Abstract:
An arrangement for treating flora and fauna waste such as garbage under subcritical pressure and temperature. A slurry preparation unit ( 10 ) mixes the flora and fauna waste ( 11 ) with water ( 12 ) and sodium hydroxide ( 13 ) to prepare a slurry. A diaphragm pump ( 16 ) then pressurizes the slurry to subcritical pressure of water (20 Mpa). Subsequently, a hydrothermal reaction tube ( 25 ) heats the pressurized slurry to cause hydrothermal reaction in a subcritical condition thereby obtaining dissolved waste. The dissolved waste is depressurized and fed to an oxidization unit ( 22 ) for oxidation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an arrangement for treating flora and fauna waste, and more particularly to such an arrangement that treats the garbage by hydrothermal reaction under a subcritical condition. 
     2. Description of the Related Art 
     Conventionally, flora and fauna waste such as garbage is collected by vehicles and carried to a particular place so that it is incinerated in a waste disposal facility, buried in the ground or used in reclamation by specialists. In recent years, however, various machines for treating the garbage were developed. 
     For example, Japanese patent Application, Laid Open publication No.  10-328699  entitled “SUPERCRITICAL HYDROXYLATION REACTOR”published Dec. 15, 1998 discloses an apparatus for oxidizing and dissolving organic waste containing water by supercritical hydroxylation reaction. Specifically, organic sludge is pressurized to more than a supercritical pressure of water (22 Mpa) together with oxygen, and heated to more than a supercritical temperature (374° C.). Then, the organic sludge is fed into a reactor for dissolving. At the same time, the oxygen mixed in the organic waste oxidizes the dissolved substances inside the reactor. 
     However, the above described dissolving and oxidizing method and apparatus requires severe conditions such as supercritical pressure and temperature so that piping and associated parts likely corrode. 
     Since the dissolving and oxidization take place under the pressure of 22 Mpa or more and the oxidization proceeds simultaneously in the reactor, the temperature rises to about 600° C. Thus, the apparatus should be made from a material which is resistive to such high pressure and temperature. In addition, that material must be resistant to the oxidization atmosphere. 
     Moreover, the organic waste has high viscosity so that it is difficult to continuously pressurize the waste to 22 Mpa or more by a plunger pump or the like. 
     SUMMARY OF THE INVENTION 
     One of the objects of the present invention is to a waste treating apparatus that can overcome the above described problems. Specifically, the present invention aims to maintain a dissolving capability of a waste treating apparatus while not subjecting the piping to corrosion. 
     According to one aspect of the present invention, there is provided an apparatus for treating flora and fauna waste, including a preparation unit for mixing the flora and fauna waste with water and chemicals to prepare a starting material (i.e., slurry), a pressuring unit for pressuring the slurry to subcritical pressure of water, a hydrothermal reaction unit for heating the pressurized slurry to cause hydrothermal reaction in a subcritical condition thereby obtaining dissolved waste, and an oxidization unit for oxidizing the dissolved waste after pressure reduction. In the present invention, therefore, the flora and fauna waste undergo the two processes, i.e., the hydrothermal reaction under the subcritical condition, and the oxidation. Thus, the flora and fauna waste can be disposed as sewage. Further, dioxins and other harmful gas are not generated. 
     The hydrothermal reaction unit may include a hydrothermal reaction tube and a heat medium circuit for heating the hydrothermal reaction tube. The hydrothermal reaction unit may further include a circulation mechanism, which connects an outlet of the hydrothermal reaction tube to an inlet of the reaction tube, for circulating the slurry to the reaction tube. The hydrothermal reaction unit may further include a heat exchanger for heat exchange between the slurry directed to the hydrothermal reaction tube and the dissolved waste directed to the oxidation unit. 
     The pressurizing unit may include a diaphragm pump for pressurizing the slurry to 6 Mpa or more, which is a subcritical pressure of water. 
     The oxidation unit may include an oxidation vessel for receiving the dissolved waste from the hydrothermal reaction unit after the dissolved waste is depressurized, and an oxygen supply unit for feeding an oxidizing agent such as air or oxygen to the oxidation vessel such that organic components such as hydrocarbon contained in and associated with the dissolved waste are deconstructed in the oxidation vessel for oxidation. 
