CALCIUM HYDROXIDE FEEDING APPARATUS HAVING FILTER, THE CALCIUM HYDROXIDE FEEDING METHODS USING THE SAME AND THE WATER PURIFYING METHODS

THEREOF Technical Field

[1] The present invention relates to an apparatus for feeding calcium hydroxide (slaked lime), including filters, and methods for feeding calcium hydroxide and purifying water using the same. More particularly, the present invention relates to an apparatus for feeding calcium hydroxide, which can maintain raw water at suitable alkalinity to improve efficiency and stability for the coagulation and settlement of raw water, can maintain purified water at suitable alkalinity to fundamentally prevent the corrosion of pipes, caused by the presence of an excess of corrosive free carbonic acid, to reduce the amount of sludge, to prevent water wasting caused by water whitening, and to prevent a coloring phenomenon caused by an increase in acidity, can improve the taste of tap water to the spring water level, and allows effective prevention of the moisture penetration into calcium hydroxide and the corrosion of electrical facilities, as well as methods for feeding calcium hydroxide and purifying water using the same. Background Art

[2] In general, water purification methods for obtaining drinking water include co¬ agulation to a suspension, solid-liquid separation, coagulation to dissolved components, oxidation, biochemical modification, adsorption, ion exchange, co¬ agulation using bacterial or virus, filtration, disinfection and neutralization with acid or alkali. These methods are used for water treatment in a suitable combination depending on various requirements, such as the quality of raw water or the purpose of water pu¬ rification.

[3] FIGS. 1 and 2 show a flow chart illustrating a process for purifying water and treating discharge water according to the prior art, and a general water purification system according to the prior art, respectively. Water purification system 100 will now be schematically described with reference to FIGS. 1 and 2 for the convenience of de¬ scription.

[4] First, undrinkable raw water taken from water-supply sources, such as rivers or reservoirs, by pressure, flows into gauging well 10 via flowmeter 11.

[5] The gauging well 10 serves to stabilize water level fluctuation in receiving raw water supplied by pressure and to control the amount of raw water and also to evenly

distribute raw water to subsequent facilities, so that water purification operations, such as chemical feed, coagulation, settlement and filtration, can be performed in an exact and easy manner.

[6] Mixing basin 20 is a facility in which various chemicals required for water pu¬ rification are fed into raw water effluent from the gauging well 10 by chemical feeder 70 and rapidly mixed by mixer 21 to produce microflocs. Examples of the chemicals fed into the mixing basin include coagulants for effectively coagulating and removing various turbid materials, for example, inorganic compounds, such as aluminum-based compounds, such as polyaluminum chloride (PAC), polyaluminum hydroxide chloride silicate (PACS), polyaluminum silicate sulfate (PASS), polyaluminum chloride calcium (PACC) and poly organic aluminum magnesium sulfate (PSOM), iron-based compounds, such as ferrous sulfate (FeSO H O) and ferric chloride (FeCl H O), and

4 2 3 2 organic compounds, such as sodium alginate, and alkalifying agents for regulating alkalinity reduced by the use of said coagulants and maintaining pH at a suitable level to exhibit a sufficient coagulation effect. Examples of such alkalifying agents include calcium hydroxide (70% CaO) for service water, soda ash (99% Na 2CO ) for service water and caustic soda (45% and 20% NaOH solutions), and activated carbon powder for removing algae, synthetic detergents, phenols and other organic materials from raw water.

[7] The coagulants cause two effects; one effect is an original function to induce the unstabilization of particles, and another effect causes a decrease in pH by hydration. Thus, since an increase in the feed amount of the coagulants leads to a great decrease in pH, it is necessary to feed calcium hydroxide in water purification.

[8] General examples of the chemical feeder 70 include a coagulant feeder, an al¬ kalifying agent feeder, and activated carbon feeder, which can be placed separately or in combination. In FIG. 2, a chlorine feeder is separately designated as reference numeral 80.

[9] The example shown in FIG. 2 concerns a solid chemical feeder, in which solid chemicals transferred by conveyor 76 are passed by the chemical feeder 70 into introduced into chemical mixer 71. Above the conveyor 76, dust collector 77 is generally placed. Meanwhile, water from water supply source 74 is stored in water tank 73 by pump 75, and then, introduced into the chemical mixer 74 in which it is mixed with the fed chemicals. In FIG. 2, reference numeral 72 designates an agitator.

[10] Generally, the transfer of solid chemicals is performed by the use of a belt conveyor, cylinder or screw type, and the transfer of liquid chemicals is performed by the use of an orifice, rota meta, rotary deeper or diaphragm type.

