Coalescence treatment technology of wastewater containing emulsified oil in coalbed methane field
With the modification and progress of coalesced fiber materials, coalescence separation method has become a high-efficiency and low-cost oil-water separation technology, and has been widely studied and applied. Since the coalescence technology adopts the physical demulsification method, it has no effect on the subsequent oil recovery and waste oil regeneration, and is widely used in the field of oil-water separation. Highly favored.
Introduction to coalescence technology
1.1 The principle of coalescence separation
The so-called coalescence, also known as coarse-graining, is to modify the surface of the material in a targeted manner, so that the diameter of the dispersed and emulsified oil droplets in the water becomes larger (coarse-grained) when flowing through the surface of the material, and floats up according to Stock’s law to achieve oil-water separation purpose.
Most viewpoints hold that there are two different mechanisms for the coalescence of oil droplets: one is “wetting coalescence”; the other is “collision coalescence”.
Collision coalescence is the physical collision of oil droplets, resulting in larger oil droplets. For example, heating oil-containing water accelerates the thermal motion of oil molecules, collides and coalesces and grows.
Wetting coalescence is that when the oily sewage flows through the coarse-grained bed composed of lipophilic materials, the dispersed oil droplets are wetted and attached to the surface of the material, so that the surface of the material is almost completely covered by oil, and the oil droplets flowing in are also more stable. It is easy to wet and adhere to it, so the attached oil droplets continue to coalesce and expand and form an oil film.
Due to buoyancy and the impact of the reverse current, the oil film begins to fall off, so the surface of the material is renewed to some extent. The peeled oil film still forms oil droplets in the water phase, and the particle size of the oil droplets is larger than that of the oil droplets before coalescence, so as to achieve the purpose of coarse-graining. The principle is shown in Figure 1.
According to the different theories of the wetting angles of the two-phase liquid on the solid material, the two phases show different wetting angles on the contact surface. 70°), the two phases can be separated.
The surface of the lipophilic and hydrophobic modified material makes the oil-water two-phase wetting angle greater than 70°, the water phase passes through the material surface, and the oil phase aggregates on the material surface, and finally becomes coarse.
1.2 Modified coalescing materials
Through the molecular modification technology of fiber materials, the modified fibers have lipophilic and hydrophobic surface properties.
The oil absorption performance of the fiber can be explained by observing the surface changes of the fibers before and after modification under different water inlet conditions (the changes of the fiber surface were observed by using an OLYMPUSBX41 optical fiber microscope). Figure 2 is a comparison of the original state of the fibers before modification and after modification.
Figure 3 shows that the modified fiber is made into a coalescing core for the treatment of 50 mg/L oily wastewater, and the coalescing core after primary filtration is observed.
Figure 4 shows that the treatment concentration is 100mg/L oily wastewater, which is stable after running for 2.5h, and the coalescence core is taken for observation.
It can be seen from Figure 4 that the fibers first capture the oil droplets (Figure 4-left, 4-middle), and then the oil droplets coalesce on the fiber surface to a certain extent, forming an oil film on the fiber surface (Figure 4-right). ).
This leads to the following conclusions:
(1) The modified coalescing material has lipophilic and hydrophobic surface properties.
(2) The oil film preferentially wets the fiber surface. When two fibers cross, the oil particles on the oil film grow up and float away from the fiber surface.
Coalescing sewage treatment system
2.1 Water quality analysis
The oily sewage in the coalbed methane treatment center mainly comes from F4, F5, F9 and other gas gathering pipelines receiving sewage from pigging operations. The water quality analysis results are shown in Table 1.
From the analysis results in Table 1, it can be seen that the oily sewage in the treatment center belongs to the cleaning industrial sewage with low salinity, high iron content and high lubricating oil content.
To sum up, the water-like suspended solids and lubricating oil in the treatment center are the key points of sewage treatment, and most of the lubricating oil exists in the form of suspension and emulsification.
2.2 Laboratory tests
After studying and analyzing the state of oil and suspended solids in the oily sewage taken by electron microscope in Fig. 5 and Fig. 6, the oily sewage was deoiled by indoor small coalescing equipment (the test machine was composed of a two-stage coalescing high-precision oil-water separator, and the flow rate was 120L/h).
The results of the small test show that the experimental equipment has significant degreasing and suspension removal effects. The effluent oil is 0.6 mg/L and the suspended solids are 7.2 mg/L, which provides basic data for the design of industrial equipment. The experimental results are shown in Table 2.
It can be seen from the test results that the oil-water separation test machine has an obvious effect of removing oil and suspended solids. The design adopts a rapid filtration device (reducing the load of the oil-water separator to ensure the oil-removing efficiency) after removing the oil slick from the raw water, and then entering the oil-water separation device. Next process.
2.3 Process route
According to the above analysis of wastewater and its own characteristics, after careful analysis, in line with the tenet of less investment, small land occupation, low operating cost, good treatment effect, convenient management and high degree of automation, the sewage treatment system of coalbed methane treatment center The process is optimized, and the main process flow of the engineering design is shown in Figure 7.
2.4 Industrial installations
It is designed and manufactured based on the experimental treatment effect in the laboratory, and an industrialized device is installed in the coalbed methane treatment center. The entire coalescing system consists of a fast filter, a secondary coalescence high-precision oil-water separator, an activated carbon filter and a clean water storage tank. .
During the working process, the PLC control system can realize automatic and manual control, with a high degree of automation.
The design rated processing capacity of the coalescing device is 5m3/h, the working pressure is 0.3～0.4MPa, the working temperature: 25～90℃, the overall skid covers an area of 6000mm(L)×2300mm(W)×3300mm(H), and the total power 5kW.
The installation, commissioning and operation have so far been without operating failure, and the effluent is clear and translucent, meeting the first-class discharge standard for suspended solids and petroleum indicators in the Comprehensive Standard for Sewage Discharge GB8978-1996, and in line with the original production wastewater designed to treat effluent ≤70mg/L and Domestic sewage inflow ≤170mg/L suspended solids index requirements, the water quality should be sent to the local environmental protection monitoring station for monitoring, and a monitoring report should be issued. The test results are shown in Table 3.
It can be seen from Table 3 that the coalescing device has a remarkable oil removal effect, and the export petroleum indexes are mostly below 1 mg/L. At the same time, the removal of suspended solids in the water also reaches the discharge standard.
Application effect evaluation
The coalescing oil removal device has collected more than 20 barrels of waste oil since the operation date, and collected about 2.5 tons of waste lubricating oil per month on average.
The oil collected by physical degreasing can be recycled, which makes the rational use of oil resources and has been unanimously recognized by the manufacturers. The characteristics of the physical degreasing include fast separation speed, high separation accuracy, low filtration resistance, energy saving, wide range of oil separation and small equipment volume. , Simple structure, modularization, small footprint, high separation efficiency, automatic operation, easy operation, convenient maintenance and reliable operation.
There is no need for power and chemical additives, and the material is the polymerization principle of micro-surface, safe physical separation, without any harmful by-products and derivatives. Due to the principle of physical separation, the service life of the modified material is extremely long.