MXPA99000546A - Measurement of the warming value of a gas using combustion without fl - Google Patents

Abstract

A heating value is calculated by a microcontroller (12) from the heating value of a reference gas, and from the flow rates and the energy levels determined as the gas is burned by a flameless combustion process. The fuel gas is mixed with a combustion support gas, such as air, and flowed to a body of material (26, 52) which is heated to a temperature sufficient for the oxidation of the gas mixture. The size of the spaces in a first mode of a heating device (9, 11, 25, 26) and in a second mode of the heating device (50) are limited to prevent the formation of an open flame. In a preferred "sparse mixing" mode, the gas-air mixture of the reference gas, and the gas-air mixture of the sample gas, respectively, are each adjusted until a selected energy level of the gas is reached. combustion at a temperature lower than that of the stoichiometric combustion point. In a second "rich mixture" mode, the gas-air mixture of the reference gas, and the gas-air mixture of the sample gas, respectively, each adjust a "rich mixture" to reach a point of stoichiometric combustion. Based on flow rates and the selected energy ratio, the heating value or the sample gas is calculated by the microcontroller (12) and output to a visual display or other output device.

Description

MEASUREMENT OF A GAS HEATING VALUE USING FLAME-FREE COMBUSTION TECHNICAL FIELD The field of the invention is that of methods and apparatus for determining the value of gas heating. DESCRIPTION OF THE PREVIOUS TECHNIQUE The measurement of the heating value of natural gas is important to control combustion and is a necessary measurement in the distribution and sale of natural gas.

There are four useful methods to measure the heating value. The first method to measure the heating value is the calorimetric measurement in which a gas volume is burned. A quantity of heat is released by the complete combustion and accumulates and measures carefully. The amount of heat released is manifested by a change in temperature. This method is the original method used and usually requires extreme control of flows and temperatures. The apparatus usually requires extensive maintenance. The second method to measure the heating value is the analysis of constituents. Using gas chromatography, the fraction of each chemical constituent in the gas is determined. Then the heating value is determined by adding the heating values for the individual constituents according to their presence fractional. The problem with the analysis of constituents is the reliability of the device and its linearity. Gas chromatographs require constant maintenance and have a limited range for measuring the heating value unless calibrated with a reference gas that is very similar to the sample gas. The third method is stoichiometry, in which combustion is completed substantially with a perfect amount of oxygen. In this case, the natural gases are burned with air and the fuel-air-to-air ratio is adjusted that the combustion results in either a maximum flame temperature or the stoichiometric point of perfect combustion, ie the cutting edge knife when there is no remaining oxygen. Clingman, in the United States Patent of North America Number: 3,777,562, is an example of the third method. In Cliugman, the heating value is measured by the combustion of a gas with quantities of air that are adjusted to obtain the maximum flame temperature. This is further described in the Patents of the United States of North America Numbers: 4,062,236; 4,125,018; and 4,125,123. In each of these patents, combustion of the air-gas mixture is carried out with a combustion flame on top of a burner and with a temperature sensing device such as a thermocouple. Certain environments can not be served by the team that presents an open flame. The fourth method uses catalytic combustion. The gas is passed over a heated catalyst and oxidized. The amount of heat released can be measured either by changes in temperature related to the catalytic reaction, by changes in the energy supplied to heat the catalyst or by measuring the temperature of the catalytic material. Catalytic combustion or catalytic oxidation is a known phenomenon with hydrocarbons. A mixture of hydrocarbon gas and air in the presence of platinum and / or palladium material will produce an oxidation reaction. The reaction occurs at temperatures below the auto-ignition temperature associated with a hydrocarbon. For example, methane when mixed with air will ignite at a temperature of approximately 730 ° C and reach an open flame at a temperature exceeding 1600 ° C. Catalytic oxidation can be carried out at catalyst temperatures as low as 400 ° C, although efficient catalytic activity is achieved at temperatures close to 500-600 ° C. A problem with catalytic oxidation is the potential to poison the catalyst. Certain chemicals such as sulfur or lead and many others, can be combined with, and disable, a catalyst and thus eliminate its usefulness for measuring the heating value. In many processes, such as gas recovery from the filling of soil, the gases contain "poisons" in sufficient quantity to have a high probability of disabling the measurement process. SUMMARY OF THE INVENTION The present invention provides methods and apparatus for measuring the heating value of a gas using flameless non-catalytic combustion and variable molar flow rates for gas mixtures of samples supplied to the combustion apparatus. The present invention utilizes a body of inert material to receive and burn gas mixtures and a carrier gas, such as air. Under normal conditions, the gas would be oxidized or burned and a flame would form. In the present invention, inert material is formed with only small voids, so that an open flame is prevented by quenching the rapid heat transfer. The combustion process operates at a temperature above the auto-ignition temperature of a gas mixture and still burns the gas without producing an open flame, thereby making the process convenient for operation in special environments. In most measurements of the heating value, extreme stability of geis and air volumes is required to achieve precision. Many of the methods