US3614074A

US3614074A - Direct-fired kiln furnace control system

Info

Publication number: US3614074A
Application number: US876733A
Authority: US
Inventors: Walker L Wellford Jr
Original assignee: Moore Dry Kiln Co
Current assignee: Coe Manufacturing Co
Priority date: 1969-11-14
Filing date: 1969-11-14
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: GB1326575A; AU2060470A; FR2067288B1; FR2067288A1; DE2055390A1; JPS5024736B1

Abstract

A direct-fired kiln furnace control system for lumber and like material utilizing a natural gas or oil burner with provision for spraying water into the furnace gases for humidification purposes wherein the furnace operation is controlled in response to not only a pair of sensor signals reflecting the dry bulb and wet bulb conditions in the kiln proper, but also in response to a sensor signal reflecting the temperature of the gases at the outlet of the furnace, so as to thereby insure the rapid, safe and effective vaporization of water introduced into the furnace gases. The three sensor signals are utilized to selectively control the combustion rate of the furnace burner, as well as a combination of vent, damper and air fan means regulating the flow rate and recirculation of the heated gases through the kiln furnace, to thereby achieve and maintain required temperature and humidity conditions in the kiln.

Description

United States Patent Inventor Walker L. Welliord, Jr. Memphis, Tenn.

Appl. No. 876,733 Filed Nov. 14, 1969 Patented Oct. 19, 1971 Assignee Moore Dry Kiln Company of Oregon North Portland, Oreg.

DIRECT-FIRED KILN FURNACE CONTROL SYSTEM 13 Claims, 3 Drawing Figs.

US. Cl 263/40 R, 34/46, 263/19 A Int. Cl F27b 3/02 Field of Search 263/19 A, 40 R; 34/46 References Cited UNITED STATES PATENTS 8/! 952 Foulder et al 34/46 3,269,715 8/1966 Wellford,Jr

Primary Examiner-John .l. Camby Attorney-Daniel P. Chernofi ABSTRACT: A direct-fired kiln furnace control system for lumber and like material utilizing a natural gas or oil burner with provision for spraying water into the furnace gases for humidification purposes wherein the furnace operation is controlled in response to not only a pair of sensor signals reflecting the dry bulb and wet bulb conditions in the kiln proper, but also in response to a sensor signal reflecting the temperature of the gases at the outlet of the furnace, so as to-thereby insure the rapid, safe and effective vaporization of water introduced into the furnace gases. The three sensor signals are utilized to selectively control the combustion rate of the furnace burner, as well as a combination of vent, damper and air fan means regulating the flow rate and recirculation of the heated gases through the kiln furnace, to thereby achieve and maintain required temperature and humidity conditions in the kiln.

PAIENTEnum 19 mm SHEET 1 [IF 3 DIRECT-FIRED KILN FURNACE CONTROL SYSTEM BACKGROUND OF THE INVENTION This invention relates to improved control apparatus for a direct-fired gas or oil-fueled kiln furnace of the type wherein water is added to the hot mixture of combusted furnace gases and recirculated air from the kiln during certain intervals of the drying and conditioning cycle to provide a circulating gaseous medium of desired temperature and moisture content for treating material contained in the kiln. More particularly, the invention relates to improved controller means for automatically regulating the operation of a direct-fired kiln furnace of the type described in a more advantageous and efficient manner, especially during those periods in the drying cycle when increased moisture content is required in the circulating gases and, in response thereto, a large quantity of water in liquid form is introduced for vaporization in the combusted furnace gases. While the control apparatus of the present invention may be advantageously employed in furnace systems supplying a heated and moisturized gaseous medium to kilns for treating various kinds of material, it is particularly suitable for application in dry kilns used for the drying and conditioning of hardwood lumber. Accordingly, the invention will be described and illustrated herein as applied to dry kilns of this type.

It is common practice in the kiln drying of materials such as lumber to supply heated air which has been heavily laden with moisture for conditioning the lumber properly during the drying process in order thereby to prevent over-rapid drying of the surface and exterior portions of the lumber which otherwise might cause warping, checking or other forms of deleterious damage or degradation of the product. In a kiln furnace of the direct-fired type the gaseous drying medium is obtained by vaporizing water, as needed, into combusted furnace gases produced by an oil or gas-fueled burner and thereafter circulating the resulting mixture through the kiln system. In two of my prior U.S. Pat. Nos. 3,269,715 and 3,151,850, I disclosed direct-fired kiln furnace systems of this general type containing associated controller means for regulating the operation of the furnace and the introduction of water spray so as to maintain predetermined temperature and humidity conditions in the kiln. As pointed out in the aforesaid prior patents, one of the major concerns in operating a kiln system of the directfired type, in contrast to the more conventional kiln designs in which steam obtained from a separate boiler is circulated through the kiln as a moisturizing medium to dry and condition the product, is the requirement that substantially all of the water injected into the combusted furnace gases be quickly and completely vaporized into the circulating air stream; otherwise, the unvaporized water tends to deposit on the walls and floor of the kiln, producing scaling and other corrosive effects, or on the lumber itself, leaving undesirable lime deposits and stain.

