NO840654L - DEVICE FOR DETERMINING AN UNKNOWN PROPERTY OF A GAS OR STEAM TEST - Google Patents

Description

The invention concerns determination of the properties of substances in gaseous form, and more specifically determination of calorific value, or heat of combustion, density, and moisture or moisture content of a gas or a vaporized liquid.

Heating value

Fuels in liquid or gaseous form are burned to produce heat for a variety of applications. These fuels may vary in composition from predominantly single carbon hydrocarbons to hydrocarbons having many carbon atoms arranged in branched chain or ring structures, or may be mixtures of many hydrocarbons. A fuel often contains compounds that are inactive with respect to normal combustion. It is useful to know the calorific value of a fuel, i.e. the amount of heat that a certain quantity of a fuel will produce when burned under a certain set of conditions. Although the calorific values for most pure substances that can be used as fuels are readily available in the literature, the fact that an innumerable amount of mixtures of compounds are used as fuels results in a continuing need to make calorific value determinations. Devices and methods for determining heat values are used both in laboratories and in industrial processes for the laboratory. It is often desirable to monitor the calorific value of a liquid stream on a continuous basis. In the following, several examples of applications for heating value monitoring are given.

As the value of a fuel largely depends

of the amount of heat it is capable of producing, it is more correct to set the fuel price in accordance with calorific value and quantity, instead of just quantity. Natural gas is a very good example. Today, natural gas is almost always sold on the basis of dollars per thousand BTU (British Thermal Units), or kroner per kilocalorie, instead

the previously used basis of dollars per SCF. This is mainly a result of the price increases in recent years. Inaccuracy in the number of transmitted BTUs is now far too costly to tolerate. Another factor that necessitates transfer of custody on the basis of heat quantity is that natural gas heating values tend to

to vary more, as gases from different places are routed through pipelines all over the country and gas is imported.

A gas stream that is a by-product of the operation of a factory or plant is often piped to a nearby plant to be burned as fuel. As in the above example with natural gas, the payment for the gas will probably be based on its heating value and the amount burned. The average calorific value can be determined by periodic laboratory analysis, or the calorific value can be measured continuously as the gas flows into the user's facility. The calorific value of the by-product gas can further be determined for reasons other than price fixing, before the actual use of the gas begins. Design and management of the burner, the combustion plant and other equipment involved in processing and burning the gas depends in part on the range of heat values that can be expected. The calorific value of a by-product gas will normally vary over a fairly large range, compared to natural gases, and the average calorific value will be different from the calorific value of natural gases.

In certain manufacturing processes, the temperature and/or oven atmosphere must be maintained in a relatively narrow range to ensure product quality. Changes in the calorific value of the fuel supplied to the furnace or heating plant may necessitate corrective treatment to avoid a deviation from the acceptable range. An increase in the heating value of a fuel indicates that more oxygen must enter into contact with it. Where it is required that a combustion plant atmosphere must be rich in oxygen, an increase in the rate of oxygen dilution in the combustion plant caused by an increased heat value can create quality problems. The solution is often to increase the oxygen flow as soon as an increase in calorific value is detected by a calorific value monitor, thereby avoiding significant dilution.

Fuel savings can be realized by using

a heating value monitor in a combustion zone control system.

The amount of air supplied to the combustion zone can be adjusted by reference to the heating value monitor, so that the excess amount of air is small and thus saves fuel that is used for heating unnecessary air, and so that the use of extra fuel as a result of incomplete combustion is avoided.

There are many applications, such as, for example, as mentioned above, where a device and a method for determining heating value on an instantaneous and continuous basis is necessary. The most common method for determining calorific value in a laboratory is by using a calorimeter in which the fuel is burned under precisely controlled conditions and the rise in temperature of a water bath that is heated with the help of burned fuel is measured. Although accurate, this method is time consuming and cannot be adapted to provide a continuous reading of calorific value for a continuous flow of a sample to the calorimeter. As previously mentioned, there are also many applications where a number of laboratory determinations of heating value need to be carried out quickly and not necessarily with the accuracy of a main standard. The present invention is expected to be significant in covering or satisfying these applications.

For the purpose of comparison with the present invention, an on-line calorimeter device shall be described. ning with continuous reading available from Fluid Data, Inc., Merrick, New York. In this instrument, variations in heat produced by a test burner are offset or equalized by setting air flow to the burner, in a zero-balancing manner, and air flow rate is related to heat value. A gas sample is piped from a stream to be sampled to the sample burner, and the gas flow rate is kept constant. The flame heats a heat expansion element whose movement adjusts the air flow to the burner via a mechanical and pneumatic joint mechanism. The air flow is measured independently by means of a measuring aperture and displayed on a scale with a division expressed in terms of heat value.

Several recently issued patents show the interest in methods for determining heating value. In US Pat. No. 4,337,654, a fixed amount of gas is burned with a measured amount of air and hydrogen or oxygen is supplied by means of an electrolytic cell. The amount of hydrogen or oxygen that is added is controlled by means of an oxygen sensor and is related to the heat value of the burned gas. US patent no. 4 355 5 33 describes a method for determining heating value where information developed using a gas chromatograph is correlated with heating value. US patents 4,326,873 and 4,329,874 describe another calorimeter in which gas is oxidized.

A recent article by Van Rossum, pointing out the need for the present invention, can be found in the Oil and Gas Journal of January 3, 1983 (page 71, part 1) and January 10

1983 (page 85, part 2).

For background information regarding various gases and liquids used as fuels and in combustion, reference may be made to the fuel section of Perry.1's Chemical Engineers Handbook, published by McGraw-Hill, and particularly to pages 9-1 to 9 - 33 of the fourth edition.

Density

It is important to know the density of a gas in many industries, particularly in the area of petroleum and petrochemical processing. A typical application is a mass flow meter where volumetric flow rate is combined with the density of the flowing stream to produce mass flow rate.

A person attempting to measure density, especially on a continuous on-line basis, has a limited range of equipment. A commercially available density meter uses an oscillating element in the fluid whose density is to be measured. Oscillation is provided by an electromagnetic field. The frequency of oscillation depends on the density of the fluid. The sensing element is contained in a one-ton fuel housing for installation in a pipeline. A standard reference, Process Instruments and Controls Handbook, 2nd edition 1974, published by Considine, lists only three techniques for measuring density, none of which are suitable for use outside the laboratory. The stated methods (pages 6 - 152)

is as follows.

