of the deflectors will throw more or less air into the various nozzle manifolds thus controlling the heating and ventilation in each of the decks of the dryer.

Heaters 27 and 28 are supplied delivering hot air and products of combustion to the fans 8 and 9 respectively.

The heaters are shown consisting of the housing 29 enclosing one or more combustion chambers 30 and 31 which are provided with Combustion devices may be gas burners, oil burners, powdered coal burners or similar equipment.

A mixture of combustible and airis de livered into the combustion chambers in the manner shown and after combustion is complete the spent products of combustion pass into the intake of the fans and circulate through the system. I prefer to construct the combustion chambers of material which is highly refractory and a good heat conductor. Silicon carbide or aluminum oxide refractories are quite satisfactory for this purpose, but I do not wish to limit my invention to these materials only. The heaters as for example 27, areprovided with a retarding wall 34 containing ports 35, 36, etc., for purposes to be later described. A damper,

as for example a series of louvers 37 and 38 is provided to control the amount of circulating air and gases which can enter the intake of fans 8 and 9 respectively.

Fans 8 and 9 are driven by pulleys 39 and 40 from belts 41 and 42 or by any other equivalent device. The heaters may well be provided with stacks as for example 43 and 44 which are used primarily for exhausting products of combustion during the starting of the equipment.

The air and circulating products of combustion after leaving nozzle manifolds 10 and 11 travel longitudinally of the dryer coming in contact with the upper and lower surface of the material being dried. These products of combustion travel to a point near the end of the dryer where they pass through ports indicated by 45, 46, 47 and 48 entering the outer ducts 6 and 7 as previously described. A portion of the air and gases which enter duct 7 is exhausted by fan 49 and 50 through exhaust stacks 51 and 52 respectively. The balance of the circulating air and gases return in the direction of the arrows and by-passes through ports 53 and 54 into duct 55 after which the circulating gases pass upward through the space in the heater housing 29 between combustion chambers 30 and 31 as shown. A damper 56 is provided for controlling the amount of returning circulating gases and therefore, balancing the pressure on the system.

It will be understood that heaters 27 and 28 may be of similar construction and may or may not be of the same size or capacity. In View of the similarity of construction of the heaters and the duct system only one of these will be described in detail it being understood that the other is similar in principle.

A portion of the circulating products of combustion and air which is travelling in ducts 6 and 7 will pass downward through ports 57 and 58 into duct 59 and then upward through port 60 into the housing 29 of the heater. This portion finds its way through dampers 37 into the intake of the circulating fan for a further cycle.

In operating an equipment of this kind it is quite important to control the relative volumes of circulating gases and also the pressure in dilferent parts of the system. For example one common use of this class of equipment is in connection with the drying of wallboard. gypsum boards, and related products. In order to obtain the maximum of production with a given size of equipment it-is desirable to operate at a maximum speed. This requires carrying high temperatures and handling of large volumes of circulating gases at high velocities. If a given deck of the dryer does not receive its'proper quota of circulating gases the product travelling through that deck will be insufliciently dried.

On the other hand if a particular'deck of the dryer receives a materially greater portion of circulating gases than should properly be delivered to it there is serious danger of destroying or at least damaging the material passing through such deck by overheating. In the case of gypsum board the net results would be a calcining of the gypsum which would materially decrease the commercial value of the board. In the case of a wallboard formed from cellulose material, the board may be burned or blackened which is obviously objectionable.

In the case of many boardsthere is a tendency for the edges to dry more rapidly than the central portion and if the stream of 'hot gases leaving the nozzles is directed squarely upon the edges this portion of the board may be damaged before the balance of the board is dried. Y

If the pressure at the ends of the dryer where the board enters and leaves is not properly controlled there will be an excessive leakage of air out of the dryer which means both a loss of heat and the creation of objectionable Working conditions for the operators feeding the equipment. If the pressure conditions existing in and around the combustion chambers are not properly controlled, com bustion will not be clean and complete and the board will be seriously discolored. I have found that one of the points requiring most critical attention when using a low grade heavy oil is the balance of pressures in am around the combustion chambers.

The total volume of circulating gases also has an important bearing on drying conditions. It is. possible to carry out satisfactory drying with fairly low temperatures (300 to 400 F.) and relatively large volumes of circulating gases, or on the other hand equally satisfactory drying may beobtained in the case of certain materials by materially reducing the volume of circulating gases, but proportionately increasing the temperature of the circulating gases, the heat transferred be- 1ng approximately the same in either case. All of these various conditions are controllable by the equipment here shown and described.

