December 8, 2008
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Home / Issue Archive / 2008 / September #9 / Microfiltration for Macroproduction

№ 9 (September 2008)

Microfiltration for Macroproduction

The term “microfiltration” is referred to a group of fluid and gas cleaning procedures intended for quite a wide range of particles (0.1 micron to 100 microns and over).

By Mikhail Terentiev

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The term “microfiltration” is referred to a group of fluid and gas cleaning procedures intended for quite a wide range of particles (0.1 micron to 100 microns and over). A micron is a unit of measurement equal to one thousandth of a millimeter. Therefore, this dimensional range includes major particles of mechanical impurities to be removed from process flows of various productions. The lower boundary of microfiltration capabilities is a dimensional level of micro-bacteria. It means that the finest filters can sterilize solutions, completely retaining bacteria.
Simpler tasks to be solved by industrial productions consist of retaining larger particles of several microns (a particle becomes visible when its size is 20-25 microns).
A majority of contaminants like silt particles, pipeline corrosion products, process fluid degradation products, mechanical trace contaminants are within a range of 5 to 50 microns. This is exactly the range of contaminants that is of current concern for macroproduction, which to some extent may include petroleum production, petroleum refining, petrochemistry, gas conditioning, gas processing, and major industry enterprises. And here we may consider in detail the problems associated with filtration of various fluids in terms of petroleum production and petroleum refining industries.
Why is it required to retain fine particles in large enterprises? From the very start of oil and gas travel from a productive stratum to the surface, available filtration processes determine operational economy and therefore industrial efficiency. In fact, a productive stratum being a porous formation filled with fossil raw materials is defined by certain permeability. When fluids carrying suspended particles are in contact with such stratum, it can impede or even block the fluid flow from the stratum, all the more that a surface area through which the fluid penetrates a well is insignificant. Using dozens cubic meters of contaminated with micro-particles completion fluids, cleansing solutions, and well-killing fluids contributes to fast clogging (colmatation) of the well bottom-hole zone and its sharp decline. An expensive process of drilling kilometer thick rock mass will be of no effect in case of no solutions filtration systems are available during drilling-in or further well workover operations.
To eliminate these negative phenomena in practice, acid-washing of the bottom-hole zone is used, though its efficiency is as a rule restricted; another way to rework a well is hydraulic fracturing, which is efficient but very expensive.
The same problem exists in the area of maintaining a reservoir pressure. Colmatation of bottom-hole zones of stimulation wells during injection of undercleaned water disables the wells, increases expenses and decreases deliverability of production wells.
Proper filtration of process solutions can significantly increase the well flow rate and ensure long-term and consistent high deliverability of wells with relatively small expenses, as well as significantly increase an on-stream period.
Being a developer of innovations, the 3 Russia company offered original engineering solutions to carry out filtration in the oil and gas production industry. Duo Flow 3M™ Cuno™ systems are systems that most widely applied for these purposes. They ensure efficient cleaning of process solutions immediately before injection into the well. This system enables cleaning of solutions with minimum expenses, for 10 wells in average, using resources of only one filtering element. Cost of filtration itself will make only 100-150 rubles (!) recalculated per one well. An example of applying such unit by a repair team for well kill operation is represented in Fig. 1. Filtration of formation-pressure maintenance systems is also successfully used based on the High Flow technology.
Now, we should consider the problem of process fluids contamination at the petroleum refining stage, which is the next stage of the oil and gas industry. Practical experience proves that higher content of solid contamination particles in feed and product streams results in serious unit failures such as:
Erosive wear, accelerated depreciation of equipment;
Scale in pipelines, heat-exchangers, and mass-transfer apparatus;
Premature nonreversible deactivation of catalysts;
Ageing, excessive consumption of recycle auxiliary chemicals;
Inadequate quality of final products.
Unscheduled shutdowns, systems cleaning and equipment repair result in significant expenses and increase unit unproductive downtime periods. Application of filters is the most widespread way to solve problems caused by mechanical impurities in raw material and petroleum derivatives.
