János KIRÁLY₁, Róbert KOVAC₂ and László LIVO₁

1- MARKETINFO, Hungary
2- HELIR, Serbia and Montenegro

Abstract:

aaThis work presents filter installation suitable for mechanical filtering of natural and other types of transported gas. Minimal
particle size can be less than 2 microns.
aaDuring the last decade Ecofilt Mikrofilter has proved its applicability in underground gas storage, gas transportation and
with other various users. Ecofilt Mikrofilter allows the user to plan his filtering costs and to ensure maintenance costs
optimization in advance. The plans are feasible and realistic, which have been proved by the experience of its current users
in gas industry in Hungary and Serbia and Montenegro.
aaEcofilt Mikrofilter is a filtering installation with working period of 10 years. Its ability to perform strict particle filtering
derives from the very technology used for its make. The filter's guaranteed layer and body are made of stainless steel, which
gives the filter longevity and hardness (high deltap) and makes it easy to clean and maintain.
aaThe filters can be installed into any existing housing. In such cases the filters can take more flow, the filtering is more
accurate, and the safety is also increased when compared to the original construction. High permeability also derives from
the technology. It allows for small initial resistance (only a few millibars) and gives rather high tolerance to impurities.
aaThe very possibility to plan ahead allows the user to select the most suitable filtering installation, which would also allow
the user to lower the initial investment costs as well as the maintenance costs.
aaIn summary, the most important fact about these filtering installations is that they have long lifetime, require low initial and
low or insignificant maintenance costs, since they lead to lower instument damage rate by protecting them. This can be proved
by dramatic cost decrease.
aaThis work presents design, construction/installation and application of the filters, as well as the users' experience in use of them.

Key words: filter, gas, costs, maintenance.

1. Mechanical filtering - introduction

aaTo introduce mechanical filtering, let us first see what it is about; an experiment would be a good starting point. Take a full
glass of drinking water and pour the content to another glass through filter paper (or through a serviette). After the filter dried,
we can see that colour of the paper has changed. This would indicate that the water had contained some elements - impurities,
which remained on the filter paper. If we repeated pouring several times, the filter would come to a point where it could no
longer let the water flow through. Particles that had kept on the filter formed an impregnable layer. If, on the other hand, we
analysed the water at lab after each pouring, we would see that it contained less and less impurities each time.
aaWhat is the explanation of this phenomenon? On the filter paper surface a filter cake is formed, which is made of impure
particles that are also part of the filtering process. This leads to the conclusion shown in Figure 1.

Fig. 1 Mechanical filtering

aaThe experiment results gives us certain knowledge: impurities can be found in both to be filtered and has been filtered medium
(influent and efluent, respectively), but in different contents. Another result is that the filter cake contains impurities of different
size and shape.

aaIf we repeated the experiment with an other filter type, for example we used a piece of cloth instead of filter paper, the results
would also differ, first in time taken to filter the water. To be more accurate, if the quantity of water was different, so would be
the time of filtering. That would lead to the difference in filter cake formed on the cloth. Taking all previous results into
consideration, we can say that the quality and refinement of filter are not the only factors that influence the filtering results. To
keep the process under control we need to consider more factors.

2. Filtering characteristics

aaAnalyzing results of the previous experiment, we can conclude that the most important characteristic of a filter is its refinement,
which is determined by separation parameter. Its mark is µm (micrometer = 0.001 mm). Other important parameters are filtering
surface (or filtering area - square meter - m²) and free light area (%).The free light area is a number directly dependent on filter
quality. This number indicates the initial size of the filter area through which a fluid can flow continually.
aaIt is now easy to conclude that over a course of time the light area is reduced, owing to formation of filter cake. On each side
of filter the allowed pressure difference (deltap) is resenst, which is a significant property to have in mind in filter manufacturing.
Filter data has great influence on fliter cake, its thickness and filtering time.
aaApart from the parameters given above, there are other equally important ones that should be considered in designing filtering
technology: filter material, filtering fluid, medium temperature, pH, electric conductivity, etc. Two aspects allow optimal filtering
results:

aaaaaa) identification of an existing system operation and possibility of improvement of filtering technology based on laboratory
aaaaaaaanalyses,
aaaaab) well selected final goal of filtering process and its results' confirmation in a lab.

