Process for monitoring the heat gradient in a heat-producing system

A process for monitoring the heat gradient in a heat-producing system is disclosed. Also disclosed is an apparatus which can be used in the process. In this process, at least three heat sensors, which are situated downstream from a heat source, determine the temperature of the exhaust gas from the heat source. Each of the heat sensors used produces a substantially identical response to a given temperature. The output from each two sequential heat sensors is operatively connected to an indicator, which evaluates whether the downstream heat sensor is reporting a temperature lower than the upstream heat sensor; if the downstream heat sensor does report a lower temperature than the upstream heat sensor, then the indicator reads positive; but if the downstream heat sensor reports a highter temperature than the upstream heat sensor, then the indicator reads negative. The output from each indicator is fed to a switching device, which is activated only if and when any one of the indicators in the system reads negative. When the switching device is turned on, an alarm is activated.

FIELD OF THE INVENTION 
A process for monitoring the heat gradient in a heat-producing system in 
which at least three heat sensors, which are situated downstream from a 
heat source, determine the temperature of the exhaust gas from the heat 
source and the data from these sensors is analyzed to determine whether a 
fire hazard exists. 
DESCRIPTION OF THE PRIOR ART 
U.S. Pat. No. 3,728,615 discloses a firm alarm system comprised of detector 
tubes 12 and 14. These detector tubes do not have substantially identical 
responses to the exhaust gas being measured, for one of the tubes is ". . 
. partially sealed from the ambient atmosphere by means of shield 
enclosure 24 . . . " whereas the other tube is not so shielded. The use of 
heat-sensing detector tubes with different properties does not allow one 
to readily determine whether the heat gradient in a combustion system 
exhaust gas is continually decreasing in temperature. 
U.S. Pat. No. 3,112,880 discloses a method for controlling the heat flowing 
from a burner to a passageway in the heater. Although the use of two 
temperature recorders is disclosed, there is no disclosure of a process of 
activating a fire alarm system when any downstream point in the heat 
gradient of an exhaust gas has a temeprature higher than any point 
upstream of it in the gradient. 
SUMMARY OF THE INVENTION 
A process for monitoring the heat gradient in a heat-producing system is 
disclosed in which at least three heat sensors, which are situated 
downstream from a heat source, determine the relative temperature of the 
exhaust gas from the heat source. Each of the heat sensors used produces a 
substantially identical response to a given temperature. The output from 
each two sequential heat sensors is operatively connected to an indicator, 
which evaluates whether the downstream heat sensor is reporting a 
temperature lower than the upstream heat sensor; if the downstream heat 
sensor does report a temperature lower than the upstream heat sensor, then 
the indicator reads positive; but if the downstream heat sensor reports a 
higher temperature than the upstream heat sensor, the indicator reads 
negative. The output from each indicator is fed to a switching device 
which is activated only if and when any one of the indicators in the 
system reads negative. When the switching device is turned on, an alarm is 
activated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention provides a process and an apparatus for measuring the 
temperature of an exhaust gas in order to determine whether each portion 
of the gas is at a lower temperature than a corresponding upstream 
portion. At least three temperature-sensing devices (such as 
thermocouples) are placed at various points along the gas stream; for any 
given temperature, each of the temperature-sensing devices has a response 
which is substantially identical to each of the other temperature-sensing 
devices. The output from each two sequential temperature-sensing devices 
(such, as, e.g., sequential thermocouples 18 and 22, and 22 and 20, in 
FIG. 1) is fed to an indicator; the indicator will read positive when the 
downstream thermocouple reports a temperature lower than the upstream one, 
and it will read negative when the downstream thermocouple reports a 
temperature higher than the upstream one. Each of the indicator devices is 
operatively connected to a switching device(such as a NAND gate) which 
activates an alarm whenever any of the indicators is negative. 
