JP2002153844A - Organic waste treatment method and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a versatile solid fuel even with organic waste having a low methane conversion rate, and to efficiently utilize the energy generated in each processing step. It is intended to provide a method and a system thereof. SOLUTION: A methane fermentation tank 2 for subjecting organic waste 10 to methane fermentation, a dehydration means 16 for dehydrating digested sludge 15 discharged from the methane fermentation tank 2, and a drying means 5 for adjusting the water content of the sludge. And a solidification means 6 for forming dried sludge to produce a solid fuel 24. A compost fermenter for aerobic fermentation of dehydrated digested sludge 15 before the drying means 5. The fermentation heat generated in the compost fermenter 4 is recovered by a heat exchanger 8 and used for heating the compost fermenter 4, and power is generated using methane gas generated by the methane fermentation as fuel. And the exhaust gas generated by the power generation is used for drying the digested sludge 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste treatment system for treating organic wastes such as garbage and sludge having different properties and concentrations by subjecting them to methane fermentation. The present invention relates to a method for treating organic waste provided with a cogeneration system for recovering valuable resources from digested sludge, converting these valuable resources to electric energy, heat energy, and the like and using the system in the system.

[0002]

2. Description of the Related Art Conventionally, the ratio of organic waste in industrial waste and general waste, such as wastewater treatment sludge and garbage from factories, is very high, and these organic wastes are incinerated,
It is processed by fertilizer, fuel, etc. One of the important issues in treating organic waste generated in large quantities is to reduce the amount of waste, and as a treatment method that aims to reduce the amount of waste by collecting valuable resources in the waste,
Japanese Patent Application Laid-Open No. 10-316982 proposes a method for producing a solid fuel that can be burned while maintaining a stable calorific value from organic waste with simple equipment and at low cost. As shown in FIG. 5, pre-treatment 020 is performed from general waste including garbage to separate hardly decomposable impurities 025, and then anaerobic treatment 021 is performed. 022, the separated digested sludge 027 was mixed with the above-mentioned contaminants, and the water content was adjusted 023.
As a solid fuel, and the biogas generated by the anaerobic digestion is desulfurized to be effectively used as electric power.

[0003] As described above, various technologies have been proposed for performing a rational waste treatment for recovering valuable resources in waste by providing a solid fuel production process in an organic waste treatment process. There is a problem that there are few kinds of organic wastes that can be applied in order to produce the organic waste. JP-A-10-
No. 316982 targets only high-calorie waste such as garbage and the like, and only those having a high methane conversion rate of about 80% can be applied. On the other hand, ordinary organic waste such as sludge, night soil, livestock manure, etc., has a methane conversion rate of about 50%, so energy cannot be recovered to the extent that the water content of solid fuel can be adjusted, and this method is applied. Can not.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 2000-167523, a method for producing compost from organic waste as valuable material has been proposed. Such a processing system is configured to produce compost from waste and to recover and use energy generated in a processing step. In FIG. 4, crushing means 01 and 02 for making garbage into a slurry, a bioreactor 05 for anaerobic-treating the slurry into a biogas G and a digestive liquid E, a fuel cell 010 using the biogas G as a raw material, A secondary processing facility 06 for producing compost from the liquid E, so that a part of the electric power of the fuel cell 010 can be supplied into the processing system.

A fuel cell used in such a processing system is a power generation system which has begun to be widely used in recent years because it has a high power generation efficiency, is excellent in environmental friendliness, and can utilize waste heat.
The principle is to purify electrical energy by electrochemically reacting hydrogen extracted from raw materials such as natural gas and biogas with oxygen in the air. Since a fuel cell generates heat in addition to electricity, a very efficient cogeneration system can be constructed by utilizing heat energy.

[0006]

However, in the above-mentioned prior art, compost is produced from digested sludge generated by anaerobic treatment, but the produced compost has problems in distribution, and the operation of the equipment is not always required. It is not done smoothly. This is because there is a seasonal variation in the demand for compost, the unit price per unit weight is low, and the bulk is bulky, causing problems in transportation and sales channels. However, in the production of a highly versatile solid fuel, the waste that can be treated is limited to high calorie with a methane conversion rate of about 80%, as described in JP-A-10-316982. Generally, it is difficult to use widely.

