WO2002031428A1

WO2002031428A1 - Shell tube type filter and auto-controlled heat recovery system of waste water

Info

Publication number: WO2002031428A1
Application number: PCT/KR2000/001122
Authority: WO
Inventors: Ki Suk Kim
Original assignee: Ki Suk Kim
Priority date: 2000-10-09
Filing date: 2000-10-09
Publication date: 2002-04-18
Also published as: JP2004511332A

Abstract

The object of this invention is to provide an auto-controlled waste heat recovery system used for recovering heat from hot wastewater discharged from buildings or factories. The system of this invention uses shell tube-type filters (130, 430), having a plurality of tube-shaped micro-holes (131), and so the system is automatically controlled during a waste heat recovering process. The shell tube-type filters (130, 430), used in the system of this invention, are designed to be automatically washed by a flushing of pressurized wash water flowing in a reverse direction when necessary, and so filtered solids, such as hairs, waste threads and waste yarns, are easily and automatically removed from the filters (130, 430) by the flushing of waste water. Due to such automatically washable shell tube-type filters (130, 430), it is possible to automatically control the operation of the waste heat recovery system of this invention.

Description

SHELL TUBE TYPE FILTER AND AUTO-CONTROLLED HEAT RECOVERY

SYSTEM OF WASTE WATER

Technical Field

The present invention relates, in general, to waste heat recovery systems used for recovering heat from hot wastewater discharged from buildings or factories and, more particularly, to a shell tube-type filter, having a plurality of tube-shaped micro-holes, and an auto-controlled waste heat recovery system using such shell tube-type filters.

Background Art

As well known to those skilled in the art, buildings using a large quantity of hot water or hot steam every day, such as spas or factories, discharge hot wastewater laden with heat energy, and so a variety of waste heat recovery systems have been proposed and used for recovering and recycling heat from such hot wastewater and thereby conserving heat energy. However, such hot wastewater typically includes a variety of solids, such as a variety of floating materials, reducing the heat recovering capacity of the heat exchanger of a waste heat recovery system, and so it is necessary to remove such solids from wastewater using filters prior to feeding the filter-processed wastewater to the heat exchanger. During an operation of the waste heat recovery system, the filters are gradually deposited with solids thereon. It is thus necessary to remove the deposited solids from the filters through a repeated cleaning process. When such deposited solids are not removed from the filters periodically, the filters are finally blocked with the solids. In such a case, the filters may undesirably allow hot wastewater to directly flow to the heat exchanger without performing any filtering process of removing solids from the hot wastewater, or may block the water passage extending to the heat exchanger and prevent the hot wastewater from reaching the heat exchanger. This finally makes the waste heat recovery system unexpectedly stop its operation of recovering heat from the hot wastewater.

Net-type filters have been conventionally used in such waste heat recovery systems. Hot wastewater, discharged from residential buildings and large-scale buildings, such as spas, typically includes a large quantity of long and fine materials, such as hairs, waste threads, and waste yarns. When a conventional net-type filter is used for filtering such hot wastewater during a waste heat recovering process, the hairs, threads and yarns are easily caught and get tangled in the net structure of the filter, thus finally blocking the filter. It is thus necessary to remove such hairs, threads and yarns from the net-type filter periodically. However, it is almost impossible to automatically remove such hairs, threads and yarns from the net-type filter since the hairs, threads and yarns are tightly wound on, firmly caught by and tangled in the net structure of the filter. Therefore, the hairs, threads and yarns have to be manually removed from the filter one by one, otherwise the filter, blocked with such hairs, threads and yarns, has to be replaced with a new one while forcing the owner to pay money for the new filter.

Since the process of cleaning the net-type filters of conventional waste heat recovery systems for recovering heat from hot wastewater has been manually performed as described above, it is impossible to automate such waste heat recovery systems in the prior art.