[11] Coagulation basin (flocculation basin) 30 serves to coagulate the microfloc particles produced in the mixing basin by increases in volume and weight, so as to

allow a settlement effect in settlement basin to be enhanced. In the coagulation basin 30, a baffle is placed to prevent the occurrence of short-circuit flows or stagnant portions interfering with flocculation, and a plurality of flocculators 31 are placed to produce large and hard floes. The flocculators are operated at a different speed to increase the effect of decelerated coagulation so that floes can be transferred to settlement basin 40 in an unblocked state.

[12] The removal of sludge in the settlement basin 40 is made by a settlement device.

Generally, the settlement basin 140 is widely used in a horizontal flow type which has simple facilities and is easy to maintain and control and hydraulically stable.

[13] Filtration basin 50 is a facility of removing suspended matters non-removed in pre- treatment processes, such as coagulation and settlement, by physical and chemical actions. For the filtration basin 50, rapid-speed, constant-pressure filtration (declining rate filtration) is widely used, and as filter medium 52, filtration sand (25 cm in thickness) and/or antracite (50 cm in thickness) are mainly used.

[14] Water purification basin 60 is a facility of storing purified water before water supply, and serves to secure a sufficient amount of purified water so as not to fail to supply water to service areas or houses.

[15] Meanwhile, the disinfection of raw water influent into a water purification plant and purified water effluent from the water purification plant is performed by the feed of water having chlorine diluted therein.

[16] The prechlorination is used not only to prevent not only the growth of algae at the inlet section of the mixing basin 20 but also to inhibit the growth of microorganisms interfering with coagulation and flocculation, so as to prevent slime or clay from adhering to the filter medium and to prevent anaerobic bacteria from proliferating in the filter medium. On the other hand, the postchlorination is performed in the water pu¬ rification basin 60 and serves to disinfect microorganisms which have not been removed in the prechlorination process.

[17] Referring to FIG. 2, chlorine stored in chlorine tank 83 is transferred into chlorine feeder 80, and mixed with water fed from water supply source 74, and then, is fed by ejector 81. Generally, the prechlorination is performed at the inlet section of the rapid mixing basin 20, the addition of chlorine during water purification is performed at the outlet section of the settlement basin 40 in order to maximize the effect of chlorination, and the postchlorination is performed at the water purification basin 60.

[18] Above the chlorine feeder 80, the ejector 81 and the chlorine tank 83, ducts 85 are placed to capture evaporated harmful chlorine gas which is neutralized by neutralizer 84 and then discharged into the atmosphere.

[19] In FIG. 2, reference numeral 61 designates a water level meter, reference numeral

62 designates a meter for measuring remaining chlorine, and reference numeral 82

designates an evaporator.

[20] Meanwhile, control panel 90 serves to control the feed amount and time of coagulants, alkalifying agents and chlorine as described above, so that the entire water purification process can be effectively progressed.

[21] A system for treating discharge water will now be described in brief with reference to FIG. 1 again. As shown in FIG. 1, the discharge water- treating system comprises: first and second concentration tanks 110 and 111 for concentrating sludge settled from the settlement basin 40; sludge storage tank 120 for storing the concentrated sludge supplied from the concentration tanks; and dewatering unit 130 for dewatering the sludge transferred from the sludge storage tank to form a sludge cake with reduced volume, which makes the final disposal and transport of the sludge easy. The sludge caked by dewatering is incinerated in incineration plant 140 or buried in landfill 150.

[22] However, in an apparatus and method for feeding chemicals, particularly al¬ kalifying agents, into the prior general water purification system as described above, moisture from a dissolution tank easily penetrates into a portion of a quantitative feed unit of calcium hydroxide because calcium hydroxide is highly hygroscopic. Thus, calcium hydroxide is changed into calcium carbonate by the following equation: Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O. As a result, the effective content of calcium hydroxide is reduced and the moisture content in calcium hydroxide is increased so that calcium hydroxide is solidified into a mass insoluble in water, to become a non- usable state, which causes damage to a rotary feeder, a screw, a blade and a conveyor belt.

[23] For this reason, a method of feeding calcium hydroxide in a liquid form was considered in the prior art, but this method has, in addition to the above-described problems, a problem in that it is actually significantly difficult to quantitatively feed calcium hydroxide because calcium hydroxide has a very low solubility of about 1.02%. Particularly, a method of feeding calcium hydroxide in a powder form by a hopper has problems in that it is inconvenient to treat dust, and it is very difficult to quantitatively feed calcium hydroxide due to the above-described problem, and thus, a possibility for calcium hydroxide to be excessively fed exists, in which case not only the whitening of the settlement basin can be caused but also the generation of sludge can be increased, leading to an increase in cost for sludge disposal. In addition, the excessive feed of calcium hydroxide can cause not only an increase in acidity, resulting in the early abrasion and damage of various facilities, including pipe lines, but also coloring phenomena (green water for iron, hazy water for zinc, and blue water for copper).

