PROJECT DESCRIPTION

BACKGROUND & PROJECT GOALS

Calcination

is

one

of

the

crucial

operations

in

catalyst

manufacturing.

In

calcination

processes,

heat

is

applied

to

ores

and

other

solid

materials

in

order

to

bring

about

a

thermal

decomposition,

phase

transition,

or

facilitate

removal

of

a

volatile

fraction.

Developing

better

process

level

understanding

of

this

operation

can

significantly

improve

the

quality

of

the

end

product

as

well

as

save

on

energy

and

material

costs.

For

a

good

product

quality

and

efficient

process,

it

is

necessary

to

raise

the

temperature

of

the

particles

uniformly

with

a

minimum

processing

time.

In

rotary

calciners,

which

are

the

most

common

devices

used

for

calcination

processes,

the

calcination

process

highly

depends

on

the

heat

transfer

in

the

radial

direction

and

on

the

axial

dispersion

of

the

particles.

The

heat

transfer

and

the

dispersion

of

particles

depend

on

the

properties

of

the

particles

and

the

calciner

operating

conditions,

such

as

speed

of

rotation

and

size

of

calciner.

Usually,

the

appropriate

process

parameters

are

determined

based

on

laboratory

or

pilot

scale

experiments.

However,

the

technology

transfer

to

larger

manufacturing

scale

productions

is

not

well

understood,

which

prohibits

efficient

production.

In

this

project,

we

use

carefully

designed

experiments

and

numerical

simulations

to

better

understand

the

effect

of

material

properties

and

operating

conditions

of

calciners

on

the

calcination

process

with

a

particular

interest

in

understanding

the

scale-up

in

rotary

calciners.

SUMMARY OF STUDIES

We use the discrete element method (DEM) to simulate the heat transfer and flow of particles in rotary calciners. The DEM is an idealistic tool as it can directly represent heterogeneity in the processed materials and the interaction among individual particles. Using these simulations, we have investigated effects of thermal properties, mechanical properties, and material properties, such as size and density of particles, on the heat transfer process in rotary calciners. We have also studied the effect of operating conditions, such as calciner size, speed of rotation, and fill level on the scaling of the heat transfer process. Figure 1 shows simulation results for various process parameters. Figure 1. Heat transfer in DEM simulations: color red represents a high temperature; color blue represents a low temperature. (a) High thermal conductivity, low density, low speed of rotation, resulting heated in layers. (b) Intermediate thermal conductivity, intermediate density, resulting a cooler core. (c) Low thermal conductivity and high density resulting uniform particle temperature We also experimentally investigate the flow and dispersion of powders in pilot scale calciners. The main goal of these experiments is to understand the mean residence time and axial dispersion of common catalyst powders. We have investigated the effects of various operating conditions, such as feed rate, speed of rotation, baffles, and calciner incline, on the residence time distribution. Figure 2 shows the colorimeter test for measuring concentration of tracer particles used to measure the residence time distribution. Along with these, we use small scale laboratory experiments to investigate thermal properties of catalyst powders and to validate our DEM simulations. Figure 3 shows the laboratory experimental set-up for heat transfer. Figure 2. Colorimeter to analyze concentration of tracer particles. Figure 3. Side view of the aluminum calciner. 10 thermocouples are inserted within the calciner through the Teflon made side-wall. The calciner rests on the computer- controlled rollers. Based on the simulations and experiments the following key observations are found: 1 ) Based on hundreds of DEM simulations, we have developed a quantitative scale-up equation in rotary calciners for heat transfer via conduction. Using this scale-up equation, the appropriate operating conditions required to raise or lower the temperature of powders can be determined. If the thermal properties of the powders are known, the operating conditions can be determined without any experiment. If the thermal properties are not known (which is usually the case), the appropriate operating conditions can be determined by measuring the temperature increase time scale in a single experiment and utilizing the scale-up model. 2 ) We have developed an online graphic user interface (GUI), so that one can access and use the model. In the GUI, we have combined the heat transfer with expected powder flow in calciners. 3 ) We have found that the heat transfer rate has very low dependence on speed of rotation and fill level, but highly depends on the size of the calciner. The heat transfer also highly depends on the thermal conductivity and heat capacity of the particles, but the effect of particle size on heat transfer is negligible. 4 ) In addition to the scale-up model, we have developed a model to predict the particles’ temperature distribution. We found that particles with higher density, low thermal conductivity, in high speed of rotation and low fill level processes, tend to have uniform temperature. 5 ) Baffles enhance the mixing, the heat transfer rate, and the uniformity of particles’ temperature. 6 ) Based on experiments, we have found that the mean residence time is indirectly proportional to the speed of rotation and angle of incline, but is only slightly affected by the feed rate. On the other hand, the axial dispersion coefficient increases with speed of rotation and angle of incline. We continue to study the scale up and effects of various parameters on the calcination process using these experiments and numerical simulations. In particular, we are studying the radiative heat transfer using numerical simulations and the effect of dams on the powder flow using experiments in rotary calciners.