In the conventional waste heat recovery system, scales are formed on the external surfaces of the heat transfer tubes of a heat exchanger by a variety of precipitated materials and/or chemicals included in the hot wastewater flowing outside the heat transfer tubes. Therefore, it is necessary to remove such scales from the external surfaces of the heat transfer tubes through a manual washing process. However, such a manually operated washing process cannot be precisely or effectively performed, and so the waste heat recovery system cannot be optimally operated. In order to recover heat from hot wastewater using the conventional waste heat recovery system, the hot wastewater has to freely flow around the heat transfer tubes of a heat exchanger. During such a flowing of the hot wastewater around the heat transfer tubes, heat of the hot wastewater is transferred to working water flowing in the heat transfer tubes and preheats the working water. The preheated working water is fed to a target device, such as a boiler. It is thus possible to conserve heat energy or fuel in the amount of recovered waste heat energy used for preheating the working fluid. However, since the conventional waste heat recovery system is designed to be manually operated, it is impossible to automatically operate the system, or to automatically measure the operational performance of the system, or to measure the amount of recovered waste heat in an operation of the system. Therefore, people do not want to purchase or install such conventional waste heat recovery systems in their buildings or factories. Even though a conventional waste heat recovery system is installed in a building, the system is not used at all, or is rarely used due to the above-mentioned defect of the system. This means that hot wastewater is discharged as sewage, and it is a mere waste of excessive amounts of heat energy. In an effort to effectively recover and use such waste heat, many governments, for example, the Korean government, in 1994, established a law that requires any person, wanting to construct a new building expected to discharge hot wastewater having a temperature not lower than 25°C, to install a waste heat recovery system in his building. However, such newly installed waste heat recovery systems fail to carry out desired operational functions in the same manner as that described above, and so the systems are not used, or are rarely used. Therefore, such newly installed systems merely increase the construction cost without effectively recovering heat from hot wastewater discharged from buildings. This finally results in a waste of money, a waste of energy and a waste of labor from a national point of view. The above-mentioned law now has become a mere scrap of paper.

Disclosure of the Invention

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a shell tube-type filter for waste heat recovery systems, which is designed to be automatically cleaned by a flushing of pressurized wash water flowing in a reverse direction when necessary, and so filtered solids, such as hairs, waste threads and waste yarns, are easily and automatically removed from the filter by the flushing of wash water. The present invention also provides an auto- controlled waste heat recovery system, which uses such shell tube-type filters, thus being automatically operated during a waste heat recovering process.

Brief Description of the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a circuit diagram, showing the construction and operation of an auto-controlled waste heat recovery system in accordance with the preferred embodiment of the present invention;

Figs. 2a and 2b are an exploded perspective view and a side sectional view of a first filter unit included in the auto-controlled waste heat recovery system of the present invention;

Fig. 3 is an exploded perspective view of an assembly, consisting of a vortex tank and a heat exchanger, included in the auto-controlled waste heat recovery system of the present invention; Fig. 4 is a side sectional view of the vortex tank of the present invention; and

Figs. 5a to 5c are a plan view, a side view and a bottom view of a wastewater swirl nozzle included in the auto-controlled waste heat recovery system of the present invention.

Best Mode for Carrying Out the Invention

Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.

Fig. 1 is a circuit diagram, showing the construction and operation of an auto-controlled waste heat recovery system in accordance with the preferred embodiment of the present invention. As shown in the drawing, the auto-controlled waste heat recovery system according to the present invention comprises a plurality of elements: a first filter unit 100, a second filter unit 400, a vortex tank 200, and a heat exchanger 300 that are connected together by a pipeline. A plurality of automatic control valves VI to V10, and DV are provided at the inlets and outlets of the elements: the filter units 100 and 400, the vortex tank 200, and the heat exchanger 300, for controlling the flow of hot wastewater, working water, and pressurized wash water in the system. The system also has a plurality of temperature sensors SI and S2, a flow meter S3, a pressure sensor S4. The system further comprises a control panel AT used for controlling the operation of the control valves, the temperature and pressure sensors, and the flow meter.

