US3393562A

US3393562A - Calorimeter apparatus

Info

Publication number: US3393562A
Application number: US411942A
Authority: US
Inventors: Harry B Breedlove
Original assignee: Harry B. Breedlove
Current assignee: HARRY B BREEDLOVE
Priority date: 1964-11-17
Filing date: 1964-11-17
Publication date: 1968-07-23
Anticipated expiration: 1985-07-23

Description

In y 3, 19 68 H. B. BREEDLOVE 3,393,562

CALORIMETER APPARATUS Filed Nov. 17, 1964 5 Sheets-Sheet l 1 o CALORIMETER OUTPUT I 24 23 22 /H I 42 FLOW MEASURE i I4 20 AIR v COMBUSTIBLE REGULATOR I T GAS l9. 4 I8 THERMOCOUPLE wIREs COMBUSTION R SUPPORTING I F GU E GAS /h SET POINT PRESSURE 38 I DIVIDER /31 CONTROLLER T T h 40 Q- J I 34 T ABSOLUTE DIFFERENTIAL PRESSURE TEMPERATURE PRESSURE 3 TRANSMITTER I TRANSM'TTER TRANSMITTER I ,as 33 TO BURNER 0 b AIR \BI INVENTOR.

SUPPLY HARRY BOLLING BREEDLOVE FIGURE 2 @044 ATTORNEY July 23, 1968 H. B. BREEDLOVE 3,393,562

CALORIMETER APPARATUS Filed Nov. 17, 1964 5 Sheets-Sheet 2 FIGURE 3 IN'VENTOR. HARRY BOLLING BREEDLOVE BY Q ATTORNEY y 3, 1968 H. B. BREEDLOVE 3,393,562

CALORIMETER APPARATUS 5 Sheets-Sheet 5 Filed Nov. 17, 1964 /MIN.

A IO

. 62 EIIF j 68\ |1 gel 60 5 j- MA|N now FIGURE 4 CONTROLLER AIR mvENToR.

FIGURE 5 HARRY BOLLING BREEDLOVE PM i. "H /5 ATTORNEY United States Patent Oflice 3,393,562 Patented July 23, 1968 3,393,562 CALORIMETER APPARATUS Harry B. Breedlove, 4625 Hyacinth St., Baton Rouge, La. 70808 Filed Nov. 17, 1964, Ser. No. 411,942 22 Claims. (Cl. 73-190) ABSTRACT OF THE DISCLOSURE A calorimeter maintains a constant temperature differential between the inlet air to a burner and the products of combustion at the burner outlet by regulating the fuel flow to the burner; the fuel flow rate is an indication of the calorific value of the fuel, this flow also corresponds to the variation in flow required to maintain a constant calorific output of any burner supplied by the fuel.

This invention relates to calorimeters generally, and more particularly to calorimeter apparatus having continuous measurement and control functions.

An object of this invention is to provide a calorimeter which is simple in design, accurate, capable of continuous operation, and easy to operate.

Another object of this invention is to provide a calorimeter operating on the principle of a controlled constant B.t.u. per minute (heat of combustion) consumption.

Another object of this invention is to provide a gas calorimeter which consumes a constant B.t.u. per minute rate of whatever gas is under test or measurement by means of gas flow regulation.

Another object of this invention is to provide a gas calorimeter having compensation means for factors which appreciably influence calorimeter measurement.

Another object of this invention is to provide a gas calorimeter having a measurement variable proportionally related to the rate of fuel flow consumed by gas burners requiring a constant calorific value per unit time input.

Another object of this invention is to provide a gas calorimeter substantially independent of environmental influences.

Still another object of this invention is to provide a gas calorimeter control system suitable for precise feedforward regulation of a gas furnace.

Yet another object of this invention is to provide a gas calorimeter metering system providing for continual B.t.u. per minute measurement of gas flow in a gas supp-1y line.

Yet another object of this invention is to provide for a B.t.u. per minute metering system which is accurate, simple, and operationally compatible with all types of combustible gases irrespective of composition or density.

Still another object of this invention is to provide a gas calorimeter detection system for measuring B.t.u. per cubic foot of a gas under test.

These and other features of the invention will become apparent from the following detailed description thereof, taken in conjunction with the several figures of the drawings, in which:

FIGURE 1 is a cross-sectional diagram of the calorimeter together with control apparatus associated therewith.

FIGURE 2 is a block diagram of the air flow regulator associated with the calorimeter.

FIGURE 3 is a schematic diagram of the calorimeter system adapted for use as a furnace control.

FIGURE 4 is a schematic diagram of the gas calorimeter system adapted for use as a B.t.u. per minute metering device with a gas supply line.

FIGURE 5 is a schematic diagram of the gas calorimeter adapted for use as a B.t.u. per cubic foot detector.

Referring to FIGURE 1, a schematic diagram of the calorimeter apparatus is shown, comprising a calorimeter together with associated components. The gas burner chamber 11 contains a burner 12. A pair of series opposed thermocouples 13-14 in the gas burner chamber 11 provide a differential temperature measurement output to a controller 15 which in turn operates valve 16 in gas line 17. Air supply 18 is regulated by regulator 19 having a regulated air output to gas burner chamber 11. Inserted in gas line 17 is metering orifice 20 which together with differential pressure measuring device 21 provides the calorimeter measurement output 22.

