WO2005099920A1

WO2005099920A1 - Food waste treating system and control method therefor

Info

Publication number: WO2005099920A1
Application number: PCT/KR2004/002804
Authority: WO
Inventors: Pil Soon Han; Hyung Soo Kim; Woo Suk Park
Original assignee: Gaia Co., Ltd.
Priority date: 2004-04-19
Filing date: 2004-11-03
Publication date: 2005-10-27
Also published as: KR200355901Y1

Abstract

A food waste treating system includes a fermentation tub for fermenting and drying a food waste; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; and a multistage deodorization unit for processing a part of the vapor that is not condensed by the condenser, removing an offensive odor-causing substance therefrom and discharging the vapor. Meanwhile, the multistage deodorization unit includes an ozone generator, a thermal deodorization device and a catalytic deodorization device. Further, the food waste treating system includes a device for sensing a temperature of the food waste and a device for sensing a moisture content thereof. By using such food waste treating system, the food waste can be safely treated while increasing an energy efficiency and an efficiency in removal of the offensive odor.

Description

FOOD WASTE TREATING SYSTEM AND CONTROL METHOD THEREFOR

Technical Field The present invention relates to a food waste treating system and a control method therefor; and, more particularly, to a food waste treating system and a control method that are capable of efficiently and safely eliminating vapor containing an offensive odor-causing substance produced during a food waste treating process by using a multistage deodorization system.

Background Art Vapors containing volatile organic compounds are produced while processing food waste having a high moisture content in a dry fermentation apparatus. The organic materials contained in the vapor cause an offensive odor, which is the most serious problem of such a dry fermentation apparatus. As for a deodorization method for removing an offensive odor-causing substance, a direct combustion method, a catalytic oxidation method or the like have been widely employed. However, the catalytic oxidation method is not capable of completely eliminating the offensive odor-causing substance. On the other hand, the direct combustion method is generally applied to deodorization process, since it has a high deodorization efficiency and can eliminate various offensive odor-causing substances such as combustible offensive odor-causing substance, hydrogen sulfide, ammonia or the like. The direct combustion method deodorizes vapor containing an offensive odor-causing substance at a high temperature (over 600 °C) through oxidation. Although the set temperature of a furnace and the residence time of gas depend on a composition ratio or the level of the offensive odor-causing substance, the offensive odor-causing substance is generally incinerated and eliminated, if gas containing the offensive odor-causing substance passes through a heating device having a temperature of 700 °C to 800 °C for 0.5 seconds. Since, however, temperature of vapor generated in the dry fermentation apparatus ranges from about 90 to 100 °C, a considerable amount of energy is required to directly heat such vapor and incinerate the offensive odor-causing substance contained therein; and which results in a cost problem. Accordingly, in order to solve these problems of the direct combustion method, a food waste treating system capable of reducing energy consumption for a fermentation process while improving the fermentation efficiency is disclosed in Korean Patent No. 0337475. The system incinerates and removes an offensive odor-causing substance by letting a part of vapor containing an offensive odor- causing substance that is not condensed while passing through a condenser pass through a deodorization device. Further, the system provides a latent heat of the gas that has passed through the deodorization device to be recovered in fermentation. However, according to the system, only a small portion of vapor that is not condensed by the condenser flows into the deodorization device. Meanwhile, a large amount of vapor flows into a heat exchanger and then returns back to the fermentation tub at a higher temperature. That is, the vapor whose offensive odor is not removed undergoes the aforementioned processes repeatedly until it is condensed or the offensive odor-causing substance thereof is removed by the deodorization device. Although the system improves the energy efficiency by recovering some latent heat of the gas that has passed through the deodorization device in the fermentation process, it has a low efficiency in eliminating offensive odor. Throughout the processing stages, food waste undergoes phase changes from an initial heterogeneous state to a non- sticky powder state via a porridge state and a sticky clay state, sequentially. The moisture content of the food waste in each state is described as follows.

