SE502021C2 - Method and apparatus for purifying a circulating liquid in a circulating circuit - Google Patents

Abstract

A method and a filter unit for cleaning a liquid which circulates in a closed circuit, such as a central heating circuit, from particulate contaminant material, such as magnetite particles, comprises introducing into the circuit liquid soluble chemicals which are active in suspending and agglomerating the contaminant particles, and filtering the circuit liquid with the aid of a filter cartridge whose smallest filter medium openings are larger than a substantial proportion of the contaminant particles. By limiting the flow rate of the liquid through the filter cartridge to a given maximum filter surface load, corresponding to a value at which at least a 70 % reduction of a standard contaminant consisting of kaolin clay Grade C, EEC International, is obtained across the filter, the filter capacity is utilized to a very high degree and favourable separation or extraction of the contaminants is achieved. The filter unit may include a rate of flow limiting means which functions to set the throughflow to a value which will provide the maximum filter surface load in question essentially independently of the pressure drop across the filter.

Description

502 10 15 20 25 30 35 021 magnetite particles will eventually contaminate the system However, the invention finds general use in circuits, for example in hydraulic circuits, district heating circuits, brine circuits and the like, where contaminant particles eventually occur and can interfere with the operation of the circuit.

In the example of central heating systems, it is thus known that over time, if no action is taken, the system will contain significant amounts of magnetite sludge which causes circulatory disturbances and damage in the form of deposition corrosion, etc. To avoid such disturbances it is well known that can filter the circulating medium and that by supplying the circuit fluid certain chemicals can be mobilized and agglomerate the contaminant particles so that they can be filtered off more easily.

It has been proposed to use filter cartridges comprising a wound wire of polypropylene, the wire having a coating of such chemicals. But the result of the use of such filters has not been satisfactory.

We have found that the formed particle aggregates rarely have individual particles> about 20 microns and that more than 50% of the particles are <about 5 microns while the formed aggregates are usually> about 5 microns but <about 30 microns, for use herein - only chemicals, where the particles consist of magnetite sludge, precipitated salts, etc. Under the influence of dispersants with insignificant or no capacity for aggregate formation, typically> 50% of the particles <approx: 2 μm are obtained.

Therefore, in order for the filter to be effective in separating such contaminants, the filter should be designed to be able to separate a substantial proportion of the assembly from. this magnitude. However, we have found that such known filters in some cases still had a low dirt capacity and low separation capacity, when following the general recommendations from the filter supplier regarding the flows over the filters.

An object of the invention is therefore to provide a method and a filter unit which give the filter unit a high dirt capacity and a high separation capacity under all operating conditions. The purpose is achieved by the procedure specified in the independent procedural requirement. Embodiments of the procedure are set forth in the dependent claims. The purpose is also achieved with the filter unit specified in the attached independent product requirement. Embodiments of the product are set out in the dependent product requirements.

According to the invention, we have found that it is possible to obtain a high utilization of the filter separation capacity, a high degree of separation of the contaminants by means of the filter unit, and a separation-promoting concentration development for the functional chemicals in the circulatory system. The process dynamically limits the surface flow (m3 / s) per unit area (m2) (= the surface load (m / sn on the filter to values that depend on the filter's separating ability (filter structure and filter material) and also depends on the particle aggregate's strength. street strength an upper limit at which problems tend to arise due to the units starting to interfere with the function of valves, throttle gaps, etc. in the circulation system. "Dynamic" limitation means that the specified maximum flow must be a maximum value, 502 Û21 10 15 20 25 30 35 and independent of the pressure drop across the filter device.

In deep filters where the filter usually has a decreasing pore size towards the outflow side, a large proportion of the filter's dirt capacity in the filter volume is closer to the inlet side, and in order to make the best possible use of this capacity, the load must be so low that the units are caught and remains whole even on the inlet side of the filter; otherwise the units would break and the unit parts / particles would clog the finest pores on the outlet side of the filter, the filter volume on the inlet side would be substantially empty of the unit and the particles when the filter is consumed / clogged.

Furthermore, we have found that it is essential that the amount and rate of release of the functional chemicals are regulated within certain limits so that the chemical concentration in the circulating liquid rises at a certain rate. It has thereby been found that the load indicated by the invention facilitates such a desired concentration development for the currently available and common functional chemicals, ie. medium and high molecular weight polyacrylates, nonionic and anionic polyacrylamides, polyacrylate silicate esters of varying molecular weights, and combinations thereof.

