Solid combustor

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. 

Catalytic combustor A device used to remove various solid, liquid, or gaseous pollutants from air or another gas, in which the gas is heated by an open burner to between 250 and 500 °C and passed through a catalyst bed in which the organic contaminants are oxidized into harmless by-products. 

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. 

In a solid-propellant rocket motor, the propellant is contained within the wall of the combustion chamber, as shown in Fig. 1. This contrasts with liquid systems, where both the fuel and oxidizing components are stored in tanks external to the combustion chamber and are pumped or pressure-fed to the combustor. In hybrid systems, one component, usually the fuel, is contained in the combustion chamber, while the other component is fed to the chamber from a separate storage tank, as in liquid systems. The solid-propellant motor also has an ignition system located at one end to initiate operation of the rocket. The supersonic nozzle affects the conversion of... 

According to APME, energy recovery should be the preferred waste disposal route for polymeric materials that are very contaminated, bonded, laminated to other materials, or are at the end of their performance with respect to their physical/chemical properties. This paper takes a detailed look at energy recovery from municipal solid waste combustors, and considers the effect of polymeric materials. 

The role of plastics in municipal solid waste combustion is discussed, and in particular, their fuel characteristics. Details are given of a state-of-art municipal solid waste combustor and the effects of plastics on the different combustion stages. In addition, the contribution of plastics to the total output spread over the various emission paths of solids, liquids and gases, is also assessed. 

Hazardous and Solid Waste Amendments Hazardous waste combustors... 

One discouraging problem is the decrease in reactor or combustor performance when a pilot plant is scaled up to a larger commercial plant. These problems can be related to poor gas flow patterns, undesirable solid mixing patterns and physical operating problems (Matsen, 1985). In the synthol CFB reactors constructed in South Africa, first scale-up from the pilot plant increased the gas throughput by a factor of 500. Shingles and McDonald (1988) describe the severe problems initially encountered and their resolution. 

Table 1 gives the values of design and operating parameters of a scale model fluidized with air at ambient conditions which simulates the dynamics of an atmospheric fluidized bed combustor operating at 850°C. Fortunately, the linear dimensions of the model are much smaller, roughly one quarter those of the combustor. The particle density in the model must be much higher than the particle density in the combustor to maintain a constant value of the gas-to-solid density ratio. Note that the superficial velocity of the model differs from that of the combustor along with the spatial and temporal variables. 

When modelling a pressurized hot bed (Table 2) the ambient temperature model fluidized with air has dimensions very close to those of the pressurized combustor. If another gas is used in the model, particularly a gas with a higher density, the model can be made much smaller than the pressurized combustor (see Table 3). Care must be taken to select a safe modelling gas and one which yields a solid density for the model which is available. 

Glicksman and Farrell (1995) constructed a scale model of the Tidd 70 MWe pressurized fluidized bed combustor. The scale model was fluidized with air at atmospheric pressure and temperature. They used the simplified set of scaling relationships to construct a one-quarter length scale model of a section of the Tidd combustor shown in Fig. 34. Based on the results of Glicksman and McAndrews (1985), the bubble characteristics within a bank of horizontal tubes should be independent of wall effects at locations at least three to five bubble diameters away from the wall. Low density polyurethane beads were used to obtain a close fit with the solid-to-gas density ratio for the combustor as well as the particle sphericity and particle size distribution (Table 6). 

Differential pressure measurements were made between several vertical elevations within the bed. The probability density function of the cold model and combustor gave very close agreement (Fig. 35). The solid fraction profiles were obtained from the vertical pressure profile with a hydrostatic assumption. The cold model solid fraction profile showed very close agreement with data taken from pressure taps in two different locations within the combustor (Fig. 36). The solid fraction shows a... 

Figure 54. Solid fraction profile comparison between pressurized circulating fluidized bed combustor and one-half size scale model based on simplified scaling law. (Glicksman et al., 1995.)...

Farrell, P. A., Hydrodynamic Scaling and Solids Mixing in Pressurized Fluidized Bed Combustors, Ph.D. Thesis, Massachusetts Institute of Technology (1996)... 

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. 

Ishida, M. et al., Application of Fe203-Al203 composite particles as solid looping material of the chemical-loop combustor, Energy Fuels, 19(6), 2514,2005. 

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