JP5222317B2 - Heat exchanger having battery function and methane fermentation treatment system using the heat exchanger - Google Patents

Description

  The present invention relates to a heat exchanger having a battery function and a methane fermentation treatment system using the heat exchanger.

  Conventionally, methane fermentation treatment (anaerobic treatment) is performed using organic waste such as garbage, livestock manure, sewage treatment sludge, etc., and methane gas is purified from the generated biogas, which is a gas engine that is an energy conversion device, etc. The technology used as a fuel for is known. The biogas produced by methane fermentation of the organic waste described above includes about 50 to 60% by volume of methane, about 40 to 50% by volume of carbon dioxide, and about 0.3% by volume of hydrogen sulfide. Degree included.

  Here, if biogas containing sulfur is used as a fuel in a gas engine or the like provided in the latter stage, sulfur deposits in the piston or cylinder of the engine part, resulting in a decrease in engine efficiency or failure of the engine itself. Therefore, the biogas is passed through a desulfurization apparatus to remove the sulfur content in the hydrogen sulfide contained in the gas, so-called desulfurization, and then supplied as fuel to a gas engine or the like.

  As desulfurization methods, there are biological desulfurization methods using sulfur-oxidizing bacteria and the like, and desulfurization methods using metal catalysts (iron catalyst, etc.). However, in Patent Document 1, microorganisms (sulfur-oxidizing bacteria etc.) are supported on the working electrode, An ion permeable membrane is provided between the working electrode, for example, sulfurating gas by supplying hydrogen sulfide gas to the working electrode and supplying a counter electrode gas such as air or oxygen to the counter electrode (air electrode) and taking out electric power. The hydrogen battery technology is described (FIG. 1). Furthermore, Patent Document 1 describes that electric power can be taken out by supplying organic substance-containing water, alkali-containing water, or methane fermentation liquid in addition to hydrogen sulfide.

  On the other hand, in the methane fermentation treatment, a medium temperature methane fermentation method, a high temperature methane fermentation method, and an ultrahigh temperature methane fermentation method are known, but a medium temperature methane fermentation (optimum temperature 37 ° C.) is about 20 to 30 days. The high temperature methane fermentation (optimum temperature 55 ° C) is about 15 days, and the ultrahigh temperature methane fermentation (optimum temperature 65 ° C) is about 10 days. Methane fermentation and ultrahigh temperature methane fermentation tend to increase. And the present condition is that the methane fermentation liquid obtained by each fermentation method is utilized for liquid fertilizer etc., after removing a nitrogen component.

However, the methane fermentation broth obtained by the high-temperature methane fermentation method and the ultra-high temperature methane fermentation method has a high liquid temperature of about 50 to 65 ° C. A technique for effectively utilizing the amount of heat possessed has been desired.
In the technique described in Patent Document 1, only a technique for extracting electric power by supplying methane fermentation broth to the working electrode is described, and there is no technique for using the amount of heat possessed by the methane fermentation broth. Not listed. In addition, high cost and advanced technology are required to manufacture the air electrode.

JP 2006-159112 A

  The present invention has been made in view of such circumstances, and the object thereof is a methane fermentation liquid obtained by a methane fermentation treatment, in particular, a methane fermentation liquid obtained by a high temperature methane fermentation method or an ultrahigh temperature methane fermentation method. An object of the present invention is to provide a heat exchanger having a battery function capable of effectively using the amount of heat generated and collecting electric power, and a methane fermentation treatment system using the heat exchanger.

  In order to achieve the above object, according to a first aspect of the heat exchanger having a battery function according to the present invention, a diaphragm is provided between the bipolar plates, and one side divided by the diaphragm is anaerobic as a negative electrode active material. The aerobic treatment liquid is supplied as the positive electrode active material to the other side, and the aerobic treatment liquid is heated by the anaerobic treatment liquid.

  According to this aspect, the anaerobic treatment liquid is supplied as the negative electrode active material on one side, and the aerobic treatment product is supplied as the positive electrode active material on the other side. Since the heat treatment liquid has a higher temperature than the aerobic treatment product, heat exchange can be performed between the two, and power can be recovered.

