# Optimization Scheme for Construction Ventilation in Large-Scale Underground Oil Storage Caverns

^{1}

^{2}

^{3}

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## Abstract

**:**

## 1. Introduction

^{2}. This paper aims to optimize construction ventilation schemes for large-scale underground oil storage caverns. Based on the analysis of the distribution of air velocity and the CO concentration with time under forced ventilation, the axial flow gallery ventilation scheme by using shafts as air inlet is proposed. The effectiveness of the optimized ventilation scheme is validated by field test values of the air velocity and CO concentration in the main cavern and construction roadway. The results provide a useful reference for construction ventilation in large-scale underground storage caverns.

## 2. Project Description

^{4}m

^{3}, which is mainly divided into two parts: underground engineering and ground engineering. The underground engineering is mainly composed of the oil storage cavern, water curtain system, connecting roadway, construction roadway, sealing plug, shaft and pump pit as shown in Figure 1a. Eight east-west direction and parallel-arranged oil storage caverns with a length of 934 m are connected by connecting roadways. The span and height of the cross-section is 19 m and 24 m, respectively, a three-center arch straight wall type is adopted in the section design, and the bottom is provided with a chamfer of 1m wide and 3 m high. The section area is 436.2 m

^{2}, the bottom elevation of the cavern is −80 m, the top elevation is −56 m, and the ground elevation is 0 m. There are four oil-inlet shafts with 3 m in diameter and four oil-outlet shafts with a diameter of 6 m. The water curtain system is arranged above the caverns, two construction roadways are set up to enter the main caverns, the profile of the oil storage caverns is shown in Figure 1b. The oil storage cavern is divided into three layers for construction, the excavation height of each layer is 8 m, 12 m and 4 m respectively, as shown in Figure 1c. Before the completion of the upper layer construction, SDZ-12.5 axial flow fans with Φ1.8 m duct arranged at the entrance of the construction roadway are used for forced ventilation as shown in Figure 2a.

## 3. Field Test

_{2}, H

_{2}S) in the main cavern and the construction roadway was carried out. The main cavern was organized with a test cross-section every 100 m in the longitudinal direction, with a total of 9 test cross-sections. The test instruments and related parameters of air velocity and harmful gas are shown in Table 1. As the air velocity and harmful gas concentration vary with the location, it is important to increase the number of measuring positions to obtain the average air velocity and harmful gas concentration of the cross-section (the average values only refer to the space). Consequently, the cross-section of the main cavern is divided into nine parts, and the cross-section of the construction roadway is divided into four parts as shown in Figure 3. The air velocity and harmful gas concentration in each part are averaged to be V

_{a}and C

_{a}separately. Hence, the value of V

_{a}and C

_{a}can be calculated by the flowing equation:

_{i}is the area of part i in the cross-section.

## 4. CFD Simulations

#### 4.1. Computational Domain and Grid

#### 4.2. Boundary Conditions

_{s}) is set as 0.57 and the equivalent sand-grain roughness height (K

_{s}) is used for roughness height, K

_{s}= 0.07 m [30]. The distance from point P in the first near-wall cell to the wall (y

_{p}) is 0.52 m. (2) The outlet of the air duct is considered to be a velocity-inlet with an airflow velocity of 15 m/s in Figure 5a. There are four velocity-inlets located at the entrance of the shaft in Figure 5b, the value is 5 m/s in the oil-inlet shaft and 10 m/s in the oil-outlet shaft. (3) The pressure outlet boundary is adopted at the entrance of the construction roadway in the two schemes.

_{0}is the initial CO concentration (mg/m

^{3}), G is the amount of explosive (kg), L

_{OT}is the throwing length (m), b is toxic gas produced per kilogram of explosive (m

^{3}/kg), b is generally valued at 0.04, and A is the excavation area (m

^{2}).

#### 4.3. Others Computational Settings

^{−6}for the energy equation and 10

^{-4}for other equations [33]. The computer with Core i7-8700 CUP and 32 G memory was used to perform all the simulations. The governing equations solved in FLUENT for the present problem can be found in the FLUENT manual [34].

