JP2011167648A - Heating system of bioreactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating system of a bioreactor configured such that a total amount of a digestion gas generated in a digestion tank can be effectively used for generating electricity or the like and thereby, promoting the energy saving. <P>SOLUTION: The heating system of bioreactor includes: a digestion tank 3 performing anaerobic treatment of discharged water and organic sludge charged thereinto by digestant; a sludge storage tank 5 primarily storing the digestion sludge discharged from the digestion tank 3; a first heat exchanger 15 recovering the heat from the digestion sludge by exchanging heat with the sludge storage tank 5; and a second heat exchanger 19 constituting a heat pump cycle with the first heat exchanger 15 and heating the digestion sludge in the digestion tank 3 at the predetermined temperature by the recovered heat in the first heat exchanger 15. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heating system for heating a biological reaction tank in order to activate a biological reaction in wastewater treatment or sludge treatment for biological treatment.

  It is known that anaerobic bacteria usually have the highest activity at about 35 to 36 ° C. when anaerobic treatment of sewage sludge or waste water is performed. For this reason, it is made to heat so that the anaerobic processing tank (digestion tank) which processes sludge and waste_water | drain keeps about 35-36 degreeC. As a heating method, there is a method in which a heater wire is disposed in or around the digestion tank and electrically heated.

  Further, in the anaerobic treatment, organic substances contained in sludge and waste water are decomposed by anaerobic fermentation by methane bacteria, which are anaerobic bacteria, to generate digestion gas. Digestion gas contains methane gas as a main component, and there is a technique for recovering and burning the generated methane gas and using it for heating an anaerobic treatment tank (for example, Patent Documents 1 and 2).

JP 57-42400 A JP 60-216899 A

  However, since the amount of methane gas generated is determined by the organic matter concentration of the object to be treated and the decomposition rate of the organic matter by methane bacteria, the amount of methane gas recovered becomes unstable. For this reason, only about 70% of the digested gas generated in methane fermentation in a general sewage sludge digester is used for heating the digester. As a result, in methane fermentation using digesters, despite the advantages of low energy consumption and methane gas energy, it has been difficult to effectively use the obtained methane gas as another energy source. .

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a heating system for a biological reaction tank that can effectively use the total amount of digestion gas generated in the digestion tank for power generation and the like and can promote energy saving. It is said.

  In order to solve the above problems, the present invention provides a biological reaction tank that performs anaerobic treatment of input wastewater and organic sludge with digestive bacteria, and heat recovery from the digested sludge discharged from the biological reaction tank. A heat pump cycle is configured between the heat exchanger 1 and the first heat exchanger, and the sludge in the biological reaction tank is heated to a predetermined temperature by the heat recovered by the first heat exchanger. And a second heat exchanger.

  In another aspect of the present invention, a sludge storage tank that primarily stores the digested sludge discharged from the biological reaction tank is provided, and the first heat exchanger exchanges heat with the sludge storage tank. It is characterized by heat recovery from digested sludge.

  Furthermore, in another aspect of the present invention, a third heat exchanger that recovers heat from the desorbed liquid discharged from the digester is provided, wherein the second heat exchanger includes the first heat exchanger and A heat pump cycle is configured with the third heat exchanger, and the sludge in the biological reaction tank is brought to a predetermined temperature by the heat recovered by the first heat exchanger and / or the third heat exchanger. It is characterized by heating.

  Furthermore, in another aspect of the present invention, a dehydrator for dewatering the digested sludge after heat recovery by the first heat exchanger, a dryer for drying the dewatered sludge discharged from the dehydrator, and the organism And a digestion gas boiler for burning the digestion gas generated in the reaction tank and generating steam for drying the dewatered sludge of the dryer.

  According to the heating system of the biological reaction tank in the present invention, the heat recovered from the digested sludge by the heat pump cycle can be used for the heating of the biological reaction tank. As a result, the digestion gas (methane gas) generated in the biological reaction tank (methane fermentation tank) can be effectively used as energy for the engine for power generation, sludge drying and sludge incineration in the subsequent process, and energy saving of anaerobic fermentation In addition, the methane gas energy can be effectively utilized as the energy for sludge drying and sludge incineration, while reducing the consumption of fossil fuels, and the environmental load can be reduced by using biomass-derived energy.

