Combustor and gasifier

Rizeq, R.G Shadman, F 1989, Alkali-induced agglomeration of solid particles in coal combustors and gasifiers, Chem. Eng, Conun. Vol.81, 83-96. 

The seeond focus of this chapter will be on the design rules for small-scale experimental models that permit the direct simulation of the hydrodynamics of a hot, possibly pressurized, pilot plant or commercial bed. By the use of this modeling technique, beds of different diameters, as well as different geometries and operating conditions, can be simulated in the laboratory. To date, this technique has been successfully applied to fluidized bed combustors and gasifiers. Rules for the use of this experimental modeling technique for fluidized bed operations with different particle sizes, as well as for the simulation of bed-to-solid-... 

Fluidized bed gasifiers and fluidized bed combustors for carbonaceous fuels are relatively simple chemical reactors that can be utilized for several industrial applications that include chemical synthesis, process heat supply, steam generation, and power generation. Only relatively recently have carbonaceous fuel fluidized bed combustors and gasifiers reached or approached commercial status, with fluidized bed combustors gaining commercial acceptance earlier than fluidized bed gasifiers. 

An important variant of the Fluid Bed system is under development. This variant eliminates use of air or oxygen in the actual gasifier. Steam and coal are the reactants. Since we know from Table 3 that the reaction of steam with coal is endothermic, a heat source must be provided. Hot solids in the form of char are heated in a combustor and are transferred to the gasification reactor as one these processes. In another, hot alkaline oxides react with the carbon dioxide in the gas to form carbonates. The exothermic reaction of carbonate formation supplies the heat requirements of the steam-carbon reaction. Both of these processes depend on a reactive coal or char to implement the steam-carbon reaction. 

The aim of the sampling system presented here is to take samples from a circulating fluidised bed gasifier at pilot plant scale (200 Nm /h of gases are released). This one has been extensively operated as a combustor and it has recently been revamped to operate as a gasifier. Different feedstocks tike oak chips, orujillo" (a residue from the olive oil making industry), etc. will be gasified in the first studies. 

The cross flow of gas between the riser-combustor and the bubbling-bed gasifier is strongly influenced by the flow through the primary air inlet but with appropriate division of gas flow between primary and secondary inlets and the total flow into the gasifier the air content of the product gas can be controlled at an acceptable level. 

Reactor Network Modeling of a Biomass Dedicated Swirling Combustor and a Fluidized Bed Gasifier... 

The catalytic activity of substituted hexa-aluminates for methane combustion is low compared with noble metals, like Pd. For use in a fully catalytic combustor, these materials will have to be combined with a first stage with higher activity. For other fuels the differences are not so pronounced, e.g. for diesel. Hexa-aluminates also show a high activity in CO and H2 combustion and gasified biomass. For these kinds of fuels the ignition temperatures over hexa-aluminates are in the same area as the outlet temperature from the gas turbine compressor. 

Reactivities of coal and other solids (limestone, dolomite, etc.) in fluidized bed combustors or gasifiers decrease as they... 

Hot Corrosion. Hot corrosion is an accelerated form of oxidation that arises from the presence not only of an oxidizing gas, but also of a molten salt on the component surface. The molten salt interacts with the protective oxide so as to render the oxide nonprotective. Most commonly, hot corrosion is associated with the condensation of a thin molten film of sodium sulfate [7757-82-6], Na2S04, on superaHoys commonly used in components for gas turbines, particularly first-stage turbine blades and vanes. Other examples of hot corrosion have been identified in energy conversion systems, particularly coal gasifiers and direct coal combustors. In these cases the salt originates from alkali impurities in the coal which condense on the internal... 

In second-generation PFBC, a topping combustor is used to raise the turbine rotor inlet temperature to state-of-the-art levels. Pulverized coal is fed to a partial-gasifier unit that operates about 870° to 925°C (1,600° to 1,700°F) to produce a low heating value fuel gas and combustible char. The char is burned in the PFBC. The fuel gas, after filtration, is piped back to the gas turbine, along with the PFBC exhaust. 

Beyond the ATS program, the DOE is looking at several new initiatives to work on -with industry. One, Vision 21, aims to virtually eliminate environmental concerns associated with coal and fossil systems while achieving 60 percent efficiency for coal-based plants, 75 percent efficiency for gas-based plants, and 85 percent for coproduction facilities. Two additional fossil cycles have been proposed that can achieve 60 percent efficiency. One incorporates a gasifier and solid oxide fuel into a combined cycle the other adds a pyrolyzer with a pressurized fluidized bed combustor. Also under consideration is the development of a flexible midsize gas turbine. This initiative would reduce the gap between the utility-size turbines and industrial turbines that occurred during the DOE ATS program. 

Heat is transferred between the two reactors by circulating sand between the gasifier and combustor. Both reactors are of the riser type with a very short residence time. They allow for a high PVC waste throughput. The gasifiers have a reducing atmosphere, which prevents the formation of dioxins. 

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