described above use flow regimes constants or constant gas volumes. The present invention eliminates the need for these constant values. In addition, the oxidation or combustion of the present invention can be carried out with concentrations of mixtures over a wide range extending beyond the stoichiometric mixture of the gas. This process can not be "poisoned" in the catalytic sense, because catalysis in combustion is not involved. The combustion energy of the gas, or the combustion temperature, is measured as the gas mixture flows into the combustion device. The associated molar flow rate of the gas is also measured. A reference gas and the sample gas are measured alternately and repeatedly. The only requirement is that the molar flow rate of the sample and the reference gas are compared to an adequate combustion power or a maximum combustion temperature for the combustion device. In one embodiment, the air flow is established in excess of the air required to burn the gas, a gas-tight condition. The combustion gas is mixed with air, and the mixture is flowed on or through a heated body of solid material and the mixture is oxidized. The combustion energy and the molar gas flow rate vary with time. At a selected combustion energy, the molar flow rate of the gas is measured by suitable sensors, and these parameters they are used to calculate the heating value of a reference combustion gas and then of a sample combustion gas. In a second embodiment, the air flow is established below the air flow required to burn the gas under stoichiometric conditions, to provide a rich gas mixture. The combustion gas is mixed again with the air, and the gas-air mixture is made to flow in contact with a heated body of solid material where the mixture is oxidized. The combustion energy is measured continuously. The molar flow rate of the gas is determined when the combustion energy reaches a minimum value corresponding to the maximum value of the combustion. At this maximum combustion energy, the molar flow rate of the gas is measured by suitable sensors. In either a "low mix" or a "rich mix" mode, a reference gas cycle is followed by one or more sample gas cycles. For the mode using the lean gas mixture, the heating value of the sample gas is calculated based on the known heating value of the reference gas and the sample gas, the flow rates of the reference gas and the gas of shows at the selected energy levels, and in some cases a proportion of the energy levels for the reference gas and the sample gas.

For the mode using the rich gas mixture, the heating value of the sample gas is calculated based on the known heating value of the reference gas, the level of combustion energy corresponding to the stoichiometric combustion, and the flow rates of the reference gas and the sample gas at the energy level for the stoichiometric combustion. In either of the two embodiments, the fuel-to-air mixture can be varied by letting the pressure drop in a volume chamber, to produce a decreasing flow of fuel that progressively shortages the fuel-to-air mixture. The molar flow rates for a reference gas and a sample gas during the respective combustion cycles occurring within the heated body of the solid material are measured. The heating value for the reference gas is typically a value stored in the memory. The fuel-air mixture can also be varied by direct control of air and gas flow rates using, for example, conventional pressure controllers. Various objects and advantages will be apparent to those with ordinary skill in the art from the description of the preferred embodiment that follows. In the description, reference is made to the accompanying drawings, which are part of the present, and which illustrate examples of the invention. However, these examples are not exhaustive of the various embodiments of the invention and, therefore, reference is made to the claims that follow the description to determine the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of an apparatus for practicing the method of the present invention; Figure 2 is a detailed schematic diagram of an electrical circuit in the catalytic apparatus of Figure 1; Figure 3a is a schematic diagram of a combustion device used in the apparatus of Figure 1; Figure 3b is a graph of temperature versus longitudinal displacement within the combustion device of Figure 3a; Figure 3c is a schematic diagram of a second embodiment of a combustion device used in the apparatus of Figure 1; Figures 4a and 4b are graphs of the energy and the regime of molar flow versus time illustrating the operation of the apparatus of Figure 1; and Figure 5 is a flow diagram of the operation of a microcontroller in the apparatus of Figure 1. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring to Figure 1, an apparatus 10 for practicing the method of the present invention receives air from an external supply through the supply line 1. The air is used as a carrier gas and to remove other gases from the combustion apparatus 8. A reference gas is received from an external supply through the supply line 3. A sample gas is received, for which the heating value has to be determined, from an external supply through the supply line 15. The reference gas and the sample gas are to be mixed with varying amounts of air and burned in a combustion apparatus 8 which includes a heating element 9, a temperature sensor 11 and a porous body of inert solids (26 in Figure 3) which are heated by the heating element 9. The porous body of the inert solids 26 is composed of solids which have high temperature and high heat capacity and is usually formed of ceramic materials. The heating element 9 is located in or within the central section of the porous body 9 to provide an initial start temperature for the reaction. Inert solids 26 are typically heated to a temperature of 800 ° C or more. The heating element 9 is energized by electricity from the power supply circuit 19 (Figure 1). The temperature sensor 11 is embedded in the porous material to capture the temperature on the surface of reaction of the porous material. The temperature sensor 11 generates a signal as an input to the power source 19. This signal is recognized by the power source 19 as representative of the reaction