CN103454344B - Device and method for simultaneously measuring components and flow of methane - Google Patents
Device and method for simultaneously measuring components and flow of methane Download PDFInfo
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 170
- 238000000034 method Methods 0.000 title claims abstract description 43
- 229920006395 saturated elastomer Polymers 0.000 claims abstract description 17
- 238000005259 measurement Methods 0.000 claims description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 20
- 238000001514 detection method Methods 0.000 claims description 19
- 230000003321 amplification Effects 0.000 claims description 16
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 16
- 238000004364 calculation method Methods 0.000 claims description 10
- 238000012545 processing Methods 0.000 claims description 9
- 238000004422 calculation algorithm Methods 0.000 claims description 4
- 230000000630 rising effect Effects 0.000 claims description 4
- 238000011144 upstream manufacturing Methods 0.000 claims description 4
- 238000000691 measurement method Methods 0.000 claims description 2
- 230000002411 adverse Effects 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 69
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 34
- 229910002092 carbon dioxide Inorganic materials 0.000 description 26
- 238000005516 engineering process Methods 0.000 description 7
- 239000001569 carbon dioxide Substances 0.000 description 6
- 230000005540 biological transmission Effects 0.000 description 4
- 239000003245 coal Substances 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 238000009614 chemical analysis method Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000009776 industrial production Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 238000004886 process control Methods 0.000 description 2
- 235000017166 Bambusa arundinacea Nutrition 0.000 description 1
- 235000017491 Bambusa tulda Nutrition 0.000 description 1
- 241001330002 Bambuseae Species 0.000 description 1
- 235000015334 Phyllostachys viridis Nutrition 0.000 description 1
- 238000007792 addition Methods 0.000 description 1
- 239000011425 bamboo Substances 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 230000027734 detection of oxygen Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000004377 microelectronic Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
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- 238000006467 substitution reaction Methods 0.000 description 1
- 230000005514 two-phase flow Effects 0.000 description 1
- 238000002604 ultrasonography Methods 0.000 description 1
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Abstract
The invention relates to a device and a method for simultaneously measuring components and flow of methane. The method comprises the following steps: controlling an output signal of an amplifying circuit through an automatic gain circuit, identifying that whether a gas to be measured is air or methane through judging the relative size of an ultrasonic signal, if the gas to be measured is the methane, measuring the sound velocity of the methane through an ultrasonic sensor, measuring the temperature of the methane through a temperature measuring unit, calculating the volume concentration of CO2 gas in the methane by using a mixed gas characteristic equation, calculating the volume concentration of vapor by using a relation between the temperature and saturated vapor pressure, finally obtaining a volume concentration of CH4 gas, and measuring the flow of the methane through measuring a time difference between fair current and adverse current of the ultrasonic signal. According to the method, through treating signals measured by one temperature sensor and one ultrasonic sensor, the components and the flow of the methane can be measured, and an effective solution is provided for low-cost requirement in methane industrial application.
Description
Technical Field
The invention relates to a device and a method for measuring gas components and flow, in particular to a device and a method for simultaneously measuring components and flow of biogas.
Background
The gas concentration detection technology in industrial production is widely applied to the fields of chemical treatment, environmental protection detection, power industry and the like, and at present, a plurality of methods for detecting the gas concentration are available, such as a chemical analysis method, an infrared absorption method, a corona discharge method, an ultrasonic detection method and the like. The chemical analysis method is not suitable for on-line detection; the corona discharge sensor has short service life and cannot work stably for a long time; the infrared absorption method is complex and large in volume, high in manufacturing cost and difficult to popularize. The method for measuring the concentration of the ternary gas by using ultrasonic waves has the characteristics of wide measurement range, small equipment volume, easiness in online detection and the like.
The gas flow detection in industrial production is also an increasingly important index, and various flowmeters for detecting the gas flow are provided, so that the theoretical basis of differential pressure type flowmeters is laid in Torricelli in the 17 th century, and the method is a milestone for measuring the flow. 18. The 19 th century flow measurement rudimentary forms of many types of meters are beginning to be developed, such as weirs, tracers, pitot tubes, venturis, volumetric and turbine flow meters, and the like. In the 20 th century, due to the rapid increase of the demands of process industry, energy metering and urban public utilities for flow measurement, the rapid development of the meters is promoted, the rapid development of microelectronic technology and computer technology greatly promotes the updating and upgrading of the meters, and the novel flow meter emerges like a bamboo shoot in spring after rain. To date, hundreds of types of flow meters have been proposed for the market, such as thermal, ultrasonic, vortex, etc. The measurement of gas flow by the ultrasonic principle has the following advantages
1. The device can be used for measuring gas flow and large-pipe-diameter flow which are not easy to contact and observe;
2. the flowing state of the fluid cannot be changed, the pressure loss cannot be generated, and the installation is convenient;
3. the flow of the strong corrosive medium and the non-conductive medium can be measured;
4. the measured volume flow is not influenced by the thermophysical parameters of the measured gas such as pressure, viscosity and density.