[24] In a prior attempt to solve the above-described problems, a method of using NaOH

(40% or 20%) for the purpose of simply increasing an OH component was proposed in

order to obtain a good coagulation reaction effect by effectively maintaining the hydration reaction rate of coagulants. However, since alkalinity is fundamentally obtained by the use of the OH ^" of divalent cationic metals, this method is a feed method unsuitable in principle, which was proposed particularly because the solubility of Ca(OH) is very low. This method has a serious problem in that an increase in Na ⁺ ion in purified water leads to an increase in a possibility to induce hypertension in people who drink it. In addition, this method has a problem in that NaOH is an expensive and toxic substance.

[25] Also, Langelier Index represented by the following equation has negative value showing corrosive properties in almost all water purification plants located in the population concentrated areas or industrialized areas of countries which adopt a rapid filtration method:

[26] LI = Water pH value-pHs

[27] (wherein pHs= 8.313-log{Ca ⁺⁺ }-log[A]-S)

[28] In the above equation, LI almost has negative value, because the pHs is greater than 7.5 in most water systems excluding clean areas, and most of raw water has a pH lower than 7.5 except for when algae propagates.

[29] Despite this fact, interests in water purification have been concentrated only on a reduction in turbidity, but not on an increase in alkalinity.

[30] Meanwhile, in water purification plants, there are various electric panels for operating and controlling the plants and storage chambers for various chemicals stored for water purification, but these electric panels or chemical storage chambers are not completely sealed from the external environment, so that these water purification plants have the above-described problems resulting from the conversion of calcium hydroxide into calcium carbonate by moisture (i.e., calcium hydroxide becomes insoluble in water by solidification), as well as a problem in that the electric panels tend to be corroded by a large amount of chlorine gas generated in a chlorine dis¬ infection process. The problem of a reduction in the ability for the quantitative feed of chemicals and the problems of the frequent trouble and life cycle reduction of electrical equipment result in a reduction of water purification efficiency of water pu¬ rification plants and an increase in operation costs.

[31] In the prior art, in order to prevent the occurrence of corrosion and the reduction of chemical titer, caused by harmful chlorine gas or moisture in the electric panels or the chemical storage chambers, there is a case where a separate corrosion prevention apparatus is disposed in water purification plants. However, this corrosion prevention apparatus is mostly expensive and still has limitations in terms of cost and efficiency.

[32] In view of the above-described problems occurring in the prior art, there has been a need for the development of an apparatus and method for feeding calcium hydroxide,

which can improve the taste of tap water, allows the effective quantitative feed of calcium hydroxide so as to avoid waste of water caused by the feed of an excess of calcium hydroxide, can prevent an increase in sludge and the whitening of a settlement basin and the downstream thereof, allows the downstream of a chemical feed chamber of a water purification plant to be maintained at a weakly acidic condition so as to prevent the abrasion and damage of metal and concrete facilities, and allows effective prevention of the moisture penetration into calcium hydroxide and the corrosion of electric facilities, as well as a method for purifying water using the same. Disclosure of Invention Technical Problem

[33] Therefore, it is a first object of the present invention to provide an apparatus for feeding calcium hydroxide, which can be used in a continuous process, allows the quantitative injection of calcium hydroxide so as to maintain raw water at suitable alkalinity, thus effectively increasing efficiency and stability for the coagulation and settlement of raw water, and can maintain purified water at suitable alkalinity so as to make a remarkable contribution in preventing the corrosion of pipes and concrete structures caused by corrosive free carbonic acid and in improving the taste of tap water to the spring water level, and is applicable as a calcium hydroxide feed facility in the chemical feed chamber of a water purification plant or as an auxiliary facility in a water purification system in high-rise buildings or apartment areas.

[34] A second object of the present invention is to provide an apparatus for feeding calcium hydroxide, which, in addition to showing the effects described for the first object, can fundamentally prevent the penetration of harmful chlorine gas or moisture into a calcium hydroxide feed chamber or storage chamber having panels including various electric facilities so as to effectively prevent the corrosion of electric facilities and the titer reduction and solidification of calcium hydroxide in the calcium hydroxide feed chamber or storage chamber.

[35] A third object of the present invention is to provide a method for feeding calcium hydroxide, which can be used in a continuous process, allows the quantitative injection of calcium hydroxide so as to maintain raw water at suitable alkalinity, thus effectively increasing efficiency and stability for the coagulation and settlement of raw water, and can maintain purified water at suitable alkalinity so as to make a remarkable con¬ tribution in preventing the corrosion of pipes and concrete structures caused by corrosive free carbonic acid and in improving the taste of tap water to the spring water level, allows an increase in the solubility of calcium hydroxide, and is applicable for water purification in water purification plants, high-rise buildings or apartment areas.

