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A process optimization of water purification of an oil refinery.


China is lack of water, on one hand, water problem is particularly outstanding, because the increasing of the number of cities. On the other hand, water resources are nervous. At the same time, the water pollution is rising; this vicious cycle has been unable to support our industrial condition of sustainable development. If not solved, it will directly affect the sustainable development [1] of our national economy [2-3].

Water supply situation is tense in China's petrochemical enterprise, so it is necessary to recycle the wastewater from the petrochemical enterprise, but the current water purification process is still not perfect. Such as some oil refinery in China [4-7], it was established in July 1977, the design capacity was 600t/h. With the expansion of the scale of oil refinery and the concentration of the contaminants in wastewater is increased. Under the contradiction of the big recycling water demand and the slants little wastewater throughput, it is necessary to establish a new wastewater purification process based on original facilities, the wastewater purification process must be feasible, high efficiency and low investment. Thus, we design a reform project aimed at the present situation of some oil refinery; it is safety feasible and efficient for the environmental protection.

The current research situation in China

So much water is used in the crude oil refinery in China, because of low technical level, the inefficient management level and the low quality of crude oil. Oil refining industry in China, water consumption is approximately 1~2.5 ton per ton crude oil process. However, for some individual old enterprises this number will achieve 3~4 ton/ton. This is a huge gap compared with some similar advanced enterprises with only 0.02~0.5 ton/ton of water consumption. Large water consumption brings more waste in water body and increase the processing cost. Also, more problems are caused on the follow-up treatment and discharge of the wastewater. The discharge wastewater from oil refinery must meet the certain countries' discharge standard of wastewater. In addition, water resources in China are lack and the quantity of wastewater from oil refinery is big. Thus, the wastewater must be purified because in order to recycle.

The current situation of wastewater discharge

All the wastewater from life area and industry area need to be treated in some oil refinery, the technology index contains pH6~9, [BOD.sub.5] 65mg/L, CODcr150 mg/L, the concentration of suspended solids are 175 mg/L, the concentration of oil is 15 mg/L, the concentration of volatile phenol is 1.5 mg/L, the concentration of sulfide is 1.5mg/L, the concentration of ammonia and nitrogen are 30 mg/L.

The main problem of the process

As shown as above, [BOD.sub.5] values are a little high in some oil refinery, because the oil's degradation makes the content of [BOD.sub.5] impermissibly high. Therefore, in the optimizing of process, we choose the oxidizing tower, at the same time, the chlorine dioxide as the catalyst. The content of COD and oil are high because the low separating effect. So it needs to be improved in the optimizing of process. We use the coarse screen to remove the big rubbish in order to reduce the concentration of suspended solids. A reformation of wastewater treatment process was put forward and the specific process optimization [8-9] will be introduced subsequently.

Optimization and transformation plan

According to the national environmental protection "eleventh five-year" plan, the target in 2012 is as follows: the total discharge capacity of COD should control under 1300 ten thousand tons, while, the total discharge capacity of ammonia and nitrogen should control under 140 ten thousand tons. The wastewater discharge capacity in 2015 will increase based around 10% in 2012. The "eleventh five-year plan" plan to promote the use ratio of the wastewater, the cut quantity of pollutant will be above 600 ten thousand tons. Especially the Songhua River was polluted seriously in last year; our country spends more effort to the environmental protection problem of oil refinery enterprise. This is a big challenge for our oil enterprises in the follow five years; this is the only road to keep the development speed with the international oil enterprises. Therefore, the main work for our country is to strengthen the wastewater reuse technology. Now, we carry out the optimization and transformation plan aimed at some existing problems of wastewater treatment plants of some oil refinery.

Technical reform of water purification equipment

We carried out the technical reform of water purification in June 2011: (1) Coarse granular tower was took place by jet dissolved gas flotation, because cost of Coarse granular tower is high and inefficient. (2) Micro porous aeration devices was install and aeration location and quantity were adjusted, for raw aeration devices were ineffective.(3) Oxidation tower was reformed into filtering tank, and set at the back of the aeration device.