In the process control of the biogas project, two important indexes of the composition and the flow of the biogas are measured, the change of the concentration of the methane in the biogas has great influence on the quality of the biogas, the flow measurement of the biogas can reflect the productivity and the usage amount, so in the process of controlling the biogas project, the flow and the concentration of the methane in the biogas are monitored, and the process control of gas production is changed according to the detection result, so that the produced biogas can meet the use requirement of the biogas project.
The Gas metering standards are established according to ISO (international organization for standardization) and are based on the related standards of AGA (American Gas Association), and the standards related to ultrasonic Gas flow metering, which are mentioned in the ninth bag official latest published by AGA 6.1998, are the only authoritative technical specifications in the world, which are based on practice in all countries in the world.
The AGA report is repeated with the following two points emphasized:
1. the pressure cannot be lower than 2MPa in the measurement because the gas density is high when the pressure is high, the acoustic impedance is high, the receiving medium and the sensor are easy to match, and the transmitting and receiving signals of the ultrasonic wave are stronger.
2. The measured gas is as pure as possible, especially CO2The content of (A) cannot be too high, and usually less than 10% is required, since CO2Attenuation of ultrasonic wave is very large, CO2The higher concentration is very detrimental to signal reception.
The pressure of household marsh gas is generally less than 10kPpa, the pressure of household marsh gas is also less than 20kPpa, and CH in the methane can be ignited4The concentration can be as low as 35%, in which case CO2The highest concentration of the carbon dioxide can reach 65 percent, and the invention can solve the problem of CO with high concentration2Measuring CH in biogas4The concentration of (c).
In patent number ZL 02800155.9, the inventor proposes a device and a method for measuring gas concentration and flow rate by using ultrasonic waves, the invention provides a device for measuring oxygen concentration and flow rate in an oxygen generator, and the measuring gas is binary gas detection of oxygen and air. However, the principle of ultrasonic wave is utilized to treat the marsh gas components (saturated steam, CH) in the marsh gas engineering4And CO2The ternary gas of (a), cannot be solved by the method of ZL 02800155.9. In patent No. 200510045723.4, the university of liaoning engineering technology proposed a two-phase flow measurement device and method using ultrasonic and capacitive sensors, also only for measuring binary gas concentrations. Zhengzhou optomechanical science and technology limited company proposed a plurality of methods and devices for measuring methane concentration and flow for coal mine wells in patents CN201220509398, CN201220423254, CN201220423320, CN201220421689, CN201220425557, CN201220425558, CN201210374788 and CN201210374786, but only can measure the concentration of methane (binary gas containing methane and air) in coal mines, the carbon dioxide content in the coal mines is very low, the reception of ultrasonic signals is hardly influenced, and the patent of Zhengzhou optomechanical science and technology limited company cannot solve the problem of high-concentration CO2Neutralization of CH in saturated water vapor4Volume concentration measurement, and even failure to measure high concentration CO2The gas component in the biogas.
In the above mentioned patents, the concentration of the same measurement gas is measured, and the gas composition is not analyzed, and the judgment is not made for different measurement gases.
In patent number EP20070765679, germany E + H proposes a device and method for simultaneously measuring the components and concentration of biogas by using ultrasonic waves, the invention uses the principle of measuring the sound velocity by using ultrasonic waves to measure the biogas Components (CH) in biogas engineering4、CO2Saturated steam), since the concentration of CH4 in the biogas component varies between 30% and 75%, typically biogas is usedThe CH4 concentration in the gas is around 60%, and at this time, the sound velocity of the biogas is exactly the same as that of the air, so the patent cannot distinguish whether the gas is biogas or air. At present, China is popularizing marsh gas as green energy, and simultaneously, China subsidizes the use of marsh gas, so that an economic method is needed to measure the components and flow of the marsh gas and can reliably distinguish whether the communicated gas is marsh gas or air. Therefore, the condition that the supplementary paste for methane gas is cheated to be taken can be avoided.
