Density of catalyst beds

Pb - packing density of catalyst bed., g / cucm. pvC - density of vanadium sulphide (S3V2). g / cucm. 

Internal diameter of single tube dRjnt (total number of tubes 2052) External diameter of single tube dR x Bulk density of catalyst bed pt,... 

In the model equations, A represents the cross sectional area of reactor, a is the mole fraction of combustor fuel gas, C is the molar concentration of component gas, Cp the heat capacity of insulation and F is the molar flow rate of feed. The AH denotes the heat of reaction, L is the reactor length, P is the reactor pressure, R is the gas constant, T represents the temperature of gas, U is the overall heat transfer coefficient, v represents velocity of gas, W is the reactor width, and z denotes the reactor distance from the inlet. The Greek letters, e is the void fraction of catalyst bed, p the molar density of gas, and rj is the stoichiometric coefficient of reaction. The subscript, c, cat, r, b and a represent the combustor, catalyst, reformer, the insulation, and ambient, respectively. The obtained PDE model is solved using Finite Difference Method (FDM). 

Our problem has four parts. First, we must determine the rate law for an infinitesimal length of catalyst bed. Second, the resulting equation must be integrated over the length of the bed. Third, the values of certain of the system parameters must be determined using the integrated equation and experimental conversions. Finally, the site density is determined from the values of these parameters. 

The rate constant given, k[" has, as its basis, unit mass of catalyst, whereas the term k er in equation 4.46 is the rate constant k, per unit volume of particles converted to a basis of unit volume of bed. To convert k similarly it has to be multiplied by p the bulk density of the bed. 

Bulk density, or packing density, includes all pores and voids (interparticle spaces) in its calculation. It is determined by filling a graduated cylinder, with or without tapping. It follows that the value obtained is dependent upon the form of the catalyst (powder, tablets, extrudates) because of the different contribution of interparticle void space to the pore volume. Tap density is the apparent density of a bed of particles in a container of stated dimensions when a given amount of powder is vibrated or tapped under controlled conditions. The use of the term bulk density should be... 

For a reaction requiring a solid catalyst the rate is usually based on a unit mass of catalyst rather than a unit volume, as defined in Chap. 2. The two rates are directly related through the bulk density of the bed of catalyst. 

Xp = global rate per unit mass of catalyst pp = density of catalyst in the bed u = superficial velocity in the axial direction... 

Another characteristic of the fluidized bed is the small size and density of catalyst particles necessary to maintain proper fluidization. The particles provide a much larger external surface per unit mass of catalyst than those, in a fixed-bed unit. This results in a higher rate of reaction (per unit mass) for a nonporous catalyst. Also, internal transport effects are negligible. 

An irreversible first-order gaseous reaction A Bis carried out in a fluidized-bed reactor at conditions such that the rate constant is = 0.076 ft /(sec) (lb catalyst). The superficial velocity is 1.0 ft/sec and the bulk density of catalyst in the bed is 5.25 Ib/ft. Suppose that the mixing conditions correspond to plug flow modified by axial dispersion. The extent of dispersion can be evaluated from Gilliland and Mason s equation,... 

Note. We have convened the specific reaction rates to a per unit volume basis multiplying the k on a per mass of catalyst basis by the bulk density of packed bed (i.e.. Jt = A pB)-... 

Notice we require the bed porosity to convert from the rate per volume of particle to the rate per volume of reactor. The bed porosity or void fraction, cb, is defined as the volume of voids per volume of reactor. The volume of catalyst per volume of reactor is therefore 1 cg. This mfonnation can be presented in a number of equivalent ways. We can easily measure the density of the pellet, pp, and the density of the bed, Pb. From the definition of bed porosity, we have the relation... 

The molar feed rate of ethanol, F o is kmol/hr, the wei t of catalyst, W 0.01 kg. At this value of W]Fm l e measured conversion is OJ62 and the reaction rate, 0.193 kmol/kg cathr. The inside diameter of the reactor is 0.035 m. The catalyst particles are of cylindrical diape with diameter = height — d = 0.002 m. The bulk density of the bed, pg amounts to 1500 kg/m and the void fiaction, , to 0.37. From these, a. = 126 m /kg. Estimate the partial inessure and temperature difference b ween the bulk p>s stream and catalyst surface. 

Reaction rate equation and aU physical properties as heats of reactions, thermal transport coefficient, density of packed bed and fluid mixture, fluid mixture viscosity, reactor and catalyst particles diameters, void fraction, etc., have to be known for the specific system. 

The fixed-bed reactor is highly desirable since it offers the highest density of catalyst/reactor volume that is attainable and, if the temperature can be made uniform, the potential for the highest productivity/reactor volume. This has not been accomplished to... 

Void fraction of catalyst bed Effectiveness factor Gas density (kg/m )... 

---