Furthermore, it has been found essential that the amount of chemicals added to the filter corresponds to the amount of chemicals that can be captured by the filter together with the particles; the amount of chemicals is adapted to and corresponds to the dirt capacity of the filter, in order to achieve an important object of the invention, to provide a self-controlling system.

A central feature of the process according to the invention is that the surface load of the filter is regulated to a value for which at least 70% total reduction of sample contamination of kaolin clay Grade C, ECC International is obtained.

As an example, such a 70% reduction of the sample contaminant over cartridge-type filters is obtained, which are formed of wound polypropylene threads having a coating of a mixture of medium and high molecular weight polyacrylates, which filters in the absence of the coating has a degree of separation according to ASTM F662-80 amounting to 30.10 and 2 microns, when the surface load on the filter is arranged so that it amounts to a maximum of 0.1 x 10-3, 1.5 x 1o'3 resp. 2.5 x 10.3 m / s.

A central feature of the invention is the method for determining useful chemicals or chemical combinations which are capable of forming aggregates with sufficiently low strength to be able to be broken down by the liquid circulating in the system if the aggregate gets stuck in a gap or other constriction in the system and which surface load can be permitted on a filter media opening with a certain separation according to ASTM F-622-80 for Beta Ratio = 10 according to ISO 4572.

It is essential here to select a sample contaminant with a well-defined particle size distribution within the particle size range that is of interest for the intended use. For inorganic contaminants in circulating water systems with mainly magnetite, precipitated salts and contaminants from manufacture and assembly, an inorganic sample contaminant should be selected and for organic contaminants an organic sample contaminant should be selected. As particles <approx. 0.5 μm in water that are in motion essentially appear as if they were in solution, they lack interest in these determinations. When, for practical reasons, sample filtrations take place with only one passage through the filter (single pass), while in practical use it is a question of multiple passes, 0.8-μm can be chosen as the lower limit for particles in single pass as this is approximately 0502 021 10 15 20 35 30 corresponds to separation at 0.5 μm in multiple passes. From what has been said before, the proportion of particles> approx. 20 μm should be moderate for the test substance to be meaningful.

For the determination of useful chemicals / chemical combinations for filter media with Beta Ratio = 10 interval 3-30 μm in single pass according to ASTM as above, experiments are made with different surface loads for a given degree of separation until a gravimetric total retention equal to or larger than e.g. 70% of the sample contaminant is obtained. The choice of gravimetric retention is made with regard to the particle size distribution of the selected sample contaminant according to the guidelines given here. The choice of test contamination should, however, be made so that particles> 0.8 μm in a single pass give 60-80% retention for the contamination and the selected retention limit «Must be used for All experiments to determine the suitability of a chemical and suitable surface load for a given filter media with Beta Ratio = 10 at a given micron number.

Plots of surface load are plotted with a tolerance of 10% for a given retention as above against micron numbers for a filter media, an approximately straight line is obtained where the slope of the line constitutes an indirect measure of the mechanical stability of the formed units. The line thus obtained constitutes for the selected combination of chemical / filter media the limit value for surface load which must be maintained by dynamic flow limitation.

Chemicals which, when extrapolated from said line to the surface load 0 give a micron number> 40 μm and when extrapolated to the micron number 1 give a surface load> 0.006 m / sec, have no practical interest in this invention. Any chemical or combination of chemicals which for a given filter media given in the test described above gives a line falling within the given limits shall be covered by the patent.

A central feature of the inventive method is that the surface load of the filter is dynamically limited to what has emerged as above in the method for selecting suitable chemicals / chemical combinations for a certain filter media.

Example A deep filter in the form of a wound cartridge with winding of polypropylene on a stainless steel support core, which filter is classified for 5 μm separation according to ASTM F-622-80 for Beta Ratio = 10 according to ISO 4572, was supplied with a supply of suspension and agglomeration chemicals in the form of a mixture of medium and high molecular weight polyacrylic acids. This mixture was touched on the filter winding by soaking the filter cartridge in a solution of these acrylic acids, after which the excess solution was allowed to drain and the solvent was removed. During this chemical application, filter cartridges were rotated about their longitudinal axis, and the solvent was removed by conventional drying. The amount of functional chemicals thus added to the filter cartridge was adapted to the amount of functional chemicals subsequently collected by the filter cartridge when its dirt capacity is substantially fully utilized.

Such a deep filter cartridge was mounted as a partial flow filter in a central heating system with significant amounts of magnetite sludge which caused circulatory disturbances and damage in the form of deposition corrosion in the system.

