RU2838589C2 - System for production of biogas using liquid mixture of water purified from liquid after splitting and dry organic substance - Google Patents

Abstract

FIELD: biogas production.

SUBSTANCE: group of inventions relates to production of biogas using a liquid mixture of water purified from liquid after splitting and a dry organic substance. System comprises a tank for liquid mixture 27 for mixing and containing water purified from liquid after splitting and organic dry substance, tank for fermentation 11 of the mixture taken from said tank for liquid mixture 27. System comprises settling tank 37 for separation of liquid after fermentation into solid and liquid phases, and subsequent direction of water into tank for liquid mixture 27, and pulp – into storage tank 13. System comprises gas holder 12 for storage of methane gas taken from said fermentation tank 11, and tank for storage 13 of split sludge and pulp. Deodorising furnace 14 is configured to use methane gas taken from gas holder 12 as fuel. Electric power generation boiler 15 is configured to use methane gas from gas holder 12 as fuel. Dryer 16 is configured to dry food wastes, as well as said split sludge and pulp taken from storage tank 13.

EFFECT: increase of production, increase of dry substance production and rate of resources processing.

6 cl, 2 dwg

Description

[Field of technology]

The present invention relates to a system for producing biogas using a liquid mixture of water purified from a liquid after splitting and dry organic matter, more particularly, to a system with maximum biogas production by mixing dry nutrient in a predetermined ratio with water purified from a liquid after splitting, taken from an anaerobic digestion tank, which is a preliminary process of a wastewater treatment system, and then adding the resulting liquid mixture to a digestion tank.

[State of the art]

In recent times, modern society characterized by mass production and mass consumption has caused serious environmental pollution problems due to the large amount of waste. Typical environmental pollution problems include soil and water pollution due to large amounts of waste and air pollution due to mass energy consumption.

Accordingly, in recent years, the method of drying organic waste such as food waste and using it as a renewable energy source has been in the spotlight. By drying organic waste in this way to reduce the moisture content, it is possible to obtain excellent solid fuel with a calorific value of 3,000 to 4,000 kcal/kg or more.

The organic waste drying equipment generally includes direct and indirect drying method dryer using hot air and steam, electromagnetic wave drying method dryer using microwave and the like.

In the process of drying waste using this equipment, a high concentration of condensed gas containing a large amount of moisture and oil is inevitably generated. In order to treat the condensed gas thus obtained, a condenser is installed at the outlet line of the dryer, and the high concentration of condensed waste water such as oil contained in the condensed gas is separated and removed by means of the condenser thus installed.

Generally, the gas released during the drying process of organic waste is sent to the condenser and undergoes condensation processing. The condensed gas generated after condensation processing is burned in the deodorizing incinerator, which is the after-treatment, and the condensed high-concentration wastewater is discharged outside or treated in its own wastewater treatment plant.

However, since a significant amount of highly concentrated food wastewater generated during the pre-treatment of organic waste is discharged to the outside and treated in external treatment facilities, this results in significant costs.

That is, the food wastewater discharged during the food waste pre-treatment process not only has a high concentration, but also has a large discharge volume, which leads to an increase in the cost of treating such volumes.

For example, at present, a large amount of food wastewater generated in the pre-treatment process of organic waste such as food waste is mainly treated in an external treatment plant after removing oil content in a three-phase separator.

Because this food wastewater contains high concentrations of organic matter (biochemical oxygen demand (BOD), biochemical oxygen demand (COD)), organic acids and SS (suspended solids) components, the concentrations of TN (total nitrogen) and TD (total dissolved solids) of treated water are high when the treated water undergoes aerobic (biological) treatment. Therefore, it is costly and difficult to treat food wastewater to or below the permissible discharge standard.

[Documents from the state of the art]

[Patent documents]

(Patent Document 1) Laid-open publication of Korean Patent Application No. 10-2019-0050474

(Patent Document 2) Laid-open publication of Korean Patent Application No. 102019-0050477

(Patent Document 3) Registered Korean Patent No. 10-1751502

(Patent Document 4) Registered Korean Patent No. 10-1845457

[Brief description of the invention]

[Problems solved by the invention]

Accordingly, taking into account the above circumstances, the present invention is intended for producing a large amount of biomass for use as an energy source, which is formed by introducing highly concentrated organic matter into the biomass in combination with dry nutrient obtained in the process of drying food waste in an anaerobic digestion tank, with its subsequent decomposition and decomposition in the anaerobic digestion tank.

