CN109140242B - Online monitoring and ventilation linkage control method for gas cabin of comprehensive pipe rack - Google Patents
Online monitoring and ventilation linkage control method for gas cabin of comprehensive pipe rack Download PDFInfo
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- CN109140242B CN109140242B CN201811063035.4A CN201811063035A CN109140242B CN 109140242 B CN109140242 B CN 109140242B CN 201811063035 A CN201811063035 A CN 201811063035A CN 109140242 B CN109140242 B CN 109140242B
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17D—PIPE-LINE SYSTEMS; PIPE-LINES
- F17D5/00—Protection or supervision of installations
- F17D5/02—Preventing, monitoring, or locating loss
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17D—PIPE-LINE SYSTEMS; PIPE-LINES
- F17D5/00—Protection or supervision of installations
- F17D5/005—Protection or supervision of installations of gas pipelines, e.g. alarm
Abstract
The invention discloses an on-line monitoring and ventilation linkage control method for a gas cabin of a comprehensive pipe rack, and relates to an on-line monitoring and ventilation linkage control method for the gas cabin of the comprehensive pipe rack. The invention aims to solve the technical problems that timely and safe monitoring and dynamic linkage ventilation cannot be realized when gas leaks from a comprehensive pipe gallery in the existing engineering, and the problems that economy cannot be guaranteed and explosion risks cannot be effectively relieved. The method comprises the following steps: firstly, determining whether the monitored signals correspond to the categories of 'no leakage', 'tiny leakage' or 'dangerous leakage', and secondly, calculating the distribution boundaries of 'no leakage', 'tiny leakage' and 'dangerous leakage' in a plane to obtain the corresponding areas of 'no leakage', 'tiny leakage' and 'dangerous leakage' in the plane; and thirdly, the controller transmits the signals of the corresponding areas and the corresponding types to the actuator, and the actuator determines the frequency conversion ventilation times according to the signals. The invention is used for the field of gas monitoring of the comprehensive pipe gallery.
Description
Technical Field
The invention belongs to the technical field of public safety, and particularly relates to a safe treatment method and a safe treatment system for gas pipeline leakage in a small closed space of a comprehensive pipe rack.
Background
Since 2013, after the national academy issues successive ideas about the guidance of the construction of the comprehensive pipe gallery, the comprehensive pipe gallery test point construction is started nationwide. The development of the urban underground comprehensive pipe gallery can efficiently utilize underground space, simultaneously provides sufficient operation and maintenance space for the operation and maintenance of pipelines, and fundamentally avoids the phenomenon of zipper on roads.
In the utility tunnel, various pipelines are laid at the same time, including electric power, communication, heat supply, gas, sewage pipes and the like. However, as the gas pipeline belongs to a high-risk pipeline, once leakage occurs, combustible gas is gathered at high concentration in the corridor, and then explosion occurs. Therefore, the national discharge in 2015 is specified in the technical Specification for urban comprehensive pipe gallery engineering (GB 50838-2015): the natural gas pipeline of the corridor should be laid in a separate cabin (a separate cabin is an enclosed space within the utility tunnel, divided by the structural body or firewall, for laying the pipeline). The cabin should be provided with one fire-protection subarea every 200m, and each fire-protection subarea needs to be provided with a plurality of relatively independent mechanical air supply systems and air exhaust systems. For a ventilation system in a gas-fired independent compartment, the specifications specify the following: the emergency ventilation of the emergency sector and its neighbors should be activated when the concentration of natural gas in the cabin is greater than 20% of its lower explosive concentration value (volume fraction of 5%), i.e. when the concentration of natural gas in the cabin reaches 1% (5% by 20%). When the air is ventilated normally, the air change times per hour are not less than 6; when in accident ventilation, the ventilation frequency per hour is not less than 12.
The method has the following problems: the monitoring points for the natural gas concentration of the independent cabin are not reasonably arranged.
Because the regulation does not stipulate how to monitor natural gas leakage in the cabin, the current comprehensive pipe gallery engineering is regulated according to technical regulations of town gas alarm control systems (CJJT 146-2011): when the gas distribution facility is positioned in a closed or semi-closed factory building, a gas monitoring alarm is arranged every 15m, and during engineering construction, a detector is arranged every 15m at the top of a gas cabin. But according to our simulation calculations for a cross-sectional area of 5.6m2In a 200m fire-proof subarea, when a detector monitors that the concentration of natural gas in the air is 1%, and a leakage point is right above a pipeline, under the normal ventilation action of 6 times/h, the nearest measuring point in a top space can be monitored only by consuming 12 s; if the leakage point occurs on the side surface of the pipeline, the high-speed jet of the natural gas will reach the wall surface of the cabin in 5s first instead of the top, which leads to the delay of the monitoring time and thus to a greater explosion risk, so the reasonable arrangement of the natural gas monitoring alarm is a key technical difficulty to be solved urgently.
