Slurry solids concentration measurement

Figure 20. A conductivity probe for local solids concentration measurement in slurry pipelines. (Reproduced with permission from reference 27. Copyright 1987.)...

An experimental run consisted of rotating the drum at a given speed and maintaining predetermined flow rates of solids and water. Steady state conditions were assumed to have been achieved when the discharge slurry had the same flow rate and composition as those of the feed inlet slurry. Steady state was usually reached about 30 minutes after start-up. When steady state conditions were reached, the drum rotation was stopped simultaneously with the slurry feed. The slurry hold-up in the drum and slurry solids concentration were determined from the mass and volume of the drum contents. The drum slurry hold-up and its solids concentration were measured within 5% of the value. The percent slurry hold-up is defined as the percentage of total volume of slurry in the drum to the drum volume. The solids volumetric concentration, C, was determined from the slurry hold-up density, P ,. using... 

Figure 21. Predicted and measured solids hold-up with various solid feed rates at different feed slurry solid concentrations.

Hydraulic transport can be achieved using a coal-water slurry, which can be efficiently pressurized by means of displacement pumps up to 70-100 bar with no inert gas detriment [1]. In addition to stability and viscosity, the main measure for slurry quality is the solids concentration. This determines the energy density and the amount of water, which hampers process efficiency. Figure 4.4 shows the influence of the slurry solids concentration on the cold gas efficiency for several solid fuels. Figures 4.4 is compiled using a GE gasifier model with radiant and... 

Separation Efficiency. Similarly to other unit operations in chemical engineering, filtration is never complete. Some soflds may leave in the hquid stream, and some Hquid will be entrained with the separated soHds. As emphasis on the separation efficiency of soHds or Hquid varies with application, the two are usually measured separately. Separation of solids is measured by total or fractional recovery, ie, how much of the incoming solids is coUected by the filter. Separation of Hquid usually is measured in how much of it has been left in the filtration cake for a surface filter, ie, moisture content, or in the concentrated slurry for a filter-thickener, ie, solids concentration. 

Roliani, S. and Paine, K., 1987. Measurement of solids concentration of a soluble compound in a saturated slurry. Canadian Journal of Chemical Engineering, 65, 163. 

In conclusion, the following experiments on filtration-washing-deliquoring should be performed to produce data (viscosity of liquids, effective solid concentration, specific cake resistance, cake compressibility, etc.) that are necessary to evaluate times of individual steps of filtration at an industrial scale, i.e. to obtain the proper basis for scale-up of filtration processes measure the filtrate volume versus time make marks on your vacuum flask and take down the time when the filtrate level reaches the mark => no more experiments are needed for preliminary evaluations of filtration properties of slurries initially fines pass the filter medium => recirculate them to the slurry,... 

Based on the above mentioned, the programme of theoretical and experimental investigation of the main parameters of coal-methanol (or its water solution) mixture pipeline transport should be opened. As the first step of the programme the comparison of power consumption (dependency of hydraulic gradient I on slurry flow velocity V and solid concentration Cs) for the pipeline transport of coal-water mixture and coal-methanol solution mixture was realised. The special laboratory measurements were made to define unknown input data of semi-empirical relationships, i.e. the limit volumetric concentration Cm and the coefficient of mechanical friction of coal in the water or water-methanol solution ka. The resultant comparison of the hydraulic gradient I of the coal-water and coal-methanol solution mixture flow is presented in Figure 2, where density of coal was pc = 1480 kg/m3, diameter of the pipe was D = 0.103 mm, the maximal grain size of coal dmax was less than 0.25 mm, volumetric concentration - C = 20 %. 

Ultraviolet spectrophotometry (DuPont 400 SO2 analyzer) was used to monitor the gas phase SO2 concentrations and SO2 removal efficiencies. The pH of scrubbing liquor in each reactor was measured hourly during pilot testing. Solid dewatering properties were characterized by hold tank slurry settling rate and filter cake insoluble solids concentration. Detailed descriptions of the test facilities and analytical procedures were reported earlier(S). 

In the design of upflow, three phase bubble column reactors, it is important that the catalyst remains well distributed throughout the bed, or reactor space time yields will suffer. The solid concentration profiles of 2.5, 50 and 100 ym silica and iron oxide particles in water and organic solutions were measured in a 12.7 cm ID bubble column to determine what conditions gave satisfactory solids suspension. These results were compared against the theoretical mean solid settling velocity and the sedimentation diffusion models. Discrepancies between the data and models are discussed. The implications for the design of the reactors for the slurry phase Fischer-Tropsch synthesis are reviewed. 

As part of the work undertaken by APCI under contract to the DOE, to develop a slurry phase Fischer-Tropsch process to produce selectively transportation fuels, a study of the hydrodynamics of three phase bubble column reactors was begun using cold flow modelling techniques (l ). Part of this study includes the measurement of solid concentration profiles over a range of independent column operating values. 

Cova (3 ) measured the solid concentration profiles of a Raney nickel catalyst with an average diameter of 15.7 ym in a h.6 cm id reactor, using water and acetone as the liquids. He developed a sedimentation diffusion model, assuming solid and liquid dispersion coefficients were equal, and slurry settling velocities were independent of solid concentration. The model was then applied to data for Raney nickel in 6.35 and kk.J cm id bubble columns, in both cocurrent and countercurrent flow. 

