Method for determining whether atomized LPG adheres to the inner wall surface of the downstream pipe of a heat quantity adjustment device

Abstract

To provide a method for determining whether or not atomized LPG adheres to an inner wall surface of piping on a downstream side of a calorific value adjustment device.SOLUTION: Provided is a method for determining whether or not atomized LPG adheres to an inner wall surface of downstream piping of a calorific value adjustment device 1 that adjusts a calorific value of NG by adding LPG from a liquid nozzle 13 to the NG flowing through a main flow pipe 3. The calorific value adjustment device comprises: an outer cylinder 5 that is provided in the main flow pipe 3 through which the NG flows, and receives the supply of the NG from a base end side to eject the NG toward a tip side; an inner cylinder 9 that is arranged coaxially with the outer cylinder 5 within the outer cylinder 5 and via a space with an inner wall of the outer cylinder, and receives the supply of the NG from a branch tube 7 branched from the main flow pipe 3; and a liquid nozzle 13 that is arranged coaxially with the inner cylinder 9 and discharges LPG into the inner cylinder 9. In the method, if Sm×t×(Psat,LPG-PLPG) is 1.5×1010 or more, it is determined that LPG does not adhere to the inner wall surface of piping, and if Sm×t×(Psat,LPG-PLPG) is less than 1.5×1010, it is determined that LPG adheres to the inner wall surface of the piping.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for determining whether atomized LPG adheres to the inner wall surface of a downstream pipe of a heat quantity adjusting device that adjusts the heat quantity by vaporizing and mixing liquefied petroleum gas (LPG) with natural gas (NG) obtained by vaporizing liquefied natural gas (LNG).

Background Art

[0002] The heat quantity adjustment of city gas is performed by vaporizing and mixing liquefied petroleum gas (LPG) with natural gas (NG) obtained by vaporizing liquefied natural gas (LNG). In recent years, the import of LNG with a high methane component such as shale gas has been increasing, and the heat increasing width by LPG tends to increase.

[0003] As such a heat quantity adjustment method, for example, it can be performed using the "fluid atomization nozzle device" disclosed in Patent Document 1. In Patent Document 1, as an embodiment of the fluid atomization nozzle device, a heat quantity adjusting device for producing city gas by adding LPG (liquid) to NG (gas) is disclosed.

[0004] As shown in FIG. 6, this heat quantity adjusting device 1 includes an outer cylinder 5 formed of a venturi tube provided in a main flow pipe 3 through which NG flows, a branch pipe 7 branched from the main flow pipe 3, an inner cylinder 9 disposed in the outer cylinder 5 and receiving the supply of NG from the branch pipe 7, and a liquid nozzle 13 provided in the inner cylinder 9 and receiving the supply of LPG from a liquid supply pipe 11. The heat quantity of NG is adjusted by adding LPG from the liquid nozzle 13 to the NG flowing through the main flow pipe 3. (See paragraph

[0042] of Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The heat quantity adjustment device incorporated with the fluid atomization nozzle device disclosed in Patent Document 1 is premised on the horizontal installation of the Venturi tube, that is, being placed horizontally, and there is no mention of whether the heat quantity adjustment functions properly when it is placed vertically.

[0007] When the installation posture of the heat quantity adjustment device is vertical (vertically upward or vertically downward), a predetermined space in the height direction is required. Therefore, in order to minimize the height of the equipment, it is necessary to shorten the straight pipe section provided downstream of the heat quantity adjustment device and provide an elbow.

[0008] Under the condition that the difference between the temperature of the production gas after heat quantity adjustment and the dew point of the production gas (hereinafter referred to as "superheat degree") is small, a certain distance is required for the vaporization of the LPG atomized by the fluid atomization nozzle device. Therefore, during the vaporization process, due to the influence of the uneven flow generated by the elbow, the atomized LPG adheres to the inner wall surface of the downstream piping of the heat quantity adjustment device, inhibiting vaporization, and it has become clear that an unexpected low temperature will occur.

[0009] In such a state, not only does the heat quantity adjustment not function properly, but there are also concerns about the adverse effects on the equipment due to the unexpected low temperature. Therefore, a quantitative determination criterion for determining whether such a situation occurs has been demanded.

[0010] The present invention has been made to solve such problems, and an object thereof is to provide a method for determining whether atomized LPG adheres to the inner wall surface of the downstream piping on the downstream side of the heat quantity adjustment device.

