KR20230100801A - Fuel cell system exclusively using biogas produced from organic waste resources - Google Patents

Abstract

The present invention relates to a fuel cell system dedicated to living net biogas.
The fuel cell system of the present invention dehumidifies biogas containing 50 to 70% of methane gas produced from organic waste resources such as livestock manure, living manure, food waste, sewage sludge, etc. Biogas from which hydrogen sulfide, organic sulfur, and corrosive halogen compounds have been removed through the removal process is directly supplied to the anode of the phosphoric acid type fuel cell to supply thermal energy generated from the fuel electrode unit.

Description

Fuel cell system exclusively for living biogas {FUEL CELL SYSTEM EXCLUSIVELY USING BIOGAS PRODUCED FROM ORGANIC WASTE RESOURCES}

The present invention relates to a fuel cell system dedicated to living net biogas, and more particularly, methane gas produced from organic waste resources such as livestock manure, living manure, food waste, sewage water, sewage sludge, etc. 50 to 70% Hydrogen sulfide, organic sulfur, and corrosive halogen compounds are directly supplied to the anode of a phosphoric acid type fuel cell, and the thermal energy generated from the fuel electrode is used for home heating. It is about a fuel cell system dedicated to living net biogas that is used on roads.

The treatment costs and environmental problems of organic waste resources such as livestock manure, living manure, food waste, wastewater, and sewage sludge, which are discharged on a daily basis, are being reviewed at the national level.

Specifically, as marine dumping of organic waste resources such as food waste, wastewater generated from food waste, livestock manure, and landfill waste has been prohibited by international conventions since 2012, land treatment technology development of organic waste resources is actively progressing. there is.

As an example, in Patent Document 1, purification and composting processes that obtain compost as a by-product and biogas processes that obtain liquid fertilizer as a by-product are linked and operated, while through this, eco-friendly organic waste that can suppress the generation of chemical sludge A resource recycling processing system and method are proposed.

However, among a series of conventional land treatment technologies for organic waste resources, there is a biogas production technology containing methane as a main component, such as natural gas, or an energy resource attempt to produce liquid fertilizer, but digestion sap generated in the process of operating a digester, etc. Due to the problem of facility investment, the efficiency is low, and the low operation rate needs to be resolved.

In the above, biogas is a main component by anaerobic microorganisms when organic waste resources such as food waste, wastewater generated from food waste, livestock manure, living manure, sewage sludge, landfill waste, etc. methane is produced.

At this time, the content of methane and carbon dioxide constituting biogas may vary depending on organic waste resources. In general, biogas generated from food waste contains 70 to 75% by volume of methane, and Biogas contains 65 to 70% by volume of methane, and biogas generated from livestock manure or landfill waste contains 50 to 60% by volume of methane.

As described above, since biogas has a different methane content depending on organic waste resources, efforts are required to improve utilization rates in order to obtain stable electrical efficiency of conventional power generation facilities that supply biogas as fuel.

In general, biogas has many gas components, but most of them are methane and carbon dioxide, so if methane and carbon dioxide are separated and high concentration methane is produced, long-distance supply is possible, and it is easy to apply to power generation, boilers, business fuel, automobiles, city gas, etc. When the concentration of carbon dioxide is over 70%, its utilization as a raw material for products increases.

Lifestyle biogas containing methane gas, which is a fuel supplied to fuel cells, contains 50 to ⁷⁰ % of CH ₄ components. In order to match the calorific value similar to that of natural gas, the methane content of biogas must be improved to 95% or more.

Conventional commercial technologies for upgrading the methane content of biogas include pressure swing adsorption, absorption methods (water scrubbing, methanol scrubbing, polyethylene glycol scrubbing, etc.), membrane separation, etc. It is important to select a technical method for separation and purification in consideration of reuse and economic feasibility.

The absorption method using amine is used, but it consumes a lot of energy, causes equipment corrosion, and causes problems such as deterioration of the solvent due to oxygen. In addition, since the purified methane gas is saturated with water, a post-processing process for removing water is required.

As another method, the adsorption method is used. It is a technology that selectively separates specific components from the mixed gas by using the difference in adsorption equilibrium amount caused by the pressure circulation of the adsorbent and the mixed gas. It mainly adsorbs carbon dioxide at high pressure and purifies methane. It is a method of desorption of adsorbed components at low pressure. Since this method operates in an abnormal state, it is difficult to predict and design various operating variables during the operation stage. It is widely used as a technology for

Compared to the understanding, the separation membrane process is more energy efficient than the absorption or adsorption process, is environmentally friendly, has a small device scale, is easy to install and operate, and can be operated with the minimum driving force required for the membrane process because it does not require the energy required for phase change. Since it is economizing and there is no phase change, there is no change in the properties of the material to be separated.

