Cement Energy and Environment

Kiln Operation Dry process Obviously. changing from a wet process to a dry process operation is the best system to save energy in the kiln department. If the necessary funds are ava ilable, about US $ IOOm or so. along with a market to sell the cement, conversion to dry process is the answer. Semi wet process The semi -wet process makes a lot of sense because in vestment costs are much lower. However, one must watch out that any proposed semi-wet process does not become a technical or operati onal nightmare. A typical in vestmen t in semi-wet process might be US $ 20m with a payback period of fi vc yea rs. Waste and other fu els These should be used wherever economically viable and technica lly feasible, incl uding coal rejects from coal mines, rubber tyres and coke. Some li quid fuels are a more hazardous undertaking and can place operators in a difficult position with respect to local environmental groups or Iicensing procedures. A typical rubber tyre insta!Jation on a kiln might cost US $ 1.2m and this investment capital would be recovered within two years. A critical factor is the transport cost or the Lyres. A proper installation poses no problems to cement qualit y or air pollution. Upgrading existing long wet kiln Recent new chain systems by Cement Energy Services have been qui te successful. Fuel savings and capacity increases were of the order of 15-30 per cent. Tn one plant. the capacity was increased from 750 tpd to 11 00 tpd and the specific fuel consumption was reduced by 20 per cent. Some of the systems include refractory li fters and refractory dams. Figure 2 shows a well-planned and tilted chain system. Typical chai n system costs range from US $0.55-0.85m, depending upon the size or the kiln, and the payback period is seldom longer than one-and-a-half tOt WO years. Along with the chain system, a kiln should have proper seals at the Iced end and discharge end, and a minimum amount of instrumentation, such as exit gas analysis equi pment, recording of temperatures of raw materials and gases at the discharge of the chain system, kiln draft recording of temperatures of raw materials and gases at the discharge of the chain system, kiIn draft recording, hood draft and kiln amps recording. Clinker grate coolers should have a minimum of 3 kg of air supply per kg of clin ker, and satell ite cooler should be equipped with updated heat exchange equipment. Cement and Dust Transportation Transport ing cement and dust should require no more than about 2.2 kWh per tonne conveyed. Many old pl ant<; still have consumption levels of 7- 11 kWh per tonne which is excessive. There are mechanical systems, batch type pneumati c systems, continuous pneumatic systems. As an example, to calculate the dillerence in cost, fi ve cents will be used to represent a kW/hour. Thus, if !Mta of cement and dust is transported at 7kW hour/tonne the annual power cost would be 1,000,000 x 7x US $0.05 = US $350,000. Figure 2 A well planned and fitted chain system Thus at 2.2kW h/tonne the annual cost is only US , $ 125,000 which means a saving of US $225,000 a year. The investment would be in the order of US $ 600,000. So, the payback period will be three years. 8 ' ·~