Tubular solid oxide fuel cell technology advances

Abstract: This paper describes the cathode, anode, electrolyte, porous ceramic tube supported on various types of solid oxide fuel cell (SOFC) Research and development; introduced Siemens - Westinghouse tubular SOFC power company and the Joint Cogeneration cycle power generation technology progress. The development of tubular SOFC combined cycle power generation as the main body - combined heat and power supply systems for clean energy can improve coal, natural gas and other fuels, power generation efficiency, the formation of the client directly electricity, heat, cooling by the network.

And flat type solid oxide fuel cell (SOFC) compared with tubular SOFC due to high mechanical strength, high thermal shock resistance, simplified seal technology, the characteristics of high performance modular, integrated, more suitable for building large-capacity power station. Preparation of tubular cells as difficult, in tubular SOFC R & D units were over 30, while the capacity to achieve 100kW or more, only Siemens - Westinghouse Power (SWPC) company. The author made tubular SOFC R & D status and SWPC company cogeneration and combined cycle power generation technology progress in two areas of related technology has been briefly introduced.

An all-tube SOFC

1.1 cathode supported tubular SOFC

SWPC Westinghouse Electric Company has been using American support structure of the company's cathode prepared from single-tube SOFC, process is: out of one end of the closed end of the opening of the LSM (La1-xSrxMnO3) YSZ (Y2O3 stability of ZrO2)-based management, using plasma spray , prepared along the tube axis width 11mm, 100μm thick compact Doped Lanthanum Chromite linkers article, electrochemical vapor deposition (EVD), in the preparation of cathode 30 ~ 40μm thick outer layer of dense YSZ electrolyte, the electrolyte membrane outside side, with a soluble preparation of 100μm thick deposited Ni YSZ cermet anode. The total length of single tube 1.680mm, diameter 22mm, thickness 2.2mm, the electrochemical activity of the reaction zone (ERZ) of the effective length of 1.500mm. Within the ERZ, the effective management of each single area 834cm2.

SWPC structure employed by the ground and the bottom 3 strings 8, formed by the 24-tube bundle. Bundles, parallel single-tube by nickel-felt connection; series of single-tube is below the single-tube doped Lanthanum Chromite body through the Ni-felt connection with the anode connected to the top of a single tube. Stack, the tubes formed by nickel-mat series bundle out, bundle out of the cathode and anode ends, nickel plate, tube out further in series to form a stack. Stack assembly, demolition and replacement single tube to tube as a unit, so bundle processing preparation is very important. General high temperature furnace tube through the pre-baked hard component can also be used - soft component connection method to connect.

Currently, SWPC company's single-tube, stack the preparation and assembly of mature technology, from the preparation of electrolyte membrane, and connectors, used in step 3 anode EVD technology a step down to prepare electrolyte membrane, but the high cost of preparation, production cycle length, production of low efficiency, SWPC is trying to use other means to replace EVD technology.

Canadian fuel cell technology (FCT) company is committed to 5kW tubular SOFC power systems research and development, the power reactor design and manufacturing companies by the SWPC. East Tao Corporation of Japan by slurry coating technique, step by step preparation of YSZ electrolyte, doped Lanthanum Chromite connectors and Ni YSZ anode, the development of their stack size of 10kW.

The support of SOFC cathode tube mechanical strength, high thermal cycling performance, technically demanding, easy-to-mobile, assembly, management, but support tube wall thick, the cathode impedance and oxidant mass transfer resistance is high, the stack to In 930 ~ 1000 °C high temperature work, the normal operating voltage, the output power density of only 0 15 ~ 0 20W/cm2.

1.2 anode supported tubular SOFC

Anode supported tubular SOFC with micro-tube technology is developed.

Keele University, UK by co-extrusion method, extrusion functional gradient of Ni YSZ anode layer and the YSZ electrolyte layer within the pipe from the pipe, the anode layer of Ni content decreased from 90% to 30%, the most outer layer of 100μm thick The YSZ electrolyte layer, with the coating method, the outer electrolyte prepared LSM cathode materials, micro-diameter 3mm, pipe wall thickness 0.3mm, length 50mm, the effective length of 25mm. Ni YSZ anode modified by the modification, you can use different hydrocarbons as fuel. Keele University, microtubules SOFC technology features: the quick start, you can use different hydrocarbon as fuel. Keele University has assembled a 20,200,400,1000 root single tubes, multiple stacks, in which 1000 single-tube stack in natural gas as fuel, the outside power 500W, the entire operation is controlled by computer. Acumentrics has developed civilian 5kW, 10kW power generation systems and uninterruptible power supplies and other products 2kW, start time is 10 ~ 30min, the fuel is natural gas, methane, propane, ethanol, methanol or hydrogen, and Keele University, The difference is that the battery management of the company All horizontal, and the fuel gas into the tube socket on the battery tube to improve the effective utilization.