In a gas specific gravity balance, a tall gas column is measured by means of a floating bottom which is attached to the gas-containing container. A mechanical joint exhibits movement of the base on a scale. A buoyant gas scale consists of a container containing a displacer mounted on a weight arm and with a manometer connected to this. Forsky-. the verbolance is established with the container filled with air and then filled with gas, the pressure necessary to do this being read from the manometer in both cases. The pressure ratio is the density of the gas in relation to air.

In a viscosity-resistance-density instrument, an air stream and a stream of the gas under test are passed through separate, identical chambers, each containing a rotating paddle wheel. The two flows are affected by the rotating vane wheels,

and each current acts in turn on a non-rotating-end^vane wheel mounted at the opposite end of the chamber. The non-rotating paddle wheels are connected by means of a joint coupling and measure the relative resistance which. is shown by the tendency of the ksovl wheels to rotate, which is a function of relative density.

Moisture

The present invention also relates to the determination of moisture, or moisture content, of a gas or a vaporized liquid. It is primarily useful for analyzing gases where the moisture content is high and there is a small difference between the molecular weight of water and the average molecular weight of the other components of the gas, or where there is a large difference between the molecular weight of water and the average molecular weight of the other components.

There are a large number of methods for measuring water content where each method is associated with at least one significant disadvantage that makes the method unsuitable for use in certain applications. The choice of method must therefore be made in light of the application. An overview of methods and devices can be found in the Process Instruments and Controls Handbook, published by Considine, 2nd edition, McGraw-Hill 1974, pp. 10 - 3 et seq.

The applications for which the present invention is suitable will become obvious upon reading the present description, and the same is the case with the void in the area of humidity measurement which is filled by the invention.

Known technique

In an article in the Oil and Gas Journal, April 5, 1982, entitled "Acoustic Measurement for Gas BTU Content," authors Watson and White suggest a method and an apparatus- . ning that utilizes the dependence of sound speed and BTU content on molecular weight, and that utilizes some of the same basic scientific principles as the present invention. LeRoy and Gorland have investigated the use of a fluidic oscillator as a molecular weight sensor for gases and reported their work in an article entitled "Molecular Weight Sensor" published in Instruments and Control Systems, January 1971, and in the National Aeronautics and Space Administration Technical Memoranda TMX-52780 (ca. 1970) and TMX-1939 (January 1970). In Fossil Energy I&C Briefs, November 1981, prepared for the US Department of Energy by the Jet Propulsion Laboratory at the California Institute of Technology, Sutton of The Garrett Corp. to the use of a fluidic oscillator to measure gas compositions, mass flow and heating value for natural gas.

In a paper entitled "Thermal Energy Measurements", presented at the 55th International School of Hydrocarbon Measurement in 1980 at the University of Oklahoma, W.A. Fox at Consolidated Gas Supply Corp., Clarksburg, West Virginia, that specific gravity methods can be used for determining heating values. The use of the fluidic oscillator when measuring composition in a methanol-water system is discussed in an article on page 407 of Ind. Meadow. Chem. Foundation. Vol. 11, No. 3, 1972. US Patent 3,273,377 (Testerman) shows the use of two fluidic oscillators in the analysis of fluid flows. A fluidic device for measuring the volume ratio between two known gases is shown in US patent 3,544,004 (Rauch et al.). US patent 4 150 561 (Zupanick) describes a method for determining the constituent gas proportions in a gas mixture which utilizes a fluidic oscillator.

In National Aeronautics and Space Administration Technical Memorandum TMX-126 9 (August 1966), Prokopius reports the use of a fluidic oscillator in a humidity sensor that was developed to study a hydrogen-oxygen fuel cell system. In NASA TMX-3068 (June 1974), Riddlebaugh describes investigations regarding the use of a fluidized oscillator in measuring fuel-air ratios in hydrocarbon combustion processes. NASA Report No. L0341 (April 16, 1976), written by Roe and Wricht at McDonnell Douglas under Contract No. NAS 10-8764 at the Kennedy Space Center, reports on work done to develop a fluidic oscillator as a hydrogen leak detector for facilities for transfer of liquid hydrogen. US patent 3,756,068 (Villarroel et al.) relates to a device that uses two fluidic oscillators to determine the percentage concentration of a particular gas in relation to a carrier gas.

The aforementioned US patent documents 4,337,654

(Austin et al.), 4 32 9 873 (Meada), 4 32 9 874 (Maeda) and 4 355 5 33 (Mulddon) show methods for determining calorific value. The aforementioned article in Oil and Gas Journal 3 and 10 January 1983) shows an overview of methods used in Europe.

Summary of the Invention

It is an object of the invention to provide

a method and a device for determining unknown properties of gases and liquids and which can be used both in the laboratory and in the field. It is also a purpose that a so-

then the device must be relatively cheap, have a minimum of moving, mechanical parts, and be compact, so that transport and installation are facilitated. It is a further object of the invention that the method and device have high accuracy and reliability at the same time as. they provide results essentially instantly.

In one embodiment, the device according to the invention comprises a fluidic oscillator, a device for establishing a flow of a sample through the oscillator, a device for measuring or controlling the pressure at which the sample passes through the oscillator and for providing a

signal that represents the pressure when this is not controlled

a previously established area, a device for measuring the temperature of the sample at the oscillator and for providing a signal representing the temperature, a device for measuring the oscillation frequency at the oscillator and for providing a signal representing the frequency, a calculation device for reading the aforementioned signals and for calculating the unknown property of the sample using equations and data stored in the calculation device, and data supplied by the devices for providing temperature and frequency signals and by the device for providing a pressure signal when the pressure is not controlled in a previous established area, and a device for transferring information that is contained in the calculation device.

