At the reactor

It will be necessary to create medical facilities (e.g., patient preparation and holding area, blood laboratory) at the reactor. These facilities should provide a hospital atmosphere for the comfort of the patients. 

Many facilities use a prompt gamma neutron activation analysis (PGNAA) system to measure boron in blood samples although there are other methods. 

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Laboratory studies indicate that a hydrogen-toluene ratio of 5 at the reactor inlet is required to prevent excessive coke formation in the reactor. Even with a large excess of hydrogen, the toluene cannot be forced to complete conversion. The laboratory studies indicate that the selectivity (i.e., fraction of toluene reacted which is converted to benzene) is related to the conversion (i.e., fraction of toluene fed which is reacted) according to ... 

The final composition of the reactor product gas is estabUshed by the water gas shift equiUbrium at the reactor outiet waste-heat exchanger inlet where rapid cooling begins. Some units quench instead of going directiy to heat exchanger. 

Some reactors are designed specifically to withstand an explosion (14). The multitube fixed-bed reactors typically have ca 2.5-cm inside-diameter tubes, and heat from the highly exothermic oxidation reaction is removed by a circulating molten salt. This salt is a eutectic mixture of sodium and potassium nitrate and nitrite. Care must be taken in reactor design and operation because fires can result if the salt comes in contact with organic materials at the reactor operating temperature (15). Reactors containing over 20,000 tubes with a 45,000-ton annual production capacity have been constmcted. 

As of 1996, the bulk of spent fuel from nuclear power plants has been stored in specially designed water-filled holding pools at the reactor site. 

The catalyst is then transferred back to the first process reactor and is reheated to the reforming process temperature at the reactor inlet using a flow of hydrogen-rich process recycle gas, thereby achieving reduction of the platinum to a catalyticaUy active state. 

While two operators were charging penicillin powder from fiber drums into a reactor containing a mixture of acetone and methanol, an explosion occurred at the reactor manhole. The two operators were blown back by the force of the explosion, and were covered with solvent-wet powder. 

At the end of the irradiation, the samples are withdrawn from the reactor and y-ray spectroscopy is carried out. Most often the laboratory performing the y-ray spectroscopy is located in a different city, in which case the samples are shipped and the reactor serves as a neutron source only. Many reactors also have y-ray spectroscopy capability so that measurements can be made at the reactor site as well. 

The distribution of tracer molecule residence times in the reactor is the result of molecular diffusion and turbulent mixing if tlie Reynolds number exceeds a critical value. Additionally, a non-uniform velocity profile causes different portions of the tracer to move at different rates, and this results in a spreading of the measured response at the reactor outlet. The dispersion coefficient D (m /sec) represents this result in the tracer cloud. Therefore, a large D indicates a rapid spreading of the tracer curve, a small D indicates slow spreading, and D = 0 means no spreading (hence, plug flow). 

Carbon Laydown. The potential for carbon laydown is readily estimated from the thermodynamics of Reactions 4 and 5. The areas where carbon laydown, according to these reactions, is thermodynamically possible were developed by Gruber (36). It is readily seen that carbon laydown via Reaction 4 is thermodynamically favorable at the reactor inlet for practically any commercially conceivable feed gas composition. As noted by Gruber (36), carbon laydown is thermodynamically unfavorable at the reactor outlet for practically all commercially conceivable methanator conditions. The methanation reactor will therefore, in practice, have two zones—the first is a finite zone between the inlet and some way down the catalyst bed where carbon laydown is thermodynamically possible, and the second zone is the balance of the reactor. 

The kinetic models are the same until the final stage of the solution of the reactor balance equations, so the description of the mathematics is combined until that point of departure. The models provide for the continuous or intermittent addition of monomer to the reactor as a liquid at the reactor temperature. 

Although they are both flow reactors, there are large differences in the behavior of PFRs and CSTRs. The reaction rate decreases as the reactants are consumed. In piston flow, the reactant concentration gradually declines with increasing axial position. The local rate is higher at the reactor inlet than at the outlet, and the average rate for the entire reactor will correspond to some average composition that is between and In contrast, the entire... 

To find u, it is necessary to use some ancillary equations. As usual in solving initial value problems, we assume that all variables are known at the reactor inlet so that (Ac)i UinPin will be known. Equation (3.2) can be used to calculate m at a downstream location if p is known. An equation of state will give p but requires knowledge of state variables such as composition, pressure, and temperature. To find these, we will need still more equations, but a closed set can eventually be achieved, and the calculations can proceed in a stepwise fashion down the tube. 

The fraction unreacted is /< > . Set z = L to obtain it at the reactor outlet. Suppose = 1 and that kai /Ui = 1 in some system of units. Then the variable-density case gives z = 0.3608 at = 0.5. The velocity at this point is 0.75m . The constant density case gives z = 0.5 at a = 0-5 and the velocity at the outlet is unchanged from The constant-density case fails to account for the reduction in u as the reaction proceeds and thus underestimates the residence time. 

For now, we assume that all operating conditions are known. This specifically includes Pout and Tout, which correspond to conditions within the vessel. There may be a backpressure valve at the reactor exit, but it is ignored for the purposes of the design equations. Suppose also that the inlet concentrations ajn,bm,..., volumetric flow rate and working volume V are all known. Then... 

An equation of state is needed to determine the mass density at the reactor outlet. Pout- Then, Qout can be calculated. 

Specify the number of radial increments, Itotal, and the values for vise (i) andrho(i) at each radial position. Also, the average density at the reactor inlet, rhoin, must be specified. 

The concentration is continuous at the reactor exit for all values of D and this forces the zero-slope condition of Equation (9.17). The zero-slope condition may also seem counterintuitive, but recall that CSTRs behave in the same way. The reaction stops so the concentration stops changing. 

When is constant, Equation (14.14) is a solution of Equation (3.1) evaluated at position z, and Equation (14.15) is a solution evaluated at the reactor outlet. The temperature counterpart of Equation (14.11) is... 

Washout experiments can be used to measure the residence time distribution in continuous-flow systems. A good step change must be made at the reactor inlet. The concentration of tracer molecules leaving the system must be accurately measured at the outlet. If the tracer has a background concentration, it is subtracted from the experimental measurements. The flow properties of the tracer molecules must be similar to those of the reactant molecules. It is usually possible to meet these requirements in practice. The major theoretical requirement is that the inlet and outlet streams have unidirectional flows so that molecules that once enter the system stay in until they exit, never to return. Systems with unidirectional inlet and outlet streams are closed in the sense of the axial dispersion model i.e., Di = D ut = 0- See Sections 9.3.1 and 15.2.2. Most systems of chemical engineering importance are closed to a reasonable approximation. 

Impulse Response and the Differential Distribution. Suppose a small amount of tracer is instantaneously injected at time 1 = 0 into the inlet of a reactor. All the tracer molecules enter together but leave at varying times. The tracer concentration at the outlet is measured and integrated with respect to time. The integral will be finite and proportional to the total quantity of tracer that was injected. The concentration measurement at the reactor outlet is normalized by this integral to obtain the impulse response function. ... 

The molecules in the system are carried along by the balls and will also have an exponential distribution of residence time, but they are far from perfectly mixed. Molecules that entered together stay together, and the only time they mix with other molecules is at the reactor outlet. The composition within each ball evolves with time spent in the system as though the ball was a small batch reactor. The exit concentration within a ball is the same as that in a batch reactor after reaction time tf,. 

Inwall when the 0th moment is Cpoiymer Viscosity at the reactor wall 5.34... 

Figure 10.3 Membranes can be applied at the reactor-, particle-, and microlevels.

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