  According to a second aspect of the heat exchanger having a battery function according to the present invention, in the first aspect, the anaerobic treatment is a methane fermentation treatment at 50 ° C. or higher.

  According to this aspect, in addition to the effect of the first aspect, the aerobic treatment product is heated with the amount of heat of the methane fermentation liquid obtained by methane fermentation treatment at 50 ° C. or higher, so-called high temperature methane fermentation or ultrahigh temperature methane fermentation. Therefore, it can be used effectively without waste. Moreover, if the temperature at the time of heat exchange is high, it is easy to improve the performance of the battery, and it is possible to increase the amount of collected power.

  According to a third aspect of the heat exchanger having a battery function according to the present invention, in the first aspect or the second aspect, the multipolar partition plate is made of carbon or iron, or a sheet-like material containing carbon or iron. It is characterized by comprising.

  According to this aspect, in addition to the effects of the first aspect or the second aspect, since the multipolar partition plate is made of carbon or iron, the thermal conductivity is good and heat is higher than those made of other materials. It has the effect that exchange efficiency is good. In addition, the same effect can be obtained when the bipolar plate is made of a sheet containing carbon or iron.

  The aspect of the methane fermentation treatment system according to the present invention is any one of the first aspect to the third aspect, upstream of the methane fermentation tank when the aerobic treatment product is put into the methane fermentation tank for methane fermentation treatment. After providing a heat exchanger having a battery function described in one, after exchanging heat between the methane fermentation liquid obtained by the methane fermentation treatment that is an anaerobic treatment and the aerobic treatment, The aerobic treatment product is configured to be charged into the methane fermentation tank.

  According to this aspect, when the processed aerobic treatment product having a low temperature is charged into the methane fermentation tank, the heat exchanger having the battery function according to any one of the first aspect to the third aspect is used. By exchanging heat between the aerobic processed product and the high temperature methane fermentation broth, which is an anaerobic processing liquid, the heat amount of the methane fermentation broth can be used effectively and the efficiency of methane fermentation is prevented from being reduced. be able to.

That is, when an aerobic treatment product (usually 15 to 20 ° C.) having a low temperature is subjected to a methane fermentation treatment, if it is put into a methane fermentation tank as it is, the temperature in the fermentation tank is lowered, and the original fermentation temperature is reduced by the amount of the lowered temperature. It is necessary to return (increase) the temperature in the fermenter. At this time, the lower the temperature of the aerobic treated product, the longer it takes for the temperature in the fermenter to return to the original temperature, and the efficiency of methane fermentation will decrease. Therefore, using the heat exchanger having the battery function according to any one of the first to third aspects, the heat amount of the methane fermentation broth is used for the temperature of the aerobic treatment product before being charged into the methane fermentation tank. And the fall of the efficiency of methane fermentation can be prevented by raising by heat exchange with an aerobic processed material.
As described above, this aspect has an effect of effectively using the amount of heat of the methane fermentation liquid, preventing the efficiency of the methane fermentation from being reduced, and collecting electric power.

The schematic block diagram of the methane fermentation system which is embodiment of this invention The enlarged view of the heat exchanger which has a battery function based on this invention Relationship between electric potential and current in anaerobic treatment liquid and aerobic treatment Schematic configuration diagram of a simple methane fermentation system that is an experimental device The figure showing the relation between time and current according to Experimental Example 1 The figure showing the relation between time and current according to Experimental Example 2

  Hereinafter, an embodiment of a heat exchanger having a battery function according to the present invention and a methane fermentation treatment system using the heat exchanger will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

[Embodiment]
FIG. 1 shows a schematic configuration diagram of a methane fermentation system using a heat exchanger having a battery function according to the present invention.