In view of the above-mentioned problems of the prior art, the present invention can produce a highly versatile solid fuel even with organic waste having a low methane conversion rate, and can efficiently use energy generated in each processing step. It is an object of the present invention to provide a waste treatment method provided with a co-generation system that is frequently used and a system thereof.

[0008]

According to the present invention, in order to solve the above-mentioned problems, an organic waste such as garbage and sludge is subjected to methane fermentation and the methane fermentation is generated by the methane fermentation. After dewatering the digested sludge, drying and shaping, in the method of treating organic waste to produce a solid fuel, while performing the compost fermentation on the dehydrated digested sludge, condensing the steam generated by the compost fermentation, The method is characterized in that the latent heat of condensation is recovered and used for heating the compost fermentation.

As described above, by performing compost fermentation in the process of producing solid fuel, solid fuel can be produced even from organic waste having a high water content such as sludge and night soil and having a low methane conversion rate. This is because the moisture in the waste evaporates due to the heat of fermentation during the compost fermentation and is dehydrated, whereby the water content is adjusted. In addition, the compost fermentation decomposes spoilage components in the waste to produce a highly conserved solid fuel. In addition, since an adhesive component that aggregates the soil is generated by the fermentation, the solidification property is improved and it is not necessary to add an additive. further,
By condensing steam at approximately 70 ° C. generated by compost fermentation, recovering the latent heat of condensation by heat exchange, and converting it into heated air at approximately 60 to 70 ° C. which is supplied during compost fermentation, wastes energy. And the system can be operated with high efficiency.

[0010] Further, the invention according to claim 2 generates electric power by using methane gas generated by the methane fermentation as at least a part of fuel, and uses exhaust gas generated by the electric power generation for drying the digested sludge. It is characterized by the following. The present invention utilizes methane gas generated in the methane fermentation effectively, and uses methane gas as a fuel to generate electric power by a gas engine, a gas turbine, or the like, or uses the methane gas as a raw material to generate electric power by a fuel cell, thereby converting methane gas into electric power. It can be converted to energy and replenish power in such processing systems. Thereby, a very energy-efficient waste treatment system can be provided.

Further, when a solid electrolyte type or other fuel cell is used for the power generation, the dried sludge is gasified by high-temperature steam discharged from the fuel cell, and the fuel gas generated by the gasification is used for the fuel cell. Good. This is because the solid oxide fuel cell can obtain high-temperature steam of about 1000 ° C. as a heat source, and convert the solid fuel generated by the compost fermentation into fuel gas of the fuel cell using the steam. Therefore, electric power can be supplied to the fuel cell without externally supplying fuel.

[0012] As a system for effectively realizing the inventions of the first and second aspects, the invention of the fourth aspect includes a methane fermentation tank for performing methane fermentation on organic waste such as garbage and sludge, and Organic waste having dewatering means for dewatering digested sludge discharged from a methane fermentation tank, drying means for adjusting the moisture content of the dewatered sludge, and solidifying means for forming dried sludge to produce a solid fuel In the material processing system, a compost fermenter for performing aerobic fermentation of the dehydrated digested sludge is provided before the drying means, and the heat of fermentation generated in the compost fermenter is recovered by a heat exchanger, and the compost fermentation is performed. It is used for heating the tank.

According to a fifth aspect of the present invention, a solid oxide fuel cell is used as the fuel cell. By introducing these systems, it is possible to reduce the amount of waste discharged from each region and office, and to build a decentralized energy system, which generates waste from each region and office. Energy can be generated semi-permanently as long as possible.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the invention thereto, unless otherwise specified, and are merely illustrative examples. Not just. FIG. 1 is a flowchart showing a waste treatment system according to a first embodiment of the present invention, FIG. 2 is a flowchart showing a waste treatment system according to a second embodiment, and FIG. 3 is a diagram showing the waste treatment system in FIG. 1 shows an overall configuration diagram showing an energy balance.