Referring now to the figures, FIG. 1 illustrates one preferred embodiment 
of applicant's invention. As is shown in FIG. 1, heat source 10 burns a 
combustible carbonaceous fuel (not shown) and produces exhaust gas (not 
shown); the path of the exhaust gas, from upstream(the heat source) to 
downstream(the atmosphere) is shown by arrows 11, 13, 15, 17, 19, 21, 23, 
and 25; the exhaust gas is vented through pipe 12 and chimney 14 to the 
atmosphere 16. A temperature gradient(not shown) exists between the point 
at which the exhaust gas initially leaves heat source 10 and enters pipe 
12(at which time it is relatively hot) and the point at which the gas 
vents to the atmosphere 16(at which time it is substantially cooler). It 
is this temperature gradient which the temperature gradient monitoring 
system of applicant's invention is designed to evaluate. This monitoring 
system is comprised of at least three temperature sensors which are 
situated at designated points in or near the flow of the exhaust gas from 
heat source 10 to atmosphere 16. Thus, as is illustrated in FIG. 1, heat 
sensor 18 is placed within pipe 12, at a point at which the exhaust gas is 
relatively hot; heat sensor is placed within chimney 14 at a point at 
which the exhaust gas is relatively cool; and heat sensor 22 is placed 
intermediate heat sensor 18 and heat sensor 20. 
As is indicated above, the temperature-sensing devices(such as 
thermocouples) are placed in sequential relationship with each other. As 
used in this specification, the term "sequential" refers to following in 
order from upstream to downstream. Thus, referring to FIG. 1, as one goes 
upstream(from heat source 10) to downstream (to atmosphere 16), 
thermocouples 18, 22, and 20 are sequentially arranged; 22 is downstream 
of 18 in the heat gradient, and 20 is downstream of 22 in the heat 
gradient. Thus, thermocouples 18 and 22 are sequentially arranged. Thus, 
thermocouples 22 and 20 are sequentially arranged. However, thermocouples 
18, 20, and 22 are not "sequential"; for this is not the order they appear 
in in the upstream--downstream heat gradient sequence. 
Heat source 10 can be any heat-producing system. Thus, by way of 
illustration and not limitation, heat source 10 can be a heat-producing 
chemical system involving one or more exothermic reactions, an atomic 
reactor, or a combustion system. In one preferred embodiment, heat source 
10 is a combustion system in which a carbonaceous(carbon-containing) fuel 
is burned. It is preferred that the carbonaceous fuel being burned in heat 
source 10 be selected from the group consisting of oil, coal, and natural 
gas. However, other carbonaceous fuels may also be burned in heat source 
10 such as, e.g., coal-water slurry, coke-water slurry, and the like. 
In the heat gradient monitoring system of applicant's invention, at least 
three heat sensors must be used. The use of at least three heat sensors 
allows the system to operate quickly and efficiently with a high degree of 
sensitivity. In general, the longer the heat gradient to be monitored, the 
more heat sensors can advantageously be used. Thus, e.g. in some 
embodiments 4, 5, 6, 7, 8, 9, 10, or more heat sensors can be used in the 
system. 
In general, any device which will generate an electrical signal in response 
to heat can be used as a heat sensor in applicant's heat gradient 
monitoring system. The heat sensor can be comprised of a temperature 
measuring instrument (such as, e.g., a thermometer, a resistance 
thermometer, or a pyrometer) whose output will be converted by an 
auxiliary electronic device into an electrical signal. Alternatively, the 
heat sensor may be a thermocouple. The use of a thermocouple is preferred, 
for in response to heat it genrates an electrical signal directly without 
the need for an auxiliary power supply and/or electronic device. 
Some suitable temperature measuring instruments are disclosed on pages 
22-23 to 22-37 of R. H. Perry's and C. H. Chilton's "Chemical Engineers' 
Handbook," Fifth Edition (McGraw-Hill, Inc., New York, 1973), the 
disclosure of which is hereby incorporated by reference into this 
specification. Thus, e.g., suitable temperature measuring instruments 
include thermocouples, resistance thermometers, filled-system 
thermometers, bimetal thermometers, liquid-in-glass thermometers, and 
pyrometers; when any of these (with the exception of the thermocouple, 
which does not require auxiliary systems) is connected to an auxiliary 
electronic device which converts its output into an electricl signal, the 
temperature measuring unit so connected can be used as a heat sensor in 
applicant's invention. 