Table 1

As shown in a graph of Fig. 1, the moisture content of food waste changes depending on heating time during the treatment process. The dotted line and the solid line represent a theoretical value and an actually measured experimental value, respectively. In the experimental value, when the moisture content reaches about 25 %, the moisture content change slopes gradually, which indicates that a considerable amount of time and energy is required to remove water when the moisture content is below 25 %. This happens because water exists within the cells of the food waste ingredients. Due to the existence of water, there is a difference between the theoretical value and the experimental value. Further, if the system is driven in the region where the moisture content is below 25 %, carbonization of the food waste occurs, thereby increasing the chance of fire. Moreover, in case the moisture content of food waste reaches below 25 %, a large amount of particulate is produced, thereby undermining the useful lives of a condenser and a blower. Meanwhile, the dry fermentation apparatus for treating food waste agitates injected food waste by force to dry the food waste quickly and effectively. To be more specific, a heating unit is attached to a lower portion of the fermentation tub into which the food waste is introduced and, further, fermented food waste is dried by heat generated from the heating unit. However, if the fermented food waste is not agitated forcibly, heat will accumulate locally to the fermented food waste located close to the heating unit whereas heat will not be spread sufficiently to the part of the fermented food waste far from the heating unit. To prevent this, a rotational axis rotated by a driving unit is installed in the fermentation tub in a longitudinal direction thereof and, further, a plurality of rods are fixed to the rotational axis to be perpendicular thereto. Thus, the driving unit operates to rotate the rotational axis, so that each of the rods rotates to agitate the fermented food waste. Fermentation tubs for improving an agitation efficiency of a food waste are disclosed in Korean Patent No. 2002-0019890 and Utility Model No. 264897, which have good agitating and crushing functions in general. However, in case of such fermentation tubs, rotating force of an impeller does not reach the fermented food waste gathering at the end of each rotational axis, so that the fermented food waste will accumulate in the part of the fermentation tub. Since the fermented food waste accumulated in the part is neither agitated nor crushed, the agitation and crushing of the entire fermented food waste is not uniform. Further, in case the fermented food waste forms a bulky lump block near a food waste outlet due to the insufficient agitation and crushing of fermented food waste, discharging thereof may become a problem. Disclosure of Invention

It is, therefore, a first object of the present invention to provide a food waste treating system having a superior efficiency in eliminating offensive odor while improving the energy efficiency by recovering a latent heat of gas that has passed through a deodorization device for a fermentation process. In accordance with a first preferred embodiment of the present invention, there is provided a food waste treating system including: a fermentation tub for fermenting and drying food waste; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; and a multistage deodorization unit for processing a part of the vapor that is not condensed by the condenser, removing an offensive odor-causing substance therefrom and discharging the vapor, wherein the multistage deodorization unit includes an ozone generator, a thermal deodorization device and a catalytic deodorization device. A second object of the present invention is to provide a food waste treating system capable of extending the useful lives of a condenser, a blower or the like by effectively removing particulates generated during a drying process of the food waste. In accordance with a second preferred embodiment of the present invention, there is provided a food waste treating system including: a fermentation tub for fermenting and drying food waste; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; and a blower for moving the vapor discharged from the fermentation tub along a flow line, wherein the fermentation tub includes a first filter for filtering particulate generated while the food waste is dried; and a cyclone filter for filtering particulate contained in the vapor discharged from the fermentation tub after going through the first filter but before being sent to the condenser and the blower. A third object of the present invention is to provide a food waste treating system capable of uniformly agitating and crushing the entire fermented food waste by way of effectively agitating and crushing even fermented food waste near an end of each rotational axis or near a food waste outlet during the agitation process. In accordance with a third preferred embodiment of the present invention, there is provided a food waste treating system including: a fermentation tub including a housing having two semi-cylindrical agitating tubs at a lower portion thereof, a pair of rotational axes disposed in parallel at a lower portion of an inner space of the housing, and a driving mechanism for rotating the rotational axes; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; and a deodorization unit for receiving a part of the vapor that is not condensed by the condenser, removing an offensive odor-causing substance therefrom and discharging the vapor, wherein a plurality of rods, each rod extending out radially through one of the rotational axes and fixed thereto at a right angle to a longitudinal direction of the rotational axes; impellers are formed by fixing curved members between ends of the respective rods; and a plurality of elongated portions extended toward wall surfaces of the respective agitating tubs are installed on outer surfaces of the rods nearest to end portions of the respective rotational axes. A fourth object of the present invention is to provide a food waste treating system capable of preventing a carbonization and a fire that may occur when the system is operated for a long time in a state with a moisture content of the food waste lower than a specific value. In accordance with a fourth preferred embodiment of the present invention, there is provided a food waste treating system including: a fermentation tub for fermenting and drying food waste; a heating unit for heating the fermentation tub to dry the food -waste; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; a thermal deodorization device for receiving a part of the vapor that is not condensed by the condenser, removing an offensive odor-causing substance therefrom and discharging the vapor; means for sensing temperature of the food waste, which is installed at a lower portion of the fermentation tub; and a controller for stopping the operation of the entire system in case the temperature of the food waste becomes equal to or above a preset temperature. A fifth object of the present invention is to provide a control method for the food waste treating system capable of preventing a carbonization and a fire that may occur when the system is operated for a long time in a state with a moisture content of the food waste lower than a specific value. In accordance with a fifth preferred embodiment of the present invention, there is provided a control method of a food waste treating system, the method including the steps of: performing a normal operation for fermenting and drying food waste while maintaining respective temperatures of a heat transfer fluid for drying the food waste and of a thermal deodorization device for removing offensive odor- causing vapor at their respective preset temperatures; and performing a finishing operation for fermenting and drying the food waste while stopping a heating unit for the heat transfer fluid and maintaining the temperature of the thermal deodorization device at the preset temperature.