Therefore, the object of the present invention is to introduce a new type of system in which water purified from the digestion liquid withdrawn from the anaerobic digestion tank after digesting and decomposing the highly concentrated organic matter in combination with the dry nutrient in the anaerobic digestion tank into solid and liquid phases in a settling tank is separated, and then the purified water is mixed again with the dry nutrient at a predetermined ratio and introduced into the digestion tank again, and also introduced the digested sludge and pulp into a drying equipment, thereby obtaining a system for producing biogas using a liquid mixture of water purified from the digestion liquid and the dry nutrient, which can maximize the production of biogas (methane) to reduce energy costs, increase the production of dry matter to reduce waste disposal costs and increase the rate of resource recycling.

[Means of solving the problem]

In order to achieve the above object, the system for producing biogas using a liquid mixture of water purified from the liquid after splitting and a dry nutrient provided by the present invention has the following characteristics.

A system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient comprises: a liquid mixture tank configured to mix and contain water purified from a liquid after splitting and a dry nutrient; a fermentation tank configured to store and decompose the resulting liquid mixture of water purified from a liquid after splitting and a dry nutrient taken from said liquid mixture tank; a settling tank configured to separate the liquid after splitting taken from the fermentation tank into a solid and a liquid phase, and then direct the water purified from the liquid after splitting into said liquid mixture tank and direct the pulp into a storage tank; a gas holder configured to store methane gas taken from the fermentation tank; a storage tank configured to store the digested sludge withdrawn from the digestion tank and the pulp withdrawn from the settling tank; a deodorizing furnace configured to use the methane gas withdrawn from the gas holder as a fuel; a power generation boiler configured to use the methane gas withdrawn from said gas holder as a fuel; and a dryer configured to dry the food waste and the digested sludge and pulp withdrawn from said storage tank.

Therefore, said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient is characterized as follows: water purified from a liquid after splitting obtained by separating a liquid after splitting withdrawn from said fermentation tank after separation into solid and liquid phases and said dry nutrient are mixed at a predetermined ratio in a mixing tank, then said mixture is introduced into said fermentation tank for processing; methane gas obtained in said fermentation tank is used as fuel for said deodorizing furnace and for said boiler for generating electricity; and said split sludge withdrawn from said fermentation tank and said pulp withdrawn from a settling tank are introduced into said dryer for drying.

Thus, the said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient may include: as a means for cooling condensed wastewater taken from a condensing condenser, which is configured to condense exhaust gases taken from a dryer, a heat exchange condenser through which condensed wastewater flows in and out, wherein heat exchange between said condensed wastewater and recycled water occurs inside it; a recycled water tank configured to store said recycled water supplied to said heat exchange condenser; a recycled water pump configured to pump said recycled water; and a recycled water cooling tower configured to cool said recycled water taken from said heat exchange condenser and then direct it to said recycled water tank.

Said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient may include: a condensing condenser configured to condense said exhaust gases collected from said dryer; a condensed wastewater tank configured to store said condensed wastewater collected from said condensing condenser; a wastewater treatment plant that comprises a digestion tank, an aeration tank, a settling tank, and an improved treatment tank as a means for treating said condensed wastewater obtained after condensing the wastewater collected from the condensed wastewater tank, cooled once more in the cooling condenser; and a purified water tank configured to store said purified water withdrawn from said wastewater treatment plant and then feed it to said condenser for condensing for use as recycled water, therefore, the condensed wastewater withdrawn from said condenser for condensing can be converted into final purified water by means of an integrated wastewater treatment process, and the resulting purified water can be reused as recycled water for condensing said exhaust gases in said condenser for condensing.

In addition, said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient may include: a water feed tank configured to store steam condensate collected from said dryer and process water supplied from a water supply; and a water feed line connecting said water feed tank and a deodorizing furnace; and a water feed pump installed on the water feed line, therefore, said steam condensate collected from said dryer can be used as a water source for said deodorizing furnace.

In a preferred embodiment, the steam generated in the power generation boiler may be fed to said dryer and used for independent use, such as drying food waste, digestate sludge and pulp, or for sale to a third party.

[Beneficial technical results]

The said system for producing biogas using a liquid mixture of water purified from the liquid after splitting and a dry nutrient, provided by the present invention, provides the following technical results.