The problem two is present: normal and accident ventilation cannot meet engineering safety.
Actually, according to our calculation, with the condition that the existing gas pipeline is provided with a cut-off valve every 2 kilometers, if the corridor gas pipeline leaks, according to a calculation formula of the natural gas leakage amount of the gas pipeline:
in the formula
Rho-gas density, kg/m3；
T-gas temperature, K;
r-gas constant, 8.314J/(kmol. K);
m is gas molar mass, 0.016 kg/mol;
z is gas compression factor, 1 is taken;
u-gas leakage velocity at the leakage hole, m/s.
A-leakage area, m2；
C0-the orifice leakage factor, taken as 0.9;
q-leakage of Natural gas, m3/s。
Considering that most of the actual natural gas pipelines are small hole leakage (the american petroleum institute defines the small hole range of the gas pipeline as (0-1/4 inches, 1/4 inches-6.35 mm), and takes a-6.35 x 3.14 x 10-4/4＝3.2*10-3m2Ambient temperature T293K, P0101325Pa, the natural gas pipeline entering the gallery is mostly in medium-high pressure grade, and the pressure P of the medium-pressure pipeline is taken20.4MPa, k 1.3, calculated to q 40.656m3/s,
According to the formula V ═ q × 100% × 3600/1%
The ventilation V required to dilute the leak is obtained:
V＝1.46*107m3/s＝4066m3/h
and about 250m of natural gas is stored in the pipe length of 2 kilometers3If the concentration is lower than the alarm concentration according to the specification, namely if the concentration of natural gas in the cabin is lower than 1%, at least 25000m is needed3The natural gas is replaced by the air, and if the accidental ventilation (12 times/h) is started for natural gas replacement, the ventilation rate can be up to L12 × 250 × 3000m3/h<4066m3And/h, it is clear that this fixed number of ventilations does not at all guarantee timely relief of the explosion hazard of the natural gas cabin.
Meanwhile, the size of leakage amount is not considered in the current specification, only two conditions of no leakage and leakage are considered, and the replacement of leaked gas is realized by fixed ventilation times, so that the explosion danger of a natural gas cabin cannot be eliminated for the leakage of a large amount of fuel gas, and the unnecessary ventilation amount is likely to occur for the leakage of a small amount of fuel gas, so that the operation energy consumption of the fan is too high.
When the gas leaks in the utility tunnel in the existing engineering, the technical problems of timely and safe monitoring and dynamic linkage ventilation cannot be realized, the economy cannot be guaranteed, and the explosion danger can not be effectively relieved.
Disclosure of Invention
The invention aims to solve the problems that the technology of timely and safe monitoring and dynamic linkage ventilation cannot be realized when gas leaks in a comprehensive pipe gallery in the existing engineering and the explosion danger cannot be economically and effectively eliminated, and provides an online monitoring and ventilation linkage control method for a gas cabin of the comprehensive pipe gallery.
An on-line monitoring and ventilation linkage control method for a gas cabin of a comprehensive pipe rack comprises the following steps:
the method comprises the following steps that firstly, a natural gas concentration monitor monitors the natural gas concentration in a gas independent cabin of the comprehensive pipe gallery in real time;
the pipeline pressure sensor monitors the pressure of the natural gas in the pipeline in real time;
determining whether the monitored signal corresponds to a "no leak", "minor leak", or "dangerous leak" category,
if the volume fraction of the gas leakage concentration measured by measuring points in the gas independent cabin of the comprehensive pipe gallery is c less than 1%, the gas leakage concentration belongs to the category of no leakage;
if the volume fraction of the gas leakage concentration measured by a measuring point in the gas independent cabin of the comprehensive pipe gallery is more than or equal to 1% and less than or equal to 5%, the value of the pressure in the pipe is more than 0 and less than or equal to 0.1MPa, and the gas leakage concentration belongs to the category of tiny leakage;
if the volume fraction of the gas leakage concentration measured by measuring points in the gas independent cabin of the comprehensive pipe gallery is c more than 1%, and the value P of the pressure in the pipeline is more than 0.1MPa at the moment, the gas leakage concentration belongs to the category of dangerous leakage;
step two, calculating distribution boundaries of 'no leakage', 'tiny leakage' and 'dangerous leakage' in a plane to obtain corresponding areas of 'no leakage', 'tiny leakage' and 'dangerous leakage' in the plane;
and step three, the controller transmits the signals of the corresponding areas and the corresponding types to the actuator, and the actuator determines the frequency conversion ventilation times according to the signals.
