WO2003037803A1

WO2003037803A1 - Method and device for liquid treatment

Info

Publication number: WO2003037803A1
Application number: PCT/NO2002/000396
Authority: WO
Inventors: Svein Olav Risvold Stornes
Original assignee: Wasto As
Priority date: 2001-11-01
Filing date: 2002-10-31
Publication date: 2003-05-08
Also published as: NO20015354D0; NO20015354L

Abstract

A method and device for the purification and treatment of a liquid, wherein the liquid is purified by flowing through a filter material (18, 20), the filter material being arranged to be cleaned by means of counter-flow flushing, and wherein, with the aim of changing the pH-value and alkalinity of the liquid, the liquid flows through a reaction material (26) in the form of magnesium oxide and/or calcium carbonate, the liquid flowing in a falling manner through the filter material, and flowing in an ascending manner through the reaction material.

Description

METHOD AND DEVICE FOR LIQUID TREATMENT

This invention relates to a method and a device for treating liquids, especially for use in connection with an energy plant, in which water is used as an energy carrier, for example in a cooling and heating plant.

A plant, in which water is used as an energy carrier, is operationally affected to a substantial degree by the chemical composition and particle content of the water used. Apart from the content of the water of particles in the form of organic and/or inorganic material, three conditions, in particular, are of importance and have to be controlled to maintain high efficiency and reliability in a plant of the kind in question:

- the hardness of the water, normally indicated as °dH on a scale from 0 to 21, expressing the content of calcium and magnesium ions in the water, a low °dH-value indicating very soft water. - the acidity of the water, normally indicated as pH on a scale from 0 to 14, expressing the content of hydrogen ions in the water, a low pH-value indicating acid water and pH 7 indicating neutral water.

- the alkalinity of the water, normally measured in milligrams of bicarbonate (HC0₃) per litre, which is a measurement of the sensitivity of the liquid to contamination, . that is, of a buffer capacity for acid additions. The measurement indicates the ability of the liquid to neutralize acids, that is, the ability of the water to bear additions of hydrogen ions H+ without responding with a reduced pH.

Experience tells that content from hard water (Ca, Mg) deposits on the warmest places in a plant, which are often the places where good heat transmission is important, such as heating elements and heat exchangers.

Corrosion of the metals of the plant creates sludge. The sludge preferably settles in areas with a low flow rate, such as heat exchangers and containers.

Corrosion is influenced by a number of factors, such as dissolved gases in the liquid, for example oxygen and carbon dioxide, too low a pH-value and alkalinity.

The use of different metals as the material in a plant, such as copper and steel, causes galvanic corrosion, increasing substantially at low pH-values. Corroding steel is converted into decomposed iron and carbon. Carbon is a very good insulator when deposited on walls and, in addition, causes abrasion in movable parts like pumps and valves.

When replenishing water is heated, oxygen separates and reacts with decomposed iron (bivalent), forming rust (trivalent). Rust precipitates from the water in areas of a relatively small water flow rate. When the oxygen reacts with other substances, the pH-value of the water falls further, leading to increased corrosion.

Impure water has a higher viscosity than pure water. The use of impure water thus results in a reduced flow rate in the plant.

To prevent corrosion in a plant of the kind in question, the relationship between pH-value and alkalinity has proved to be important. In the Baylis equilibrium curve, see graph 1, the area above the curve "A" represents values, in which the formation of a calcium carbonate coating can be expected, the curve "B" indicates carbon equilibrium, whereas the area below the curve "C" indicates that corrosion will occur.

Graph 1, Baylis equilibrium curve 10

pH-value

0 50 100 150 200 250 300 350

Due to the conditions mentioned above, the use of purifying and treating plants in installations where water/liquid is used as an energy carrier, is increasing.

According to the prior art, for example Norwegian patent 303968, a partial flow of the circulation water, for example 10 %, is pumped through a purifying/treating device. The water to be cleaned, is pumped in at the top of a closed container containing several layers of different materials, through which the water is flowing down, then returning to the plant.

Typically, a tank of the kind mentioned contains a filter layer of granulated filter material at the top. Below the_. filter material is disposed a layer of granulated magnesium oxide and calcium carbonate, under which is disposed filter sand. and, at the bottom, a layer of glass balls.