The methane fermentation treatment system of the present embodiment is a methane fermentation tank 3 for subjecting the aerobic treatment S and fermented material M that have been subjected to aerobic treatment and precipitated in the precipitation tank 2 to methane fermentation treatment (anaerobic treatment), And it comprises the heat exchanger 1 which has the battery function which can also collect | recover electric power, exchanging heat with the methane fermentation liquid L and the aerobic processed material S.
In addition, the desulfurization apparatus 4 for removing the sulfur content in the hydrogen sulfide contained in the biogas G1 generated in the methane fermentation tank 3 by the methane fermentation treatment is provided on the downstream side of the methane fermentation tank 3. Yes.

Examples of the aerobic treated product S used in this embodiment include activated sludge when aerobic treatment is performed on sewage by aeration, but the target of aerobic treatment is not limited to sewage. Includes organic waste such as livestock manure. In addition, the temperature of an aerobic processed material is about 15-20 degreeC normally.
Examples of the material to be fermented M include livestock waste, sewage treatment sludge (activated sludge), and green farm waste. Examples of livestock waste include manure of livestock (eg, pigs, cows, chickens, etc.), carcasses and / or processed products thereof. Green farm waste includes agricultural waste, food processing waste, and the like as household waste, as well as household waste.

  Methane fermentation can be applied to any of the so-called medium temperature type, high temperature type, and ultra-high temperature type. However, considering the efficiency of heat exchange between the methane fermentation liquid and the aerobic treatment, the high temperature type or the ultra high temperature type can be used. preferable.

  The methane fermenter 3 is constituted by a tank in which air is shut off in order to maintain the activity by the absolute anaerobic methane fermentation bacteria. Fermenter 3 has a solids concentration (usually in the range of 3 to 40% by weight) and fermentation temperature (usually about 32 to 37 ° C for medium temperature fermentation, about 52 to 55 ° C for high temperature fermentation, about 60 to 70 ° C for ultra high temperature fermentation. ), The shape and operating conditions vary. For example, in the case of a raw material having a high water content (up to a solid concentration of 10% by weight), a wet type complete mixing type fermenter is used.

  In the case of a raw material with a high water content (solids concentration up to about 10% by weight), a complete mixing system fermenter is used, and the residence time is about 20 to 30 days in a medium temperature methane fermenting bacterium (optimum temperature 37 ° C.). For high-temperature methane-fermenting bacteria (optimum temperature 55 ° C), the retention time (Retention Time) is about 15 days. For ultra-high-temperature methane-fermenting bacteria (optimum temperature 65 ° C), the retention time (Retention Time) is about 10 days. Is possible. In consideration of the efficiency of methane fermentation and the efficiency of heat exchange between the methane fermentation solution and the aerobic treatment product, it is preferable to perform methane fermentation using a high-temperature methane-fermenting bacterium or an ultra-high-temperature methane-fermenting bacterium having a short residence time.

  On the other hand, in the case of a raw material having a low water content (solids concentration of about 20 to 40% by weight), the solid content concentration of the object to be processed is set to 30 to 40% by weight so that the extrusion fermenter can be used. adjust. The residence time can be set similarly to the case of high water content. Further, in order to adjust the C (carbon) / N (nitrogen) ratio, some organic components can be introduced as needed.

  The methane fermentation tank 3 is provided with a temperature rise maintaining means 3 ', which may be any device capable of heating or keeping warm, and known ones such as a hot water heater can be used.

The biogas G1 produced by the methane fermentation process is sent to a desulfurization apparatus 4 for removing (desulfurization) sulfur in hydrogen sulfide contained in the biogas G1, and after desulfurization, purified methane gas is used as a gas engine or the like. Used for fuel
As the desulfurization apparatus 4, a known apparatus such as biological desulfurization or a packed tower using a metal catalyst such as iron can be used.

  FIG. 2 shows an enlarged view of the heat exchanger 1 having a battery function used in this embodiment.