Firstly, by applying a new food waste processing system in which the digestion liquid withdrawn from said anaerobic digestion tank, which is a preliminary process of a wastewater treatment system, and the dry nutrient are mixed at a predetermined ratio and then introduced into said digestion tank to produce methane gas, which can be used as a fuel for said deodorizing furnace and a fuel for a boiler for generating electricity, and also, the digested sludge withdrawn from said anaerobic digestion tank and the pulp withdrawn from a settling tank are introduced into said dryer for drying, it is possible to reduce the cost of electricity by maximizing the production of biogas, and to reduce the cost of waste disposal by increasing the production of solid fuel or compost and relatively decreasing the amount of waste.

Secondly, by re-introducing dry nutrient which is the raw material of organic matter, the operation of drying equipment can be easily and evenly maintained, for example, the raw material stock during periods of difficulty in consignment (sale) processing of raw materials can be reduced to a minimum, etc.

Thirdly, by reusing the condensed wastewater taken from the said condenser for condensation as process water in the process of complex wastewater treatment, that is, by reusing the final purified water, it is possible to significantly reduce the costs of water supply services associated with the operation of the system.

Fourthly, the waste disposal cost can be reduced by recycling the resources obtained as solid fuel and composting the final dried material, and the production of dried organic waste can be increased, and the self-purification of dry material and wastewater generated in the process of industrial activities can be increased, thereby contributing to the government's policy of suppressing pollutant (waste) emission and resource circulation policy by reducing the amount of pollutant discharge through recycling.

[Brief description of drawings]

Fig. 1 is a process diagram showing a system for producing biogas using a liquid mixture of water purified from digestion liquid and dry nutrient according to one embodiment of the present invention.

Fig. 2 is a process diagram showing the operating state of said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient according to one embodiment of the present invention.

[Method of carrying out the invention]

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a process diagram showing a system for producing biogas using a liquid mixture of water purified from digestion liquid and dry nutrient according to one embodiment of the present invention.

As shown in Fig. 1, the said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient comprises a liquid mixture tank 27 as a means for mixing and storing water purified from a liquid after splitting and a dry nutrient.

The said dry nutrient (organic dry matter) and water purified from the liquid after splitting can be fed and stored in the said liquid mixture tank 27, and, if necessary, the recycled water obtained from the purified water tank 23 from the wastewater treatment plant 22 can be fed and stored there.

Such a tank for liquid mixture 27 and the tank for fermentation 11 are connected by a line 39 of liquid mixture, and said tank for liquid mixture 27 and the settling tank 37 are connected by a line 40 for water purified from the liquid after splitting, so that said water purified from the liquid after splitting can be supplied from the side of the settling tank 37 to said tank for liquid mixture 27, and can be supplied from the side of said tank for liquid mixture 27 to said tank for fermentation 11.

Accordingly, the dry nutrient and the water purified from the liquid after splitting, stored in the said liquid mixture tank 27, are mixed under stirring by the stirrer 43, and the resulting liquid mixture obtained after mixing can be supplied to the said fermentation tank 11 through the liquid mixture line 39 under operation of the pump.

Here, said dry nutrient and water purified from the liquid after splitting, mixed in said liquid mixture tank 27, may be mixed in a predetermined ratio, for example, at a concentration of about 10 to 20% depending on the quality level of the food wastewater.

That is, it is desirable that the quality level of the food wastewater be maintained at a concentration of about 100,000 to 200,000 mg/L based on the controlled concentration (range) of the organic matter (wastewater) introduced into the said digestion tank 11 by mixing the dry nutrient and the water purified from the digestion liquid in a suitable ratio.

In addition, said system for producing biogas using a liquid mixture of water purified from the liquid after splitting and a dry nutrient comprises a settling tank 37 as a means for separating the liquid after splitting, taken from said fermentation tank 11, into a solid and a liquid phase.

Such settling tank 37 can be connected to the fermentation tank 11 via a line 41 for liquid after splitting so as to receive liquid after splitting, and can be connected to said tank for liquid mixture 27 via a line 40 for water purified from liquid after splitting so as to supply water purified from liquid after splitting to said tank for liquid mixture 27, and can be connected to the storage tank 13 via a line 42 for pulp so as to supply pulp to the storage tank 13.