[36] A fourth object of the present invention is to provide a method for feeding calcium

hydroxide, which, in addition showing the effects described for the third object, can fundamentally prevent the penetration of harmful chlorine gas or moisture into a calcium hydroxide feed chamber or storage chamber having panels including various electric facilities so as to effectively prevent the corrosion of electric facilities and the titer reduction and solidification of calcium hydroxide in the calcium hydroxide feed chamber or storage chamber.

[37] A fifth object of the present invention is to provide an effective method for purifying water, which includes the calcium hydroxide feeding method according to the third and fourth objects, which use the calcium hydroxide feed apparatus according to the first and second objects. Technical Solution

[38] In a preferred embodiment for achieving the first object, the present invention provides an apparatus for feeding calcium hydroxide, comprising a calcium hydroxide agitation tank including: a body; a baffle dividing the region excluding the lower portion of the body into two compartments; a speed-reducing motor placed above the body, a rotating axis extending from the motor, and impellers fixed to the lower end of the rotating axis; a purified water feed pipe communicating with one side of the upper portion of the body and including a float valve; and a first filter placed in a region defined by the inner peripheral edge of the body at an opposite side to the purified water feed pipe and by the baffle, and a second filter formed above the first filter; in which the first filter is a sieve filter for the filtration of calcium hydroxide sludge or slurry, the second filter is a microfilter, a nanofilter or a combination thereof, and the level of the second filter is lower than the level of the purified water feed pipe.

[39] In another preferred embodiment for achieving the first object, the present invention provides an apparatus for feeding calcium hydroxide, comprising a calcium hydroxide agitation tank and a recrystallized material-filtering tank, the calcium hydroxide agitation tank including: a body; a baffle dividing the region excluding the lower portion of the body into two compartments; a speed-reducing motor placed above the body, a rotating axis extending from the motor, and impellers fixed to the lower end of the rotating axis; a purified water feed pipe communicating with one side of the upper portion of the body and equipped with a float valve; and a first filter placed in a region defined by the inner peripheral edge of the body at an opposite side to the purified water feed pipe and by the baffle, and a second filter formed above the first filter; the tank for filtering recrystallized materials comprising: a body; a baffle dividing the region excluding the lower portion of the body into two compartments; and a filter formed on the inner peripheral edge of the body; in which the level of the purified water feed pipe, the level of the second filter of the calcium hydroxide

agitation tank, and the level of the filter of the recrystallized material- filtering tank, are lowered stepwise, and a first filtration pipe is placed between the second filter of the calcium hydroxide agitation tank and the filter of the recrystallized material- filtering tank, and a second filter pipe is placed in the filter of the recrystallized material- filtering tank.

[40] In a preferred embodiment for achieving the second object, the present invention provides an apparatus for feeding calcium hydroxide, comprising, in addition to the elements of the calcium hydroxide feed apparatus according to the above embodiment, an air compressor for compressing a predetermined amount of air and supplying the compressed air at a predetermined pressure; a regulator placed at the outlet of the air compressor and serving to regulate the pressure of the compressed air to a higher pressure than the standard atmospheric pressure; and a supply pipe for supplying the compressed air from the regulator into a closed calcium hydroxide feed chamber or storage chamber so as to maintain the pressure within the calcium hydroxide feed chamber or storage chamber higher than atmospheric pressure.

[41] According to a preferred embodiment for achieving the third object, the present invention provides a method for feeding calcium hydroxide comprising: (a) a step of agitating calcium hydroxide-containing water, in which purified water is introduced to which calcium hydroxide is then added, and the calcium hydroxide-containing water is subjected to physical agitation; (b) a step of adding inert salt, in which inert salt selected from hydroxides of divalent cationic metals, such as sodium chloride, Mg(OH) , Sr(OH) and Fe(OH) , is added to the calcium hydroxide-containing water at a weight ratio of calcium hydroxide : inert salt of 1: 0.001-0.1, and the inert salt- containing mixture is agitated, so as to increase the solubility of the calcium hydroxide from 1.02% up to 1.5% by an inert salt solution effect; (c) a first filtration step in which sludge or slurry caused by the calcium hydroxide is removed by a first filter through upward flow; (d) a second filtration step of performing filtration by a second filter; (e) a step of addition to raw water in which the resulting water containing the calcium hydroxide completely dissolved therein is quantitatively added to raw water.

[42] According to another preferred embodiment for achieving the third object, the present invention provides a method for feeding calcium hydroxide, further comprising, after the step (d) of the above embodiment, the step (dl) of filtering re¬ crystallized materials by a filter.

[43] According to a preferred embodiment for achieving the fourth object, the present invention provides a method for feeding calcium hydroxide, comprising, before the step (a) of the above embodiment, the steps of: (al) injecting compressed air from an air compressor by a supply pipe into the ventilation passage of a calcium hydroxide feed chamber or storage chamber sealed airtight from the external environment except

for the ventilation passage; and (a2) maintaining the pressure within the calcium hydroxide feed chamber or storage chamber higher than the standard atmospheric pressure by means of a regulator placed at the outlet side of the air compressor.