temperature. The products of combustion escape from the combustion apparatus 8 into an exhaust stream 17. Additional steps can be taken to process the exhaust stream. The microcontroller 12 is a central processing unit (CPU) with interface circuits of A-to-D and D-to-A. The microcontroller 12 operates by executing instructions of the program, some of which are represented by blocks in the flow diagram in Figure 5, the instructions being stored in a memory also generally represented by reference 12. The apparatus 10 includes elements for producing regimes Variable flow of air and fuel gas to vary the mixtures for the reference gas and the sample gas, respectively. The apparatus 10 more particularly includes the outlet control valves 2 and 6 for controlling the flow of the sample gas or reference gas, respectively, for the restrictor 7. The flow rate (Expense) output is determined by the initial charge pressure in the chamber; volume 5, 14 and the flow properties of the flow restrictor 7. It is preferred that the flow rate of air-gas mixtures can vary continuously over some rank. However, the invention could also be employed with constant flow rates in other embodiments. And, although the preferred embodiments described more fully herein adjust the mixtures by adjusting the flow rates of the combustible gases, it is also known that these mixtures can be adjusted by adjusting the air flow rate. The supply line 3 for the reference gas is connected through the inlet flow control valve 4 to the volume chamber 5. The flow control valve 6 is closed during filling of the volume chamber 5 for close the exit. When the gas pressure in the volume chamber 5 reaches a predetermined but not critical level, usually set by the pressure of the external supply line 3, then the control valve 4 is closed. After the closing of the valve 4, the outlet control valve 6 opens allowing the gas flow of the volume chamber 5 through the flow restrictor 7, where it is then mixed with the air flow of the supply line 1 and passes through the porous body of inert solids 26. One way to measure the combustion temperature is to monitor the electrical power that is provided to the heater device 8 from the power supply circuit 10 to maintain a constant temperature in the sensor 11. Changes in this electrical power supplied to the heater 9 is a measure of the change in combustion energy or the combustion temperature of the combustion process in the combustion apparatus 8. As the gas flows out of the volume chamber 5, the pressure in the volume chamber is reduced. The microcontroller 12 monitors changes in pressure in the volume chamber 5 using a pressure transducer 13. At a previously selected level of combustion, as captured through the power supply circuit 19, a rate is measured or calculated. of the molar flow or a change in the molar content in the chamber 5 and is stored by the microcomputer 12. When the gas pressure in the volume chamber 5 reaches a low level, previously determined, but not critical, the control valve 6 is closed, thereby stopping the flow of the reference gas to the combustion apparatus 8. While a reference gas has been flowing to the combustion apparatus 8, the control valve 16 has been opened to fill the volume chamber 14 with the Sample gas from the supply line 15. The flow to the volume chamber 14 increases the pressure in the volume chamber 14 until a predetermined pressure is reached. It does not criticize, usually determined by the pressure in the supply line 15, and then the control valve 16 is closed. When the sample gas is going to flow into the combustion 8, the microcontroller 12 opens the control valve 2 to establish the flow of the sample gas through the restrictor 7 towards the combustion apparatus 8, when the mixture of the sample gas and air is burned. The power supply circuit 19 continuously adjusts the energy to the heater 8 to maintain a constant temperature as it is picked up by the sensor 11. As the gas flow rate is reduced, the energy changes for the heater 9 are inversely proportional to the combustion heat energy in the apparatus 8. Depending on the mode, the microcomputer 12 calculates and stores the molar flow rate from the volume chamber 14 for (a) a previously determined combustion level or (b) a previously changed determined at the level of combustion energy or (c) the condition of maximum temperature. It should be noted that the measurement of the molar flow rate using the pressure change rate in the volume chamber 5, 14, is of the type described in Kennedy, US Pat. Number: 4,285,245 to capture the molar flow rate in response to pressure changes due to the flow of gas out of a chamber. This eliminates the consideration of the molecular weight of the gas in the gas measurements. This flow meter is incorporated into a product offered by the transferee under the trade designation "TRU-THERM". It is not required to use two volume chambers, 5 and 14, but it is a preferred embodiment. Using a camera would slow down the measurement process because a single camera using two gases would require several cycles to discharge a residue of a combustible gas that remained in the chamber of a previous cycle. If the response speed is not a primary design goal, the measurement can be modified to use reference gas only infrequently and a single volume chamber can be used. Figure 2 illustrates the power supply circuit 19, the temperature sensor 11 and the heater 9 described above in relation to Figure 1. The circuit 19 is a bridge that maintains a constant resistance by heating and cooling by electrical elements. In ICL preferred embodiment, resistor 9 in Figure 2 is provided by a wire-wound platinum resistor. Platinum is selected due to its stable temperature coefficient over a wide range of temperature. The. resistance is Rj. = R ^ Q (1 + a-? T). The value of the resistor 20 and the resistor 9 is selected to provide the desired operating temperature at the energy levels selected for the operation of the porous body of solids 25 (Figure 3a). The wound wire resistor provides both the resistive heating element 9 and the temperature sensor 11 for the porous material 26. The resistors 21 are a pair of resistors that divide the applied voltage 24 to the bridge. In Figure 