Method for calculating pollutant concentration change in new clean partitioned ventilation mode of long tunnel

Abstract

The invention discloses a method for calculating pollutant concentration change in a new clean partitioned ventilation mode of a long tunnel. The method comprises the following steps: acquiring the total volume and the initial pollutant volume of a dirty air region, the dirty air and fresh air density, and operating parameters of an air curtain machine and an exhaust fan; the relational expressions between the pressure change in the dirty air area and the air inlet volume flow rate and the air inlet air velocity are obtained through calculation; obtaining a relational expression between the power of the exhaust fan and the air velocity of the suction opening according to the relational expression, and obtaining an air velocity expression of the air inlet; the fresh air volume flow rate of the air inlet and the pollutant content in the discharged mixed gas are obtained, and a differential equation is established to calculate the pollutant volume in the current polluted air area; the current pollutant concentration of the polluted air area is obtained. The ventilation adaptability of the ventilation mode during different tunnel construction periods and selection of ventilation parameters such as exhaust fan power are analyzed, the tunnel face dirty air area air curtain jet flow and exhaust fan optimization parameters and the arrangement method are achieved, ventilation in a long and large tunnel construction hole is achieved, and the safe and comfortable tunnel environment is guaranteed.

Description

Technical Field

[0001] The present invention relates to a method for calculating the change in pollutant concentration, and in particular to a method for calculating the change in pollutant concentration in a new mode of clean partition ventilation for long tunnels. Background Art

[0002] With the rise of China's strategy of building a transportation power and the continuous expansion of the scale of transportation infrastructure construction, the number of long tunnels under construction is also increasing. According to the "Action Plan for the Construction of New Infrastructure in the Transportation Field", it is necessary to build tunnels intelligently and use new technologies to improve the safety and construction efficiency of tunnel construction. During the construction of long tunnel projects, due to special geographical environments and construction conditions, the air flow inside the tunnel is restricted, the ventilation distance is long, and the ventilation effect is difficult to meet expectations. Construction ventilation faces a series of problems and challenges. This will result in poor air quality inside the tunnel, affecting the health and work efficiency of construction workers. Therefore, carrying out research on the new mode of clean partition ventilation for long tunnels has important theoretical significance and application value.

[0003] In order to improve the tunnel construction environment and ensure the health and safety of construction workers, effective ventilation measures are particularly important. At present, the main tunnel construction ventilation technologies include forced ventilation, exhaust ventilation, roadway ventilation, etc. Forced ventilation presses fresh air into the tunnel, causing the polluted air to be discharged from the other end of the tunnel. However, in long tunnels, the ventilation distance is limited, and the air flow is prone to short-circuit phenomena, making it difficult to effectively control the spread of pollutants. Exhaust ventilation, on the other hand, extracts the polluted air inside the tunnel through a suction fan. However, when used alone, its ability to control the source of pollutants is weak. Especially in the case of a large amount of dust generated after blasting operations, the exhaust effect is limited. Roadway ventilation uses the excavated cross tunnels, pilot tunnels, etc. to form ventilation roadways to assist the ventilation of the main tunnel. However, under certain special geological conditions or construction layouts, the implementation of roadway ventilation is difficult, and the ventilation effect is greatly affected by the location and number of roadways. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a method for calculating the change in pollutant concentration in a new mode of clean partition ventilation for long tunnels. By studying the change in pollutant concentration in the new mode of clean partition ventilation for long tunnels, the problem of construction ventilation in long tunnels is solved, the construction environment state inside the long tunnel is improved, and a new method is provided for the ventilation design of long tunnels.