The aforesaid U.S. Pat. Nos. 3,269,715 and 3,151,850 were directed to forms of dual-mode controllers for such directfired kiln furnace systems in which rapid and complete evaporation of the water introduced into the circulating gaseous medium during certain periods in the drying cycle was achieved by operating the furnace burner at a higher combustion rate during such periods, regardless of whether or not additional heat demand was called for by the dry bulb conditions then present in the kiln chamber proper. Thus, even during periods when the kiln environment might be at the desired dry bulb temperature level so that the instantaneous heat demand from the kiln furnace would be relatively low, if additional moisture content were needed in the circulating gases the furnace controller would operate to increase the burners combustion rate during such periods so as to insure that sufficient caloric energy was available in the furnace gases to rapidly and effectively vaporize the water as it was introduced into the gas stream.

SUMMARY OF THE INVENTION In practice, in the operation of direct-fired kiln furnace systems of the type disclosed in the aforementioned patents, it has been found that more satisfactory and complete evaporation of the introduced water, together with improved control over the temperature and humidity conditions pertaining in the kiln, could be effected if additional provisions were made for regulating the temperature and flow rate of the circulating kiln gases. Accordingly, innovations have been made to the basic direct-fired kiln furnace control systems of the aforesaid prior patents so as to achieve the dual objectives of 1) better evaporation of the water spray introduced into the furnace gases during periods when added moisture content is needed in the kiln conditioning medium, and (2) improved efficiency and response time of the system in reaching and maintaining prescribed temperature and humidity conditions in the kiln environment during various stages of the drying cycle.

In the direct-fired kiln furnace system of the present invention, a combination of vents, dampers and, in some cases, variable speed air fan elements are provided which, in response to actuating signals received from a controller unit, regulate the circulation and recirculation of combusted furnace gases through both the kiln furnace and the remainder of the kiln system in a manner so as to obtain rapid and effective adjustment to changes in the dry bulb or wet bulb temperature needs in the kiln chamber. Through selective actuation of the vents, dampers and air fan elements, the flow rate of the air mass circulating through the kiln system, and the portion of that air flow which is recirculated through the system as tempering air, are varied in response to the instantaneous temperature and humidity demands of the kiln as determined from comparison with prearranged settings.

Control of the flow rate of the gaseous air medium circulated through the kiln, together with the control over the percentage of heated tempering air recirculated through the kiln furnace, provide effective means for controlling the kiln environmental conditions. In particular, during periods when water is being added to increase the moisture content of the conditioning gases circulating through the kiln system, the flow rate of the furnace gases is decreased in conjunction with an increase in the relative percentage of tempering air recirculating through the furnace. In this manner the temperature of the furnace gases may be substantially increased to a level sufficiently high to effectively vaporize substantially all of the injected water spray without altering the combustion rate of the burner, the latter being controlled solely in response to the dry bulb temperature demand requirements present in the kiln chamber. Even though the temperature in the kiln furnace rises sharply during such periods, the reduced flow of air into the kiln chamber proper ensures that the dry bulb temperature will not overshoot but instead will be maintained at its prescribed level. The foregoing arrangement is highly efficient as it minimizes the caloric heat demand required from the furnace burner to both maintain desired dry bulb temperature conditions in the kiln chamber and to also satisfactorily vaporize water introduced into the furnace combustion chamber during periods when the circulating kiln gases require increased moisture content.

In order to obtain safe yet effective regulation of the temperature and humidity conditions in the gaseous medium circulating through the kiln furnace and kiln chamber, the controller unit, which controls the furnace burners combustion rate and actuates the vents, dampers and air fan components controlling the circulation of the drying and conditioning gases through the kiln system, is responsive not only to the dry bulb and wet bulb temperatures present in the kiln chamber proper, but the unit also receives a third sensory input responsive to the temperature conditions pertaining at the outlet duct or exhaust of the furnace which couples to the kiln chamber. This last-mentioned sensor, which typically registers a reading several hundred degrees (Fahrenheit) hotter than the dry bulb temperature of the gases circulating in the kiln area itself, is utilized to prevent operation of the kiln furnace in an overheated condition above a safe temperature level. The signal received from the outlet duct temperature sensor serves as a limit signal, to override the other control elements in the system which regulate the burner combustion rate and the flow of the circulating gases through the kiln, so as to maintain the furnace temperature within a safe operating range below a predetermined danger threshold. By reason of the comprehensive and cooperative regulation provided over the burner combustion rate and the circulating gaseous flow through the kiln, together with the override safety feature provided by the sensor monitoring the temperature of the furnace gases, the kiln furnace control system of the present design is capable of rapidly yet safely adjusting to meet changed temperature and/or humidity demand conditions in the kiln.

It is therefore a principal objective of the present invention to provide an improved direct-fired kiln furnace system of the type wherein water in liquid form is vaporized into the furnace gases to provide a heated and moisturized gaseous medium for treating kiln material.

It is another objective of the present invention to provide an improved controller circuit for a kiln furnace system of the type described wherein the system is operated in a more economical, efficient and safe manner by reducing the amount of caloric heat energy required to rapidly and effectively vaporize water introduced into the furnace gases and by tempering and regulating the flow rate of the furnace gases circulating through the kiln system.