In addition, there is an advantage in that the facility is compact as it is composed of pumps, pipes, membranes, and control parts without an evaporator or condenser.

In the case of a polymer membrane, the gas molecules pass through the fine gap between the side chains of the polymer by the difference in speed moving inside the membrane after absorption or dissolution in the case of a polymer membrane. As in the case of the latter, gas permeates depending on the spacing of the side chains of the polymer, and water vapor or CO ₂ is absorbed or dissolved and transmitted through the membrane. The initial gas separation membrane process was started for hydrogen separation (H ₂ /CO, H ₂ /CH ₄ ) and recovery. Currently, it is expanding into various fields such as nitrogen generation, oxygen enriched air production, hydrogen and volatile organic vapor recovery, and carbon dioxide separation. However, conventional methods have limitations in producing high-purity methane.

Patent Document 2 is a separation membrane system capable of recovering methane, including a pretreatment means for removing trace contaminants from biogas; a multi-stage membrane means having at least one first-stage separation membrane and a second-stage separation membrane for receiving the biogas passed through the pretreatment unit and separating methane and carbon dioxide; And a pressure control valve that allows the two-stage compressor to continuously operate; thereby disclosing a multi-stage membrane system capable of improving methane recovery from biogas (landfill gas, anaerobic digestion gas, etc.).

However, in the case of introducing a membrane separation method, there is a problem of introducing expensive membranes and equipment costs.

From the above, biogas methane produced in the anaerobic digestion process by recycling organic waste resources can directly replace fossil fuels such as city gas.

Therefore, the inventors of the present invention have found that if the supply is made locally to urban areas through appropriate energy conversion of organic waste resources such as livestock manure, living manure, food waste, wastewater, sewage sludge, etc., rather, it is to expand anaerobic digestion facilities. By devising that it can play a positive role as a virtuous cycle structure, hydrogen sulfide, organic sulfur and The present invention has been completed by providing a fuel cell system exclusively for living biogas that supplies thermal energy generated from the fuel electrode to urban areas by directly supplying biogas from which halogen compounds, which are corrosive components, are directly supplied to the anode of a phosphoric acid type fuel cell.

Republic of Korea Patent No. 1366374 (Announced on February 24, 2014) Korean Patent Publication No. 2018-0007519 (published on January 23, 2018)

An object of the present invention is to provide a fuel cell system in which live biogas produced from organic waste resources is directly supplied to a fuel cell.

Another object of the present invention is to directly supply biogas containing 50 to 70% of methane gas obtained from organic waste resources such as livestock manure, living manure, food waste, sewage sludge, etc. It is to provide an energy system using thermal energy.

In order to achieve the above object, the present invention provides a biogas production unit 10 containing 50 to 70% methane gas discharged from organic waste resources, a pre-processing unit 20 of biogas supplied from the production unit, and the pre-treatment It consists of a fuel cell unit 30 that operates by directly supplying biogas from which desulfurization or halogen compounds have been removed by the unit to a phosphoric acid fuel cell (PAFC) fuel electrode, and utilizes the thermal energy generated in the fuel cell unit. Provides a fuel cell system exclusively for life-style pure biogas, using only pure biogas as a raw material.

The methane gas content of the biogas directly supplied to the fuel cell anode is 50 to 70%, and the methane gas upgrading step of the biogas is omitted.

In addition, 99.98% of hydrogen sulfide (H ₂ S) and 88% of organic sulfur are removed by the pretreatment unit, and 96% or more of total halogen compounds are removed, and the pretreatment process is repeatedly performed until the above removal rate is achieved.

The thermal energy generated in the fuel cell unit is used as a heating supply for a home or used as a heat supply to a heat exchanger in a biogas production unit.

The present invention can provide an eco-friendly and highly efficient energy system from organic waste resources such as livestock manure, living manure, food waste, sewage sludge, and the like that are routinely discharged.

In particular, biogas containing methane gas produced from organic waste resources is directly supplied to the anode of a phosphoric acid fuel cell (PAFC) while omitting an expensive membrane process to increase the methane gas content, thereby utilizing thermal energy. As a result, it is possible to utilize clean hydrogen, thereby providing a leading position in accordance with the Clean Hydrogen Generation Mandatory System (CHPS).