The block diagram which shows 1st Embodiment of the heating system of the biological reaction tank which concerns on this invention. The energy balance of the Example by the conventional digester heating method is shown. 2 shows the energy balance of an embodiment according to the present invention. The block diagram which shows 2nd Embodiment of the heating system of the biological reaction tank which concerns on this invention. The block diagram which shows 3rd Embodiment of the heating system of the biological reaction tank which concerns on this invention. The block diagram which shows 4th Embodiment of the heating system of the biological reaction tank which concerns on this invention. The block diagram which shows 5th Embodiment of the heating system of the biological reaction tank which concerns on this invention. The block diagram which shows 6th Embodiment of the heating system of the biological reaction tank which concerns on this invention. The block diagram which shows 7th Embodiment of the heating system of the biological reaction tank which concerns on this invention.

  FIG. 1 shows a first embodiment of a biological reaction tank heating system according to the present invention.

  1st Embodiment which concerns on this invention is the sludge storage which stores the digestion sludge produced | generated by the digestion tank 3 which takes in the excess sludge in distribution waters, such as sewage, performs anaerobic microbial treatment, and digests, and the digestion tank 3 The combustion gas generated in the digestion tank 3 is combusted by the tank 5, the dehydrator 7 that removes moisture from the digested sludge once stored in the sludge storage tank 5, the dryer 9 that dries the dehydrated dehydrated sludge, and the digestion gas generated in the digestion tank 3. A digester gas boiler 11 that generates steam for drying the dewatered sludge by the dryer 9 is provided.

  On the other hand, as a heat circulation system constituting the heat pump cycle, a first heat exchange for recovering heat from the digested sludge is provided with an expansion valve 13 for expanding the circulating refrigerant and a coil 15b for circulating the digested sludge in the sludge storage tank 5. The compressor 15 for compressing the refrigerant heated by the heat recovered by the first heat exchanger 15 and the coils 19a and 19b for circulating the hot water between the digester tank 3 and compressed. The second heat exchanger 19 for warming the hot water with the refrigerant, the sludge circulation pump 21 for circulating the sludge between the sludge storage tank 5 and the first heat exchanger 15, the digester tank 3 and the second heat A hot water pump 23 that circulates hot water with the exchanger 19 is provided.

  Next, the operation of the first embodiment will be described.

In the digestion tank 3, the input excess sludge is biologically treated by the action of methane fermentation bacteria that are anaerobic bacteria. Thus, the surplus sludge is subjected to the anaerobic digestion treatment in the digestion tank 3, so that the organic matter in the surplus sludge is decomposed, and the digested gas mainly composed of methane gas and the solid matter of the surplus sludge that has been added are in volume. It is separated into digested sludge that has been reduced to about half the ratio.

  The sludge after the anaerobic digestion treatment is temporarily stored in the sludge storage tank 5 as digested sludge. The stored digested sludge is circulated between the coil 15 b disposed in the first heat exchanger 15 and the sludge storage tank 5 by a sludge circulation pump 21. In the heat exchanger 15, the circulating refrigerant evaporates by opening the expansion valve 13, takes heat from the circulating digested sludge, and the temperature of the digested sludge decreases. Thus, the heat in the digested sludge is recovered in the first heat exchanger 15.

  The evaporated refrigerant is compressed and liquefied by the compressor 17 and releases heat at that time. The warm water circulating through the second heat exchanger 19 and the digestion tank 3 is heated by the released heat, thereby heating the excess sludge in the digestion tank 3 and performing 35 anaerobic digestion treatment. It is kept at a temperature of about ~ 36 ° C. For example, in the 2nd heat exchanger 19, warm water is heated to about 75 degreeC, and 75 degreeC warm water heats the excess sludge in the digestion tank 3 via the coil 19a by the warm water pump 23, and promotes digestion. Although the temperature of the hot water used for heating has decreased to about 55 ° C., it is returned to the second heat exchanger 19 and heated again to about 75 ° C. via the coil 19b. By repeating such temperature circulation, the excess sludge in the digester 3 is maintained at a temperature of about 36 ° C. On the other hand, the liquefied refrigerant expands and evaporates again by the expansion valve 13 and takes heat from the digested sludge, and thereafter repeats the same operation.

  The digested sludge after heat exchange in the sludge storage tank 5 is sent to the dehydrator 7 and dehydrated. The dewatered sludge after dehydration is sent to the dryer 9, and after being dried, it is discharged as dry sludge.

  Digestion gas mainly composed of methane gas generated in the anaerobic digestion process is used as fuel for the digestion boiler 11. The digestion gas boiler 11 also uses heavy oil as auxiliary fuel.

  Thus, in the embodiment of the present invention, the digested sludge extracted from the digestion tank 3 is once received by the sludge storage tank 5, and the digested sludge is circulated between the sludge storage tank 5 and the first heat exchanger 15. . In the first heat exchanger 15, the heat retained by the sludge is absorbed from the sludge, the temperature is raised by a heat pump cycle, and the sludge in the digestion tank 3 is heated by the second heat exchanger 19.

