Patent Application
20110217622
The present invention relates to an electrochemical-catalytic converter, particularly to an electrochemical-catalytic converter for exhaust emission control with power generation to effectively reduce nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HCs) in exhaust gas.
Air is indispensable for the living of human beings. Fresh and clean air is essential for the health of people. The remarkable advance of science and technology has brought the prosperous development of economics. However, the exhaust emission of automobiles and factories has become the main source of air pollution and greatly degraded the quality of air.
Take automobiles for an example. The vehicle exhaust emission standard is growing more and more stringent. However, the air pollution caused by vehicles is still getting more and more serious because the number of vehicles increases day by day. Generally, different types of fuels are burned in a cylinder to release thermal energy and generate dynamic power for engine operation of an automobile. However, the combustion of fuel also generates exhaust gases including harmful pollutants, such as nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HCs), particulate matter (PM) and the like. These pollutants not only form photochemical smog, but also destroy the ozone layer, aggravate the greenhouse effect, cause acid rain, damage ecological environment, and harm health of human beings.
Incomplete combustion generates carbon monoxide, which combines with hemoglobin to form carboxyhemoglobin (COHb). The hemoglobin's combination affinity for carbon monoxide is 300 times greater than that for oxygen. Thus, too high a concentration of carbon monoxide in air will affect the oxygen delivery ability of hemoglobin. A nitrogen oxide comes from the chemical combination of nitrogen and oxygen and is usually exhausted in form of nitric oxide (NO) or nitrogen dioxide (NO2). After illuminated by ultraviolet (UV), nitrogen oxides react with hydrocarbons to form toxic photochemical smog which has special smell, irritates people's eyes, injures plants, and reduces visibility in atmosphere. Also nitrogen oxides react with moisture in the air to form nitric acid and nitrous acid which are elements of acid rain. A low concentration of hydrocarbon will irritate the respiratory system. A higher concentration of hydrocarbon will affect the function of the central nervous system.
Therefore, many regions, including European Union, USA, Japan and the Republic of China, have established stringent exhaust emission standards, such as US Bin5 and Euro6, which regulate the exhaust emission standards of nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HCs) and the like to control and decrease the emission of polluting gases and encourage the manufacturers to produce, develop or introduce the latest products adopting pollution prevention technologies.
In the conventional emission control technology for lean burn exhaust, no single device or converter can simultaneously undertake the conversion of nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HCs). Catalytic converters of automobile emission systems for the lean burn exhaust can only catalyze carbon monoxide and hydrocarbons. Another auxiliary device or system is needed to convert nitrogen oxides. For example, in addition to a catalytic converter for oxidation of carbon monoxide and hydrocarbons, most of the tailpipes of current diesel vehicles are equipped with an EGR (Exhaust Gas Recirculation) system to control emission of nitrogen oxides. The latest diesel vehicles may be equipped with an SCR (Selective Catalytic Reduction) system to reduce nitrogen oxides.
The SCR system adopts ammonia (NH3) or aqueous solution of urea (CO(NH2)2) as the reactant. The aqueous solution of urea is injected into the tailpipe via a nozzle and reacted with water to form ammonia. The ammonia reacts with nitrogen oxides to generate nitrogen (N2) and water (H2O). However, ammonia is toxic and hard to store and may leak. The incomplete reaction of ammonia causes secondary pollution. Further, the SCR system is bulky and needs to be equipped with precision sensors to provide auxiliary control.
An U.S. Pat. No. 5,401,372 discloses an “Electrochemical Catalytic Reduction Cell for the Reduction of NOx in an O2-Containing Exhaust Emission”, which is a device dedicated to remove nitrogen oxides, and which utilizes electrochemical catalytic reduction reaction and adopts vanadium pentaoxide (V2O5) as the catalyst to convert nitrogen oxides into nitrogen. The device has to add a power supply to operate the electrochemical cell thereof. Thus the device of this prior art not only consumes energy resources, also cannot remove harmful exhaust gases simultaneously.