Calorimeter 10 continuously burns the combustible gas sample supplied through sample line 17 in an environment of combustion-supporting gas, such as air, which 1s supplied at a constant rate by air regulator 19 several times in excess of the mass required for full oxidation of the sample gas. This excess air supply insures that the entire heat of combustion of the sample gas is utilized in calorimeter 10. To the extent the air supply is excessive, it increases its preponderant effect upon calorimeter temperature rise and thus minimizes the effect of variation in specific heat of the unknown sample gas.

The heat of combustion referred to herein is the lower heat of combustion measurement obtained when water resulting from combustion passes off in a vapor rather than a liquid phase. The higher heat of combustion is that obtained when resulting water is condensed thus adding the heat evolved by the water condensate to the heat of combustion measurement.

Calorimeter 10 supports combustion in chamber 11 which is isolated from ambient temperature by several concentric convolutions of

baflles

23, 24, and 25. These bafiles conduct the products of gas-air combustion together with admixed excess air through three layers surrounding chamber 11 prior to dispersion into the surrounding atmosphere. These hot layers of the products of combustion mixed with heated excess air about the gas burner chamber 11 effectively insulate chamber 11 from the ambient temperature of the surrounding environment. This arrangement minimizes heat loss by radiation and conduction from chamber 11, and contributes to make all points in chamber 11 above burner 12 have temperatures closely corresponding to the temperature of products of combustion. More particularly, the concentric baflie arrangement assures that the heat rise in chamber 11 afforded by air-gas combustion is unaffected by the ambient environment.

Located within calorimeter 10 are thermocouples 13- 14. Thermocouple 13 is located above the flame of burner 12 so as to sense the temperature of the exhaust gases achieved by absorbing the heat of combustion. Thermocouple 14 is located beneath burner 12 to sense the temperature of the air supply immediately prior to its heating. Thermocouples 13-14 are connected in series opposition so as to provide a differential temperature measurement across the series combination. This differential temperature is a measure of the total heat rise between the air-gas inputs prior to combustion and the heated exhaust products therefrom. A constant temperature differential indicates a constant heat of combustion flow through the calorimeter.

The heat of combustion may be measured in heat units such as calories or British thermal units. The flow rate of heat of combustion is conveniently expressed in British thermal units per minute (B.t.u. per minute).

A constant B.t.u. per minute gas flow may be attributed to a constant B.t.u. per minute heat value of the sample gas on condition that the air supply is constant, thus not influencing calorimeter accuracy. In critical measurement applications the air supply must be constant in terms of pounds per minute. To obtain this, the air supply 3 is corrected for temperature and barometric variations; this removes any spurious influence of the air supply upon calorimetric operation, thus optimizing accuracy.

The effect of humidity in the air supply upon calorimetric measurement is negligible. At 100 degrees F., 14.7 p.s.i. barometric pressure, there is only 0.1 percent difference between bone dry and fully saturated air upon the effective heat absorption of the air supply. This very small effect is owing to the mutual cancellation of two factors: on one hand, at 100 percent relative humidity the air is less dense than when dry and so the mass flow rate is less through the fiow regulating orifice with constant differential pressure across the orifice; but on the other hand, the moist air has a greater heat capacity per unit mass than when dry. These two factors tend to nearly cancel, making the heat absorption owing to the heating of the air remain Within 0.1 percent. A constant heat absorbency of the air and combustion products per minute keeps the temperature rise in the calorimeter dependent upon the B.t.u. per minute flow rate of the gas input. The temperature rise through the calorimeter is then a simple function of the B.t.u. per minute flow rate of the sample gas and remains constant when the B.t.u. sample gas input is constant.

For holding the temperature differential constant (the heat rise through the calorimeter) the B.t.u. per minute input of the sample gas must be maintained at a constant rate. Inasmuch as the sample gas may vary in composition, density, and B.t.u. per pound or volume content, sample gas flow must be adjusted appropriately to obtain the desired constant B.t.u. per minute flow into the calorimeter.

Any deviation from a constant B.t.u. per minute input of the sample gas results in a corresponding deviation in the temperature rise afforded by sample gas combustion. This change in temperature rise is detected by thermocouples 13-14 as a change in temperature differential. The temperature differential is applied to controller 15 at inputs 26-27.

Controller 15 is conveniently a proportional plus reset with or without derivative control having a no droop characteristic with load change and having an output operating a pneumatic valve.

Controller 15 responds to the change in temperature differential and adjusts valve 16 in sample gas line 17 in a direction and to an extent altering sample gas flow so that the temperature differential is made to restore to its desired operating value. In accomplishing this restoration of temperature differential, the constant B.t.u. per minute input has necessarily been reestablished. In operation these regulatory variations are minute in amplitude and tend to cancel over long term operation, substantially eliminating the internal loop control function of the calorimeter as an influence on calorimeter measurement.