[0005] Technical Solution: The method for calculating the change in pollutant concentration in a new mode of clean partition ventilation for long tunnels according to the present invention includes the following steps:

[0006] (1) Obtain the total volume of the polluted air area in the tunnel, the initial volume of pollutants, the density of polluted air and fresh air, the operating parameters of the air curtain machine, and the operating parameters of the suction fan;

[0007] (2) Calculate the relationship between the magnitude of the pressure change in the polluted air area and the volumetric flow rate of the extraction opening based on the operating power of the extraction fan;

[0008] (3) Calculate the relationship between the magnitude of the pressure change in the polluted air area and the fresh air velocity at the air inlet based on Bernoulli's equation;

[0009] (4) Obtain the relationship between the extraction fan power and the fresh air velocity at the air inlet based on the relationships in (2) and (3), and calculate the expression for the fresh air velocity at the air inlet;

[0010] (5) Based on the constant air pressure in the polluted air area, obtain the fresh air volumetric flow rate at the air inlet according to the volumetric flow rate of the extraction opening, the area of the air inlet, and the fresh air velocity at the air inlet;

[0011] (6) Calculate the volume of pollutants in the polluted air extracted after the extraction fan operates for a time Δt based on the volumetric flow rate of the extraction opening, the operating time of the extraction fan, and the pollutant concentration in the polluted air area at the previous moment, and establish a differential equation to calculate the volume of pollutants in the current polluted air area;

[0012] (7) The ratio of the volume of pollutants in the current polluted air area obtained in (6) to the total volume of the polluted air area is the relationship between the pollutant concentration in the polluted air area and time change.

[0013] Preferably, in step (1), calculate the cross-sectional area of the tunnel according to the tunnel cross-section design drawing, measure the distance between the tunnel blasting face and the barrier device, and calculate the total volume of the polluted air area; the operating parameters of the air curtain machine include the air curtain jet area and the air curtain jet diversion wind speed, and the operating parameters of the extraction fan include the extraction fan power and the operating time of the extraction fan.

[0014] Preferably, in step (2), the volumetric flow rate of the extraction opening is equal to the volumetric flow rate of the air inlet, and the calculation formula is as follows:

[0015]

[0016] Q = A·v1

[0017]

[0018] Wherein, P is the extraction fan power, ΔP is the magnitude of the pressure change in the polluted air area, Q is the volumetric flow rate of the extraction opening or the air inlet, W represents the work done by the extraction fan with power P in a certain time, t is the operating time of the extraction fan, F is the attraction generated by the extraction fan, A represents the area of the air inlet, v1 represents the fresh air velocity at the air inlet, and d represents the operating distance of the extraction fan.

[0019] Preferably, the relationship in step (3) is as follows:

[0020]

[0021] Among them, ΔP is the magnitude of the pressure change in the polluted air area, ρ f is the fresh air density, and v1 is the fresh air flow velocity at the air inlet.

[0022] Preferably, in step (4), the relationship between the power of the exhaust fan and the fresh air flow velocity at the air inlet is calculated, and the expression of the fresh air flow velocity at the air inlet is obtained as follows:

[0023]

[0024] Obtained:

[0025]

[0026] Among them, P is the power of the exhaust fan, ΔP is the magnitude of the pressure change in the polluted air area, Q is the volume flow rate at the exhaust port or the air inlet, ρ f is the fresh air density, v1 is the fresh air flow velocity at the air inlet, and A represents the area of the air inlet.

[0027] Preferably, the volume flow rate at the exhaust port in step (5) is equal to the volume flow rate at the air inlet, and the calculation formula for the fresh air volume flow rate at the air inlet is as follows:

[0028]

[0029] Among them, P is the power of the exhaust fan, Q is the volume flow rate at the exhaust port or the air inlet, ρ f is the fresh air density, v1 is the fresh air flow velocity at the air inlet, and A represents the area of the air inlet.

[0030] Preferably, the calculation formula in step (6) is as follows:

[0031] V out = Q·Δt

[0032] V op = V p (t)·Q·Δt

[0033] V p (t + Δt) = V p (t) - V p (t)·Q·Δt

[0034] Among them, V out is the volume of pollutants in the polluted air extracted by the exhaust fan after running for a time Δt, V op is the content of pollutants in the polluted air extracted at the previous moment, V p is the volume of pollutants in the polluted air area, V p (t + Δt) is the change in the volume of pollutants.

[0035] Preferably, the relationship of the volume change of the pollutant is as follows:

[0036]

[0037] That is:

[0038]

[0039] Wherein, P is the power of the exhaust fan, t is the action time of the exhaust fan, A represents the area of the air inlet, V p is the volume of the pollutant in the polluted air area, V p (t + Δt) is the volume change of the pollutant, Q is the volume flow rate of the air outlet or air inlet, ρ f is the density of fresh air, and V is the volume of the polluted air area.