The invention shall be described in more detail below

in connection with design examples with reference to the drawings, where fig. 1 shows a schematic representation of a fluidic oscillator, fig. 2 shows a schematic representation of an embodiment of the invention comprising a calorific value monitor in which the calorific value of gas flowing through a pipeline is measured on a continuous basis and displayed at a remote location, fig. 3 shows a schematic representation of an embodiment of the invention comprising a density monitor in which the density of gas flowing in a pipeline is measured on a continuous basis and displayed on

a distant place, fig. 4 shows a schematic representation of an embodiment of the invention comprising a moisture monitor that uses two oscillators in parallel and where the moisture content of gas flowing through a pipeline is measured on a continuous basis and displayed at a remote location, and fig. 5 shows an unfolding in block diagram form of the parts of fig. 2, 3 and 4 which are labeled electronics.

A device known as a fluidic oscillator is used in the present invention. This is one of a class of devices used in the field of fluidics. A fluidic oscillator may have any of a number of different designs in addition to that shown in FIG. 1. The publications mentioned under the heading "Known technique" describe fluidic oscillators and their control principles in detail, and it is therefore unnecessary here to present more than the following simple description.

A fluidic oscillator (English: fluidic oscillator) or fluidistor can be described as a set of passages, in a massive block of material, which is designed in a special way. If the passages are centered in the block, and the block is cut

in two at the right place, an outline of the cutting surface will appear as in the schematic representation in fig. 1. Referring to fig. 1, a gas stream enters the inlet, flows through a nozzle 109 and "attachs" itself to one of two stream retaining walls 105 and 106 in accordance with the principle known as the Coanda effect. Gas flows through either an outlet passage 107 or an exit passage 8, depending on whether the flow is attached to wall 105 or wall 106. The exit passages 107 and 108 can be thought of as extending to the outside of the block of material in a direction normal to the plane in which the other passages are located. In the following, a gas stream is considered which sticks to the wall 105 and flows through the exit passage 10 7. A pressure pulse is generated which passes through a delay line 10 4. The pressure pulse hits the gas stream at the outlet of the nozzle 109 and forces the gas stream to "stick" to the wall 106 and flow through the output passage 108. A pulse passing through a delay line 103 then causes the current to be coupled back to the wall 105. It is in this way that an oscillation is established. The oscillation or swing frequency is a function of the propagation time through the delay line and the time delay or lag involved in the current switching from one retaining wall to the other. For a delay line of a given length, the pressure propagation time is a function of the properties of the gas, as shown in the above-mentioned publications and also by means of the equations to be presented in the following. The swing frequency can be sensed by a pressure sensor or microphone located in one of the passages, as shown by a sensing port 102. A differential

sensing device connected to both passages can also be used. A sensing port 101 is shown to indicate one possible location for a temperature.

The invention can most easily be described by initial reference to fig. 2, 3, 4 and 5 which show particular embodiments of the invention. Reference should also be made to a special prototype heat value monitor that was manufactured and tested. Referring to fig. 2, 3 and 4, gas flows through a conduit 50. A sample or sample flow loop 51 is formed by a line, such as a 3/4" diameter pipe, which is connected to the conduit 50 upstream and downstream of a pressure drop element 53. The purpose of the pressure drop element 53 is to cause a pressure drop in the pipeline 50 which is the same as the pressure drop in the flow loop 51 when a sufficient amount of gas passes through the flow loop 51. Gas flow through the flow loop 51 is sufficient when the gas composition in the sample point 54 is essentially the same as the composition in the pipeline 50 at any given moment. eg a control valve. A sufficient length of the pipeline 50 can serve as a pressure drop element 53, or a throat flange can be inserted into the pipeline 50 to serve this purpose. Valve is 52 used to isolate the flow loop 51 from the pipeline 50.

With respect to only FIG. 3, the pressure and temperature of the gas flowing in the pipeline 50 are provided by means of a pressure sensor 75 and a temperature sensor 76. These are located close to the pipeline 50, so that differences in pressure and temperature between their locations and the pipeline 50 are not significant . The pipeline 50 is covered by thermal insulation of a type that is commonly used on pipelines. The location shown in fig. 3, has the advantage of allowing the density monitor to be a stand-alone or complete package. If, however, the pressure and temperature differences are significant, the sensors 75 and 76 can be located directly on the pipeline 50. The measured pressure and the

measured temperature is denoted here as T^ and P^ respectively.

Fig. 4 represents an alternative embodiment of the invention where it is desired to determine the moisture content in a gas sample. Flow of a gas sample is provided in parallel through a first fluidic oscillator 56 and a second fluidic oscillator 78, with a device for adjusting the water content of a portion of the sample before it passes through the second oscillator 78.

In all three embodiments as shown in fig. 2, 3 and 4, sample lines 55 transport samples of gas from the sample points 54 to the fluidic oscillators 56. A sample line 77 is branched to supply a gas sample to the fluidic oscillator 78 in the embodiment, in fig. 4. Filters 57 are provided to remove particles that may be present in the sample so that the narrow passages in the fluidic oscillators 56 and 78 or other flow paths will not be re-clogged. Pressure regulators 58, of the complete type with an integrated gauge, are provided so that the gas flowing through the oscillators 56 and that flowing through the oscillator 78 has a substantially constant pressure. The oscillation frequency in the oscillators can vary with the pressure, depending on the particular oscillators used and the relevant pressure in the oscillators. As will be appreciated, the frequencies are correlated with humidity, moisture content and density, so variation for any other reason is unacceptable. Any pressure control device capable of maintaining flow through the oscillators at a substantially constant value may be used. Under certain circumstances, sufficient pressure regulation will be present by virtue of system configuration and pressure level, so that no separate pressure regulation device is required.

In connection with the pressure regulators 58, openings 60 are provided for the purpose of maintaining a constant gas flow through each oscillator. Pressure gauges 59 indicate the pressures on the downstream side of the orifices 60. Normally, it is not necessary to install the orifices 60, as the sample lines or inlet ports of the oscillators serve the same purpose. Pipelines 71 (Figs. 2, 3, 4) and 79 (Fig. 4) transport the tubes away from the oscillators 56 (Figs. 2, 3, 4) and 78 (Fig. 4) to the atmosphere at a location where outflow of the gas will not cause any damage, or to a process container where it can be utilized.

