Flue gas recycling

Clearly, these figures suggest that the plant is very sensitive to the amount of flue gas recycled. There appears to be no full parametric or economic calculation published in the literature for this FG/TCR cycle, which suggests that it has not been considered as an attractive option. 

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]. 

In large-scale applications, fiuidized-bed boilers are now dominant on the market. Both bubbling fluidized beds (BFBs) and circulating fluidized beds (CFBs) are used for biofuel firing. BFBs were originally limited to a rather narrow specification of fuels but now flue-gas recycling is used in both types of boilers. Especially, CFBs are considered... 

Figure 16. Effect of flue gas recycling on NO emission (15-25% excess air) (Hiltunen and Tang, 1988)...

The economics seem to be better for systems where dry powdered fresh hme plus ground recycled hme is injected along with a relatively coarse spray which impinges on and dries out from the reagent, as described by Stouffer et al. [Hs EC Res., 28(1) 20 (1989)]. Witnum et al. [9th Ann. Pitt. Coal Prep. Util. Euv. Control Contractors Conf. (1993)] describes an advanced version of that system that has been further optimized to the point that it is competitive with wet hme-stone scrubbing for >90 percent flue gas desirffurization. 

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. 

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... 

MSWIs (several flue gas cleaning options) Mechanical recycling ... 

This article presents details of the gloomy picture of the environmental impacts associated with PVC waste which has been painted by four PVC waste management studies carried out for the European Commission. The studies cover mechanical recycling, feedstock recycling, behaviour in landfill, and the influence of PVC on incinerator flue gas cleaning residues. 

Details are given of recycling plastic materials with emphasis on incineration. Its combination with chemical plants to use the flue gas as syngas is briefly mentioned. 5 refs. 

All the CO resulting from the pseudo solid-solid reaction is conducted, together with entrained char, from the top fluidized section through a constriction, in which the high-velocity gas flow prevents backflow, to a transport combustor, where the CO is burned to C02 with preheated air, along with as much of the char as is called for by heat balance to maintain the endothermic FeO-C reaction. The heated recycled char is separated from the off gas at the top of this transport combustor in a hot cyclone and is returned as a thermal carrier to the lower part of the lowest j igged section, while the hot flue gas from the transport combustor is used to preheat the incoming air in a recuperator. 

Citrate A process for flue-gas desulfurization by absorption of the sulfur dioxide in aqueous sodium citrate, reacting with hydrogen sulfide to produce elemental sulfur, and recycling the citrate solution. Subsequent modifications involved removing the sulfur dioxide from the citrate solution by steam stripping, or by vacuuming the gas used to make sulfuric acid. 

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