2, resistors 21 are shown with equal values, R0, which is not a strict requirement. In Figure 2, the amplifier 22 captures a difference between the central branch voltages in each bridge section and amplifies that difference. The result is applied to the FET energy 23 and changes the voltage 24 in the bridge until the central derivation voltages of the two sections are equal. Therefore, the electric power level in the heater-sensor 9, 11 is that required to maintain the resistance and temperature of the constant heater-sensor 9, 11. If combustion of the gas takes place, the combustion heating will raise the temperature of the material 26 and the applied electrical energy will be reduced proportionally to maintain the temperature constant to the sensor heater 9, 11. Figure 3a represents the general construction of a heating device forming a column of porous inert material 26. A tube 25 supports the porous material, in this example beads 26 of different sizes, and forms a column Ceramic or foam beads such as porous solids 26 can be used, and if uses foam the body can be a unitary body.The beads can be sized and have a changing surface character to control the emission of radiation components, which affects the regime of heat transfer of combustion products. The sensor heater 9, 11 is located in the central section of the porous material 26 and through the heating of the resistance the temperature of the material 26 is raised to a level higher than the auto-ignition temperature of the gas-air mixture. The small voids in the porous body of the solid material 26 are selected and characterized having a linear dimension of the order of the damping dimension of the gas flame. With methane, for example, the damping dimension is approximately 2.5 millimeters (0.060 inches). Methane does not burn with an open flame when the voids in the body of the solid materials 26 are less than 2.5 millimeters. The heat is transferred through the solid material 26 at a rate sufficient to prevent large increases in temperature that would be accompanied by an open flame. The combustion produces combustion products such as CC > 2 and (-> vapor A flame is a visual indication that the combustion products have insufficient heat capacity to carry out the heat of combustion by convection and conduction alone.The temperature of the products of combustion must then rise until the radiation level is high enough to radiate excessive heat.The conduction and convection regime increases in linear relation to the temperature. The radiation responds in proportion to the fourth power of the temperature, and provides an additional and stabilizing factor for the heat transfer rate. The temperature of the burned gases increases until the heat of combustion equals the heat losses. For natural gases, the temperature reaches frequencies of radiation in the visible spectrum and the flame is visible. In the present invention, the gas flow rates through the combustion apparatus 8 are also limited by the design to limit the total heat available from the combustion reaction. If the available energy of the combustion is too large, the electrical energy can not be reduced enough to control combustion. Therefore, limits are placed on the flow rate of the gas-air mixture to limit the heating energy available for combustion to less than the electrical energy required to heat the solid material 26 above the auto-temperature. ignition. The structure of the solids surrounding the small spaces allows the transfer rate between the products of the combustion gas and the heater to be large enough to avoid large increases in temperature and thereby stabilize the combustion temperature. The material body 26 should have enough heat transfer capacity to deaden the flame without requiring high radiation temperatures. Air and gas are introduced into the base of the column and travel through the body of material 26. Due to the heat flow from the central section, the temperature 28 (Figure 3b) of the inlet section of the combustion material 26 increases and the gas-air mixture is heated and mixed as it flows to the reaction zone in the center- Beyond the reaction zone, temperature 29 (Figure 3b) in column 25 cools as the gases pass to the exhaust 17 The temperature profile of the porous bed is indicated in the graph attached in Figure 3b. When the air-gas mixture reaches the reaction zone, and when the temperature is above the point of self-ignition, the gas is oxidized or burned to release energy as the heat of combustion. The heat released raises the temperature of the reaction zone and raises the resistance of the platinum heater 9. The power supply circuit 19 for the heating element 9 captures this rising temperature and reduces the electrical energy to maintain a constant temperature in the reaction zone. The change in energy corresponds to the increased combustion energy or temperature of the porous bed and is the indicator of the activity of the porous bed. Figure 3c illustrates an alternative mode of a heating device 50. A spiral of platinum wire 51 is molded in a body of ceramic material 52. An external structure for the heating device 50 comprises the vertical wall (s) 53, and the device is cylindrical , but it can be rectangular or have other forms in cross section in other modalities. The filter elements 54, 55 are made of porous material to allow passage of gas mixtures, while filtering particulate matter. The filter elements 54, 55 form the upper and lower end walls of the heating device 50. The vertical wall 53 and the filter elements 54, 55 are closely spaced from the heating element 51, 52, so as to provide the spaces 56, 57 of adequately small dimension to dampen any higher temperature reaction before a flame forms. The spaces 56, 57 are selected and characterized by having a linear dimension of the order of the damping dimension of the gas flame. With methane, for example, the damping dimension is approximately 2.5 millimeters (0.060 inches). Methane does not burn with an open flame when the voids in the body of solid materials 56, 57 are less than 2.5 millimeters. The heat is transferred through the solid material 52 at a rate sufficient to prevent large increases in temperature that would be accompanied by an open flame.