However, the amount of gas is sufficiently small that it is possibly not economical to do anything other than venting it to the atmosphere. Pressure transmitters 61 are switching or switching devices that provide signals for triggering alarms if the pressures do not stay within pre-established ranges. In this way, notification is obtained that inaccurate results can be obtained. As reference is only made to fig. 4, a dryer 80 is provided to remove substantially all water from the gas passing through the oscillator 78. There are many commercially available devices for

to achieve this. A typical device contains two layers of a desiccant material, so that gas to be dried passes through one layer, while the other layer is regenerated using supplied heat.

Obtaining a representative sample stream from a pipeline, feeding it to the inlet port of a fluidic oscillator, removing the sample stream from the oscillator's outlet port, and maintaining a substantially constant pressure drop across the oscillator can be accomplished by a number of different devices and methods for each given set of conditions, such as the desired flow rate through the oscillator and pipeline pressure. These devices and methods, which can be used as alternatives to those shown in fig. 2, 3 and 4, are well known to professionals in the field.

A fluidic oscillator can be designed and fabricated with reference to the literature, such as that mentioned under the section "Known Technique", or it can be purchased. By

. test work relating to the present invention, an oscillator supplied by the company Garrett Pneumatic Systems Division of Phoenix, Arizona was used. This oscillator is of a different configuration than that shown in fig. 1 in that the "loops" formed by the delay lines 103 and 104 are open, so that the "loops" form hollow spaces, and in that there is only one output passage. Drawings

of this design can be found in the listed publications. The flow rate through this oscillator when testing natural gas is approx. 250 cm 3/min. when the upstream pressure is approx. 1.4 kg/cm and the oscillator is vented directly to the atmosphere. A flow rate range of 200 - 500 cm 3/min. considered to be feasible for commercial use and sufficient to provide acceptable humidity results.

The temperature sensors 67 (fig. 2, 3, 4) and 81 (fig. 4) provide the temperature of the gas in each oscillator. Any of the well-known devices for sensing temperature can be used, such as a thermistor, a thermocouple or a solid state semiconductor sensor. The sensor can be located in a passage in the oscillator, as shown in fig. 1 (sensing port 101), or in the sample line' or pipeline near the oscillator. Microphones 66 (fig. 2, 3, 4) and 82 (fig. 4) sense the oscillation frequency in each oscillator.

A microphone is located in a position to sense when the gas stream adheres to one of the walls, such as the position shown in fig. 1 (sensing port 102). There are a number of different sensors that can be used, for example a piezoceramic transducer, in which pressure induces a voltage change, or a piezo-resistive transducer,

in which pressure induces a resistance change. In test work relating to the present invention, a SeriesEA 1934 microphone supplied by Knowles Electronics, Franklin Park, 111, was used.

Signals from the microphones 66 and 82, the temperature transmitters 67 and 81 and the pressure transmitters 61 are processed using equipment designated field electronics 6 8 and control room electronics 6 9. The field electronics are located near the oscillators while the control room electronics are located in a central control room at a certain distance from the oscillators. This equipment processes the signals to obtain moisture content of the gas and also performs other functions which will be described in the following. A display unit 70 receives signals from the control room electronics 6 9 and communicates the humidity of the sample gas and other information in readable form. This can, for example, be a liquid crystal 1 indicator. The information can be transferred to other equipment, such as a strip-curve recorder to make a permanent record, or to a computer for further processing.

Two containers 64 and 65 for calibration gas are provided to check that the monitor is working correctly. Normally, one of the calibration gases has properties in the lower part of the range Low values expected for the gas flowing in the pipeline 50, and the other has properties in the higher part of this range. The monitor is placed in the correct calibration mode by means of one of a number of input switches 18 (fig. 5). By manipulating valves 63, 72 and 73, the calibration gases are allowed to flow in sequence through the calibration line 62 and the test line 55 to the oscillator 56. The monitor can be arranged so that properties of the calibration gases are displayed, and if necessary a human technician must set the monitor to the known calibration gas property values, or it may be arranged so that the monitor is capable of self-tuning. For example, the monitor can recalculate the values of constants stored in it which are used when calculating sample humidity or sample densities or heat values. Periodic calibration must be performed to check for malfunctions and changes that may occur in the device, such as electrical drift, corrosion and substances that accumulate in the device.

As the pressure and temperature of the calibration gases will vary as conditions such as ambient temperature change, the calibration gas densities calculated by the monitor must be adjusted to a pressure and temperature at which the calibration gas densities are known. If, for example, the pressure sensor 61 measures a pressure of 140 kPa and the temperature sensor 6 7 measures a temperature of -1.1° C when calibration gas from the container 64 flows and the density of the gas in the container 64 is known to be 0.718 kg/m at 0° C and 1 atmosphere (101 kPa), the density reported by the monitor must be at 0° C and 101 atmospheres (101 kPa). If the reported density is significantly different from 0.718 kg/m, the monitor is not working correctly. Adjusting a density value from one pressure and one temperature to another pressure and another temperature is easily achieved using the equation of state stated below. The monitor may be arranged so that densities of the calibration gases are displayed and a technician, if necessary, must adjust the monitor to the known calibration gas densities, or it may be arranged so that the monitor is able to adjust itself. As was done in the prototype device, the monitor can, for example, recalculate the values of constants stored in it which are used when calculating sample densities.

The procedure just described does not calibrate the pressure sensor 75 and the temperature sensor 76 (see Fig. 3). These units can be calibrated separately using common devices. If desired, the calibration gases can be introduced into the flow loop 51 upstream of these units to include them in the calibration. It is also possible to compare a value determined by the monitor with the density of a calibration gas by manual means. Pressure, temperature and density can be reported by the monitor, and an operator can refer to a standard curve sheet or tables to compare the reported results with the actual density of the calibration gas. Another method is to provide a device in line 55 to set the pressure and temperature of calibration gas flowing into the oscillator to particular, predetermined values. However, this method will only be used in rare cases, as it is less expensive to manipulate numbers than to manipulate the physical state of the calibration gases.