In operating my equipment I have found that the relative pressures existing in the different portions of the dryer, heater, ducts and flues is of considerable importance when it is desired .to obtain the best results. This condition I describe as a condition of balanced pressures, although the term is obviously not intended to imply that all terms throughout the device are equal. One feature which requires careful control of relative pressures is the combustion chamber. It will be noted by referring to the drawings that the discharge from the combustion chamber is in direct communication with the intake of the large circulating blower. The intake of the large circulating blower is of course the point in the system subject to the lowest absolute pressure. If the suction to which the combustion chamber is subjected exceeds a limiting value the products of combustion are likely to be drawn through the combustion chamher with an excessive speed which is not conducive to the most satisfactory combustion. Under these conditions soot, dirt or unburned oil (in case the fuel used is oil) are likely to be withdrawn into the system and distributed through the dryer thus discoloring the board or sheet and causing the collection of objectionable materials inside the dryer. On the other hand, if the suction to which the combustion chamber is subjected is not sulficiently large, combustion is again likely to be imperfect with the formation of soot or dirt. One important feature of my invention, therefore, is to provide means whereby the pressure conditions within the combustion chamber may be maintained at an optimum.

In order to obtain complete combustion with my device it is necessary when burning certain fuels such as tars, high gravity oils and related substances, to maintain extremely high temperatures within the combustion chamber. Obviously a high temperature within the combustion chamber results in what is known as a short, sharp flame or in other words, what is known as rapid, intense combustion which is quite complete and entirely consumes all vapors, soot, carbon particles, etc. 1

I therefore prefer to maintain as high temperatures as possible within the combustion chamber. In order to withstand such high. temperature I prefer to employ refractory materials having the general characteristics of aluminum oxide, silicon 'carbide, sillimanite, etc. Even these refractory materials are not proof against the temperatures whichmay be obtained in a combustion cham ber of light equipment under certain conditions, unless some provision is made for carrying off a portion of the heat from the outside walls of the combustion chamber.

I, therefore, provide means for delivering a controlled portion of the circulating gases or air around the outside of the combustion chamber. These gases in traveling over the surface of the combustion chamber become heated thus reducing the temperature and maintaining it within desired limits.

Thus for example the duct 55 delivers air from the dryer through an opening in the floor of the heater. The air travels upward over the sides of the combustion chamber and then enters the intake of fan 8 by passing through the angular sets above wall 34 and through outlets 35 and 36 which may if desired be made controllable in size by means of a damper or other equipment.

In any case louver 0r damper 56 in duct 55 controls he amount of return air or circulating gases which can pass through the circuit outlined above.

Another portion of the return air travels through duct 59 directly to the intake of fan 8. The portion of circulating gases travcling through duct 59 is also controllable by means of the louvers 70. Obviously by the relative adjustment of louvers 56 and louvers the relative proportion of air or circulating gases required to pass over, the combustion chamber, and return direct without passing over the combustion chamber, may be varied to suit conditions. It will also be apparent that with a given volume of return circulating gases delivered through duct 55 to the space around the combustion chamber, the pressure existing around the combustion chamber may be controlled by regulating the area of the angular opening above wall 34 and the area of the openings through ports 35 36, etc. It will also be apparent that with a fixed opening in ports 35, 36 and above wall 34, the greater the amount of circulating air delivered through duct 55 the greater will fie the pressure around the combustion cham- The system outlined, therefore, provides means for controlling the amount of circulating gases around the combustion chamber thus regulating the temperature of the walls of the combustion chamber and, at the same time, the pressure around the outside of thecombustion chamber may be,independently controlled.

One advantage of maintaining a pressure In the operation of my equipment, it isusually advisable to exhaust a pre-determined amount of the circulating gases continuously. Th1s arrangement permits the .maintenance of a substantially constant pressure within the device and also makes it possible to prevent the accumulation of undesirable amounts of watervapor, explosive solvents or other materials which may be evaporated from the sheet or boards. The exhaust may be removed at any desired point in the cycle, but I find it convenient to locate the inlet of the exhaust fan adjacent to the point at which the circulating gases leave the dryer. At this point the gases have performed the maximum amount of thermal work in transferring heat from the heater to the material in the dryer, and at the same time, they contain the maximum amount of solvent. At this point, therefore, the thermal loss from the exhaust gases is a minimum. In order to control the pressures resulting from the operation of the exhaust fans I may employ a damper as for example 71 and 72 (Figure 2) which operate respectively in connection with exhaust outlet 52 and exhaust outlet 51. I also prefer to install dampers 73 and 74 or their equivalent in the exhaust ducts 52 and 51 respectively.

The manipulation of dampers 71, 72, 73 and 74 has an important bearing on the control of pressures in various parts of the dryer heater and ducts. For example if all of the above dampers are open wide the exhaust is likely to be so high as to cause the heater to operate on relatively low pressures which may require careful adjustment in order to obtain complete combustion. It is, therefore, desirable to have dampers 71, 72, 7 3 and 74- partly closed. Dampers 71 and 72 also control the amount of air which is drawn in from the end of the kiln. For example if dampers 71 and 72'were closed while dampers 73 and 74 are open the suction of the exhaust fans will normally result in the driving of greater volumes of gases through ducts 48 and 46 than are supplied by the circulating fans 8 and 9 through the nozzles and dryer. This will result therefore in drawing considerable amounts of air from the room outside the dryer into the dryer. It is desirable to balance conditions, so that a controlled amount .of air will be drawn-in from the rooms surrounding the dryer as this presents leakage of the moist and impure circulating air into the room. If conditions are not balanced and a portion of the circulating gases into the system escapes into the room a very unpleasant fog or mist collects in cool weather and at all times the products of combustion render the working conditions Within the room unpleasant. One feature of my invention, therefore, relates to the control of conditions of this kind by a proper balancing of pressures.

