Optimisation of furnace operation

The amount of dust and exhaust gases resulting are directly related to the amount of coke charged per tonne of iron. Therefore, all measures that improve the thermal efiieieney of the cupola will also reduce the emissions from the furnace. 

Possible good melting practice measures include  

Uniform charging taking care during charging to get a uniform distribution of metal and coke 

Increased energy efficiency, reduction of cokes consumption, reduction of residues. 

This technique applies to all new and exisiting cupola ftimaces. 

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The selection and optimisation of furnace operating conditions will be dealt with in more detail in section VIIA of the next chapter (page 57). 

Optimisation of furnace operation and to increase the melting efficiency. 

The optimisation of the bio-oil was aimed at adjusting the operating conditions of the fast pyrolysis process to maximize the concentration of these reactive groups in the bio-oil, while maintaining a high overall oil yield. Figure 1 shows the main part of the small-scale production facility for small amounts of the oil. It consists of the biomass feeder, the reactor and a bio-oil collection system. Before each experiment, a batch of sand was preheated inside an electrical furnace to about bOO°C, where after it is mixed with cold sawdust in the bottom of the cone. The produced vapours could be immediately removed from the hot reactor, and collected in several water-cooled vessels. 

Long distillation times and frequent crucible failures made the VIR furnace the bottleneck for silver production in the early days of operation. The main issues dealt with through the commissioning and optimisation of the VIR furnaces were ... 

Medium frequency (250 Hz) furnaces have a higher power density (up to 1000 kW/tonne) than mains frequency (50 Hz) furnaces (300 kW/tonne). This allows the use of a smaller crucible (up to a factor of three smaller) which results in a smaller total heat loss. The thermal efficiency of medium frequency furnaces is 10 % higher than for the mains frequency types. Additionally, mains frequency units need to be operated with a molten heel of up to 2/3 of the crucible capacity to optimise specific energy consumption and also require specific starter-blocks for cold start-up. Medium frequency furnaces can readily be started with a cold charge and can be emptied at the end of each working shift or melting batch. 

The principles of the optimisation are generally valid for iron melting in rotary furnaces using oxygen burners. The operational data have been established for a 3 tonnes/h furnace. For furnaces of other sizes, a site-specific optimisation is necessary. 

For the operation of rotary furnaces, BAT is to implement a combination of measures to optimise furnace yield and to use an oxybumer. BAT is to collect the off-gas close to the furnace exit, apply post combustion, cool it using a heat-exchanger and then to apply dry dedusting. For the prevention and minimisation of dioxin and fiiran emissions, BAT is to use a combination of specified measures. Similarly to the situation with cupola furnaces, industry has expressed doubts on the implementation of secondary measures for dioxin and for an abatement that have only been proven in other sectors and in particular questions their applicability for smaller foundries. 

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