First, evaporation loss
Strong evaporation is one of the main properties of petroleum refined oil, especially light oil products, such as gasoline, kerosene, light diesel oil (especially gasoline) and so on. The density of these kinds of refined oil is small, when heated, the free molecules on the surface of its liquid can easily overcome the gravitational force of the liquid, and become vapor molecules to leave the liquid surface and spread to the space, resulting in evaporation loss of the liquid oil, which is evaporation loss yak. Evaporation loss not only causes a reduction in the quantity of oil, but also causes a decrease in quality. The oil vapor lost to the atmosphere pollutes the environment on the one hand, and creates a potential fire hazard on the other. The size of evaporation loss has a direct relationship with the density of refined oil, evaporation area, liquid surface pressure, atmospheric temperature and oil temperature and other factors. Therefore, the evaporation loss of oil products reflected in different oil products, different regions, different seasons and different storage conditions are different. However, evaporation loss runs through the whole flow process of oil operation and every operation link. Therefore, it can be determined that evaporation is the main cause of loss of refined oil products, must attract sufficient attention.
Evaporation loss in the process of refined oil operations are:
1, storage and custody process
(1) bulk
a, small breathing loss: non-mobile storage tanks, daytime heat, tank temperature rise oil evaporation rate accelerated, and vapour pressure increases, when the gas pressure increases to the tank breathing valve control pressure limit, you have to breathe out the gas! ; On the contrary, the night temperature reduction, oil and oil vapor volume contraction, gas pressure reduction, when the pressure is reduced to the negative pressure limit of the vacuum valve of the breathing valve, the tank should be sucked into the air, accelerate the oil vapor. For non-moving tanks, due to day and night changes in the temperature of the gas space inside the tank, resulting in oil tanks exhaling oil vapor and inhaling air in the process called small breathing loss. According to the actual determination of a place, a good technical conditions of 1000m3 above ground metal tanks, filled with gasoline storage for a year, due to the formation of small breathing natural evaporation loss amounted to 117 tons. Small breath evaporation loss and oil tank storage, empty capacity, oil tanks allowed to withstand gas pressure and temperature changes have a close relationship. Temperature difference is large, evaporation loss is large, temperature difference is small, evaporation loss is less; empty capacity is large, evaporation loss is large, empty capacity is small, evaporation loss is small.
b, big breathing loss: when the oil tank into the oil, due to the increase in the volume of liquid tank, the volume of oil and gas in the tank is compressed resulting in increased pressure in the tank, when the pressure increased to the limit of the breathing valve control pressure, the tank began to breathe; on the contrary, by the output of the tank oil, the volume of liquid in the tank is reduced, so that the tank pressure is reduced, when the pressure drops to the limit of the breathing valve negative pressure, it is the inhalation of air. This kind of oil loss due to the transfer of oil tanks resulting in the loss of oil vapor and inhalation of air in the process, called the big breath loss. If the transfer of oil from tank A to tank B, will cause a, B two tanks at the same time to produce large breathing loss. A tank output oil, tank empty capacity increases, more than the negative pressure limit, inhalation of air; B tank to increase the stock, the volume of oil increases, more than the positive pressure limit, exhaled oil vapor, resulting in evaporation losses.
c, empty tank oil evaporation loss: new production or after overhaul of the tank, into the oil, the oil began to evaporate loss, due to the tank empty capacity is very large, the amount of evaporation loss is large.
d, cleaning loss: according to the safety regulations of cleaning tanks, cleaning tanks must be excluded before all the petroleum vapors in the tank, resulting in loss. In the same storage conditions, the size of the evaporation loss is also affected by the following factors:
evaporation area; tank wall surface paint color (silver gray tanks evaporation loss is minimal, while the black tanks is the largest); tanks are not tight, leakage (if the top of the tank there are cracks, holes, the formation of tanks inside and outside of the convection gas, so that the tank oil vapors escaping, increasing the amount of evaporation loss).