  The work coefficient (COP) of the heat pump is about 3 to 6 due to recent technological advances, and the temperature of the recovered heat source, that is, the digested sludge is about 35 ° C. as in the present invention, so the COP is close to 6.

  A COP of 6 means that a heat energy of 6 kW can be obtained by applying a power of 1 kW to the heat pump, so that very efficient heating can be realized.

  By the way, comparing the fuel cost when heating by burning heavy oil and the power cost of the heat pump according to the present invention, the power cost according to the present invention can be reduced to 1/2 to 1/3 when using heavy oil. Become.

  FIG. 2 shows an energy balance according to a conventional digester heating method, and FIG. 3 shows an energy balance according to an embodiment of the present invention.

  As shown in FIG. 2, conventionally, the digestion gas is used only as boiler fuel for heating the digestion tank 3. Since the digester heating boiler is operated by feedback control, it becomes unstable due to fluctuations in the amount of digestion gas generated. For this reason, the operation must be performed with a sufficient amount of digestion gas used, and a large amount of excess digestion gas is generated. All of this excess digestion gas was discarded. In addition, a dryer boiler for drying digested sludge has been operated using heavy oil as fuel.

  On the other hand, as shown in FIG. 3, in the embodiment of the present invention, all the digestion gas is used as fuel for the boiler for the dryer, and the heating of the digestion tank 3 is provided by using a heat pump cycle. Therefore, as the energy consumption, only the electric power for operating the heat pump cycle and the heavy oil used as an auxiliary for the operation of the dryer boiler are sufficient. Comparing FIG. 2 and FIG. 3, it can be seen that the energy consumption is reduced to less than half in the conventional example and the example of the present invention. Moreover, since all the digestion gas is used and the change in the digestion gas generation amount is covered with heavy oil as an auxiliary, waste of surplus digestion gas can be eliminated.

  FIG. 4 shows a second embodiment of the biological reaction tank heating system according to the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals.

  The second embodiment shown in FIG. 4 is shown in FIG. 1 in that the refrigerant is passed through the coil 15a disposed in the sludge storage tank 5 and the heat in the digested sludge is recovered directly through the coil 15a. This is different from the first embodiment.

  FIG. 5 shows a third embodiment of the biological reaction tank heating system according to the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals.

  In the third embodiment shown in FIG. 5, the refrigerant is passed through a coil 15a disposed in the sludge storage tank 5, and the heat in the digested sludge is recovered directly through the coil 15a. 1 is different from the first embodiment shown in FIG. 1 in that the refrigerant is passed through the coil 19a disposed therein and the digested sludge in the digester 3 is directly heated via the coil 19a.

  FIG. 6 shows a fourth embodiment of the biological reaction tank heating system according to the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals.

  In the fourth embodiment shown in FIG. 6, a heat exchanger 25 is disposed in the inlet side piping of the digestion tank 3, and the excess sludge is heated before being introduced into the digestion tank 3. In this case, the heat exchanger 25 can be constituted by a double pipe 25a through which the refrigerant passes through the central portion and excess sludge passes through the peripheral portion. The refrigerant compressed and liquefied by the compressor 17 releases heat by the heat exchanger 25, and the excess sludge passing through the double pipe by the released heat is heated to about 36 ° C. It is thrown. In addition, the point which makes a refrigerant pass through the coil 15a arrange | positioned in the sludge storage tank 5, and collect | recovers the heat | fever in digested sludge directly via the coil 15a is the same as that of 2nd Embodiment.

  In each embodiment described above, as in the first embodiment, the digestion gas generated in the digestion tank 3 can be effectively used as the energy for drying the sludge in the subsequent process, and while making use of the energy-saving property of anaerobic fermentation, By effectively using digestion gas energy as sludge drying and sludge incineration, the consumption of fossil fuels such as heavy oil can be suppressed, and the environmental load can be reduced by using biomass-derived energy.

  FIG. 7 shows a fifth embodiment of the biological reaction tank heating system according to the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals.

  In the fifth embodiment shown in FIG. 7, the heat exchanger 27 is directly arranged without arranging the sludge storage tank 5 in the outlet side pipe of the digestion tank 3, and the heat exchanger 27 discharges from the digestion tank 3. The heat is absorbed and recovered from the digested sludge. In this case, the heat exchanger 27 can be constituted by a double pipe 27a through which the refrigerant passes through the central part and the digested sludge passes through the peripheral part. This makes it possible to recover heat from the digested sludge with simple equipment. Other configurations are the same as those of the embodiment shown in FIG. 1 and FIG.

