World Cement - July 2020

The Vassiliko plant has always been at

the forefront of acquiring and implementing

cutting-edge technologies; in 2014, new

alternative fuels and raw materials feeding

systems were installed. Its recent ‘green

initiative’ saw the commissioning of an 8 MWp

photovoltaic park in early 2020, making it one

of a few plants in Europe to generate its own

solar power. The Vassiliko Plant therefore,

where possible, collaborates and works with

its international technical associates in order to

stay ahead of the curve. One such initiative has

been to model its inline calciner for reducing

, co-fired with petcoke and a combination

of alternative fuels. This article presents some

results from the calciner modelling exercise

spanning over five years.

The model used was

Cinar’s internally developed MI-CFD (mineral

interactive computational fluid dynamics)

model.

2,3,4

The calciner is designed to burn a variety

of fuels, including petcoke and oil, as well as

certain types of alternative fuels. Approximately

five seconds of total gas residence time is

available within the calciner, including the time

in the exit loop duct, which is sufficient to fully

combust the petcoke and oxide CO. The NO

formation/reduction in the calciner very much

depends on the mixing of the tertiary air duct

(TAD) and riser gas duct (RGD) – one of the

modelling objectives. In the present design,

a single ‘Venturi’ section was built at about

half of the calciner’s height for enhancing

the mixing of the TAD and RGD stream, as

well as for accelerating the fuel burnout and

calcinations of the meal particles.

In the calciner, combustion products from

the kiln enter the riser duct at the bottom at

a relatively higher temperature (~1200˚C).

Initially, there were two petcoke burners

located at two elevations on the east and

south sides (Figure 2), which were designed

to be multi-channel, placed in a downward

orientation with a 30° angle to the vertical.

Additionally, tertiary air was supplied to the

calciner via a duct connecting the calciner

at the lower cone-section and the bottom of

the mid-cylindrical section with a downward

orientation and a 30° angle to the vertical.

Two meal inlets were located above the conical

section of the calciner.

The plant has been designed to comply

with the EU CO and NO

emission limits. The

mixing ensures lower CO emissions, while the

emissions are reduced through

kiln-generated-NO

destruction in the

calciner, as well as use of selective

non-catalytic reduction (SNCR).

In summary, in order to deal with

efficiency and emission targets,

the process/flow and combustion

interactions inside the kiln, calciner

and cyclones must be analysed in

detail. Generally, some of the KPIs

(kiln performance indicators) are

readily available (e.g., pressure,

temperature and exit concentrations

of gas species) but local phenomena,

like near reaction-zone information

which influences the variables of

interest (e.g., meal calcination, CO/NO

reduction/formation and fuel burnout)

are difficult to quantify and require

detailed analysis. The only practical and

economical way forward is to perform

analysis using advanced computer

models, based on mineral interactive

computational fluid dynamics (MI-CFD)

which were used at various stages of

plant improvement phases.

In most in-line calciners,

kiln-generated CO and NO

are

reduced more than 70%, provided that

favourable conditions of calciner fuel,

kiln combustion products and tertiary

air mixing are maintained. Through

modelling, one can identify all important

Figure 1. Vassiliko Cement Works, Cyprus.

World Cement

July 2020