In addition, biogas containing 50 to 70% of methane gas produced from organic waste resources such as livestock manure, living manure, food waste, sewage sludge, etc. is directly supplied to the fuel cell and turned into resources, thereby reducing energy and reducing livestock odor. In addition to reducing the heat energy from the fuel cell using the biogas, it is possible to use the heat energy from the fuel cell to supply heating to the home or to develop a heat supply use for a heat exchanger in the biogas production unit.

Therefore, it is possible to reduce the treatment cost of livestock manure, living manure, food waste, wastewater, sewage sludge, etc. containing organic substances, and the fuel cell system using pure biogas of the present invention can reduce the concentration of conventional methane gas to a high level. By omitting the conversion step, it is possible to provide the effect of cost reduction and the use of heat energy resulting therefrom.

1 is a block diagram of a fuel cell system dedicated to living net biogas of the present invention;
Figure 2 schematically shows a facility system diagram of the biogas preprocessing unit of the present invention,
Figure 3 shows the removal of impurities through the biogas pre-processing unit of the present invention.

Hereinafter, the present invention will be described in detail.

Figure 1 shows a block diagram of a fuel cell system dedicated to living net biogas of the present invention, specifically, a biogas production unit 10 containing 50 to 70% of methane gas discharged from organic waste resources, and included in the production unit A biogas pre-processing unit 20 that removes impurities except for methane and carbon dioxide and a fuel cell unit 30 that operates by directly supplying the biogas from which impurities are removed by the pre-processing unit to the anode of a phosphoric acid fuel cell (PAFC) It is made, and provides a fuel cell system (1) using pure biogas, characterized in that it utilizes the thermal energy generated in the fuel cell unit.

In terms of each component, the organic waste resources in the biogas production unit 10 include all organic wastes such as livestock manure, living manure, food waste, wastewater, sewage sludge, and the like.

The biogas production unit 10 ferments the organic waste resources by anaerobic microorganisms to reduce waste and produce biogas at the same time. Specifically, a concentration tank for concentrating the sludge generated in the first and final sedimentation tanks and moving it to a digestion tank, decomposing organic matter in the concentrated sludge in an anaerobic state, reducing and stabilizing, and passing through a digestion tank for producing methane gas Biogas with methane as the main component can be produced and delivered to the next step.

In addition, the liquid sludge that has undergone the digestion process of the biogas production unit 10 is dehydrated and passed through a dehydration tank to produce a solid sludge cake (moisture content at this time is around 80%), and the sludge cake is passed through a sludge drying facility to obtain a moisture content of 10% It is eco-friendly as it can be dried and recycled as fuel for thermal power plants.

In the present invention, the biogas supplied from the biogas production unit 10 includes methane (CH ₄ ), carbon dioxide (CO ₂ ), hydrogen sulfide (H ₂ S), carbonyl sulfide compound (COS), methyl mercaptan (CH ₃ SH) It contains impurities such as sulfur and siloxane, and in order to supply it as a fuel for fuel cells, a purification process is required to remove impurities contained in the gas.

Figure 2 schematically shows a system diagram of the biogas preprocessing unit 20 of the present invention, using a demister cooler 21 to dehumidify the moisture of the biogas, and the temperature of the biogas through the cooler 24 is constantly controlled. The demister cooler or the cooler may be controlled by the integrated control unit (not shown).

At this time, the high-humidity gas that has passed through the gas inlet (100% RH) through the biogas dehumidifier 24 in the biogas preprocessing unit 20 is generated as a dehumidified gas by the internally filled dehumidifier and temperature conditions, and moves to the top of the dehumidifier. It rises and is discharged to the gas outlet (1 to 5 vol% or less), and the condensate generated during the dehumidification process is collected in the condensate storage provided at the bottom of the dehumidifier or discharged toward the condensate outlet.

The gas dehumidified through the biogas dehumidifier is supplied to the on-site control panel 25 of the gas boost blower, and an appropriate amount of air or oxygen is introduced, and the air or oxygen and the biogas are supplied to the dry desulfurization device 26 and siloxane removal. Passing through the device 27, impurities such as hydrogen sulfide and siloxane contained in the biogas whose temperature and humidity are constantly controlled by the temperature and humidity control are removed.

The dry desulfurization device 26 is a method of adsorbing and removing sulfur components by chemically treating the surface of the solid adsorbent, which can adsorb and remove sulfur components with adsorbents such as activated carbon, silica gel, and zeolite, and is preferably a desulfurization medium filled with iron hydroxide. By removing hydrogen sulfide by, it is possible to improve the stable and sulfur component removal efficiency.