In operation, the spiral 51 is supplied by electrical energy from the power circuit 19 (Figure 1). as the mixed gas flows through the heater 50, it oxidizes and produces heat in a normal manner but the heat transfer rate to the surrounding wall 53 is fast enough to allow the gases to cool - without significantly increasing product temperatures of combustion. This is known as "cushioning" the flame. If the heater is heated to a constant temperature above the auto-ignition temperatures for the mixed gases, then the combustion power increases, the electrical energy must decrease to reflect the magnitude of the combustion energy released by the mixed gases . In a preferred embodiment of "sparse mixture", the gas-air mixture of the reference gas, and the gas-air mixture of the sample gas, respectively, are variably lowered to a selected energy level of combustion at a lower temperature of the level at which the stoichiometric combustion point is reached. In a second "rich mixture" mode, the gas-air mixture of the reference gas, and the gas-air mixture of the sample gas, respectively, are each variablely decreased from a "rich mixture" to reach a stoichiometric combustion point, which corresponds to the largest combustion energy within the body of solids 26, 52.

The molar heating value, Hm, is defined as the amount of heat that can be released by the combustion of one mole of gas. The molar heating value is expressed in units of energy per mole. In the mode of "sparse mixing", the molar flow rate of a gas,? G, with units of moles per second, is multiplied by the molar heating value. The result is the combustion power described as Pgas = Hm? Rig and the change in combustion energy can be written as? Pgas = Hp? An .. If the changes in the combustion energy of the gas sample and the reference gas are measured between the same two energy levels selected (see Figure 4a), then equalizing the two changes of combustion energy gives as result equation 1 as follows: where the subscripts r and s refer to the reference gas and the sample gas, respectively. A desirable feature of this invention is that the response speed can be improved by terminating the individual measurement cycles before completing them. If the changes in combustion energy during the reference cycle and the sample cycle are not equal, but are related by a known proportion, then Equation 1 can be modified by introducing a correction factor? , which is the proportion of the changes in the energy of combustion and equation 1 can be rewritten as: where ? is the proportion of the two changes in combustion energy. It should be clear that? it can take values that vary between zero and unity. A mole of gas contains a fixed number of molecules, known as Avogadro's number, and occupies a definite volume Vm, which is a function of temperature and pressure. At 0 ° C and 14,696 psia, the volume for an ideal gas is 22.4138 liters. The compressibility effect must be recognized and used to define the molar volume of a real gas as Vm rea = Vm idealzreal with units of volume per mole and where the compressibility, zreaj, is calculated at the temperature and pressure of the measurement. Therefore the volume heating value (energy per unit volume) of the gas is written as: The heating value, as defined in Equations (1) to (3), is related to a standard temperature and pressure according to the general gas laws and the factors known in the gas physics and gas measurement technique.