Therefore, in the biogas project in China, when the biogas is not produced, the gas flowing through the device is air, and at this time, the flow rate and the total amount of the biogas cannot be recorded by the device, so that firstly, the components of the gas flowing through the device need to be judged, and the method mentioned in the above patent cannot solve the problem.
The following illustrates the problem of determining gas composition solved by the present invention.
The theoretical derivation of the speed of ultrasound propagation in dry biogas and air is as follows:
from the list it can be seen that the gas travels at different speeds in the biogas and in the air. At 20 ℃ the speed of sound in air is 343.0164739m/s, 60% CH4The speed of sound in the concentrated biogas is 341.0643366m/s, so at 60% CH4The transmission speed of the marsh gas is basically consistent with that of the air, the concentration of methane in the marsh gas is usually about 60%, then the output signal of the amplifying circuit can be controlled by the gain control unit to be consistent with the ultrasonic signal output in the air (the attenuation degree of the ultrasonic signal in different gases is different, the peak value of the ultrasonic signal transmitted in the air and the marsh gas is greatly different), and the relative size of the ultrasonic signal is judged, namely the amplitude of the ultrasonic signal directly output by the amplifying circuit is divided by the gain set by the gain control unit, so that the measured marsh gas is identifiedThe gas is air or methane, and when the relative magnitude of the amplitude of the ultrasonic signal is less than 0.4, the measured gas is methane.
In summary, no people or companies have studied to measure the components and flow rate of the biogas simultaneously by using the ultrasonic principle, a simple analyzer for detecting the concentration of methane in the biogas by using the infrared technology has a price of ten thousand yuan, and a common precession vortex flowmeter for measuring the gas flow rate has a price of about 5 thousand yuan. The invention can complete the measurement of the components and the flow of the marsh gas only by processing the signals measured by the temperature sensor and the pair of ultrasonic sensors, and provides an effective solution for the low-cost requirement in the industrial application of the marsh gas.
Disclosure of Invention
The invention mainly solves the technical problems existing in the prior art; the device and the method for simultaneously measuring the components and the flow of the methane can be used for simply processing signals measured by a temperature sensor and a pair of ultrasonic sensors, achieving the purpose of measurement under the condition of meeting the requirement of precision through the low-cost design of an ultrasonic measuring unit, and providing a very simple solution for the low-cost requirement in the industrial application of the methane.
The technical problem of the invention is mainly solved by the following technical scheme:
a device for simultaneously measuring components and flow of biogas is characterized by comprising:
a single chip microcomputer: controlling a driving unit to send a driving signal and simultaneously controlling a counter to start counting; receiving a peak signal of a peak detection unit, obtaining an amplification factor required by adjusting the signal through a signal amplitude closed-loop control algorithm in the single chip microcomputer, and sending an instruction of the amplification factor to a gain control unit; receiving a voltage signal of a temperature sensor, and converting the voltage signal into temperature; controlling the human-machine interface system.
Two ultrasonic sensors arranged in the methane pipeline, namely a first ultrasonic sensor and a second ultrasonic sensor: for transmitting and receiving ultrasonic signals to measure the sound velocity and flow rate of the biogas; when the first ultrasonic sensor transmits an ultrasonic signal, the second ultrasonic sensor receives the signal transmitted by the first ultrasonic sensor, and when the second ultrasonic sensor transmits an ultrasonic signal, the first ultrasonic sensor receives the signal transmitted by the second ultrasonic sensor;
a drive unit: the ultrasonic sensor is controlled by the singlechip and is used for driving the ultrasonic sensor to transmit an ultrasonic signal;
an amplifying circuit: the ultrasonic wave sensor is used for receiving ultrasonic wave signals of the first ultrasonic wave sensor and the second ultrasonic wave sensor and amplifying the signals;
a peak detection unit: receiving the ultrasonic signal amplified by the amplifying circuit and transmitting a peak signal to the singlechip;
a gain control unit: and receiving an instruction of the amplification factor sent by the singlechip, and controlling the amplification factor of the amplification circuit according to the instruction.
A comparator: receiving the signal adjusted by the amplifying circuit; the output level is output according to the high and low of the signal and is used for controlling the counter to stop counting;
a counter: the singlechip controls to start counting, and the comparator outputs a level rising edge to control the counter to stop counting.
A temperature sensor: the output voltage changes along with the temperature, and the voltage signal is transmitted to the singlechip for operation processing to obtain the methane temperature;
a human-machine interface system: and receiving and displaying the final output methane component and flow information of the singlechip.