Means for Solving the Problems

[0011] An empirical test was conducted on the case where the installation posture of the heat quantity adjustment device is vertical, the superheat degree is small, and an elbow is installed downstream of the heat quantity adjustment device, and the conditions under which atomized LPG adheres to the inner wall surface of the piping were specified. Then, from the specified conditions, factors affecting the vaporization of LPG were identified, and using these factors, a unique index was found to determine whether LPG adheres to the inner wall surface of the pipe without vaporizing. Specifically, it is as follows.

[0012] The present invention provides an outer cylinder provided in a main flow pipe through which NG flows, receiving the supply of the NG from the base end side and ejecting it from the tip end side, an inner cylinder disposed coaxially with the outer cylinder within the outer cylinder and receiving the supply of the NG from a branch pipe branched from the main flow pipe with a space between the inner wall of the outer cylinder, and a liquid nozzle disposed coaxially with the inner cylinder and discharging LPG into the inner cylinder. By adding LPG from the liquid nozzle to the NG flowing through the main flow pipe, a method for determining whether atomized LPG adheres to the inner wall surface of the downstream pipe of a calorific value adjustment device that adjusts the calorific value of the NG, S m ×t×(P sat,LPG -P LPG ) is 1.5×10 10 or more, it is determined that LPG does not adhere to the inner wall surface of the pipe, and S m ×t×(P sat,LPG -P LPG ) is less than 1.5×10 10 , it is characterized in that it is determined that LPG adheres to the inner wall surface of the pipe. Here, S m : Specific surface area of LPG [m 2 / m 3 t: Residence time of LPG droplets [s] P sat,LPG : Saturated vapor pressure of LPG at the production gas temperature [Pa] P LPG : Partial pressure of LPG in the production gas [Pa]

Advantages of the Invention

[0013] According to the present invention, regardless of the installation posture of the calorific value adjustment device, it is possible to determine whether LPG droplets before vaporization adhere to the inner wall surface of the downstream pipe of the calorific value adjustment device. Therefore, when the installation posture of the heat quantity adjustment device is vertical and an elbow is installed downstream of the heat quantity adjustment device with a small overheat degree, it can be used as an index to prevent the downstream pipe of the heat quantity adjustment device from becoming low in temperature. That is, if the device is manufactured to meet this index, it is not necessary to use a low-temperature material for the downstream pipe of the heat quantity adjustment device, which leads to a reduction in material costs and construction costs.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0015] As shown in FIG. 1, the present embodiment is a method for determining whether atomized LPG adheres to the inner wall surface of the downstream pipe of a heat quantity adjustment device 1 that includes an outer cylinder 5 provided in a main flow pipe 3 through which NG flows, receiving the supply of the NG from the base end side and ejecting it from the tip end side, an inner cylinder 9 disposed coaxially with the outer cylinder 5 inside the outer cylinder 5 and receiving the supply of the NG from a branch pipe 7 branched from the main flow pipe 3 with a space between the inner wall of the outer cylinder, and a liquid nozzle 13 disposed coaxially with the inner cylinder 9, receiving the supply of LPG from a liquid supply pipe 11 and discharging the LPG into the inner cylinder 9, and adjusting the heat quantity of the NG by adding LPG from the liquid nozzle 13 to the NG flowing through the main flow pipe 3. Specifically, S m × t × (Psat,LPG -P LPG ) is 1.5×10 10 or more, it is determined that LPG does not adhere to the inner wall surface of the pipe, and S m ×t×(P sat,LPG -P LPG ) is less than 1.5×10 10 , it is determined that LPG adheres to the inner wall surface of the pipe. Here, S m : Specific surface area of LPG [m 2 / m 3 t: Residence time of LPG droplets [s] P sat,LPG : Saturated vapor pressure of LPG at the production gas temperature [Pa] P LPG : Partial pressure of LPG in the production gas [Pa] The derivation method of the above judgment criteria will be described below.