The temperature rise throughout the calorimeter is selected for about 700 degrees F. in most applications; high enough to obtain accuracy through easy discrimination of small B.t.u. per minute deviations, but not so high as to be destructive of continuous gas burner operation and measurement.

The sample gas input will have a particular B.t.u. per cubic foot content, which when burned with the excess air supply willyield a temperature rise mainly determined by the B.t.u. absorption by the combustion products mixed with the excess air. For example, 24 pounds of air may conveniently be used with one pound of sample gas. The B.t.u.s required to heat the air in excess of that required for gas oxidation 700 degrees F. may be easily calculated from standard tables. Also, the B.t.u.s absorbed by the combustion products of the sample gas and oxidizing air may similarly be calculated. Sample gas flow rate is selected to provide a B.t.u. per minute flow consonant with the 700 F. rise in temperature of the air-gas combustion products mixed with excess air.

The output variable of the calorimeter is a measurement of the controlled variation in sample gas flow necessary to obtain the required constant B.t.u. per minute input of the sample gas to the gas burner. The sample gas flow in line 17 is metered by a suitable device such as metering orifice 20 in conjunction with differential pressure indicator 21, which provides the calorimeter output.

The differential pressure from a metering orifice is a measure of mass flow (pounds per minute) on condition that the gas density remains constant. Mass flow in pounds per minute is proportional to: /hd where h is the metering orifice differential pressure and d is the absolute density of the gas. I

In the calorimeter control system the B.t.u. per minute flow of the sample gas is maintained at a constant by virtue of calorimeter internal loop operation. Mathematical formulas for the expression of calorimeter signal output 22 under this condition of operation may be derived from the self-evident relation:

B.t.u. lbs.

min. min.

/H and Heat Rate of Flow (B.t.u./min.) is maintained constant. Then It is to be kept in mind that the significance of the above term for /F depends upon the particular condition of the calorimeter system, wherein B.t.u. per minute is controlled to a constant value. That is, the equations including the constant c for B.t.u./min. express an operational balance more properly than an equality. Under the condition of a constant B.t.u./min. flow, the term B.t.u./ 1b. must reciprocate with lbs/min. (mass flow). Then, in the calorimeter, the measurement /d has an inversely proportional relationship both to B.t.u./lb. (if B.t.u./lb. increases, then flow rate must be proportionally reduced) and to /h (if d increases and B.t.u./lb. is stable, /h must decrease, so that the product /h d which is proportional to mass flow, will remain constant).

The calorimeter output is directly related to the Wobbe index. This index, also referred to as Wobbe number or Wobbe Index of Rate of Thermal Delivery is defined as B.t.u./std. cu. ft. w specific gravity Though seldom used in U.S.A., it is quite common in European practice, where manufactured gas with widely varying calorific values is used. The property of the Wobbe index is that, multiplied by /hp/t, and a suitable constant, it gives Thermal Delivery directly. That is t IIIID.

Where c is a constant, 11 is differential pressure across an orifice, P and T are the absolute static pressure and absolute temperature of the gas at the measuring orifice, and WI is the Wobbe index.

Since the calorimeter involves a flow across an orifice, controlled to supply a constant value of B.t.u./min, the Wobbe index of a gas can be determined directly from Where h, P and T are differential pressure, absolute pressure and absolute temperature of the sample gas at the calorimeter measuring orifice. The constant c may be determined by passing a gas of known calorific value and specific gravity (known Wobbe index) through the calorimeter. I

By suitably combining the calorimeter signal output It with a density or volume measurement, B.t.u. per pound or B.t.u. per cubic foot are readily obtainable. This is easily accomplished when the sample gas is of known chemical composition wherein the density is a constant.

Where density is a constant, the calorimeter signal output: /;z

B.t.u./lb. /?l -fl In such a case the B.t.u. per pound value of the sample gas can be read directly on a suitably calibrated scale or chart actuated by the calorimeter signal output 22.

For exact measurements of the sample gas, a more strict control of the air supply is required than for simple applications such as controlling a furnace gas burner. For exact measurement, air supply temperature and barometric pressure must be monitored to assure a constant air mass flow into calorimeter 10. It is considered the temperature of the sample gas and the pressure upon it will be essentially the same as the temperature and pressure of the air supply inasmuch as both air and gas are supplied through lengths of tubing at ambient temperature and are operated at very nearly atmospheric pressure. Thus the temperatures of both air and gas are essentially that read by thermocouple 14.

Changes in sample gas density have a negligible effect upon calorimeter operation inasmuch as changes in the sample gas contribution to the total weight and heat capacity of the total exhaust gases is minute. This effect is the more minute to the extent the air supply is maintained at a higher rate than that necessary for full oxidation of the sample gas. When the air supply is many times that necessary for full oxidation, variations in sample gas density do not appreciably affect the temperature differential through calorimeter.

To provide the regulation required by the air supply for the applications employing critical measurement, the air supply must be maintained constant in terms of mass flow (pounds per minute). This is the best criterion for a constant air supply under the most exacting requirements of calorimeter accuracy.

To obtain constant mass flow of the air supply, the air flow control of FIGURE 2 may be conveniently used to accomplish the regulation function of air regulator block 19 shown in FIGURE 1.