The objective of the present invention is to provide an electrochemical-catalytic converter for exhaust emission control with power generation, which can remove the nitrogen oxides, carbon monoxide and hydrocarbons in the exhaust gas without consuming power.
To achieve the abovementioned objective, the present invention proposes an electrochemical-catalytic converter, which comprises at least one cell module, a heating unit, a fuel input unit, a fuel output unit, an exhaust gas input unit, and an exhaust gas output unit. The cell module includes a cathode compartment, an anode compartment and a membrane-electrode assembly. The membrane-electrode assembly is interposed between the cathode compartment and the anode compartment. The cathode compartment includes an oxidation catalyst. The fuel input unit and the fuel output unit are respectively coupled to two sides of the anode compartment to function as the fuel input terminal and the fuel output terminal of the cell module while operating. The exhaust gas input unit and the exhaust gas output unit are respectively coupled to two sides of the cathode compartment to function as the exhaust gas input terminal and the exhaust gas output terminal of the cell module to be treated as desired.
The heating unit heats the membrane-electrode assembly to a working temperature to make the fuel to perform an electrochemical reaction in the membrane-electrode assembly to generate power. The nitrogen oxides in the exhaust gas react electrochemically in the membrane-electrode assembly to form nitrogen. The carbon monoxide and hydrocarbons in the exhaust gas are catalyzed to form carbon dioxide and water by the oxidation catalyst. Thereby, the exhaust gas is decontaminated.
Below, the technical contents of the present invention are described in detail with the embodiments in cooperation with the drawings.
The embodiments of the present invention are described in accompany with the following drawings.
The present invention proposes an electrochemical-catalytic converter for reducing nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HCs) in an exhaust gas with power generated simultaneously. The electrochemical-catalytic converter of the present invention can be applied to various exhaust emission devices, such as the chimneys of factories and the exhaust emission devices of generators, automobiles and boats. There is no limitation to the exhaust emission device in the present invention. In the present invention, the “exhaust gas” is referred to the gas to be decontaminated and includes at least one of the harmful gases mentioned above. Therefore, the exhaust gas does not necessarily include all of the three abovementioned harmful gases. The technical contents of the present invention are described in detail in cooperation with the drawings below.
Refer to
The cell module 10 may be an SOFC (Solid Oxide Fuel Cell) stacking structure, such as a tubular or planar SOFC stacking structure. However, the present invention does not limit the cell module 10 to be an SOFC stacking structure. The cell module 10 further comprises a cathode compartment 11, an anode compartment 12 and a membrane-electrode assembly (MEA) 13, which are stacked one by one with the membrane-electrode assembly 13 interposed between the cathode compartment 11 and the anode compartment 12.
The membrane-electrode assembly 13 further comprises a cathode layer 131, an anode layer 132 and an electrolyte layer 133, and the electrolyte layer 133 is interposed between the cathode layer 131 and the anode layer 132. The electrochemical reaction of the present invention takes place in the membrane-electrode assembly 13. The electrolyte layer 133 conducts ions and separates the reactant gases respectively existing in the cathode layer 131 and the anode layer 132.
In one embodiment, the electrolyte layer 133 is a solid electrolyte which is a non-porous membrane structure able to separate the gases at two sides and conduct ions. The electrolyte layer 133 is made of a material selected from a group consisting of fluorite metal oxides, perovskite metal oxides, and the combinations thereof, such as fluorite YSZ (yttria-stabilized zirconia), stabilized zirconia, fluorite GDC (gadolinia-doped ceria), doped ceria, perovskite LSGM (strontium/magnesium-doped lanthanum gallate), and doped lanthanum gallate.