A method for simultaneously measuring components and flow of biogas is characterized by comprising the following steps:
a step of detecting whether the currently detected gas is methane in real time: and judging the methane and the air based on a signal amplitude closed-loop control algorithm, namely judging the methane and the air according to a signal relative amplitude, wherein the signal relative amplitude is the peak detection amplitude detected by a peak detection unit divided by an amplification factor, and the methane is used when the relative amplitude is less than 0.6 and the air is used when the relative amplitude is more than 0.6.
A step of measuring the components of the biogas: the method comprises measuring the components of biogas by a binary method, namely measuring the sound velocity c of the biogas by an ultrasonic sensor, measuring the temperature of the biogas by a temperature measuring unit, and calculating the CO in the biogas based on a characteristic equation of mixed gas2Volume concentration of gasCalculating the volume concentration of water vapor from the relationship between the temperature and the saturated water pressureFinally, the CH can be obtained by calculation4Volume concentration of gas
A step of measuring the flow of the biogas: the flow velocity of the biogas is measured by measuring the time difference between the downstream flow and the upstream flow of the ultrasonic signals, so that the flow of the biogas is calculated.
In the above method for simultaneously measuring components and flow rate of biogas, the specific measurement method of the sound velocity c of biogas is as follows: defining the path length of ultrasonic wave walking as L, wherein the path length is the sound path; the included angle between the axes of the two ultrasonic sensors and the axis of the pipeline is theta, then: firstly, an ultrasonic signal in the downstream direction is transmitted by a first ultrasonic sensor and received by a second ultrasonic sensor, and a counter records the propagation time as ta(ii) a Secondly, the ultrasonic signal in the reverse flow direction is emitted by the ultrasonic sensor II, received by the ultrasonic sensor I, and the propagation time t is recorded by the counterb(ii) a The speed of sound of the biogas <math>
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In the above method for simultaneously measuring the components and the flow rate of the biogas, the specific method for measuring the components of the biogas comprises the following steps:
step 3.1, the sound velocity of the marsh gas measured by the ultrasonic sensor is c, and the temperature t of the measured marsh gas is directly measured by the temperature measuring unit, namely CO can be obtained2Volume concentration of gas
step 3.2, calculating the volume concentration of the water vapor according to the relation between the temperature and the saturated water pressureNamely, it isWherein,
Ps=0.0004276201987×t4+0.02650568145×t3+1.348945011×t2+45.38104831 × t +606.36944, where t is the biogas temperature measured by the temperature measurement unit; p is the local atmospheric pressure;
step 3.3, CH in the biogas4The volume concentration of the gas being
In the above method for simultaneously measuring the components and the flow rate of the biogas, the specific method for measuring the flow rate of the biogas comprises the following steps: the sound velocity of the biogas is c, and the flow velocity of the biogas is u; obtaining the flow q = & udt of the biogas according to the integral of the instantaneous flow rate of the biogas by time, namely completing the measurement of the biogas flow q, wherein the flow rate is <math>
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Therefore, the invention has the following advantages: the measurement of the components and the flow of the biogas can be completed by simply processing signals measured by one temperature sensor and one pair of ultrasonic sensors, the purpose of measurement is achieved by the low-cost design of the ultrasonic measurement unit under the condition of meeting the requirement of precision, and a very simple solution is provided for the low-cost requirement in the industrial application of the biogas.
Drawings
FIG. 1 is a schematic structural diagram of the present invention.
Detailed Description
The technical scheme of the invention is further specifically described by the following embodiments and the accompanying drawings.
Example (b):
a method and apparatus for measuring biogas composition and flowrate at the same time, the apparatus includes the man-machine interface system, temperature pick-up, one-chip computer, drive unit, ultrasonic sensor one, ultrasonic sensor two, amplifier circuit, comparator, counter, peak value detecting element and gain control unit;
a human-computer interface system in the device is connected with a single chip microcomputer, the single chip microcomputer is respectively connected with a temperature sensor, a driving unit, a counter, a peak value detection unit and a gain control unit, the driving unit controls the work of a first ultrasonic sensor and a second ultrasonic sensor, the signal output ends of the first ultrasonic sensor and the second ultrasonic sensor are respectively connected with an amplification circuit, the gain control unit controls the amplification circuit, the output end of the amplification circuit is respectively connected with a comparator and the peak value detection unit, and the comparator is connected with the counter.