The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of an illustrative embodiment of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front elevational view, partly sectional and partly schematic, of an illustrative type of direct-fired kiln furnace which may be advantageously used with the improved controller apparatus of the present invention.

FIG. 2 is a block diagram of a kiln furnace system employing the improved controller of the present invention for providing automatic operation and regulation of a direct-fired kiln furnace.

FIG. 3 is a schematic circuit diagram of an illustrative embodiment of an electropneumatic controller unit for use with the kiln furnace system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a direct-fired kiln furnace, designated generally as 20, connected to a lumber kiln of conventional design. The furnace walls may be lined with refractory material or any suitable high-temperature scale-resisting alloy such as nickel, chromium and iron. In the combustion region A of the furnace gas or oil fuel supplied from a source (not shown) via a pipe line 32 to burner 30 is intermixed and combusted with a quantity of air forced at high velocity over air line 34 by blower fan 36. The combustion rate of the fired gases is varied in conventional manner by means of a pneumatically actuated valve 38 controlling the air-fuel mixture by regulation of the rate of air flow in the air line 34.

The combusted hot gases, fired by the burner 30 in combustion portion A of the furnace 20, then flow out through passageway 22 into region B of the furnace where water is evaporated therein, if needed, to increase the moisture content of the drying medium prior to its circulation through the kiln chamber. In the vaporization region B water from a pressurized source (not shown) is supplied over water line 92 and under control of valve 94 to nozzle 91 which disperses the water into a spray 90 of fine droplets. The water spray is directed within the region B so as to thoroughly intermix with the combusted hot gases emergent from the combustion section A of the furnace. The small amount of water spray which is not immediately vaporized by the heat of the gases is carried away by a drain 98 and, if desired, it may be returned to a sump pump for recirculation. An eliminator 101 is preferably provided in the passageway 22, as far downstream from the spray nozzle 91 as is practical, for precipitating out the unvaporized particles of water entrained in the air stream while permitting the moisturized heated air to pass freely therethrough. The moisturized gases then exit from the furnace, through an outlet duct 24 connecting to the kiln chamber proper, where they serve as the drying and conditioning medium for the material under treatment in the kiln 10.

After circulation within the lumber kiln the gas is drawn therefrom by suitably located ducts (not shown) and directed into a passageway 40 which couples to the gas-fired furnace 20. Control of the inlet air to the furnace is provided by a pair of

vents

42 and 44, which may be located along the passageway 40 as indicated in FIG. 1 or alternatively on the roof or sidewalls of the kiln chamber 10, and a damper element 46 positioned in the passageway 40 across thepath of the air stream exhausting from the kiln. The vent and damper elements are of conventional design with vanes adjustable from a fully opened to a fully closed position. The combination of the

vents

42, 44 and the damper 46 permits complete regulation of the proportion of tempering return air from the kiln chamber 10 in relation to the proportion of fresh ambient air introduced for circulation in the kiln furnace system. For example, it will be seen that with damper 46 fully closed and

vents

42 and 44 fully open, the exhausted kiln gases are expelled to the atmosphere, and all of the air supplied to the inlet of the kiln furnace is in the form of fresh cold air drawn from the outside. On the other hand, with damper 46 fully opened and

vents

42, 44 fully closed, all of the air supplied to the kiln furnace is in the form of recirculating gases from the kiln chamber 10. In any intermediate position of the ventdamper combination the air supplied to the inlet of the kiln furnace 20 comprises a mixture of tempering air with cold air drawn from the outside, with the relative percentages of each component determined by the respective settings of the vanes in the circulation control elements.

Proceeding downstream in the passageway 40 from the vent damper combination, an air fan is provided at the inlet to the furnace chamber 20 which is driven by a variable speed motor 82. (In lieu of utilizing a variable speed motor, the motor drive 82 could remain constant and the fan 80 instead provided with propeller blades of adjustable pitch). The speed (or pitch) of the air fan 80 is regulated so as to permit the flow rate of the gaseous medium circulated through the kiln furnace and into the kiln chamber to be varied in accordance with control signals supplied thereto, as will be hereinafter described.

As an alternate to, or in conjunction with, the control of the temperature of the circulating kiln gases effected by regulation of the gas flow rate with the air fan 80, a bypass passageway 41 may be provided, as shown, connecting the post-combustion region B of the furnace to its air inlet downstream from the vent-damper combination. This bypass passageway 41 is provided with a damper 48 which, when opened, permits the shunting of a portion of the combusted hot gases emergent from combustion region A into the inlet passageway 40 for recirculation through the furnace. Through internal recirculation in this manner, the temperature of the gas mixture formed in the furnace can be quickly raised without need for altering the combustion rate of the furnace burner 30.

With the capability provided by the aforementioned ventdamper, fan and bypass means for increasing the temperature of the furnace gases through regulation of their flow rate and recirculatory flow paths, a rapid and substantially complete vaporization of the water spray introduced by the nozzle 91 at region B can be achieved, even though there be at that time a relatively low calorie heat demand required from the furnace to maintain prescribed dry bulb temperature conditions in the kiln.