The formula for mass flow may be expressed:

lbs. (per unit time)-k /m k being a scaling constant, h the orifice differential pressure, and d the absolute air density. In addition becomes x/h which is simply the classical gas law whereby the density of a gas is proportional to the absolute static pressure (Boyles law) and inversely proportional to its absolute temperature (Charles law). Substituting, mass flow of air is proportional to:

max?

In order to maintain constant air mass flow, the term must be held to a constant. The circuit configuration of the functional blocks in FIGURE 2 actually solve the formula:

which is the identical term transposed.

Referring to FIGURE 2, air supply line 31 is regulated by valve 32. Metering orifice 33 and associated differential pressure transmitter 34 provide term h of the above formula. The temperature of the air is measured by probe 35 and associated temperature transmitter 36 provides term T of the above formula. These terms T and h are taken from their respective transmitters and applied to divider 37, which generates an output term T /h which is employed to adjust the set point of pressure controller 38. Pressure controller 38 regulates valve 32 so that the absolute static pressure of the air P is equal to the set point T/h of the controller, thereby determining a constant air mass flow. Absolute static pressure P is determined by pressure tap 39 with associated pressure transmitter 40 whose output supplies term P to pressure controller 38. These elements of the air flow control are conveniently conventional components, such as pneumati: Cally-operated instruments, though electronic substitutions may be readily made where suitable, which are also available as conventional components.

In the air flow controller of FIGURE 2, the orifice 33 should be sized to operate with minimum practical differential, so that measured absolute pressure P is close to the actual pressure of the air supply at gas burner 10.

It is contemplated that pressure tap 39 may be disposed on the burner side of orifice 33.

Referring now to FIGURE 3, a schematic diagram of the calorimeter apparatus is shown incorporated into a large gas burner application, as for instance, to a gas fired furnace which heats a flowing fluid. A typical requirement is for a constant temperature in the heater fluid output 53 of heat exchanger 52 as measured by thermocouple 49. Because of the mass of the furnace 51, mass of heat exchanger 52, and the mass of the fluid in heat exchanger 52, a considerable time delay intervenes between a change of heat input to heat exchanger 52 from furnace 51 and a consequent response of temperature change as measured by element 49 in heat exchanger output line 53. Therefore, considerable transient errors in fluid temperature may result from sudden change in the heating value of the gas before the feedback temperature control can alter gas flow to compensate for the effect.

The calorimeter apparatus provides a simple and efficient means of feedforward control to a furnace requiring a constant -B.t.u. per minute input irrespective of changes of gas supply composition, density, and B.t.'u. content.

The simple proportional relation between the calorimeter signal output and the requirements of a gas burner fired with a gas of unknown characteristics is readily apparent. On the one hand, the unknown gas is consumed in the calorimeter apparatus at a variably controlled rate which maintains a constant unknown gas input to the calorimeter in terms of B.t.u. per minute. On the other hand, the identical variations in gas furnace control are required to maintain the same unknown gas at a constant B.t.u. per minute supply to the main burner. The only difference obviously is the constant of proportionality to adjust for the difference in size between the small calorimeter burner and the large gas furnace.

Referring to FIGURE 3, the components of the calorimeter apparatus of FIGURE 1 are again shown. In additon, in FIGURE 3 is shown a gas-fired furnace 51 with a gas flow control system associated therewith. The gas supply is furnished to inlet 41 of supply line 42. This gas supply may be, typically, a mixture of a known gas and an unknown gas such as a byproduct of some industrial process. A sample of the gas supply is taken at tap 43 and supplied to the calorimeter apparatus for measurement. The supply gas is conducted through valve 44 which controls the flow, through orifice 45 to the main burner 51. Orifice 45 together with differential pressure transmitter 46 measure the gas flow to the main burner 51, providing as an output main burner 51 gas flow indication to controller 47.

The set point of controller 47 is controlled from ratio multiplier 48, which combines the calorimeter signal output 22 with the temperature of the fluid output from heat exchanger 52 as measured by temperature sensor 49 and transmitted by temperature transmitter 50.

Assuming the temperature of the heated fluid to be at the desired temperature, sensor at 49 and transmitter 59 contribute no variation to ratio multiplier 48. Under this condition the set point of controller 47 is only changed by the calorimeter signal output. Upon the occurrence of a rapid change in supply gas density, or calorific value, or both, the sample gas will require a new flow rate by the calorimeter control loop to maintain the constant B.t.u. per minute input to the calorimeter. This new gas flow rate to the calorimeter is measured by orifice 20, transmitted by differential pressure transmitter 21 through output 22 to ratio multiplier 48 and thence providing a proportional set point change at controller 47. The new set point setting of controller 47 compensates for the change in gas composition so that the gas supply sent down line 42 to gas furnace 51 is constant in B.t.u. per minute flow. This compensation operates to maintain the temperature of gas furnace 51 at its desired point. It is to be noted that this compensation obtains immediately upon the sample gas reaching the calorimeter, thus avoiding the difficulties inherent in the feedback control approach which must await a registered change in temperature sensor 49 and additional time lags before corrective action is taken. Thus the control of temperature of gas furnace 51 can be held within more exacting limits than otherwise by means of the feedforward type of control provided by the calorimeter shown in FIGURE 3. The

temperature sensing device 49 together with temperature transmitter 50 provide a feedback control to ratio multiplier 48, which operates over a long term basis to maintain the exact temperature desired. The feedforward control provided by the calorimeter apparatus, and the feedback control provided by the gas furnace 51 temperature sensor 49 parallel one another into ratio multiplier 48. The feedforward system provides short term stability: that is, quick corrective response to fuel change; the feedback system provides for long term stability, that is, accuracy.