The invention has the beneficial effects that:
the invention provides a method for safely treating natural gas leakage in a gas independent cabin of a comprehensive pipe gallery, wherein a natural gas concentration monitor monitors the natural gas concentration in the gas independent cabin of the comprehensive pipe gallery in real time; the pipeline pressure sensor monitors the pressure of the natural gas in the pipeline in real time; determining whether the monitored signals correspond to the categories of 'no leakage', 'tiny leakage' or 'dangerous leakage', calculating the distribution boundaries of 'no leakage', 'tiny leakage' and 'dangerous leakage' in a plane, and obtaining the corresponding areas of 'no leakage', 'tiny leakage' and 'dangerous leakage' in the plane; the controller transmits the signals of the corresponding areas and the corresponding types to the actuator, and the actuator determines the frequency conversion ventilation times according to the signals; the gas cabin safe operation method based on the on-line monitoring, the partition identification and the ventilation linkage control system can achieve the purpose of rapidly and effectively monitoring leaked natural gas, and meanwhile, the frequency conversion ventilation is adopted according to the intelligent identification of the leakage amount of the natural gas so as to ensure the safe, efficient and energy-saving operation of the natural gas cabin of the comprehensive pipe gallery.
The natural gas concentration monitor is adopted to monitor the natural gas concentration in the gas independent cabin of the comprehensive pipe gallery in real time; monitoring the pressure of the natural gas in the pipe in real time by adopting a pipeline pressure sensor; the gas leakage condition in the comprehensive pipe gallery can be monitored safely in time;
the controller transmits the signals of the corresponding areas and the corresponding types to the actuator, and the actuator determines the frequency conversion ventilation times according to the signals; dynamic linkage ventilation is realized;
according to the invention, the size of the leakage amount is considered, the ventilation times are determined according to the size of the leakage amount, and the economic and effective explosion danger is guaranteed to be eliminated; the problem of current only with do not leak and leak two kinds of situations consider to realize the replacement to leaking gas with fixed ventilation number of times, to the great leakage of gas, can't guarantee to remove the explosion danger in natural gas cabin at all, and to the leakage of less volume, still probably take place the ventilation volume that does not need, lead to the too high operation energy consumption of fan.
To sum up, when having solved among the existing engineering gas leakage in the utility tunnel, can't realize in time monitoring safely and dynamic linkage ventilation's technical problem and can't guarantee economy and relieve explosion danger effectively.
The existing specifications specify the following: the emergency ventilation of the emergency sector and its neighbors should be activated when the concentration of natural gas in the cabin is greater than 20% of its lower explosive concentration value (volume fraction of 5%), i.e. when the concentration of natural gas in the cabin reaches 1% (5% by 20%). When the air is ventilated normally, the air change times per hour are not less than 6; when in accident ventilation, the ventilation frequency per hour is not less than 12. The invention can monitor in real time, calculate the frequency conversion ventilation times according to the specific leakage amount, and ensure economy and effectively eliminate explosion danger.
Drawings
FIG. 1 is a system diagram of the present invention;
FIG. 2 is a control flow diagram of the coordinated ventilation control system of the present invention;
FIG. 3 is a sample distribution diagram of natural gas concentration in a gas independent cabin of the utility tunnel;
FIG. 4 is a control system overview;
FIG. 5 is a schematic diagram of a digital to analog converter;
FIG. 6 is a working schematic diagram of a variable frequency fan;
FIG. 7a is a natural gas cloud distribution diagram of a section of a natural gas cabin when diffusion is carried out for 6 s;
FIG. 7b is a diagram of the natural gas concentration distribution contour line and the selected monitoring points in the independent cabin;
FIG. 8 is a classification chart of the degree of gas leakage in the gas independent compartment of the utility tunnel;
fig. 9 is a control flow chart of the ventilation control system.
