Cement, Energy and Environment

and transports this heat to some other loca on such that the fluid acts as a carrier. Two forms of convec on are dis nguished. In the first place convec on may arise naturally. If for example a hot object at temperature T1 is in contact with a cooler fluid of temperature T2, heat is transported from the object to the boundary layer through conduc on. This leads to density changes in the boundary layer and as a result the fluid in the boundary layer will rise and be replaced by cooler fluid that is heated again etc. This phenomenon is called free convec on. The second form of convec on arises if the flow is brought about by for example a pump or a fan. In principle this form of convec on, known as forced convec on, is generally more efficient since the period of contact between the hot object and the fluid is shortened. This effec vely comes down to an increase of the temperature difference between the solid and the fluid and with that an increase of the heat transfer to the boundary layer through conduc on. The heat transfer per unit surface through convec on was first described by Newton and the rela on is known as Newton's law of cooling. According to this law the heat exchange is, under normal atmospheric condi ons, propor onal to the temperature difference at the interface. Here the heat exchange q'' is -2 measured in [W m ]. The temperature of the surface and the fluid are indicated by T and 1 T respec vely, where it is ∞ implied that the fluid is present in such large quan es that its temperature may be taken to be constant. The constant of propor onality h is called the convec on heat transfer -2 -1 coefficient in [W m K ]. The total power removed from an object with surface although convec on then is: Note that this expression accounts for the heat that is transferred from the object at hand to the 'infinite' body of surrounding fluid. IMPACT OF THERMAL LOSSES IN CEMENT PLANT 1. Increase of Power Consump on 2. Increase of Fuel Consump on 3. Increase in Produc on Cost. 4. Decrease in Efficiency of System. 5. Environmental Pollu on. SHELL SCANNER/THERMAL SCANNER Thermal scanner, enables con nuous surveillance of kiln shell temperature, has a central posi on in the control room of hundreds of modern cement plants around the world. One of the unique advanced features of Shell Scanner is the thermal warp computa on. The thermal warp analysis is made available to the operator for · Protec ng the kiln and its equipment through a be er control of mechanical and thermo-mechanical stresses. · Keeping trace of the kiln thermo-mechanical behavior when opera ng condi ons are altered (flame, meal flow rate, kiln rota on speed, gas draught). The system works from the real- me synchronous acquisi on of the following measurements- · Kiln shell temperature, by the infrared scanner, · Synchroniza on by kiln rota on contact switch, · Tyre slippage. From the screen menu, the operator can display: · The shell thermal chart and 41