1 treatment of natural gas
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As a clean energy and a high quality industrial chemical source, natural gas plays an important role in economy development and environment protection. However, natural gas contains unacceptable levels of hydrocarbon and hydrosulfide, with which use of natural gas will cause operation problems in engines and turbines. So it is necessary to purify natural gas. The normal treatments include dehydration, acid gas removal and recovery of light hydrocarbon. For dehydration, cryogenic condensation, absorption and solid adsorption are commonly used. For acid gas removal, alkylol amine method and alkaline salt solution are mostly used. And for recovery of light hydrocarbon, cryogenic separation is widely used. Membrane separation technology, as an alternative method for treatment of natural gas, is a convenient and completely passive way to purify the raw natural gas. Advantages of membrane systems include skip-mounted structure, minimal maintain cost, least footprint, convenient operation, etc.

Membrane for carbon dioxide separation

In the natural gas industry, membrane carbon dioxide separation is mainly applied in the fields below:
•  Purification of natural gas to make its CO2 concentration meet the requirement of pipeline transportation.
•  Recycle of CO2 by recovering it from natural gas and inject it into the oil well in the process of CO2 enhanced oil extraction.
•  Combination with traditional absorption process, optimize whole process.

Membrane for fuel gas conditioning

Gas engine is widely used for increasing pressure of natural gas, which uses natural gas as fuel at the same time. Natural gas has a high heating value, high hydrocarbon dew point, and low octane number, which can cause operating problems. In gas engine, the enriched fuel may pre-detonate, which can severely damage the internals of the combustion chamber. In addition, condensation of hydrocarbon (due to day-night temperature variations) may damage the combustion chambers, increasing maintenance costs and downtime. Flow diagram of our membrane system is shown below:
 
The membrane system for fuel gas conditioning can:
1 reduce dew point 30 Celsius
2 remove 70% acid gas hydrosulfide and carbon dioxide
3 keep stable running of gas engine

Dehydration

All natural gas must be dried before entering the gas pipeline to control corrosion of the pipeline and to prevent formation of solid hydrocarbon/water hydrates that can choke valves. Currently glycol dehydrators are widely used. However, glycol dehydrators are not well suited for use on small gas streams or on offshore platforms, increasingly common sources of natural gas. Membrane process offer an alternative approach to natural dehydration. Due to high methane loss and high operation cost, membranes are then only competitive in special situations where glycol dehydration is not possible or less economical.
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Light hydrocarbon recovery and dew point adjustment
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Condensation or super-condensation (cryogenic) isn’t suitable for use on small gas streams or on offshore platforms. The usually used is air-cooling or water-cooling for light hydrocarbon recovery. The equilibrium temperature of air-cool or water-cool is about 20-30oC. There are still significant amount of light hydrocarbon in the gas stream after cooling. For example, there will be 3000ton/year loss of light hydrocarbon to an offshore platform with a capacity of 50km3/day. Below is the flow diagram of membrane system. Normally membrane system can lower the dew point of the gas by 20-30oC, which satisfies the criterion required by the natural gas pipeline. The membrane system can place on the above stage of cooling equipment for those processes that have applied the cooling equipment.. And the “bottle” problem can be solved of the gas turbine and the gas engine.


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Oilfield Re-injection Water Treatment
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Low permeability oil reservoirs account for about 10% of the exploited onshore oilfields and more than half of the discovered but unexploited ones in China. In the process of the onshore fields exploitation, it is of great practical significance to develop and employ well the Low permeability oilfields for the realization of the “Stabilize East, Go West” strategy

The pore-throat radii of low permeability sandstone layers range below 0.5μm, sometimes 0.2～0.3μm, which leads to high permeation resistance and rapid energy consumption. After the oil well is put into production, both the pressure and the yield of the crude oil descend dramatically and are very hard to be recovered. As a result, a passive situation is prone to be induced at the very beginning of the exploitation.

To avoid such situation, the low permeability oilfields shall be injected with water to maintain the formation pressure at the early stage. It is a long-term fundamental guarantee to complement energy and stabilize productivity for the low permeability oilfields by injecting water of sufficient quantity and proper quality.

Oilfield produced water is the byproduct of the crude oil pre-processing. To various degrees, the crude oil produced from oil wells contains water and is suitable for pipeline transportation only after being dewatered to meet certain requirements. A great part of the produced water is used for re-injection, which favors environment protection as well as solves the problem of injection water supply. Water quality is the key point of the water injection technology because the low permeability oil layers are characterized with small pore-throat radii and are apt to be plugged by contamination, requiring the oil-content ≤1ppm and SS (suspended solid) ≤1ppm.

Currently, the requirements can hardly be met by the traditional precise filtration equipments. However, the naissance of ultrafiltration technology throws light on the problem solving. Hydrophilic UF membrane technology of Dalian Eurofilm Industrial, Ltd. produces water meeting the above-mentioned requirements completely and the cost of water product can be controlled within an acceptable range.

　
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