Accordingly, when the liquid after splitting (for example, the supernatant separated upward in said fermentation tank) collected from said fermentation tank 11 is fed to the settling tank 37, the separation of solid and liquid phases into water purified from the liquid after splitting and pulp can be carried out inside the settling tank 37. In this case, the supernatant separated upward, that is, the water purified from the liquid after splitting, will be directed to said tank for liquid mixture 27 through the line 40 for water purified from the liquid after splitting, and the pulp settling downward will be directed to the storage tank 13 through the line 42 for pulp.

In addition, said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient comprises a fermentation tank 11 configured to split the resulting liquid mixture taken from said tank for liquid mixture 27.

The said fermentation tank 11 serves to split the obtained liquid mixture obtained from the said tank for liquid mixture 27, for example, a liquid mixture of dry nutrient and water purified from the liquid after splitting, or a liquid mixture of dry nutrient, water purified from the liquid after splitting, and recycled water.

Such a fermentation tank 11 comprises an inlet for a liquid mixture into which the obtained liquid mixture flows, an outlet for methane gas from which methane gas flows out, and an upper outlet for a split liquid from which the liquid after splitting flows out, and a lower outlet for a split sludge from which the split sludge flows out.

In this case, the inlet for the liquid mixture of the fermentation tank 11 is connected to the line 39 of the obtained liquid mixture passing from the said tank for the liquid mixture 27, the outlet for the methane gas is connected to the line 28 for the methane gas passing to the gas holder 12, the outlet for the liquid after splitting is connected to the line 41 for the liquid after splitting passing to the settling tank 37, and the outlet for the split sludge is connected to the storage tank 13 by means of a line.

In addition, the temperature of the internal space of the fermentation tank 11, where the obtained liquid mixture is decomposed, can be maintained at a temperature of about 30 to 40°C.

Accordingly, when the obtained liquid mixture flows into the said fermentation tank 11, the obtained liquid mixture at this time remains inside the fermentation tank 11 for a predetermined period of time, and the methane gas generated as a result of this storage and splitting process accumulates in the upper part inside the fermentation tank 11. Among the obtained liquid mixtures stored inside the fermentation tank 11, the liquid after splitting is collected in the upper layer of the water level, and the split sludge with a large weight is collected in the lower layer, respectively.

Ultimately, the methane gas from the fermentation tank 11 is sent to the gas holder 12 through the methane gas line 28, and the liquid after splitting and the split sludge are sent to the settling tank 37 and the storage tank 13 through the corresponding lines.

In addition, said system for producing biogas using a liquid mixture of water purified from the liquid after splitting and a dry nutrient substance comprises a gas holder 12 configured to store methane gas taken from said fermentation tank 11.

Gas holder 12 serves to collect methane gas transferred from fermentation tank 11 and direct it to each supply point.

Such a gas holder 12 comprises an inlet for methane gas, into which methane gas enters, and an outlet for methane gas, from which said methane gas exits. In this case, said inlet for methane gas is connected to a line 28 for methane gas coming from the fermentation tank 11, and the outlet for methane gas is connected to two lines 29a and 29b for feeding methane gas, which are connected respectively to the deodorization furnace 14 and to the boiler for generating electricity 15.

In addition, manual or automatic valves 30 are respectively installed on the lines 29a and 29b for supplying methane gas, and the amount of methane gas supplied to the deodorizing furnace 14 and the electric power generating boiler 15 can be controlled by opening and closing each valve 30 installed on this line.

Accordingly, the methane gas transmitted through the methane gas line 28 is stored inside the gas holder 12, and the methane gas thus stored can be supplied to the deodorizing furnace 14 and/or to the electric power generating boiler 15 by operating the opening and closing of the valves 30, in order to be used as fuel, etc.

Here, the amount of methane gas supplied from the gas tank 12 to the deodorizing furnace 14 and to the power generation boiler 15 is preferably 50%, respectively.

In addition, said system for producing biogas using a liquid mixture of water purified from the liquid after splitting and a dry nutrient comprises a storage tank 13 configured to store split sludge taken from said fermentation tank 11 and pulp taken from a settling tank 37.

The storage tank 13 serves to store the pulp taken from the settling tank 37, as well as the split sludge taken from the said fermentation tank 11.

Such a storage tank 13 is connected to two lines going from the fermentation tank 11 and the settling tank 37, and one line going to the dryer 16. In this case, a pump is installed on the line going to the dryer 16.

Accordingly, the split sludge collected from said fermentation tank 11 and the pulp collected from the settling tank 37 are stored in the storage tank 13, and when the pump operates, the split sludge and the pulp in the storage tank 13 are introduced into said dryer 16 for drying.