In addition, since the desulfurization media can be regenerated by supplying air or oxygen, there is an effect of extending the replacement cycle of the desulfurization media and reducing filter media replacement costs.

The dry desulfurization device 26 is made in the form of a desulfurization medium filled inside, a gas inlet is formed at the bottom of the dry desulfurization reaction tank, and a gas outlet for discharging the treated gas is formed at the top, and is provided in multiple stages can increase efficiency.

In order to remove hydrogen sulfide in biogas, if the chemical absorption reaction of iron chelate, an inorganic compound, which is a chemical absorbent, is used, sulfur precipitation can be safely and easily separated, chemically stable, harmless to the human body, and non-corrosive. In addition, since it can be reused after use and highly efficient separation and purification is possible, a method for separation and purification under optimal conditions for biogas separation can be considered.

For the separation of carbon dioxide and methane gas, a polysulfone material with excellent thermal stability and high permeability and selectivity is used as a separation membrane material, and more preferably, a polysulfone hollow fiber is used [internal/outer diameter: 0.24/0.42, tensile strength 15.2 MPa, elongation 29.0%].

In general, gas permeability in a membrane is determined by solubility and diffusion, and is expressed as a product of diffusion coefficient and solubility as shown in Equation (2). Here, gas diffusion increases in proportion to the kinetic diameter and permeation pressure of the permeation gas, but solubility does not necessarily increase in proportion to the permeation pressure because the solubility is determined by the physical mutual attraction between the polymer membrane and the permeation gas. In many cases, the permeability is reduced by the latter, which is determined by numerous physicochemical parameters of the membrane material. First, when the polymeric material of the separation membrane is exposed to pressure, the permeability changes due to the plasticization of the membrane due to the pore size of the membrane and the physical properties of hydrocarbons.

In addition to methane and carbon dioxide in biogas, hydrogen sulfide has metal ions (Fe ²⁺ , Fe ³⁺ ) that have an affinity for hydrogen sulfide, oxidizes sulfur ions in an aqueous solution, and forms an iron chelate that is reduced to itself, which is oxidized again by oxygen in the solution. It can be removed by a chemical reaction.

In the aqueous phase, hydrogen sulfide gas in the liquid phase is decomposed into S2- at pH 7 or higher, which reacts with Fe ³⁺ -EDTA as shown in equation (5), and the sulfur compound is oxidized to insoluble sulfur to form inert Fe ²⁺ -EDTA. do.

However, these metal ions react with sulfur ions in aqueous solution to form precipitates such as FeS, which reduces the activity of the catalyst. Therefore, in order to overcome these disadvantages, iron and chelate (EDTA) is used to oxidize hydrogen sulfide to S using a liquid catalyst. Iron chelate is a stable complex and is widely used in the oxidation reaction of hydrogen sulfide because it can perform oxidation-reduction reactions while suppressing the formation of sulfur precipitates.

Since the oxidation reaction of hydrogen sulfide according to the concentration of iron chelate is stably performed as the concentration of iron chelate increases, it is more effective to proceed with the oxidation reaction at a complex concentration of 0.1 M or more, which consumes a lot of hydrogen sulfide, in order to carry out an efficient hydrogen sulfide oxidation reaction. and more than 98% of hydrogen sulfide is removed.

In addition, the biogas that has passed through the dry desulfurization device is continuously supplied to the siloxane removal device.

The siloxane refers to a state in which silicon (Si) and oxygen (O) are bonded to each other to form a polymer, and it is a main skeleton of silicon called a siloxane bond, and the bond energy of a carbon bond (CC) is 356 KJ / mol, The siloxane bond (Si-O) is large at 444KJ/mol and is characterized by being very stable. When these siloxanes are included in biogas, they are oxidized in the combustion chamber of a gas engine or micro gas turbine to form silica (SiO ₂ ) and remain in the combustion chamber in a powder or crystal state, so removal is required.

Siloxane removal in general is performed by activated carbon adsorption, and known adsorbents may also be included to improve performance.

Figure 2 shows that the biogas passes through the pre-processing unit of the present invention and is directly supplied to the fuel cell fuel electrode.

Figure 3 shows the removal of impurities through the biogas pre-processing unit of the present invention, by the pre-processing unit, 99.98% of hydrogen sulfide (H ₂ S) and 88% of organic sulfur are removed, and a total of 96% or more of halogen compounds, which are corrosive components, are removed and the pretreatment process is repeated until the removal rate is achieved.