The heat exchanger 1 includes a multipolar partition plate 102, a diaphragm 103 provided between the multipolar partition plates 102, a part (A) on one side where the multipolar partition plate 102 is divided by the diaphragm 103, and the other side A structure having the portion (B), so-called flow paths (A) and (B) is defined as one unit (cell), and the unit (cell) is stacked (stacked cell). Note that a current collecting plate 101 is provided on the stacked terminals and terminals.
The one side part (A) is supplied with a high-temperature methane fermentation liquor L as a negative electrode active material, and the other side part (B) is a low-temperature aerobic treated product S (for example, activated sludge) as a positive electrode active material. Is provided so that heat exchange is performed between the two and also has a battery function.
In this embodiment, the methane fermentation liquor L and the activated sludge S are supplied in a state of facing each other, but they may be supplied in parallel.

A known material can be used as the material of the bipolar partition plate 102, but carbon or iron having high thermal conductivity is preferable. Further, the multipolar partition plate may be in the form of a sheet, and in that case, a sheet-like material containing carbon or iron is preferable.
By using a material having high thermal conductivity for the bipolar partition plate, heat exchange can be performed between the units, so that the efficiency of heat exchange can be improved.

  As the diaphragm 103, it is possible to use a microporous membrane or an ion exchange membrane having a small pore diameter. The microporous membrane is less expensive than the ion exchange membrane, and it is preferable to use the microporous membrane in view of cost. In view of preventing the occurrence of an internal short circuit, an ion exchange membrane is preferable.

As the material of the current collector plate 101, the material of the bipolar partition plate can be used as it is, or a conductive substance such as a copper sheet can be used. Among them, an iron sheet or the like is preferable from the viewpoint of cost (price) because there is not much power taken out.
In this embodiment, three units are stacked. However, the number of stacked units can be appropriately set in consideration of the recovered power.

  The above-described anaerobic treatment liquid L heat-exchanged in the heat exchanger 1 is used for liquid fertilizer and the like through a nitrogen removal process, and the aerobic treatment product S is sent to the methane fermentation tank 3 and methane fermentation treatment (anaerobic treatment). Is done.

  Next, referring to FIG. 3, the high-temperature methane fermentation broth is supplied to one part (A) and the flow path (A) of each unit constituting the heat exchanger 1, and the other part (B). The relationship between the electric potential and current generated when a low-temperature aerobic treatment product (for example, activated sludge) is supplied to the flow path (B) will be described.

  Note that a silver-silver chloride electrode was used as the reference electrode in the measurement of the potential in FIG.

In (1) of FIG. 3, after inserting a carbon electrode in the methane fermentation liquid (anaerobic processing liquid) at the time of carrying out methane fermentation of the excrement of the milking cow, and changing an electric potential from the plus direction to the minus direction (arrow a Next, a graph showing the change in potential and the corresponding change in current when the potential is changed from the minus direction to the plus direction (arrow b) is described.
On the other hand, in (2), after inserting a carbon electrode into sewage sludge (aerobic treated product) obtained by aerobically treating sewage and changing the potential from positive to negative (arrow a ′), A graph showing a change in potential and a corresponding change in current when the potential is changed from the minus direction to the plus direction (arrow b ′) is described.

  Here, in the case of (1) which is the case of methane fermentation liquid, when the potential is changed from the plus direction to the minus direction (arrow a), the potential is also changed in the case of activated sludge (2) from the plus direction to the minus direction. The relationship between the potential and the current will be described by taking the case of changing to (arrow a ′) as an example.

Regarding (1), when the potential is changed from the plus direction to the minus direction (arrow a), a slightly convex portion appears in the vicinity of −0.4 V (X). That is, it means that the substance in the methane fermentation liquid was reduced around −0.4 V, and the flowing current changed.
On the other hand, for (2), when the potential is changed from the plus direction to the minus direction (arrow a ′), a downward convex portion (peak) appears near +0.35 V (Y). In other words, it means that the substance in the activated sludge is oxidized near +0.35 V, and the flowing current is changed.

  That is, in the methane fermentation broth, the substances in the methane fermentation liquor are reduced around −0.4V, and in the activated sludge, the substances in the activated sludge are oxidized around + 0.35V, and the current flowing through each changes. . Therefore, the methane fermentation liquor is supplied to the part (A) and the flow path (A) on one side of the heat exchanger 1 of the present invention shown in FIG. 2, and the part (B) and the flow path (B) on the other side are supplied. By supplying an aerobic treated product (for example, activated sludge), an electromotive force of about 0.75 V (0.4 V + 0.35 V) can be obtained.

