Hidrociclon

Tz Mz Lz Jz

Tf Mf Lf Jf

   
Tg Mg Lg Jg

TG TZ MF MZ LF LZ

 

For values of Vs(U) greater than the right hand side of Eqs. (12.29) and (12.30), roping is likely to occur. Eq. (12.30) suggests that a higher underflow density can be achieved, without the risk of roping, if the cyclone is operated with a high overflow density. A higher solid density willalso allow a higher underflow density before roping occurs. For example, for an overflow of 30% solids and a solid S.G. of 2.7 the underflow will start to rope at approximately 78% solids by mass whereas for a solid S.G. of 3.7, the underflow density can be increased to around 82% solids before roping occurs [11].. Plitt et al [32] indicate that the particle size of the underflow is thecontrolling factor for changing from a normal spray to roping discharge but Bustamante [33] asserts that the ratio of the underflow to overflow discharge diameters are the governing factors. Concha et al [34] has quantified this ratio in relation to roping conditions. These authors state that roping will occur if the air core diameter is greater than the spigot diameter. Since the air core diameter dependson the surface tension, viscosity and overflow and underflow diameters, the ratio ill be a determining variable. Table 12.10 gives some limiting values. Table 12.10 Transition from spray to roping discharge. Bustamante [33] Concha et al [34] Du/Do 0.5 0.56 Condition Roping discharge Roping or spray Spray discharge Roping Roping or spray Spray discharge

n

A

Fig. 12.17.

Hydrocyclonedischarge. A - Normal spray discharge, B - rope discharge

where

Fs(u) = the volume fraction of the solids in the underflow and = the volume fraction of the solids in the feed stream.

For values of Vs(U) greater than the right hand side of Eqs. (12.29) and (12.30), roping is likely to occur. Eq. (12.30) suggests that a higher underflow density can be achieved, without the risk of roping, ifthe cyclone is operated with a high overflow density. A higher solid density will also allow a higher underflow density before roping occurs. For example, for an overflow of 30% solids and a solid S.G. of 2.7 the underflow will start to rope at approximately 78% solids by mass whereas for a solid S.G. of 3.7, the underflow density can be increased to around 82% solids before roping occurs [11]..Plitt et al [32] indicate that the particle size of the underflow is the controlling factor for changing from a normal spray to roping discharge but Bustamante [33] asserts that the ratio of the underflow to overflow discharge diameters are the governing factors. Concha et al [34] has quantified this ratio in relation to roping conditions. These authors state that roping will occur if the air corediameter is greater than the spigot diameter. Since the air core diameter depends on the surface tension, viscosity and overflow and underflow diameters, the ratio ill be a determining variable. Table 12.10 gives some limiting values. Table 12.10 Transition from spray to roping discharge. Bustamante [33] Concha et al [34] Du/Do 0.5 0.56 Condition Roping discharge Roping or spray Spray dischargeRoping Roping or spray Spray discharge

n

A

Fig. 12.17.

Hydrocyclone discharge. A - Normal spray discharge, B - rope discharge

An important factor in designing control loops is the instrumental and programmable time delays, hi the case of hydrocyclone automation, the sources of time delays is given in Table 18.5. Each instrument has to have a separate time delay factor which could beup to 3 seconds Programmable time delays introduced during iteration could be greater than instrumental time delays Table 18.5 Source of time delays in a hydrocyclone circuit. Equipment Motor pump set Vortex finder positioner Time delay source Frequency controller, Inertia in motor load. Vfl and I/P conversions, Pressure transmission, Mechanical movements, Servo- Mechanism operations V/I and...