In an operation of the waste heat recovery system according to this invention, hot wastewater primarily flows into the first filter unit 100 so as to be primarily filtered. The primarily filtered wastewater is, thereafter, fed into the vortex tank 200, thus actively swirling within the tank 200 prior to being fed to the heat exchanger 300. Heat of the hot wastewater is transferred to low temperature working water flowing in the heat transfer tubes while the wastewater flows around the heat transfer tubes of the heat exchanger 300, thus heating the working water. The processed wastewater is. thereafter, discharged from the heat exchanger 300 to a drainage system or a sewage tank. In the system of this invention, the second filter unit 400 is connected to the vortex tank 200 through a connection pipe with a control valve V8. When the control valve V8 is opened, the swirling hot wastewater is fed from the vortex tank 200 to the second filter unit 400, thus being secondarily filtered by the filter unit 400. The secondarily filtered wastewater is, thereafter, returned from the filter unit 400 to the vortex tank 200 by a pump P.

In the operation of this system, the second filter unit 400 is periodically and intermittently operated. In such a case, the operational interval and operational time of the second filter unit 400 is preset in accordance with concentration of solids laden in the hot wastewater to be processed. That is, the second filter unit 400 is selectively used in the following cases. First, when the filtering process of the first filter unit 100 does not achieve a desired filtering effect, the primarily filtered wastewater is secondarily filtered by the second filter unit 400 prior to being returned to the vortex tank 200. Second, the second filter unit 400 is used for processing the wastewater when it is necessary to actively swirl the wastewater using a swirling nozzle 230 of the vortex tank 200 in order to finally prevent a depositing of precipitated materials of the wastewater onto the external surfaces of the heat transfer tubes of the heat exchanger 300 or to prevent the precipitated materials from blocking the passage of the wastewater.

The construction of the auto-controlled waste heat recovery system of this invention will be described in more detail herein below. Figs. 2a and 2b are an exploded perspective view and a side sectional view of the first filter unit 100.

As shown in Fig. 2a, the first filter unit 100 comprises a hollow cylindrical housing 110 with an open top, a top lid 120 covering the open top of the housing 110, and a shell tube-type filter 130 set within the housing 110. TWO upper spouts 111 and 112 outwardly extend in a radial direction from the sidewall of the housing 110 at opposite positions. Of the two upper spouts 111 and 112, the first one 111 provided at the upper position is used as a wastewater inlet spout, while the second one 112 provided at the lower position is used as a wastewater outlet spout, through which the primarily filtered hot wastewater is discharged from the filter unit 100 to the vortex tank 200. Two control valves VI and V2 are provided at the two spouts 111 and 112. The above control valves VI and V2 are automatically controlled during an operation of the system.

One lower spout 114 vertically extends downwardly from the center of the bottom wall of the housing 110. This lower spout 114 is used as a wash water inlet spout for introducing pressurized wash water into the first filter unit 100. The wash water inlet spout 114 is provided with a third control valve V3 for controlling the flow of wash water relative to the first filter unit 100. A sediment drain pipe 115 is branched from the wash water inlet spout 114, and is provided with a drain control valve DV for selectively draining sediments from the first filter unit 100 to a drain tank.

The top lid 120 covers the open top of the housing 110, with a wash water outlet spout 121 provided at the center of the top lid 120. The wash water outlet spout 121 is provided with a fourth control valve V4.

The shell tube-type filter 130 comprises a thick bed-shaped body with a predetermined thickness. This filter 130 also has a circular cross-section, and is sized to be closely fitted in the housing 110 of the first filter unit 100, and is vertically and densely perforated from its upper surface 13 OS to its lower surface 130B, thus having a plurality of shell tube-type vertical holes 131 with a small diameter circular cross-section. When hot wastewater is introduced into the filter 130 from the upper surface 130S, the wastewater flows down through the vertical holes 131 prior to being discharged from the lower surface 13 IB of the filter 130. When hot wastewater passes through the filter 130 as described above, a variety of solids, such as hairs, waste threads, waste yarns, and the other materials having a size larger than the diameter of the holes 131, in addition to precipitated impurities do not pass through the holes 131, but are removed from the wastewater and are deposited on the top surface 13 IS of the filter 130.

