INTERNATIONAL CLEANER PRODUCTION INFORMATION CLEARINGHOUSE

CASE STUDY #4
1.   Headline: Pollution and waste reduction by improved
     process control
2.   Background: Cement is made by burning a fuel together with
limestone and clay, shale or slate, (shale being used here),
yielding a clinker which is then ground with gypsum to produce
cement. The process, which is carried out in large rotating
kilns, is a complex one, and it is easy to lose control and
make substandard product. Conversion of the kilns from oil/gas
to coal firing has the penalty of making control even more
difficult. The limestone and shale are quarried locally,
combined and ground to a fine powder, referred to as raw meal.
Heat transfer between the kiln exhaust gases and the raw meal
initiates the calcination process which continues in the kiln.
When the calcination is complete, the material temperature
rises rapidly causing sintering that produces clinker. The
clinker is discharged, cooled and ground to give the finished
product. The small amount of sulphur in the coal takes in the
chemical reactions and is transformed into part of the sulphur
content of the cement. The use of coal increases slightly the
dust content of the exhaust gases which is removed in the bank
of electrostatic dust precipitators usually used with these
plants.
     PT Semen Cibinong is a cement company near Jakarta, which
     operates two 2000 tons per day dry process kilns
     converted for economic reasons from gas/oil fuel to a low
     sulphur coal. ABB LINKman Systems of London was set up
     six years ago to develop expert systems and laser
     scanning devices. The company is now part of the Asea
     Brown Boveri Group.
3.   Cleaner Production Principle: New technology
4.   Description of Cleaner Production Application: The
     quality of the cement is determined largely by the firing
     temperature. However, both the NOx and the SOx levels
     increase with higher temperatures. The process must,
     therefore, be operated within a certain band of
     temperature with the optimum at the lower end. If the
     process is operated too far below this optimum, off-
     specification product is produced. If the temperature is
     too high the fuel is wasted, cement quality is reduced
     and air pollution is increased. The LINKman system is
     designed to mimic best operating practice and maintain
     optimum process conditions. The objectives were to
     stabilize the running of the kiln, reduce fuel
     consumption and increase output, and produce a consistent
     quality of clinker with optimum free-lime levels. This
     final objective also reduces the energy required to grind
     the clinker. Note that the temperature is not uniform
     along the length of the kiln. The LINKman system monitors
     the NOx, CO and O2 levels, the temperature at the bottom
     of the four-stage preheater and the power required to
     turn the kiln. The process is optimized by controlling
     the feedrate to the kiln, its rotational speed, the fuel
     supply to the main and auxiliary burners and the speed of
     the kiln induced draft fan.
     The system has been made possible by improvements in:
          - The science of expert system control
              - Measurement technology using a reliable and
          sensitive NOx analyzer.
5.   Economics:    9% capacity increase
                  3% fuel saving
                                40% reduction in off-
                    specification             material
                    produced.
                  The clinker requires less energy to grind.
     Cost saving                       US$/year
     Power & fuel saving approx           350,000
     Capital investment                 375,000
     Payback period                less than one
year
6.   Advantages: The wastage of coal at high temperature is
avoided. Higher quality clinker is produced. The lining of the
kiln has longer life. Some reductions in NOx and SOx emissions.
7.   Constraints: N/A
8.   Contacts:Ir Sugiharto
                  P T Semen Cibinong
                  JI Let Jen M T Ilaryono
                  Jakarta
                  Indonesia
                  Tel: +62 21 819 0808
                  Fax: +62 21 819 8362
                  Mr Robert Harrison
                  ABB LINKman Systems Ltd
                  County House
                  221-241 Beckenham Road
                  Kent
                  BR3 4UF
                  Tel: +44 81 778 1200
                  Fax: +44 81 776 8898
9.0                 Keywords:Indonesia, UK, United Kingdom,
                    cement, new technology, NOx, SOx, energy
                    saving, expert system
10.  Reviewer comments: This case study was originally
     published in the UNEP IE document "Cleaner Production
     Worldwide". In the process of preparing the document the
     case study underwent a technical review.