Dalian Institute of Chemical Physics, Chinese Academy of preparation of anode current single tube cell, open circuit voltage at 800 °C up to 1.10V, the maximum output current density of 911 86mA/cm2, the maximum output power density 283.12mW/cm2; work in 0 7V , the output current density over 346.08mA/cm2, output power density of 242.60mW/cm2; in the 200h stability test, no significant performance degradation. As planned, in 2005, the Institute will assemble 2kW tube SOFC stack.

Anode supported tubular SOFC prepared by low-cost method of achieving electrolyte membrane, lowering operating temperature. Wet chemical method using low-cost alternative EVD, chemical vapor deposition (CVD) films prepared electrolyte, not only to reduce costs and shorten the preparation period, to improve efficiency, but also allows the battery in the 600 ~ 800 °C work under medium temperature.

1.3 electrolyte SOFC support tube

Keele University, UK is the first out of the early work of YSZ tube, and then dipping the anode and cathode preparation. G J Saunders and other prepared tube diameter 2.5mm, wall thickness of 200μm, the anode and cathode nickel wire and silver were used to collect current. Adelan Ltd. Portable Power SOFC stack size 5 ~ 500W, and can be activated within 1min to 800 °C, with propane, methane, ethanol or isooctane, or petrol as fuel, the stack assembly of the metal package sealing technology. Electric stacker electric mode relies on a separate set for each single flow tube after the tube outside the current export.

C Hatchwell and other support to the tubular SOFC electrolyte preparation of the electrolyte material, thermal expansion coefficients, mechanical strength, thermal shock resistance were studied. Ni YSZ anode with a syringe to the extrusion materials, dipping the GDC (Gd2O3 doped CeO2) electrolyte tube inside, dry roasting, then La0.6Sr0.4CoO3-GDC cathode material to the electrolyte tube brush the outside, dry roasting, anode nickel wire set with two streams, the cathode assembly with a silver stream, with humidification of hydrogen as fuel and air as oxidant, 600 °C open circuit voltage of 0.911V, at 0.7V, the output current density is only 12.3mA/cm2. On the diameter of 3mm, thickness 0.3mm, length 25mm of YSZ, GDC, LSGM (La0.9Sr0.1Ga0.8Mg0.2O2.85) electrolyte test tube and found that thermal shock performance ranked in descending order. Such as Gadolinium gypsum mold, the improved grouting and vacuum grouting, were prepared and 226 ~ 260mm length 140mm, wall thickness 0.4 ~ 0.9mm and 0.2mm of dense YSZ electrolyte tubes, 900 °C, the single cells maximum output power was 0.46W, and 0.48W.

Used as supporting electrolyte tube, electrolyte tube anode or cathode materials inside the hard coating evenly, if the magnification scale preparation, is difficult to ensure the quality of the battery tube.

1.4 SOFC porous ceramic support tube

Westinghouse Electric Company early adopted stable CaO ZrO2 porous support tube structure, the structure after the few reports. C J Li such as flame spraying, prepared by the thickness of 1mm of Al2O3 Ni porous support tubes, using atmospheric plasma spraying on the support tube, the preparation of 25μm thick Ni YSZ anode layer, 150μm thick YSZ electrolytes layer and 10μm thick LSM cathode layer, battery operation 930 °C, open circuit voltage 1.04V, maximum output 101mW/cm2.

1.5 flat tube type SOFC type and set to take over

Tubular SOFC, the use of connectors connected to the stack in the series mode, current flows from the relative increase of cell internal ohmic impedance increases; In considering the battery efficiency, leading to low battery output power density. Make improvements to this, a set of tube and plate type in one of the advantages of flat-tube high power density SOFC structure of the acclaimed.

H Orui other developed flat tubular cathode supported Ni YSZ / YSZ / LSM YSZ cell, electrolyte thickness of 20μm, the cathode support body containing gas channel 14, the battery length 100mm, width 43mm, high-4.5mm. Battery operation in 1000 °C, current density 1.6A/cm2, the maximum power density 0.83W/cm2. J H Kim and other developed anode supported flat-tube SOFC, anode Ni YSZ, electrolyte, YSZ, the cathode for the multi-layer structure of LSM YSZ / LSM / LSCF (La0.6Sr0.4Co0.2Fe0.8O3), at 750 °C, voltage of 0.6V, the output current density 375mA/cm2, output power density 225mW/cm2. H Tsukuda and other stable ZrO2 CaO developed to support the pipe as a sleeve-type SOFC, prepared in the process of EVD, CVD and other techniques, the biggest advantage is obtained for the tandem cell structure, high voltage, but the high production cost, process complexity, Seal the problem more serious. Mitsubishi Heavy Industries has plasma spraying method and the preparation of electrolyte film printing technology, used in connection Preparation of the slurry coating technology, developed the stack size of 15kW.