[44] According to a preferred embodiment for achieving the fifth object, the present invention provides a method for purifying water, comprising mixing, coagulation, settlement and filtration steps, in which, at the mixing step, calcium hydroxide is quan¬ titatively fed according to the embodiment for achieving the second object.

[45]

Brief Description of the Drawings

[46] FIG. 1 is a flow chart illustrating a general process for purifying water and treating discharge water according to the prior art.

[47] FIG. 2 shows a system for purifying water according to the prior art.

[48] FIG. 3 is a schematic diagram showing an apparatus for feeding calcium hydroxide according to a preferred embodiment of the present invention.

[49] FIGS. 4 and 5 are longitudinal cross-sectional and top views showing the basic structure of a calcium hydroxide agitation tank, respectively, which can be preferably used in the calcium hydroxide feed apparatus shown in FIG. 3.

[50] FIG. 6 shows the schematic structure of a device for preventing the solidification of calcium hydroxide, which can be preferably used in the calcium hydroxide feed apparatus shown in FIG. 3.

[51] FIG. 7 is a flow chart illustrating a process for preventing the solidification of calcium hydroxide using the calcium hydroxide solidification-preventing device shown in FIG. 6.

[52]

Best Mode for Carrying Out the Invention

[53] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[54] FIG. 3 is a schematic diagram showing calcium hydroxide feed apparatus 1 according to a preferred embodiment of the present invention, and FIGS. 4 and 5 are longitudinal cross-sectional and top views showing the basic structure of calcium hydroxide agitation tank Ia, respectively, which can be preferably used in the calcium hydroxide feed apparatus 1 shown in FIG. 3. For the convenience of description, the basic structure of the calcium hydroxide agitation tank Ia shown in FIGS. 4 and 5 will first be described. The basic structure of the agitation tank Ia is substantially the same as the structure of recystallized material-filtering tank Ib except for an agitation device.

[55] As shown in a longitudinal cross-sectional view of FIG. 4, the basic structure of the

calcium hydroxide agitation tank Ia comprises cylindrical body 2, and baffle 3 dividing the region excluding the lower portion of the body 2 into two semi-cylindrical compartments. Above the body, speed-reducing motor 181 is placed, and to the lower end of rotating axis 4 extending from the speed-reducing motor 181, impellers 4a are fixed.

[56] The rotating axis 4 is received within the baffle 3, and the impellers 4a are placed below opening 3b at the lower end of the baffle.

[57] In the present invention, the number and shape of the impellers 4a are optional and not limited.

[58] From the top view of FIG. 5, the concrete shape of the baffle 3 can be clearly understood. In the example shown in FIG. 5, the baffle 3 consists of two walls which converge to each other at a portion making a contact with the body and diverge from each other at a central portion receiving the rotating axis 4. However, as long as the rotating axis can be received in the central portion of the double baffle, the shape of the double wall is not optional in the present invention and not limited to the shape shown in FIG. 5. For example, the double baffle may consist of two walls parallel to each other, or may have a hollow pipe at the central portion thereof and single walls placed on both sides of the hollow pipe, or may have other optional shapes.

[59] Turning to FIG. 3 again, the calcium hydroxide feed apparatus 1 according to a preferred embodiment of the present invention will now be described.

[60] As shown in FIG. 3, the calcium hydroxide feed apparatus comprises the calcium hydroxide agitation tank Ia and the recrystallized material-filtering tank Ib. However, the recrystallized material-filtering tank Ib is optional in the present invention, and the present invention may also consist of only the calcium hydroxide agitation tank Ia.

[61] The basic structure of the calcium hydroxide agitation tank Ia comprises: body 2

(it has a cylindrical shape in the example shown in FIG. 3, but its shape is optional in the present invention); baffle 3 having a cavity and dividing the region excluding the lower portion of the body 2 into two compartments; speed-reducing motor 181 placed above the body, rotating axis 4 extending from the motor, and impellers 4a fixed to the lower end of the rotating axis; purified water feed pipe 7 communicating with one side of the upper portion of the body; and first filter 5 horizontally placed in a region defined by the inner peripheral edge of the body 2 at an opposite side to the purified water feed pipe 7 and by the baffle 3, and second filter 6 vertically placed above the first filter 5.

[62] The first filter 5 is disposed at an optional location (preferably, a middle portion or a lower portion) of a compartment other than a compartment having the purified water feed pipe located therein, among the two compartments divided by the baffle 3. The first filter 5 serves to prevent the migration of sludge or slurry resulting from the feed

of calcium hydroxide and may be various kinds of filters suitable to achieve this purpose. However, from a point of view of durability and maintenance, it is preferable that the first filter should be a disc- or box-shaped sieve filter, particularly a sieve filter made of metal.

