Energy catalytic combustion

The main converter, which is located downstream of the EHC, heats to functional temperature much more quickly because of catalytic combustion of exhaust gases that would otherwise pass unconverted through the catalyst during the cold start period. The EHC theoretical power required for a reference case (161) was 1600 watts to heat an EHC to 400°C in 15 s in order to initiate the catalytic reactions and obtain the resultant exotherm of the chemical energy contained in the exhaust. Demonstrations have been made of energy requirements of 15—20 Wh and 2 to 3 kW of power (160,161). Such systems have achieved nonmethane HC emissions below the California ULEV standard of 0.025 g/km. The principal issues of the EHC are system durabihty, battery life, system complexity, and cost (137,162—168). 

New research in combustors such as catalytic combustion have great promise, and values of as low as 2 ppm can be attainable in the future. Catalytic combustors are already being used in some engines under the U.S. Department of Energy s (DOE), Advanced Gas Turbine Program, and have obtained very encouraging results. 

In such a device, the electrons liberated at the anode by the oxidation of methanol circulate in the external electrical circuit, producing electrical energy, and reach the cathode, where they reduce the oxidant, usually oxygen from air. The overall reaction thus corresponds to the catalytic combustion of methanol with oxygen, i.e.,... 

However, catalytic combustion deposits a portion of the liberated energy directly into the structure complicating thermal management. 

In recent decades, catalytic combustion has been explored as a primary control method for the production ofheat and energy with two main goals (i) to achieve ultra-low emissions of NO, CO and unburned hydrocarbons (UHCs) and (ii) to obtain stable combustion under conditions not allowed by conventional methods. 

Numerous studies have been published on catalyst material directly related to rich catalytic combustion for GTapplications [73]. However, most data are available on the catalytic partial oxidation of methane and light paraffins, which has been widely investigated as a novel route to H2 production for chemical and, mainly, energy-related applications (e.g. fuel cells). Two main types of catalysts have been studied and are reviewed below supported nickel, cobalt and iron catalysts and supported noble metal catalysts. 

Rich catalytic combustion will offer wide opportunities with respect to most of the above issues, including flexible integration in different machines, low-temperature ignition ability, tolerance to fuel concentration and temperature non-uniformities and fuel flexibility. Further, the production of syngas in short contact time catalytic reactors could be exploited in several energy-related applications such as fuel cell and oxy-fuel combustion. 

Finally, the development of microcombustors for energy conversion in small devices appears to be a stimulating field for catalytic combustion research, which once more will require the combined study of engineering solutions with advanced catalytic materials. 

In renewable energy processes, the measurement of 02 can be used to optimize the efficiency of combustion processes or to guarantee the safety of H2 production and distribution. Oxygen analyzers can depend on the paramagnetic and electrochemical properties of 02, or can utilize the catalytic combustion and spectroscopic techniques. 

At present, one catalytic combustion system has been implemented at a full scale the XONON Cool Combustion technology, developed by Catalytica Energy Systems 157,158). The system is operated as follows Fuel from a lean-mix prebumer and the main fuel stream together with compressed air pass through the catalyst module (palladium oxide catalyst deposited on corrugated metal foil) in which the gas reaches a temperature up to 1623 K. The UHC and CO are combusted to essentially full conversion, downstream of the catalyst in the homogenous combustion zone. The guaranteed emission levels are as follows NOj < 3 ppm. 

Fig. 11. Experimental setup for the in situ detection of chemisorbed CO during catalytic combustion of CO on Pt using optical infrared-visible sum frequency generation (SFG) and mass spectrometry. A mode-locked Nd YAG laser system is used to provide the visible laser beam (second harmonic 532 nm) and to pump an optical parametric system to generate infrared radiation (wir) tunable with a pulse duration of 25 ps. MC monochromator, PMT Photomultiplier, AES Auger Electron Spectrometer, LEED Low Energy Electron Diffraction Spectrometer, QMS Quadrupole Mass Spectrometers for CO Thermal Desorption (TD) and CO2 production rate measurements.

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