Particularly, different from conventional net-type filters, the shell tube- type filter 130 of this invention prevents long and fine impurities, such as hairs, waste threads and waste yarns, from getting tangled together even though they partially enter into the holes 131 during a wastewater filtering process. It is thus possible to easily remove filtered solids from the upper surface of the shell tube- type filter 130 through a flushing process and to use the filter 130 for a desired lengthy period of time.

That is, the shell tube-type filter 130 of this invention is automatically washed by a flushing of pressurized wash water flowing in a reverse direction when necessary, and so the waste heat recovery system using such shell tube-type filters of this invention is automatically operated.

During an operation of the waste heat recovery system of this invention, hot wastewater flows into the first filter unit 100 through the wastewater inlet spout 111, and passes through the shell tube-type filter 130, thus being primarily filtered. The primarily filtered wastewater is, thereafter, discharged from the first filter unit 100 through the wastewater outlet spout 112, and is fed into the vortex tank 200. When the first filter unit 100 is used for a lengthy period of time, the shell tube-type filter 130 is finally blocked with filtered solids at its holes 131, thus being reduced in its filtering function. In such a case, it is necessary to flush the filter 130 using pressurized wash water so as to remove the filtered solids from the filter 130. When it is desired to flush the filter 130, the first and second control valves VI and V2 of the wastewater inlet and outlet spouts 111 and 112 of the housing 110 are closed, while both the third control valve V3 of the wash water inlet spout 114 formed at the bottom wall of the housing 110 and the fourth control valve V4 of the wash water outlet spout 121 formed at the top lid 120 of the housing 110 are opened so as to introduce pressurized wash water into the housing 110. Therefore, the wash water flows in the reverse direction within the housing 110 of the first filter unit 100, and forcibly removes the filtered solids, such as hairs, threads, yams, solid materials and precipitated materials deposited on the upper surface 130S of the filter 130, prior to being discharged along with the solids from the housing 110 to a sediment tank (not shown) through the wash water outlet spout 121. During such a flushing process of washing the filter 130, it is possible to almost completely remove solids from the holes 131 of the filter 130.

Fig. 3 is an exploded perspective view of an assembly, consisting of the vortex tank 200 and the heat exchanger 300, included in the auto-controlled waste heat recovery system of this invention. Fig. 4 is a side sectional view of the vortex tank 200.

As shown in the drawings, the vortex tank 200 comprises a hollow cylindrical housing 210, which is opened at its upper and lower ends, and is provided with both a top lid 220 and a wastewater swirling nozzle 230. The housing 210 of the vortex tank 200 has the same diameter as that of the heat exchanger 300, and is concentrically mounted to the upper end of the heat exchanger 300. In such a case, the interior of the housing 210 of the vortex tank 200 communicates with the housing of the heat exchanger 300. The housing 210 of the vortex tank 200 is provided, at opposite positions of its sidewall, with two spouts used as a wastewater inlet spout 211 and a wastewater outlet spout 212.

The wastewater inlet spout 211 is connected to the first filter unit 100, while the wastewater outlet spout 212 is connected to the second filter unit 400.

The top lid 220 of the vortex tank 200 covers the open top of the housing 210, with an opening formed at the center of the lid 220. A wastewater inlet spout 221 is vertically fitted into said opening of the lid 220, and is used for introducing secondarily filtered wastewater from the second filter unit 400 into the housing 210 of the vortex tank 200. Mounted to the lower end of the wastewater inlet spout 221 within the housing 210 of the vortex tank 200 is the wastewater swirling nozzle 230. This swirling nozzle 230 is a cylindrical member, which is closed at opposite ends thereof and is transversely arranged within the housing 210 while being slightly inclined.

Figs. 5a to 5c are a plan view, a side view and a bottom view of the wastewater swirling nozzle 230. As shown in the drawings, the swirling nozzle

230, comprising a hollow cylindrical body, is mounted to the lower end of the wastewater inlet spout 221 at its central portion while communicating with the inlet spout 221. In such a case, the swirling nozzle 230 is slightly inclined at a predetermined angle of inclination relative to the vertical spout 221.