In the first embodiment shown in FIG. 1, reference numeral 1a denotes a cogeneration power generator equipped with a gas engine;
Is a methane fermentation tank, 3 is a dehydration means, 4 is a compost fermentation tank for performing activated sludge treatment, etc., 5 is a drying means, 6 is a solidification means,
Reference numeral 7 denotes methane purification means, and reference numeral 8 denotes a heat exchanger provided in the compost fermenter. In the present embodiment, the organic waste that is the substance to be treated is not particularly limited as long as it contains an organic substance, such as high-calorie waste such as garbage or high-moisture waste such as sludge and human waste. . The cogeneration power generation device 1a is a power generation device configured to be able to recover electric energy or heat energy such as exhaust gas using methane gas, fuel gas, or the like as fuel. In the present embodiment, a gas engine is used for the power generation device 1a, a driving device such as an engine or a turbine is provided, and heat such as exhaust gas and cooling water discharged from the driving device is collected and obtained by the power generation device. It is configured so that it can be used in such a system as thermal energy together with the generated electric power. The power generation device is not limited to a gas engine, and may be any device having a function of generating power from fuel gas such as a fuel cell.

The methane fermentation tank 2 is a well-known technique, and thus a detailed description is omitted. However, as a suitable condition for increasing the methane gas yield, it is preferable to add an animal and plant residue to the waste to be input to form a slurry. . In addition, since methane fermentation requires a long time, it is desirable to maintain the gasification temperature at about 35 to 55 ° C. in order to promote fermentation. In addition, the digested sludge is partially left without being extracted, and the inside of the methane fermentation tank 2 is configured to be sufficiently mixed. In the methane fermenter 2, the compost fermenter 4 provided on the downstream side is maintained at approximately 60 to 70 ° C., and aerobic fermentation is performed. The methane fermentation tank 2 is provided with a heat recovery heat exchanger 8 and is configured to return the heat energy of the high-temperature steam generated in the compost fermentation tank 4 to the compost fermentation tank 4 again.

The flow of the first embodiment will be described with reference to FIG. First, the organic waste 10 is supplied to the methane fermentation tank 2.
And gasified by anaerobic bacteria such as methane bacteria present in the methane fermentation tank 2. Since the generated methane gas 12 contains impurities such as hydrogen sulfide, ammonia, and chloride, the impurities in the methane gas 12 are removed by the methane gas purification means 7 having a desulfurization device and the like. Is supplied to the cogeneration power generator 1a.

On the other hand, the digested sludge 15 generated by the methane fermentation 2 is dewatered by the dewatering means 3 and the dewatered cake 16
Is introduced into the compost fermenter 4. The compost fermenter 4 is maintained at approximately 60 to 70 ° C., where the dehydrated cake 16 is sufficiently fermented by aerobic bacteria to produce compost 17. The compost fermenter 4
Then, during the fermentation, steam 19 of about 70 ° C. is generated, so the steam is condensed in the heat exchanger 8 to collect latent heat of condensation, and the air 20 sent to the compost fermenter 4 is used for fermentation. Heat to a suitable temperature, approximately 60-70 ° C. As a result, the compost fermenter 4 is always maintained at approximately 60 to 70 ° C., and the inside of the tank becomes at least three times the steam pressure at room temperature.
The moisture in the dewatered cake is removed by air as saturated steam in the exhaust gas 28 discharged from the compost fermenter 4. The compost 17 discharged from the compost fermenter 4 is further dried by the drying means 5, formed and solidified by the solidification means 6, and used as a solid fuel (RDF) 24.

The solid fuel 24 thus produced is
Because of the compost fermentation, putrefactive components in the solid fuel are decomposed to improve preservability, and the fermentation produces a highly adhesive component that aggregates the soil, improving solidification. There is no need to add additives. Furthermore, since the moisture in the waste evaporates due to the heat of fermentation in the compost fermenter 4, solid fuel can be produced even from organic waste having a low methane conversion rate.

The methane gas 13 generated and purified in the methane fermenter 2 is supplied to the cogeneration power generator 1.
a, power is generated using the methane gas 13 as fuel. A part of the electricity 22 generated here is supplied to the methane fermentation tank 2, the dehydration means 3, the compost fermentation tank 4, the drying means 5,
The remaining electricity 23 is supplied to the solidification means 6 and used in the waste treatment system 9, and the remaining electricity 23 is transmitted to the outside. Further, in the cogeneration power generation device 1a, exhaust gas is generated together with generation of electric power. By sending a part of the exhaust gas to the drying unit 5, the exhaust gas is directly and effectively used without disposing a boiler or the like. be able to. In addition, other heat energy such as exhaust gas, water vapor, and hot water can be converted into electric power by heating equipment in the processing system 9 or by attaching a gas engine or the like, and can be used inside or outside the system.