FIG. 2 is a block diagram of the aforedescribed kiln furnace system incorporating the improved controller apparatus of the present invention. This kiln control system provides automatic operation and regulation of (l) the kiln furnace combustion rate, (2) the water spray means for evaporating moisture into the kiln gases as needed, and (3) the circulatory flow and composition of the furnace air. The direct-fired furnace 20, whose construction is shown in detail in the previous figure, is illustrated in a schematic representation as juxtaposed next to a kiln chamber of conventional design. A dry bulb temperature sensor 65 and a wet bulb temperature sensor 60 are suitably located within the kiln 10 for monitoring, respectively, the temperature and humidity of the drying medium circulating within the kiln. The signal indications from the dry and wet bulb thermometers are supplied over respective

lead wires

67, 62 to a heat and humidity regulator 100. 100. As more particularly shown in FIG. 3, the heat and humidity regulator 100 may be of conventional design, such as for example a Foxboro vacuum pneumatic temperature-humidity recording controller or other suitable type wherein an pneumatic output signal is derived responsive to the difference between the input signal, corresponding to the actual measured dry bulb or wet bulb temperature parameter, and a predetermined value of temperature or humidity preset in the regulator. Thus, referring again to FIG. 2, two pneumatic output signals are supplied from the regulator 100: the first is a Heat Signal, appearing on lead line 102, which represents the difference between the dry bulb temperature present within the kiln 10 and the desired temperature as set on the regulator; and the second output is a Humidity Signal, appearing over lead line 104, which similarly represents the difference between the actual and desired wet bulb temperature or moisture content of the drying medium in the kiln. These two signals, together with a third temperature signal which is provided over lead line 72 by a thermocouple 70 located in the outlet duct 24 of the furnace for monitoring the temperature of the furnace exhaust gases, are supplied as inputs to a controller unit 110 which controls and regulates the operation of the kiln furnace system.

The controller unit 110 has

outputs

120, 130, 140 and 150 for controlling the operation respectively of the vent positioners 125a, 1256, the servomotor 135

positioning dampers

46 and 48 and the variable speed motor 82 driving fan 80; the burner air control 38; and the spray valve 94. Through regulating of the aforementioned elements, in response to heat and humidity signals supplied to the controller, the temperature and air circulation through the kiln furnace are controlled so as to reach and maintain desired dry bulb and wet bulb temperature conditions in the kiln chamber 10 in a quick and highly efficient manner.

Referring now to FIG. 3, there is illustrated an electropneumatic schematic diagram of the construction and circuit configuration of the controller unit 110. The pneumatic Heat Signal 102 and Humidity Signal 104, together with the signal provided over lead line 72 from the sensor 70 representing the temperature at the outlet duct of the furnace, are supplied as inputs to the controller 110. The Humidity Signal 104, responsive to any instantaneous deviation existing between the preset and the actual wet bulb temperature in the kiln, is utilized to actuate via line 150 the spray control valve 94 thereby introducing water spray into the combusted furnace gases for increasing the moisture content of the drying medium. During such periods, when water is being added to the furnace gases, the

vent elements

42, 44 are also being positioned toward a closed position by respective pneumatically actuated motors 1250, 125k acting in response to the Humidity Signal 104 appearing over line 120. Closing of the vanes of these vents decreases the proportion of fresh air introduced into the kiln, while at the same time increasing the proportion of heated return air from the kiln chamber which is available for recirculation within the kiln system. Also during such periods when water spray is being introduced into the kiln furnace gases, the temperature of the furnace gases may be further raised by having the damper element 46 biased towards the closed position, the bypass damper 48 biased toward the open position, and the speed of the air fan in the kiln furnace decreased, all in response to actuating signals received over line in a manner hereinafter to be explained.

The Heat Signal 102, the magnitude of which represents the difference existing between the desired and actual dry bulb conditions in the kiln chamber, is utilized to regulate the operation of the furnace burner and also, together with the Humidity Signal, to regulate the air circulation through the kiln furnace system. The Heat Signal is supplied as an input both to a limit controller element 106 and also to differential pressure control element 108. The limit controller 106, which receives a control signal on line 72 representing the temperature of the gases detected by sensor 70 in the outlet duct of the furnace, acts as a gating unit to block passage of the Heat Signal 102 therethrough when the furnace gas temperature exceeds a predetermined safe limit, for example 450 F. Thus, when the temperature of the furnace gases are within a safe operating range beneath the 450 F. level, the pneumatic Heat Signal 102, proportional to the added caloric heat demand required from the furnace, passes through the limit controller element 106 without diminishment in amplitude. However, as the temperature of the furnace gases approach the 450 F. threshold level, the element l06 commences to act as a shutoff valve, decreasing the amplitude of the pneumatic signal appearing on the output line 140.