The cathode layer 131 and the anode layer 132 are respectively made of porous materials. In one embodiment, the anode layer 132 is made of a material selected from a group consisting of cermet of nickel and fluorite metal oxides, perovskite metal oxides, fluorite metal oxides, metal-doped perovskite metal oxides, metal-doped fluorite metal oxides, and the combinations thereof, such as Ni-YSZ (nickel-yttria-stabilized zirconia) cermet and Ni-GDC (nickel-gadolinia-doped ceria) cermet. The cathode layer 131 is made of a material selected from a group consisting of perovskite metal oxides, fluorite metal oxides, metal-doped perovskite metal oxides, metal-doped fluorite metal oxides, and the combinations thereof, such as perovskite lanthanum strontium cobalt iron oxides, lanthanum strontium manganese oxides, the combination of lanthanum strontium cobalt iron oxides and gadolinia-doped ceria, the combination of lanthanum strontium manganese oxides and gadolinia-doped ceria, vanadium-doped lanthanum strontium cobalt iron oxides, vanadium-doped lanthanum strontium manganese oxides, the combination of vanadium-doped lanthanum strontium cobalt iron oxides and gadolinia-doped ceria, and the combination of vanadium-doped lanthanum strontium manganese oxides and gadolinia-doped ceria.
Two ends of the cathode compartment 11 are respectively coupled to the exhaust gas input unit 30 and the exhaust gas output unit 40. The cathode compartment 11 has a cathode channel 111 and a cathode current collecting layer 112. Refer to
Two ends of the anode compartment 12 are respectively coupled to the fuel input unit 50 and the fuel output unit 60. The anode compartment 12 has an anode channel 121 and an anode current collecting layer 122. Refer to
The exhaust gas input unit 30 inputs the exhaust gas that is to be decontaminated to the cathode channel 111 of the cathode compartment 11. The nitrogen oxides in the exhaust gas are delivered to the cathode layer 131 and electrochemically reacted to form nitrogen. The carbon monoxide and hydrocarbons in the exhaust gas are oxidized to form carbon dioxide and water via the oxidation catalyst in the cathode compartment 11. Then, the unreacted exhaust gas and the reacted gas are transferred from the cathode channel 111 to the exhaust gas output unit 40 to be exhausted. Similarly, the fuel input unit 50 inputs the fuel that is to be transferred to the anode channel 121 of the anode compartment 12. The fuel in the anode channel 121 is delivered to the anode layer 132 and electrochemically reacted to generate power. Then, the unreacted fuel and the reacted products are transferred from the anode channel 121 to the fuel output unit 60 to be exhausted.
In the cell module 10 of the present invention, the harmful gases in the exhaust gases are removed via the electrochemical reaction in the membrane-electrode assembly 13 and the catalyzed reaction in the cathode compartment 11 with electric power generated simultaneously. The electrochemical reactions in the cathode layer 131 and the anode layer 132 and the reaction of the abovementioned harmful gases will be described in detail below.
In the present invention, the fuel may be hydrogen (H2), methanol, ethanol, gasoline, diesel, natural gas, liquefied petroleum gas, etc. The fuel is input to the anode compartment 12 by the fuel input unit 50 and gasified in the anode compartment 12. The gasified fuel is reformed into a fuel consisting of hydrogen (H2) and carbon monoxide (CO). The fuel including hydrogen (H2) and carbon monoxide (CO) can react with oxygen ions (O2−) in the anode layer 132 and generate electrons as electric power. The chemical reactions of hydrogen and carbon monoxide can be expressed by Formulae (1) and (2):
H2+O2−→H2O+2e− (1)
CO+O2−→CO2+2e− (2)
The reactant oxygen ions are generated in the cathode layer 131 and transported to the anode layer 132 through the electrolyte layer 133. The oxygen ions may be originated from the oxygen in the exhaust gas and generated in the cathode layer 131 according to Formula (3):
O2+4e−→2O2− (3)
Alternatively, the oxygen ions are the reactant generated by performing DeNOX (nitrogen oxide abatement) in the cathode layer 131, which will be described in detail below.
The unreacted fuel and the reacted products are transferred to the fuel output unit 60 and exhausted there. In practice, the reactant output by the fuel output unit 60 can be recycled to the furnace or engine generating the exhaust gas as the fuel thereof. If the electrochemical-catalytic converter 1 of the present invention is applied to a vehicle exhaust treating system, the gas output by the fuel output unit 60 can be guided into the carburetor of the vehicle engine and re-used.