In the control system of FIGURE 3, the temperature of air and gas is common to both systems, so that ambient temperature changes cancel out. So too, barometric changes have the same effect on both systems and also cancel out. Therefore regulator 19 with the calorimeter apparatus of FIGURE 3 is conveniently a simple pressure regulator in this application.

Where the gas supply is at extremely high pressures, it is more convenient to place sample gas tap 43 on the main burner side of orifice 45, thus alleviating the necessity of reducing sample gas pressure to a convenient operating value.

Referring now to FIGURE 4, a schematic diagram is shOWn illustrating the application of the invention to a B.t.u. metering system. In this application the calorimeter is employed to continuously measure the B.t.u.s flowing per minute through a gas supply line.

In order to accomplish the measurement in terms of B.t.u. per minute several primary measurements are combined to yield the desired result. The main gas line 60 is tapped at point 73 by gas sample line 61 which provides a constant gas flow in terms of B.t.u. per minute to calorimeter owing to the regulatory action of the associated control loop and described in conjunction with FIGURE 1. In this embodiment, the metering orifice for the sample line is installed adjacent to the orifice which handles the main gas flow to be measured, so that the temperature, pressure and density of the gas flowing through the main line orifice is the same as the temperature, pressure and density of the gas flowing through the sample orifice, regardless of actual flowing composition, pressure and temperature.

As described, the calorimeter control loop maintains a constant temperature differential as measured by thermocouples 13-14. The loop thus maintains a constant sample gas flow in terms of B.t.u. per minute.

Returning to the formulas described above: B.t.u./ min.=mass flow times B.t.u./ pound. This formula simply expresses the evident observation that the amount of heat in a gas (B.t.u./pound) multiplied by its rate of fiow (pounds/min.) yields the rate of heat flow in a gas (B.t.u./min). Or to put it another way the rate of heat flow (B.t.u./min.) in a gas is proportional both to its heat content (B.t.u./pound) and to its mass flow (pound/ min). As described above the term B.t.u./min. is a constant c, owing to the operation of the calorimeter apparatus in controlling the sample gas flowing in line 61.

Substituting in this formula, c=mass flow l3.t.u./ pound; and transposing,

Sample line mass flow is proportional both to the square root of sample line 61 pressure h and to the square root of absolute gas density a that is to say, mass flow= /h, d. Pressure i is measured as the pressure differential at orifice 66 which is associated with the differential pressure indicator 67.

Substituting:

B.t.u. 0

lb. {T d That is to sit when the B.t.u. per minute is held constant the amount of heat per unit weight (B.t.u./pound) of the sample gas is inversely proportional to its mass flow (pounds/min.) in the sample line 61.

This relationship may also be expressed by saying that the amount of heat per unit weight of the sample gas is inversely proportional both to the square root of the sample line pressure /h and to the square root of the gas density /d.

In the main gas line 60 metering orifices 68 together with differential pressure transmitter 69 indicate differential pressure h This primary measurement may be related to the formula:

B.t.u./min.=pounds/min. B.t.u./pound Substituting the formula:

Vm=pounds/min.

when I2, is main flow line 40 pressure and a is gas density,

B.t.u. B.t.u. min. (main line) 1 11).

This last relationship applies to the supply gas flowing in the main flow line 60.

B.t.u./ pound of the gas has already determined to have the relationship in the sample line. Substituting this relationship in the formula for the gas and the main supply line 60 yields the result:

B.t.u. w Td X 0 min. 1 [5 71 Simplifying and cancelling the numerator and denominator:

together with differential pressure transmitter 67, and the term It, is obtained from main flow line 60 by orifice 68 density term from together with differential pressure transmitter 69. These terms are supplied to divider 63 having an output h /h The term h /h, is operated on by square rooter 64 yielding the term /h /h which has been shown above to be a term proportional to the B.t.u. per minute rate of the gas flowing in main line 60.

Another way of looking at the process is in terms of Wobbe Index. The square root of metering orifice 68 output 69 h, is multiplied by Wobbe Index (l /h to give a constant B.t.u./minute control signal. Thus v'h /h =constant B.t.u. per minute in the gas line 60.

Thus the arrangement of components illustrated in FIGURE 4- provides a means to measure the B.t.u. per minute rate supply in a main line owing to the simplification obtained by having the gas density term cancelled out in the calculation of B.t.u.s per minute.