Another feature of my invention resides in the application of the circulating medium within the dryer. In the case of certain boards or sheets the edges naturally dry most rapidly and are, therefore, most subject to damage in case of overheating or discoloration. In the case of gypsum boards the gypsum is subject to calcination on the edges which naturally destroys the strength and impairs the commercial value of the boards. Fiber boards may be discolored or burned on the edges if conditions are not properly controlled.

In order to control this situation I have provided adjustable deflectors 13, 14, and 16 operated respectively by control rods 17, 18, 19 and 20. The deflectors may be adjusted from the outside of the kiln and may be placed in one or all of the nozzles. The

deflectors serve to direct the stream of hot circulating gases away from the edges of the board and toward the center of the board. Since the heat conveyed to the board is directly proportional to the flow of hot circulating gases this arrangement protects the edges of the board or sheet from overheating or related damage due to a high velocity of the circulating gases at this point.

In the operation of a device in accordance with my invention it is customary as outlined above to continuously discard a controlled portion of the circulating gases. The volume of the remaining circulating gases is continually augmented by the products of combustion and the materials vaporized from the substance being dried. In addition it is usually advisable to add a definite controlled amount of room air in order to maintain the pressures under the most desirable conditions. The room air thus added may enter the system through a port in the heater, preferably located in the front of the heater or if desired by being drawn downward through stacks 43 and 44, the quantities being controlled by dampers 7 5 and 76 respectively.

Having now fully described my inventionv what I claim as new and wish to secure by Letters Patent in the United States, is as follows:

1. A drying unit comprising a drying chamber, a heater, a combustion chamber within said heater, a gas moving device, a duct connecting said heater with said gas moving device, a series of distributing nozzles supplied with circulating gases from said gas moving device, deflectors controlling the flow of gases into said nozzles, deflectors controlling the flow of gases out of said nozzles, a duct delivering a portion of the circulating gases back to said heater, a duct for delivering another portion of said circulating gases back to said gas moving device, and control means for regulating the amount of return gases passing back to said heater.

2. A drying unit comprising a drying chamber,'a conveyor within said chamber, a heater, a combustion chamber within said heater, a gas moving device, a duct connecting said heater with said gas moving device, a distributing nozzle above said conveyor supplied with circulating gases from said gas moving device, a duct delivering a portion of circulating gases back to said heater, a duct for delivering another portion of said circulating gases back to said gas moving device and control means for regulating the amount of return gases back to said heater.

3. A longitudinally extending dryer unit, comprising a drying chamber, a heater adjacent thereto, a combustion chamber within said heater, a conveyor extending through said drying chamber, a duct connecting said heater with said gas moving device, a series of distributing nozzles supplied with circulating gases from said gas moving device, deflectors controlling the flow of gases into said nozzles, a duct delivering a portion of circulating gases back to said heater, a duct for delivering another portion of said circulating gases back to said gas moving device and control means for regulating the amount of return gases passing back to said heater.

4. A drying unit consisting of a multideck drying chamber, a fuel burning heater, a combustion chamber within said heater, a gas moving device, a duct connecting said gas moving device with said drying chamber, a multiple of nozzles delivering gases to each of said multiple decks, and deflectors arranged to deliver the proper volume of gases to each of said multiple decks.

5. A drying unit consisting of a longitudinally extending multi-deck drying chamber, a fuel burning heater, a combustion chamber within said heater, a gas moving device, a duct connecting said gas moving device with said drying chamber, means for regulating the flow of gases through said duct, a multiple of nozzles delivering gases to each of said multiple decks and a deflecting device, cooperating with said nozzles for controlling the direction of flow of gases on leaving said nozzles.

6. A drying unit consisting of a multideck drying chamber, a fuel burning heater, a combustion chamber Within said heater, a gas moving device, a duct connecting said gas moving device with said drying chamber, as control mechanism regulating the ow through said duct, a multiple of nozzles delivering gases to each of said multiple decks WILLIAM A. DARRAH.

and deflectors arranged to deliver the proper I volume of gases to each of said nozzles.

7. A drying unit consisting of a multi-deck drying chamber, a fuel burning heater, a combustion chamber within said heater, a gas moving device, a duct connecting said gas moving device with said drying chamberhgas control mechanism regulating the ow through said duct, :1 multlple of nozzles delivering gases to each of said multiple decks,

deflectorsarranged todeliver the proper volume of gases to each of said multiple decks, and end deflectors on said multiple nozzles for controlling the direction of flow of gases leaving said nozzles.

8. A-drying unit comprising a multi-deck drying chamber, a fuel burning heater, a

combustion chamber within said heater, a. gas moving device, a duct system connecting said heater, gas moving device and drying chamber in a closed circuit, a series of nozzles delivering gases from said heater to said multiple decks, deflectors arrangedto deliver the proper volume of gases to each of said multiple decks, and controlled means for regulating the volume of gases circulating through said system.

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