Two rows of orifices 231 are individually and axially formed along the sidewall at each half part of the cylindrical nozzle 230 in such a way that the two rows of orifices 231 are linearly arranged at two positions, angularly and equally spaced apart from the bottom axial line of the nozzle 230 by an angle of 45° in opposite directions.

During an operation of the system, secondarily filtered wastewater under pressure from the second filter unit 400 flows into the swirling nozzle 230 through the inlet spout 221, and is sprayed into the vortex tank 200 through the orifices

231. In such a case, the secondarily filtered wastewater discharged under pressure from the orifices 231 of the nozzle 230 is sprayed onto and mixed with the primarily filtered wastewater within the tank 200. This primarily filtered wastewater already flowed from the first filter unit 100 into the tank 200 through the wastewater inlet spout 211. Such spraying and mixing of the wastewater within the vortex tank 200 causes the wastewater to swirl actively. In such a case, the object of the inclined arrangement of the nozzle 230 relative to the inlet spout 221 within the vortex tank 200 is to create a desired active swirling action of the wastewater within the tank 200.

When the wastewater swirls within the vortex tank 200 by the spraying action of the swirling nozzle 230 as described above, it is possible to almost completely prevent an undesired attachment of any unfiltered impurities to the external surfaces of the heat transfer tubes of the heat exchanger 300 during a flowing of the hot wastewater within the heat exchanger 300. This finally prevents an unexpected reduction in the operational function of the heat exchanger 300.

The heat exchanger 300 of this invention is shown in Figs. 1 and 4 in detail. As shown in the drawings, the general construction of the heat exchanger 300 remains the same as that of a conventional heat exchanger, but the cylindrical housing 310 of the heat exchanger 300 is open at its upper end so as to communicate with the vortex tank 200. Therefore, wastewater naturally and directly flows down from the vortex tank 200 into the housing 310 of the heat exchanger 300 due to gravity, thus accomplishing a desired heat exchanging action between the hot wastewater and low temperature working water. After the heat exchanging process, the wastewater is collected within a sewage collecting tank 330 provided under the heat exchanger 300.

A plurality of heat transfer tubes 320, through which low temperature working water flows, are set within the housing 310 of the heat exchanger 300 in the conventional manner, thus forming a conventional lamellar structure. During an operation of the system, hot wastewater naturally flows through the gaps between the tubes 320 due to gravity, and so heat is transferred from the hot wastewater to the low temperature working water within the tubes 320 through the sidewalls of the tubes 320 made of a thermal conductive material, thus heating the working water to a desired temperature.

In such a case, the low temperature working water flows into the heat transfer tubes 320 of the heat exchanger 300 through a working water inlet spout 311 provided on the sidewall of the housing 310 at a lower position, and is heated by the hot wastewater prior to being discharged from the tubes 320 to a target device, such as a boiler, through a working water outlet spout 312 provided with a fifth control valve V5. The two temperature sensors SI and S2 are provided at the two spouts 311 and 312 of the housing 310, and are used for measuring the temperatures of inlet and outlet working water, thus finally measuring the quantity of heat recovered by the working water. In addition, the flow meter S3 is provided at the working water inlet spout 311, and is used for measuring the quantity of inlet working water, or measuring flow rate of the inlet working water.

In order to drain the processed wastewater from the sewage collecting tank 330 to a sewage system, a wastewater drain spout 313 is provided at the bottom wall of the tank 330. A wash water inlet spout 316, having a sixth control valve V6, is provided at the center of the bottom wall of the heat exchanger 300. In addition, a sediment drain pipe 317 is branched from said wash water inlet pipe connected to the wash water inlet spout 316, and is provided with a drain valve DV for selectively draining sediments from the bottom wall of the heat exchanger 300 to the drain tank.

