There are many factors that affect the loss of "small breathing", mainly the following points.
(1) Related to the size of the temperature difference between day and night. The larger the temperature difference between day and night, the greater the "small breathing" loss; conversely, the smaller the temperature difference between day and night, the smaller the loss.
(2) Related to the sunshine time at the location of the oil tank. The longer the sunshine, the greater the "small breathing" loss; conversely, the loss is less.
(3) Related to the exposed area of the storage tank. Generally, the larger the storage tank, the larger the total area when exposed, the larger the evaporation area, and the greater the "small breathing" loss; conversely, the smaller the storage tank, the smaller the evaporation area, and the smaller the "small breathing" loss.
(4) Related to the atmosphere. The lower the atmospheric pressure, the greater the "small breathing" loss; conversely, the loss is reduced.
(5) Related to the degree of filling of the oil tank. When the oil tank is filled with gas, the space volume is small, and the "small breathing" loss is small; the space volume is large, and the loss is also large.
In addition, the "small breathing" loss is also related to the properties of the oil (such as boiling point, vapor pressure, component content, etc.) and the level of oil management. Therefore, the use of formulas to calculate the "small breathing" loss has great limitations. It is usually more accurate to use the measured data as the static storage loss of the oil tank.
6. "Big Breathing" Loss
When the oil tank is receiving and sending operations (including unloading, transferring, sending oil, etc.), the rise and fall of the oil level causes the gas space in the oil tank to change, which in turn brings about the rise and fall of the gas pressure, causing the mixed oil and gas to be discharged or the outside air to be sucked in. The loss caused by this process is called the "big breathing" loss of the oil tank, sometimes also called the dynamic loss of the oil tank.
When the oil tank receives oil, the oil level in the tank rises, the volume of the gas space shrinks, the oil and gas are compressed, and the pressure gradually increases. When the mixed oil in the tank When the gas pressure exceeds the rated positive pressure value of the breathing valve, the breathing valve disc automatically opens and the mixed oil and gas are discharged from the tank. When the oil tank is delivering oil, the oil level in the tank gradually decreases, the gas space increases accordingly, the oil and gas pressure decreases, the oil and gas concentration decreases, and the oil product continues to evaporate to maintain a certain balance. When the gas space pressure in the tank is lower than the rated negative pressure value of the breathing valve, the vacuum valve disc automatically opens and the outside air is sucked into the tank.
If the oil product is transferred between two oil tanks (inverting the tank or transferring oil to an elevated tank), the liquid level in the sending tank continues to drop, the tank empty space increases, and the negative pressure value continues to increase until air is sucked in, while the liquid level in the receiving tank continues to rise, the tank empty space decreases, and the pressure increases until the oil and gas are discharged. Therefore, when the oil product is transferred, the "big breathing" loss occurs simultaneously between the two tanks, and it can usually be expressed as a transfer loss.
There are many factors that affect the "big breathing" loss, the most important of which are the following:
(1) Related to the properties of the oil product The lower the density of the oil product, the more light fractions there are, the greater the loss; the higher the vapor pressure, the smaller the loss; the lower the boiling point, the greater the loss.
(2) Related to the speed of receiving and sending oil. The faster the oil inlet and outlet speeds, the greater the loss; conversely, the slower the oil inlet and outlet speeds, the smaller the loss.
(3) Related to the pressure level in the tank. The "big breath" of the open tank at normal pressure is the largest.
(4) Related to the number of oil tank turnovers. The more frequent the oil tank is sent and received, the greater the "big breath" loss.
In addition, the "big breath" loss is also related to many factors such as the geographical location of the oil tank, atmospheric temperature, wind direction, wind force, humidity and oil management level. Therefore, the use of formulas to calculate the "big breath" loss of oil tanks also has great limitations. In production management and scientific research experiments, measured data are often used as the basis.
According to its operating nature, this type of loss is often called oil collection loss or transfer loss in oil depots. For example, when sending and receiving gasoline, the loss of the oil tank "big breathing" is 1.08~1.65kg/(t·time), and the maximum can reach 2.4kg/(t·time).
7. Filling loss
The oil is loaded into the tank truck (or oil tanker) from the tank area through the pier (or oil terminal) loading crane pipe (hose or oil transfer arm), and poured into the oil barrel through the oil filling nozzle. Due to the high flow rate and high pressure, the oil will be impacted, splashed, and stirred, and a large amount of oil and gas will escape and be lost. This loss is also a kind of evaporation loss. According to the nature of the operation, it is usually divided into loading (ship) loss and barrel filling loss.
The factors affecting the filling loss of oil products mainly include the nature of the oil product, oil temperature, oil filling pressure, oil filling flow rate, oil filling method and climatic conditions. Generally speaking, the filling loss of light oil is large, and the loss of heavy oil is small; the oil temperature is high, the pressure is high, and the flow rate is fast, the oil loss is large; the high-level splash filling loss is large, and the low-level liquid filling loss is small. According to relevant information, the maximum unit consumption of gasoline splashing high-level loading is 3kg/t, the loss of low-level underwater loading is 0.4~0.8kg/t, the loss of kerosene is 0.21~0.24kg/t, and the loss of diesel is 0.03~0.06kg/t.
Ⅱ. Hazards caused by evaporation loss of oil products
For example, the explosion limit of gasoline is 1.0%~6.0% (volume fraction), the density of gasoline vapor is about 3.0~3.1kg·m-3 (STP), and the density of air is 1.1kg·m-3 (STP). Therefore, during the storage, receipt, delivery and sales of oil products, a large amount of high-concentration oil and gas with a density greater than air that seriously exceeds the fire and explosion limit evaporates and spreads, and mainly floats and accumulates in the ground space, bringing many serious hazards to enterprises and society.
1. Endangering the safety of various links in oil storage and transportation
Since most light oil products are volatile, flammable and explosive substances, they are easy to accumulate. After forming an explosive mixture with air, they are deposited and accumulated in depressions or trenches. When they encounter fire, they are very likely to explode or fire accidents, causing significant losses of life and property. If the hydrocarbon concentration is between 1% and 7%, it is in the explosion range. For this kind of hazard, people are currently more likely to prevent accidents by strengthening management and increasing investment in safety facilities. Nevertheless, due to the wide range of oil and gas explosion limits, the wide range of oil and gas diffusion, and the many factors affecting production safety, fire and explosion accidents caused by them occur from time to time. Statistics show that among the 222 fire and explosion accidents, 101 were caused by oil and gas, accounting for 45.5%. The statistical results of the fire incidence rate in each area of the finished oil depot are as follows: tank area: 6.94%, loading and unloading area: 27.78%, oil delivery area: 36.11%, and these three areas account for 71%.