[0016] The factors affecting the vaporization of LPG are S m (= Specific surface area of LPG), t (= Residence time of LPG droplets) and (P sat,LPG -P LPG )(Difference [Pa] between the saturated vapor pressure P sat,LPG of LPG at the production gas temperature and the partial pressure P LPG of LPG in the production gas), and S m and t are obtained by the following equations. S m =(πD 2 )×n / F LPG ···(1) t = L / u t,LPG ········(2) Here, D: Droplet diameter of atomized LPG [m / particle] (can be estimated by previous equations) n: Number of droplets [particle] F LPG : Amount of LPG [m 3 L: Length of the Venturi section [m] u t,LPG : Terminal velocity of LPG droplets [m / s]

[0017] Here, the terminal velocity u of LPG droplets​​t,LPG The method of obtaining Considering the situation where the LPG droplets flowing out of the liquid nozzle 13 are decelerated by the flow of the surrounding gas, the following equation of motion for the LPG droplets holds. ρ LPG V D (du / dt)=(ρ LPG -ρ Gas )V D a - C D S(ρ Gas u 2 / 2) ····(3) Here, ρ LPG : Density of LPG [kg / m 3 V D : Volume per LPG droplet (=πD 3 / 6)[m 3 ρ Gas : Density of the production gas [kg / m 3 C D : Drag coefficient (=24 / Re, Re: Reynolds number (=Du t ρ Gas / μ Gas ))[-] u t : Terminal velocity u of the LPG droplet t,LPG and the difference from u2 (u2 will be described later) μ Gas : Viscosity of the production gas [Pa s] S: Projected area in the direction of motion per LPG droplet (=πD 2 / 4)[m 2 u: Velocity of the LPG droplet [m / s] a: Deceleration acceleration of the gas [m / s 2 Note that the drag coefficient C D has different equations depending on the range of Re. However, the LPG droplet diameter D is very small on the order of μm, and generally Re = Du t ρ Gas / μ Gas <2, so C D = 24 / Re.

[0018] ​​​​​Here, the method for obtaining the deceleration acceleration \(a\) of the gas will be described based on FIGS. 2 and 3. FIG. 2 shows typical flow velocity changes of NG and LPG droplets from the nozzle outlet to the venturi outlet. Here, \(u\) G is the NG flow velocity at the time of nozzle outflow, \(u_1\) is the NG flow velocity at a certain part of the venturi, \(u_2\) is the NG flow velocity at the venturi outlet, and \(L\) is the venturi length. As shown in FIG. 2, the NG flow velocity decreases as the flow path expands, and the LPG droplet passes through a certain part of the venturi at the higher velocity of \(u\) G or \(u_1\) (=MAX(\(u\) G , \(u_1\))), and the LPG droplet is decelerated to the terminal velocity \(u\) t,LPG by the surrounding gas. Assuming that the gas flow velocity decreases linearly with time, the venturi length \(L\) is the area of the gray part in the graph of FIG. 3, and the following equation holds.

Equation

[0019] Also, the deceleration acceleration \(a\) of the gas is obtained by the following equation.

Equation

[0020] From equations (4) and (5), the deceleration acceleration \(a\) of the gas is obtained as follows.

Equation

[0021] The difference \(u\) t,LPG between the terminal velocity \(u\) t of the LPG droplet and \(u_2\) is the velocity when the acceleration becomes zero. This is when the left side of equation (3) becomes zero, and when \(u = u\) t in equation (3), the following equation for \(u\) t is obtained. \(u\) t = D 2 (\(\rho\) LPG - \(\rho\) Gas)a / (18μ Gas ) In the above equation, further considering the correction ((3μ LPG +3μ Gas ) / (3μ LPG +2μ Gas )) for the decrease in the terminal velocity due to the deformation of the droplet, the Hadamard-Rybczinski equation of the following formula can be obtained. u t =D 2 (ρ LPG -ρ Gas )a / (18μ Gas )×(3μ LPG +3μ Gas ) / (3μ LPG +2μ Gas ) ····(7) Here, μ LPG : Viscosity of LPG [Pa s] Adding u2 to the absolute value |u t | of this u t gives the terminal velocity u t,LPG of the LPG droplet.

[0022] An experimental test was conducted to obtain the LPG adhesion distance under each condition using the test apparatus shown in Fig. 1. Here, as shown in Fig. 4, the LPG adhesion distance is the distance at which the surface temperature of the pipe becomes -5°C or lower on the downstream side of the heat quantity adjustment device 1. In the assumed operating range, tests were conducted to measure the surface temperatures of the heat quantity adjustment device and the downstream pipe under conditions combining the main pipe NG flow rate, branch pipe NG flow rate, NG temperature at the inlet of the heat quantity adjustment device, and LPG flow rate. Here, the main pipe NG flow rate affects the NG flow velocity in the venturi and thus the terminal velocity u t,LPG of the LPG droplet, the branch pipe NG flow rate affects the droplet diameter D of the LPG, the NG temperature at the inlet of the heat quantity adjustment device affects the saturation vapor pressure P sat , LPG of the LPG at the superheat degree and the production gas temperature, the LPG flow rate affects the specific surface area S m of the LPG droplet, the droplet diameter D of the LPG, and the partial pressure P LPG of the LPG in the production gas, respectively.