The single chip microcomputer of the invention alternately controls a first ultrasonic sensor and a second ultrasonic sensor to emit ultrasonic signals through a driving unit, the first ultrasonic sensor receives the signals emitted by the first ultrasonic sensor when the first ultrasonic sensor emits the ultrasonic signals, the first ultrasonic sensor receives the signals emitted by the second ultrasonic sensor when the second ultrasonic sensor emits the ultrasonic signals, a counter is started to count when the driving unit controls the first ultrasonic sensor to emit the ultrasonic signals, meanwhile, the other ultrasonic sensor receives the ultrasonic signals and transmits the ultrasonic signals to a peak value detection unit after passing through an amplifying circuit, the peak value detection unit transmits the detected peak value signals to the single chip microcomputer, the single chip microcomputer obtains a reasonable amplification factor after comparison and calculation, then sends an instruction to a gain control unit, and the gain control unit controls the amplifying circuit to adjust the size of the ultrasonic peak value signals, the signal is kept at a certain amplitude, the processed signal is transmitted to a comparator, when the signal reaches a threshold level and is overturned, the counter is controlled to stop counting (in this embodiment, a low level is output when the signal is lower than 0.92V, a high level is output when the signal is higher than 1.25V, the output level is used for controlling the counter to stop counting, the counter is controlled to stop counting at the rising edge of the output level of the comparator (the rising edge is the process of changing the low level to the high level), 0.92V and 1.25V refer to input voltage, and 0V and 3.3V are output level), and the counting value at the moment is transmitted to the singlechip for operation processing, meanwhile, the temperature sensor directly measures the temperature of the measured methane, the methane temperature signal is transmitted to the single chip microcomputer for operation processing, and after the single chip microcomputer completes operation processing of all received signals, the required methane component and flow information is output to the human-computer interface system.
A method and a device for simultaneously measuring components and flow of biogas, the method comprises the following steps:
(1) the ultrasonic signal output by the amplifying circuit is controlled to be consistent with the ultrasonic signal output in the air through the gain control unit, the relative size of the ultrasonic signal is judged, namely the amplitude of the ultrasonic signal directly output by the amplifying circuit is divided by the amplitude of the ultrasonic signal output by the gain control unit to control the amplifying circuit to output, whether the measured gas is air or methane is identified, and when the relative amplitude of the ultrasonic signal is smaller than 0.4, the measured gas is methane; (generally, when the relative amplitude of the ultrasonic signal is 1, the gas is air, when the relative amplitude is less than 0.2, the gas is methane, and when the signal is less than 0.6, the signal is methane, when the signal is greater than 0.6, the signal is air, in this embodiment, the signal is less than 0.4, and the measured gas is methane)
Relation between ultrasonic signal amplitude and CH4 concentration (for example, ultrasonic air chamber diameter DN32 mm)
| CH4 concentration% | CO2 concentration% | Amplitude V | Actual gain | Relative amplitude |
| AIR | 0 | 3 | 3.68 | 100.00% |
| 100 | 0 | 1.44 | 12.972 | 13.62% |
| 90 | 10 | 1.41 | 13.887 | 12.45% |
| 80 | 20 | 1.34 | 15.23 | 10.79% |
| 70 | 30 | 1.3 | 16.86 | 9.46% |
| 60 | 40 | 1.26 | 20.346 | 7.60% |
| 50 | 50 | 1.2 | 24.84 | 5.93% |
| 40 | 60 | 0.83 | 30.64 | 3.33% |
| 30 | 70 | 0.55 | 38 | 1.78% |
(2) If the measured gas is the methane, firstly measuring the sound velocity of the methane through the ultrasonic sensor, measuring the temperature of the methane through the temperature measuring unit, and then calculating the volume concentration of CO2 gas in the methane through a mixed gas characteristic equationCalculating the volume concentration of water vapor from the relationship between the temperature and the saturated water pressureFinally, the volume concentration of the CH4 gas can be obtained through calculation
(3) Meanwhile, the flow velocity of the biogas is measured by measuring the time difference between the downstream flow and the upstream flow of the ultrasonic signals, so that the flow of the biogas is calculated.
The ultrasonic signal propagation direction and the airflow direction are consistent and are transmitted downstream, as shown in fig. 1, the ultrasonic sensor two transmits signals, and the ultrasonic sensor one receives signals and is transmitted downstream;
the ultrasonic signal propagation direction and the airflow direction are opposite to each other and are transmitted in a counter-current manner, as shown in fig. 1, a signal is transmitted by the ultrasonic sensor, and a signal received by the ultrasonic sensor is transmitted in a counter-current manner.