[63] The second filter 6 is vertically disposed above the first filter 5 but slightly below the location of the purified water feed pipe. The second filter 6 is made of a microfilter and/or a nanofilter. Descriptions for the first and second filters will be omitted because these filters are known in themselves and commercially available.

[64] Meanwhile, at the upper portion of the body 2, calcium oxide or calcium hydroxide inlet 8 is formed, and at the lower portion of the body 2, drain 9 may be formed. Also, under the body 2, base may be placed.

[65] Furthermore, in the opening of the purified water feed pipe 7, float valve 7a may be disposed to allow the use of a continuous process.

[66] Accordingly, mixture 200 of purified water introduced from the purified water feed pipe 7 by the operation of the float valve 7 a and calcium hydroxide is thoroughly agitated by the rotation of impellers 4a, and then, calcium hydroxide sludge or slurry cannot move upwardly due to the first filter 5, and only water containing calcium hydroxide completely dissolved therein is filtered through the second filter 6 and discharged through first filtration pipe 171.

[67] It is preferable in view of filtration efficiency that the first filtration pipe 171 should have a cross-sectional area gradually decreasing from one end making a close contact with the second filter 6 to the other end.

[68] Meanwhile, the basic structure of the recrystallized material-filtering tank Ib comprises: body 2a (it has a cylindrical shape in the example shown in FIG. 3 but its shape is optional in the present invention); baffle 3a dividing the region excluding the lower portion of the body 2a into two compartments; first filtration pipe 171 com¬ municating with one side of the upper portion of the body 2a; and second filter 6a formed on the inner peripheral edge of the body 2a at an opposite side to the first filtration pipe 171.

[69] In the recrystallized material-filtering tank Ib, the above-described agitation means may, if necessary, be disposed which consists of speed-reducing motor 181, rotating axis 4 extending from the motor and impellers 4a fixed to the lower end of the rotating axis.

[70] In a region defined by the inner peripheral edge of the body 2a at an opposite side to the first filtration pipe 171 and by the baffle 3a, first filter 5a may be horizontally placed below the second filter 6a, but it is optional in the present invention.

[71] Meanwhile, it is preferable that the level of the second filter 6a be slightly lower than the level of the first filtration pipe 171 but higher than the first filter 5 a.

[72] The second filter 6a communicates with the second filtration tube 172 whose shape is similar to the first filtration pipe 171. One end of the second filtration tube 172 com¬ municates with water storage tank 160.

[73] The materials of the first filter 5a and the second filter 6a are the same as described above, and thus, their repeated description will be omitted.

[74] In a position to which the first filtration pipe 117 is communicated, a float valve may be placed, if necessary.

[75] The recrystallized material-filtering tank Ib serves to remove calcium hydroxide fine particles, sludge or slurry which can occur by recrystallization. As described above, the recrystallized material-filtering tank Ib may have drain 9b formed at the lower portion thereof and be located on base 182a.

[76] In the example shown in FIG. 3, the calcium hydroxide-containing water in the upper portion of the left side of the recrystallized material-filtering tank Ib may be in the state where calcium hydroxide is completely dissolved in water.

[77] The schematic structure of calcium hydroxide solidification-preventing device 300, which can optionally included in the calcium hydroxide feed apparatus of the present invention, will now be described with reference to FIG. 6. The calcium hydroxide so¬ lidification-preventing device 300 is disposed in the calcium hydroxide feed chamber or storage chamber 306, but is not limited thereto. Namely, the calcium hydroxide so¬ lidification-preventing device 300 may be included in all industrial facilities or ap¬ paratuses in need of the prevention of corrosion or titre reduction, for example, panels including electric facilities, and storage chambers for various chemicals, such as a chlorine feed chamber.

[78] As shown in FIG. 6, the calcium hydroxide solidification-preventing device 300 according to the present invention comprises: air compressor 301 for compressing a given amount of air and supplying the compressed air at a given pressure; regulator 303 disposed in the outlet side of the air compressor and serving to regulate the pressure of the compressed air to a higher pressure than the standard atmospheric pressure; and supply pipe 305 for supplying the compressed air from the regulator 303 into storage chamber 306.

[79] The air compressor 301 serves to compress and store air in a given space by the rotation of impellers or rotors or the reciprocation of a piston while discharging air as needed. The air compressor 301 includes an air tank (not shown) capable of storing compressed air, a compression pump (not shown) placed above the air tank, and a motor (not shown) at an opposite side to the compression pump. However, in the present invention, the kind of the air compressor 301 is not limited, and any air compressor may be used if it may compress a given amount of air and supply the compressed air at a given pressure.