Next, the flow of the second embodiment shown in FIG. 2 will be described. In this embodiment, as in the first embodiment, methane fermentation 2 and dehydration 3 are performed on the organic waste 10 to perform compost fermentation. Then, the produced compost 17 is dried to produce a dry cake 18, which is converted into a fuel gas 27 by the dry cake 18 gasifier 25,
The methane gas 13 from the methane fermenter 2 is used as a raw material for the cogeneration power generator 1b. In the present embodiment, a solid oxide fuel cell is used for the cogeneration power generator 1b. When the fuel cell is used, hydrogen extracted from methane gas 13 as a raw material is electrochemically reacted with oxygen in the air in the power generator 1 to obtain electric energy and heat energy. Such a fuel cell has a laminated structure in which positive and negative thin electrode plates sandwich a layer containing an electrolyte, and a reaction occurs when hydrogen and oxygen pass therethrough. Thereby, a very high power generation efficiency can be obtained. In addition, the fuel cell may be appropriately used depending on the type of electrolyte, such as a phosphoric acid type, an alkaline type, and a solid electrolyte type.

The solid oxide fuel cell can obtain high-temperature steam of about 1000 ° C. as a heat source.
Synthetic fuel gas can be easily generated by the following reaction using the high-temperature steam.

Dried cake (organic matter) + high temperature steam (H ₂
O) + oxygen (O ₂ ) → CO + H ₂ + CO ₂ + CH ₄ + H
₂ O As described above, it is possible to easily generate a fuel gas by using a solid oxide fuel cell, and to provide an economical waste treatment system with high power generation efficiency even in an area where the demand for solid fuel is small. Can be.

FIG. 3 shows the energy balance of the waste treatment system according to the first embodiment.
This means that the amount of waste input to the processing system 9 is 252.
The energy balance at the time of 5 t / day (100 t / day by dry weight) is shown.
95 GJ / day, and 9 of them in methane fermentation tank 2
22 GJ / day is methane gas 12, 1048 GJ / day is digested sludge 15, and the rest is discharged as waste heat. The power consumed in the methane fermenter 2 is the largest in the system, 28
7 GJ / day. Next, the dehydrated cake 1 that has been subjected to the dehydration treatment 3
In the compost fermenter 4 for composting 6, the fermentation heat generated by the fermentation is 523 GJ / day, and the sum of the latent heat of evaporation and the sensible heat evaporated by the fermentation heat is 600 GJ / day. 115 GJ
/ Day.

In the compost fermenter 4, 52
A compost 17 having a calorific value of 4 GJ / day is generated. 99G from the cogeneration power generator 1a
J / day of exhaust gas is supplied to the drying means 5, whereby the compost 17 generates 94.2 GJ / day of steam. The dried cake produced by the drying means is 524 GJ /
It has a daily calorific value, and is compressed to produce a solid fuel 24 having the same calorific value. The power generation efficiency of the cogeneration power generation device 1a using the gas engine is approximately 30%, and the engine cooling water, the exhaust heat boiler,
Since the heat recovery rate for dry use and the like is approximately 51% and the exhaust heat is approximately 19%, the electric energy generated by the power generation device 1 is 27%.
7 GJ / day, the recovered heat energy is 472 GJ / day.
When a fuel cell is used, the power generation efficiency is approximately 40%,
The heat recovery rate is approximately 50%, and the exhaust heat is approximately 11%. The power energy generated by the power generator 1 is 369 GJ / day, and the recovered heat energy is 454 GJ / day.

As described above, 2095 GJ / day of waste input into the system is obtained as 868 GJ / day as valuable resources such as solid fuel, electric energy, heat energy and the like, and heat of compost fermentation, heat of methane fermentation tank, 1226GJ as system exhaust heat such as methane fermentation heat and drying means exhaust heat
/ Day, the system can be operated with very high energy efficiency by effectively utilizing the waste heat of these systems in addition to the electric energy and heat energy.