Obsolete design filters are metal screens or cloth bags. Such filters are not capable to ensure consistent high quality filtration; they are quickly clogged and require frequent cleaning and replacing. That is why filters of such design applied in majority of units were just eliminated from the existing process flows in the course of time.
Meanwhile, problems of solid contaminants can be eliminated by installation of modern efficient filters that are reliable in operation and do not require expensive maintenance. These are self-washing, self-cleaning filters and removable filter elements operating on the basis of the depth filtration principles; they are easily replaceable and ensure consistent high quality filtration, with a large contaminant capacity. These types of filters are improved year by year and are widely applied abroad, with their design standardized by all filter manufacturers.
In modern technologies, filtration is expedient for all feed lines in order to prevent incident pollution. Filters are especially efficient in preventing failures when applied in old worn-out equipment.
General use of filtration in the petroleum refining industry:
Protection of catalytic processes;
Filtration of amines when cleaning sour gases and glycols during gas dehydration;
Cleaning of process water (recycling, stripping, boiler);
Cleaning of oils (motor, industrial, electrical insulating, etc.);
Filtration of fuels (for boilers and ovens);
Final treatment of products.
Recently, the most strict requirements in terms of mechanical impurities content have been specified for oils and hydraulic fluids used at high pressures. In lubrication systems with high fabrication accuracy of lapped faces, the finest particles with a size of even several microns cause increased wear of moving equipment parts. Hydraulic fluids and oils applied in these systems must be of cleanliness level 8-9 according to GOST 17216, which corresponds to contamination content of not more than 0.00025 percent (mass). Content of impurities within this range may be determined only by means of microscopes or optical particle counters. Filters rated for 1-5 microns, which are applied for receiving products of such high cleanliness, are to combine consistent high quality cleaning and economic efficiency.
At present, there is a wide variety of filtering equipment, but rigid filtering elements (cartridges) of depth filtration are mostly widespread. Depth filtration in combination with the cartridges’ gradient porous structure (Fig. 2) ensures their high operational resource. Adequately rated filtering elements can operate without replacement for several months. Cartridges are installed in standard filter holders accommodating from 1 to 560 single filtering elements. Maximum filter capacity may reach 500 cu. m/hour.
There is a wide variety of deep filters (Fig. 3). The following filter types are mostly spread in petroleum refining and petrochemical industries:
Micro-Klean is an inexpensive filter with a nominal filtration rate of 1-200 microns. It is applied for fuels, oils, steam condensate, and water.
Beta-Klean is an absolute filter (filtration efficiency is 99.9 percent) with a filtration rate of 5-70 microns. It ensures filtration of oils to cleanliness level 8-9 and conformance of jet fuel to international standards in terms of mechanical impurities content.
Petro-Klean is an absolute filter, compatible with oil products, with a filtration rate of 10-40 microns. It is applied for fuels, amines and glycols.
In recent years, depth filtration elements Micro-Klean and Petro-Klean demonstrated their efficiency in a number of oil refineries in Russia in the process of cleaning alkanolamines (MEA, DEA, and MDEA) that are applied for separation of hydrogen sulphide and carbon dioxide from sour gases (Fig. 4). Amine filtration enables to efficiently control foam formation and increased corrosion in amine systems. Under such specific conditions, when majority of contamination is represented by deformable resinous particles, depth filters have undeniable advantages as compared to surface filters (screens and bags).
Turno-Klean (Fig. 5) is a unique filter of a slot-type design, self-cleaning in the process of operation without stopping the flow. Filtration is carried out in calibrated spacing gaps between steel rings collected in a cylindrical cartridge. In this case, filtration level is 35 microns and over. Such filters are quite lasting. There is an example when a Turno-Klean filter was continuously operating with oils for more than 40 years.
High Flow filters (Fig. 6) are the most efficient ones for filtration of process water in water intakes; their capacity is from 80 to 1,200 cu. m/hour.
Thus, a necessity to include filtration in various processes of petroleum production and petroleum refining becomes an essential requirement for further efficient development of the industry as a whole. Filtration allows for significant reduction in process costs, improvement of final products quality, and significant increase in overhaul life of expensive equipment.

Mikhail Terentiev is the Candidate of Biosciences, Senior Technical Specialist of Fluid Filtration Department 3M Cuno™.
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