Cement, Energy and Environment

- - / ....... penalising use of that energy source in short supply. The points is that: • • • The most efficient system may not be the least expensive to operate. Actual cost of energy may not be correlated to actual energy used. Availability of the type of power can have a dramatic impact on cost. + The type of power most plentiful in an area is subject to change. + The cost ratio of the type of power can change with availability. Many past articles have detailed the benefits of ball mill systems, and high pressure grinding roll systems. It would seem that now would be a good time to take a closer look at the vertical roller mill, which has come into its own as a viable slag grinding system. Courtesy : World Cement, Mar. 02, Pp47-56, Enquiry no. 5. Email: mail@worldcement. com Web: www. worldcement.com • • Excess heat fromexhaust gases leaving the preheater; approximately 20 MW. Heat from excess clinker cooler air; approximately 10 MW. Approxima,tely 375 000 Nm 3 /h of exhaust gas leaves the preheater at 385 to 405°C. This is cooled in a boiler producing suprheated steam sufficient to dry the raw material in the vertical raw mill. The excess air from the clinker cooler used to be 275°C. Presently, the combustion air is preheated to 70°C by recirculation of the clinker cooler excess gas, which increases clinker tempera ture by 10°C and clinker cooler excess air to 310°C at a flow rate of 275 000 Nm 3 /h. This concept will itself improve the heat exchange f<?r heat recovery. The temperature limit is set by the electrical precipitating fi lter (ESP), which operates upstream of the heat recovery equipment. The annual electricity production is estimated to be 50 GWh. The produced electricity is delivered to Cementa and w ill be beneficial to the electrical grid, which is expec ted to be COGENERATION strengthened by the operating steam turbine Anders Lyberg, Technical Director, cementa AB, generator set. The total cost for the electricity Sweden, HeidelbergCement production is expected to be lower than the long te rm market p ri ce, achieving economical In the year 2001, Cementa AB's 2 million tpa benefits for both companies. The hi gh production plant in slite on the Isle of Gotland environmentalprofile of this concept is positive in Sweden, indirectly, became a producer of for both Cementa and Vattenfall. electricity, based on the use of excess process heat. Cementa and energy company Vattenfall, formed a partnership, which at an early stage carried out necessary prestudies regarding t~s co-generation concept. The driving force for the electricity generating project has been: The waste heat recovered as electlicity p"rovides a net 2%lower emission of C02 at a power plant per tone of cement produced. Using waste heat for electricity generation from cement plant is one important way to contribute to a more sustainable cement industry.