The transform for the process flow of water purification

The transform for the process flow of water purification [10-11] contains wastewater purification system and sludge drying system. The flow chart of water purification is shown as Fig.1; the plan is shown as Fig.2.



The wastewater purification system

The industrial wastewater and the sewage from various of process units in some oil refinery enter into the wastewater treatment plant, first, it removal the thick rubbish through the mechanical grid. Second, it will enter the sump to separate the oil-water and muddy water. Third, the rising sump oil will be transported outward, submerged sludge will be cleaned.

The wastewater in the sump will be input into the floating tank with the lift pump, and it is used to adjust the water quantity and water yield. at the time of water leakage, the wastewater enter into oil separation tank depends on the different liquid level, in the oil separation tank, the oil and the wastewater will be separated, then, the sump oil flow into the sump by itself; and the sludge in the sludge tank will be send into the sludge drying system by the sludge pump.

The object of flotation pool is to removal the emulsified oil and the suspended matter from the wastewater. Air flotation device adopts the process of part backflow. One part of water leakage from the flotation pool flow into the aeration tank by itself, the other part of the water leakage from the flotation pool is rose into the dissolved air tanks. The jet injector is used to snort the air, in this process, and it will cause negative pressure, the negative pressure can snort the air into the tank. Then, the much air can dissolve in the water. Solution gas-water can produce micro bubbles after the pressure venting in the reaction chamber of the air flotation pool, it mixed with the influent from the under air flotation pool, the micro bubbles bring the emulsified oil and the suspended matter to the surface of the air flotation pool, then, they will flow into the sludge tank by themselves, finally, they are sent to the sludge mummification system.

The water leakage from the air flotation fully contacted with the activated sludge, the activated sludge will proceed the biochemical reaction with the organic pollutant from the wastewater, after the adsorption and the oxygenolysis, the mixed liquor will proceed Slurry separation in the settling zone, the submerged sludge will backflow to the aeration zone, the clear water will outflow the aeration pool.

The water leakage from the aeration basin can be discharged; it also can discharge into the ShenFu canal after removal the suspended matter.

The sludge drying system

After the sludge settle down the pool, scum and the excess sludge discharge into the sludge pool, they will be proceed the initial dehydration in the sludge drying device [12], a part of sludge will enter into the centrifugal dehydrator for slurry separation.

After the drying, they will be sent into the water purification device.

Operation Effect

The wastewater purification device was activated and came into use from June to September in 2011; the operating data is shown as Table 1.


In this paper a reformed process of wastewater treatment based on original wastewater treatment facilities was performed, it contains wastewater purification system [13] and sludge drying system, the efficiency of this process is high and the investment is low compared with the facilities previously, it has already put into use, and it brings considerable value for some oil refinery. Now the reuse for wastewater is an effective way to solve the problem of water shortage, the development strategy of our country is to proper distribute the water resource, protect the environment and carry out the sustainable development. The way of wastewater reusing is different, such as, direct reuse, indirect reuse, combination of processing reuse, closed cycle, dual water supply- cascade stage- circulate, drainage system and so on. The next step for some oil refinery is to achieve the wastewater reuse with a higher-efficiency treatment process.


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Shuangchun Yang, Xiaozhen Wang, Dandan Liang, Jinhui Zhang and Yi Pan*

Liaoning Shihua University, No.1 West Dandong Rd., Fushun City, Liaoning Province-113001, China
Table 1: The operating data

The Technological index of wastewater purification

 New index mg/L Current Old index mg/L
 index mg/L

PHvalue 6-9 6-9 6-9
[BOD.sub.5] 60 60 65
CODcr 100 100 150
Suspended matter 100 150 175
Oil 8 10 15
Volatile phenol 0.5 1 1.5
Chloride 0.5 0.5 1
Sulfide 1 1 1.5
Ammonia nitrogen 15 25 30
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Author:Yang, Shuangchun; Wang, Xiaozhen; Liang, Dandan; Zhang, Jinhui; Pan, Yi
Publication:International Journal of Applied Environmental Sciences
Geographic Code:9CHIN
Date:Sep 1, 2012
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