Partial calibrations, or operational checks,

can be performed in a number of different ways. Application of a calibration gas can be combined with operational checks that are carried out electronically. A fully electronic operational control can be carried out. For example, means for generating appropriate oscillation tones may be provided at microphones 66 (Figs. 2, 3, 4) and 82 (Fig. 4), so that new values of K-^

and K2 can be calculated. Of course, this procedure only checks the electronics and not the oscillator. In another simple control, tuning forks are used to generate tones by micro-

phones 66 and 82, and the synthetic "value" resulting from the tone input signals is compared to the expected correct value in a computing device. Operational or operational checks can be carried out by switching from one oscillator to the other in the embodiment of fig. 4. Temperature changes can be used to carry out operational checks. This can be done • by using a heating device, such as electric resistance coils, to heat gas flowing into the oscillators, and comparing values of properties for heated and unheated gas. If the gas used in the control comes from a varying process source, measures must be taken to prevent changes during the control period. This can be achieved by ensuring that a container collects a sufficient amount of gas to perform the control, or by recirculating gas from the outlet of the oscillators back through the system. When given a particular purpose to be fulfilled, other controls will become obvious.

An assembly of electronic devices for processing signals from the sensors and microphones (variables) and providing signals to the display unit can be manufactured from standard components by a person skilled in the art. Fig. 5 shows one such construction in simplified form.

A line 19 indicates which units are located in the field and which are located in the control room. To facilitate understanding, fig. 5 drawn for the cases in which only one oscillator is used. It can be readily realized that certain units would need to be duplicated so that data relating to two oscillators can be provided to the computing device. Although the following description mentions only the oscillators 56 and associated units, the operation of the oscillator 78 (Fig. 4) and associated units is the same as that of the oscillators 56. A signal from the microphone 66 is fed to an amplifier 1, passes through filter 2 and is transformed into a square wave pulse in a square waveform 3. The output signal from the square waveform 3 is supplied to a counter 6 by means of a transmitter 4 and a receiver 5. The counter 6 counts a number of cycles that occur in the oscillator 56 in a unit of time, as that

a frequency information is produced. The signals from pressure

the sensor 61 and the temperature sensor 6 7 are selected one at a time by means of an analog switch device 7 and are continuously sent to an analog/digital converter 8 where they are converted into digital form. A serial input/output device 9 transforms the output signal from the analogue/digital converter 8 into a serial pulse train which, by means of a transmitter 10 and a receiver. 11 is supplied to a serial input/output device 12 which is located in the control room.

A memory or storage device 15, a RAM chip, is used to store the variables. A program for controlling the electronic device and performing calculations is stored in a storage device 14, a programmable read-only storage chip (PROM). Constants. which are necessary for the calculation, are stored in a storage device 16, an electronically erasable, programmable read-only storage chip (EEPROM). A central processing unit or central unit 13 performs the necessary calculations and provides output signals to the display unit 70 (Fig. 2, 3, 4). Input switches 18 are used to provide human input signals to the electronics components. These are rotary click-stop switches that can be set to any number from 0 to 9. One of the switches is the mode switch and the others are used to enter numerical values. The mode brewer's function "instructs" the device on what to do. In the calculation mode, the device displays the moisture content of a sample. When the mode switch is placed in the "constant load" position, numerical values of constants can be set manually on the other switches and fed into the system by pressing a button. Another position of the mode selector allows values of variables to be displayed in sequence on the display unit 70. When one wishes to calibrate the device, further other positions are used. Supplementary positions are used as needed.

A parallel input/output device 17 provides a device for transferring information from the input switches 18 and also controls the counter 6. It will be clear to a person skilled in the art that certain of the electronic devices can collectively be referred to as a calculator or calculating device, or can be contained in a calculator or calculating device.

The basic equation which is used in the practice of the present invention and which describes the operation of a fluidic oscillator is

where

M = molecular weight of the gas flowing through the oscillator, G = specific heat ratio of the gas flowing through the oscillator,

T = temperature of the gas flowing through the oscillator,

F = frequency of the oscillator's output signal, and

K-^and K2= constants.

The quantity G can be provided as a constant stored in calculator or computer memory, or it can be calculated using a correlation such as the equation

where K-cf K4, Kr and Kg are constants.

The calculator is programmed to solve these equations for each oscillator, using values of F and T which are provided as described above, and values of constants that exist in the calculator storage. It can be easily realized that these molecular weights can be used to obtain the moisture content of the sample using the equations

where

X = weight fraction,

X = X of water present in the sample,

Xtø= X of all components of the sample except water,

Mg = M of the sample before water content adjustment,

= M of the sample components except water (average),

and

M = M of water.

M is calculated using the basic equation applied to data from oscillator 56, and M is derived from data from oscillator 78 in the same way. There are thus two equations and two unknowns, so that Xw can be calculated in the calculator.

The calorific value of the gas can be calculated using an equation such as

where and C 2 are constants and H = heating value.

The calculator is programmed to solve these equations to obtain H, using values of F and T provided as described above, and values of constants existing in the calculator memory.

The density of the gas can be calculated using the equation

where

D = density,

m = mass,

V = volume,

P-^= pressure at the place of density measurement,

T^= temperature at the place of density measurement,

Z = compressibility factor, and

R = universal gas constant.

This equation is derived from the well-known equation of state

where n = number of moles. Z can be expressed using equations that depend on M and data available in the literature, as described here.

The calculator is programmed to solve these equations to obtain the density D, using F, T, T^ and P^ provided as described above, and values of constants present in the calculator memory.

The equation for G used in the prototype unit was developed using a conventional curve fitting method using values of G available in the literature for such gases as methane, ethane, etc. As will be appreciated by those skilled in the art, there are other ^ways to develop and express the quantity G and store this in the calculator. The most appropriate method depends on the particular application.

A method for developing a basic oscillator equation on a theoretical basis is as follows. As an example, reference is made to fig. 1. A pressure pulse passing through the above-described delay line 103 or 104 travels at the local speed of sound u. As the length of each delay line is denoted as L, the time required for the pulse to travel one delay line is equal to L/u . The time for one complete oscillation cycle comprises that required for a pulse to travel through each delay line. An equation for the local sound speed is

where

u = speed of sound,

g = gravitational constant, and

R = universal gas constant.