Detailed Description
The first embodiment is as follows: the utility model provides an on-line monitoring and ventilation linkage control method for utility tunnel gas cabin is:
the method comprises the following steps that firstly, a natural gas concentration monitor monitors the natural gas concentration in a gas independent cabin of the comprehensive pipe gallery in real time;
the pipeline pressure sensor monitors the pressure of the natural gas in the pipeline in real time;
determining whether the monitored signal corresponds to a "no leak", "minor leak", or "dangerous leak" category,
if the volume fraction of the gas leakage concentration measured by measuring points in the gas independent cabin of the comprehensive pipe gallery is c less than 1%, the gas leakage concentration belongs to the category of no leakage;
if the volume fraction of the gas leakage concentration measured by a measuring point in the gas independent cabin of the comprehensive pipe gallery is more than or equal to 1% and less than or equal to 5%, the value of the pressure in the pipe is more than 0 and less than or equal to 0.1MPa, and the gas leakage concentration belongs to the category of tiny leakage;
if the volume fraction of the gas leakage concentration measured by measuring points in the gas independent cabin of the comprehensive pipe gallery is c more than 1%, and the value P of the pressure in the pipeline is more than 0.1MPa at the moment, the gas leakage concentration belongs to the category of dangerous leakage;
step two, calculating distribution boundaries of 'no leakage', 'tiny leakage' and 'dangerous leakage' in a plane to obtain corresponding areas of 'no leakage', 'tiny leakage' and 'dangerous leakage' in the plane;
and step three, the controller transmits the signals of the corresponding areas and the corresponding types to the actuator, and the actuator determines the frequency conversion ventilation times according to the signals.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the specific setting process of the natural gas concentration monitor in the first step is as follows:
the fire-proof subareas are arranged every 200m in the independent gas cabin, so that the principle of monitoring the natural gas leakage in the cabin is to achieve the purpose of rapidly monitoring the leaked natural gas with the minimum number of monitors;
according to the operating pressure (less than or equal to 1.6MP) of a natural gas pipeline in an independent cabin of the comprehensive pipe rack and the most unfavorable small hole leakage condition (when the small hole is 0-6.35mm, the most unfavorable small hole leakage condition is 6.35mm), a numerical simulation method (a physical model of natural gas leakage diffusion in the comprehensive pipe rack is established by using preprocessing software ICEM in ANSYS and is subjected to grid division, a corresponding mathematical model and boundary conditions are given, calculation is carried out by using Fluent numerical simulation software, the obtained data cloud picture is subjected to post-processing by using post-processing software such as tecplot) to obtain a concentration field distribution cloud picture of natural gas leakage in the gas independent cabin of the comprehensive pipe rack, natural gas concentration monitors are sequentially arranged along a maximum change point of a step of a concentration field distribution contour line (namely, the position with the maximum curvature of the contour line), orthogonal processing is carried out on the monitors at different positions, and monitoring information is filtered out to form a linear correlation monitor, all on-line monitor signals are wirelessly transmitted to the integrated detection module;
in order to achieve the purpose of monitoring the natural gas leakage most quickly and accurately by using the least natural gas concentration monitors, the arranged natural gas concentration monitors are used for carrying out orthogonalization processing on monitoring points of the natural gas concentration, so that the natural gas concentration information acquired by the subsequently selected monitors is zero (namely the monitoring information of the monitors at the subsequently selected positions can be linearly related to the monitoring information of the monitors at the selected positions, so that the identification effect of the subsequently arranged monitors on the concentration parameters can be omitted), and the method can achieve the purpose of rapidly monitoring the natural gas leakage by using the least number of monitors;
the implementation method comprises the following steps: according to the operating parameter conditions of the pipeline of the gas cabin, a numerical simulation method is adopted to simulate the concentration field distribution of natural gas leakage under the worst working condition, natural gas concentration monitors are sequentially arranged along the maximum change point of the step of the concentration field distribution isoline, then orthogonal processing is carried out on the monitors at different positions, monitoring information is filtered out to form linear correlation monitors, and all signals of the online monitors are wirelessly transmitted to an integrated detection module.