[80] Also, the regulator 303 serves to increase/regulate the pressure of air compressed in the air compressor to a higher pressure than the standard atmospheric pressure and inject the compressed air by supply pipe 305 into the ventilation passage 304 of the storage chamber 306 maintained at the standard atmospheric pressure. As used herein, the standard atmospheric pressure (1 atm) designates an atmospheric pressure cor¬ responding to a mercury column height of 760 mmHg, and is expressed as 1 atm, 760 torr, 760 mmHg, 10,332 mmH O, 1.0332 kg/cm ² , 1.013 bar, 1013 mbar and the like. In the present invention, the pressure within the calcium hydroxide feed chamber or storage chamber 306 may be higher than 1 atm, and preferably slightly higher (about 1 mbar) than 1 atm in view of an increase in efficiency.

[81] If the pressure within the calcium hydroxide feed chamber or storage chamber 306 is slightly higher than atmospheric pressure as described above, chlorine gas or moisture from the external environment can be fundamentally prevented from penetrating into the calcium hydroxide feed chamber or storage chamber 306. Thus, it is possible to prevent the corrosion of electric facilities within the calcium hydroxide feed chamber or storage chamber 306, or the solidification of calcium hydroxide by moisture, which leads to a difficulty in the quantitative feed of calcium hydroxide or causes damage to facilities.

[82] In addition, to effectively prevent the solidification of calcium hydroxide and the corrosion of electric facilities, the calcium hydroxide feed chamber or storage chamber 306 is preferably sealed with, for example, silicone, before the calcium hydroxide so¬ lidification-preventing device is placed in the chamber 306.

[83] Furthermore, at the outlet of the air compressor 301, air filter 302 is placed to filter harmful gas, dust and moisture in air, so that more effective prevention of titre reduction and corrosion is made. Examples of the air filter which can be used in the present invention include, but are not limited to, a network filter using a louver or a grill, a pretreatment filter, a medium filter, an HEPA filter, an Ulpa filter and a carbon filter.

[84] The inventive method for feeding calcium hydroxide using the inventive calcium hydroxide feed apparatus 1 having the filters will now be described. The inventive method comprises the following steps:

[85] (a) A step of agitating calcium hydroxide-containing water:

[86] Purified water is introduced to which calcium hydroxide is added. The calcium hydroxide-containing water is subjected to physical agitation.

[87] (b) A step of adding inert salt:

[88] In order to increase the solubility of calcium hydroxide from about 1.02% up to about 1.5% by an inert salt solution effect, inert salt is added to the calcium hydroxide- containing water at a weight ratio of calcium hydroxide: inert salt of 1:0.001-1, and the

mixture is agitated.

[89] Preferred examples of the inert salt include hydroxides of divalent cationic metals, such as sodium chloride, Mg(OH) , Sr(OH) , and Fe(OH) .

[90] (c) A first filtration step:

[91] Sludge or slurry caused by calcium hydroxide is removed by a first filter through upward flow.

[92] (d) A second filtration step:

[93] More precise filtration is performed by a second filter.

[94] (e) A step of addition into raw water:

[95] The resulting water containing calcium hydroxide completely dissolved therein is quantitatively added to raw water.

[96] Also, the calcium hydroxide feed method according to the present invention may additionally comprise, after step (d), the following steps:

[97] (dl) A first filtration step for recrystallized materials:

[98] Subsequently to the above-described second filtration step, recrystallized materials may be filtered by the first filter through upward flow.

[99] (d2) A second filtration step for recrystallized materials:

[100] Subsequently to the first filtration step for recrystallized materials or to the second filtration step, a second filtration step for recrystallized materials may be performed.

[101] A process for preventing the solidification of calcium hydroxide using the calcium hydroxide solidification-preventing device shown in FIG. 6 will now be described with reference to a flow chart of FIG. 7 together with FIG. 6. As shown in FIG. 7, the process comprises the steps of: (SlO) removing the ventilation device of the calcium hydroxide feed chamber or storage chamber 306; (S20) cleaning the ventilation passage of the calcium hydroxide feed chamber or storage chamber 306; (S30) sealing the inside of the calcium hydroxide feed chamber or storage chamber 306; (S40) placing the calcium hydroxide solidification-preventing device; and (S50) injecting air having increased pressure.

[102] In the step (SlO) of removing the ventilation device of the calcium hydroxide feed chamber or storage chamber 306, the ventilation device (e.g., a fan) of the calcium hydroxide feed chamber or storage chamber 306 having panels including electric facilities is removed or shielding facilities are disposed.

[103] In the step (S20) of cleaning the ventilation passage of the calcium hydroxide feed chamber or storage chamber 306, after the ventilation device (not shown) is removed, the ventilation passage 304 is cleaned with a cleaning tool to remove dust.

