How to Deal with the Waste Water in the Oil Depot with Cast Steel Valves?

With the expansion of storage scale and changes in the nature of stored oil products, the amount of sewage in oil depots has increased correspondingly, and the water quality has become more complicated. At the same time, the national environmental protection policy continues to strengthen, and "environmental protection" will surely become one of the important signs of the advanced nature of the oil depot. As the main environmental protection index of petroleum depots, the sewage water quality index in the reservoir area can be reasonably controlled and discharged to a certain extent, which restricts the development of storage capacity to a certain extent. Therefore, it is necessary to analyze and control the pollution sources of the oil depot in order to clean up the sewage and reduce the amount of sewage and pollution load. And on this basis, strengthen the adjustment measures to provide suitable conditions for sewage treatment to ensure that the sewage treatment process is stable and discharges up to standards.

Types of sewage

Petroleum depot sewage can be divided into three categories: oily sewage, polluted rainwater, and domestic sewage. Among them, oily sewage includes oil tank water cutting drainage, storage tank flushing drainage, ground flushing drainage in oil loading and unloading area, machine pump and metering and other drainage.

Sewage characteristics

Different causes and discharge points determine the characteristics of the volume and quality of sewage in the oil depot.

(1) Water volume characteristics. The sewage discharge is discontinuous, the amount of water change is large, the change regularity is poor, and it is difficult to control. The nature, storage area, water content, maintenance cycle, operation management, etc. of the stored oil products will cause irregular changes in the amount of oily sewage. In particular, the initial oil content is most affected by rain, and the rainy areas in the south are more severe. In addition, oil tank cleaning and drainage, ballasting and tank washing drainage may all cause rapid changes in water volume.

(2) Water quality characteristics. Due to the intermittent discharge of various kinds of sewage, human factors and the contingency of natural conditions, the water quality of the sewage in the reservoir area has the characteristics of large change range, poor change regularity, and difficult treatment.

Sewage pollution source analysis

Oily sewage is the main component of petroleum depot sewage, and its source is mainly oil tank water cut.

(1) Cut water from the oil tank. Its water quantity and quality are closely related to the nature, origin and operation management of stored oil. The water volume of artificial water cut is not easy to control, the oil content generally exceeds 500mg / L, and the oil content will increase greatly in the later stage of water cutting. For example, the maximum oil content of a gasoline storage tank's manual water cut is up to 14828mg / L; mechanical or electronic automatic dehydrators are usually used now, which eliminates the influence of human factors and can reduce the oil content of sewage to 300mg / L the following. Oil tank cutting water (bD content is relatively high, accounting for more than 80% of the total oily sewage COD, may also contain a small amount of} 3-N, sulfide, volatile phenol and other pollutants. Therefore, oil tank cutting water is oily sewage The main control object.

(2) Oil tank cleaning and drainage. Oil tank cleaning is divided into water washing and oil washing. The instantaneous drainage volume of the washed oil tank is relatively large and is closely related to the operation and management. Its drainage oil content is up to 3000mg / L or higher, and the pollution components are basically the same as the oil tank water cut.

(3) Changes in the amount of oily sewage caused by leakage of underground oily sewage pipeline system. Oil-bearing sewage pipes are mostly made of drainage socket cast iron pipes and buried laying, which makes it difficult to maintain. After long-term use, the subsidence of the foundation will cause leakage of pipeline joints and cracks in the inspection well, causing a vicious cycle of leaking in rainy days and leaking in non-rainy days, which not only pollutes the environment, (soil, groundwater, etc.) but also directly increases the difficulty of treating oily sewage.

(4) Other oily sewage. Including the oily sewage discharged from the ground washing, pump and metering in the oil loading and unloading area, the pollution degree is relatively light.

