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Show Operating Patterns -*• Fuel Consumption (GJ/tonne) Annual Saving (£) Single Shift 5.6 Double Shift 4, 2,130 Continuous Operation 2.5 j 4,400 Table 1. Predicted fuel savings due to improved working practices B G Technology has many years experience of modelling gas, oil and coal-fired processes using a "zone" approach. This approach essentially assumes that variations in temperature in the process can be simulated either by a single zone or by a small number of zones at different temperature. The validity of this approach stems from the fact that high velocity burners can often produce enough momentum to produce substantially uniform conditions in an enclosure. Alternatively, situations which are definitely non-uniform (e.g. long furnaces) often have distinct preheat, heating and soak zones which again can be approximated as uniform. The zone approach is applied in situations in which heat transfer is the main parameter of interest. Hence, flow is prescribed and radiation and convection are accurately modelled so that overall efficiencies, effects of design changes etc... can be easily assessed. Both steady state and transient models have been used to predict factors such as:- • fuel consumption (oil or gas)/thermal efficiency • load heat flux distribution • furnace gas and flue temperatures • flame lengths • load surface and internal temperatures • insulation requirements • furnace start up times • recuperator and regenerator performance • emissions The modelling technique is particularly effective at answering "what if types of question. Striving for High Efficiency and Low Emissions Over many years, significant improvements have been made in the thermal efficiency of high temperature plant. However, today not only is there pressure to improve efficiencies further (manifesting itself as a drive to lower C 0 2 emissions), but this needs to be achieved without increasing other potential pollutants. In some instances, these other emissions (e.g. N O x ) also need to be reduced, and this presents new challenges to those designing high temperature plant and combustion equipment. Problems Associated with Air Preheating - NOx Although there are significant energy savings that can be made by preheating the air used for combustion, this presents a new problem - N O x . The increased temperature of the incoming air into a combustion system, results in increased flame temperatures. Thermal N O x formation is highly temperature sensitive, and such an increase in the flame temperature can have significant effects on the N O x emissions from burners, Figure 6. Emission limits for N O x are becoming even more |