The time required for the pulse to connect the two delay lines is thus 2 L/u or

As explained above, the total time for an oscillation cycle also depends on the switching time, i.e. the time required for the switching of the current from one attachment wall to the other, or the period between the arrival of a pulse propagating through a delay line, at the nozzle 10 9 and the start of a pulse through the second delay line. The switching time can be expressed as inversely proportional to u, i.e. as

Since L is a constant for any given oscillator and the inverse of time is frequency, the following equation can be written By solving the equation with respect to M and letting g, 1 and R form part of the constant, the equation becomes

If the above constant is denoted as K-^, and K2 is added to the right-hand side, the basic equation is obtained as

is indicated in front. It has been found necessary to add the constant K2 to the equation to describe the oscillator accurately. It is not possible to use a purely theoretical equation, partly as a result of imperfections in hardware and measuring equipment. For example, no two fluidic oscillators will behave identically. In a special oscillator used in a natural gas application, K₂ and K₂ were determined empirically by passing such gases as methane, ethane, propane, butane and pentane through the monitor. The values of and K 2 established in this way were 7.5 38 x 10^ and 1.58, respectively. This calibration procedure must be followed for each monitor that is manufactured, using gases that are similar to the gas for which the monitor is to be used. However, only two calibration gases are necessary to define and K2

The compressibility factor Z from the equation of state for calculating density is a measure of the deviation of the sample gas from the ideal, and is added to the expression commonly known as the ideal gas law to make the ideal gas law applicable to real gases. As compressibility factors are covered by a large amount of literature containing a number of different methods for calculating them, it is not necessary to explain the basic theory here. For further information and reference to the literature, reference is made to Basic Principles and Calculations in Chemical Engineering, 2nd edition, 1967, Prentice-Hall. Inc., by Himmelblau, pp. 149 et seq. Also useful are Chemical Process Principles, 2nd edition, 1954, John Wiley&Sons, by Hougen et al., pp. 8 7, and Perry's Chemical Engineers<1>Handbook, 4th edition, McGraw-Hill, pp. 4 - 49 .

In the prototype device, the size Z is calculated using the equation

where for M between 16 and 21.75, or

for

M between 21.76 and 27.55, and

Z0 B = 0.999287 + 9.25222 x 10~<5>M - 1.06605 x 10~<5>M<2>, where

Z^ ts = Z at special basic conditions,

S = supercompressibility factor,

P1= psig, and

T1= °R.

The equations for S are derived empirically. These equations and the equation for Z can be found in Principles and Practices of Flow Meter Engineering, 9th edition, 1967, by Spink, published by Foxboro Co. and Plimpton Press of Norwood, Massachusetts. The expression for Z_ was derived using correlation values of Zg for gases of different molecular weights. This was done by converting values of base temperatures and base pressures for different gases, using critical temperatures and pressures obtained from the literature, to reduce pressure and temperature and then using curve sheets or diagrams prepared by Nelson and Obert to achieve Z_.

B

The calorific value equation given above can be found in Report No. 5 of the Transmission Measurement Committee of the American Gas Association (Arlington, Virginia, Catalog No. XQ 0776). When H is expressed in BTU per standard cubic feet of gas, C-^= 54.257 and C 2 = 144. If one wishes to express H in MTU per pound of fuel gas, Report No. 5 indicates that and C2 assume different values and l/M is inserted instead of M. It is of course possible to use other correlations for calculating H for natural gas when practicing the invention. Furthermore, a different correlation is necessary for the determination of H for substances other than hydrocarbons that have one to approx. six carbon atoms. This correlation would probably be developed using empirical methods.

It is possible to present information derived from the practice of the invention in several different forms. For example, H can be provided in metric units by appropriate programming of the calculator, or the Wobbe index of the sample gas can be presented. The Wobbe index is a parameter used in the gas industry. One method of expressing this is

where k = the square root of the molecular weight of air.

The sample gas may contain compounds that are non-flammable. The concentrations and molecular weights of these compounds must be provided to the calculator to produce an accurate calorific value. This can be done with the help of an analyzer through which the sample gas is led and which is designed to automatically provide correct signals to the calculator. A number of different analyzer devices are available for use, such as a gas chromatograph. Alternatively, average values of concentrations and molecular weights of the non-combustible components can be entered manually into the calculator. For example, natural gas often contains carbon dioxide and nitrogen, and their concentrations do not vary much from hour to hour. It will often be satisfactory to analyze with regard to these once per day and enter values using the aforementioned input switches. The equation for H must be modified to take into account these constituents which contribute to the volume of gas but not to the calorific value. If, for example, two non-combustible components are present whose concentrations are expressed by volume fractions X-j^ and X2 and have molecular weights M-j_ and M2, the above equation becomes

The derivation of this and similar forms is carried out

easily by means of algebraic manipulation.

In some applications, it may be desirable to provide the calculator with concentrations and molecular weights of combustible constituents in the same manner as non-combustible constituents to improve accuracy. The equation used to calculate H can easily be modified for these applications. An example is the measurement of the calorific value of waste gas (off-gas) from a hydrogen-producing hydrogen recycling process, such as catalytic reforming or dehydration. As background in this area, US patent specification 3,974,064 (Bajek et al.) can be consulted. The waste gas is often used in whole or in part as fuel. It consists of both hydrogen and various hydrocarbon compounds. As the heating value of hydrogen is not accurately represented by many correlations used for hydrocarbons, it can be realized that using accurate hydrogen concentrations and a correlation for hydrocarbons gives greater accuracy than using a correlation that takes into account both hydrogen and hydrocarbons. Furthermore, since the hydrogen concentration in hydrogen recycling processes is often measured for other purposes, the improvement in accuracy may be available without the purchase of an additional analyzer.