A possible way to increase the accuracy of this immersion approach is to use the slurry method and to analyse a weighed sample of the slurry in the bottom of the test-tube, instead of analysing the supernatant (Nunn etal., 1981). One then simply makes use of Equation (5.49), the operational expression of the relative surface excess of the solute with respect to the solvent. Here n1 and n2 are the total amounts of solute and solvent in the sample of slurry (either adsorbed or in solution) and c[ and c their concentrations in the solution. If one uses a liquid-solid ratio large enough to avoid any measurable change in concentration on adsorption, then c and c are simply the concentrations in the starting solution. The measurement is accurate provided the quantitative analysis of the slurry, which involves measuring the total amounts of 2 and 1... 

In hydroseparator tests, it is necessary to measure solids concentrations and size distributions of both the supernatant sample withdrawn and the fraction remaining in the cylinder. The volume of the latter sample should be such as to produce a solids concentration that would be typical of a readily pumped underflow slurry. 

Raphael and Rohani [55] developed a method for on-line estimation of solids concentration or mean size of crystals in a crystallizer. The method was only applicable to slurries in the absence of background particles. Later, an on-line double-sensor turbidimeter was proposed [56]. The technique is based on measuring the transmittance of an infrared light beam through the suspension, once in the presence of soluble particles and a second time when the particles have been dissolved. 

Thin L-shaped probes are commonly used to measure solids concentration profile in slurry pipelines (28-33), However, serious sampling errors arise as a result of particle inertia. To illustrate the effect of particle inertia on the performance of L-shaped probes, consider the fiuid streamlines ahead (upstream) of a sampling probe located at the center of a pipe, as shown in Figure 2. The probe has zero thickness, and its axis coincides with that of the pipe. The fluid ahead of the sampler contains particles of different sizes and densities. Figure 2A shows the fluid streamlines for sampling with a velocity equal to the upstream local velocity (isokinetic sampling). Of course, the probe does not disturb the flow field ahead of the sampler, and consequently, sample solids concentration and composition equal those upstream of the probe. 

Rushton (35) was the first to draw attention to the errors associated with wall sampling. Sharma and Das (37) mentioned that the mechanism of particle collection using an opening flush with the wall is different from the concept of isokinetic sampling. Moujaes (38) used wall sampling to measure solids concentration in upward vertical slurry flows. He found the sample concentration to be consistently lower than the true values in the pipe, especially with the coarse sand particles. 

One way of measuring the solids concentration, similar to that used by previous workers, is to relate the field circuit current change to the solids concentration. This method has a serious disadvantage because the field circuit current depends on both the slurry resistivity and the polarization resistance developed on the surfaces of the field electrodes. This polarization resistance is velocity dependent. This method yields calibration curves that are functions of velocity (59). 

Electromagnetic flowmeters are mainly applied to single-phase conducting fluids, for example liquid metals, water-based industrial liquids, and blood. However, they are also being used to measure solid/liquid flows such as water-based slurries and sludge as long as conductivity of the liquid medium exceeds 50 microsiemens per centimeter (pS/cm). Output signals from an EM flowmeter are basically proportional to the volumetric flow rate, which is applicable to solid/liquid flows only if the solids particles are uniformly distributed in the liquid. Moreover, to obtain the mass flow rate of a solid/liquid flow, the EM flowmeter requires other means to measure solids concentration. 

The ANL capacitive flowmeter was installed at the vertical line of the SLTF (see Fig. 6.19), thus, particle settling problems would not occur. The only parameter that affected the velocity measurement was the velocity profile. Figure 6.24 shows that particle velocities were measured over a range of solids concentrations. For coal concentrations of 3.5-33 wt.%, the measured velocities were independent of coal concentration and 7% accurate when compared with timed-diversion measurements. For higher coal concentrations, the measured velocities deviate from the diversion measurements velocity measurements were = 30-80% higher for 43 and 49 wt.% slurries, but 40%... 

Velocity and concentration profiles are two important parameters often needed by the operator of slurry handling equipment. Several experimental techniques and mathematical models have been developed to predict these profiles. The aim of this chapter is to give the reader an overall picture of various experimental techniques and models used to measure and predict particle velocity and concentration distributions in slurry pipelines. I begin with a brief discussion of flow behavior in horizontal slurry pipelines, followed by a revision of the important correlations used to predict the critical deposit velocity. In the second part, I discuss various methods for measuring solids concentration in slurry pipelines. In the third part, I summarize methods for measuring bulk and local particle velocity. Finally, I review models for predicting solids concentration profiles in horizontal slurry pipelines. 

Conductivity methods have been successfully used to measure solid concentration in multiphase systems, where the conductivity of continuous phase is greater than zero, for example, sand-water slurries and oil-in-water emulsions (65). These methods have been used to measure bulk and local solids concentration in the slurry pipelines. Nasr-El-Din et al. (27) developed a four-electrode conductivity probe for measuring local solids concentration in slurry pipelines (Figure 20). The probe is... 

Capacitance Methods. Capacitance methods have been used to measure solids concentration in slurry pipelines (79). This method requires the dielectric constant of the solids and the carrying fluid to be significantly different. Sand-water slurry is a good example to use the capacitance method. In this case, the dielectric constant for water is 80, whereas that of the sand particles is 5. The method relies on the variation of the dielectric constant of the mixture, Em, with the solids concentration, C. For homogeneous slurries of spherical particles at low solids concentration, Maxwell s correlation can be used to predict the dielectric constant of the mixture. However, several investigators assumed that the relationship of the dielectric constant of the mixture and solids concentration was linear, as follows ... 

Gamma-ray methods have been used to measure solids concentration in slurry pipelines. Usually, the gamma-ray source and detector are mounted in the opposite sides of the pipe as shown in Figure 22. It should be mentioned that the gamma-ray absorption method in this case will measure solids concentration averaged over a chord in the pipe. It is worth noting that the chord-average concentration can be different from local solids concentration in some applications. Examples of such... 

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