(2) the whole
a, due to the barrel cover is not tight or gasket aging failure, so that the barrel oil vapor escape, resulting in loss.
b, barrels of refined oil canning operations, oil and atmospheric contact, oil vapor volatilization caused by loss.
2, the transportation process
(1) due to the car, the ship in the operation of the oscillation, bumps, accelerated the loading container of refined oil evaporation. Especially when the transportation container sealing degree is poor, loading more than the safe height, not only cause evaporation loss, and even cause the oil spillage, increasing the amount of transportation loss.
(2) to the car, the ship filling oil, or from the car, the ship unloading oil, in the car, the ship oil inlet caused by oil evaporation loss.
3, filling barrels of refined oil process
Whether it is filling barrels to receive and unloading bulk cars, ships, or to the user barrels on sale of refined oil, can produce refined oil vapor evaporation, resulting in filling loss.
Second, sporadic spillage loss
When filling the car or ship, when full or empty, from the car or ship to take out the crane pipe (or hose), the residual oil in the pipe spilled on the ground caused by the loss; reversing operation, the sporadic spilling loss; continuous filling operation, the mouth of the barrel or filling nozzle of the drip loss.
Third, the storage and transmission of oil containers and equipment adhesion, infiltration loss
Viscosity of lubricating oil and grease products oil, packaging containers of strong adhesion, such as the impact of low temperatures, resulting in loss is difficult to avoid.
The second section of the oil loss classification and statutory loss rate
Petroleum products in the entire operation of the storage and transportation process, each through a flow link will cause loss. But the number of flow links and the size of the loss, and oil storage, transportation, marketing sector management level has a direct relationship. In order to strengthen business management, effective control of oil loss, the state of the oil business storage and transportation loss using the "quota management" method, the loss of each business link to develop a legal loss rate.
The third section of measures to reduce oil loss
Oil in the storage and transportation and business process, due to natural evaporation loss and run, risk, drip, leakage caused by the number of losses is amazing. Oil loss not only directly affects the economic benefits of enterprises, but also cause pollution to the environment.
One, oil evaporation loss
Evaporation loss is the largest oil loss, volatility and temperature and pressure, the higher the temperature, the faster the evaporation, the greater the loss of oil; the higher the pressure, the slower the evaporation, the smaller the loss. The evaporation loss of oil and the nature of oil, density, storage conditions (liquid surface area, oil pressure, oil temperature, tank space size and atmospheric temperature), operating environment, regional location and production management and other factors. The evaporation loss of oil products has caused a staggering waste of energy and pollution of the atmosphere, both destroying the ecological environment and damaging human health.
(A) the type of evaporation loss
The evaporation loss of oil can be roughly divided into: natural ventilation loss, "small breath" loss, "big breath" loss of three.
Oil filling will also have a lot of oil volatilization out of the loss, therefore, filling loss can also be done as a kind of evaporation loss.
1, natural ventilation loss
Natural ventilation loss is due to the top of the tank has an eyelet or in the two eyelets between the existence of a height difference, because the density of the gas mixture than the air density, resulting in the tank mixture from the lower eyelets discharged into the atmosphere, the outside world air from the higher eyelets into the tank, the difference in the position of the eyelets and the different density of the gas, resulting in gas convection caused by the loss of the called natural ventilation loss.
Natural ventilation loss occurs in the top of the tank, the tank body corrosion perforation or weld with sand holes, the fire fighting system foam room glass damage, breathing valve valve plate is not covered tightly, the hydraulic valve is not loaded with oil or oil seals are not enough, the amount of oil holes, light holes are not covered, and so on.
As the natural ventilation loss causes both equipment problems and management problems, so as long as the strengthening of management, timely maintenance of good equipment, natural ventilation loss can be avoided.