3. Main types of mechanical filters

aaMechanical filters can be divided in two main types. Surface filters are those with flat surface, e.g. net, sift, or those of
certain geometric shapes, which surface can also be used as filter (cylinder, cone, dome). These filters are candle or plate
shaped, and filter cake is formed on the surface (Fig. 1).

aaAnother type is the deep bed filters, which spread into the third dimension. The third direction is usually much smaller than
the other two.

aaOperation of the two filter types is basically different. While the surface filter strictly separates suspended solids from the
filtered fluid, the deep bed filter's separation can not described with one dimension, only with thickness territory.

aaIn deep bed filters, there is no filter cake formation; any changes are made in the third direction, and they depend on how and
where certain granules are positioned; the granules then flow through or are suspended in channels that are formed during the
filtering process. The channels' dimensions are influenced by design, material, geometry (diameter) and permeable layre of the
deep bed filter (Fig. 2).

Fig. 2 Deep bed filter with flowing channels.

4. ECOFILT Mikrofilteraa

aaThis filter construction is adapted to existing technologies in gas production, transport and storage. Its application allows a
simple way of requested level of gas separation and purification. Pipeline solids, corrision products, compressor oil, oil droplets
and oil fog can be filtered with Ecofilt Mikrofilter. By applying adequate technology, liquid phase and mechanical impurities
can be separated from associated gas.

aaFiltering purity is 5 to 2 µm; filtering accuracy is 95-98%; filter flow and pressure are significant. Average initial resistance of
filter group is 0.1 bar.
aaThere is a significant advantage of Ecofilt Mikrofilter when compared to other filters, and that is its operating lifetime of 10
years. In effect, this would mean that after cleaning, this filter is not wasted, but returned to the system, which, as a result,
minimizes maintenance costs. The user can plan the maintenance cycles in advance, which makes it an input to the system design.
Another advatage of Ecofilt Mikrofilter is that it can be installed into existing systems to replace the existing filters, and can even
be installed into existing housings.

aaA unique statement of our business partners that have been using Ecofilt Mikrofilter is that it allows them to achieve lower
costs of compressor repairs and significantly reduce presence of impurities in the systems; Ecofilt Mikrofilter also allows for
better protection of test wells and layers. Its use can also reduce overwork labour costs and chermical treatment of wells.

4.1 Candle shaped filters - introduction

aaCandle shaped filters are widely used. Its main advantage is easy installation, and another is a relatively large filtering area on
a relatively small surface.
aaCandle or cylinder shaped filter core serves as a base for spreading filter net - metal, plastic, or cotton - or filter paper. The
filter core is determined by the user's design; its shape is defined by the final goal that the user wishes to achieve by the filtering
process.
aaThe usual candle shaped filter core is shown in Fig. 3.

Fig. 3 Candle shaped filter's principle

aaThe usual filter design allows for target application and training. The L/d ratio affects the mode of flow. Filtering quality, free
area, flitering fluid and other technical parameters have significant effect on initial resistance, saturation time and possibility of
cleaning.

4.2 Cascade filter

aaFilter cores can easily be rearranged in such shapes that would allow the filtering fluid to flow through several filtering surfaces.
The surface filter can be supplemented also with deep bed filter. This principle allows the user to design such filtering systems
that would result in higher level of separation and solid suspension from the filtering fluid.
aaOne of the most important characteristics of cascade filters is the low initial resistance. Another advantage is high deltap value,
wich can be achieved by a robust system consruction.
aaAn important point is to have a quality surface system that would allow filtering fluid flow for a lengthy period of time, which
would lead to conditions for a longer filter life cycle before replacement and a good chance to flush the filter. The following
Figure shows one candle shaped filter cascade type.

Fig. 4 Cascade filter (3 stairs)

aaOf course the cascades are selected according to previously conducted lab tests and requested filtering quality. Figure 5
shows a scheme of a practically applied two-stairs cascade filter, one surface and one deep bed filter (prefilter).