Other steps and parameters are the same as those in the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: the natural gas concentration monitor monitors the natural gas concentration in the gas independent cabin of the comprehensive pipe gallery in real time;
the pipeline pressure sensor monitors the pressure of the natural gas in the pipeline in real time;
determining whether the monitored signal corresponds to a "no leak", "minor leak", or "dangerous leak" category;
the specific process is as follows:
sending the monitored analog signals to an analog-to-digital converter (or called A/D converter), processing the analog signals by the analog-to-digital converter (or called A/D converter) to convert the analog signals into a corresponding set of digital signals, transmitting the digital signals to a controller, and carrying out operation comparison on the set of data by the controller,
if the volume fraction of the gas leakage concentration measured by a measuring point in the gas independent cabin of the comprehensive pipe gallery is c less than 1%, no matter what the value of the pressure of the gas independent cabin of the comprehensive pipe gallery is (P is more than 0 and less than 0.6MPa), the gas leakage concentration should belong to the category of no leakage;
if the volume fraction of the gas leakage concentration measured by a measuring point in the gas independent cabin of the comprehensive pipe gallery is between 1% and 5%, and the value of the pressure in the pipe is more than 0 and less than or equal to 0.1MPa, the gas leakage concentration should belong to the category of micro leakage;
if the volume fraction of the gas leakage concentration measured by a measuring point in the gas independent cabin of the comprehensive pipe gallery is c more than 1%, and the value P of the pressure in the pipeline is more than 0.1MPa, the gas leakage concentration should belong to the category of dangerous leakage;
determining whether the monitored signal corresponds to a "no leak", "minor leak", or "dangerous leak" category;
the controller converts the digital signals corresponding to the category into analog signals through a digital-to-analog (or D/A) converter, and then transmits the analog signals to the actuator.
Other steps and parameters are the same as those in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: in the second step, distribution boundaries of 'no leakage', 'small leakage' and 'dangerous leakage' in the plane are calculated to obtain corresponding regions of 'no leakage', 'small leakage' and 'dangerous leakage' in the plane, and the specific process is as follows:
because the natural gas leakage amount in the gas independent cabin of the comprehensive pipe gallery is related to the pressure in the pipeline, the natural gas leakage concentration and the pressure P in the pipeline are selected asIs the feature vector, x ═ CH4,P)TForming a plane in a space by two eigenvectors of natural gas leakage concentration and pressure P in a pipeline;
the upper subscript T is transposed; CH (CH)4Is the natural gas leakage concentration;
active "○" means "no leakage",
indicating a "micro-leak",
representing a "hazardous leak," the distribution of the sample in space is shown in fig. 3. The three regions represent three different classes of samples, these boundary lines being called class boundaries, also called partition functions.
The distribution boundaries of no, minor and dangerous leaks in a plane, called partition functions;
the partition function is a decision function, and it is considered that the decision function is not necessarily a polygonal line, and may be other types of curves or curved surfaces. An expression of a decision function is proposed:
e1(x)＝a1x1+b1x2+c1＝0
e2(x)＝a2x1+b2x2+c2＝0
in the formula: x is the number of1，x2Respectively the natural gas leakage concentration and the pipeline internal pressure P; a is1，b1，a2，b2Determining the slope of the decision function for the weight coefficients; c. C1，c2Respectively, the deviation values are the intercept of the decision function;
utilize the decision function, divide into three parts to the independent cabin of whole space utility tunnel gas:
wherein the region corresponding to "no leakage" is e1(x)＜0；
The region corresponding to "minute leak" is e1(x)＞0∩e2(x)＜0；
The area corresponding to the "dangerous leak" is e2(x)＞0。
Other steps and parameters are the same as those in one of the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: the controller transmits signals of the corresponding areas and types to the actuator, and the actuator determines the frequency conversion ventilation times according to the signals; the specific process is as follows:
the leakage amount can be calculated through the leakage aperture and the pipeline pressure, and the calculation formula of the leakage amount q is as follows:
wherein q is the pinhole leakage intensity, m3/s；ρ0Is gas density, kg/m3；c0Is the orifice leakage coefficient; u. of0The gas leakage speed at the leakage hole is m/s; a is the area of the leakage opening, m2；P2Is the natural gas pipeline pressure, Pa; t' is the natural gas temperature, K; r is a gas constant, J/(kmol. K); m is gas molar mass, kg/mol; z is a gas compression factor; p0Atmospheric pressure, Pa; k is the natural gas adiabatic coefficient;
according to the requirement that the alarm concentration of leaking the independent cabin indoor natural gas of volume and utility tunnel gas is no more than 1%, calculate the required air volume V of this volume of leaking, the formula is:
converting the air change times per hour according to the ventilation volume V, wherein the formula is as follows:
in the formula, n is the number of times of ventilation and times/h;
s is the sectional area of the gas independent cabin of the comprehensive pipe gallery, m2；
L is the length of a fire-proof interval, and is 200 m;
v is the amount of ventilation required for leakage, m3/h。
When the number of times of ventilation is counted,
other steps and parameters are the same as in one of the first to fourth embodiments.
The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: the controller is Siemens S7-200 PLC.
Other steps and parameters are the same as those in one of the first to fifth embodiments.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: the natural gas concentration monitor is an alarm for detecting methane leakage from Ying energy in east China;
the pipeline pressure sensor is a power T12 universal pressure sensor.