In the system of the present invention, impurities are removed through the preprocessing unit 20 and biogas having a methane gas content of 50 to 70% is directly supplied to the anode of the phosphoric acid type fuel cell to operate. Includes a fuel cell unit 30 do. At this time, the biogas reforming unit may be additionally installed, and the enriched biogas is reformed into hydrogen to provide reformed hydrogen fuel.

As the reforming method, a single reformer (eg, a steam reformer) is provided to reform biogas having a methane purity of 95% or more into hydrogen. At this time, the reformed gas may have a hydrogen content of 70% by volume or more.

In the case of biogas containing 50 to 70% of methane gas supplied to the fuel cell unit 30, it is difficult to apply to power generation, boilers, business fuel, automobiles, city gas, etc. due to its low calorific value, but fuel cell unit ( 30) can be used as a heating supply for homes.

In addition, it will be possible to use it for the purpose of supplying heat to the heat exchanger in the biogas production unit 10.

Therefore, it is possible to develop downstream uses along with the effect of cost reduction by omitting the process for separating methane from biogas and enhancing the concentration.

The fuel cell unit of the present invention uses a phosphoric acid fuel cell (PAFC) that uses liquid phosphoric acid as an electrolyte.

At this time, as a raw material of the fuel cell, biogas containing 50 to 70% of methane gas may be directly supplied to the fuel electrode to obtain thermal energy in the process of generating water. Specifically, when oxygen obtained from air is supplied to the porous anode and cathode electrodes, respectively, and a load is applied between the two electrodes to connect them, hydrogen is oxidized as H ₂ → 2H ⁺ + 2e ^- at the anode electrode. Hydrogen ions are generated and electrons are released to the load circuit. On the other hand, in the anode, oxygen moves electrons and phosphoric acid electrolyte through the load circuit and reacts with hydrogen ions to form water, such as 1/2 0 ₂ + 2H + 2e ^- → H ₂ O.

The generated power capacity is 440 to 880 kW, and biogas methane produced in the anaerobic digestion process can be substituted for fossil fuel without upgrading, and the thermal energy obtained therefrom can be used as a resource for heating in nearby residential areas.

The phosphoric acid fuel cell (PAFC) employed in the present invention has an in-house required rate of return (P-IRR) of 5.54 and 5.36, respectively, compared to the high-temperature (operating temperature 600 to 1,000 ° C) fuel cell of the solid oxide fuel cell (SOFC). It is advantageous in terms of economic feasibility considering costs and the like.

Therefore, by increasing the concentration of methane from the life-type biogas of the present invention and supplying the biogas containing methane as a main component to the anode of the phosphoric acid fuel cell, it is possible to improve the efficiency, stability and economic efficiency of the fuel cell system.

In addition, according to the present invention, the heat (105 to 120° C.) generated in the fuel cell unit 30 can be used to treat sewage sludge caught in the biogas production unit 10.

The sewage sludge is recycled by dewatering sewage treatment sediment → sludge → drying → powdering and forming into pellets, thereby providing profitability as well as recycling of waste resources.

Although the present invention has been described in detail only with respect to the specific embodiments described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention, and it is natural that such changes and modifications fall within the scope of the appended claims.

10: biogas production department
20: biogas pre-processing unit
21: demister cooler, 22: heat exchanger, 23: air-cooled cooler, 24: dehumidifier, 25: gas boost blower field control panel, 26: dry desulfurization device, 27: siloxane removal device, 28: particle removal filter
30: fuel cell unit
1: Fuel cell system dedicated to living net biogas

Claims (5)

Lifestyle biogas production unit containing 50 to 70% of methane gas discharged from organic waste resources,
A pre-processing unit of the biogas supplied from the production unit and
It consists of a fuel cell unit that operates by directly supplying biogas from which impurities are removed by the preprocessing unit to a phosphoric acid fuel cell (PAFC) fuel electrode, and uses the thermal energy generated in the fuel cell unit. Gas-only fuel cell system. [Claim 2] The fuel cell system of claim 1, wherein the biogas directly supplied to the fuel cell fuel electrode has a methane gas content of 50 to 70%. According to claim 1, wherein the hydrogen sulfide (H ₂ S) 99.98% and organic sulfur 88% of the impurities are removed by the pre-processing unit, characterized in that the life-type net biogas-only fuel cell system. According to claim 1, Life type pure biogas-only fuel cell system, characterized in that 96% or more of the total halogen compounds are removed by the pretreatment unit. [Claim 2] The fuel cell system for living net biogas only according to claim 1, wherein the thermal energy generated in the fuel cell unit is supplied to a heat exchanger in a home heating supply or biogas production unit.

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