#### 4.4. Validation

## 5. Results and Discussion

#### 5.1. Original Scheme of Forced Ventilation

#### 5.1.1. Air Velocity Field

#### 5.1.2. CO Concentration Field

^{3}.

#### 5.2. Axial-Flow Gallery Ventilation Scheme

#### 5.2.1. Air Velocity Field

^{2}to 363 m

^{2}after entering the middle layer excavation, causing a sharp drop in the air velocity. The value near the middle bench is approximate 0 m/s due to the height of the middle bench, and then it tends to be stable after about 50 m. The air velocity in the middle bench of the two caverns is not very different, about 0.4 m/s. The cross-section area further enlarges to 436 m

^{2}after entering the bottom layer excavation and the steady air velocity of the two caverns further decreases to 0.35 m/s. Since large-scale caverns generally adopt the method of layered excavation, the air velocity presents a more obvious step-like distribution. The current “Technical Specifications for Construction of Highway Tunnel” (JTG F60-2009) [37] and “Safety Regulations for Coal Mines” [38] stipulate that the minimum air velocity in the cavern must reach 0.15 m/s. Thus, the axial-flow gallery ventilation scheme, by using shafts for the fresh air, can meet the air velocity requirements of the relevant regulations.

#### 5.2.2. CO Concentration Field

^{3}after 25 min of ventilation. The velocity of pollutant discharge in the construction roadway is greater than the main cavern due to its smaller section area and the airflow collection of four caverns, thus, the CO gas can be quickly discharged outside.

^{3}after 15 min of ventilation, which meets the requirements for safe and rapid construction. Figure 14b presents the CO concentration distribution at breathing height (1.6m from the ground) with ventilation time. It can be seen that the high concentration of CO in the cavern continues to migrate toward the connecting roadway with the increase of ventilation time, and the maximum CO concentration decreases gradually. The CO concentration of the whole cavern decreases below the safety standard value after 30 min of the axial-flow gallery ventilation scheme, which is much better than the effect of forced ventilation.

## 6. Conclusions

- (1)
- The construction of large underground caverns usually adopts layered excavation, and the forced ventilation method is mostly applied in the upper layer construction. Due to the restriction of the construction roadway size and the clearance requirements for transportation, the duct diameter and air volume cannot be increased Consequently, the ventilation quality cannot meet the requirements of the cavern environment. Because the ventilation distance exceeds 1500 m, the stable air velocity in the cavern is only 0.15 m/s, which is below the minimum air velocity requirement of the relevant standards. In addition, there is a very complicated eddy zone in the area of about 20 m from the heading face.
- (2)
- The axial-flow gallery ventilation scheme is carried out when the excavation of the cavern upper layer is completed and connected with the shaft. The scheme utilizes the shafts as the fresh air inlet and the construction roadway as the polluted air outlet to create the gallery ventilation. It can ensure that the direction of the airflow is the same as that of heavy trucks, fresh air is always near the excavation face, and the disturbance of the process is greatly reduced. It reduces energy consumption and has good prospects for popularization and application.
- (3)
- There is no need to set up the air duct in the axial-flow gallery ventilation scheme, which greatly facilitates the cavern construction and avoids duct damage caused by blasting. The scheme is suitable for the large-scale caverns with a ventilation distance less than 2 km, each channel is effectively used, and the intermediate construction shaft is not needed. If the ventilation distance exceeds than 2 km, it is possible to use jet fans to assist the axial flow gallery ventilation mode or to completely adopt jet-flow gallery ventilation.
- (4)
- The power of the axial fan and the jet fan should be no less than 135 kW and 75 kW, respectively. The jet fan should be arranged at the airflow steering place. The axial fan placed at the top and bottom of the shaft has little impact on the field ventilation effect, so the position can be selected independently according to the convenience of the fan installation.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**(

