Transient operating mode

An impulse graphite reactor IGR (O Fig. 59.10) with a central channel to test fuel assemblies at the NPP transient operation modes and a research reactor IVG-1 (O Fig. 59.11) to test full-scale fuel assemblies (FA) of nuclear rocket engines of 3 x 10 -4 x 10 N and higher thrust were built at the Semipalatinsk nuclear test site. Further, an experimental NPP model of a low thrust was mounted at the same site. 

All processes may be classified as batch, continuous, or semibatch depending on how materials are transferred into and out of the system. Also, the process operation may be characterized as unsteady state (i.e., transient) or steady state, depending on whether the process variables (e.g., pressure, temperature, compositions, flowrate, etc.) are changing with time or not, respectively. In a batch process, the entire feed material (i.e., charge) is added instantaneously to the system marking the beginning of the process, and all the contents of the system including the products are removed at a later time, at the end of the process. In a continuous process, the materials enter and leave the system as continuous streams, but not necessarily at the same rate. In a semibalch process, the feed may be added at once but the products removed continuously, or vice versa. It is evident that batch and semibatch processes are inherently unsteady state, whereas continuous processes may be operated in a steady or unsteady-state mode. Start-up and shut-down procedures of a steady continuous production process are examples of transient operation. 

An attractive property of monolithic reactors is their flexibility of application in multiphase reactions. These can be classified according to operation in (semi)batch or continuous mode and as plug-flow or stirred-tank reactor or, according to the contacting mode, as co-, counter-, and crosscurrent. In view of the relatively high flow rates and fast responses in the monolith, transient operations also are among the possibilities. 

Various laboratory reactors have been described in the literature [3, 11-13]. The most simple one is the packed bed tubular reactor where an amount of catalyst is held between plugs of quartz wool or wire mesh screens which the reactants pass through, preferably in plug flow . For low conversions this reactor is operated in the differential mode, for high conversions over the catalyst bed in the integral mode. By recirculation of the reactor exit flow one can approach a well mixed reactor system, the continuous flow stirred tank reactor (CSTR). This can be done either externally or internally [11, 12]. Without inlet and outlet feed, this reactor becomes a batch reactor, where the composition changes as a function of time (transient operation), in contrast with the steady state operation of the continuous flow reactors. 

One is the secondary- coolant reduction test by partial secondary loss of coolant flow in order to simulate the load change of the nuclear heat utilization system. This test will demonstrate that the both of negative reactivity feedback effect and the reactor power control system brings the reactor power safely to a stable level without a reactor scram, and that the temperature transient of the reactor core is slow in a decrease of the secondary coolant flow rate. The test will be perfonned at a rated operation and parallel-loaded operation mode. The maximum reactor power during the test will limit within 30 MW (100%). In this test, the rotation rate of the secondary helium circulator will be changed to simulate a temperature transient of the heat utilisation system in addition to cutting off the reactor-inlet temperature control system. This test will be performed under anticipated transients without reactor scram (ATWS). 

Multiphase reactors can be batch, fed batch, or continuous. Most of the design equations derived in this chapter are general and apply to any of these operating modes. They will be derived for unsteady operation. The unsteady material balances include the inventories in both phases and mass transfer between the phases so that steady-state solutions fonnd by the method of false transients will be true transients if the initial conditions are correct. Compare Section 10.6. 

Nuvera will design, build, test, and deliver a 15 kilowatt electrical (kWe ) direct current (DC) fuel cell power module that will be specifically designed for stationary power operation using ethanol as a primary fuel. Two PEM fuel cell stacks in parallel will produce 250 amps and 60 volts at rated power. The power module will consist of a fuel processor, carbon monoxide (CO) clean-up, fuel cell, air, fuel, water, and anode exhaust gas management subsystems. A state-of-the-art control system will interface with the power system controller and will control the fuel cell power module under start-up, steady-state, transient, and shutdown operation. Temperature, pressure, and flow sensors will be incorporated in the power module to monitor and control the key system variables under these various operating modes. The power module subsystem will be tested at Nuvera and subsequently be delivered to the Williams Bio-Energy Pekin, Illinois site. 

To overcome these problems, the operation of the diffusion cell in the transient mode will reveal the contribution of the dead end pores. It is important to obtain the information of these dead end pores as they are usually the pores providing most of the adsorption capacity in the pellet. The principles of the steady state and transient operations of the diffusion cell are very similar to the principles of the time lag presented in the last chapter. The dead end pores are not reflected in the time lag information. Their information must be obtained from the analysis of the transient curve describing the approach of the receiving reservoir s pressure towards steady state. Thus, in order to understand the diffusion characteristic of a pellet, both the steady state and transient operations should be carried out. 

There are many ways that we can invoke a transient operation. The common ways used widely are as follows. A component (usually an inert gas but this is not necessary) is allowed to flow in both chambers. Once this is achieved and the pressures of both chambers are equalized, the other solute is injected into one chamber either as a pulse or a step input. In either mode of injection, the concentration of this solute is monitored at the other chamber (Figure 13.1-2). 

Due to the lack of sensitivity, most of the LC/NMR applications requires the accumulation of many transients for achieving a satisfactory detection of the compounds of interest. For the recording of detailed structural information, measurement of 2D correlation experiments is also often mandatory. Consequently, LC/NMR can be operated not only in dynamic but also in static conditions. These main operation modes are described below and require different level of automation ... 

Reactor operation includes discontinuous and continuous operations, steady-state and transient-state modes, and a group of intermediate modes that can be referred to collectively as semicontinuous operation. The modes of operation are compared in Fig. 3.30. 

The principal advantages of this type of cyclic system with transient operating techniques are apparent in bioprocesses whose maximum productivity is in a transient region. The products of secondary metabolism (Pirt, 1974) are a typical example of this group of processes. Another group consists of processes whose optimal operation requires an optimal substrate concentration— biomass production with bakers yeast, for example (Aiba et al., 1976)—or where the process is subject to substrate inhibition. An important area of application for this is in biological waste water purification. These periodic modes of operation generally show increased productivity. More systematic and detailed study is needed in this area. 

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