Walnut shell filtration technology was developed in China in the middle and late 1980s. The complete set of production technology has long been mature and has been widely used in onshore and offshore oilfields.
With the expansion of application, walnut shell filter material has been used for a long time, resulting in poor filtration effect. Even if backwashing is carried out, the filter material can not be reused well. Therefore, this requires us to deeply clean the walnut shell filter material to achieve the effect of reuse.
Up to now, walnut shell has been widely used in the production of activated carbon, extraction of brown pigment, production of antioxidants, production of anti polymerization agent, plugging material, processing of organic dilution fertilizer, filter material and so on.
According to the analysis of the basic properties and pollution interception performance of walnut shell, each 100g walnut shell contains 38.05g ash, 30.88g cellulose and 27.26g hemicellulose. Because of its composition, it has its own physical properties, and even makes a great contribution to the filter material as a filter.
Walnut shell filter material is a kind of water treatment filter material made of high-quality hickory shell as raw material after crushing, polishing, steam washing, drug treatment and twice screening.
It can be inferred from its properties that the interception process of walnut shell filter material and the properties of intercepted dirt mainly include the following aspects: A. settling dirt formed by suspended particles deposited on the surface of filter material under the action of gravity.
Dirt attached to the surface of filter material under the action of physical adsorption or adhesion on the surface of filter material.
Dirt attached to the surface of filter material under the action of electrostatic attraction. Dirt infiltrating into the internal channels of the filter material under the action of diffusion.
In the treatment of oily water in oil field, quartz sand, walnut shell, microporous ceramics, membrane and fiber medium are used as filter materials.
Among them, walnut shell has the characteristics of wide source, strong adsorption and sewage interception ability, strong hydrophilic ability, oil immersion resistance, high hardness, good wear resistance, stable chemical properties, low particle density, easy hydraulic recoil, low required backwash intensity and relatively high reuse. Therefore, now most oil fields use walnut shell as filter material.
On the one hand, walnut shell as filter material has the sewage interception capacity of ordinary filter material, which can directly intercept suspended particles in wastewater. On the other hand, it can rely on its unique surface physical and chemical properties to adsorb the emulsified oil particles in oil production wastewater on the filter material surface or the condensate on the filter material surface through adhesion.
Walnut shell can be used as an adsorbent, which has been confirmed by a lot of science.
However, the viscosity and surface tension of oil affect the adsorption rate of walnut shell inversely. At the same time, the recovery rate of oil from walnut shell is higher than that of other aqueous media, which can be achieved only by force compression.
At the same time, walnut shell filter material is suitable for the filtration of well washing wastewater after pretreatment.
In a certain backwash lift pump sewage recovery tank, it is understood from here that during the filtration cycle, with the increase of the particle size of the filter material, the removal rates of oil and turbidity in the West show a downward trend, but the filter material with smaller particle size is easier to be saturated and penetrated.
At the same time, hot water is used as backwashing water during backwashing. The backwashing strength is less than that of ordinary quartz sand filter material. The strength and flushing time here depend on the particle size of filter material, and the filter material with larger particle size is easier to backwash.
After special treatment, walnut shell has increased surface area and strong adsorption capacity, so the removal rate of oil is high.
Walnut shell filter is the key equipment in oilfield water treatment system. Its structure affects the filtration process, filtration effect, evaporation and environmental pollution.
The combination with the cleaning tank will also affect the filtration and cleaning effect, which determines the recovery and reuse of filter materials.
It is applicable to the filtration treatment of reuse treatment of oily sewage and other oily wastewater circulation systems in iron and steel, metallurgical industry and coal industry.
It is suitable for fine filtration of large amount of oilfield reinjection water, produced water of offshore oil platform and reclaimed water treatment of thermal recovery boiler in heavy oil oilfield。
It is suitable for filtration and advanced treatment of cooling circulating water in power plants, refineries and petrochemical plants.
With the development of polymer flooding technology and the increase of polymer in water, there are some problems in walnut shell filtration, such as backwashing, pressure holding, material running, incomplete cleaning of filter material and so on. Therefore, the transformation of walnut shell filter is imperative.
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