By a dynamic flow limitation of the partial flow through the deep filter cartridge, a flow of the corresponding 0.002 m / s is set in 10% over the filter medium of the filter cartridge. Here, a reduction of the iron content in the system water by 70% of the content before the test was obtained. According to the instructions here for selection of chemicals, for a 10 μm filter with all other factors equal to the dynamic flow restriction would set to 0.00l5 m / s 1 10% for an equivalent result, when the sample contaminant is paper coating clay GradeC from English China Clays ECC International GB. 80 - 90% reduction of the iron content over the filter is obtained after complete release of the polyacrylates due to the maximum water velocity through the filter pores being dynamically limited to a predetermined maximum value for the surface load. This avoids the migration of separated material to the clean side of the filter even in the event of mismanagement, if the filter is arranged as a partial flow filter, since the only thing that happens if the filter is not replaced at a suitable interval is a failure of the filtering function when the filter is clogged .

Fig. 1 illustrates the operating conditions of a filter system operated according to prior art.

Fig. 2 illustrates the operating conditions for the same system but with a limited surface load of the filter according to the above.

Fig. 3 shows the essential co-operation between the maximum permissible surface load and the filter degree of the filter for 70% retention on a given filter type with a specific chemical.

Attached Figures 1 and 2 illustrate operation of filter systems each having the basic design indicated above with functional chemical prepared filter elements, however, Figure 1 illustrates operating characteristics where the surface load is set arbitrarily by a static throttling of the flow to the corresponding average 0.0020 m / si surface load. Pga. changes in the flows in the filtered main circuit, variations are obtained in the actual flow in the partial flow circuit and thus in the surface load, even if the flow on average over a longer period of time is within values corresponding to the desired one, but at this time unknown, maximum surface load. For shorter periods, flows corresponding to a surface load of 0.0035 m / s have been noted.

Figure 2 shows the operation with a dynamic flow limitation that gives a maximum surface load of 0.0022 m / s even in the event of rapid flow / pressure changes in the main circuit and normally maintains a constant surface load of 0.0020 m / s 1 5% below the practical life of the filter elements.

Filter elements used for the reported samples are from the same manufacturing batch from the filter manufacturer, which indicates a typical spread in separation performance between batches to I 2% from the specified degree of separation. All filter elements used are chemically prepared at the same time_with the same chemical solution.

The horizontal arrows in the figures have approximately the same length scale as the time axis which is linear. In Figure 1, the typical rapid decrease to zero is not obtained at the end of the practical operating time of the filter. This must be attributed to the fact that significant amounts of material to be mobilized are present in the system, which can be seen in the measured iron contents and the relatively rapid release of the functional chemical. The functional chemical is also consumed by materials out in the system that have not been mobilized to a sufficient extent to follow the water flow. After about half the operating time, it is therefore probable that the content of iron before filters increasingly consists of mobilized material that has migrated through the filter pgs. too high surface load, to later be measured again as iron before filter. However, the extent of the migration in Figure 1 is completely unacceptable from both a technical and operational point of view. 502 021 10 15 20 25 30 35 10 In figure 2 which relates to the invention, the time axis represents approximately: 3 times longer than figure 1. The iron contents are significantly lower representing a cleaner system which is also seen in the slower rate of increase in iron content directly after installation. of new filter elements. It follows that a smaller amount of functional chemical is consumed for mobilization out in the system and the concentration of this in incoming water to the filter is therefore higher for a longer time, which reduces the release of the same from the deep filter medium. This is the main explanation for the significantly longer release phase and not a restricted flow, total filtered volume below this part is about: 2.5 times the volume of Figure 1.

In view of the fact that the characteristics of the selected filter element such as filter surface and degree of separation are known and that for a selected chemical or combination of chemicals, a maximum acceptable surface load can be determined, the maximum surface load of the filter element in an installation can be limited to the desired value. for dynamic flow limitation. This dynamic flow limiting device can be an integral part of the filter element, form part of the filter unit itself (filter housing) or device with such an effect arranged in a line in which the filter unit is located.

In the diagram according to Fig. 3, the result is depicted with filters prepared with an agglomeration chemical consisting of polyacrylate, which is sold under the trade name Polytreat 2065, by Houseman Scandinavia A / S.

The kaolin used as a test pollutant is kaolin Grade C from EEC International AB, Box 37, S-421 21 Västra Frölunda, Sweden. 10 15 ll 502 021.

A plant according to the invention for carrying out the method can have the design which appears from the preamble of the method requirement, and is mainly characterized in that the flow control equipment, which allows adjustment of the surface load value, is arranged to be substantially independent of pressure drop changes across the filter in the system.

