Recycled flue gases

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]. 

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. 

The necessity for regeneration arises from the fact that catalyst activity declines with time on reaction, owing to small deposits of carbonaceous material and sulfur compounds on the catalyst. This deposit, of course, varies with feed stock, catalyst, and process conditions. The regeneration is carried out by oxidizing the deposits on the catalyst with a stream of air diluted to 2 to 3% oxygen with recycled flue gas. 

Operating Conditions and Flue Gas Analyses for the Experimental and Numerical Investigations of Burner C2-Stacked Furnace Combination in Recycled Flue Gas Mode... 

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. 

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. 

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. 

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. 

In the lime or limestone FGD process, SO2 is removed from the flue gas by wet scrubbing with a slurry of calcium oxide or calcium carbonate [3]. The waste solid product is disposed by ponding or landfill. The clear hquid product can be recycled. Many of the lime or limestone systems discharge scrubber waters to control dissolved solids levels. 

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