In addition, said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient comprises a deodorizing furnace 14 configured to use methane gas taken from said gas holder 12 as fuel.

The deodorizing furnace 14 is a combustion chamber for general deodorization, used in drying equipment for burning odors generated during the drying process, and connected to the said condenser 17 for condensation via a line 31 for condensed gas. A fan is installed on the condensed gas line 31.

In addition, the methane gas supply line 29a coming from the gas holder 12 is connected to the deodorizing furnace 14, and the methane gas supplied through the methane gas supply line 29a connected in this way can be used as an auxiliary fuel for said deodorizing furnace 14.

Accordingly, said exhaust gases from the dryer 16 are condensed on the condenser 17 for condensation, and said exhaust gases (condensed gas) generated in the condensation process are sent to the deodorizing furnace 14 through the condensed gas line 31 for combustion. Meanwhile, methane gas supplied from the gas tank 12 can be sent to the deodorizing furnace 14, and can be used as a heat source for burning odors, that is, as an auxiliary fuel.

In particular, the deodorizing furnace 14 is characterized by using steam condensate taken from said dryer 16 as a water source.

For this purpose, said system comprises a water supply tank 24 configured to store process water supplied from a water supply system, as well as steam condensate taken from said dryer 16, a water supply line 25 connecting said water supply tank 24 and a deodorization furnace 14, and a water supply pump 26 installed on the water supply line 25.

Accordingly, the steam condensate collected from said dryer 16 and the process water supplied from the water supply are stored and mixed in the water supply tank 24, and said water mixed in this way can be sent to the deodorizing furnace 14 through the water supply line 25 by operating the water supply pump 26, and thus used as a water source.

In addition, said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient comprises a boiler for generating electricity 15, configured to use methane gas taken from said gas holder 12 as fuel.

The electric power generating boiler 15 is connected to the methane gas supply line 29b coming from the gas holder 12. Thus, the electric power generating boiler 15 can operate using the methane gas supplied from the gas holder 12 as fuel.

A part of the steam generated in the power generation boiler 15 is introduced into said dryer 16 for use as a heat source for drying food waste and split sludge (including pulp), or can be sold to nearby places for use or to the Korea Electric Power Corporation (KEPCO), etc. In addition, the steam generated in the power generation boiler 15 operates in a steam turbine (not shown) to generate electricity, and all of the electricity thus generated can be sold to KEPCO.

In addition, said system for producing biogas using a liquid mixture of water purified from the liquid after splitting and a dry nutrient comprises a dryer 16 configured to dry food waste, as well as split sludge and pulp, collected from said storage tank 13.

A conventional dryer 16 that dries food waste in a drying equipment, that is, a dryer 16 that dries the input food waste using steam, can be used as the dryer 16.

The dryer 16 is connected to the deodorizing furnace 14 via a line 32 for producing steam. Accordingly, the dryer 16 can dry food waste using high-temperature steam produced from the deodorizing furnace 14 as a heat source.

The dry material discharged after drying in this dryer 16 can be used as solid fuel, compost, etc., and the steam condensate generated during the drying process in the dryer 16 can be sent to the water supply tank 24.

In addition, the exhaust gases generated in the drying process in the dryer 16 sequentially pass through the cyclone 33 and the trap 34. In this process, foreign substances, oil and moisture contained in said exhaust gases are filtered, and said exhaust gases passing through the trap 34 can be directed to the condenser 17 for condensation.

The condenser 17 for condensing is a condenser configured to condense said exhaust gases taken from said dryer 16, mainly said exhaust gases passing through the cyclone 33 and the trap 34 serve to condense high-temperature exhaust gases using low-temperature circulating water. In this case, a condenser used in a conventional drying equipment can be used as the condenser 17 for condensing.

Such a condenser 17 for condensing comprises an inlet for exhaust gases, into which said exhaust gases flow, an outlet for condensed gas, from which said condensed gas comes out after condensation, an inlet for circulating water and an outlet for circulating water for the inflow and outflow of circulating water, and a drain for draining condensed waste water.

In addition, the condenser 17 for condensing comprises a cooling tower for circulating water 35b, a tank for circulating water 36, and a pump as a means for obtaining circulating water.