The molar flow rate of the gas flowing from the volume chambers 5, 14 is captured by measuring the rate of change or pressure change in the volume as the gas is removed. The relationship between the molar gas flow regime and the pressure change regime is obtained from the general gas law and is expressed as follows: PV (4) n R where n is the molar flow regime, P is the rate of change of pressure, and Z is the compressibility factor. For the "rich mix" mode, the reference gas is introduced at sufficiently frequent intervals to ensure that the moisture has not changed, and this allows the ambient air to be used as the combustion support gas. If the reference gas is not introduced at these sufficiently frequent intervals, then the air is preferably dried to a very low humidity, such as less than 5 percent relative humidity. In the "rich mix" mode, the maximum combustion temperature corresponding to the minimum level of energy input (See Figure 4b) identifies the stoichiometric combustion point. This mode requires the measurement of the molar flow rate of the gas, n "in units of moles per second. Since the stoichiometric points of the sample gas and the reference gas are measured, the heating value is formed using a ratio of the molar flow rates (n) and the volume heating value (H) of the reference gas according to Equation 5 as follows: where the subscripts r and s refer to the reference gas and the sample gas, respectively. Figures 4a and 4b illustrate the combustion rate against the molar flow rate for the mixture mode of "scarce gas" and the "rich mixture" modality, respectively. When the gas flow is not present, only air is supplied to the combustion material and the electric power (P) supplied to the heated body of material is maximum and stable. The temperature of the combustion material is constant, and this is represented by the constant levels of electrical energy in Figures 4a and 4b. When the reference gas or sample gas is flowed to the combustion heater, the combustion process adds heat to the body of material and the energy controller reduces the electrical energy (P) to the heater in the exact amount as energy is added Of gas. As the gas flow rate is reduced due to the reduced gas pressure in the volume chambers 5, 14, the energy of the combustion gas is reduced. The electrical energy must then be increased to maintain a constant temperature in the heated material. When the The combustion temperature is at a maximum, the minimum electrical energy needs to be supplied to heat the material as shown in Figure 4b. As shown in Figure 4a, the molar flow rates for the reference gas are determined for two selected energy levels. The molar flow regimes for the sample gas are then determined for the same two selected energy levels. As shown in Figure 4b, a gas mixture rich in the reference gas, which contains more gas molecules than those necessary for stoichiometric combustion, is flowed to the combustion material. As the flow rate of the reference gas is reduced, the maximum temperature state and the maximum gas combustion energy (minimum level of electrical energy) are reached. There, the molar flow rate of the referenced gas is measured. This cycle is then repeated for the sample gas, until the maximum temperature state and the maximum gas combustion energy (minimum level of electrical energy) is reached and the molar flow rate of the reference gas is measured. These data are read by the microcontroller 12, which then calculates the heat content of the sample gas. The rate of air flow through the porous material 26 is not critical and can vary by ± 10 percent in a slow manner, but must be stable between the cycles of Reference and sample. Figure 5 shows the operation from the point of view of the microcontroller 12 when executing its control program. The start of the operation is represented by the start block 30. The microcontroller 12 executes instructions to select either the reference gas cycle or the sample gas cycle as represented by the process block 31. If the reference gas cycle, the microcontroller 12 executes additional instructions represented by the process block 32, to open the valve 16 and allow the sample gas to fill the volume chamber 14 in preparation for the sample gas cycle. Next, as represented by the process block 33, the microcontroller 12 executes other instructions to open the valve to allow the reference gas to flow to the combustion device 8. The microcontroller 12 executes instructions instructions represented by the process block 34 to start sampling the molar flow rate (n) and the changes in electrical power (? P) required by the combustion device 8. The microcontroller 12 then executes the instructions represented by the decision block 35 to test the regime of molar flow corresponding to a maximum temperature and a maximum gas combustion energy (minimum electrical energy) (Figure 4b) or for the molar flow regimes corresponding to two energy levels selected during the same cycle (Figure 4a). If the result is "NO", cycle again to continue with another sample. If the result is "YES", the instructions represented by block 36 are executed to finish the first cycle and prepare for the next cycle. As represented by the process block 36, the microcontroller 12 executes instructions to stop the gas flow of the reference gas by closing the valve 6. The microcontroller 12 then executes the instructions represented by the process block 37 to change the selection to the other gas cycle. The microcontroller 12 then executes the instructions represented by the process block 38 for cleaning the chamber 5 and the combustion apparatus 8. Next, the microcontroller 12 then executes the instructions represented by the process block 39 for storing the final flow rate and the energy values for the cycle that has just been completed. A check is then made, as represented by the decision block 40, to see if both a reference cycle and a sample gas cycle have been completed within a recent period of time. If the result is "YES", the data can be used to calculate the heating value as represented by the process block 41. The heating value is then taken to a visual display (not shown in Figure 1) or other type of output device. If the data is not complete, the result of decision block 40 is "NO", and the program returns to start a new gas measurement cycle, such as the sample gas cycle, in block 32. This has been a description of examples of how the invention can be carried out. Those of ordinary skill in the art will recognize that various details can be modified to arrive at other detailed embodiments, and these embodiments will be within the scope of the invention. Therefore, to make known to the public the scope of the invention and the embodiments covered by the invention, the following claims are made.