Other steps and parameters are the same as those in one of the first to sixth embodiments.
The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: the actuator is a variable frequency fan.
Other steps and parameters are the same as those in one of the first to seventh embodiments.
The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: the power supply modes of the digital-to-analog (or D/A) converter and the controller are both 24V direct-current power supplies.
Other steps and parameters are the same as those in one to eight of the embodiments.
The detailed implementation mode is ten: the present embodiment differs from one of the first to ninth embodiments in that: the power supply mode of the variable frequency fan is 380V alternating current power supply.
Other steps and parameters are the same as those in one of the first to ninth embodiments.
Fig. 2 is a control flow chart of the linkage ventilation control system of the present invention, and the specific implementation process is as follows:
when the gas leakage ventilation control system in the gas independent cabin of the comprehensive pipe gallery works, a group of CH4 and P values are obtained through data acquisition of sensors (a gas concentration monitor and a pipeline pressure monitor), and then the sensors transmit the group of data to the controller. And the controller performs operation comparison on the group of data to determine the danger category of the leakage area corresponding to the group of data. The controller then communicates a signal of the corresponding category to the actuator, which effects a holding action or a changing action, i.e. changes the rotational speed of the fan, depending on the signal.
The gas leakage ventilation automatic control system comprises the following components: the PLC controller, an analog-to-digital (or called A/D) converter, a digital-to-analog (or called D/A) converter, a variable frequency fan, a pressure sensor, a CH4 sensor, a relay, a circuit breaker, a 24V direct-current power supply and the like, wherein all the parts are connected through a connecting terminal. An overview of the control system is shown in fig. 4.
The automatic control system is connected to an industrial computer, the compiling and modification of programs are realized through the computer, and the recording, the storage and the export of data acquired by the natural gas concentration monitor can also be realized;
the automatic control system comprises two ports, namely a digital quantity input end and a digital quantity output end;
the digital quantity refers to a discontinuous digital signal of "0" and "1";
the signals collected by the sensor belong to analog signals, and cannot be directly input into the controller for processing, so that an analog-to-digital converter (or called A/D converter) is arranged between the sensor and the automatic control system to process and convert the analog signals into a corresponding group of digital signals, and then the digital signals are transmitted into the controller;
after calculation and comparison, the category of 'no leakage', 'tiny leakage' or 'dangerous leakage' corresponding to the group of data is determined, a controller converts a digital signal corresponding to the category into an analog signal through a digital-to-analog converter, the analog signal is transmitted to an actuator, and finally the actuator completes the action;
the digital-to-analog converter and the controller are both supplied by a 24V DC power supply.
A related schematic diagram of the digital-to-analog converter is shown in fig. 5;
the working principle diagram of the variable frequency fan is shown in fig. 6;
the frequency conversion fan is powered by a 380V alternating current power supply, the frequency converter judges a digital signal from the controller, M in the figure refers to the fan, STF is a forward rotation signal interface output by the PLC host to the frequency converter, RL and RM are frequency signal interfaces output by the digital-to-analog converter to the frequency converter, and a return signal interface of the frequency converter is connected with the digital-to-analog converter.
The following examples were used to demonstrate the beneficial effects of the present invention:
the first embodiment is as follows: taking the pressure of natural gas in the comprehensive pipe gallery as an example of 0.6MPa, the leakage aperture is a small hole (the aperture leakage range is 0-6.35 mm), the arrangement scheme of the monitoring points is determined through numerical simulation and calculation, and as shown in FIGS. 7a and 7b, "×" is the monitoring point.
Vector in hypothesis space
Three categories of criteria are discussed. If the gas concentration (volume fraction) c measured by a measuring point in the gas independent cabin of the comprehensive pipe gallery is less than 1%, no matter how much the value of the pressure in the pipe is (0 is more than P and less than 0.6MPa), the gas concentration (volume fraction) c is not more than 1%, the gas concentration (volume fraction) should belong to the category of no leakage; if the gas leakage concentration is more than or equal to 1% and less than or equal to 5%, and the value of the pressure in the pipe is more than 0 and less than or equal to 0.1MPa, the gas leakage belongs to the category of micro leakage; if the gas leakage concentration c is greater than 1%, and the value P of the pressure in the pipeline is greater than 0.1MPa, the gas leakage is classified as dangerous leakage.