Application of a heating value monitor when controlling a combustion zone may be highly desirable or necessary to achieve acceptable control. Consider a process in which the temperature in a furnace or a heating plant must be kept in a relatively cold area. A typical control arrangement is to measure the combustion plant temperature and adjust the fuel throttle to keep it constant.... As the amount of heat absorbed by the process increases, the temperature drops and more fuel is burned to raise the temperature to the correct value. Changes in fuel calorific value will also cause heating plant temperature changes for which the control system must compensate. As the behavior of a control system deteriorates as the number of factors for which it must compensate increases, it is desirable to eliminate fluctuations in temperature resulting from changes in fuel heating value. This can be achieved by measuring fuel flow and heating value, establishing a signal that represents their product, and setting the fuel flow by reference to this product. The product represents the amount of heat flow to the process. The amount of heat flow is set in relation to the process temperature. When the system is expressed by a conventional analog control device, a temperature controller receiving a signal representing the combustion plant temperature will provide the set point, in cascade form, to a controller receiving a signal representing the heat content of the fuel, setting the fuel flow control valve.

A calorific value monitor can be used to improve fuel economy. Consider a combustion zone where the fuel flow is adjusted to maintain a constant zone temperature. Combustion air flow rate is normally established by measuring fuel flow and combining a signal representing the fuel flow with a previously established ratio value to obtain a signal used to set the air rate. This control method is unable to respond to changes in fuel calorific value, so normal practice is to install the system so that excess air is supplied to the combustion zone. Excess air is the amount of air that is not necessary to enter into contact with the fuel. It is desirable to keep excess air to a minimum, as the amount of fuel used for heating represents a complete loss. As the fuel heating value increases, more combustion air is required. If insufficient combustion air is supplied, fuel is lost as a result of incomplete combustion.

A signal representing the fuel gas heating value can be used to set the air flow rate, usually by setting the ratio value, so that the excess amount of air is small and thus fuel is saved for heating unnecessary air and the use of extra fuel is avoided.

In the above, simple examples, reference is made to purposes such as precise steering, or steering in a narrow area, and steering to improve fuel economy. These purposes are of course not mutually exclusive. Control systems can be designed to achieve both purposes by adjusting both fuel and air flows. These systems can utilize conventional, analog control instrumentation or more advanced devices, such as those that include digital computing devices. Furthermore, there are other purposes, for example as described here, which may be necessary to achieve by controlling a particular combustion zone. Although it is not possible to present all the variations in purposes and methods for achieving these, the effectiveness of the present invention in achieving this will be realized by those skilled in the field when considering particular situations.

Fig. 2 shows an embodiment of the invention where a continuous test flow through the oscillator is established to obtain a continuous heat value for gas flowing in a process pipeline. An embodiment of the invention for use in a laboratory would not require the flow loop shown in FIG. 2. Sample can be collected in an evacuated, pressure-resistant container, usually called a "sample bomb", which is then connected to the sample line 55. In applications where the heating values of liquids are to be determined, a device for vaporizing the liquids is necessary. This can, for example, be achieved by using electric resistance heating elements that surround a part of a pipeline through which the sample passes. The term "gas" is often used in the present description. This must be understood to include vapors that arise from fuels that are originally in liquid form. For example, it may be desirable to determine the heating value of a sample of fuel oil No. 2, which is liquid at normal ambient temperatures.

In a relatively simple embodiment of the invention, it is shown in fig. 3 showed test loop omitted. Sample is collected in an evacuated, pressure-resistant container which is then connected to the sample line 55, either upstream or downstream of the filter 57. The density reported by the device,

is the density at the temperature and pressure measured by the pressure sensor 61 and the temperature sensor 67. There is no need to divide electronics into two sets at two different locations. This design can possibly be used in a laboratory. To this embodiment, it may be desirable to add the feature that the device is able to calculate a density value for sample gas at pressures and temperatures that are different from the values measured by sensors 61 and 67, and which are provided to the device in the following way. A temperature and a: pressure can be introduced manually into the device by means of such means as the input switches 18, or they can be provided by means of a device which measures temperature and pressure at one or another place of interest and transmits suitable signals to the calculation device according to the invention.

Fig. 3 shows a more complex embodiment of the invention where a continuous flow of sample through the oscillator (with a temperature T) is established in order to obtain a continuous density value for gas flowing in a process pipeline (with temperature T^ and pressure P-^ ). In this embodiment, the device is arranged to provide a density which represents the sample gas at a point upstream of the pressure-controlling device which is represented by the unit 58 in fig. 3, and further arranged so that the upstream point represents the main stream from which the sample is taken.

As previously noted, a variation in the pressure at which the gas passes through the oscillator can affect the accuracy of the monitor. This is the case even if the pressure is a variable used to calculate density, i.e. a calculated density value can be incorrect if the pressure method used in the calculation is correct, but outside a special range. It is therefore desirable to monitor the pressure and report any deviation from a pre-established range. This can be achieved by several devices, including the addition of a main sensor, such as a pressure switch, in the correct location, such as line 55 in fig. 3, or adding the correct device in the electronics part of the device to utilize the pressure signal provided for use in the equation, such as the signal transmitted by the pressure transmitter 61 in fig. 3. This monitoring measure is not shown in fig. 3.

The present invention can be incorporated into a device for determining the mass flow rate of gas in a pipeline. This can be done by combining a device, such as that shown in fig. 3, with a device for measuring the volumetric flow rate of the gas in the pipeline, and multiply density by . volumetric flow rate in such a device as the calculation device in fig. 3. If the device for measuring the volumetric flow rate includes a calibrated flow obstacle, such as a throat flange, and a device for measuring the pressure drop across the obstacle, such as a differential pressure cell, the pressure drop can be provided to the calculation device for calculating the mass flow rate instead of calculating the volumetric speed outside the be-re bn in gs device.

An alternative to the use of the dryer 80 in fig. 4 is to use a device to saturate the part of the sample that passes through the oscillator 78. This device is readily available. For example, a saturation device may comprise a small chamber into which a fine shower of water is introduced through a nozzle. After gas passes through this saturation chamber, the gas is led through another chamber to remove any water droplets that may be present in the stream.

The equations used to practice this embodiment

of the invention, are similar to those set forth above. An eczema-

pel is as follows. For the oscillator through which a sample flows before adjusting the water content:

For the oscillator through which saturated sample flows:

Previously undefined clauses are

M EL<=>M of sample after saturation,

X aw = X of water in p*robe post-saturation,

X ^ = X of all components of the sample except water after saturation.

It can be realized that there are five unknowns and only four equations, so that it is necessary to know one quantity more when practicing this embodiment of the invention than when using the drying device described above. However, this information is often available.