Polluted rainwater

(1) Oil and gas discharge pollution from the tank top. In the process of discharging oil and gas, the tank top exhaust valve and breathing valve may bring out small oil beads or oil and gas. When they are discharged, they meet the outside cold air to form small oil beads, which pollutes the roof of the tank; when the oil inlet speed is faster, oil injection will occur. Uneven oil in and out of the floating roof tank may cause tilting of the floating plate, leakage of oil products or partial emergence. In addition, after years of use, the sealing ring of the floating roof tank will be deformed and the sealing is not tight, which makes the leakage of oil or oil and gas possible. Many factors can pollute rainwater.

(2) Leakage pollution. Valves, flanges, pumps, tank bottoms, etc. all have the possibility of oil leakage, and rainwater can be contaminated if not handled in time.

(3 Pollution of the tank wall. With the change of the oil level in the tank, some oil stains will remain on the tank wall and seal, etc. These oil stains are difficult to clean manually and enter the rainwater.

Domestic sewage

Wastewater discharged from auxiliary facilities such as laboratory, office, and control room.

Sewage control measures in the reservoir area

Oily sewage is the main component of sewage in the reservoir area. Its content of oil, COD and other pollutants are much higher than other sewage, and due to the influence of oil or other harmful pollutants and its relatively low BOD / COD value, biochemical treatment is more difficult. This will directly affect the wastewater treatment process and discharge to the standard in the reservoir area. Therefore, necessary measures should be taken to control the source and reduce its water volume and pollution load.

(1) Automation and installation of water cut for oil tank. The use of an automatic dehydrator reduces the oil content of water cut to a certain extent. However, due to defects in the quality or installation of the dehydrator, the dehydrator cannot function well. Some dehydrators have mechanical failures or electronic detection failures soon after use. In addition, an oil tank is equipped with a dehydrator and only one connecting pipe extends to the sump. This simple installation method is possible for small oil tanks, but it is not enough for large-capacity oil tanks, especially large oil tanks with a diameter of nearly 100 meters. This will cause incomplete drainage, uneven water quality, and oil content increasing with dehydration time. Therefore, the cutting water of the oil tank should use the advanced and reliable automatic dehydrator as far as possible, and strictly guarantee the installation accuracy, ensure its quality and the sensitivity of the oil-water interface detection. At the same time, it is necessary to increase the number of dehydrators according to the diameter of the oil tank or to install complete and uniform dehydration improvement facilities to install automatic dehydrators.

(2) Standardization of oil tank cleaning. First of all, this part of sewage should be eliminated or minimized by strengthening management and standardizing operations. Secondly, it can prolong the oil tank cleaning cycle and reduce the number of cleanings. For example, large oil tanks can be cleaned once every 8-10a. In addition, the cleaning of oil tanks should adopt advanced technology and be implemented by a professional team. Oil washing or washing with less water (recycling of flushing water, etc.) should be used to limit the amount of water used for washing and also reduce drainage.

(3) Achieve leak-free drainage pipes through engineering measures. Change the pipe connection method, such as changing the socket connection to flange or welding. Use integral inspection wells, such as FRP or cement mortar internal and external corrosion-resistant steel inspection wells. Locally use flexible joints to improve the adaptability of the pipeline system to changes in the foundation and prevent water leakage caused by subsidence caused by soil dehydration. Or consider using other conveying methods.

(4) Timely removal of other oily sewage. For "point" pollution caused by other loading and leakage, management should be strengthened, timely detection, timely control and removal to avoid expansion.

The current national standard oil depot design specifications only require oil depot sewage discharge to meet national comprehensive sewage discharge standards without giving specific indicators. However, "Comprehensive Wastewater Discharge Standards" (GBB8978-1996) does not have a "petroleum depot". It is designed to monitor multiple sets of "petrochemical industry" indicators. Whether this is appropriate is open to question. According to the nature or type of oil depot, it is recommended to establish the "emission standard for oil depot sewage" and "total pollutant discharge control" indicators to provide clear and specific quantitative requirements for the treatment of oil depot sewage.

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