The second filter unit 400 has a construction similar to that of the first filter unit 100, but is used for secondarily filtering the primarily filtered wastewater from the vortex tank 200. The secondarily filtered wastewater is pumped up by a pump P, provided at an outlet spout 412 of the second filter unit 400, so as to be fed to the swirling nozzle 230 through the inlet spout 221 provided at the top lid 220 of the tank 200, thus being sprayed onto wastewater within the tank 200 and actively swirling the wastewater.

A pressure sensor S4 is provided on the housing 410 of the second filter unit 400 for sensing pressure within the housing 410 and determining whether the shell tube-type filter 430 of the second filter unit 400 is desirably operated. In an operation of the waste heat recovery system of this invention, the second filter unit 400 is selectively operated under the control of the control panel AT.

In Fig. 1 showing the construction of the system including the second filter unit 400, the reference numerals 410, 420, 411, 412, 421 and 414 denote the housing, top lid, wastewater inlet spout, wastewater outlet spout, wash water outlet spout, and wash water inlet spout of the second filter unit 400. In addition, the reference characters V7, V8, V9 and VI 0 denote seventh to tenth control valves provided at the spouts of the second filter unit 400.

In the waste heat recovery system of this invention, a plurality of water supply pipes are branched from the working water supply pipe of the heat exchanger 300, and extend to the elements of the system, thus supplying a part of the working water under pressure to the elements so as to allow the elements to use the working water as wash water.

In an operation of the auto-controlled waste heat recovery system using the shell tube-type filters, the system automatically senses the temperature, pressure and flow rate of water using the sensors SI, S2, S3 and S4, and automatically controls the control valves VI to VI 0 and the pump P using the control panel AT. The operation of the system is thus automatically controlled, different from conventional waste heat recovery systems. That is, in the operation of the system, the control panel AT automatically controls the operational time of the elements of the system in accordance with the sensed temperature of heated working water and the temperature of discharged wastewater. The control panel AT also controls the valves VI, V2, V3 and V4 of the first filter unit 100, the pump P and valves V7, V8, V9 and VI 0 of the second filter unit 400, the valve V5 of the vortex tank 200, and the valve V6 of the heat exchanger 300. In such a case, the operational time of the above-mentioned pump and valves is automatically controlled by the control panel AT in accordance with concentration of solids laden in the hot wastewater. In addition, the operational time of the drain valves DV of the elements 100, 300 and 400 is automatically controlled by the control panel AT in accordance with the concentration of solids laden in the hot wastewater. The control panel AT also automatically displays the quantity of recovered heat on a display device by operating the signals output from the inlet and outlet working water temperature sensors S3 and S4 in addition to the signal output from the flow meter S4.

Industrial Applicability

As described above, the present invention provides a shell tube-type filter and a waste heat recovery system using such shell tube-type filters. Different from conventional net-type filters, the shell tube-type filter 130 of this invention prevents long and fine impurities, such as hairs, waste threads and waste yarns, from getting tangled together even though they partially enter into the holes 131 of the filter 130 during a wastewater filtering process of the system. It is thus possible to easily remove filtered solids from the upper surface 130S of the shell tube-type filter 130 through a flushing process and to use the filter 130 for a desired lengthy period of time.

Particularly, the filtered solids are easily and automatically removed from the upper surface of the shell tube-type filter by a flushing of pressurized wash water flowing through the holes 131 of the filter in a reverse direction from the lower surface 130B when necessary.

Therefore, the waste heat recovery system, using such shell tube-type filters, is thus automatically operated during a waste heat recovering process different from a waste heat recovery system using conventional net-type filters.

The system of this invention is thus operated at low cost. In addition, the operation of the elements of the system and the process of flushing the elements of the system using pressurized wash water are automatically controlled in accordance with concentration of solids laden in hot wastewater, and so the system is improved in its operational durability and is convenient to users. In addition, the system of this invention has a vortex tank 200 and the second filter unit 400, thus effectively filtering hot wastewater even though the wastewater is laden with a high concentration of solids. The present invention thus provides a very effective waste heat recovery system. In addition, the control panel of the system of this invention is provided with a display device for displaying the amount of recovered waste heat, and so it is possible to make a prediction about the amount of recovered heat energy and to effectively manage the consumption of energy. The display device also allows the user of the waste heat recovery system to directly learn the amount of recovered heat energy and the utility of the system. Although the preferred embodiments of the present invention have been disclosed 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.