  FIG. 8 shows a sixth embodiment of the biological reaction tank heating system according to the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals.

  In each of the embodiments described above, heat recovery is intended only for digested sludge, but the sixth embodiment shown in FIG. 8 recovers heat from the desorbed liquid discharged from the digestion tank 3 together with the digested sludge. It is composed.

  That is, the heat exchanger 29 is disposed in the desorbed liquid discharge pipe, and the coil 29 a of the heat exchanger 29 is connected to the coil 15 a disposed in the sludge storage tank 5. In this case, like the coil 15a, the coil 29a can be constituted by a double pipe through which the refrigerant passes through the central portion and the desorbed liquid passes through the peripheral portion.

  Like the digested sludge, the desorbed liquid has a heat of about 35 ° C., and has been discharged to the water treatment facility as it is. According to the present embodiment, heat can be absorbed also from the desorbed liquid, so that further energy saving can be achieved.

  FIG. 9 shows a seventh embodiment of the biological reaction tank heating system according to the present invention. The same members as those in FIG. 1 are denoted by the same reference numerals.

  In the seventh embodiment shown in FIG. 9, the heat exchanger 31 is directly arranged to absorb and recover heat from the digested sludge without arranging the sludge storage tank 5 in the outlet side pipe of the digester 3. As in the sixth embodiment shown in FIG. 8, the heat exchanger 31 also recovers heat from the discharge pipe for the desorbed liquid. That is, the heat exchanger 31 is connected to the coil 31a composed of a double pipe through which the refrigerant passes through the central part and the digested sludge passes through the peripheral part, and the refrigerant passes through the central part. The coil 31b can be configured by a double pipe through which the desorbed liquid passes through the peripheral portion. This makes it possible to recover heat not only from digested sludge but also from the desorbed liquid with simple equipment, and to achieve further energy saving effects.

  As mentioned above, embodiment mentioned above is only an example for implement | achieving this invention. Although illustration is omitted, in the first to fourth embodiments, the sludge storage tank 5 is not necessarily an indispensable configuration, and may be any configuration that can recover heat from the digested sludge by a heat exchanger. Moreover, it is also possible to collect | recover heat | fever from the desorption liquid discharged | emitted from the digestion tank 3 with respect to the structure of 1st Embodiment-4th Embodiment. In addition, although each embodiment mentioned above showed the example which applied this invention to the digestive tank of a general sewage sludge, it is not necessarily a digester of a sewage sludge, For example, in methane fermentation tanks, such as UASB and digester There may be.

DESCRIPTION OF SYMBOLS 3 Digestion tank 5 Sludge storage tank 7 Dehydrator 9 Dryer 11 Digestion gas boiler 13 Expansion valve 15 1st heat exchanger 17 Compressor 19 2nd heat exchanger 21 Sludge circulation pump 23 Hot water pumps 25, 27, 29, 31 Heat exchanger

Claims (4)

A biological reaction tank that performs anaerobic treatment of the input wastewater and organic sludge with digestive bacteria,
A first heat exchanger that recovers heat from the digested sludge discharged from the biological reaction tank;
A second heat exchanger that constitutes a heat pump cycle with the first heat exchanger, and heats the sludge in the biological reaction tank to a predetermined temperature by heat recovered by the first heat exchanger; ,
A biological reaction tank heating system comprising: In the heating system of the biological reaction tank of Claim 1,
A sludge storage tank that primarily stores digested sludge discharged from the biological reaction tank,
The heating system for a biological reaction tank, wherein the first heat exchanger exchanges heat with the sludge storage tank to recover heat from the digested sludge. In the heating system of the biological reaction tank of Claim 1 or 2,
A third heat exchanger for recovering heat from the desorbed liquid discharged from the digester,
The second heat exchanger constitutes a heat pump cycle with the first heat exchanger and / or the third heat exchanger, and the first heat exchanger and / or the third heat exchanger. A biological reaction tank heating system, wherein the sludge in the biological reaction tank is heated to a predetermined temperature by the heat recovered in step (b). In the heating system of the biological reaction tank of any one of Claims 1 thru | or 3,
A dehydrator for dewatering the digested sludge after heat recovery by the first heat exchanger;
A dryer for drying the dewatered sludge discharged from the dehydrator;
A digestion gas boiler for burning the digestion gas generated in the biological reaction tank and generating steam for drying the dewatered sludge of the dryer;
A biological reaction tank heating system comprising:

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