Equations for other cases can easily be written.

Fig. 4 shows an embodiment of the invention when a continuous flow of sample through the oscillators is established to obtain a continuous moisture value of gas flowing in a pipeline. An embodiment of the invention for use in a laboratory would not require the test loop shown in fig. 4. Sample could be collected in an evacuated, pressure-resistant container, usually called a sample bomb, which is then connected to the sample line 55. In applications where the moisture content of liquids is to be determined, a device for vaporizing the liquids is necessary. This can be achieved, for example, by using electric resistance heating elements which surround a part of the pipeline through which the sample passes. The term "gas" is often used here. It is understood that this includes vapors that form from substances that are originally in liquid form.

In the parallel flow arrangement shown in fig. 4, the sample is divided into two parts and each part is passed through a different oscillator. The water content of one of the parts is adjusted before passing through the oscillator, and the moisture of the sample is calculated by reference to differences in signals obtained from the transducers associated with each oscillator. An alternative flow arrangement involves serial flow where the entire sample is passed through one oscillator and then through another. The device for moisture adjustment is located so that the sample passes through the first oscillator, has its moisture content adjusted, and then passes through the second oscillator. This can be easily visualized by changing fig. 4 so that the sample line 77 is connected to the drain line 71 instead of to the sample line 55. The flow sequence would thus be from the oscillator 56 via the dryer 80 to the oscillator 78. In this embodiment of the invention, the moisture content in the sample can be calculated in the same way, i.e. by reference to the differences in each oscillator. However, it should be noted that when a continuous stream of sample is provided, a rapidly changing sample humidity could result in inaccuracies as there is a time delay between the measurement of a "particle" of sample in the first oscillator and the measurement of the same humidity-adjusted "particle" " in the second oscillator. Compensation for this time delay can easily be achieved in the electronics part of a monotor to remove any inaccuracy. One of the compensation methods simply involves placing the same time delay in the signal path associated with the correct oscillator, just before the signal differences are noted.

In another embodiment of the invention, only one oscillator is used. A device for adjusting the water content of the sample is provided together with a device for periodically bypassing the sample flow around the water content adjustment device. If, for example, a dryer is used, the current that continuously passes through the oscillator will alternately contain water and not contain water. This can be easily visualized by changing fig. 4 so that the sample line branch for the oscillator 56 is eliminated, to place a three-way valve in the sample line 77 just before the dryer 80,

and place a length of pipeline between the valve and the sample line 77 on the downstream side immediately after the dryer 80. The three-way valve is then cycled periodically to direct

generate sample flow "around" the dryer 80. The moisture content of the sample is calculated by reference to differences in signals received by the transducers associated with the oscillator for each condition, i.e. when dried sample is flowing through and when non-dried sample is flowing through the oscillator. The same time-delay problem discussed above exists when the sample moisture changes rapidly. Compensation can be obtained in the same way.

The use of the foregoing examples is not intended as a limitation of the broad scope of the invention as stated in the claims. It is also intended that further applications of the price tips for the invention as they would normally appear to a person skilled in the art are included in the claims. Mixtures of gases that do not contain water can be analyzed by applying the principles according to the invention. The term "gas" is often used in the foregoing, but this must be understood to also include vapours.

Claims (10)

1. Device for determining a ^k-jen^ property of a gas or vapor sample, characterized in that it comprises a fluidic oscillator, a device for establishing current from the sample through the oscillator, a device for measuring or controlling the pressure at which the sample passes through the oscillator and for providing a signal representing the pressure when this is not controlled in a previously established range, a device for measuring the temperature of the sample in the oscillator and for providing a signal representing the temperature, a device for measuring the oscillation frequency in the oscillator and for providing a signal representing the frequency, a calculation device for reading said signals and for calculating the unknown property of the sample using equations and data stored in the calculation device, and data provided by the devices for providing temperature - and frequency signals and of the device for providing of a pressure signal when the pressure is not controlled in a previously established area, and a device for communicating information that is contained in the calculation device. 2. Device according to claim 1, characterized in that it further comprises a device for establishing a flow of one or more calibration gases in sequence through the mentioned oscillator, and a device for adjusting the device so that the property calculated by the device for the calibration gases, is essentially identical to the known property of the calibration gases. 3. Device according to claim 1, characterized in that the unknown property is heat value, and that the aforementioned device for pressure measurement or pressure increase and for providing a pressure representative signal is a device for controlling the pressure of the sample in a previously established area. 4. Device according to claim 1, characterized in that the unknown property is density, and that the aforementioned device for pressure measurement or pressure control and for providing a pressure representative signal is a device for measuring the pressure and for providing a pressure signal to the calculation device. 5. Device according to claim 1, characterized in that the unknown property is moisture content, that the aforementioned device for pressure measurement or pressure control and for providing a pressure representative signal is a device for controlling the pressure of the sample in a previously established area, and that the device comprises a device for adjusting the water content of the gas sample before it passes through the aforementioned oscillator, and a device for periodically bypassing the flow of sample around the water adjusting device, and for providing a signal to the calculating device that the water adjusting device has been bypassed. 6. Device according to claim 1, characterized in that the unknown property is moisture content, that the mentioned device for pressure measurement or pressure control and for providing a pressure representative signal is a device for controlling the pressure of the sample in a previously established area, and that the device comprises a second fluidic oscillator with a device which is essentially identical to the first-mentioned oscillator, and a device for adjusting the water content of the gas sample before it passes through the second oscillator. 7. Device according to claim 6, characterized in that the oscillators are arranged in series, so that the sample initially flows through the first oscillator and then through the second oscillator, and that the device for adjusting the water content acts on the sample before it passes through the second oscillator , but after it passes through the first oscillator. 8. Device according to claim 6, characterized in that the oscillators are arranged in parallel, so that a first part of the sample passes through the first oscillator and a second part of the sample passes through the second oscillator, and that the device for adjusting the water content works only on the other part. 9. Device according to claim 5 or 6, characterized in that the device for adjusting the water content essentially removes all water from gas that passes through the device. 10. Device according to claim 5 or 6, characterized in that the device for adjusting the water content • mainly saturates gas passing through the device.