In addition, when the potential is changed from the minus direction to the plus direction (arrow b) for the methane fermentation broth (1) and for the activated sludge (2), the potential is changed from the minus direction to the plus direction. The same can be said for the above (arrow a ′). That is, with respect to (1), an upward convex portion appears around −0.15 V (X ′). On the other hand, as for (2), a convex portion appears at around +0.6 V (Y ′).
Accordingly, the electromotive force obtained is about 0.75 (0.15 V + 0.6 V), which is the same as when the potential is changed from the plus direction to the minus direction (a, a ′).

  The substances contained in the methane fermentation broth and activated sludge that cause the oxidation-reduction reaction include polyphenols, quinones, coenzymes, etc., and these are included depending on the type of methane fermentation broth and aerobic treatment product. Types and ratios are different. Therefore, the electromotive force obtained will differ depending on the type of methane fermentation broth and aerobic treatment.

Hereinafter, the present invention will be described by experimental examples.
First, the apparatus used for the experiment will be described.
FIG. 4 (1) shows a schematic configuration diagram of a simple methane fermentation treatment system used in the experiment.
In addition, in order to understand the heat exchanger which is the characteristic of this invention easily, in FIG. 4, the part of heat exchanger 1 'is expanded and described.
Reference numeral 30 is a 1 L methane fermentation tank (anaerobic treatment tank), and reference numeral 20 is a 1 L activated sludge settling tank. The cylinder pump is 10 ml / min from each tank, and the heat exchanger 1 ' It is comprised so that a methane fermentation liquid and activated sludge can be sent into the flow path A and the flow path B. FIG.

The structure of the multipolar partition plate 102 ′ is shown in (2-1) of FIG.
The multi-pole partition plate 102 ′ includes a frame part F, a plate part C fitted into the frame part F, a pair of manifolds D provided above and below the frame part F, and one of the pair of manifolds D. And a slit E that allows the plate C to communicate with each other.
For the plate part C, a glassy carbon plate (effective area: vertical 80 mm × horizontal 50 mm) subjected to surface treatment with nitric acid having a length of 300 mm, a width of 200 mm, and a thickness of 1 mm is used.

(2-2) in FIG. 4 (2) shows the structure of an ion exchange membrane 103 ′ which is an example of a diaphragm.
As the ion exchange membrane 103 ′, a polystyrene sulfonic acid cation exchange membrane is used, and a pair of manifold holes D are provided on the upper and lower sides thereof at positions corresponding to the manifold D of the multipolar partition plate.

The heat exchanger 1 ′ used in this experiment is a unit (cell) having a structure in which the ion exchange membrane 103 ′ is provided between the above-described multipolar partition plates 102 to form the flow paths A and B. ) And a three-layer structure in which three of them are stacked.
Experiments were performed using the apparatus described above.

[Experiment 1]
Digested sludge as an anaerobic treatment liquid (methane fermentation liquid obtained by methane fermentation of milk cow's manure) having the characteristics described in Table 1, and activated sludge as an aerobic treatment product, respectively, Using a cylinder pump (flow rate: 10 ml / min) from the activated sludge settling tank 20, the digested sludge was sent to the flow path A of the heat exchanger 1 'and the activated sludge was sent to the flow path B of the heat exchanger 1'. In addition, the methane fermentation liquid and activated sludge that passed through each channel were returned to the methane fermentation tank 30 and the activated sludge settling tank 20 for reuse.
Thereafter, the electromotive force generated in the heat exchanger 1 ′ and the change in current with time change were measured. The results are shown in FIG.

  From Table 1, the temperature (starting temperature) before sending the activated sludge to the heat exchanger 1 ′ is 15 ° C., while the temperature before sending the digested sludge to the heat exchanger 1 ′ (starting temperature) is 55. The outlet temperature when passing through the heat exchanger 1 ′ is 27 ° C. for the activated sludge and 35 ° C. for the digested sludge, and the heat is appropriately exchanged.

