Combustion recycled flue gases

To complete the. set of possible chemical reactions, consider the combustion of a fuel such as methane with a recirculated flue gas containing m moles of carbon dioxide, but assuming that water vapour has been removed from the recycling flue gas. If the additional air supply (n moles) is assumed to be sufficient for complete combustion, then... 

The zero-emission energy recycling system (ZEROS) is a closed-loop thermal oxidation process that incinerates waste and recycles flue gas emissions for electrical co-generation. The technology uses a two-stage plasma torch combustion system, energy recovery system, and combustion gas cleanup systems. 

Oxyfuel combustion with flue gas recirculation represents a method of CO2 capture that could be implemented today. In this technique, input air is replaced by a mixture of recycled nitrogen-free flue gas (mainly CO2) and pure oxygen. The recirculated CO2 maintains an optimal oxygen concentration in intake gas, which, for a retrofit, would be near that of ambient air. The major cost and energy penalty in such a plant results from the operation of the oxygen plant, which consumes approximately one-third of the electricity output of the power station. At the current price of oxygen (US 4 per 100 the oxygen... 

In AFBC units, heat is removed from the flue gas by a convection-pass tube bank. The particulates leaving the boiler with the flue gas consist of unreacted and spent sorbent, unburned carbon, and ash. Multiclones after the convection pass remove much of the particulate matter and recvcle it to the combustor, increasing the in-furnace residence time an improving combustion efficiency and sulfur retention performance. Bubbling PFBC units do not have convection-pass tube banks and do not recycle solids to the boiler. 

The boilers are of water-wall construction with the walls in the bed region lined with refractory to protect against erosion and abrasion damage. The heat released in the bed is removed from the flue gas by the exposed water walls and by convection pass tubing set in the gas path after the boiler. The coal boilers included multiclones to collect elutriated carbon and recycle it back to the boiler to increase combustion efiiciency. However, because biomass is more reactive, recycle is not required. 

Psia, (b) co-current CO2 rinse at that pressure with recycle of effluent gas as feed, (c) counter-current evacuation to - 2.5 Psia with simultaneous steam pui e, and (d) counter-current pressurization with a part of CO2 depleted product gas from step (a). The effluent gas from step (c) is partly used as the purge gas in step (b) after recompression, and the balance is withdrawn as the recovered CO2 product gas. The inert gas and CO2 recoveries from the feed gas are, respectively, - 100 and 78% [21]. This application may be attractive for green house gas emission control (CO2 sequestration from a hot flue gas or CO2 removal from combustion gases for power generation). 

In order to avoid a social shock when the global energy system should transfer from fossil system to the CO2 recycling system using renewable energy, a hybridization between fossil and solar energy should be also discussed. That is, there are various kind of energy sources (solar, fossil fuels and their complex sources), and of carbon sources (CO2 from flue gas of combustion, CO2 from exhaust gas of fossil fuel chemical conversion, and carbon of fossil fuel itself). 

The carbon source for the synthetic fuels is primarily the CO2 from flue gas of fossil combustion, but finally, perfect recycling CO2 will be supplied without any fossil fuel. 

To produce a CO2 rich flue gas stream amenable for use or storage, oxy-fuel combustion typically involves replacing combushon air with pure oxygen, either parhally or completely, and usually in combination with recycled flue gases in order to temper the flame. In this particular investigation, the concept of flue gas recycling was tested in a pilot-scale test facility [3]. 

The dust removed in the flue gas scrubbing system is recycled to the combustion furnace together with the coal. A recycling system is thus achieved, in which the flow of material is only approximately quasi-sta-tionary after several cycles. As a result of dust recycling, the gas phase becomes enriched with volatile components (alkali compounds) which condense on cooling the flue gas, and a proportion of them return to the combustion furnace together with the dust. 

The convection pass cools the flue gas and entrained particulate matter from about 1145 K (1600°F) to below 645 K (700°F). For bituminous coal with a combustion temperature of 1115 K (1550°F), a recycle ratio of 2.5 (mass rate of particulate recycle to coal feed rate) increases combustion efficiency to over 97 percent from around 90 percent without recycle. For a bituminous coal containing 3 percent sulfur, 90 percent sulfur capture is achieved with limestone as sorbent at a calcium-to-sulfur (Ca/S) molar ratio of 2.3 and a recycle ratio of 2.5. A Ca/S molar ratio of over 3.4 is required when there is no recycle. The recycled material also enters the bed through T nozzles, one per 7 m (72 ft ) of bed floor area. A means of distributing the particulate flow from the multiclones to the feed lines and overcoming the... 

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