Brief Description of Drawings The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with accompanying drawings, in which: Fig. 1 is a graph showing changes in the moisture content of food waste depending on heating time; Fig. 2 provides a block diagram illustrating an overall composition of a food waste treating system in accordance with the present invention; Fig. 3 depicts a schematic cross-sectional view showing the structure of a cyclone filter in accordance with the present invention; Fig. 4 shows a block diagram depicting a vapor flow through a multistage deodorization system in accordance with the present invention; Fig. 5A illustrates a cross-sectional perspective view showing an inner structure of a deodorization device in accordance with the present invention; Fig. 5B offers a perspective view illustrating an outer structure of another preferred embodiment of a deodorization device in accordance with the present invention; Fig. 5C demonstrates a cross-sectional perspective view showing an inner structure of the deodorization device illustrated in Fig. 5B; Fig. 6A describes a perspective view depicting an outer shape of a food waste treating system in accordance with the present invention; Fig. 6B is a perspective view showing an outer shape of another preferred embodiment of a food waste treating system in accordance with the present invention; Fig. 7A presents a cross-sectional view showing an inner composition of a fermentation tub in accordance with the present invention; Fig. 7B represents a cross-sectional view illustrating an inner structure of another preferred embodiment of a fermentation tub in accordance with the present invention; Fig. 7C sets forth a cross-sectional view depicting an inner structure of still another preferred embodiment of a fermentation tub in accordance with the present invention; Fig. 8 offers an enlarged view of the portion "A" shown in Fig. 7A; Fig. 9 provides an enlarged view of the portion "B" illustrated in Fig. 7A; and Figs. 10A and 10B illustrate diagrams for describing a control method for the food waste treating system in accordance with the present invention.