It is preferred that the heat sensor be either a resistance temperature 
detector(which requires an auxiliary electronic device) or a thermocouple 
(which does not require such auxiliary device). The most preferred heat 
sensor is a thermocouple. 
As is well known to those skilled in the art, a thermocouple is a device 
that uses the voltage developed by the junction of two dissimilar metals 
to measure temperature difference. Two wires of dissimilar metals welded 
together make up the basic thermocouple. One junction, called the sensing 
or measuring junction, is placed at the point where temperature is to be 
measured. The other junction, called the reference or cold junction, is 
maintained at a known reference temperature. The voltage developed between 
the two junctions is proportional to the difference between the 
temperatures of the two junctions; it is caused by the "Seebeck effect," 
discovered in 1821, in which an electric current flows in a continuous 
circuit of two different metallic wires if the two junctions are at 
different temperatures. Thermocouples are well known to those skilled in 
the art and are described in, e.g., pages 584-585 of Volume 13 of the 
"McGraw-Hill Encyclopedia of Science & Technology" (McGraw-Hill, Inc., New 
York, 1977), the disclosure of which is hereby incorporated by reference 
into this specification. 
Regardless of which heat sensor is used in applicant's system, it is 
essential that, for any given temperature, it have an output which is 
substantially identical to that of each other sensor used in the system. 
Thus, although one can use different temperature measuring instruments 
which have the same output, it is preferred to use the same type 
temperature measuring instrument for each sensor. In a preferred 
embodiment, the same type and model of thermocouple is used for each heat 
sensor in the system. 
In applicant's system, each of the heat sensors is disposed downstream of 
heat source 10. As used in this specification, the term "downstream" 
refers to the direction of the flow of exhaust gas from heat source 10 to 
atmosphere 16; one point is said to be downstream of another point if the 
former point is further along said stream than is the latter point. On the 
other hand, one point is said to be upstream of another point if the 
former point is closer to the heat soruce 10 than is the latter point. 
In applicant's system, the first heat sensor(such as, e.g., heat sensor 18 
in FIG. 1) is disposed downstream of heat source 10 but upstream of the 
other heat sensors(such as heat sensors 22 and 20 in FIG. 1). The last 
heat sensor(see heat sensor 20 of FIG. 1.) is preferably located near the 
end of the gradient, downstream of both heat sensors 18 and 22; whereas 
the first heat sensor is preferably located near the beginning of the 
gradient. One or more intermediate heat sensors (see, e.g., heat sensor 22 
of FIG. 1) is/are located downstream of the first heat sensor 18 and 
upstream of the last heat sensor 20. 
In the remainder of this specification, the heat sensor will be described 
by reference to a thermocouple, it being understood that other heat 
sensors can also be used. 
Referring now to FIG. 2, thermocouple 18 is connected by wire 24 to 
indicator 26 and by wire 28 to thermocouple 22. Thermocouple 22 is 
conected by wire 30 to indicator 26 and by wire 32 to thermocouple 18. 
Thermocouple 20 is connected by wire 34 to indicator 36 and by wire 38 to 
thermocouple 22. Thermocouple 22 is connected by wire 40 to indicator 36 
and by wire 42 to thermocouple 20. 
It is preferred that wires 24, 28, 30, 32, 34, 38, 40, and 42 which connect 
the thermocouples with each other and with indicators 26 and/or 36 be made 
from thermocouple extension wire. As used in this specification, the term 
"thermocouple extension wire" includes wire whose properties are 
substantially identical to the thermocouple lead to which it is connected. 
Thus, e.g., the thermocouple extension wire can be identical to the wire 
used for the thermocouple. Alternatively, the thermocouple extension wire 
may be made from compensating thermocouple extension wire which, although 
it consists of different material than the thermocouple, has substantially 
identical properties. 
