Chimney reactor

An elegant new reactor concept for the growth of SiC epitaxial layers was introduced by Ellison et al. [34, 53] and is called the chimney reactor. This technique is similar to the HTCVD technique in that it is a vertical system and the material transport is achieved by allowing large clusters of Si to form. This is achieved by reducing the carrier flow, which thereby increases the partial pressure of the precursors. Hydrogen is used as the carrier gas but, again, only very small flow rates are required. 

Several different types of CVD reactors exist. The cold wall design, which used to be the most common type of reactor, is now less frequently used and the hot-wall reactor has filled its place. Some new and interesting concepts exist as well. These are referred to as chimney-type reactors. The main difference between the hot- or old-wall type reactors and the chimney-style reactor is the transport of materials, which will be explained in the following sections. 

When gases from the reactor or the high-pressure separator are discharged through the chimney into the air, explosive mixtures can be formed. The explosion limits of mixtures of ethylene with air, as well as methane, hydrogen, and vinyl acetate with air are listed in Table 7.2-1 together with the ignition temperature. 

FALLOUT (Radioactive . The term fallout generally has been used to refer to particulate mutter that is thrown into the atmosphere by a nuclear process of short time duration. Primary examples are nuclear weapon debris and effluents from a nuclear reactor excursion. The name fallout is applied both to matter that is aloll and to matter that has been deposited on the surface of the earfh. Depending on the conditions of formation, this material ranges in texture from an aerosol to granules uf considerable size. The aerodynamic principles governing tls deposition are the same as for any Other material of comparable physical nature that is thrown into the air. such as volcanic ash or particles from chimneys. Therefore, many of the principles learned in. studies of fallout from nuclear weapons can be applied lo studies of other particulate pollution in the atmosphere. 

The reactor 07) consists of 5 by 28 cm flat flame burner downfired into a chimney of similar dimensions, fitted with Vycor windows for optical access. Access ports for droplet injection and sample probing are provided. As illustrated in Figure 3, fuel droplets are normally injected ballistically across the face of the burner. 

When gases are introduced into the retort, they are heated immediately and consequently experience the volumetric expansion correspondingly. The density variations of the gases result in a natural convection of gases within the retort, which is very common in our daily lives, such as the rising smoke from a cigarette or from a chimney. Natural convection (or free convection) is very undesirable in a CVD reactor because it is a kind of uncontrolled gas flow. 

Air pollution control APC units (cyclone, venturi scrubber, tangential spray scrubber, spray tower, ID fans, chimney) This is required to absorb the gases evolved from reactor and den for air pollution control HF will be released into atmosphere and cause air pollution Monitor operation of APC units and exit gases all the time... 

During normal operation the reactor core coolant outlet temperature is kept constant at 290°C, the inlet temperature varies with the power level (260°C at full power). The primary circuit coolant and the pool water are in direct contact below the core inlet plenum and at the top of the riser. The heated water from the core will rise up through the riser since its density is lower than the pool water density (the chimney effect), and the flow rate is determined by the temperature differences. By controlling the speed of the recirculation pump its flow is adjusted to the flow rate up through the riser to maintain the lower hot/cold Interface at a constant position - no pool water will enter the primary circuit. 

In terms of catalyst utilization, the most relevant reactor hardware is the distributor tray as it is responsible for the liquid distribution across the catalyst bed. In general, traditional distributor designs such as sieve trays, chimney trays, and bubble cap trays are known for their poor performance, whereas state-of-the-art distributors facilitate complete irrigation of the catalyst bed (e.g.. Sheiks HD tray, Topsoe Vapor-Lift tray, Exxon s Spider Vortex technologies, Akzo Nobel s Duplex tray, and Fluor s Swirl Cap tray) [65]. 

The air blower produces a pressure of about 0.3 bar above atmospheric pressure and this is sufficient to push the air and all of the product gases formed through the drying tower, the combustion chamber, the reactor, the absorbers, the filters in the top of the absorbers and up the chimney stack at the end of the plant. Quite clearly, techniques to calculate pressure drops are important because the correct sizing of the inlet air blower is vital. 

The uncontrolled loss of heat sink also terminates safely if the SGAHRS holds the safety passive function. The reactor vessel auxiliary coolant system (RVACS), which removes heat through the reactor wall to the chimney, serves as a passive system to back up the function of the SGAHRS in accident conditions. 

The PBWFR is designed to generate electricity. The cycle type is direct and the system pressure is the same as in conventional boiling water reactors (BWRs), see Fig. XXVII-2. Steam is generated in the chimneys in direct contact with hot Pb-Bi coolant above the core. There are no steam generators and intermediate heat transport systems. 

The molten salt coolant natural circulation loop includes the reactor core filled with spherical fuel elements and absorber and graphite elements the top, bottom and annular side reflectors the draught section (chimney) and salt-air heat exchangers. The side reflector material consists of the circulating molten salt coolant. 

I - Core 2 - Radial reflector 3 - Bottom reflector 4 - Top reflector 5 - Reactor vessel 6 - Protective shielding 7 - Slag layer on the reactor vessel inner surface 8 - Salt-air heat exchanger 9 - Draught section (chimney) 10 - Displacer ... 

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