Reactor bundle features

At present the direct synthesis of alkyl- and arylchlorosilanes is often carried out in apparatuses which operate using the phenomenon of fluidising. Turbulent movement of components in such a reactor guarantees good contact of reactants with contact mass, as well as steady temperature. Reactors with the fluidised layer are cylindrical apparatuses of various diameter with heat exchange elements. Fig.9 features a reactor with a heat exchange element in the form of a Field tube, and Fig. 10 shows a reactor with a heat exchange element in the form of a small-diameter tube bundle. 

Stratco Reactors. These reactors designed by Stratco, Inc. produce about 34% of the alkylate produced worldwide (P. Pyror, personal communication). In 2003, Stratco was purchased by E.I. du Pont de Nemours, Inc. A reactor, often called a Contactor, is a horizontal cylindrical vessel, as shown in Fig. 1, with the following features. An impeller at one end recirculates the acid/hydrocarbon dispersion many times (on average) over a U-tube bundle to regulate the temperature of the dispersion at about 5-10°C. A cylindrical circulation shell located in the reactor provides an annular space so that the dispersion flows from one end of the reactor to the other, where it makes a 180° turn and flows back over the tube bundle. 

We shall develop next a single-channel model that captures the key features of a catalytic combustor. The catalytic materials are deposited on the walls of a monolithic structure comprising a bundle of identical parallel tubes. The combustor includes a fuel distributor providing a uniform fuel/air composition and temperature over the cross section of the combustor. Natural gas, typically >98% methane, is the fuel of choice for gas turbines. Therefore, we will neglect reactions of minor components and treat the system as a methane combustion reactor. The fuel/air mixture is lean, typically 1/25 molar, which corresponds to an adiabatic temperature rise of about 950°C and to a maximum outlet temperature of 1300°C for typical compressor discharge temperatures ( 350°C). Oxygen is present in large stoichiometric excess and thus only methane mass balances are needed to solve this problem. 

To demonstrate the viability of these multi-scale solutions, the multi-scale reactor is first considered as a bundle of parallel tubes or channels, corresponding to the subflows, with a channel diameter D, a length L and a total number of channels N. The heat-transfer characteristic time, the reactor volume and the specific mechanical energy can be expressed as a function of these independent geometric parameters. Moreover, the ratio of the specific energy of a reactor after intensification (subscript 2) and before intensification (subscript 1) can be related to the features of interest as follows ... 

On-power fuelling is a feature of all PHWRs which have veiy low excess reactivity. In this type of reactor, refuelling to compensate for fuel depletion and for overall flux shaping to give optimum power distribution, is carried out with the help of two fuelling machines, which work in unison on the opposite ends of a channel. One of the machines is used to fuel the channel while the other one accepts the spent bundles. In addition, the fuelling machines facilitate on-power removal of failed fuel bundles. 

The SG features an annular tube bundle with helical tubing. The steam is generated tube-side. The feed water piping is connected to two feed water headers, located symmetrically inside the reactor vessel within a calm zone, provided each with two tube plates laid out vertically. The tubes depart circumferentially from the tube plates. 

A variety of fuel elanents are used for different types of reactors, but there are some common features. In most conunercial nnclear power plants (BWR [boiling water reactors] and PWR [pressurized water reactors] that are called in Russian VVER), the pellets are inserted into rods or tubes (usually zirconium alloys) that provide a barrier to prevent escape of fission products, the tubes or rods are arranged in bundles that are loaded into the reactor core. Usually a number of short rods are inserted into the sealed tube and held in place by a spring as described earlier. In some cases, like advanced gas cooled reactors (AGR), peUets are inserted into short narrow steel pins. Magnox reactors use magnesium alloys (usually with aluminum) rather the zirconium alloys. The fuel in some advanced reactors (TRISO) is in the form of microfuel particles with a UO2 (or UC (uranium carbide)) core surrounded by layers of pyrolytic carbon and... 

SSTAR has been designed from the outset to incorporate technical features to prevent the diversion of nuclear materials. One feature is the cassette/ cartridge core that is a single large assembly and is not composed of individual removable fuel assemblies/ bundles. The reactor vessel upper head/ cover does not incorporate openings that could be used to facilitate removal of individual assemblies/ bundles. 

Reactor shutdown is assured by two independent and diverse basic shutdown systems which guarantee very high reliability so as to relegate shutdown failure into the domain of residual risk. In the domain of residual risk, however, the "Third Shutdown Level" becomes effective. It consists of a bundle of additional engineered safety features which are incorporated in the design as a result of extensive risk-minimization studies. The system consists of active and passive subsystems and is supported by beneficial natural core behaviour. For example, the following features of the absorber rod actuators are part of the "Third Shutdown Level" ... 

Figure A1.18 Simplified iayout of typicai BWR NPP (courtesy of US NRC) geneiai basic features (1) thermal neutron spectrum (2) UO2 fuel (3) fuel enrichment about 3% (4) direct cycie with steam separator (steam generator and pressurizer are eiiminated), ie, singie-flow circuit (singie loop) (5) RPV with verticai fuel rods (elements) assembled in bundle strings cooled with upward flow of fight water (water and water—steam mixture) (6) reactor coolant, moderator, and power cycle working fluid are the same fluid (7) reactor cooiant outlet parameters pressure about 7 MPa and samration temperature at this pressure is about 286°C and (8) power cycle subcritical-pressure regenerative Rankine steam turbine cycie with steam reheat.

SBWR (USA) The simplified boiling water reactor (SBWR) [2] is a 600 MW(e) design. It is based on natural circulation, with a nominal core power output of 2000 MW(th), and incorporates a number of innovative features to achieve plant simplifications. Among others, it includes introduction of passive safety systems, instead of or as supplement to the traditional active safety systems. The core configuration consists of 732 bundles — 648 interior bundles and 84 peripheral bundles. The core power density is 41.5 kW/L. 

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