Best Mode for Carrying Out the Invention Fig. 2 provides a block diagram illustrating an overall composition of a food waste treating system in accordance with the present invention. The food waste treating system in accordance with the present invention includes a fermentation tub 10 into which food waste is injected; a condenser 30 for condensing vapor containing an offensive odor-causing substance discharged from the fermentation tub 10; a heat exchanger 70 for heating the vapor discharged from the condenser 30 and air flowing in from outside; and a deodorization device 80 for removing the offensive odor-causing vapor. In Fig. 2, for illustration purpose, the components of the food waste treating system in accordance with the present invention are shown at the exterior of a dry fermentation apparatus. However, those components are actually disposed inside the dry fermentation apparatus, i.e., in a lower portion of the fermentation tub 10. Hereinafter, a composition and a function of the food waste treating system in accordance with the present invention will be described following a vapor flow path through a flow line. The food waste injected into the fermentation tub 10 is fermented and dried during a heating process by a heating unit 12 installed at a lower portion of the fermentation tub 10 and, further, generates vapor containing an offensive odor-causing substance (hereinafter, referred to as "offensive odor-causing vapor" in order to distinguish it from vapor whose offensive odor-causing substance is removed) during a fermentation process. The offensive odor- causing vapor flows into a cyclone filter 20 through a line A and then into the condenser 30 through a line B. A part of the offensive odor-causing vapor is condensed in the condenser 30, and such condensate flows into a check valve 16 through a line CI and then into a drain active carbon tank 18 through a line C2. In the drain active carbon tank 18, the condensed liquid is filtered by an active carbon and then discharged externally. The offensive odor-causing vapor that is not condensed by the condenser 30 is moved through a line Dl by a blower 60, and then flows into the heat exchanger 70 through a line D2. The temperature of the offensive odor-causing vapor increases by absorbing heat while passing through the heat exchanger 70. A part of the vapor whose temperature has increased is supplied into the fermentation tub 10 through a line E to promote fermentation of the food waste. The process in which the offensive odor-causing vapor absorbs heat in the heat exchanger 70 will be described later. The other part of the offensive odor-causing vapor whose temperature has increased by absorbing heat in the heat exchanger 70 flows into the deodorization device 80 through a line FI to be heated. A high-temperature gas that has passed the deodorization device 80 (i.e., vapor whose organic material is burnt and removed, and hereinafter, referred to as "purified gas") is sent to a catalyst portion 90 through a line F2. Next, in the catalyst portion 90, the offensive odor-causing thereof is completely removed through oxidation using a noble metal catalyst such as palladium, platinum, or the like. The purified gas whose offensive odor-causing substance is removed while passing through the deodorization device 80 and the catalyst portion 90 is sent to a radiator 100 provided inside the heating unit 12 through a line F3. The high-temperature purified gas releases its latent heat to heat transfer fluid of the heating unit 12 while passing through the radiator 100, and the heated heat transfer fluid is used in fermenting and drying of the food waste. Although the purified gas that has passed through the radiator 100 has lost some of its latent heat, the temperature thereof is still considerably high. Then, the purified gas flows into the heat exchanger 70 through a line F4. The heat exchanger 70 is composed of a heat radiating line (not shown) through which the high-temperature purified gas discharged from the radiator 100 flows; and a first and a second heat absorbing line (not shown) through which outside air provided through the purifying filter 40 and low-temperature offensive odor-causing vapor discharged from the condenser 30 flow respectively. Therefore, the latent heat of the high-temperature purified gas flowing through the heat radiating line is transferred to the outside air and the offensive odor-causing vapor flowing through the first and the second heat absorbing line. The purified gas discharged from the heat exchanger 70 after the heat exchange is completed is discharged into the atmosphere through a line F5 after an ash-type inorganic material is filtered and removed by an exhaust active carbon tank 14. Meanwhile, since vapor supplied from the condenser 30 and the heat exchanger 70 cannot provide a sufficient amount of air required for fermentation, outside air is used. The outside air flows from the purifying filter 40 into the heat exchanger 70 through a line D2 and, further, as described above, increases its temperature by taking the latent heat from the high-temperature purified vapor flowing through the heat radiating line while passing through the first heat absorbing line of the heat exchanger 70. Next, the heated outside air is supplied into the fermentation tub 10 through a line E. Hereinafter, compositions and functions of individual devices included in the food waste treating system in accordance with the present invention will be described in detail. Fig. 3 depicts a schematic cross-sectional view describing a composition of the cyclone filter 20. As shown, the cyclone filter is mainly composed of an outer duct 24 and a conic section 25. An outward shape of the cyclone filter 20 is similar to that of a typical cyclone particulate collector. However, operation principals thereof are different from each other. The offensive odor- causing vapor, which is primarily filtered by a first filter 15 installed in the fermentation tub 10, flows into the cyclone filter 20 through an inlet 21 formed at a sidewall of the outer duct 24. The offensive odor-causing vapor flown thereinto goes down along an inner surface of the outer duct 24, and then moves to a bottom surface of the cyclone filter 20 along the conic section 25. Thereafter, the offensive odor-causing vapor flows into an inner duct 23 by turning back at a central portion of the bottom surface and then is discharged through an outlet 22. During such process, moisture-containing particulate is adsorbed into an active carbon 26 provided in the cyclone filter and then filtered. Herein, a size of the active carbon 26 is chosen to be about 2 mm to 4 mm, which is enough to remove every moisture-containing particulate passing through the active carbon 26. By using the cyclone filter 20 of which shape is similar to that of the cyclone particulate collector, the offensive odor-causing vapor is moved down and up in the inner space of the filter, thereby increasing an efficiency in removing moisture-containing particulates which will shorten the useful lives of a condenser and a blower. Hereinafter, a multistage deodorization system will be described in detail with reference to Fig. 4. The offensive odor-causing vapor, which is discharged from the fermentation tub 10 and then not condensed by the condenser 30, is purified by ozone (0₃) supplied from an ozone generator 50. Ozone is excellent in deodorization, sterilization, bleaching or the like and, accordingly, is able to remove bacteria, mold or the -like. The offensive odor-causing vapor that is primarily purified by 0₃ is sent to the deodorization device 80 and purified again. The deodorization device 80 used in the present invention is described in detail in Korean Patent No. 0352151 owned by the present applicants, and a major point of its configuration is as follows. The deodorization device 80 can achieve a high deodorization efficiency with a low energy consumption by heating vapor containing an offensive odor-causing substance, which is generated during a dry fermentation process of food waste, during the vapor is sequentially passing through a plurality of members. First, although the deodorization device 80 has a sealed outer housing, Fig. 5A does not illustrate the outer housing in order to show an inner composition of the deodorization device 80. A sealed first housing 36 is installed within the outer housing. Further, the first housing 36 has therein a second housing 38, a vapor inlet pipe 71 and a vapor outlet pipe 72. The inner space of the second housing 38 is divided into a plurality of compartments 31, 32 and 33 by a plurality of partition walls 34 and 35. The plurality of compartments 31, 32 and 33 have therein a plurality of heating pipes 41, 42 and 43, respectively. Further, the multiple heating pipes 41, 42 and 43 are connected to each other and have therein respective heating units connected to an outer power supply unit. The vapor inlet pipe 71 supplies outside vapor into a space between the second housing 36 and a third housing 38.