     The oxidation unit may further include a gas-liquid separator located downstream of the oxidation vessel for separating the oxidized waste to a gas component and a liquid component, and a return line for returning the liquid component to the oxidation vessel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 illustrates a system diagram of a waste treating apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, an embodiment of the present invention will be described in reference to the accompanying drawing. 
     Referring to FIG. 1, a tank  10  is provided for receiving a raw material (flora and fauna waste)  11  such as food residue. Water is fed from a water tank  12 , and used for hydrothermal reaction with subcritical water (will be described later). A chemicals tank  13  holds sodium hydroxide or the like and supplies it to the tank  10 . 
     A slurry feed line  15  extends from the raw material tank  10 , and a pressurization unit  16  is provided on the material feed line  15 . 
     A water pipe  18  extends from the water tank  12  to the raw material tank  10  and the water tank  12  has a water pump  17  such that water is fed to the raw material tank  10  through the water pipe  18 . 
     Likewise, a chemicals pipe  20  extends from the chemicals tank  13  to the raw material tank  10  and the chemicals tank  13  is equipped with a feed pump  21  such that chemicals are fed to the raw material tank  10  through the chemicals pipe  20 . 
     The pressurizing unit  16  includes a feeder  60  such as single shaft axial screw type pump with a motor for continuously feeding the slurry to subsequent units from the raw material tank  10 , and a diaphragm pump  61  for pressurizing the slurry, coming from the feeder  60 , to a subcritical pressure (6 Mpa or more). 
     The diaphragm pump  61  has a cylinder chamber  62  equipped with check valves (not shown) at its inlet and outlet, a sandwich-type diaphragm  63  placed in the cylinder chamber  62 , and a hydraulic drive (motor)  64  for actuating the diaphragm  63  such that suction and discharge occur alternately. 
     The outlet of the feeder  60  is communicated with the inlet of the diaphragm pump  61  by a line  15   a  such that the slurry is forced into the cylinder chamber  62  of the diaphragm pump  61  during the suction (admission) stroke of the diaphragm pump  61 . A return pipe  65  extends from the line  15   a  to the raw material tank  10  to feed back the slurry to the tank  10  during the discharge stroke of the diaphragm pump  61 . 
     A double-tube type heat exchanger  24  is provided on the slurry feed line  15 . After the heat exchanger  24 , the slurry line  15  connects to a circulation line  26  of a hydrothermal reaction tube  25 . 
     The hydrothermal reaction tube  25  has a heat medium circulation line  27 , on which are provided a pump  28  for causing the heat medium to circulate and a heater  29  for heating the heat medium. 
     The hydrothermal reactor  25  also has a double-tube structure such that the slurry flows in an inner tube  30 , and the heat medium flows between the inner tube  30  and an outer tube  32 . 
     The circulation line  26  connects the outlet of the inner tube  30  of the hydrothermal reactor  25  to the inlet of the same. A circulation pump  31  is provided on the circulation line  26 . Upstream of the circulation pump  31 , a line  33   a  is branched from the circulation line  26  to transfer part of dissolved matters to the heat exchanger  24 . A dissolved matters line  33  extends from the heat exchanger  24  to an oxidization vessel  22 . 
     On the dissolved matters line  33 , provided are a trim cooler  34  and backing pressure regulation valve  35 . 
     An oxidation agent feed line  36  connects to the oxidation vessel  22  for oxidation of the dissolved matters by deconstructing. A line  72  extends from the oxidation vessel  22  to a gas-liquid separator  23 . A liquid discharge line  37  extends to the oxidation vessel  22  from the bottom of the gas-liquid separator  23  so that part of the oxidized dissolved matters is returned to the oxidation vessel  22 . A pump  40  is provided on the liquid discharge line  37  for this returning. 
     A line  41  is branched from the liquid discharge line  37  and extends to a liquid disposal tank  14  to return a liquid-after-the-treatment to the liquid tank  14 . On this branch line  41 , provided are a trim cooler  42  and backing pressure regulation valve  43 . 
     The gas-liquid separator  23  also has a gas discharge line  50 , on which a condenser  38  and backing pressure regulation valve  52  are provided. A line  53  extends from the condenser  38  to the gas-liquid separator  23  to return liquid, resulting upon condensation in the condenser  38 , to the gas-liquid separator  23 . 
     The treating liquid tank  14  has a line  44  extending from its top to discharge dissolved/oxidized gas and another line  45  extending from the bottom for drain. The dissolved gas discharge line  44  has a deodorant device  46  including, for example, activated carbon. The drain line  45  has a branch line  47  with a pump  48  to make it available to return part of the sewage to the raw material tank  10  if necessary. 