The method for measuring the components and the flow of the biogas comprises the following steps:
measuring the sound velocity and flow velocity of the measured methane;
when ultrasonic waves are transmitted in the biogas, the transmission time in the downstream direction is ta, the transmission time in the upstream direction is tb, the sound velocity of the biogas is c, the flow velocity of the biogas is u, the ultrasonic measurement distance L is a fixed value, and the included angle between the axis of the ultrasonic sensor and the axis of the pipeline is theta, then
Transport time ta = Lcos θ/(c + u) in the downstream direction;
the transit time in the counter-flow direction tb = Lcos θ/(c-u);
simple arithmetic processing is performed to obtain:
the sum of the propagation time of the ultrasonic waves in the biogas is (tb + ta) =2Lccos theta/(c 2-u 2);
the time difference of the ultrasonic wave propagating in the biogas is (tb-ta) =2Lucos theta/(c 2-u 2);
since the flow speed of the biogas itself is much smaller than the propagation speed of the ultrasonic wave in the biogas, that is, the c value is much larger than the u value, then (c2-u2) is approximately regarded as c2, and the following can be obtained after simplification:
the sound velocity c =2Lcos theta/(ta + tb) of the biogas can be obtained according to the time and formula of the ultrasonic wave transmitted in the biogas,
the flow rate u =0.5c2(tb-ta)/Lcos theta of the biogas can be obtained according to the time difference formula of the ultrasonic wave transmitted in the biogas
Measuring the temperature t of the biogas being measured
The temperature T of the measured marsh gas is directly measured by the temperature measuring unit, the Kelvin temperature of the measured marsh gas is T = T +273, the temperature signal is transmitted to the singlechip for calculation, and the volume concentration of CO2 gas in the marsh gas can be obtained
The biogas is a ternary mixed gas of methane, carbon dioxide and saturated steam, the sound velocity of the biogas and the temperature of the biogas are measured, and the volume concentration of CO2 gas in the biogas is calculated by a characteristic equation of the mixed gasThe calculation method is as follows:
a. for biogas containing three gases of methane, carbon dioxide and saturated steam,c is the sound velocity of the measured methane gas,is the average specific heat capacity ratio of the marsh gas, R is the constant of the universal gas, T is the temperature in Kelvin,is the average molecular weight of the biogas; wherein: is the constant volume specific heat capacity of saturated vapor,is the constant volume specific heat capacity of methane,is the constant volume specific heat capacity of the carbon dioxide,is the constant pressure specific heat capacity of saturated water vapor,is the specific heat capacity at constant pressure of the methane,is the specific heat capacity at constant pressure of the carbon dioxide, <math>
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</msub>
</msup>
<mo>,</mo>
</mrow>
</math> R=8.3145，T=t+273；
b. by <math>
<mrow>
<mi>c</mi>
<mo>=</mo>
<msqrt>
<mfrac>
<mrow>
<msup>
<mn>10</mn>
<mn>3</mn>
</msup>
<mover>
<mi>γ</mi>
<mo>‾</mo>
</mover>
<mi>RT</mi>
</mrow>
<mover>
<mi>M</mi>
<mo>‾</mo>
</mover>
</mfrac>
</msqrt>
</mrow>
</math> To obtain <math>
<mrow>
<mi>c</mi>
<mo>=</mo>
<msqrt>
<mfrac>
<mrow>
<msup>
<mn>10</mn>
<mn>3</mn>
</msup>
<mover>
<mi>γ</mi>
<mo>‾</mo>
</mover>
<mi>RT</mi>
</mrow>
<mover>
<mi>M</mi>
<mo>‾</mo>
</mover>
</mfrac>
</msqrt>
<mo>=</mo>
<msqrt>
<mfrac>
<mrow>
<msup>
<mn>10</mn>
<mn>3</mn>
</msup>
<mover>
<mi>γ</mi>
<mo>‾</mo>
</mover>
<mi>RT</mi>
</mrow>
<mrow>
<mn>16</mn>
<mo>+</mo>
<mn>2</mn>
<msub>
<mi>n</mi>
<mrow>
<msub>
<mi>H</mi>
<mn>2</mn>
</msub>
<mi>O</mi>
</mrow>
</msub>
<mo>+</mo>
<mn>28</mn>
<msub>
<mi>n</mi>
<msub>
<mi>CO</mi>
<mn>2</mn>
</msub>
</msub>
</mrow>
</mfrac>
</msqrt>
<mo>;</mo>
</mrow>
</math>
c. After the formula is transformed, the volume concentration calculation formula of CO2 gas is obtained: <math>
<mrow>
<msub>
<mi>n</mi>
<msub>
<mi>CO</mi>
<mn>2</mn>
</msub>
</msub>
<mo>=</mo>
<mfrac>
<mrow>
<msup>
<mn>10</mn>
<mn>3</mn>
</msup>
<mover>
<mi>γ</mi>
<mo>‾</mo>
</mover>
<mi>RT</mi>
</mrow>
<mrow>
<mn>28</mn>
<msup>
<mi>c</mi>
<mn>2</mn>
</msup>
</mrow>
</mfrac>
<mo>-</mo>
<mfrac>
<mn>16</mn>
<mn>28</mn>
</mfrac>
<mo>-</mo>
<mfrac>
<msub>
<mi>n</mi>
<mrow>
<msub>
<mi>H</mi>
<mn>2</mn>
</msub>
<mi>O</mi>
</mrow>
</msub>
<mn>14</mn>
</mfrac>
<mo>;</mo>
</mrow>
</math>
d. and checking physical characteristic data of three mixed gases in the biogas to obtain: cv H2O-2.474, Cp H2O-1.860,CvCH4＝2.839，CpCH4＝2.189，CvCO2＝1.078，CpCO2＝0.829，