The test contaminant kaolin clay Grade C ECC International, is illustrated in the attached Fig. 4 with respect to the particle size distribution, which was evaluated using ECC test method P 109 for particles with a size of 0.5 μm and above and Ladal centrifuge for sizes smaller than 0.5 Um .

In Fig. 4, the ordinate refers to "% by weight greater than" and the abscissa refers to "the equivalent spherical diameter of the particles um".

Claims (8)

502 021 10 15 20 25 30 35 12 Patent claim A method of purifying a circulating liquid in a circulating circuit such as a district heating circuit, a hydraulic circuit, a central heating circuit or the like, wherein at least a partial flow of the liquid of the circuit is passed through a filter housing containing a filter having a filter coating in the form of a filter coating. chemicals which are soluble in the liquid and which serve to suspend and agglomerate contaminant particles in the circuit, the filter being selected to have dimensioning openings which are larger than a substantial proportion of the particles, characterized in that the surface load of the filter is regulated to a value for which at least 70% reduction is obtained in simple passage with the filter of a standardized suspension suspended in the liquid with a particle size distribution corresponding to that for kaolin clay Grade C, ECC International, that the surface load of the filter is limited to a maximum of 0.006 m / s, resp. 0 m / s and a straight line in between, for filters which without chemical coating have a separation according to ASTM F-662-80 amounting to l um resp. 40 μm and a linear scale in between, and that the surface load of the filter is arranged so that the set value is not substantially exceeded by pressure variations across the filter. A method according to claim 1, characterized in that the size of the chemical supply is selected to substantially correspond to the amount of chemical that is removed together with the filtrate on the filter when the filter's dirt capacity is substantially fully utilized. 3. A method according to claim 1 or 2, characterized in that the chemical supply is bound to the filter to be leached out at approximately an even rate for approximately the first third of the filter time. 10 15 20 25 30 35 13 502 021 Method according to one of Claims 1 to 3, characterized in that the maximum permissible surface load for a filter with a given filter degree and a given chemical coating or a corresponding indication of the resulting agglomerate strength is determined by comparison with the results of evaluation tests with filters of different filter grades and chemicals or agglomerate strengths derived therefrom, which results have been obtained using a standardized contaminant of a type substantially corresponding to the expected contaminants in the systems to be purified, the evaluation tests offering a relationship between load and filter degree for a 70% pollution retention. Process according to one of Claims 1 to 4, characterized in that the surface load on the filter is set at a maximum of 0.7 x 10 -3, 1.7 x 10 -3 2.4 x 10 -3 a degree of separation according to ASTM F662-80 amounting to 20.10, respectively 3 microns, and for a test contamination of kaolin Grade C, ECC International in water, which filter has a surface coating of polyacrylate on the polypropylene fibers. respectively m / s for cartridge filters of polypropylene and with A filter unit for purifying a circulating liquid in a circulating circuit such as a district heating circuit, a hydraulic circuit, a central heating circuit or the like, which filter unit is arranged to be mounted in a filter housing connected in the circuit, the filter unit comprising a filter with a supply of liquid soluble chemicals for suspending and agglomerating contaminant particles in the liquid of the circuit, the dimensioning filter media openings of the filter being larger than a substantial proportion of the contaminant particles, characterized in that the filter unit has a flow control device which is arranged to limit the surface load of the filter to a For which at least 70% reduction is obtained over the filter of a suspended standardized sample impurity with a particle size distribution corresponding to that of kaolin clay Grade C, ECC International, that the flow control device is arranged to limit the surface load to a maximum of 0.006 m / s resp. 0 m / s and a rectilinear limit therefor for filters which without chemical coating have a separation according to ASTM F662-80 amounting to 1 μm resp. 40 μm and linear scale therebetween, and that the flow control device is arranged to substantially prevent increase in set surface load even in variations in the pressure drop across the filter. characterized in that the surface load does not exceed 0.7 x 103, 1.7 x 10 "polypropylene and with a degree of separation according to ASTM F-662-80 amounting to 20.10 and 3 microns, respectively, and Filter unit according to claim 6, respectively 2.4 x 10-3 m / s for cartridge filters of for a test contamination of kaolin Grade C, ECC International, in water, which filter has a surface coating of polyacrylate on the polypropylene fibers. Filter unit according to claim 6 or 7, characterized in that the amount of chemical supplied to the cartridge is selected to substantially correspond to the amount of chemical removed together with the filtrate on the filter when the filter's dirt capacity is substantially fully utilized.