When the water flows down through the filter material, free particles, if any, will bind to the filter material. The cleaned water flows through the layers of granulated magnesium oxide and calcium carbonate, in which the pH-value and alkalinity of the water are affected in such a manner, that the corrosiveness of the water is reduced. The filter sand is arranged to prevent the rest of the content within the tank, apart from the cleaned water, from sinking into the glass ball layer on the bottom of the tank. The glass balls are arranged to form an insulating layer, in which a zinc ■ electrode is disposed, insulated from the container. The zinc electrode is connected through an ammeter to the container material. The ammeter shows an amperage between the electrode and the container material, which varies depending on the pH- value of the water. When, after some time in operation, the container is to be cleaned, the flow lines to the plant are shut off, and liquid flows from below up through the layers, after which the liquid flows to a drain. In order to achieve satisfactory cleaning, it is necessary for the flow rate of the water through the container to be high enough to whirl up the layered materials of the container. Due to different specific weights, the layers will settle back into their correct relative positions within the container. However, practice has shown that, after cleaning, the desired separation of materials does not always occur to the degree desired.

The liquid flow down through the material layers has turned out to compress the materials in such a way that there is an increased pressure fall through the container. The compression of the material layers causes formation of flow channels, through which the liquid will flow, not having the desired surface of contact with the material layers. It has also proved difficult to maintain sufficient cleanliness in the glass ball layer, as fine material deposits on the balls. Such contamination interferes with the flow passage through the zinc electrode and results in the amperage of the ammeter not reflecting the pH-value of the water.

The invention has as its object to remedy the drawbacks of the prior art.

The object is realized, according to the invention, through the features specified in the description below and the following Claims.

It has proved convenient to separate the cleaning layer and the pH- and alkalinity controlling layers in two separate containers .

The liquid to be treated is first led down from the upper end portion of a first container into a granulated filter material and a sand filter layer below that, after which the liquid flows from the bottom of the first container to the bottom of a second container, where it flows up through layers consisting of granulated magnesium oxide and/or granulated calcium carbonate. At the upper portion of the second container the treated liquid flows past a zinc electrode, which is electrically insulated from the container. The zinc electrode is connected through an ammeter to the material of the container.

By the use of two discrete containers, the separated sludge and other contaminations may be flushed out of the filter material without any risk of the filter material and the other material layers becoming mixed up. It has also proved advantageous in normal operation to let the liquid flow upwards through the granulated magnesium oxide and calcium carbonate, whereby the layers maintain a relatively porous state compared to the conditions prevailing when the liquid is flowing downwards through said layers.

The method is highly suitable when it is relevant to circulate the liquid through materials with properties inhibiting bacterial growth.

In the method according to the invention it is unnecessary to use a layer of glass balls to keep the area at the zinc electrode clean.

In the following will be described a non-limiting example of a preferred method and embodiment which is visualized in the accompanying drawings, in which:

Fig. 1 shows schematically an energy plant comprising a purifying-Vtreating plant in operation;

Fig. 2 shows the plant of Fig. 1 during flushing of the first container; and

Fig. 3 shows the plant of Fig. 1 during flushing of the second container.

In the drawings the reference numeral 1 identifies a purifying-/treating plant connected to an energy plant 2, like for example a cooling-, drying- or heating-plant. The energy plant 2 is connected to a circulation pump 4 through pipes 6 and 8.

From the pipe 8, which is connected to the pressure side of s the circulation pump 4, a partial flow of liquid flows, in normal operation, through a pipe 10, a first shut-off valve 12 and a pipe 14 to the upper portion of a first container ' 16. In the drawings arrows indicate the flow direction of the liquid.

o Then, the liquid flows down at a relatively low rate through an upper filter layer 18 located in the first container 16 and then through a lower filter layer 20 to the bottom portion of the first container 16. From the bottom portion of the first container 16 the liquid flows through a pipe 22 to 5 the bottom portion of a second container 24. The second container is filled with at least one layer of a reaction material 26. The liquid flows through the reaction material 26 to the upper portion of the second container 24, from where it flows through a pipe 28, a flow control valve 30 and a second shut-off valve 32, a pipe 34 and the pipe 6 back to the suction side of the circulation pump 4.

The upper portions of the containers 16, 24 are connected to a three-way valve 36 through pipes 38 and 40, respectively. A pipe 42 connects the third passage of the three-way valve 36 to a drain 44.

A pipe 46, which may be connected to, for example, a water distribution system, not shown, carries clean flushing liquid through a third shut-off valve 48 to the pipe 22.