[0023] Under each condition of the experimental test, (Sm ×t×(P sat,LPG -P LPG ) for the distance required for vaporization of LPG (LPG adhesion distance) is shown in Fig. 5. The vertical axis in Fig. 5 is the LPG adhesion distance, and the horizontal axis is (S m ×t×(P sat,LPG -P LPG ). The reason for taking the horizontal axis as (S m ×t×(P sat,LPG -P LPG ) is that it is organized as factors considered to contribute to the vaporization of LPG droplets, that is, the mass transfer of LPG. That is, as the above factors, (i) the gas-liquid interface area (the larger the interface area, the easier it is to vaporize) (S m ), (ii) how long the LPG droplets flowing out from the liquid nozzle exist in the venturi (residence time t), (iii) how much LPG can be vaporized (theoretically, it can be vaporized up to the saturated vapor pressure) (the difference between the saturated vapor pressure and the partial pressure P sat,LPG -P LPG ) are considered.

[0024] From Fig. 5, it can be seen that if the value of S m ×t×(P sat,LPG -P LPG ) is 1.5×10 10 or more, the LPG adhesion distance becomes 0, and it can be understood that LPG does not adhere to the inner wall surface of the pipe.

[0025] For example, under the conditions of the NG temperature at the inlet of the heat quantity adjustment device being 40°C, the NG flow rate in the main pipe being 2100 m 3 N / h, the NG flow rate in the branch pipe being 700 m 3 N / h, and the LPG flow rate being 200 kg / h, S m ×t×(P sat,LPG -P LPG ) = 1.6×10 10 , which is above the threshold value of 1.5×10 10 . Therefore, it can be determined that LPG does not adhere to the inner wall surface of the pipe and the pipe does not become cold.

[0026] As described above, according to the determination method of the present embodiment, it is possible to determine whether or not LPG adheres to the inner wall surface of the pipe regardless of the installation posture of the calorific value adjustment device 1. Therefore, when the installation posture of the calorific value adjustment device 1 is vertical as shown in FIG. 1, and the superheat degree is small and the elbow 15 is installed downstream of the calorific value adjustment device, it can be used as an index for preventing the downstream pipe of the calorific value adjustment device from becoming low temperature. That is, if the device is manufactured to satisfy this index, droplets will not adhere to the bent portion (the portion surrounded by the broken-line square in the figure) of the elbow 15 in FIG. 1, and it is not necessary to use a low-temperature material for the downstream pipe of the calorific value adjustment device, which leads to a reduction in material costs and construction costs.

Explanation of Signs

[0027] 1 Calorific value adjustment device 3 Main flow pipe 5 Outer cylinder 7 Branch pipe 9 Inner cylinder 11 Liquid supply pipe 13 Liquid nozzle 15 Elbow

Claims

【Claim 1】 An outer cylinder provided in a main flow pipe through which NG flows, receiving the supply of the NG from the base end side and ejecting it to the tip side; an inner cylinder disposed coaxially with the outer cylinder within the outer cylinder and receiving the supply of the NG from a branch pipe branched from the main flow pipe with a space between the inner wall of the outer cylinder; and a liquid nozzle disposed coaxially with the inner cylinder and discharging LPG into the inner cylinder. A method for determining whether atomized LPG adheres to the inner wall surface of a downstream pipe of a calorific value adjustment device that adjusts the calorific value of the NG by adding LPG from the liquid nozzle to the NG flowing through the main flow pipe, comprising: S m ×t×(P sat,LPG -P LPG ) is 1.5×10 10 or more, it is determined that LPG does not adhere to the inner wall surface of the pipe, and S m ×t×(P sat,LPG -P LPG ) is less than 1.5×10 10 If it is less than, it is determined that LPG adheres to the inner wall surface of the pipe downstream of the calorific value adjusting device, characterized in that it is a method for determining whether atomized LPG adheres to the inner wall surface of the pipe or not. Here, S m : Specific surface area of LPG [m 2 / m 3 ​ t: Residence time of LPG droplets [s] P sat,LPG : Saturated vapor pressure of LPG at the manufacturing gas temperature [Pa] P LPG : Partial pressure of LPG in the production gas [Pa]

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