2, small breathing "loss
Tank oil in the absence of sending and receiving operations in static storage, with the external temperature, pressure in a day's cycle of change in the rise and fall of the temperature of the gas space inside the tank, the oil evaporation rate, the depth of the oil and gas and vapor pressure changes, this discharge of oil vapor and inhalation of air caused by the process of loss of oil called "small breathing". "Small breathing" loss, usually also called the tank static storage loss. Caused by the oil tank "small breath" loss is the main reason for the atmospheric temperature changes. When the temperature from dawn with the increase in sunlight and rise, the temperature of oil in the tank also changes, resulting in faster evaporation, evaporation pressure increases, when the pressure exceeds the positive pressure rating of the breather valve, the tank oil and gas mixture through the breather valve into the atmosphere, which is the tank's "breath" process. When the sunshine gradually weakened, the oil temperature inside the tank is also reduced, the evaporation rate gradually slowed down, the pressure inside the tank is also reduced. When the pressure inside the tank is lower than the negative pressure rating of the breathing valve, the outside air is sucked into the tank through the open vacuum valve, which is the tank of the "suction" process. Therefore, the tank's "breathing" and "breathing" process, every day in a regular cycle of change. Generally speaking, the duration of the daily "exhalation" is longer than the duration of the "inhalation". Influence "small breathing" loss of many factors, mainly the following:
(1) and the size of the temperature difference between day and night. The greater the temperature difference between day and night, the greater the "small breath" loss; conversely, the temperature difference between day and night is small, the loss is small.
(2) and the location of the tank sunshine time. The longer the sunshine, the more "small breath" loss; and vice versa, the less loss.
(3) and the open area of the tank. Usually the larger the tank, the larger the total open area, the larger the evaporation area, the larger the "small breath" loss; on the contrary, the tank is small, the evaporation area is small, the "small breath" loss is also small.
(4) and the atmosphere. The lower the atmospheric pressure, "small breathing" loss is greater; on the contrary, the loss is reduced.
(5) and the degree of filling the tank. Tank full of gas space volume is small, "small breath" loss is less; space volume is large, the loss is also large.
In addition, "small breath" loss is also related to the nature of the oil (such as boiling point, vapor pressure, component content, etc.) and oil management level and other factors. Therefore, using the formula to calculate the "small breath" loss has great limitations, usually measured data as the tank static storage loss is more accurate.
3, "big breath" loss
The tank in the receipt and delivery operations (including unloading, transfer, oil, etc.), due to changes in the oil level caused by changes in the gas space inside the tank, which in turn brought about changes in the gas pressure rise and fall, so that the mixture of oil and gas discharged or outside the inhalation of air, the process caused by loss called tank "loss". The loss of this process is called the tank "big breathing" loss, sometimes also called the tank dynamic loss.
When the tank receives oil, the tank oil level rises gas space volume is reduced, the oil and gas is compressed, the pressure gradually rises, when the tank pressure of the gas mixture exceeds the rated value of the positive pressure of the respiratory valve, the respiratory valve disk is automatically opened, the mixture of oil and gas excluded from the tank. And when the tank sends oil, the oil level in the tank gradually decreases, the gas space increases, the oil and gas pressure decreases, the oil and gas concentration decreases, and the oil keeps evaporating to maintain a certain equilibrium. When the pressure of the gas space in the tank is lower than the rated negative pressure value of the breathing valve, the vacuum valve disk opens automatically and the outside air is sucked into the tank. If the oil is transferred between two tanks (inverted tanks or to the elevated tank oil transfer), the oil tank level continues to fall, the tank empty increase, the negative pressure value continues to increase until the inhalation of air, while the receiving tank level continues to rise, the tank empty decrease, the pressure increases until the oil and gas discharged. Therefore, in the oil transfer, "big breath" loss between the two tanks is the same time, usually also available transfer loss to express.
There are many factors affecting the "big breath" loss, the most important are the following:
(1) and the nature of the oil, oil density is small, the more light fractions, the greater the loss; the higher the vapor pressure, the smaller the loss; the lower the boiling point, the greater the loss.