The signal derived from the limit controller 106 and appearing on line is used for two purposes. Firstly, the signal 140 is employed to regulate the operation of the air supply to the burner 30 by actuation of the pressure-responsive air valve 38, thus controlling the combustion rate of the furnace. In this way the furnace burner is regulated in response to dry bulb temperature conditions in the kiln chamber, the controller acting to turn up the burner during periods when added heat is required and to decrease it when the actual dry bulb temperature conditions in the kiln chamber are at or near the desired level set on the heat-humidity regulator 100. The output 140 of the limit controller is also supplied as a second input to the differential pressure control element 108 which, as previously mentioned, receives as its other input the Heat Signal 102 derived from the regulator 100. So long as the temperature of the furnace gases remain within the predetermined safe operating range, as monitored by the outlet duct temperature sensor 70, the limit controller element 106 will pass through the Heat Signal 102 unimpeded, and thus the respective inputs to the differential pressure control element 108 will be equal, producing a zero or minimum signal on the output line 112. However, as the temperature of the furnace gases approach the predetermined limit (450 F.), the action of the limit controller element 106 causes a differential pressure to exist between the

respective inputs

102 and 140 to the control element 108, thereby producing a pneumatic pressure signal on the output line 112. The presence of a signal on line 112, representing a condition in which the temperature of the furnace gases has risen to the limit of the safe operating range concurrently with a demand that the kiln furnace provide greater heat content in the circulating kiln gases in order to achieve desired dry bulb temperature conditions in the kiln chamber, is supplied to' a restrictor tee 114 controlling a supply line 116 of pressurized air.

The controlled air supply line 116 as well as the Humidity Signal 104 are both supplied as inputs to a blocking relay element 118 which performs the function of passing through to its output line 130 the greater of the two input signals. Thus, in this respect, relay element 118 functions similarly to a logical OR device to pass through the signal of greater amplitude as between the

respective inputs

116 and 104. The amplitude of the control signal appearing on line 130 is used to regulate the positioning of the

respective dampers

46 and 48 in the inlet and bypass passageways of the furnace as well as the motor speed of the air fan 80. In this fashion, the output signal 130 from the controller unit 110 regulates both the flow rate and the circulatory path of the gases traveling through the kiln furnace and the kiln chamber. Thus, with a minimum or zero level output on line 130, the

dampers

46 and 48 are both biased towards the closed position and this arrangement, in conjunction with the concurrent positioning of

vents

42 and 44 towards the open position, produces a circulatory path for the kiln furnace system in which very little if any of the furnace gases are either bypassed internally or recirculated as tempering air, so that virtually all of the air is drawn fresh from the outside and then exhausted upon a single pass through the kiln chamber. Under the foregoing condition of operation, with the

dampers

46 and 48 biased to their closed positions, the presence of the minimum amplitude signal on output line 130 controls the operation of motor 82 so as to produce a maximum speed of revolution for the circulatory air fan 80, thus providing a high rate of flow for the movement of the heated furnace gases through the kiln system Upon the occurrence of a Humidity Signal 104 representing the need for water to be added to the furnace gases to increase their moisture content, or upon the occurrence of a Heat Signal 102 representing the need for added caloric content in the furnace gases to increase the dry bulb temperature conditions in the kiln, or upon the occurrence of both conditions, the controller output signal appearing on line 130 regulating the positioning of the dampers and the speed of the air fan will be the greater of the respective amplitudes of the input signals to the relay 118. Thus, the signal of greater amplitude will operate to bias the

respective dampers

46 and 48 towards their open positions and to decrease the speed of, or even shut off, the fan 80, these actions having the joint effect of increasing the relative percentages of tempering and fumace-bypass air recirculated through the furnace and at the same time decreasing the flow rate of the furnace gases.

As previously mentioned, the foregoing operations will serve to substantially increase the temperature of the furnace gases independently of any temperature increase produced through regulation of the combustion rate of the furnace burner. Consequently, any increase in the amplitude of the output signal appearing on line 130, responsive to the presence of extra heat or humidity demand for the furnace gases, will produce corresponding changes in the settings of the respective dampers and fan speed so as to increase the temperature of the furnace gases and thereby increase the temperature of the circulating kiln gases or insure effective vaporization of the injected water spray, as the case may be. However, in the event that the temperature of the furnace gases should approach the safe operating limit (e.g., 450 F.) preset in the limit controller 106, this element, acting through the medium of the differential pressure control element 108 and the restrictor tee 114, reduces the amplitude of the signal 116 supplied as an input to the relay 118. This decrease in input amplitude in turn is reflected as a signal of decreased amplitude on controller output line 130, thus moving the

dampers

46 and 48 towards the closed position and increasing the speed of the fan motor 82 so as to thereby produce both a decrease in the percentage of tempering air as well as an increase in the circulatory flow rate. These adjustments result in a consequent reduction in the temperature of the furnace gases so as to restore operation within the safe temperature range.

Control valve 115 is preferably provided in the line 116 supplying the pressurized air signal to the relay 118 so that, during startup of the kiln furnace system, this line could be blocked off thus insuring that the dampers and fan control will be maintained during this initial period at settings providing maximum circulation flow of the furnace gases through the kiln system.