[104] In the step (S30) of sealing the inside of the calcium hydroxide feed chamber or storage chamber 306, the calcium hydroxide feed chamber or storage chamber 306 is tightly sealed from the external environment except for the ventilation passage 304.

Namely, in the case of a panel including electric facilities, various sites of the panel are sealed with a sealant, such as silicone, such that the external air cannot be introduced into the panel.

[105] In the step (S40) of placing the calcium hydroxide solidification-preventing device, one end of the supply pipe 305 is connected to the outlet of the air compressor 301, and the other end is air-tightly connected to the ventilation passage 304 from which the ventilation device has been removed. As the supply pipe 305, a stainless pipe (e.g., 316L) is preferably used, but a pipe of any kind or material may be used in the present invention without limitations if it fits the size of the ventilation passage so that it can be maintained airtight.

[106] As described above, by removing the ventilation device previously placed in the calcium hydroxide feed chamber or storage chamber 306 and connecting the supply pipe to the chamber to form the ventilation passage 304, an advantage is provided in that a passage for the connection of the supply pipe 305 does not need to be separately formed. However, in the case where the calcium hydroxide feed chamber or storage chamber has no separate ventilation device, a separate connection passage may also be formed which is connected to the supply pipe 305 for providing a higher air pressure than atmospheric pressure.

[107] In the step (S50) of injecting air having increased pressure, after the calcium hydroxide solidification-preventing mean 300 is placed in the calcium hydroxide feed chamber or storage chamber 306, the regulator 303 operates to regulate the air pressure to a slightly higher pressure than the standard atmospheric pressure. The air with increased pressure is injected into the calcium hydroxide feed chamber or storage chamber 306 through the supply pipe 305 so that the pressure within the calcium hydroxide feed chamber or storage chamber 306 maintained airtight is maintained at a slightly higher pressure than the standard atmospheric pressure. Thus, the penetration of external harmful chlorine gas or moisture into the chamber 306 is fundamentally inhibited so that the corrosion of electric facilities or the coagulation of calcium hydroxide in the calcium hydroxide feed chamber or storage chamber 306 can be prevented from occurring.

[108] It will be understood that the air filter 302 can be replaced at a regular interval

(e.g., one time every year), and water accumulated within the air compressor 301 needs to be drawn out at a regular interval (e.g., one time every year). In the present invention, however, the intervals of replacement of the air filter and water drainage from the air compressor are not limited and may vary depending on the kind of air filter and air compressor.

[109] The inventive method for feeding calcium hydroxide using the calcium hydroxide feed apparatus 1 including the calcium hydroxide solidification-preventing device 300

is essentially the same as the above-described method, except that, prior to the step (a), the following steps are performed: (al) injecting compressed air from the air compressor via the supply pipe into the ventilation passage of the calcium hydroxide feed chamber or storage chamber sealed airtight except for the ventilation passage; and (a2) maintaining the pressure within the calcium hydroxide feed chamber or storage chamber higher than the standard atmospheric pressure by means of the regulator placed at the outlet side of the air compressor. Thus, further description for this method will be omitted.

[110] Finally, the inventive water purification method comprising the method for feeding calcium hydroxide using the calcium hydroxide feed apparatus having filters will now be described in brief. By the above-described calcium hydroxide feed method according to the present invention, calcium hydroxide and a coagulant are added to raw water, and the additive-containing water is coagulated and the resulting floes are settled and filtered.

[I l l] The present invention as described above may be effectively applied in the chemical feed chambers of water purification plants, but is not limited only to the ap¬ plication in these chambers. It will be understood that the present invention can be ef¬ fectively applied as auxiliary equipment in places in need of middle- or large-scale water purification equipment, such as high-rise buildings, apartment areas or schools.

[112]

Industrial Applicability

[113] As can be seen from the foregoing, according to the inventive calcium hydroxide feed apparatus and the inventive methods for feeding calcium hydroxide and purifying water the same, calcium hydroxide can be quantitatively fed to raw water, such that the raw water can be maintained at suitable alkalinity, thus effectively increasing efficiency and stability for the coagulation and settlement of the raw water. Also, water wasting caused by the addition of an excess of calcium hydroxide can be avoided, and an increase in sludge and the whitening of a settlement basin and the downstream thereof can be prevented. Also, purified water can be maintained at suitable alkalinity, so that the corrosion of metal pipes and concrete structures, caused by corrosive free carbonic acid, can be prevented, and at the same time, the taste of tap water can be improved to be similar to spring water. In addition, by maintaining the pressure within the calcium hydroxide feed chamber or storage chamber slightly higher than at¬ mospheric pressure, the corrosion of electric facilities or the solidification of calcium hydroxide in the calcium hydroxide feed chamber or storage chamber can be prevented from occurring by the penetration of external harmful chlorine gas or moisture into the chamber.

[114] Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

[115]