[0040] Preferably, the relationship of the volume change of the pollutant in the polluted air area with time is:

[0041]

[0042] C = ln aV

[0043] That is:

[0044]

[0045] Wherein, P is the power of the exhaust fan, t is the action time of the exhaust fan, A represents the area of the air inlet, v1 represents the fresh air flow velocity at the air inlet, ρ f is the density of fresh air, V is the volume of the polluted air area, and ɑ is a coefficient representing the ratio of the initial volume of the pollutant to the entire space.

[0046] Preferably, step (7) includes: the ratio of the change in the volume V p of the pollutant in the polluted air area with time t, V p (t) to the volume V of the polluted air area to obtain the relationship of the change in the pollutant concentration in the polluted air area with time The formula is as follows:

[0047]

[0048] Wherein, V p is the volume of the pollutant in the polluted air area, V is the volume of the polluted air area, P is the power of the exhaust fan, t is the action time of the exhaust fan, A represents the area of the air inlet, ρ f is the density of fresh air.

[0049] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) The calculation method provided by the present invention for the change of pollutant concentration in the polluted air area with the action time of the exhaust fan is applicable to the calculation and selection of parameters such as the exhaust fan power selection, the volume of the polluted air area, and the area of the fresh air inlet, so as to achieve the purpose of more efficiently reducing the pollutant concentration in the polluted air area and ensuring a good construction environment in the tunnel; (2) Applicable to the selection and calculation of exhaust fan power, the diameter of the exhaust duct, the area of the fresh air inlet, and the volume of the polluted air area; (3) Realize the timely adjustment of the volume of the polluted air area and the area of the fresh air inlet during the ventilation process, which is beneficial to promoting the ventilation method of the new model of clean partition ventilation for long tunnels and has good engineering application value. Description of the Drawings

[0050] Figure 1 It is a flow chart of the method of the present invention.

[0051] Figure 2 It is a calculation model diagram of the present invention.

[0052] Figure 3 It is a schematic diagram of the change relationship of pollutant concentration in the polluted air area with time. Detailed Embodiments

[0053] The technical solution of the present invention will be further described below with reference to the drawings.

[0054] As Figure 1 shown, a calculation method for the change of pollutant concentration in a new model of clean partition ventilation for long tunnels includes the following steps:

[0055] (1) Obtain the total volume of the polluted air area in the tunnel, the initial volume of pollutants, the density of polluted air and fresh air, the operating parameters of the air curtain machine, and the operating parameters of the exhaust fan;

[0056] (2) Calculate the relationship between the pressure change magnitude in the polluted air area and the volume flow rate at the exhaust outlet according to the action power of the exhaust fan;

[0057] (3) Calculate the relationship between the pressure change magnitude in the polluted air area and the fresh air flow velocity at the inlet according to Bernoulli's equation;

[0058] (4) Obtain the relationship between the exhaust fan power and the fresh air flow velocity at the inlet according to the relationships in (2) and (3), and calculate the expression of the fresh air flow velocity at the inlet;

[0059] (5) According to the constant air pressure in the polluted air area, obtain the fresh air volume flow rate at the inlet according to the volume flow rate at the exhaust outlet, the inlet area, and the fresh air flow velocity at the inlet;

[0060] (6) Calculate the volume of pollutants in the exhausted dirty air after the operation time Δt of the exhaust fan according to the volume flow rate of the exhaust opening, the action time of the exhaust fan, and the pollutant concentration in the dirty air area at the previous moment, and establish a differential equation to calculate the volume of pollutants in the current dirty air area;

[0061] (7) The ratio of the volume of pollutants in the current dirty air area obtained in (6) to the total volume of the dirty air area is the relational expression of the pollutant concentration in the dirty air area changing with time.

[0062] Specifically, obtain the tunnel section design drawing and calculate the tunnel section area, measure the distance between the tunnel blasting face and the blocking device, and calculate the volume of the dirty air area; obtain the volume of pollutants, the density of dirty air, and the density of fresh air in the dirty air area after tunnel blasting.