2 type SOFC power generation technology

SOFC to achieve high energy conversion rate, to rely on cogeneration or combined power generation. Achieved using tubular SOFC cogeneration has SWPC company, Keele University, Adelan Limited and Acumentrics companies to realize the joint power generation only SWPC company. SWPC has a pressure of single cycle cogeneration system (CHP), atmospheric pressure SOFC combined cycle gas turbine (SOFC / GT), pressurized SOFC Gas Turbine Combined Cycle (PSOFC / GT) and other methods, the development direction set of fuel cells, gas turbines, steam turbines, combined heat and power for the integrated power supply, heat, cooling system.

2.1 Atmospheric single cycle cogeneration system (CHP)

Amlem built in the Netherlands near the 100kW power generation system was completed in 1997 designed and built at the beginning of operation 4000h later, due to some problems, replacement of a number of batteries, battery run 12500h in succession process, no performance degradation. To November 2000, the system total running 16500h, the public power supply 110kW, the net AC efficiency 46%; the local heating 64kW, the energy conversion rate of nearly 75% of the total. July 2001, that the system moved to the city of Essen, Germany demo site up and running, the total accumulated running time of more than 20000h.

100kW power generation system is composed of natural gas desulfurization, fuel reforming, SOFC power generation, high and low temperature heat exchanger, heat output etc., SOFC stack from the 48 bundles of 1152 simply type SOFC component. The stack can be viewed as the two 576-tube constitutes a sub-stack, each sub-stack has its own intake, the reaction tube after the recycling of fuel moisture, fuel reformer, unreacted fuel other parts of the combustion chamber. The power generation system fueled by natural gas, natural gas before entering the stack after desulfurization processing, the sulfur content down to 1 × 10-5%, desulfurization agent can be heated at room temperature the activated carbon or zinc oxide, if necessary, increase the hydrotreating process.

SWPC developed in partnership with KinectricsFacility 250kW power generation system project, the structure of the system is EDB/ELSAM-100kW amplification system, the stack formed by the 2292 single-tube, the current is running. StadwerkeHannover in Germany in 2004 and the BP U.S. companies built 250kW power generation system also began commissioning.

2.2 pressure combined cycle (PSOFC / GT)

SWPC company Southern California Edison, the construction of a 220kW pressurized SOFC-microturbine (PSOFC / MGT) Combined Cycle Power Generation System (PH200). Installation and commissioning in June 2000, a total run of the 3000h, power generation efficiency of 52%. SOFC power stacked in a vertical cylindrical pressure vessel, and EDB / ELSAM 100kW SOFC CHP system similar to the pressure, the pressure device, no obvious changes in the power heap. Under atmospheric pressure operation, the stack output power 100kW, pressurized to 0.3MPa, the stack power 180kW.

Magnified by the scale of 300kWPSOFC/MGT system (PH300) to install and then sent to RWEEnergie company of the stack from the 1704 single-tube cell structure, installed in the horizontal cylindrical pressure vessel, the power generation system for the CHP mode, with the heater from the system Recovery of exhaust heat to provide hot water in this region. The difference is that with PH200, PH300 uses a single axis drive SolarTurbines gas turbine.

SWPC company resolved PSOFC / MGT system, the main technical problems: A The high temperature heat exchange with the material of SOFC single cell optimization; B gas turbine combustion temperature and voltage optimization; C improved heat recovery method and intermediate cooling ; D Development of the use of low concentrations of gas turbine fuel burner; E guarantee start, load changes and system reliability when problems arise.

SWPC company that: PSOFC / GT system as efficient and low cost installation, the dispersion in the 200kW to 10MW power plant markets, a greater competitive advantage. Amplification in the process of generating system capacity, SOFC stack up in numbers only to enlarge, MW PSOFC / GT system, levels of pressure vessel, placed in 10 576 cells sub-stack, gas turbine model with the 300kW SolarTurbines ; the 20MW level PSOFC / ATS GT design of the system using high-pressure SOFC generator / high-pressure gas turbine, SOFC generator low voltage / low pressure gas turbine hybrid unit commitment, gas turbine gas turbine using Mercury50; in the 300MW class PSOFC / IRsofc GT system, and the 20MW level systems, according to high and low pressure form of independence, will SOFC generators and gas turbines together.

3 application prospects

SWPC SOFC single tube tube company to run more than 8a, the performance degradation rate 0 1% / kh; after 1000 °C from room temperature to 100 thermal cycles, no performance degradation, technology can substitute fire station, the key is To reduce the battery manufacturing costs. The development of tubular SOFC is the main, set SOFC, gas turbine, one steam turbine combined cycle power to - Cogeneration system clean energy systems, increased natural gas and coal power generation efficiency for the raw materials to form an integrated power, heat, cold CHP system, has great and far-reaching social and economic benefits.

 

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