e. to simplify the calculation, when actually calculating, orderThe effect of the error thus introduced on the methane concentration was evaluated:
for the marsh gas containing saturated steam, the method comprises the following stepsThe extreme case of maximum deviation is: saturated steam n1=10%, the working temperature range according to the instrument is-20-40 ℃, and the maximum content of the water vapor is 40 DEG CCH4 volume concentrationCO2 volume concentrationSubstitution into
To obtainSo in the actual marsh gas
Order toCalculated to obtain the followingThe maximum quote error introduced is less than 0.45%, soThe introduced reference error is negligible, so the calculation formula of the volume concentration of the CO2 gas can be simplified as follows:
f. for simplifying the operation, the maximum volume concentration of the water vapor is 7.28% in the actual calculation, so that the error of the volume concentration of the CO2 gas introduced by the water vapor is 0.5%, and the volume concentration of the CO2 gas can be ignored, namely the volume concentration of the CO2 gas is obtained
g. The measured Kelvin temperature T and the sound velocity c of the marsh gas are obtained, and the volume concentration value of CO2 gas in the marsh gas can be obtained
Calculating the volume concentration of water vapor from the relationship between the temperature and the saturated water pressure
In the range of-20 ℃ to 50 ℃, the relation between the saturated water pressure Ps and the temperature t is as follows:
Ps=0.0004276201987*t4+0.02650568145*t3+1.348945011*t2+45.38104831*t1+606.36944
the temperature t of the marsh gas is measured by the temperature measuring unit, the saturated water pressure Ps can be calculated by the relational expression, and the formulaCalculating the volume percentage of the water-gas contentWherein P is the local atmospheric pressure and is set as 101.325 kPa;
the volume concentration value of CO2 gas in the biogas is obtainedAnd the volume concentration of saturated water vaporThe volume concentration of CH4 gas in the biogas can be calculated to be
The flow rate of the biogas is measured by measuring the time difference between the forward flow and the reverse flow of the ultrasonic waves, and the method comprises the following steps:
the flow velocity u of the biogas can be measured by adopting the time difference principle of ultrasonic wave transmission in the biogas, so that the biogas flow is calculated and recorded as q;
and (3) obtaining the flow q = & udt of the biogas according to the integral of the measured flow u of the biogas obtained in the step (1) and the instantaneous flow rate of the biogas by time, namely completing the measurement of the flow q of the biogas.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (1)
1. A method for simultaneously measuring components and flow of biogas is characterized in that the following devices are adopted for measurement:
a single chip microcomputer: controlling a driving unit to send a driving signal and simultaneously controlling a counter to start counting; receiving a peak signal of a peak detection unit, obtaining an amplification factor required by adjusting the signal through a signal amplitude closed-loop control algorithm in the single chip microcomputer, and sending an instruction of the amplification factor to a gain control unit; receiving a voltage signal of a temperature sensor, and converting the voltage signal into temperature; controlling a human-machine interface system;
two ultrasonic sensors arranged in the methane pipeline, namely a first ultrasonic sensor and a second ultrasonic sensor: for transmitting and receiving ultrasonic signals to measure the sound velocity and flow rate of the biogas; when the first ultrasonic sensor transmits an ultrasonic signal, the second ultrasonic sensor receives the signal transmitted by the first ultrasonic sensor, and when the second ultrasonic sensor transmits an ultrasonic signal, the first ultrasonic sensor receives the signal transmitted by the second ultrasonic sensor;
a drive unit: the ultrasonic sensor is controlled by the singlechip and is used for driving the ultrasonic sensor to transmit an ultrasonic signal;
an amplifying circuit: the ultrasonic wave sensor is used for receiving ultrasonic wave signals of the first ultrasonic wave sensor and the second ultrasonic wave sensor and amplifying the signals;
a peak detection unit: receiving the ultrasonic signal amplified by the amplifying circuit and transmitting a peak signal to the singlechip;