(2) and send and receive oil speed. Into the oil, the faster the speed of oil, the greater the loss; conversely, into the oil, the slower the speed of oil, the smaller the loss.
(3) with the tank pressure level. Atmospheric open tank "big breath" maximum.
(4) and the number of turnover of the tank, the more frequent the tank receipt and delivery, the greater the "big breath" loss.
In addition, the "big breath" loss and the tank is located in the geographic location, atmospheric temperature, wind direction, wind, humidity and oil management level and many other factors. Therefore, using the formula to calculate the tank "big breath" loss also has great limitations. In
production management and scientific research experiments, more measured data to prevail.
4, filling loss
Oil from the tank area through the trestle (or oil terminal) loading crane (hose or arm) into the tanker (or oil tanker), through the loading pipe nozzle into the drum, due to the high flow rate, high pressure, the oil impact, splashing, churning, there will be a large number of oil escaping and loss of loss of evaporation losses, which is also a loss of loss of a kind of evaporation. According to the nature of the operation, it is usually divided into loading (ship) loss and filling barrel loss.
The factors that affect the oil filling loss are mainly the nature of the oil, oil temperature, the size of the loading pressure, the flow rate of oil loading, oil loading and climatic conditions. Generally speaking, light oil filling loss is large, heavy oil loss is small; high oil temperature, pressure, flow rate of oil loss; high spatter filling loss is large, low liquid filling loss is small.
Second, reduce oil loss measures
Oil is easy to evaporate is the main feature of petroleum and its products, from loading, storage containers and other equipment discharged from the gas mixture is a very important part of the oil loss. The loss of how much usually depends on the vapor concentration in the mixture! The volume of gas discharged", as well as the density of the oil and gas!
Reduce oil loss measures summarized in the following aspects:
1, strengthen equipment maintenance, strict implementation of operating procedures Strengthen equipment maintenance, serious implementation of technical procedures, is to reduce oil loss is an important guarantee. This is to start from the following aspects:
(1) all tanks, pumps, pipelines, valves, crane, unloading arm quick connectors and other parts of the connection, the running parts and static sealing point parts should be firmly connected to achieve a tight, no seepage, no leakage, no air.
(2) All attachments on the tank should be flexible and well used tightly. Measurement of oil holes, manholes in a timely manner after use cover tight. Breathing valve pressure is reasonable, regular inspection, cleaning and calibration. Hydraulic safety valve sealing oil height is appropriate, insufficient oil, dirty and timely replacement.
(3) all containers of oil, including tanks, oil tankers, railroad tank cars, tank cars, oil drums, etc., the technical status of the equipment should be intact, no leakage. Problems found should be promptly inverted to deal with.
(4) receiving and unloading oil, must be unloaded, scraping, pouring net, try to avoid the oil in the container adhering to the oil or residual oil is too much.
(5) Oil filling should not be super high, not excessive, not overpressure, not running oil, not overflow tank.
(6) comply with the rules and regulations, to prevent and eliminate all human responsibility accidents.
2, control the operating process
Improvement of management, control the operating process and installation of breathing valve baffle is to reduce the evaporation of oil loss is an important link.
(1) Reasonable arrangement of tank utilization. Tanks as full as possible to reduce the volume of space, minimize the number of inverted tanks (transfer) can also greatly reduce the tank breathing loss.
(2) Rationalize the time of sending and receiving oil. Tanks should try to collect oil in the cooling, without affecting the tanker out of storage under the premise that can be arranged in the evening to midnight cooling faster time to collect oil; as far as possible to arrange for the collection of oil tanks in the first oil, which reduces the big breath loss; collect oil should try to increase the flow of pumps, so that the oil can not be too late to a large number of evaporation to reduce losses; oil is the opposite of the end of the hair should be slower, so as to avoid the hair of oil end of the return to the reverse respiratory Phenomenon.