Indicators 26 and 36 can be any electrical or electronic device which can 
compare the electrical outputs from sequential thermocouples in the system 
(such as thermocouples 18 and 22, or 22 and 20) and indicate which output 
is greater. In the embodiment illustrated in FIGS. 2 and 3, indicators 26 
and 36 are voltmeters. 
Referring again to FIG. 2, when, as is normal, thermocouple 18 is subjected 
to more heat than is thermocouple 22, the electron flow through wire 24 
from thermocouple 18 exceeds the electron flow through wire 30 from 
thermocouple 22, and indicator/voltmeter 26 reads positive. Similarly, 
when, as is normal, thermocouple 22 is subjected to more heat than is 
thermocouple 20, the electron flow through wire 42(from thermocouple 22) 
exceeds the electron flow through wire 38(from thermocouple 20), and 
indicator/voltmeter 36 reads positive. As long as the temperature gradient 
in the combustion system is the way it is supposed to be, with the vent 
gas continuously becoming cooler as it approaches the atmosphere, then 
indicators 26 and 36 will read positive. If, however, there is a fire 
between sensors 18 and 22 and/or between sensors 22 and 20, one or both of 
indicators 26 and 36 will read negative, and this negative reading will be 
noted by device 38 which will activate alarm 40. 
Referring now to FIG. 3, there is disclosed thermocouples 18, 22, and 20 
connected to indicators 26 and 36. As will be apparent to those skilled in 
the art, additional thermocouples can also be utilized in the system; each 
additional thermocouple so utilized will require the presence of an 
additional indicator/voltmeter(such as indicators/voltmeters 26 and 36) 
and an additional lead from the additional indicator/voltmeter to device 
38. 
Switching device 39 can be comprised of a switching circuit which will 
switch on alarm only when the output from each and every 
indicator/voltmeter is not positive. In the circuit shown in FIG. 3, 
switching device 39 will activate alarm 41 if either or both of indicators 
26 and 36 is negative. In a situation, e.g., where five thermocouples and 
four indicator/voltmeters are used(not shown), switching device 39 will 
activate alarm 41 if one, two, three, or all of the indicator/voltmeters 
are negative. 
The switching device 39 may be comprised of a switching circuit, which 
usually consists of conducting paths interconnecting discrete-valued 
electrical devices. Some suitable switching circuits are described on 
pages 806-824 of the "McGraw-Hill Encyclopedia of electronics and 
Computers" (McGraw-Hill, Inc., New York, 1982), the disclosure of which is 
hereby incorporated by reference into this specification. 
When switching device 39 is activated (by any one of the 
indicator/voltmeters being negative), it will turn on alarm 41. Alarm 41 
can be any of the alarms well known to those skilled in the art. Thus, 
e.g., alarm 41 can be a sonic alarm. Thus, e.g., alarm 41 can contain an 
output 43 to a remote alarm(not shown). 
It will be appreciated that, although the invention has been described with 
reference to the specific embodiments described in FIGS. 1, 2, and 3, 
other embodiments are within the scope of the invention. Thus, e.g., 
although heat source 10 has been depicted in FIG. 1 as a stove, any means 
for generating heat can be used. For example, a means for generating heat 
and flue gases can be used as the heat source. Thus, e.g., any of the 
furnaces described on pages 606-612 of Volume 5 of the "McGraw-Hill 
Encyclopedia of Science & Technology" (McGraw-Hill, Inc., 1977), the 
disclosure of which is hereby incorporated by reference into this 
specification, can be used. 
Although a pipe has been depicted in FIG. 1, any other means communicating 
with heat source 10 to facilitate the passage of exhaust gas from heat 
source 10 to the atmosphere 16 can be used. 
FIG. 1 depicts chimney 14 comprised of trap 44. In general, any vertical, 
hollow structure of masonry, steel, or concrete which is built to convey 
gaseous products of combustion from a building can be used to vent the 
exhaust gas from heat source 10 to the atmosphere 16. Instead of, or in 
addition to, said chimney, one can use an exhaust gas pipe. Any other 
means for conveying the exhaust gas from heat source 10 to atmosphere 16 
can also be used. 
