Closed oxygen cycle

This method is based on electrochemical reduction of oxygen in a closed oxygen cycle (COC) and electrochemical oxidation of hydrogen in a closed hydrogen cycle within the cell. The above electrochemical reactions proceed on auxiliary catalytic electrodes partially immersed in the electrolyte and connected by means of electronic devices (ED) to the negative electrode (for oxygen reduction) and to the positive electrode (for hydrogen oxidation), respectively. 

The above processes form the so-called closed oxygen cycle (COC). The latter reduces substantially the water loss during charge and overcharge of the battery, making it maintenance-free. 

Fig. 8.2.1. Cycle D6. Matianl closed CICICBTBTBTX cycle burning methane with oxygen, and with CO,...

Dense gases are stable and inert. They are non-reactive towards the extract and they can be recirculated in the process without changing their properties. The excess pressure in the equipment prevents the entry of oxygen and damage by oxidation and the closed extraction cycle excludes the loss of highly volatile top notes. 

The Cu-Cl thermochemical cycle was first proposed by Carty et al. and was designated H-6 in a Gas Research Institute (GRI) report 151. In that study, H-6 consisted of four reactions, three thermal and one electrochemical. ANL s preliminary study indicated that two additional reactions should be added to the original H-6 cycle. So the proposed ALTC-1 cycle consists of six reactions. Reaction-1 is the hydrogen generation reaction and Reaction-6 is oxygen generation reaction [5]. The other reactions close the cycle. 

The carrier, QH, can be shown to react in one pot with molecular oxygen and propylene to produce propylene oxide, water, and the corresponding oxidized precursor Q. The latter is separately hydrogenated to close the cycle of reactions (equations 1-2). Actually, equation 1, hydrogen peroxide is produced in a first step in the reaction medium by QH and Oj and, in a second step, reacts with propylene at Ti-sites as previously reported (equations 3-4) (12-13). 

Strictly speaking these relations are valid only at 100% of efficiency of the internal oxygen cycle. But they can be transferred to most VRLA batteries, since usually such a high efficiency is closely approached. 

In the geochemistry of fluorine, the close match in the ionic radii of fluoride (0.136 nm), hydroxide (0.140 nm), and oxide ion (0.140 nm) allows a sequential replacement of oxygen by fluorine in a wide variety of minerals. This accounts for the wide dissemination of the element in nature. The ready formation of volatile silicon tetrafluoride, the pyrohydrolysis of fluorides to hydrogen fluoride, and the low solubility of calcium fluoride and of calcium fluorophosphates, have provided a geochemical cycle in which fluorine may be stripped from solution by limestone and by apatite to form the deposits of fluorspar and of phosphate rock (fluoroapatite [1306-01 -0]) approximately CaF2 3Ca2(P0 2 which ate the world s main resources of fluorine (1). 

The quantity of breathing gas consumed in deep dives is of both economical and logistical concern at depths of 300 m, a reasonably active diver requites ca 1.8 m (64 fT at STP) of breathing gas per minute. In closed-cycle breathing systems, of both the self-contained and umbiHcal types, the helium is recitculated after carbon dioxide is removed and the oxygen replenished (147). 

An unusual appHcation is the use of KO2 in a closed-cycle diesel system. Oxygen is suppHed and CO2 is removed in a KO2 bed, through which the... 

The function of the oxygen sensor and the closed loop fuel metering system is to maintain the air and fuel mixture at the stoichiometric condition as it passes into the engine for combustion ie, there should be no excess air or excess fuel. The main purpose is to permit the TWC catalyst to operate effectively to control HC, CO, and NO emissions. The oxygen sensor is located in the exhaust system ahead of the catalyst so that it is exposed to the exhaust of aU cylinders (see Fig. 4). The sensor analyzes the combustion event after it happens. Therefore, the system is sometimes caUed a closed loop feedback system. There is an inherent time delay in such a system and thus the system is constandy correcting the air/fuel mixture cycles around the stoichiometric control point rather than maintaining a desired air/fuel mixture. 

A signihcant problem in tire combination of solid electrolytes with oxide electrodes arises from the difference in thermal expansion coefficients of the materials, leading to rupture of tire electrode/electrolyte interface when the fuel cell is, inevitably, subject to temperature cycles. Insufficient experimental data are available for most of tire elecuolytes and the perovskites as a function of temperature and oxygen partial pressure, which determines the stoichiometty of the perovskites, to make a quantitative assessment at the present time, and mostly decisions must be made from direct experiment. However, Steele (loc. cit.) observes that tire electrode Lao.eSro.rCoo.aFeo.sOs-j functions well in combination widr a ceria-gadolinia electrolyte since botlr have closely similar thermal expansion coefficients. 

CBT and CCGT plant. with full oxidation (D4. D5). We next consider two semi-closed cycles for CO2 removal (Cycles D4 and D5) with air replaced as the oxidant for the fuel, by pure oxygen supplied from an additional plant. 

Cycle D5 is another variation of a CCGT plant with full oxygenation of the fuel as shown in Fig. 8.22 again it is a semi-closed cycle using pure oxygen. But now the CO2 is abstracted after compression, which may require the use of physical absorption plant. 

The Matiant cycle (D6). Fig. 8.23 shows a more complex and ingenious version of the semi-closed cycle burning fuel with oxygen—the so-called Matiant plant [16]. A stage... 

Finally, Fig. 8.26. shows Cycle E3—a semi-closed IGCC plant with oxygen fed to the main syngas combustion process in a semi-closed cycle [18J. Now the exhaust from the HRSG is cooled before removal of the CO2 at low pressure, without need of complex equipment. 

Chiesa. P, and Lozza, G. (1999), CO2 emission abatement in IGCC power plants by semi-closed cycles— Part A with oxygen-blown combustion, ASME J. Engng Gas Turbines Power 121(4). 635-641. 

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