The vapor outlet pipe 72 is connected to an outermost heating pipe 41 and, thus, outwardly discharges gas whose offensive odor-causing substance is removed. Vapor flown into the aforementioned deodorization device 80 flows through the space between the first housing 36 and the second housing 38 and, then, sequentially passes through each compartment 31, 32 and 33. The vapor that has passed through the last compartment 33 flows into the heating pipe 43 through an opening (not shown) formed thereat. Next, the vapor is heated by direct contact with the heating units provided in the heating pipes 41, 42 and 43 while moving to the heating pipe 41 via the heating pipe 42. A temperature of the gas in the last heating pipe 41 is about 700 to 800 °C and, thus, the vapor evaporates and an organic material contained in the vapor is incinerated and removed. The high-temperature purified gas that has passed through the deodorization device 80 is sent to the catalyst portion 90 containing a palladium catalyst 92 and a platinum catalyst 94. Further, the high-temperature purified gas that has moved to the catalyst is adsorbed on a surface active region of the catalyst and then oxidized. The purified gas sequentially undergoes oxidation reactions using the noble metal catalysts, so that the offensive odor- causing thereof is completely removed. In the meantime, Figs. 5B and 5C provide another preferred embodiment of a deodorization device 80' in accordance with the present invention. An operation principal of the deodorization device 80' is approximately same as that of the aforementioned deodorization device 80 shown in Fig. 5A except that the deodorization device 80' has an approximately cylindrical shape and includes therein a catalyst portion 90' . Vapor containing an offensive odor-causing substance flows into a space between a third housing 58 and a second housing 56 through a vapor inlet pipe 51 formed at the third housing 58 and, further, moves as indicated by an arrow Wl . Then, the vapor flows into a space between the second housing 56 and a first housing 54 and moves along an arrow W2. Meanwhile, each of the spaces formed between the first, the second and the third housing 54, 56 and 58 is already preheated by the aforementioned heat transfer fluid of the heating unit 12 and heating units HI, H2 and H3 in the first housing 54. Accordingly, the vapor is heated while moving along the spaces between each of the housings. The vapor which has moved along the arrow W2 in the space between the second housing 56 and the first housing 54 flows into the first housing 54 and moves along an arrow W3. At this time, the vapor is effectively heated by direct contact with the heating units HI, H2 and H3 installed in the first housing 54. The vapor that has passed through the inner space of the first housing 54 flows into the catalyst portion 90' connected to a rear end of the first housing 54, so that residual offensive odor-causing vapor is completely removed. The vapor discharged from the catalyst portion 90' moves along an arrow W4 between the first housing 54 and the outer housing. The vapor that has moved along the arrow W4 is discharged to the outside of the deodorization device 80' through the vapor outlet pipe 52. While the vapor is passing through the deodorization device 80' to which the heating units are attached, the offensive odor-causing substance contained in the vapor is mostly removed. While the purified gas that has undergone the above- described processes passes through the exhaust active carbon tank 14, an ash-type inorganic material is filtered and removed, so that a completely purified gas is discharged to the atmosphere. Fig. 6A is a perspective view of the food waste treating system in accordance with the present invention, and Fig. 7A presents a cross-sectional view showing an inner structure of the fermentation tub 10 in accordance with the present invention. The fermentation tub 10 includes a sealed housing 110 and rotational axes 120 and 130 installed in the housing 110. An input port 112 is formed at an upper portion of the sealed housing 110 and, thus, a food waste is injected into the fermentation tub 10 through the input port 112. An inner bottom surface of the fermentation tub 110 forms a first and a second semi-cylindrical agitating tub 122 and 132 parallel to each other in a longitudinal direction of the housing 110. The rotational axes 120 and 130 rotated by respective driving units (not shown) are installed in each of the agitating tubs 122 and 132 in a longitudinal direction thereof. Further, the heating unit 12 for heating a fermented food waste is installed under the agitating tubs 122 and 132 (see Fig. 2) . A plurality of rods 124 and 134 are perpendicularly attached to each of the rotational axes 120 and 130 installed in each of the agitating tubs 122 and 132. The rods on a single rotational axis 120 or 130 may be installed while maintaining a uniform gap therebetween. Each of the rods 124 and 134 penetrates each of the rotational axes 120 and 130 and extends to both sides of the axes, respectively. Meanwhile, each