FIG. 1 depicts thermocouples 18, 22, and 20 situated at various points 
along the heat gradient produced by heat source 10, but it does not depict 
means for connecting the thermocouples with indicators 26 and 36. Any 
means known to those skilled in the art can be used to operatively connect 
the thermocouples with the indicators. Thus, for example, each of the 
thermocouples can have its output electrically connected with an 
amplifier, and the amplified output from the thermocouples can then be 
electrically connected with the indicators; suitable means for amplifying 
the outputs of the thermocouples are disclosed on pages 386-391 of Volume 
1 of the "McGraw-Hill Encyclopedia of Science & Technology" (McGraw-Hill, 
Inc., New York, 1977), the disclosure of which is hereby incorporated by 
reference into this specification. 
Although FIGS. 1, 2, and 3 depict thermocouples, any other means for 
depicting whether a continuously decreasing heat gradient exists in the 
combustion system can be used in this invention. As used in this 
specification, the term "continuously decreasing heat gradient" refers to 
a system wherein, as the exhaust gas travels further away from the heat 
source, the temperature of the exhaust gas continuously decreases. Any 
combustion system wherein, at any given point, the temperature of the 
exhaust gas is substantially higher than it was at a prior, downstream 
point, does not have a "continuously decreasing heat gradient." 
One means of operatively connecting the output of the thermocouples with 
the indicators 26 and 36 is to operatively connect the output of the 
thermocouples to one or more transmitters, transmit said output to one ore 
more receivers, and operatively connect the output from the receivers to 
one or more of the indicators. Another means of operatively connecting the 
output of the thermocouples with the indicators is to directly connect the 
thermocouples, by means of thermocouple extension wire, with the 
indicators. Regardless of whether one uses indirect means of connecting 
the output of the thermocouples with the indicators (such as the 
transmitter--receiver system) or direct means(such as extension wire), or 
a combination of indirect or direct means, one may utilize amplifiers in 
the system to increase the output of the thermocouples. 
Indicators 26 and 36 determine whether the temperature sensed by each of 
the thermocouples in the system is lower than the temperature sensed by 
each other thermocouple which is upstream of the reference thermocouple. 
Although FIGS. 2. and 3. disclose that this determination may be made by 
electrical means, any means may be used in the invention. Thus, e.g., 
indicators 26 and 36 may be operatively connected to the thermocouples in 
any manner which allows them to make such determination, be it electrical 
means, physical means, chemical means, mechanical means, or any other 
suitable means. 
Switching device 39 can be any suitable device, utilizing electronic and/or 
other means, for evaluating whether each of the indicators(such as 
indicators 26 and 36) are positive or negative. When all of the indicators 
are positive, this indicates that every heat sensor in the system is 
reported a temperature lower than that reported by all heat sensors 
upstream of it, and no alarm will be sounded by the system. When, however, 
any one or more of the indicators is negative, at least one of the heat 
sensors is reported a temperature higher than that reported by the heat 
sensor upstream of it, and switching device 39 will activate alarm 41. 
In one preferred embodiment, switching device 39 utilizes a gate circuit to 
determine whether conditions are suitable for switching on alarm 41. Any 
of the gate circuits well known to those skilled in the art can be so 
used. Thus, e.g., the gate circuits disclosed on pages 689-695 of Bernard 
Grob's "Basic Electronics," Fourth Edition (McGraw-Hill, Inc., New York, 
1977), the disclosure of which is hereby incorporated by reference into 
this specification, can be used. Thus, e.g., a NAND gate circuit can be 
used. 
The terms I have employed are used as terms of description and not 
limitation, and I have no intention, in the use of such terms and 
expressions, of excluding any equivalents of the features shown and 
described or portions thereof, but recognize that various modifications 
are possible within the scope of the invention claimed.