According to the above partition conditions, two partition functions can be obtained as shown in the following formulas:
in the representation space, the three categories analyzed as above correspond to the spatial regions shown in fig. 8, respectively;
the controller selected here is Siemens S7-200PLC, sensors used are Dongyi Ying energy methane leakage detection alarm and Linuo T12 universal pressure sensor, and the actuator is a variable frequency fan.
The following is a specific determination process of the frequency conversion ventilation times during dangerous leakage:
the calculation formula of the small hole leakage q is as follows:
wherein q is the pinhole leakage intensity, m3/s；ρ0Kg/m3 for gas density; t is the gas temperature, K; r is a gas constant, J/(kmol. K); m is gas molar mass, kg/mol; z is a gas compression factor; u. of0The gas leakage speed at the leakage hole is m/s; a is the area of the leakage opening, m2；c0Is the orifice leakage coefficient; p2Is the natural gas pipeline pressure, Pa; p0Atmospheric pressure, Pa; k is the natural gas adiabatic coefficient;
the leakage rate can be calculated through the leakage aperture and the pipeline pressure, according to the requirement that the alarm concentration of the natural gas in the pipeline corridor is not more than 1 percent,
the ventilation volume V required by the leakage volume is inversely calculated, and the ventilation frequency per hour is further converted into the ventilation frequency.
n is the number of times of ventilation/h;
s-sectional area of independent cabin, m2
L-length of fire-proof zone, 200m
V-air quantity m of air supply outlet3/h。
The present invention is capable of other embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and scope of the present invention.
Claims (10)
1. The utility model provides a utility tunnel gas cabin on-line monitoring and ventilation coordinated control method which characterized in that: the method comprises the following specific processes:
the method comprises the following steps that firstly, a natural gas concentration monitor monitors the natural gas concentration in a gas independent cabin of the comprehensive pipe gallery in real time;
the pipeline pressure sensor monitors the pressure of the natural gas in the pipeline in real time;
determining whether the monitored signal corresponds to a "no leak", "minor leak", or "dangerous leak" category;
if the volume fraction of the gas leakage concentration measured by measuring points in the gas independent cabin of the comprehensive pipe gallery is c less than 1%, the gas leakage concentration belongs to the category of no leakage;
if the volume fraction of the gas leakage concentration measured by a measuring point in the gas independent cabin of the comprehensive pipe gallery is more than or equal to 1% and less than or equal to 5%, the value of the pressure in the pipe is more than 0 and less than or equal to 0.1MPa, and the gas leakage concentration belongs to the category of tiny leakage;
if the volume fraction of the gas leakage concentration measured by measuring points in the gas independent cabin of the comprehensive pipe gallery is c more than 1%, and the value P of the pressure in the pipeline is more than 0.1MPa at the moment, the gas leakage concentration belongs to the category of dangerous leakage;
step two, calculating distribution boundaries of 'no leakage', 'tiny leakage' and 'dangerous leakage' in a plane to obtain corresponding areas of 'no leakage', 'tiny leakage' and 'dangerous leakage' in the plane;
and step three, the controller transmits the signals of the corresponding areas and the corresponding types to the actuator, and the actuator determines the frequency conversion ventilation times according to the signals.
2. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 1, characterized in that: the specific setting process of the natural gas concentration monitor in the first step is as follows:
the method comprises the steps that fire partitions are arranged in the gas independent cabin, a concentration field distribution cloud chart of natural gas leakage in the gas independent cabin of the comprehensive pipe rack is obtained by adopting a numerical simulation method according to the running pressure of a natural gas pipeline in the gas independent cabin of the comprehensive pipe rack and the worst small hole leakage condition, natural gas concentration monitors are sequentially arranged along the maximum change point of a concentration field distribution contour line step, then orthogonal processing is carried out on monitors at different positions, and filtered monitoring information is a linear correlation monitor.
3. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 2, characterized in that: the natural gas concentration detector monitors the natural gas concentration in the gas independent cabin of the comprehensive pipe gallery in real time;
the pipeline pressure sensor monitors the pressure of the natural gas in the pipeline in real time;
determining whether the monitored signal corresponds to a "no leak", "minor leak", or "dangerous leak" category;
the specific process is as follows:
sending the monitored analog signals to an analog-to-digital converter, processing the analog signals by the analog-to-digital converter to convert the analog signals into a corresponding group of digital signals, transmitting the digital signals to a controller, carrying out operation comparison on the group of data by the controller,
if the volume fraction of the gas leakage concentration measured by measuring points in the gas independent cabin of the comprehensive pipe gallery is c less than 1%, the gas leakage concentration belongs to the category of no leakage;
if the volume fraction of the gas leakage concentration measured by a measuring point in the gas independent cabin of the comprehensive pipe gallery is more than or equal to 1% and less than or equal to 5%, the value of the pressure in the pipe is more than 0 and less than or equal to 0.1MPa, and the gas leakage concentration belongs to the category of tiny leakage;
if the volume fraction of the gas leakage concentration measured by measuring points in the gas independent cabin of the comprehensive pipe gallery is c more than 1%, and the value P of the pressure in the pipeline is more than 0.1MPa at the moment, the gas leakage concentration belongs to the category of dangerous leakage;
determining whether the monitored signal corresponds to a "no leak", "minor leak", or "dangerous leak" category;
the controller converts the digital signals corresponding to the category into analog signals through the digital-to-analog converter, and then transmits the analog signals to the actuator.
4. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 3, characterized in that: in the second step, distribution boundaries of 'no leakage', 'small leakage' and 'dangerous leakage' in the plane are calculated to obtain corresponding regions of 'no leakage', 'small leakage' and 'dangerous leakage' in the plane, and the specific process is as follows:
selecting natural gas leakage concentration and pressure P in the pipeline as characteristic vectors, wherein x is (CH)4,P)TForming a plane in a space by two eigenvectors of natural gas leakage concentration and pressure P in a pipeline;
the upper subscript T is transposed; CH (CH)4Is the natural gas leakage concentration;
the distribution boundaries of no, minor and dangerous leaks in a plane, called partition functions;
the partition function is a decision function, and an expression of the decision function is provided:
e1(x)＝a1x1+b1x2+c1＝0
e2(x)＝a2x1+b2x2+c2＝0
in the formula: x is the number of1，x2Respectively the natural gas leakage concentration and the pipeline internal pressure P; a is1，b1，a2，b2Determining the slope of the decision function for the weight coefficients; c. C1，c2Respectively, the deviation values are the intercept of the decision function;
utilize the decision function, divide into three parts to the independent cabin of utility tunnel gas:
wherein the region corresponding to "no leakage" is e1(x)＜0；
The region corresponding to "minute leak" is e1(x)＞0∩e2(x)＜0；
The area corresponding to the "dangerous leak" is e2(x)＞0。
5. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 4, characterized in that: the controller transmits signals of the corresponding areas and types to the actuator, and the actuator determines the frequency conversion ventilation times according to the signals; the specific process is as follows:
the leakage amount can be calculated through the leakage aperture and the pipeline pressure, and the calculation formula of the leakage amount q is as follows:
wherein q is the pinhole leakage intensity, m3/s；ρ0Is gas density, kg/m3；c0Is the orifice leakage coefficient; u. of0The gas leakage speed at the leakage hole is m/s; a is the area of the leakage opening, m2；P2Is the natural gas pipeline pressure, Pa; t' is the natural gas temperature, K; r is a gas constant, J/(kmol. K); m is gas molar mass, kg/mol; z is a gas compression factor; p0Atmospheric pressure, Pa; k is the natural gas adiabatic coefficient;
according to the requirement that the alarm concentration of leaking the independent cabin indoor natural gas of volume and utility tunnel gas is no more than 1%, calculate the required air volume V of this volume of leaking, the formula is:
converting the air change times per hour according to the ventilation volume V, wherein the formula is as follows:
in the formula, n is the number of times of ventilation and times/h;
s is the sectional area of the gas independent cabin of the comprehensive pipe gallery, m2；
L is the length of a fire-proof interval, and is 200 m;
v is the amount of ventilation required for leakage, m3/h。
6. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 5, characterized in that: the controller is Siemens S7-200 PLC.
7. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 6, characterized in that: the natural gas concentration detector is an alarm for detecting methane leakage from Ying energy in east China;
the pipeline pressure sensor is a power T12 universal pressure sensor.
8. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 7, characterized in that: the actuator is a variable frequency fan.
9. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 8, characterized in that: the power supply modes of the digital-to-analog converter and the controller are both 24V direct-current power supplies.
10. The utility tunnel gas cabin on-line monitoring and ventilation linkage control method according to claim 9, characterized in that: the power supply mode of the variable frequency fan is 380V alternating current power supply.
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| CN113408884B (en) * | 2021-06-09 | 2023-04-07 | 天津大学 | Method for determining load of gas leakage explosion of underground comprehensive pipe gallery |
| CN115773473A (en) * | 2022-04-29 | 2023-03-10 | 重庆大学 | Monitoring system and monitoring method for natural gas leakage in tunnel |
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