The harmful gases of the exhaust gases are converted into harmless gases in the cathode compartment 11 and the cathode layer 131. The harmful nitrogen oxides are mainly nitric oxide (NO) and nitrogen dioxide (NO2). Nitric oxide (NO) and nitrogen dioxide (NO2) can electrochemically react to form nitrogen in the cathode layer 131 according to Formulae (4) and (5):
2NO→N2+2O (4)
2NO2→N2+4 (5)
Among the reaction products, oxygen atom therein can be transformed to an oxygen ion according to Formula (6):
O+2e−→O2− (6)
The oxygen ions can pass through the electrolyte layer 133 to take part in the reaction in the anode layer 132.
At the beginning of the electrochemical reaction, the heating unit 20 provides heat to drive the oxygen ions in the cathode layer 131 to pass through the electrolyte layer 133 and take part in the reaction in the anode layer 132. Considering the system structure of the present invention and that the anode layer 132 can generate electric power and that precise temperature control is required for the heating unit 20, the heating unit 20 of the present invention can be realized with an electrical heating element.
In one embodiment, the heating unit 20 can be embedded in the anode compartment 12 of the cell module 10 by a sheathed electric heating coil manner to heat the membrane-electrode assembly 13, such as embedded in the anode channel 121 or the anode current collecting layer 122 of the anode compartment 12. However, the present invention is not limited by this embodiment. In one embodiment, the heating unit 20 can heat the membrane-electrode assembly 13 to a working temperature of 450-900° C. to increase the efficiency of oxygen ion transport in the electrolyte layer 133. The working temperature can be appropriately decreased if the material of the electrolyte layer 133 has improved quality or the requirement of converting nitrogen oxides is lowered.
The oxidation catalyst of the cathode compartment 11 can catalyze a reaction to convert carbon monoxide (CO) and hydrocarbons (HCs) into harmless gases, wherein carbon monoxide in the exhaust gas is oxidized into carbon dioxide and hydrocarbons are oxidized into carbon dioxide and water respectively according to Formulae (7) and (8):
2CO+O2→2CO2 (7)
HCs+O2→H2O+CO2 (8)
In one embodiment, the elements of the oxidation catalyst is made of a material selected from a group consisting of metal, alloy, fluorite metal oxides, perovskite metal oxides, and the combinations thereof.
Refer to
Refer to
Via the electrochemical reaction and catalytic reaction, the present invention can remove harmful gases in the exhaust gases and generate electric power at the same time. In practice, the voltage of the generated electric power is able to achieve a level of 0.6 volt and less likely to vary with electrochemical reaction of nitrogen oxides in the cathode layer 131 so that the generated electric power can be a relatively stable power supply. After the heating unit 20 heats the membrane-electrode assembly 13 to achieve a working temperature, the exothermic electrochemical oxidation reaction of the anode layer 132 and the exothermic catalytic oxidation reaction of the cathode compartment 11 can persistently supply heat. Thereby, the power consumption of the operation of the cell module 10 can be reduced. The reactions may even generate heat more than that required to sustain the working temperature. In such a case, the surplus heat may be used otherwise. On the other hand, the higher the oxygen concentration in the exhaust gas is, the higher the operation efficiency of the electrochemical-catalytic converters 1 and 2 can be. Therefore, the present invention is particularly suitable to apply to the exhaust gas treatment of lean burn engines, such as the exhaust emission systems of diesel vehicles. In comparison with the conventional technology, the present invention integrates a NOx reduction system and an oxidation catalytic converter to achieve a better exhaust gas treating mechanism and higher exhaust gas treating efficiency. Further, the present invention can function as an auxiliary power unit (APU), which can generate electric power whether to treat the exhaust gas or not.
The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Any equivalent modification or variation according to the technical contents and drawings disclosed in the specification is to be also included within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 099106250 | Mar 2010 | TW | national |