[0063] Set the power of the exhaust fan as P, the magnitude of the pressure change in the dirty air area as ΔP, and the volume flow rate of the exhaust opening as Q, where the volume flow rate of the exhaust opening is equal to the volume flow rate of the air inlet. The formula is as follows:

[0064]

[0065] Q = A·v1

[0066]

[0067] Among them, W represents the work done by the exhaust fan with power P in a certain time, t represents the action time of the exhaust fan, F represents the attraction generated by the exhaust fan, A represents the area of the air inlet, v1 represents the fresh air flow velocity at the air inlet, and d represents the action distance of the exhaust fan.

[0068] Calculate the relational expression between the pressure change ΔP in the dirty air area, the fresh air density ρ f and the fresh air flow velocity v1 at the air inlet as follows:

[0069]

[0070] Among them, ΔP is the magnitude of the pressure change in the dirty air area, ρf is the fresh air density, and v1 is the fresh air flow velocity at the air inlet.

[0071] Calculate the relational expression between the power of the exhaust fan and the fresh air flow velocity at the air inlet, and obtain the expression of the fresh air flow velocity at the air inlet as follows:

[0072]

[0073] Obtain:

[0074]

[0075] Among them, P is the power of the exhaust fan, ΔP is the magnitude of the pressure change in the polluted air area, Q is the volumetric flow rate at the exhaust or inlet, ρf is the density of fresh air, v1 is the fresh air velocity at the inlet, and A represents the area of the inlet.

[0076] The formula for calculating the volumetric flow rate of fresh air at the inlet is as follows:

[0077]

[0078] Among them, P is the power of the exhaust fan, Q is the volumetric flow rate at the exhaust or inlet, ρ f is the density of fresh air, v1 is the fresh air velocity at the inlet, and A represents the area of the inlet.

[0079] Set V out as the volume of pollutants in the polluted air extracted after the exhaust fan operates for a time Δt, V op as the content of pollutants in the polluted air extracted at the previous moment, V p as the volume of pollutants in the polluted air area, and obtain the volume change of pollutants V p (t + Δt) The formula is:

[0080] V out = Q·Δt

[0081] V op = V p (t)·Q·Δt

[0082] V p (t + Δt) = V p (t) - V p (t)·Q·Δt

[0083] Rewrite the above relationship of pollutant volume change into the form of a differential equation,

[0084]

[0085] That is,

[0086]

[0087] Among them, P is the power of the exhaust fan, t is the action time of the exhaust fan, A represents the area of the inlet, V p is the volume of pollutants in the polluted air area, V p (t + Δt) is the volume change of pollutants, Q is the volumetric flow rate at the exhaust or inlet, ρ f is the density of fresh air, and V is the volume of the polluted air area.

[0088] Set the initial volume of pollutants in the polluted air area at t = 0 as V p(0) = aV, a ∈ (0, 1). By separating variables, integrating the differential equation and substituting the initial conditions for solution, the volume V of the pollutants in the polluted air area is obtained. p The relationship between V p changing with time t, specifically the formula is:

[0089]

[0090] C = ln aV

[0091] That is,

[0092]

[0093] Dividing the volume V of the pollutants in the polluted air area p changing with time t, V p (t), by the volume V of the polluted air area, the relationship between the pollutant concentration in the polluted air area and time is obtained. That is:

[0094]

[0095] Among them, V p is the volume of the pollutants in the polluted air area, V is the volume of the polluted air area, P is the power of the exhaust fan, t is the operating time of the exhaust fan, A represents the area of the air inlet, and ρ f is the density of the fresh air.

[0096] As Figure 2 shown, for a calculation model of the change in pollutant concentration in a new ventilation mode of clean partition ventilation for long tunnels, through a barrier device, the distance between the jet of the air curtain machine and the tunnel blasting construction face with an area of S is L, and the two form a polluted air area with a volume of V through the barrier. The air curtain jet area (i.e., the fresh air inlet area) is A, and the exhaust fan extracts the polluted air in the polluted air area with a power of P. The function of the volume of the pollutants in the polluted air area changing with the operating time of the exhaust fan is V p (t), and the function of the pollutant concentration in the polluted air area changing with the operating time of the exhaust fan is

[0097] The present invention is applicable to a new ventilation mode of clean partition ventilation for long tunnels. In this ventilation mode, a spray-type air curtain machine is set behind the tunnel face, and a tunnel air curtain partition wall is formed through the jet air curtain, dividing the tunnel face into a blasting construction polluted air area and a fresh air area, restricting the diffusion of the polluted air. Fresh air enters the tunnel along the whole length from outside the tunnel. A polluted air bin is set in the tunnel, and the polluted air in the tunnel face is discharged through an exhaust fan and a compressor to meet the ventilation requirements for the single-heading construction of long tunnels.