Accordingly, when said pump operates, the circulating water from the circulating water tank 36 is supplied to said condenser 17 for condensing and undergoes heat exchange with said exhaust gases inside the condenser 17 for condensing. The circulating water that has performed heat exchange is cooled while passing through the cooling tower for circulating water 35b, then is again introduced into said circulating water tank 36. For the circulation process of this circulating water, said exhaust gases can be condensed inside the condenser 17 for condensing.

In this case, the circulating water, that is, the purified water obtained from the wastewater treatment plant 22, can be used as circulating water for heat exchange in the said condenser 17 for condensation.

Further, said system for producing biogas using a liquid mixture of water purified from the liquid after splitting and a dry nutrient comprises a condenser 10 for heat exchange as a means for reducing the temperature of the condensed wastewater for sending to the wastewater treatment plant 22.

The heat exchange condenser 10 serves to cool the high-temperature condensed wastewater having a temperature of about 65 to 75°C, taken from the said condenser 17 for condensing, which is configured to condense the high-temperature condensed wastewater that is subjected to a condensation process, for example, the said exhaust gases from the dryer.

For this purpose, said system comprises a condenser 10 for heat exchange, through which condensed waste water flows in and out, wherein heat exchange between said condensed waste water and circulating water occurs inside it, and also comprises a tank for circulating water 36a, configured to store circulating water supplied to said condenser 10 for heat exchange, a pump for circulating water 38, configured to pump said circulating water, and a cooling tower for circulating water 35a, configured to cool said circulating water, taken from said condenser 10 for heat exchange, and then direct it to said tank for circulating water 36a.

Such a condenser 10 for heat exchange comprises an inlet for circulating water, into which low-temperature circulating water flows, and an outlet for circulating water, from which said circulating water flows out after heat exchange, as well as an inlet for condensed waste water, into which high-temperature condensed waste water flows in, and an outlet for condensed waste water, from which low-temperature condensed waste water flows out after heat exchange. In this case, indirect heat exchange between said circulating water and condensed waste water flowing through said condenser 10 for heat exchange can occur until they mix with each other.

Here, the internal structure of the heat exchange condenser 10 is the same as the internal structure of a general condenser used in drying equipment, so it will not be described in detail.

In addition, the outlet for condensed wastewater of the heat exchange condenser 10 is connected to the condensed wastewater tank 18b via a line so that said condensed wastewater whose temperature has been lowered by the heat exchange condenser 10 can be directed to the condensed wastewater tank 18b via said line.

Accordingly, when said low-temperature circulating water and high-temperature condensed wastewater simultaneously flow into said heat exchange condenser 10, heat exchange between said circulating water and condensed wastewater will occur inside the heat exchange condenser 10. As a result, the condensed wastewater with a lower temperature can be sent to the condensed wastewater tank 18b of the wastewater treatment plant 22 for comprehensive wastewater treatment through said line, and the circulating water with an elevated temperature can be sent to the circulating water cooling tower 35a for circulation.

Further, said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient comprises a tank for condensed wastewater 18b, a line 19 for condensed wastewater, and a pump 20 for condensed wastewater as a means for feeding condensed wastewater to said condenser 10 for heat exchange.

The tank for condensed waste water 18b is connected to the drain of the condenser 17 for condensing and serves to store high-temperature condensed waste water taken from the said condenser 17 for condensing.

The line 19 for condensed wastewater is a line connecting said tank for condensed wastewater 18b and the heat exchange condenser 10. In this case, the condensed wastewater in the tank for condensed wastewater 18b can be supplied to the heat exchange condenser 10 through the line 19 for condensed wastewater.

Pump 20 for condensed waste water is installed on line 19 for condensed waste water and serves to pump condensed waste water.

Accordingly, said high-temperature condensed wastewater taken from said condenser 17 for condensing is stored in a condensed wastewater tank 18b. When the condensed wastewater pump 20 operates, the condensed wastewater from the condensed wastewater tank 18b is directed to said condenser 10 for heat exchange through the condensed wastewater line 19, and heat exchange occurs between said high-temperature condensed wastewater directed in this way and the low-temperature circulating water supplied to said condenser 10 for heat exchange. In this way, the condensed wastewater is cooled to a predetermined temperature, for example, to a temperature lower than the temperature before the heat exchange with the circulating water occurs, and then directed to the condensed wastewater tank 18a of the wastewater treatment plant 22.

In addition, said system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient comprises a wastewater treatment unit 22 and a condensed wastewater tank 18a as a means for comprehensively treating condensed wastewater collected from said heat exchange condenser 10 after heat exchange is completed therein, and then using it as process water in a drying system.