(3) control loading oil temperature and flow rate can also play a role in reducing oil volatilization to reduce losses. Because the oil temperature is high, volatile, fast flow rate, high pressure, oil spattering, churning is large, resulting in large losses.
(4) tank installation breathing valve baffle, so that the tank internal space oil and gas stratification, the exhaled gas is mainly the upper layer of lower concentration of oil and gas, thus reducing the evaporation loss.
3, reduce heat radiation
The way to reduce heat radiation, at present, the main use of silver gray or white anti-corrosion coatings and drenching oil temperature, in order to reduce the temperature difference between the tank changes.
(1) the tank surface brushing strong reflective silver paint, not only has the role of anticorrosion, but also reduces the tank to accept the heat of the sun, reduce the temperature of the oil inside the tank, thereby reducing the tank "small breath" evaporation loss.
(2) light oil tank water cooling, reduce the "small breath" loss is very obvious. Because the ground tank, the sun's radiant heat is transmitted to the oil through the tank top, summer from the top of the tank to the light oil tank drenching, cold water flowing down along the tank wall, so that the top of the tank and the tank wall is covered by the flow of cold water curtain film, the heat is taken away from the tank, the tank gas space temperature will be lowered, the tank of oil temperature difference between day and night will also be greatly reduced, the tank, "small breath" loss The oil tank "small breathing" loss can thus be reduced.
Tank spraying can achieve better results in reducing consumption but need to increase investment, and water consumption is larger in addition to the tank paint easily damaged, tank corrosion will be aggravated, if the lower discharge is not smooth, the tank foundation will also be affected. In order to avoid the unfavorable factors brought about by the drenching and the waste of water, should consider the use of recycled water facilities, in order to reuse.
Although the drenching cooling effect is good, but can not be intermittent, otherwise the temperature difference between the gas space in the tank is greater, not only can not reduce consumption, but will increase the "small breath" loss. In addition, but also to master the water time, the usual practice is to start after sunrise water.
(3) in the top of the tank "installed" thick insulation or reflective insulation board, can reduce the oil vapor < / p>
hair loss.
(4) construction of underground water sealing hole library, soil-covered oil depot, trying to maintain a constant temperature inside the tank, can avoid the tank "small breathing" loss, while the "big breathing" loss will also have a certain reduction.
4, the use of new technology under the liquid closed loading, reduce loading losses
Oil loading, crane pipe into the car depth and oil volatile loss is very close. The shallower it is, the greater the impact of the oil on the liquid surface, the faster the oil evaporates, the greatest loss. In recent years, the crane tube under the liquid closed quantitative loading new technology has been widely used in petrochemical sales enterprises, large crane tube under the liquid closed quantitative loading technology has been identified as a success.
5, the construction or reconstruction of floating roof tanks, eliminating gas space on the liquid surface
Floating roof tanks, the liquid surface of all the floating roof covered, there is no gas space, the temperature difference between the oil change is small. Therefore, the oil size breathing loss can be greatly reduced. Data show that the floating roof tanks and vault tanks, compared to reduce oil evaporation losses, and vault tanks converted to floating roof tanks, short payback period, most of the year can be recovered within the full investment. Most of the foreign gasoline storage floating roof tanks, the domestic promotion of the use of floating roof tanks, China's new gasoline tanks, kerosene tanks are more often used in the assembly of aluminum alloy floating roof tanks.
6, the use of gas collection method, the construction of gas tanks and gas return pipeline
In order to prevent the volatilization of oil and gas into the atmosphere, the storage of oil and gas tanks of the same type of oil tank space, from the top of the tank with a pipeline connection, and gas tanks are connected. When the tanks have to receive and send operations, the tanks of oil and gas can be exchanged with each other, the collection tank can be adjusted according to the pressure of the system itself, for the tanks exhaust, suction to play a role in regulating the balance. Therefore, this tank will not inhale air, discharge oil, thus preventing oil evaporation and loss of purpose.