Pressure reducer 62 is inserted into the sample gas line 61 in order to allow calorimeter operation in conjunction with main gas lines operating under extremely high pressures. Note that pressure reducer 62 is inserted on the calorimeter side of sample gas line orifice 66 so that as previously stated the gas densities at the same orifice 66 and the main line orifice 68 are the same.

Referring now to FIGURE 5, a schematic diagram of apparatus suitable for monitoring the lower explosion limit of a test gas is shown. The lower explosion limit of a flammable gas is designated as the minimum percentage of the flammable gas in air which will just sustain combustion. In general, at the lower explosion limit, the flammable mixture contains the same number of B.t.u.s per cubic foot, regardless of the particular flammable gas. It is frequently desirable to monitor a gasair mixture to assure that the flammable gas content is sufliciently small so that the mixture is safely below this lower explosion limit. For instance, where some types of electrical equipment are operated in areas which are potentially though normally not actually hazardous from an explosive standpoint, it is necessary either to go to the expense and inconvenience of enclosing the electrical apparatus in explosion proof housings, or to monitor the area to assure that ventilation, etc., is sufficient to keep the flammable material in the air at a level safely below the lower explosive limit.

The calorimeter apparatus of FIGURE 1 is employed to maintain a constant B.t.u. per minute to calorimeter 10. Air input 81 is regulated to a constant rate. Gas input 82 to burner 12 has a bifurcated inlet 83-84. To inlet 83 is supplied a gas of known calorific value, such as methane. Inlet 84 is supplied with a constant volume of the gas under test. The two inlet gases mix in throat 85, and pass through gas input 82 into burner 12.

The calorimeter control loop operates on the known gas (methane) supplied to inlet 83 by controller 15 and valve 16, maintaining a constant total B.t.u. per minute input to burner 12 thereby.

If the B.t.u. per cubic foot of the test gas is constant, the test gas provides thereby a constant B.t.u. per minute input to inlet 84 inasmuch as the test gas flows at a constant volume. Should the test gas vary in B.t.u.s per cubic foot, the constant volume input of the test gas to inlet 84 will provide a correspondingly changed B.t.u. per minute flow thereto. The total gas mixture composition in terms of B.t.u.s per minute is changed thereby and a consequent change in temperature differential ensues. This causes controller 15 to regulate the methane by means of valve 16 to a new B.t.u./minute flow into inlet 83 such that the new methane B.t.u. per minute rate cancels the test gas variation. The methane B.t.u. per minute rate may be calibrated in terms of test gas B.t.u. per minute rate, or what is equivalent with constant volume flow, B.t.u. per cubic foot. A particular B.t.u. per minute rate of methane indicates a complementary B.t.u. per minute rate in the test gas in order to make up the total constant B.t.u. per minute rate established by the calorimeter loop. (Methane B.t.u./min.+test gas B.t.u./min.=constant B.t.u./min.) It is a direct proportional conversion from test gas B.t.u. per minute to the B.t.u.s per cubic foot of the test gas inasmuch as test gas volume is constant as supplied to inlet 84. Therefore an increase in the B.t.u. per minute flow of methane is equal to a decrease in the B.t.u. per minute (and per cubic foot) of the gas under test; and vice versa. The change in B.t.u. per minute flow of methane is directly obtainable from a flow meter inasmuch as methane density at atmospheric pressure and temperature is substantially constant.

While there has been shown what is considered to be a preferred embodiment of the invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims to cover all such changes and modifications as fall within the true scope of the invention.

What is claimed is:

1. Calorimeter apparatus comprising:

a combustion chamber,

a gas burner positioned within said combustion chamber,

controllable means to supply a variable rate of flow of combustible gas to said gas burner,

means to supply combustion-supporting gas to said gas burner,

a first temperature-sensing means positioned proximate to said gas burner for measuring the temperature of said combustion-supporting gas prior to its heata second temperature-sensing means positioned above said gas burner for measuring the temperature of the products of combustion, and control means responsive to said first and second temperature-sensing means adapted for operative interconnection with said controllable means for varying the flow rate of said combustible gas supplied to said burner to maintain the diiference between the temperature measured by said first and second temperature-sensing means to a substantially constant value, over an operational range of calorific values of said combustible gas thereby providing a constant calorific rate supplied to said burner, and

flow measuring means responsive to the flow of said combustible gas as regulated by said controllable means for measuring the flow rate of said combustible gas.

2. The calorimeter apparatus of claim 1 with an exhaust passage adjacent to the outside of said combustion chamber.

3. Calorimeter apparatus comprising;

a combustion chamber,

a gas burner positioned within said combustion chamber,

controllable means to supply combustible gas to said gas burner at an adjustable rate of flow,

means to supply combustion-supporting gas in excess to said combustion chamber,

a first temperature-sensing means positioned near said gas burner within the path of said combustion-supporting gas for measuring the temperature thereof prior to its heating by heat liberated by combustion,

a second temperature-sensing means positioned near said gas burner in the path of the products of combustion admixed with excess combustion-supporting gas for measuring the temperature of the admixture,

with said adjustable rate of flow of said combustible gas supplied to said burner being regulated to a rate maintaining a substantially constant temperature differential between the measurements of said first and second temperature-sensing means, over an operational range of calorific values of said combustible gas, and

fiow measuring means responsive to the flow of said Ill combustible gas as regulated by said controllable means for measuring the flow rate of said combustible gas.