The condensed waste water tank 18a serves to store condensed waste water taken from said heat exchange condenser 10, that is, condensed waste water whose temperature has been reduced by heat exchange.

The wastewater treatment plant 22 serves to transform the condensed wastewater obtained from the condensed wastewater tank 18a into process water, which can be used in the drying system by means of a complex wastewater treatment process.

Such a wastewater treatment plant 22 comprises a fermentation tank 22a, an aeration tank 22b, a settling tank 22c, and an improved cleaning tank 22d, which are arranged sequentially from above. In this case, it is preferable that the settling tank 22c comprises a primary settling tank and a secondary settling tank.

In addition, the wastewater treatment plant 22 comprises a purified water tank 23 configured to store purified water obtained therefrom and subsequently feed it to said condenser 17 for condensation as recycled water.

Accordingly, the condensed wastewater which has completed heat exchange with the circulating water in said heat exchange condenser 10 passes successively through the condensed wastewater tank 18a → the fermentation tank 22a → the aeration tank 22b → the settling tank 22c → the advanced purification tank 22d, and then is stored in the purified water tank 23. When the pump operates, the purified water from the purified water tank 23 can be sent to said circulating water tank 36, thus it can be reused as circulating water for condensing said exhaust gases in said condenser 17 for condensing.

Fig. 2 is a process diagram showing the operating state of a system for producing biogas using a liquid mixture of water purified from a liquid after splitting and a dry nutrient according to one embodiment of the present invention.

As shown in Fig. 2, water purified from the liquid after splitting and dry nutrient are added and mixed in said liquid mixture tank 27, and the liquid thus mixed is sent to the fermentation tank 11.

The resulting liquid mixture is contained in the fermentation tank 11, that is, the medium temperature is maintained in the methane fermentation tank, and the methane gas formed during this process is accumulated in the gas holder 12, and then supplied to the deodorization furnace 14 as an auxiliary fuel, thereby reducing fuel costs. The steam formed in the deodorization furnace 14 is supplied to the dryer 16, and is used for drying the split sludge, pulp, food waste, etc.

The split liquids processed during a given residence time in the fermentation tank 11 are directed to the settling tank 37 and separated into solid and liquid phases. Then, the water purified from the split liquid is again introduced into the said tank for liquid mixture 27 at this time, and the split sludge from the fermentation tank 11 and the pulp from the settling tank 37 are introduced into the said dryer 16 for drying.

Said exhaust gases generated during the drying process in the dryer 16 are passed through 33 and trap 34, and then separated and taken from said condenser 17 for condensation. The remaining gas containing odors is sent to the deodorization furnace 14 for combustion together with air.

Finally, the dry material collected from said dryer 16 is processed through processes such as solidification into solid fuel and composting.

The temperature of the high-temperature condensed wastewater obtained in the condensation process in said condenser 17 for condensing is lowered by heat exchange with the circulating water, and said condensed wastewater whose temperature has been lowered is supplied to the wastewater treatment unit 22 and finally purified by the integrated wastewater treatment process. The purified water obtained in this way is used as the circulating water for the condenser 17 for condensing.

In this way, the split sludge generated in the digestion tank and the pulp generated in the settling tank are introduced into the said dryer for drying. In this way, the finally discharged raw materials can be sold as solid fuel or compost, reducing the cost of waste disposal and maximizing the production of biogas (methane). Consequently, the cost can be reduced by producing and selling the generated electricity through the operation of the electric and steam power boiler, and the cost of waste disposal can be reduced by reducing the amount of waste generated by drying the sludge and pulp. As a result, it is possible to protect the earth's environment by minimizing the emission of pollutants and contribute to the government's policy of reducing pollutant emissions.

As described above, in the present invention, by providing a new type of system in which the digestion liquid collected from the anaerobic digestion tank is separated, which is a preliminary process of said wastewater treatment system, into a solid phase and a liquid phase in a settling tank, and then the water purified from the digestion liquid is mixed with dry raw materials at a predetermined ratio and introduced into the digestion tank again, and the digested sludge and pulp are introduced into a drying equipment, it is possible to maximize the production of biogas (methane gas), reduce the cost of electricity, increase the production of dry matter, reduce the cost of waste disposal, and increase the speed of resource recycling.