Fig. 5 Ecofilt Mikrofilter

4.3. Ecofilt Mikrofilter

aaWhat does this trademark or name stand for?
aaEcofilt Mikrofilter is a candle shaped cascade or multiphase filter. As shown on Fig. 5, it is a candle shaped filter made of
stainless steel.
aaOwing to its design, this filter is highly resists to and allows great pressure differences (deltap) of up to several bars.
aaFiltering surface is cylinder - candle - shaped wrapped around the base core.
aaThe wrapping has one layer, therefore the free surface of the filter is set with high precision (even 98%). Thanks to the
wrapping the shape and size of the slits are also of high precision, which is between 95-98%. This property gives highly reliable
and precise separation of filtering surfaces.
aaMicron-gauge wire wrapped around the base core is also made of stainless steel.

4.3.1. Based on our experience, we can say that we have designed a robust candle shaped filter core with low initial resistance,
which can stand great strains, and has a long operating life of up to 10-15 years.

aaProduction technology in petroleum industry allows us also to manufacture and/or alter certain elements of the filter base core
according to the user's specific requests.
aaAs a result, it is now possible to replace existing filter cores existing housings.

4.3.1.1 The possibility to change the filtering parameters allows us to maintain the existing filter surrounding. This leads to
significant investment cost reduction.

Fig. 6 Prefilter under a microscope

aaPrefilter can be single or multilayered, which depends on the targeted filtering process goal. By its adequate positioning and
calibration, it can filtrate and storage large quantities of impurity.
aaSuch filters then simplify and increase maintenance level, since they only require replacement of the deep bed filter.

4.3.2 Our experience has proved that the prefilters can easily be washed (in suitable solvent); then reused, and this
process can be repeated several times.

4.3.2.1 These particular types of cascade filters can be applied to industries that operate in high temperatures.

4.3.2.2 With the aEcofilt Mikrofilter such influenst, as gas, steam, liquids, emulsion, etc. can be cleaned with selected methods.

4.3.2.3 This filter is highly precise, has a long operating life, gives the user the possibility to plan its replacement, and has a
remarkable filtering efficiency to 2 µm.

Fig. 7 Filter unit

aaCascade filters can be cleaned in a few ways, which are very simple, unless the filtered medium contains sticky solids.

Fig. 8 Filter unit for gas injection into underground strorage

4.3.3 Ecofilt Mikrofilter can be supplied with various control instruments, such as flowmeter, gauge, velocity meter, etc.

4.3.4 All information registered by control instruments can be gathered into a computer data base.

aaWith the support of control instruments there is only a step towards complete process automation. Based on required
technical characteristics of the instruments, Ecofilt Mikrofilter allows filtering process management from PC, by applying PLC.
aaPLC can make daily reports on filtering process. To analyze and gather instrument information a PLC can be upgraded
with such software that would include control, correction and training.

Fig. 9 PLC

4.3.5 Ecofilt Mikrofilter supported filtering unit can be operated, controlled and cleaned using PLC control.

4.3.5.1 All electronic devices are adapted to the existing electronic surrounding and processes, with which complete accord
and communication is established.

5. Summary

aaEcofilt Mikrofilter is a cascade candle shaped filter that adapts to existing industrial processes; it is easy to design and
calibrate, does not require high maintenance, and eventually can be automated.
aaRobust construction of cake filter made of stainless steel allows it to be applied to any industrial environment where the
following is required:
- high filtering standards,
- high accuracy and precision,
- long operating cycle (long maintaining cycle that can be planned ahead),
- safe operating in emergency situations,
- strict separation,
- long operating life,
- low maintenance costs,
- possibility of automation,
- filtration in abrasive media (gas-steam, liquid, chemicals, etc.).

aaEcofilt Mikrofilter expands and allows the possibility to calculate and measure mechanical filtration without making
additional stress to the medium, and the possibility to appley effective cleaning and flushing in both domestic and
industrial environments to up to 2 µm. Reference of its operation can be seen in Hungary and Serbia and Mintenegro.

Back to the News