Application of double media filter in oilfield wastewater treatment

In view of the problem that the quality of reinjection sewage in low permeability oilfield is not up to the standard, glwa270 / 016 (s) double filter automatic filter is adopted to transform the sewage treatment system in Linnan Oilfield. This paper introduces the structure, working principle and main technical parameters of the filter, and compares it with other filter tanks. It is considered that the automatic filter with double filter media has the characteristics of large flow rate and strong regeneration capacity of filter media, which can backwash and control the particle size of filter media from top to bottom.

Through the comparison of the water quality indexes before and after the sewage treatment, it shows that the filter can effectively guarantee the sewage quality.

With the deepening of oilfield development, the water content of crude oil is rising, and the treatment of oil production wastewater has become an important work in water injection oilfield development. At present, the amount of wastewater in Linnan Oilfield is 5000m3 / D, and all the wastewater is reinjected into Linnan Oilfield after treatment.

Linnan Oilfield is a low-permeability oilfield, which requires high reinjection water quality, and the wastewater quality is not up to the standard, which directly affects the oilfield development effect.

Linpan Oil Production Plant reformed Linnan sewage treatment system in 2000. Glwa270 / 016 (s) double filter material full-automatic filter of Jianghan Petroleum machinery plant was used in the filter tank, which improved the water quality after sewage treatment and met the requirements of formation water injection.

ANALYSIS OF SEWAGE TREATMENT PROCESS

(1) Sewage treatment process and existing problems before transformation.

Gravity oil removal process is adopted: 200m3 receiving tank → 1000m3 settling tank → 100m3 buffer tank → lifting pump → walnut shell filter tank → 1000m3 water injection tank → export pump → export to Linnan Oilfield.

The sedimentation separation in the station mainly depends on gravity sedimentation (tox sedimentation separation principle). The suspended impurities in the oily water are separated by physical methods, but the suspended solids with small particle size and tiny oil drops are difficult to remove.

After the walnut shell filter tank was put into operation in 1996, due to the serious harm of waste oil and gum to the walnut shell filter material, the filter material was polluted, hardened, the filtration rate was reduced, and the effluent quality was deteriorated. Although measures such as increasing the backwashing intensity and extending the backwashing time were taken, the filtered water still could not meet the water quality requirements of water injection.

(2) The sewage treatment process after transformation and its advantages.

After transformation, the sewage treatment process is as follows: 200m3 receiving tank → mixing reactor → 1000m3 coagulation settling tank → 100m3 buffer tank → lift pump → double filter material filter tank → 1000m3 water injection tank → export pump → export to Linnan Oilfield.

After the transformation, the original gravity sedimentation process is retained, and the mixed reactor is added, which improves the water quality before the filter, makes full use of the original equipment and process, and reduces the transformation cost; The filter tank is installed in parallel in a skid, which increases the sewage treatment capacity, improves the sewage filtration accuracy, and meets the requirements of reinjection sewage in low permeability oilfield.

The automation degree of sewage treatment is improved, and the labor intensity of operators is reduced.

STRUCTURE PRINCIPLE AND MAIN PARAMETERS

(1) Structure.

The double filter automatic filter is mainly composed of filter tank, manifold, backwash pump and automatic control device. The structure of filter tank is shown in Figure 1.

The filter tank is divided into three parts: pre filtration water chamber area, filter material area, filter material cushion area and post filtration water chamber area. In order to overcome the defect that the upper filter material is easy to escape during backwashing, the height of the water chamber before filtration is increased by 0.5m on the basis of the original design.

(2) How it works.

The sewage enters the filter layer of the filter through the lift pump, the suspended solids are intercepted by the filter layer, and the filtered water is discharged from the drainage outlet through the water collection system.

In filtration, the filtration flow of the filter remains unchanged, and the removed suspended solids stay on the filter bed, which increases the filtration resistance, reduces the treatment capacity, and affects the water quality index after filtration. Therefore, according to the water quality of filtration, the filter tank should be backwashed every 12-15h for 10min to remove the suspended solids staying on the filter bed.

The time is set by the automatic control device for backwashing. In order to make up for the loss of filter media in the backwashing process, filter media should be added regularly.

(3) Main technical parameters.

The rated flow of single tank is 90m3 / h; The design pressure is 016 ~ 1MPa; The design temperature is 80 ℃; The water quality indexes before filtration were as follows: suspended solids content ≤ 30mg / L, oil content ≤ 20mg / L; After filtration, the water quality indexes are as follows: suspended solids content ≤ 3mg / L, oil content ≤ 5mg / L, particle size ≤ 3mg / L μ M (more than 85% of the total particle volume); The backwash centrifugal pump is 45KW.

COMPARISON of DOUBLE MEDIA FILTER AND OTHER FILTER TANKS

• The double media automatic filter is not filled with a single filter material, but with anthracite, quartz sand, Emery and other filter materials, forming two layers of filter materials with different densities.
• According to the requirements of water quality, the filter materials adopt different gradation. The upper layer is light filter material with smaller density and material diameter, and the lower layer is filter material with larger density and particle size.
• Due to the large density difference between the two kinds of filter media, the falling speed in the water is also different. The sinking speed of high density filter media is faster than that of low density filter media.
• Its advantages are: after several cycles of backwashing, the “light and fine” filter material can still be kept on the top, and the “heavy and coarse” filter material can be layered on the bottom, forming a step filter layer with the particle size of filter material from top to bottom from small to large, which improves the penetration ability of the filtered water and maximizes the pollutant interception ability of the filter layer under different densities and grading indexes.
• The automatic device is set to backwash once every 12h (15min), so that the filter material can be regenerated thoroughly and the filtration performance can be guaranteed. Compared with the filter tank with single filter material, the double filter material automatic filter has the characteristics of large filtration capacity and strong regeneration ability of filter material.
• Single quartz sand filter tank uses quartz as filter material, which has poor sewage interception capacity. The particle size varies from 0.6 to 3.5mm, the upper layer is 0.6 to 1.2mm, the middle layer is 1.2 to 2mm, and the lower layer is 2 to 3.5mm. After a period of backwashing, the quartz sand is stratified according to the size of the material, and a filter layer with gradually increasing particle size is formed from top to bottom. The main problems of walnut shell filter tank are that the filter material is easy to be polluted by dirty oil and gum, the filter material is expensive, difficult to regenerate, and poor backwashing effect.