On the other hand, the electromotive force generated when the heat exchange was performed was 0.9 V. Therefore, in addition to the heat exchange, the activated sludge having the characteristics described in Table 1 is used as the positive electrode active material and anaerobic. It was found that digested sludge, which is an aqueous treatment solution, functions as a negative electrode active material and can obtain an electromotive force of 0.9 V.
Further, in FIG. 5, it can be seen that a current of 5 to 6 mA flows until 10 hours have passed with respect to an electromotive force of 0.9 V (constant voltage), and 4.5 to 5.4 W of power can be recovered.

[Experiment 2]
As an anaerobic treatment liquid and an aerobic treatment product, digested sludge and an aerobic treatment product as an anaerobic treatment solution (methane fermentation solution when dairying dairy manure of milking cows) having the characteristics described in Table 2 It is the same as that of Experimental example 1 except having changed to manure of the milking cow of No. 1. The results are shown in FIG.

  From Table 2, the temperature before feeding the cow's manure to the heat exchanger 1 ′ (temperature at the start) is 15 ° C., while the temperature before sending the digested sludge to the heat exchanger 1 ′ (temperature at the start). Is 55 ° C. (high-temperature methane fermentation), and the outlet temperature when passing through the heat exchanger 1 ′ is 30 ° C. for the activated sludge and 32 ° C. for the digested sludge, so that heat is appropriately exchanged.

On the other hand, the electromotive force generated when the heat exchange was performed was 0.9V.
In FIG. 6, it can be seen that a current of about 17 mA flows until 10 hours have passed with respect to an electromotive force of 0.9 V (constant voltage), and about 15.3 W can be recovered as power.

Note that the current generated by the same electromotive force is different between Experimental Example 1 and Experimental Example 2 because of the difference in redox equivalents in the anaerobic processing solution and the aerobic processing product.
In Experimental Example 1, the redox equivalent of activated sludge is 10 meq / l, and the redox equivalent of digested sludge is 15 meq / l, whereas in Experimental Example 2, the redox of manure of milking cows is shown in Table 2. The equivalent is 30 meq / l, and the redox equivalent of digested sludge is 55 meq / l, which is much larger in Experimental Example 2 than in Experimental Example 1. That is, Experimental Example 2 shows that more substances that function as electrode active materials are included. For the above reasons, the generated current is different even with the same electromotive force.

  As described above, the present invention is an invention capable of recovering power while exchanging heat between the anaerobic treatment liquid and the aerobic treatment product.

1, 1 'heat exchanger, 2 sedimentation tank, 3 methane fermentation tank, 3' hot water heater,
4 Desulfurization equipment, 101, 101 ′, current collector plate 102, 102 ′, multipolar partition plate,
103, 103 'diaphragm

Claims (4)

  A diaphragm is provided between the bipolar plates, an anaerobic treatment liquid is supplied as a negative electrode active material to one side divided by the diaphragm, and an aerobic treatment product is supplied as a positive electrode active material to the other side, A heat exchanger having a battery function, wherein the temperature of an aerobic treatment product is raised by the anaerobic treatment liquid.   The heat exchanger having a battery function according to claim 1, wherein the anaerobic treatment is a methane fermentation treatment at 50 ° C. or higher.   The heat exchanger having a battery function according to claim 1 or 2, wherein the multipolar partition plate is made of carbon or iron, or a sheet-like material containing carbon or iron. Having heat exchanger.   A heat exchanger having a battery function according to any one of claims 1 to 3 is provided upstream of the methane fermentation tank when the aerobic processed product is charged into the methane fermentation tank for methane fermentation treatment. The methane fermentation liquid obtained by the methane fermentation treatment, which is an anaerobic treatment, and the aerobic treatment product are subjected to heat exchange, and then the aerobic treatment product is charged into the methane fermentation tank. A methane fermentation treatment system characterized by

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