of the rods 124 and 134 has a length which enables both ends thereof to be adjacent to the bottom surface of each of the agitating tubs 122 and 132 to the maximum within the range of not affecting a rotation of the rotational axes 120 and 130. Moreover, each of the rods (e.g., 124) fixed to a single rotational axis (e.g., 120) is perpendicular to an adjacent rod. Around each of the rotational axes 120 and 130 are supported two impellers having different spiral direction by each of the rods 124 and 134. In other words, two impellers 126 and 128 are supported by leading end portions of the rods 124 around the rotational axis 120, and two impellers 136 and 138 are supported by leading end portions of the rods 134 around the rotational axis 130. Incised portions R are formed at each of curved members constituting each of the helical-type impellers 126, 128 and 136, 138. Further, crushing protrusions E are formed at wall surfaces forming a boundary 140 of each of the agitating tubs 122 and 132. Therefore, when the respective impellers 126, 128 and 136, 138 rotate according to a rotation of the respective rotational axes 120 and 130, each of the incised portions R of the impellers 126, 128 and 136, 138 penetrates each of the protrusions E. With such configuration, when the impeller rotates, a fermented food waste or a foreign substance between the incised portion R and the protrusion E is crushed by force. Although the fermentation tub 10 composed of the two agitating tubs 122 and 132 parallel to each other and the two rotational axes 120 and 130 respectively attached thereto has been described in this embodiment, a fermentation tub 10' illustrated in Figs. 6B and 7B, which is composed of a single agitating tub and a single rotational axis, can be used for a small capacity food waste treating system. Further, the fermentation tub 10 in which two respective impellers 126, 128 and 136, 138 are supported by leading end portions of the respective rods 124 and 134 around each of the rotational axes 120 and 130 has been described in this embodiment. However, as illustrated in Fig. 7C, if impellers 127, 129 and 137, 139 are further attached to central portions of the respective rods, double spiral impellers can be formed at the entire rotational axes. In this case, it is possible to provide a system having an improved agitating and crushing performance. Fig. 8 illustrates a front wall surface portion of the agitating tub 122 in accordance with the present invention, which is an enlarged view of the portion "A" shown in Fig. 7A. As described in Fig. 8, a plurality of elongated portions 142 are orthogonally installed at an outer surface of the rod 124 attached to a leading end of the rotational axis 120. The elongated portions 142 have uniform gaps therebetween. Further, it is preferable that each of the elongated portions 142 maintains a minimum gap with the front wall surface of the agitating tub 122 within the range of not affecting a rotation of the rotational axis 120 in the agitating tub. In case the agitation apparatus having such elongated portions 142 is driven, a fermented food waste inside the agitating tub 122 is agitated and crushed by the helical- type impellers 126 and 128 and, at the same time, the fermented food waste moved toward the front wall surface of the agitating tub 122 is agitated and crushed by the elongated portions 142 formed at the outer surface of the rod 124 attached to the leading end of the rotational axis 120. Although Fig. 8 and the aforementioned description have illustrated and described only the front wall portion of the agitating tub 122, a rear wall portion of the agitating tub 122 and a front and a rear wall portion of the agitating tub 132 have the same configuration. Fig. 9 depicts a vicinity of a food waste output port 114 of the fermentation tub 10 in accordance with the present invention, which is an enlarged view of the portion "B" shown in Fig. 7A. Incised portions R are formed at a curved member near the output port 114. Further, crushing protrusions E same as those formed at the wall forming the boundary 140 of the respective agitating tubs 122 and 132 are formed at a peripheral portion of the output port 114 of the agitating tub 122. Therefore, in case each of the rotational axes 120 and 130 rotates, each of the protrusions E penetrates each of the incised portions R. Accordingly, a fermented food waste existing in the peripheral portion of the output port 114 is agitated and crushed, so that the output port 114 can be prevented from being clogged by the fermented food waste forming a bulky lump. Hereinafter, a control method for the food waste treating system in accordance with the present invention will be described with reference to Figs. 10A and 10B. An operation of the food waste treating system in accordance with the present invention is divided into two modes, i.e., a setting mode and an auto mode. Figs. 10A and 10B provide diagrams for describing operations of the food waste treating system in accordance with the present invention in the setting mode and the auto