4. The calorimeter apparatus of claim 3 with an exhaust passage adjacent to the outside of said combustion chamber.

5. Calorimeter apparatus comprising;

a combustion chamber,

a gas burner mounted Within said combustion chamber,

means to supply combustion-supporting gas to said gas burner surround at a constant rate in excess of the amount yielding full combustion with said combustible gas,

a first temperature-sensing means located below said gas burner for measuring the temperature of said combustion-supporting gas prior to its heating,

a second temperature-sensing means located above said gas burner for measuring the temperature of the products of combustion admixed with excess combustion-supporting gas,

said adjustable rate of flow of said combustible gas supplied to said burner being regulated to a rate resulting in a substantially constant temperature differential between the measurements of said first and second temperature-sensing means, over an operational range of calorific values of said combustible gas, and

6. The calorimeter apparatus of claim 5 with a baffled exhaust chamber at least partially surrounding the outer surface of said combustion chamber.

7. Calorimeter apparatus comprising;

a combustion chamber having an opening for removal of gases at the upper portion thereof,

a gas burner having its orifice positioned within said combustion chamber,

a gas inlet line supplying said orifice and extending outside said combustion chamber,

valve means controlling combustible gas flow through said gas inlet line,

an air inlet into said combustion chamber having its discharge postioned substantially beneath said gas burner,

an air regulator providing a constant air supply to said air inlet in excess of the amount required for full oxidation of said combustible gas,

a first temperature-sensing means located beneath said gas burner and above said discharge of said air inlet for measuring the temperature of said air supply prior to its heating,

a second temperature-sensing means for measuring the temperature of the products of combustion of said gas and air admixed with excess air,

differencing means for obtaining the temperature differential measurement between said first and second temperature-sensing means and control means responsive to said temperature differential measurement having an output for regulating said valve means to control the rate of flow of said combustible gas in a manner to maintain a substantially constant said temperature differential over an operational range of calorific value of said combustible gas, and

fiow measuring means responsive to the fiow of said combustible gas as regulated by said controllable means for measuring the flow rate of said com-bustible gas.

8. Calorimeter apparatus comprising;

an exhaust chamber adapted to receive said gases from said opening in said combustion chamber and having at least one bafile for directing said gases in a convoluted path through said exhaust chamber and having a portion of said exhaust chamber substantially surrounding the upper portion of said combustion chamber,

a gas burner having its orifice positioned within said combustion chamber,

21 gas inlet supplying said orifice and extending outside said combustion chamber,

valve means controlling combustible gas flow through said gas inlet line,

an air inlet into said combustion chamber having its discharge positioned substantially beneath said gas burner,

differencing means for obtaining the temperature dif ferential measurement between said first and second temperature-sensing means,

and control means responsive to said temperature differential measurement having an output for regulating said valve means to control the rate of flow of said combustible gas in a manner to maintain a substantially constant said temperature differential over an operational range of calorific values of Said combustible gas to there-by provide for a constant calorific rate for said burner by appropriately varying the flow rate of said combustible gas, and

flow measuring means responsive to the flow vof said combustible gas as regulated by said controllable means for measuring the flow rate of said combustible gas.

9. Calorimeter apparatus comprising;

a combustion chamber,

a gas burner positioned within said combustion cham' ber,

controllable means to supply combustible gas to said gas burner,

means to supply combustion-supporting gas to said gas burner,

a first temperature-sensing means positioned proximate to said gas burner for measuring the temperature of said combustion-supporting gas prior to its heating,

a second temperature-sensing means positioned above said gas burner for measuring the temperature of the products of combustion,

differencing means for obtaining the temperature differential measurement between said first and second temperature-sensing means,

a controller responsive to said temperature differential measurement controlling said controllable means whereby the flow of said combustible gas is regulated to maintain said temperature differential closely to a constant value, and

flow-measuring means responsive to the flow of said combustible gas as regulated by said controllable means for measuring the rate of flow of said combustible gas.

10. Calorimeter apparatus comprising:

a combustion chamber,

an exhaust passage adjacent to the outside of said combustion chamber,

"means to supply combustion-supporting 13 a gas burner positioned Within said combustion chamber.

, controllable means to supply combustible 'gas to said gas burner,

gas to said gas burner, r

a controller responsive to said temperature difierential measurement controlling said controllable means whereby the flow of said combustible gas is regulated to maintain said temperature differential closely to a constant value, and

11. A calorimeter comprising;

a source of combustible gas whose calorific value is to be determined supplied to,

a gas burner mounted in a combustion chamber,

a supply of a constant mass flow rate of air to said combustion chamber,

said flow rate of air being sufiiciently large so that the heat absorbing capacity of the total air fiowris large compared to the heat absorbing capacity of the total products of combustion,

a control of the flow of combustible gas to the burner such that the temperature rise of air and products of combustion due to liberation of the lower heat of combustion of the combustible gas is maintained constant whereby the flow of the combustible gas is maintained at a rate so that the total thermal energy supplied by the gas, as measured by its lower heat of combustion, is maintained substantially constant, and

a measurement of the flow rate of the combustible gas said measured flow rate of gas being a determinate function of its calorific value.