Claims (37)

1. CLAIMS 1. A method for measuring the heating value of a combustible gas, characterized in the method by the steps of: flowing a first mixture of a reference gas and a combustion support gas in contact with a heated body of material ( 26, 52) to cause flameless combustion of the reference gas; varying the first mixture of the reference gas and the combustion support gas to obtain a changing level of combustion energy; detecting a flow regime of the reference gas at one or more selected first combustion energy levels; flowing a second mixture of a sample gas and a combustion support gas in contact with the heated material body (26, 52) to cause the flameless combustion of the sample gas; varying the second mixture of the sample gas and the combustion support gas to obtain a changing combustion energy level; detecting a flow regime of the sample gas at one or more second selected combustion energy levels; and calculate the heating value of the sample gas in response to the ratio of the flow rate of the reference gas and the flow rate of the sample gas in the first and second selected combustion energy levels, respectively. The method of claim 1, further characterized in that the combustion energy levels selected correspond to a first level of electric power selected for the combustion of the reference gas at the maximum combustion energy, and a second level of selected electrical energy for combustion of the combustible gas at the maximum combustion energy, respectively. The method of claim 1 or 2, further characterized in that the body of the material (26, 52) is heated to a temperature that is above the auto-ignition temperature of the gas-air mixture. The method of claim 1, further characterized in that the flow rate of the sample gas is limited to supply less combustion energy than an amount of electric power supplied to heat the body of the material. The method of claim 1 or 2, further characterized in that the combustion support gas is air. The method of claim 1 or 2, further characterized in that the step of varying the first mixture and the step of varying the second mixture further comprises regulating the supply of at least one of the gases in the mixtures. The method of claim 1 or 2, further characterized in that the step of varying the first mixture and the step of varying the second mixture further comprises regulating the supply of the combustion support gas. The method of claim 1 or 2, further characterized in that a supply of combustion support gas in the reference gas flow is equal to the supply of combustion support gas in the sample gas flow. The method of claim 1 or 2, further characterized in that the regimes of the reference gas and the sample gas are molar flow regimes. The method of claim 1, further characterized in that each of the steps of varying the first mixture of the reference gas and varying the second sample gas mixture further comprises allowing a variable decrease in the reference gas pressure and the sample gas, respectively. The method of claim 1, further characterized in that at least one of the first mixture and the second mixture is varied to obtain at least two levels of combustion energy having a common energy value for two different compsitions of the respective one of the mixtures The method of claim 1 or 2, further characterized in that the method is carried out at ambient temperatures from about -22.00 ° C (-40 ° F) to 71.50 ° C (130 ° F). The method of claim 1 or 2, further characterized by heating the body of material (26, 52) and capture the temperature of the material body through a constant resistance bridge circuit (19). The method of claim 1 or 2, further characterized by the passage of air flowing only through the material body (26, 52) to establish a baseline value for the measurement of combustion. 14. An apparatus for determining the heating value of a combustible gas, the apparatus being characterized by: a heated body of material (26, 52) for burning gas mixtures without the formation of a flame; a first flow element (1, 7, 8) for flowing a mixture of the fuel gas and a combustion support gas in contact with the heated body of material to cause oxidation of the mixture; a second flow element (2, 5, 6, 14) for selectively flowing either a reference fuel gas or a fuel gas to a first element; a first sensor element (19) for capturing a combustion energy of the fuel gas when the fuel gas is made to flow in contact with the body of material; a second sensor means (13) for capturing at least one molar flow rate of the fuel gas corresponding to at least one combustion energy selected from the fuel gas; and an element (12) that responds to the first sensor element (19) and the second sensor element (13) to calculate the heating value of the sample fuel gas. The apparatus of claim 14, further characterized in that the first sensor element (19) is operable to capture an electrical level corresponding to a maximum combustion energy for the sample fuel gas; and further characterized in that the second sensor element (13) is operable to capture at least one mode of molar loosening of the fuel gas corresponding to a maximum combustion energy for the sample fuel gas. 16. The apparatus of claim 14 or 15, further characterized in that the material body (26, 52) is heated to a temperature that is above the auto-ignition temperature of the gas-air mixture. 17. The apparatus of claim 14, further characterized by an element to limit the regime of gas flow (12) supply less energy than an amount of electric power supplied to heat the body of material. 