[0098] The present invention constructs a calculation model for the change of pollutant concentration in a new type of clean partition ventilation mode suitable for long tunnels. By deeply studying the change of pollutant concentration in the new type of clean partition ventilation mode of long tunnels, it helps to solve the problem of construction ventilation in long tunnels, improve the construction environment state in long tunnels, and provide a new method for the ventilation design of long tunnels.

[0099] The following combines specific examples to apply a calculation method for the change of pollutant concentration in a new type of clean partition ventilation mode of long tunnels proposed by the present invention:

[0100] Taking a double-track high-speed railway tunnel as an example, where the area S of the tunnel blasting construction face is 100.059 m 2 , the distance L between the construction face and the barrier device is 500 m, and the volume V of the polluted air area is 50029.5 m 3 , the initial pollutant concentration V p (0) accounts for 10% of the total volume, that is, 5002.95 m 3 , the jet area A of the air curtain machine is 100 m 2 , the density ρ p of the polluted air is 2.0 kg / m 3 , the density ρ f of the fresh air is 1.225 m 3 , and the power P of the exhaust fan is 23.5 kW. Use Python language programming to analyze the relationship between the pollutant concentration in the polluted air area and the action time of the exhaust fan. The analysis results are as Figure 3 shown.

[0101] By measuring data such as the volume of the tunnel polluted air area, the initial pollutant concentration, the jet area of the air curtain machine, the density of the polluted air, and the density of the fresh air, and using Python language to program and analyze the data, when the power of the exhaust fan is 23.5 kW and the initial pollutant concentration is 10%, this ventilation method can reduce the pollutant concentration in the tunnel polluted air area to nearly 0 at time t = 400 s, meeting the relevant ventilation specifications for long tunnel construction. In the actual design process, combined with the actual situation of tunnel construction, relevant calculation parameters such as the power of the exhaust fan and the volume of the polluted air area are selected.

Claims

1. A calculation method for the change in pollutant concentration of a new cleaning partition ventilation mode in long tunnels, characterized in that, It includes the following steps: (1) Obtain the total volume of the tunnel polluted air area, the initial volume of pollutants, the density of polluted air and fresh air, the operating parameters of the air curtain machine, and the operating parameters of the exhaust fan; (2) Calculate the relationship between the magnitude of the pressure change in the polluted air area and the volumetric flow rate at the exhaust port according to the acting power of the exhaust fan; (3) Calculate the relationship between the magnitude of the pressure change in the polluted air area and the fresh air velocity at the air inlet according to Bernoulli's equation; (4) Obtain the relationship between the power of the exhaust fan and the fresh air velocity at the air inlet based on the relationships in (2) and (3), and calculate the expression for the fresh air velocity at the air inlet; (5) According to the constant air pressure in the polluted air area, obtain the fresh air volumetric flow rate at the air inlet based on the volumetric flow rate at the exhaust port, the area of the air inlet, and the fresh air velocity at the air inlet; (6) Calculate the volume of pollutants in the polluted air extracted by the exhaust fan after running for a time Δt based on the volumetric flow rate at the exhaust port, the acting time of the exhaust fan, and the pollutant concentration in the polluted air area at the previous moment, and establish a differential equation to calculate the volume of pollutants in the current polluted air area; (7) The ratio of the volume of pollutants in the current polluted air area obtained in (6) to the total volume of the polluted air area is the relationship between the pollutant concentration in the polluted air area and time.