a gain control unit: receiving an instruction of the amplification factor sent by the singlechip, and controlling the amplification factor of the amplification circuit according to the instruction;
a comparator: receiving the signal adjusted by the amplifying circuit; the output level is output according to the high and low of the signal and is used for controlling the counter to stop counting;
a counter: the singlechip controls to start counting, and the comparator outputs a level rising edge to control the counter to stop counting;
a temperature sensor: the output voltage changes along with the temperature, and the voltage signal is transmitted to the singlechip for operation processing to obtain the methane temperature;
a human-machine interface system: receiving and displaying the final methane component and flow information output by the singlechip;
the method comprises the following steps:
a step of detecting whether the currently detected gas is methane in real time: judging the biogas and the air according to a signal relative amplitude which is the peak detection amplitude detected by a peak detection unit divided by an amplification factor based on a signal amplitude closed-loop control algorithm;
a step of measuring the components of the biogas: the measurement of the biogas components is carried out based on a binary method, namely firstly, the measurement is carried outMeasuring the sound velocity c of the biogas through an ultrasonic sensor, measuring the temperature of the biogas through a temperature sensor, and calculating CO in the biogas based on a characteristic equation of mixed gas2Volume concentration of gasCalculating the volume concentration of water vapor from the relationship between the temperature and the saturated water pressureFinally, the CH can be obtained by calculation4Volume concentration of gas
A step of measuring the flow of the biogas: measuring the flow velocity of the biogas by measuring the time difference between downstream flow and upstream flow of the ultrasonic signal, thereby calculating the flow of the biogas;
the specific measurement method of the sound velocity c of the biogas comprises the following steps: defining the path length of ultrasonic wave walking as L, wherein the path length is the sound path; the included angle between the axes of the two ultrasonic sensors and the axis of the pipeline is theta, then: firstly, an ultrasonic signal in the downstream direction is transmitted by a first ultrasonic sensor and received by a second ultrasonic sensor, and a counter records the propagation time as ta(ii) a Secondly, the ultrasonic signal in the reverse flow direction is emitted by the ultrasonic sensor II, received by the ultrasonic sensor I, and the propagation time t is recorded by the counterb(ii) a The speed of sound of the biogas
The specific method for measuring the components of the biogas comprises the following steps:
step 3.1, the sound velocity of the marsh gas measured by the ultrasonic sensor is c, the temperature t of the measured marsh gas is directly measured by the temperature sensor, and then CO can be obtained2Volume concentration of gas
step 3.2, calculating the volume concentration of the water vapor according to the relation between the temperature and the saturated water pressureNamely, it isWherein,
Ps＝0.0004276201987×t4+0.02650568145×t3+1.348945011×t2+45.38104831 × t +606.36944, whereintIs the methane temperature measured by the temperature sensor; p is the local atmospheric pressure;
step 3.3, the volume concentration of CH4 gas in the biogas is
The specific method for measuring the biogas flow comprises the following steps: the sound velocity of the biogas is c, and the flow velocity of the biogas is u; obtaining the flow q ═ udt of the biogas by integrating the instantaneous flow rate of the biogas according to time, namely completing the measurement of the biogas flow q, wherein the flow rate is
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| CN104897219A (en) * | 2014-03-05 | 2015-09-09 | 陕西多奇电子科技有限公司 | High-accuracy low-power consumption ultrasonic flowmeter |
| CN103900651B (en) * | 2014-04-09 | 2016-06-22 | 浙江威星智能仪表股份有限公司 | A kind of ultrasonic wave gas meter mixed signal processes circuit |
| JP6379069B2 (en) * | 2015-04-09 | 2018-08-22 | 東京瓦斯株式会社 | Calorific value derivation device and calorific value derivation method |
| CN109708729B (en) * | 2018-12-14 | 2020-10-20 | 金卡智能集团股份有限公司 | Automatic gain adjustment method for metering signal of ultrasonic meter and ultrasonic gas meter |
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