Mean apparent density

Mean apparent density. As the heat treatment of individual lumps in a commercial lime kiln can vary widely, their apparent densities also vary. The mean apparent density is used to characterise the average degree of sintering of a particular quicklime. For a particular high-calcium quicklime, the mean apparent density correlates with the reactivity to water (see Fig. 13.2). 

Bulk density. This depends on the mean apparent density of the particles and on the voidage between them. The latter is related to the particle size distribution and particle shape. Most commercial screened quicklime products have bulk densities in the range 900 to 1200 kg/m. Inclusion of fines, which fill the interstices, can increase the bulk density by 30 %. 

Figure 13.2 shows how the reactivity of a dense high-calcium quicklime is related to its mean apparent density. 

Figure 13J2. Relationship between reactivity and mean apparent density for a dense, high-calcium quicklime...

In the absence of calcium hydroxide, quicklime only reacts with carbon dioxide at temperatures above about 300 °C and below 800 °C. This reaction can occur in the cooling zone of lime kilns under abnormal conditions. It results in carbonation of quicklime at the surface of the pores, and can give abnormally low reactivities for a given mean apparent density. 

Thus the properties of quicklime from a given kiln reflect the average properties of individual lumps, each of which has experienced a particular time-temperature history. Fig. 15.8 compares the distribution of particle densities for a light-burned quicklime from an annular shaft kiln, with a mean apparent density of 1.66 g/cm with that of a solid-burned quicklime from a coal-fired traditional shaft kiln with a mean apparent density of 2.15 g/cm. Table 15.4 presents some typical... 

The sintering of dolomite is primarily of commercial interest in connection with the manufacture of refractory products with mean apparent densities in excess of 3.0g/cm. This involves heating calcined dolomite at temperatures of 1400 to 1800 °C [15.17]. The sintering process is affected by grain size and crystallite size, but the predominant factor is the amount of impurities present with fluxing properties. Iron oxide has a particularly pronounced influence on the rate and extent of sintering [15.18-15.23]. 

Excessive re-carbonation by either mechanism is generally indicated by an abnormally low reactivity, which is not associated with the expected high mean apparent density. 

The mean apparent density depends on both the porosity of the parent limestone and the degree of burning of the lime. Thus, a quicklime produced from a porous limestone may have a similar reactivity to one made from a dense limestone, but different hydration characteristics. 

Anderson and Vernon [27.1] reported that the rate of solution of lime increased as the mean apparent density decreased and as the particle size was reduced. For a given quicklime, reactivity correlated with mean apparent density (see Fig. 13.2), but reactivity was not the fundamental parameter. Moreover, reactivity could be affected by absorption of atmospheric water and carbon dioxide (see section 13.2). 

Oates [27.16] reported laboratory results for a study of the solution rates, in a synthetic BOS slag, of quicklimes with a range of mean apparent densities and... 

A recent paper [27.11] indicates that at least one steelmaking company is considering the use of mean apparent density and particle size to characterise quicklime quality for the BOS process. Increasing solution rates may become increasingly important as blow times are reduced to maximise production rates. 

Another aspect of reactivity and mean apparent density is that, as reported in [27.17], at the final temperature in the BOF of 1,600 °C, lightly burned quicklime sinters to medium burned within 5 min. and to hard burned within 10 min. (Table 27.5). 

The mean density of the emulsion particles was determined both from the specific gravity of the solid and from the specific gravity of an emulsion containing a known amount of the solid in the dispersed state, no effect due to dispersion on the apparent density could be detected. 

Mean Particle Size (jim) Pt % Dispersion Surface Area (m2/g) Real Density (g/ml) Apparent Density (g/ml) Pore Volume (ml/g) Mean Pore Radius (A)... 

F) Apparent Density. It can be detd by means of a "Scott Volumeter 1, described in Ref 4,p 745. The procedure for US specification grade Ba chromate is briefly described in Ref 5>p 5. 

Note 1 As was mentioned in Note 1 under item B the US MIL-STD-650 (Ref 21) does not make any distinction betw Bulk Apparent Densities. It defines them in Method 201.1 as "weight per unit of outside volume, which may include voids in Method 201.2 as "weight per unit of apparent volume and in Method 201.3 as "weight per unit of packed volume , which means that the specimen is dropped and tapped to dispel voids Note 2 Accdg to Ref 13, p 877, "It is not always possible to say whether a given measurement refers to bulk specific gravity, to apparent specific gravity, or to some intermediate value, since the determination of solid volume depends on the nature of the substance used to permeate the voids and on the nature of the pores in the solid ... 

There is no established relationship between variables affecting the above diffusion. However, if we assume that the slippage forces are negligible as compared to the pressures applied to the particulate mass, and if we confine the mass within an immovable boundary, by means of dimensional analysis we may arrive at a sort of possible diffusion relationship. Let the diffusion 3D be regarded as a function of some average particle diameter dy the apparent density of the mass pa and the pressure intensity py that is... 

When these assumptions are accepted, we see that the identity of the apparent density of the clay in water and the crystallographic density of the dry clay means that the system behaves as if the dry clay expands in water by admitting a sheet... 

Textural characterisation of the samples was carried out by measuring apparent density (mercury at 0.1 MPa), mercury porosimetry and N2 and CO2 adsorption isotherms, at -196 and 0 °C, respectively. The apparent surface areas of the samples were obtained by using the BET equation [5]. The micropore size analysis was performed by means of the t-plot and the Dubinin-Astakhov methods [6]. 

The activated samples exhibit different textural properties. The apparent densities decrease significantly in accordance with the degree of activation, from 1.3 to 0.6 g cm for PC 12 and PC76, respectively. This means that the activation process creates and/or enlarges pores, thereby producing carbon materials that are more porous. 

Particle size, mean, microns Apparent density, g/cc (Ref 1) Density (pressed at 15000 psi), g/cc... 

---