In some embodiments of kiln furnace systems constructed in accordance with the teachings of the present invention provision for regulating the speed of the circulatory air fan 80 can be dispensed with, as adequate control over the kiln gas temperature and flow conditions can be achieved through the regulation provided by the combination of vents and dampers determining the percentage of tempering and internally recirculated air introduced into the furnace. In a further variation of the exemplary kiln furnace controller disclosed herein, the positioning of the

respective vents

42 and 44 could also be regulated by the signal produced on the output line from the blocking relay 118, rather than directly from the Humidity Signal 104 as shown in FIG. 3, so that control of the vents, as well as the damper and fan elements, would be in response to the greater of the respective signals reflecting heat and humidity demands in the kiln chamber, and the operation of these vents would then also be subject to the override safety control provided by the outlet duct temperature sensor 70 and its associated control elements.

The terms and expressions which have been employed in the foregoing abstract and specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described, or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow. 4

What is claimed is:

1. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material,

b. a kiln furnace having an air intake, a burner, and a duct coupling heated furnace gases to the inlet of said kiln chamber,

c. spray means in said kiln furnace for injecting water for vaporization into said heated furnace gases,

d. intake air control means for adjusting the relative constituents of fresh ambient air and tempering heated air returning from said kiln chamber, the mixture of which constituents is supplied as intake air to said furnace, and

e. controller means for regulating the operation of said intake air control means during periods when water is interjected into said heated furnace gases by said spray means, whereby the caloric heat content of said furnace gases is maintained at a level sufficient to effect a rapid and substantially complete vaporization of said water spray therein.

2. The kiln system of claim 1 further including a passageway provided with an adjustable damper coupling said furnace duct directly to said furnace air intake for internally recirculating within said furnace a selectable portion of said heated furnace gases, the operation of said adjustable damper also being regulated by said controller means.

3. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material,

b. a kiln furnace having a burner for heating gases and a spray means for injecting water for vaporization into said heated furnace gases for increasing the moisture content thereof, said heated and moisturized furnace gases being thereafter supplied to said kiln chamber for circulation therethrough,

c. fan means controlling the rate of flow of said gases through said furnace, and

d. controller means for regulating the operation of said fan means during periods when water spray is added to said furnace gases, whereby the caloric heat content of said furnace gases is maintained at a level sufficient to effect a rapid and substantially complete vaporization of said water spray therein.

4. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material.

d. an adjustable damper coupling said furnace duct directly to said furnace air intake for internally recirculating within said furnace a selectable portion of said heated furnace gases, and

e. controller means for regulating the operation of said adjustable damper during periods when water is interjected into said heated furnace gases by said spray means, whereby the caloric heat content of said furnace gases is maintained at a level sufficient to effect a rapid and substantially complete vaporization of said water spray therein.

5. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material,

b. a kiln furnace having an air intake, a burner, a spray means for injecting water for vaporization into heated furnace gases for increasing the moisture content thereof, and a duct for supplying said heated and moisturized furnace gases to said kiln chamber for circulation therethrough,

c. fan means controlling the rate of flow of said furnace gases through said furnace,

d. intake air control means for adjusting the relative constituents of fresh ambient air and tempering heated air returning from said kiln chamber, the mixture of which constituents is supplied as intake air to said furnace,

e. a passageway provided with an adjustable damper coupling said duct directly to said air intake for bypassing said furnace chamber and internally recirculating within said furnace a selectable portion of said heated furnace gases,

f. a pair of sensors positioned in said kiln chamber for monitoring respectively the instantaneous temperature and humidity conditions prevailing therein, and

g. controller means connected to receive signals from said sensor pair and acting on said water spray means, said fan means, said intake air control means, and said adjustable damper, whereby the operation of said kiln furnace is regulated so as to restore and maintain desired predetermined temperature and humidity conditions in said kiln chamber.

6. A kiln system according to claim further including a third sensor positioned in said furnace so as to measure the temperature of said heated furnace gases and connected as a signal input to said controller means, whereby the operation of said fan means, said intake air control means and said damper are regulated so as to reduce the temperature of said heated furnace gases when the signals received from said third sensor indicate that the temperature of said gases is closely approaching a predetermined maximum level.

7. in a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material,

c. intake air control means for adjusting the relative constituents of fresh ambient air and tempering heated air returning from said kiln chamber, the mixture of which constituents is supplied as intake air to said furnace,

d. a first sensor located in said kiln chamber for measuring the dry bulb temperature of the gases circulating therein,

e. a second sensor located in said kiln chamber for measuring the wet bulb temperature of said circulating kiln gases,

f. a regulator connected to receive signals from said first and second sensors and generating a pair of heat and humidity" output signals indicating, respectively, the instantaneous heat and humidity requirements of said circulating kiln gases as determined by comparison of said sensor signals with predetermined settings of said regulator, and

g. a controller connected to said regulator containing circuit means which actuate said spray means when increased humidity is needed and which regulate the operation of said intake air control means in response to the greater of the respective magnitudes of said heat" and humidity" signals received from said regulator.