mode, respectively. In Fig. 10A, if a user sets a normal operation time to be 7 to 10 hours and a finishing operation time to be 1 to 2 hours and, then, pushes a start button, the operation of the system starts. During the normal operation time, a first temperature controller controls the heat transfer fluid heating unit 12 to repeat on/off state to thereby maintain a temperature of the heat transfer fluid at 140 ± 20 °C. Furthermore, a second temperature controller controls the heating unit of the deodorization device 80 to repeat on/off state to thereby maintain an inner temperature of the deodorization device 80 at 700 ± 50 °C. After the preset normal operation time has elapsed, the finishing operation starts. At this time, as illustrated in Fig. 10A, the heat transfer fluid heating unit 12 becomes an off state, and the deodorization device heating unit repeats on/off state as in the normal operation. The operation of the heat transfer fluid heating unit 12 is stopped to prevent carbonization of the food waste and a probable fire. However, since the offensive odor-causing vapor is still generated during the finishing operation, the deodorization device 80 maintains an operation state. Such finishing operation is carried out for a time preset by the user, e.g., 1 to 2 hours. The auto mode will be described with reference to Fig. 10B. If the food waste treating system starts an operation of the auto mode, an operation of an agitation motor for driving an agitation apparatus is started. At this time, if a food input port or an output port is opened, a door sensor (not illustrated) operates and, thus, the agitation motor stops. When the input port and the output port are all closed, the operation of the agitation motor is restarted. After the system starts operation, if an inner temperature of the deodorization device 80 gradually increases up to a specific temperature, e.g., over 700 °C, the blower 60 starts its operation. In case the blower 60 starts its operation before the temperature of the deodorization device 80 reaches over 700 °C, the offensive odor-causing vapor whose offensive odor-causing substance is not removed can be discharged at the outside of the system. Therefore, the operation of the blower 60 and that of the system are not simultaneously started. In the meantime, a moisture sensor 116 (see Fig. 6A) installed at a lower portion of the fermentation tub 10 senses a moisture content of a food waste in the fermentation tub 10. If the moisture sensor 116 senses that the moisture content of the food waste is lower than or equal to, e.g., 25 % or 30 %, the finishing operation described in the setting mode is performed. That is, the heating unit of the deodorization device 80 is exclusively operated for a preset time while the heat transfer fluid heating unit 12 is stopped and, then, the system stops. As for the moisture sensor 116, a high frequency resistance moisture sensor or the like can be used, for example. An electric overload control relay (EOCR) senses operations of the agitation motor and the blower and, further, generates a signal for stopping the agitation motor and the blower in case an overload is sensed. As in the setting mode, the first temperature controller controls the heat transfer fluid heating unit 12 to repeat on/off state to thereby maintain the temperature of the heat transfer fluid at 140 ± 20 °C. Further, the second temperature controller controls the deodorization device heating unit to repeat on/off state to thereby maintain the inner temperature of the deodorization device 80 at 700 ± 50 °C. Meanwhile, in order to ensure a system safety, the first temperature controller turns off the heat transfer fluid heating unit 12 in case the temperature of the heat transfer fluid reaches a high temperature limit, e.g., over 200 °C. Further, the second temperature controller turns off the deodorization device heating unit in case the temperature of the deodorization device 80 reaches a high temperature limit, e.g., over 800 °C. A food waste temperature sensor 118 (see Fig. 6A) , e.g., a bimetal sensor, installed at a lower portion of the fermentation tub 10 measures temperature of the food waste. If the temperature thereof is higher than or equal to, e.g., 110 °C, operation of the entire system is stopped in order to prevent carbonization of the food waste and a probable fire. Moreover, an electric leakage circuit breaker senses an electric leakage of the system and, further, stops the operation of the entire system when the electric leakage occurs in the system. The food waste treating system in accordance with the present invention uses a multistage deodorization system and, thus, a high efficiency in removal of an offensive odor- causing is provided while improving an energy efficiency by using a latent heat of gas that has passed through a deodorization device in a fermentation process. Further, by using the food waste temperature sensor, it is possible to prevent a probable fire caused by excessive heating of a food waste. While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims .

Claims

What is claimed is:

1. A food waste treating system comprising: a fermentation tub for fermenting and drying food waste; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; and a multistage deodorization unit for processing a part of the vapor that is not condensed by the condenser, removing an offensive odor-causing substance therefrom and discharging the vapor, wherein the multistage deodorization unit includes an ozone generator, a thermal deodorization device and a catalytic deodorization device.

2. The food waste treating system of claim 1, further comprising a heat exchanger for exchanging heat between uncondensed vapor out of the condenser before going through the multistage deodorization unit and high-temperature gas discharged from the multistage deodorization unit.

3. The food waste treating system of claim 1, wherein the catalytic deodorization device includes palladium or platinum.

4. A food waste treating system comprising: a fermentation tub for fermenting and drying food waste; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; and a blower for moving the vapor discharged from the fermentation tub along a flow line, wherein the fermentation tub includes a first filter for filtering particulate generated while the food waste is dried; and a cyclone filter for filtering particulate contained in the vapor discharged from the fermentation tub after going through the first filter but before being sent to the condenser and the blower.

5. The food waste treating system of claim 4, wherein the cyclone filter includes a cylindrical outer duct; a conic section disposed below the outer duct; an inner duct disposed in the outer duct; and an active carbon portion provided between the outer duct and the inner duct.

6. A food waste treating system comprising: a fermentation tub including a housing having two semi-cylindrical agitating tubs at a lower portion thereof, a pair of rotational axes disposed in parallel at a lower portion of an inner space of the housing, and a driving mechanism for rotating the rotational axes; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; and a deodorization unit for receiving a part of the vapor that is not condensed by the condenser, removing an offensive odor-causing substance therefrom and discharging the vapor, wherein a plurality of rods, each rod extending out radially through one of the rotational axes and fixed thereto at a right angle to a longitudinal direction of the rotational axes; impellers are formed by fixing curved members between ends of the respective rods; and a plurality of elongated portions extended toward wall surfaces of the respective agitating tubs are installed on outer surfaces of the rods nearest to end portions of the respective rotational axes.

7. The food waste treating system of claim 6, wherein an incised portion is formed at an outer portion of the curved member, and a protrusion corresponding to the incised portion is formed on a boundary surface of a first and a second agitating tub.

8. The food waste treating system of claim 7, wherein a protrusion corresponding to the incised portion of the curved member is formed around a food waste output port of the fermentation tub.

9. The food waste treating system of claim 6, wherein additional curved members are fixed -between approximately mid sections of the respective rods, thereby forming double impellers about the rotational axes.

10. The food waste treating system of claim 6, wherein the respective elongated portions maintain a minimum gap with the wall surfaces of the agitating tubs without interfering with rotations of the rotational axes in the agitating tubs.

11. A food waste treating system comprising: a fermentation tub for fermenting and drying food waste; a heating unit for heating the fermentation tub to dry the food waste; a condenser for condensing vapor generated in the fermentation tub and discharging condensate; a thermal deodorization device for receiving a part of the vapor that is not condensed by the condenser, removing an offensive odor-causing substance therefrom and discharging the vapor; means for sensing temperature of the food waste, which is installed at a lower portion of the fermentation tub; and a controller for stopping the operation of the entire system in case the temperature of the food waste becomes equal to or above a preset temperature.

12. The food waste treating system of claim 11, wherein the means for sensing temperature of the food waste is composed of a bimetal sensor.

13. The food waste treating system of claim 11, further comprising means for sensing moisture content of the food waste in the fermentation tub installed at a lower portion thereof, wherein the controller stops the heating unit in case the moisture content of the food waste is below a preset level.

14. The food waste treating system of claim 13, wherein the means for sensing moisture content of the food waste is composed of a high-frequency resistance moisture sensor.

15. A control method of a food waste treating system, the method comprising the steps of: performing a normal operation for fermenting and drying food waste while maintaining respective temperatures of a heat transfer fluid for drying the food waste and of a thermal deodorization device for removing offensive odor- causing vapor at their respective preset temperatures; and performing a finishing operation for fermenting and drying the food waste while stopping a heating unit for the heat transfer fluid and maintaining the temperature of the thermal deodorization device at the preset temperature.

16. The control method of a food waste treating system of claim 15, further comprising the step of: stopping the entire system in case temperature of the food waste becomes equal to or above a preset temperature.

17. The control method of a food waste treating system of claim 16, further comprising the step of: performing the finishing operation in case moisture content of the food waste becomes equal to or below a preset level.

18. The control method of a food waste treating system of claim 15, further comprising the step of: stopping the heating unit for the heat transfer fluid or a heating unit of the thermal deodorization device in case respective temperatures of the heat transfer fluid or the thermal deodorization device become equal to or above their respective preset high temperature limits.