18. The apparatus of claim 14 or 15, further characterized in that the first sensor element (19) includes a sensor for capturing combustion energy without a flame. The apparatus of claim 14 or 15, further characterized in that the second flow element (2, 5, 6, 14) includes an element for providing a variable, decreasing flow rate for the fuel gas to obtain variant combustion energy of combustible gas. The apparatus of claim 14 or 15, further characterized in that the first flow element (1, 7, 8) is controlled separately from the second slack element (2, 5, 6, 14). The apparatus of claim 14 or 15, further characterized in that the element for separately controlling the flow of the fuel gas (2, 5, 6, 14) includes a molar flow meter (12, 13). 22. The apparatus of claim 14 or 15, further characterized in that the combustion support gas is air. 23. The apparatus of claim 14 or 15, further characterized in that the first flow element includes an element for interrupting the flow of the fuel gas (12, 4, 16) to flow only a combustion support gas in contact with the body of material to establish a baseline value for the combustion temperature. The apparatus of claim 14 or 15, further characterized in that the heated body of material (26) further comprises a plurality of solids (26) bonded together so as to provide a porous body of solid material. 25. The apparatus of claim 14 or 15, further characterized in that the heated body of material (52) further comprises a heating element (52) enclosed by closely spaced walls (53) to prevent any flames as from gas mixtures. air will rust. 26. An apparatus of the type for determining the value of a combustible gas, the apparatus comprising: a porous body of material (26, 52, 53) containing one or more spaces with linear dimensions (56, 57) not greater than one dimension damping for fuel gas; a heating element (11, 51) disposed in the porous body of the material (26, 52) for heating a portion of the porous body of material (26, 52) to at least the auto-ignition temperature of the fuel gas; a sensor (9, 19) for capturing the combustion level and for generating a signal that responds to it; and a processor (12) that responds to the sensor signals (9, 19) to calculate the heating value of the fuel gas. 27. The apparatus of claim 26, further characterized in that the porous body of material (26,52) is formed of non-catalytic material. The apparatus of claim 27, further characterized in that the porous body of material (26) further comprises a plurality of solids (26) accommodated in a column to provide a porous body of material with a plurality of spaces between the solids. 29. The apparatus of claim 28, further characterized in that the spaces have a linear dimension of not more than about 2.5 millimeters (0.060 inches). 30. The apparatus of claim 29, further characterized in that the plurality of solids (26) are beads of ceramic material. 31. The apparatus of claim 30, further characterized in that the beads (26) of ceramic material are sized. 32. The apparatus of claim 30, further characterized in that the beads (26) of material ceramic are formed of non-catalytic material. The apparatus of claim 26, further characterized in that: the porous body of material (52, 53) further comprises a housing (53) and a body of ceramic material (52) disposed in said housing; further characterized in that the heating element (51) is disposed in the body of ceramic material (52); and further characterized in that the porous body of material (52, 53) has an interior space (56, 57) between the housing (53) and the body of ceramic material (52) with linear dimensions that are not greater than the damping dimension for fuel gas. 34. The apparatus of claim 33, further characterized in that the housing (53) and the ceramic material (52) are formed of non-catalytic material. 35. The apparatus of claim 34, further characterized in that the heating element (51) further comprises a spiral of platinum wire contained in a body of ceramic material. 36. The apparatus of claim 33 or 35, further characterized in that the interior space (56, 57) has linear dimensions no greater than 2.5 millimeters (0.060 inches). 37. The apparatus of claim 33 or 36, further characterized in that the housing (53) has opposite ends with one inlet for the gas at an opposite end and one outlet for the gas at another opposite end and wherein the combustion device comprises filters (54, 55) disposed at opposite ends of the accommodation (53. SUMMARY A heating value is calculated by a microcontroller (12) from the heating value of a reference gas, and from the flow rates and the energy levels determined as the gas is burned by a flameless combustion process. The fuel gas is mixed with a combustion support gas, such as air, and flowed to a body of material (26, 52) which is heated to a temperature sufficient for the oxidation of the gas mixture. The size of the spaces in a first mode of a heating device (9, 11, 25, 26) and in a second mode of the heating device (50) are limited to prevent the formation of an open flame. In a preferred "sparse mixing" mode, the gas-air mixture of the reference gas, and the gas-air mixture of the sample gas, respectively, are each adjusted until a selected energy level of the gas is reached. combustion at a temperature lower than that of the stoichiometric combustion point. In a second "rich mixture" mode, the gas-air mixture of the reference gas, and the gas-air mixture of the sample gas, respectively, each adjust a "rich mixture" to reach a point of stoichiometric combustion. Based on flow rates and the selected energy ratio, the heating value of the sample gas is calculated by means of the microcontroller (12!) and goes to a visual display or to another output device. • k -k -k -k -k