8. A kiln system according to claim 7 further including a passageway provided with an adjustable damper coupling said furnace duct to said furnace air intake for internally recirculating through said furnace a selectable portion of said heated furnace gases, the operation of said adjustable damper also being regulated by said controller means in response to the greater of the respective heat" and humidity" signals received from said regulator.

9. A kiln system according to claim 7 further including a fan means controlling the rate of flow of said furnace gases through said furnace, the operation of said fan means also being regulated by said controller means in response to the greater of the respective heat" and humidity" signals received from said regulator.

10. A kiln system according to claim 7 including a third sensor positioned so as to measure the temperature of said heated furnace gases and connected as a signal input to said circuit means in said controller whereby, in the event the temperature of said heated furnace gases closely approaches a predetermined safety threshold, said third sensor signal acts an an override on the operation of said controller so as to regulate said furnace air intake means in a manner so as to reduce the temperature of said heated furnace gases.

1!. In a direct-fired kiln system, the combination comprising a kiln chamber for drying and conditioning material,

means controlling the rate of flow of said furnace gases through said furnace,

d. means for controlling the temperature of the intake air supplied to said furnace,

a pair of sensors positioned in said kiln chamber for monitoring respectively the instantaneous temperature and humidity conditions prevailing therein, and

. controller means connected to receive signals from said sensor pair and acting on said water spray means, said fan means and said intake air control means, whereby the operation of said kiln furnace is regulated so as to restore and maintain desired predetermined temperature and humidity conditions in said kiln chamber.

12. In a direct-fired kiln system, the combination comprising a kiln chamber for drying and conditioning material,

b. a kiln furnace having an air intake, a burner, a spray means for injecting water for vaporization into heated furnace gases for increasing the moisture content thereof. and a duct for supplying said heated and moisturized furnace gases to said kiln chamber for circulation therethrough,

an adjustable damper coupling said furnace duct to said furnace air intake for internally recirculating through said furnace a selectable portion of said heated furnace gases,

. a first sensor located in said kiln chamber for measuring the dry bulb temperature of the gases circulating therein,

. a second sensor located in said kiln chamber for measuring the web bulb temperature of said circulating kiln gases,

f. a regulator connected to receive signals from said first and ble portion of said heated furnace gases,

d. temperature sensor means located in said kiln chamber for monitoring the temperature of said circulating kiln gases, and

e. controller means connected to receive signals from said temperature sensor means and regulating the operation of said adjustable damper in response to heat demand requirements for said furnace.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 614 O74 Dated October 19 1971 Inventor) Walker L. Wellford, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 5 line 19, delete "100." (second occurrence);

line 46, "1256 should read l25b;-.

Col. 10, line 21, "an an should read as an;

line 62, "web" should read wet-.

Signed and sealed this Lrth day of April 1 972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSGHALK Attesting Officer Commissioner of Patents QM P0405) (10-591 USCOMM-DC wan-Pea 9 U 54 GOVERNNENY PRINTING OFFICE I," 0-355-33

Claims

1. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material, b. a kiln furnace having an air intake, a burner, and a duct coupling heated furnace gases to the inlet of said kiln chamber, c. spray means in said kiln furnace for injecting water for vaporization into said heated furnace gases, d. intake air control means for adjusting the relative constituents of fresh ambient air and tempering heated air returning from said kiln chamber, the mixture of which constituents is supplied as intake air to said furnace, and e. controller means for regulating the operation of said intake air control means during periods when water is interjected into said heated furnace gases by said spray means, whereby the caloric heat content of said furnace gases is maintained at a level sufficient to effect a rapid and substantially complete vaporization of said water spray therein.

3. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material, b. a kiln furnace having a burner for heating gases and a spray means for injecting water for vaporization into said heated furnace gases for increasing the moisture content thereof, said heated and moisturized furnace gases being thereafter supplied to said kiln chamber for circulation therethrough, c. fan means controlling the rate of flow of said gases through said furnace, and d. controller means for regulating the operation of said fan means during periods when water spray is added to said furnace gases, whereby the caloric heat content of said furnace gases is maintained at a level sufficient to effect a rapid and substantially complete vaporization of said water spray therein.

4. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material, b. a kiln furnace having an air intake, a burner, and a duct coupling heated furnace gases to the inlet of said kiln chamber, c. spray means in said kiln furnace for injecting water for vaporization into said heated furnace gases, d. an adjustable damper coupling said furnace duct directly to said furnace air intake for internally recirculating within said furnace a selectable portion of said heated furnace gases, and e. controller means for regulating the operation of said adjustable damper during periods when water is interjected into said heated furnace gases by said spray means, whereby the caloric heat content of said furnace gases is maintained at a level sufficient to effect a rapid and substantially complete vaporization of said water spray therein.

5. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material, b. a kiln furnace having an air intake, a burner, a spray means for injecting water for vaporization into heated furnace gases for increasing the moisture content thereof, and a duct for supplying said heated and moisturized furnace gases to said kiln chamber for circulation therethrough, c. fan means controlling the rate of flow of said furnace gases through said furnace, d. intake air control means for adjusting the relative constituents of fresh Ambient air and tempering heated air returning from said kiln chamber, the mixture of which constituents is supplied as intake air to said furnace, e. a passageway provided with an adjustable damper coupling said duct directly to said air intake for bypassing said furnace chamber and internally recirculating within said furnace a selectable portion of said heated furnace gases, f. a pair of sensors positioned in said kiln chamber for monitoring respectively the instantaneous temperature and humidity conditions prevailing therein, and g. controller means connected to receive signals from said sensor pair and acting on said water spray means, said fan means, said intake air control means, and said adjustable damper, whereby the operation of said kiln furnace is regulated so as to restore and maintain desired predetermined temperature and humidity conditions in said kiln chamber.

6. A kiln system according to claim 5 further including a third sensor positioned in said furnace so as to measure the temperature of said heated furnace gases and connected as a signal input to said controller means, whereby the operation of said fan means, said intake air control means and said damper are regulated so as to reduce the temperature of said heated furnace gases when the signals received from said third sensor indicate that the temperature of said gases is closely approaching a predetermined maximum level.

7. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material, b. a kiln furnace having an air intake, a burner, a spray means for injecting water for vaporization into heated furnace gases for increasing the moisture content thereof, and a duct for supplying said heated and moisturized furnace gases to said kiln chamber for circulation therethrough, c. intake air control means for adjusting the relative constituents of fresh ambient air and tempering heated air returning from said kiln chamber, the mixture of which constituents is supplied as intake air to said furnace, d. a first sensor located in said kiln chamber for measuring the dry bulb temperature of the gases circulating therein, e. a second sensor located in said kiln chamber for measuring the wet bulb temperature of said circulating kiln gases, f. a regulator connected to receive signals from said first and second sensors and generating a pair of ''''heat'''' and ''''humidity'''' output signals indicating, respectively, the instantaneous heat and humidity requirements of said circulating kiln gases as determined by comparison of said sensor signals with predetermined settings of said regulator, and g. a controller connected to said regulator containing circuit means which actuate said spray means when increased humidity is needed and which regulate the operation of said intake air control means in response to the greater of the respective magnitudes of said ''''heat'''' and ''''humidity'''' signals received from said regulator.

8. A kiln system according to claim 7 further including a passageway provided with an adjustable damper coupling said furnace duct to said furnace air intake for internally recirculating through said furnace a selectable portion of said heated furnace gases, the operation of said adjustable damper also being regulated by said controller means in response to the greater of the respective ''''heat'''' and ''''humidity'''' signals received from said regulator.

9. A kiln system according to claim 7 further including a fan means controlling the rate of flow of said furnace gases through said furnace, the operation of said fan means also being regulated by said controller means in response to the greater of the respective ''''heat'''' and ''''humidity'''' signals received from said regulator.

11. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material, b. a kiln furnace having an air intake, a burner, a spray means for injecting water for vaporization into heated furnace gases for increasing the moisture content thereof, and a duct for supplying said heated and moisturized furnace gases to said kiln chamber for circulation therethrough, c. means controlling the rate of flow of said furnace gases through said furnace, d. means for controlling the temperature of the intake air supplied to said furnace, e. a pair of sensors positioned in said kiln chamber for monitoring respectively the instantaneous temperature and humidity conditions prevailing therein, and f. controller means connected to receive signals from said sensor pair and acting on said water spray means, said fan means and said intake air control means, whereby the operation of said kiln furnace is regulated so as to restore and maintain desired predetermined temperature and humidity conditions in said kiln chamber.

12. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material, b. a kiln furnace having an air intake, a burner, a spray means for injecting water for vaporization into heated furnace gases for increasing the moisture content thereof, and a duct for supplying said heated and moisturized furnace gases to said kiln chamber for circulation therethrough, c. an adjustable damper coupling said furnace duct to said furnace air intake for internally recirculating through said furnace a selectable portion of said heated furnace gases, d. a first sensor located in said kiln chamber for measuring the dry bulb temperature of the gases circulating therein, e. a second sensor located in said kiln chamber for measuring the web bulb temperature of said circulating kiln gases, f. a regulator connected to receive signals from said first and second sensors and generating a pair of ''''heat'''' and ''''humidity'''' output signals indicating, respectively, the instantaneous heat and humidity requirements of said circulating kiln gases as determined by comparison of said sensor signals with predetermined settings of said regulator, and g. a controller connected to said regulator containing circuit means which actuate said spray means when increased humidity is needed and which regulate the operation of said adjustable damper in response to the greater of the respective magnitudes of said ''''heat'''' and ''''humidity'''' signals received from said regulator.

13. In a direct-fired kiln system, the combination comprising a. a kiln chamber for drying and conditioning material, b. a kiln furnace having an air intake, a burner, and a duct for supplying heated furnace gases to said kiln chamber for circulation therethrough, c. an adjustable damper coupling said furnace duct directly to said furnace air intake for bypassing said kiln chamber and internally recirculating within said furnace a selectable portion of said heated furnace gases, d. temperature sensor means located in said kiln chamber for monitoring the temperature of said circulating kiln gases, and e. controller means connected to receive signals from said temperature sensor means and regulating the operation of said adjustable damper in response to heat demand requirements for said furnace.