2. The method for calculating the change in pollutant concentration according to claim 1, wherein In step (1), calculate the cross-sectional area of the tunnel according to the tunnel cross-section design drawing, measure the distance between the tunnel blasting face and the barrier device, and calculate the total volume of the polluted air area; the operating parameters of the air curtain machine include the air curtain jet area and the air curtain jet split flow velocity, and the operating parameters of the exhaust fan include the exhaust fan power and the acting time of the exhaust fan.

3. The method for calculating the change in pollutant concentration according to claim 1, wherein, In step (2), the volumetric flow rate at the exhaust port is equal to the volumetric flow rate at the air inlet, and the calculation formula is as follows: Q = A·v1 Where, P is the power of the exhaust fan, ΔP is the magnitude of the pressure change in the polluted air area, Q is the volumetric flow rate at the exhaust port or the air inlet, W represents the work done by the exhaust fan at power P in a certain time, t is the acting time of the exhaust fan, F is the attraction generated by the exhaust fan, A represents the area of the air inlet, v1 represents the fresh air velocity at the air inlet, and d represents the acting distance of the exhaust fan.

4. The method for calculating the change in pollutant concentration according to claim 1, wherein The relationship in step (3) is as follows: where ΔP is the magnitude of the pressure change in the polluted air area, ρ f is the fresh air density, and v1 is the fresh air flow velocity at the air inlet.

5. The method for calculating the change in pollutant concentration according to claim 1, wherein In step (4), calculate the relationship between the power of the exhaust fan and the fresh air velocity at the air inlet, and the expression for the fresh air velocity at the air inlet is obtained as follows: Obtain: Wherein, P is the power of the exhaust fan, ΔP is the magnitude of the pressure change in the polluted air area, Q is the volumetric flow rate of the air extraction port or the air inlet, ρ f is the density of fresh air, v1 is the fresh air flow velocity at the air inlet, and A represents the area of the air inlet.

6. The method for calculating the change in pollutant concentration according to claim 1, wherein In step (5), the volumetric flow rate at the exhaust port is equal to the volumetric flow rate at the air inlet, and the calculation formula for the fresh air volumetric flow rate at the air inlet is as follows: where P is the power of the exhaust fan, Q is the volumetric flow rate of the exhaust or intake opening, ρ f is the density of fresh air, v1 is the fresh air velocity at the intake opening, and A represents the area of the intake opening.

7. The method for calculating the change in pollutant concentration according to claim 1, wherein The calculation formula in step (6) is as follows: V p (t + Δt) = V p (t) - V p (t)·Q·Δt Among them, V out is the volume of pollutants in the polluted air extracted by the exhaust fan after the elapsed time Δt, V op is the content of pollutants in the polluted air extracted at the previous moment, V p is the volume of pollutants in the polluted air area, V p (t + Δt) is the volume change of pollutants.

8. The method for calculating the change in pollutant concentration according to claim 7, characterized in that, The relationship for the change in the volume of pollutants is as follows: That is: Among them, P is the power of the exhaust fan, t is the action time of the exhaust fan, A represents the area of the air inlet, V p is the volume of the polluted object in the polluted air area, V p (t + Δt) is the volume change of the pollutant, Q is the volume flow rate of the air outlet or air inlet, ρ f is the density of fresh air, and V is the volume of the polluted air area.

9. The method for calculating the change in pollutant concentration according to claim 8, characterized in that The relationship for the change in the volume of pollutants in the polluted air area with time is: C = ln a V That is: Among them, P is the power of the exhaust fan, t is the action time of the exhaust fan, A represents the area of the air inlet, v1 represents the fresh air flow velocity at the air inlet, ρ f is the fresh air density, V is the volume of the polluted air area, and ɑ is a coefficient, representing the ratio of the initial volume of pollutants to the entire space volume.

10. The method for calculating the change in pollutant concentration according to claim 1, wherein The said step (7) includes: the volume V of the polluted objects in the polluted air area p The variation of V p with time t, and the ratio of the volume V of the polluted air area is used to obtain the relational expression of the concentration of pollutants in the polluted air area changing with time The formula is as follows: Among them, V p is the volume of the polluted object in the polluted air area, V is the volume of the polluted air area, P is the power of the exhaust fan, t is the action time of the exhaust fan, A represents the area of the air inlet, and ρ f is the density of fresh air.

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