[Description of reference symbols]

10: Heat exchange condenser

11: Fermentation tank

12: Gas holder

13: Storage tank

14: Deodorizing oven

15: Electricity generation boiler

16: Dryer

17: Condenser for condensation

18a, 18b: Condensed wastewater tank

19: Condensed wastewater line

20: Condensed wastewater pump

22: Wastewater Treatment Plant

23: Purified water tank

24: Water supply tank

25: Water supply line

26: Water supply pump

27: Liquid mixture tank

28: Methane Gas Line

29a, 29b: Methane gas supply line

30: Valve

31: Condensed Gas Line

32: Steam line

33: Cyclone

34: Trap

35a, 35b: Cooling tower for circulating water

36a, 36b: Recirculating water tank

37: Sedimentation tank

38: Recirculating water pump

39: Liquid Mix Line

40: Line for water purified from liquid after splitting,

41: Liquid line after splitting

42: Pulp Line

43: Stirrer.

Claims (14)

1. A system for producing biogas using a liquid mixture of water purified from the liquid after splitting and organic dry matter, comprising: a liquid mixture tank 27 configured to mix and contain water purified from the liquid after splitting and organic dry matter; a fermentation tank 11 configured to split the resulting liquid mixture of water purified from the liquid after splitting and organic dry matter taken from said tank for liquid mixture 27; a settling tank 37 configured to separate the split liquid collected from the fermentation tank 11 into a solid and liquid phase, and then direct water purified from the split liquid to a liquid mixture tank 27 and the pulp to a storage tank 13; a gas holder 12 configured to store methane gas taken from said fermentation tank 11; a storage tank 13 configured to store the split sludge collected from said fermentation tank 11 and the pulp collected from the settling tank 37; a deodorization furnace 14 configured to use methane gas taken from the gas holder 12 as fuel; a power generation boiler 15 configured to use methane gas withdrawn from the gas holder 12 as fuel; and a dryer 16 configured to dry food waste as well as said split sludge and pulp collected from the storage tank 13. 2. The system according to claim 1, comprising means for cooling condensed wastewater taken from a condenser 17 for condensing exhaust gases taken from said dryer 16, which comprises: a heat exchange condenser 10 through which condensed wastewater flows in and out, wherein heat exchange between said condensed wastewater and circulating water occurs inside it; a circulating water tank 36a configured to store circulating water supplied to said condenser 10 for heat exchange; a circulating water pump 38 configured to pump said circulating water; and a circulating water cooling tower 35a configured to cool with said circulating water taken from said condenser 10 for heat exchange and then direct it to the circulating water tank 36a. 3. The system according to claim 1 or 2, comprising: a condensed wastewater tank 18b configured to store condensed wastewater collected from a condenser 17 for condensing, which is configured to condense exhaust gases collected from a dryer 16; a wastewater treatment unit 22, which comprises a fermentation tank 22a, an aeration tank 22b, a settling tank 22c, and a cleaning tank 22d as a means for cleaning condensed wastewater collected from the condensed wastewater tank 18b; and a purified water tank 23 configured to store purified water withdrawn from the wastewater treatment plant 22 and then feed it to the condenser 17 for condensing as recycled water, wherein said condensed wastewater withdrawn from the condenser 17 for condensing is converted into purified water by the integrated wastewater treatment plant 22, and the resulting purified water is reused as recycled water for condensing said exhaust gases in said condenser for condensing. 4. The system according to claim 1, comprising: a water supply tank 24 configured to store steam condensate taken from the dryer 16 and process water supplied from a water supply; a water supply line 25 connecting the water supply tank 24 and the deodorization furnace 14; a water supply pump 26 installed on the water supply line 25, wherein the steam condensate taken from said dryer is used as a water source for said deodorization furnace. 5. A method for producing biogas using a system according to any one of claims 1 to 4, wherein water purified from the split liquid obtained by separating the split liquid taken from the fermentation tank 11 into solid and liquid phases and organic dry matter are mixed in a predetermined ratio in a tank for liquid mixture 27; then, said mixture is maintained and split in the fermentation tank 11; methane gas obtained in said fermentation tank 11 is used as fuel in a deodorization furnace 14 and in a boiler for generating electricity 15; and the split sludge taken from said fermentation tank 11 and the pulp taken from the settling tank 37 are introduced into a drying dryer 16. 6. The method according to item 5, characterized in that the steam generated in the boiler for generating electricity 15 is introduced into the dryer 16 for independent use, for example for drying waste, contaminated sludge and pulp, or for sale to a third party organization.