**a**) Three-dimensional layout of underground structures; (

**b**) The profile of oil storage caverns; (

**c**) The shape and size of each cavern section.

**Figure 2.**(

**a**) The plan for the forced ventilation scheme; (

**b**) The plan for axial-flow gallery ventilation scheme; (

**c**) The profile of the axial-flow gallery ventilation scheme.

**Figure 3.**Layout of test points in each section: (

**a**) Section of the upper layer; (

**b**) Section of the middle layer; (

**c**) Full section of the cavern; (

**d**) Construction roadway.

**Figure 4.**Field test of ventilation environment in the caverns: (

**a**) Test of air velocity; (

**b**) Test of dust; (

**c**) Air quality after ventilation.

**Figure 5.**Three-dimensional geometrical model: (

**a**) Forced ventilation scheme; (

**b**) Axial-flow gallery ventilation scheme.

**Figure 7.**The comparison between the simulated result and field test: (

**a**) Air velocity in the main cavern and construction roadway; and (

**b**) The change of CO concentration with time.

**Figure 8.**Distribution of airflow field near the working face: (

**a**) Velocity vector at z = 5.5 m; (

**b**) Velocity vector at y = 18 m.

**Figure 10.**CO mass concentration distribution in the central axial plane. (

**a**) Ventilation for 5 min; (

**b**) Ventilation for 10 min; (

**c**) Ventilation for 15 min; (

**d**) Ventilation for 20 min; (

**e**) Ventilation for 25 min; (

**f**) Ventilation for 30 min.

**Figure 13.**CO concentration distribution with time in caverns under the optimized ventilation scheme: (

**a**) Ventilation for 5 min; (

**b**) Ventilation for 10 min; (

**c**) Ventilation for 15 min; (

**d**) Ventilation for 20 min; (

**e**) Ventilation for 25 min; (

**f**) Ventilation for 30 min.

**Figure 14.**(

**a**) CO concentration in monitoring section with ventilation time; (

**b**) CO concentration distribution at the breathing height.

Test Content | Test Instrument | Test Resolution | Control Value |
---|---|---|---|

Air velocity | Hot wire anemometer | 0.01 m/s | / |

CO | M4 gas detector | 0.1 ppm | ≤30 mg/m^{3} |

SO_{2} | M4 gas detector | 0.1 ppm | ≤14.3 mg/m^{3} |

H_{2}S | M4 gas detector | 0.1 ppm | ≤10 mg/m^{3} |

Above 10% free SiO_{2} dust | CCZ-1000 direct-reading dust detector | 0.1 mg/m^{3} | ≤2 mg/m^{3} |

Below 10% free SiO_{2} dust | CCZ-1000 direct-reading dust detector | 0.1 mg/m^{3} | ≤4 mg/m^{3} |

Section | A (m^{2}) | G (kg) | L_{OT} (m) | The Amount of CO (m^{3}) | C_{0} (mg/m^{3}) |
---|---|---|---|---|---|

Upper layer | 135.1 | 320 | 79 | 12.8 | 1499.1 |

Middle layer | 228 | 420 | 99 | 16.8 | 930.4 |

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## Share and Cite

**MDPI and ACS Style**

Zhang, H.; Sun, J.; Lin, F.; Chen, S.; Yang, J. Optimization Scheme for Construction Ventilation in Large-Scale Underground Oil Storage Caverns. *Appl. Sci.* **2018**, *8*, 1952.
https://doi.org/10.3390/app8101952

**AMA Style**

Zhang H, Sun J, Lin F, Chen S, Yang J. Optimization Scheme for Construction Ventilation in Large-Scale Underground Oil Storage Caverns. *Applied Sciences*. 2018; 8(10):1952.
https://doi.org/10.3390/app8101952

**Chicago/Turabian Style**

Zhang, Heng, Jianchun Sun, Fang Lin, Shougen Chen, and Jiasong Yang. 2018. "Optimization Scheme for Construction Ventilation in Large-Scale Underground Oil Storage Caverns" *Applied Sciences* 8, no. 10: 1952.
https://doi.org/10.3390/app8101952