Claims

1. A shell tube-type filter used for filtering solids and impurities from wastewater, comprising: a thick bed-shaped body having a predetermined thickness, with a plurality of tube-type vertical holes (131) extending from an upper surface (130S) to a lower surface (13 IB) of said body.

2. An auto-controlled waste heat recovery system, comprising: a first filter unit (100), a second filter unit (400), a vortex tank (200), and a heat exchanger (300) connected together by a pipeline, with a plurality of automatic control valves (VI to V10, and DV) provided at wastewater inlets, wastewater outlets, wash water inlets, wash water outlets, and sediment drain pipes of the first filter unit (100), the second filter unit (400), the vortex tank (200), and the heat exchanger (300), and a control panel (AT) used for controlling an operation of the system.

3. The auto-controlled waste heat recovery system according to claim 2, wherein hot wastewater is introduced into the first filter unit (100) so as to be primarily filtered within the first filter unit (100), and is fed from the first filter unit (100) into the vortex tank (200) so as to swirl in the tank (200), and is fed from the tank (200) into the heat exchanger (300) so as to heat low temperature working water to a desired temperature, and is finally discharged from the heat exchanger

(300) into a sewage system through a drain port, said vortex tank (200) being also connected to the second filter unit (400) through a connection pipe provided with the seventh control valve (V7), said seventh control valve (V7) being selectively opened under the control of said control panel to feed the primarily filtered wastewater from the vortex tank (200) to the second filter unit (400), thus allowing the wastewater to be secondarily filtered within the second filter unit (400) prior to being returned to the vortex tank (200) by pumping force of a pump (P).

4. The auto-controlled waste heat recovery system according to claim 2 or 3, wherein said first filter unit (100) comprises a hollow cylindrical housing (110), a top lid (120), and a shell tube-type filter (130), with a wastewater inlet spout (111) and a wastewater outlet spout (112) provided at a sidewall of said housing (HO) and provided with the first and second control valves (VI and V2), said housing (110) also having a wash water inlet spout (114) at its bottom wall and a wash water outlet spout (121) at the top lid (120), said wash water inlet and outlet spouts (114 and 121) being provided with the third and fourth control valves (V3 and V4) for controlling the flow of wash water in a direction from the bottom wall to the top lid (120).

5. The auto-controlled waste heat recovery system according to claim 2 or 3, wherein said vortex tank (200) comprises a hollow cylindrical housing (210) opened at its upper and lower ends and provided with both a top lid (220) and a wastewater swirling nozzle (230), said housing (210) being concentrically mounted to an upper end of a hollow cylindrical housing of said heat exchanger

(300) and communicating with the housing of the heat exchanger (300), said top lid (220) having an opening, with a wastewater inlet spout (221) vertically fitted into said opening of the lid (220), said wastewater swirling nozzle (230) comprising a cylindrical body transversely mounted to a lower end of said wastewater inlet spout (221) within the housing (210) and communicating with the wastewater inlet spout (221), with two rows of orifices (231) individually and axially formed along a sidewall of the nozzle (230) at each half part of said nozzle (230) in such a way that the two rows of orifices (231) are linearly arranged at two positions, equally spaced apart from a bottom axial line of the nozzle (230) in opposite directions.

6. The auto-controlled waste heat recovery system according to claim 2 or 3, wherein said heat exchanger (300) is provided with two temperature sensors (SI and S2) at its working water inlet and outlet spouts (311 and 312) for measuring temperatures of inlet and outlet working water, said heat exchanger (300) being also provided with a flow meter (S3) at said working water inlet spout (311) for measuring flow rate of the inlet working water.

7. The auto-controlled waste heat recovery system according to claim 2 or 3, wherein said second filter unit (400) is provided with a pressure sensor (S4) for sensing pressure within the second filter unit (400).