12. Calorimeter apparatus comprising:

a gas burner having its orifice positioned within said combustion chamber,

valve means controlling combustible gas flow through said gas inlet line,

an .air inlet into said combustion chamber having its discharge positioned substantially beneath said gas burner,

a second temperature-sensing means for measuring the temperature of the product of combustion of said gas and air admixed with excess air,

a valve controller responsive to said temperature differential measurement controlling said valve means as a function of said temperature differential measurement whereby said combustible gas is regulated to a constant rate of thermal delivery regardless of combustible gas composition so as to produce a constant temperature differential measurement, and

flow measuring means including a metering orifice responsive to the regulated flow of said' combustible gas in said gas inlet line for continually measuring the flow rate of said combustible gas whereby said flow rate measurement is an inverse function of the heat of combustion of said combustible gas.

13. Calorimeter apparatus comprising;

a combustion chamber having :an opening for removal of gases at the upper portion thereof,

an exhaust chamber adapted to receive said gases from said opening in said combustion chamber and having at least one bafiie for directing said gases in a convoluted path through said exhaust chamber and having a portion of said exhaust chamber substantially surrounding the upper portion of said combustion chamber,

a gas burner having its orifice positioned within said combustion chamber,

valve means controlling combustible gas flow through said gas inlet line,

a valve controller responsive to said temperature differential measurement controlling said valve means as a function of said temperature differential measurement whereby said combustible gas is regulated to a constant rate of thermal delivery regardless of combustible gas composition os as to produce a constant temperature differential measurement, and

flow measuring means including a metering orifice responsive to the regulated flow of said combustible gas in said gas inlet line for continually measuring the flow rate of said combustible gas whereby said flow rate measurement is an inverse function of the heat of combustion of said combustible gas.

- 14. The calorimeter apparatus of claim 12 wherein the reciprocal of the square root of said flow rate measurement of said combustible gas is proportional to a Wobbe Index defined as the calorific value of the gas per standard cubic foot divided by the square root of the gas specific gravity.

15. The calorimeter apparatus of claim 12 having the output of said flow-measuring means control the flow of a supply gas in a gas supply line having a like composition to said combustible gas whereby a constant rate of thermal delivery of said supply gas is maintained through said gas supply line.

16. The calorimeter apparatus of claim 9 with;

a test gas inlet to said gas burner connected thereto in parallel with said controllable means to supply combustible gas,

means for supplying test gas to the input of said test gas inlet at a constant volumetric flow whereby the output of said flow-measuring means responsive to the flow of said combustible gas is inversely proportional to the thermal content per cubic foot of the 15 test gas so long as said combustible gas composition is constant.

17. The calorimeter of claim 9 together with;

a second controllable means for supplying a test gas to said gas burner at .a controlled constant volume connected in parallel with the first controllable means to supply combustible gas whereby the heat content per volumetric unit of said test gas is determined by said floW-measuring means.

18. The calorimeter apparatus of claim 9 with;

a main gas line flow-measuring device in a main gas supply line,

a divider having a first input responsive to the output of said main gas line flow-measuring device and having a second input responsive to the output of said flow-measuring device of said calorimeter apparatus,

a provision for supplying combustible gas to said calorimeter apparatus from said main gas supply line,

and a square root extractor responsive to the output of said divider whereby the output of the square root extractor produces a measurement of the British thermal unit per minute flow in said main gas supply line.

19. The calorimeter apparatus of claim 1 wherein said first and second temperature-sensing means are thermocouples connected in series providing said temperature diflerential measurement across the series combination.

20. The calorimeter apparatus of claim 11 in combination with a flow-measuring device in a main gas flow line whereby said combination produces a rate of thermal delivery measurement.

21. A method of determining the calorific value of a combustible gas comprising the steps of;

mixing said combustible gas with a supply of combustion-supporting gas and burning the resulting mixture,

ascertaining the temperature differential between the combustion-supporting gas and the products of combustion of said mixture,

regulating the flow of said combustible gas to maintain said temperature differential substantially constant, and

meansuring the resulting fiow rate of said combustible gas which flow rate is related to the calorific value of said combustible gas.

22. A method of determining the calorific value of a combustible gas comprising the steps of;

ascertaining the temperature difierent-ial between the combustion-supporting gas and the products of combustion of said mixture, and

regulating the flow of said combustible gas to maintain said temperature diflerential substantially constant,

whereby the resulting flow rate of said combustible gas is related to the calorific value of said combustible gas.

References Cited UNITED STATES PATENTS 2,349,521 5/1944 Schmidt 137-6 2,674,879 4/1954 McEvoy 73-190 2,105,017 1/1938 SufirOn 73194 2,141,453 12/1938 Schmidt 73l90 2,285,866 6/1942 Markle 73190 2,574,665 11/1951 Schuller 73-190 2,847,850 8/1958 Spink 73-30 JAMES J. GILL, Primary Examinler.

EDDIE SCOTT, Assistant Examiner.