[0027]

As described above, according to the present invention, since a compost fermenter is provided, a solid fuel can be produced even in an organic waste having a high water content and a low methane conversion rate. Since the fuel has high solidification properties, it is not necessary to use an additive, and the putrefactive component is decomposed, so that a solid fuel having high storage stability can be obtained. In addition, the recovered heat from the compost fermenter is used for heating the fermenter, and the exhaust gas from cogeneration is used as a drying heat source, so that rational exhaust heat can be used. Further, by using a solid oxide fuel cell, a system with high power generation efficiency and economic merit can be provided even in an area where the demand for solid fuel is small.

As described above, such a treatment system can be applied to various organic wastes and has very high energy efficiency, so that a system suitable for various business establishments can be provided. In addition, by introducing these systems, it is possible to reduce the amount of waste discharged from each region and office, and to build a decentralized energy system. Energy can be produced semi-permanently as long as

[Brief description of the drawings]

FIG. 1 is a flowchart showing a waste disposal system according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a waste disposal system according to a second embodiment of the present invention.

FIG. 3 is an overall configuration diagram showing an energy balance of the waste treatment system in FIG.

FIG. 4 is an overall process diagram showing a compost manufacturing / energy recovery system according to the related art.

FIG. 5 is an overall process diagram showing an example of a solid fuel production method according to a conventional technique.

[Explanation of symbols]

 1a, 1b Cogeneration power generator 2 Methane fermenter 3 Dehydration means 4 Compost fermenter 5 Drying means 6 Solidification means 7 Methane purification means 8 Heat exchanger 9 Waste treatment system 10 Organic waste 12 Methane gas 15 Digested sludge 21 Exhaust gas 22 Electricity 24 RDF 25 Solidification means 26 High temperature steam 27 Exhaust gas 28 Exhaust gas

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C02F 11/12 C10L 5/46 5H027 C05F 9/00 H01M 8/06 R C10L 5/46 8/10 H01M 8/06 B09B 3/00 ZABC 8/10 D (72) Inventor Hideaki Aiki 1-1-1, Wadazakicho, Hyogo-ku, Kobe-shi, Japan Inside Kobe Shipyard, Mitsubishi Heavy Industries, Ltd. (72) Inventor Yasuhiro Konno Hyogo-ku, Kobe-shi 1-1-1 Wadazakicho Sanshi Heavy Industries Co., Ltd. Kobe Shipyard F-term (reference) 4D004 AA02 AA03 AB01 BA03 CA13 CA14 CA18 CA19 CA22 CA42 CB04 CB06 CB36 CB44 CC07 4D059 AA01 AA07 BA05 BA15 BA31 BA34 BA41 BA56 BD00 BE01 BK08 BK12 CA04 CA08 CA10 CA11 CA12 CB11 CC03 EB10 4H015 AA01 AA02 AB01 BA09 BA12 BA13 BB03 BB11 CB01 4H061 AA02 AA10 CC47 CC51 CC55 EE66 GG18 GG19 GG48 GG49 GG70 5H026 AA06 5H0DD A06 DD06

Claims (5)

[Claims] 1. Organic waste such as garbage and sludge is subjected to methane fermentation. Digested sludge generated by the methane fermentation is dehydrated, dried and molded to produce a solid fuel. In the treatment method, the dewatered digested sludge is subjected to compost fermentation, steam generated by the compost fermentation is condensed, and the latent heat of condensation is recovered and used for heating the compost fermentation. How to handle things. 2. The method according to claim 1, wherein the methane gas generated by the methane fermentation is used as at least a part of fuel to generate power, and exhaust gas generated by the power generation is used for drying the digested sludge. Organic waste treatment method described 3. A methane fermentation tank for performing methane fermentation on organic wastes such as garbage and sludge, a dewatering means for dewatering digested sludge discharged from the methane fermentation tank, and a water adjustment of the dewatered sludge. In a system for treating organic waste having drying means for performing and solidifying means for forming dried sludge to produce a solid fuel, a compost for performing aerobic fermentation of dehydrated digested sludge before the drying means. An organic waste treatment system comprising a fermentation tank, wherein fermentation heat generated in the compost fermentation tank is recovered by a heat exchanger and used for heating the compost fermentation tank. 4. A power generator using a fuel cell using methane gas generated in the methane fermentation tank as fuel, and high-temperature exhaust gas discharged from the power generator is used for drying dehydrated sludge by the drying means. The organic waste treatment system according to claim 3, wherein 5. The organic waste treatment system according to claim 4, wherein a solid oxide fuel cell is used as the fuel cell.