The filter material of the upper filter layer 18 of the container 16 may with advantage be formed by a granulated filter material, which may achieve, as the liquid flows down through the material, a removal of particles larger than 0,01 millimetres. To achieve adequate purification, the height of the upper filter layer 18 must be at least 0,4 metres. With a smaller filter layer height the ability of the filter to remove small particles is reduced, and so is the ability of the filter to accumulate sludge without increasing the pressure fall across the filter.

As the lower filter layer 20 of the first container 16 relatively fine sand is used with advantage. The task of the lower filter layer 20 is to prevent sludge from flowing together with liquid through the pipe 22 into the lower portion of the second container 26.

The reaction material 26 of the second container 24 comprises granulated magnesium oxide and/or calcium carbonate. A possible mixture must be adapted to the liquid quality. When the liquid flows relatively slowly up through the reaction material 26, part of the reaction material is dissolved in the liquid, favourably influencing the pH-value and alkalinity of the liquid with respect to corrosion.

A zinc electrode 50 is installed in an insulated manner in the upper portion of the second container 24. Through an ammeter 52 and wires 54 and 56 the zinc electrode is connected to the material of the second container 24. The amperage through the ammeter 52 reflects the pH-value of the liquid.

As the filter material 18, 20 of the first container 16 is being filled up with sludge, the flow resistance in the first container 16 increases. By counter-flow flushing through the filter material 18, 20, preferably with a sufficiently large quantity of liquid for the upper filter layer 18 and the lower filter layer 20 to be whirled up, the sludge present in the first container 16 is loosened, see Fig. 2.

The counter-flow flushing is carried out by closing the first shut-off valve 12 and the second shut-off valve 32, then opening of the three-way valve 36 to flow from the upper portion of the first container 16 through the pipes 38 and 42 to the drain 44. The third shut-off valve 48 is opened and' clean liquid flows from the pipe 46 through the third shut- off valve 48, the pipe 22, the first container 16, the pipe 38, the three-way valve 36 and the pipe 42 to the drain 44. The counter-flow flushing may be stopped when the exiting flushing liquid is clean. If desired, also the reaction material 26 may be flushed correspondingly in order for the granulated material to be loosened. The flushing is carried out as described above, but the three-way valve 36 is turned in such a way that it opens to liquid flow from the upper portion of the second container 24 through the pipes 40 and 42 to the drain 44 while closing, at the same time, the pipe 38, see Fig. 3. Thus, clean liquid flows from the pipe 46 through the third shut-off valve 48, the pipe 22, the second container 24, the pipe 40, the three- way valve 36 and the pipe 42 to the drain 44. The counter- flow flushing is stopped after a predetermined flushing time.

The method and device according to the invention allows a granulated filter material 18, 20, which is cleaned by means of counter-flow flushing, to be kept separated from the reaction material 26, whereby the direction of flow through the reaction material may be an upward one. By an upward flow, undue packing of the reaction material 26 is prevented, whereby the formation of channels with a subsequently reduced treating effect is essentially avoided.

The upward flow through the reaction material 26 permits installation of the zinc electrode 50 in the upper end portion of the second container 24, where it is exposed to sludge only to an insignificant degree.

Claims

C L A I M S

1. A method for the purification and treatment of liquid, wherein the liquid is purified by flowing through a filter material (18, 20), the filter material being arranged to be cleaned by means of counter-flow flushing, and wherein, with the aim of changing the pH- value and alkalinity of the liquid, the liquid flows through a reaction material (26) in the form of magnesium oxide and/or calcium carbonate, c h a r a c - teri z ed in that the liquid flows in a descending manner through the filter material, and flows in an ascending manner through the reaction material.

2. A device in purifying and treating equipment for a liquid, wherein the liquid is purified by flowing through a filter material (18, 20), the filter material being arranged to be cleaned by means of counter-flow flushing, and wherein, with the aim of changing the pH- value and alkalinity of the liquid, the liquid flows through a reaction material (26) in the form of magnesium oxide and/or calcium carbonate, c harac ter i z ed i n that a first container (16) containing the filter material (18, 20) is connected at its lower end portion through a pipe (22), in a communicating manner, to a second container (24) containing the reaction material (26).

3. A device according to claim 2, c haracteri z ed i n that the second container (24) is provided, at its upper end portion, with a zinc electrode (50) electrically insulated from the second container (24), the zinc electrode (50) being connected through an ammeter (52) and associated wires (54, 56) to the material of the second container (24).