     Gas generated in the raw material tank  10  is introduced to the exhaust gas line  44  via a line  49 . 
     The trim coolers  34  and  42  and condenser  38  are fed a cold water “w”from respective cooling towers (not shown). After used in the cooling process in the trim coolers  34  and  42  and condenser  38 , the water “w”returns to the cooling towers and air cooled. Then, the water “w” is supplied to the trim coolers and condenser again. 
     Now, an operation of the illustrated waste treating apparatus will be described. 
     First, the raw material (flora and fauna waste)  11  is fed into the tank  10 , and the water is fed into the tank  10  from the water tank  12  via the line  18 . The chemicals are also supplied to the tank  10  from the chemicals tank  13  via the line  20 . In this way, the slurry is prepared in the tank  10 . Then, the slurry is transmitted to the feed line  15  by the pump  16  and delivered to the hydrothermal reactor  25 . The slurry is dissolved in the hydrothermal reactor  25 . The dissolved substances transferred to the heat exchanger  24  heat exchanges with the slurry inside the heat exchanger  24  before the slurry enters the hydrothermal reactor  25 . 
     In the hydrothermal reactor  25 , the water contained in the slurry is subjected to a subcritical condition with high pressure and temperature (250° C. and 6 Mpa) so that the organic substances in the flora and fauna waste are dissolved to hydrocarbon, etc. In this hydrothermal reaction, the slurry is repeatedly circulated by the line  26  to insure a certain flow (moving) speed of the slurry. This promotes thermal transfer between the slurry and heat medium inside the hydrothermal reactor  25  and prevents carbonizing inside the pipes. The liquid chemicals such as sodium hydroxide facilitate dissolving of the slurry. 
     An amount of circulation in the line  26  may be determined or limited by an inner diameter of the inner tube  30 , but in this particular embodiment the slurry flowing speed in the inner tube  30  is 2 to 3 m/sec. 
     The dissolved substances are then discharged to the heat exchanger  24  via the line  33   a,  as mentioned earlier. After heating the newly coming slurry in the heat exchanger  24 , the dissolved substances are cooled in the trim cooler  34  and their pressure is reduced in the backing pressure regulation valve  35 . Subsequently, the dissolved matters are transmitted to the oxidation vessel  22  such that combustible matters and remaining hydrocarbon, which is not reacted in the hydrothermal reactor  25 , are burned for oxidization. The resulting matters proceed to the gas-liquid separator  23 , and part of them is returned to the oxidation vessel  22  to keep flow (moving) speed inside the oxidation vessel. 
     Since the heat of the substances discharged from the hydrothermal reactor  25  is used to heat the slurry in the heat exchanger  24  (heat recovery), the slurry is already heated to a certain extent when it enters the hydrothermal reaction reactor  25  so that the heat medium heater  29  is required to generate less heat. 
     After the gas-liquid separator  23 , the liquid proceeds into the line  41 , is cooled in the trim cooler  42  and its pressure drops to the atmospheric pressure in the backing pressure regulation valve  43 . Then, the liquid is disposed into the tank  14 . On the other hand, the gas is guided to the condenser  38  via the line  50 . Upon condensation, the condensed liquid component returns to the gas-liquid separator  23  whereas the gas component is introduced to the backing pressure regulation valve  52  to reduce its pressure. The gas component is then introduced to the tank  14 . 
     A gaseous component in the tank  14  is admitted to the deodorant device  46  via the pipe  44  whereas a liquid component is drained to the sewage line  45 . 
     As understood from the foregoing, as compared with the conventional arrangement employing supercritical pressure/temperature, the present invention uses moderated reaction temperature and pressure. Accordingly, slurry dissolving capability is deteriorated to a certain extent, i.e., capability of reducing COD (chemical oxygen demand) is lowered, but it is possible to reduce or eliminate a problem of corrosion of piping. Further, although the dissolving capability in the hydrothermal reactor itself is lowered, the oxidation vessel  22  performs the oxidation after the hydrothermal reaction. Therefore, as a whole, a sufficient dissolving is obtained. 
     The illustrated and described arrangement is disclosed in Japanese Patent Application No. 11-330000 filed on Nov. 19, 1999, the instant application claims priority of this Japanese patent Application, and the entire disclosure thereof is incorporated herein by reference.