Division 1.10.2 NOX emissions
United Kingdom
| Technique | Description |
|---|---|
| Combustion modifications | |
| (i) Reduction of air/fuel ratio | The technique is mainly based on the following features:
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| (ii) Reduced combustion air temperature | The use of recuperative furnaces, in place of regenerative furnaces, results in a reduced air preheat temperature and, consequently, a lower flame temperature. However, this is associated with a lower furnace efficiency (lower specific pull), lower fuel efficiency and higher fuel demand, resulting in potentially higher emissions (kg/tonne of glass) |
| (iii) Staged combustion | — Air staging involves substoichiometric firing and the addition of the remaining air or oxygen into the furnace to complete combustion. a low impulse primary flame is developed in the port neck (10 % of total energy); a secondary flame covers the root of the primary flame reducing its core temperature |
| (iv) Flue-gas recirculation | Implies the reinjection of waste gas from the furnace into the flame to reduce the oxygen content and therefore the temperature of the flame. The use of special burners is based on internal recirculation of combustion gases which cool the root of the flames and reduce the oxygen content in the hottest part of the flames |
| (v) Low-NOX burners | The technique is based on the principles of reducing peak flame temperatures, delaying but completing the combustion and increasing the heat transfer (increased emissivity of the flame). It may be associated with a modified design of the furnace combustion chamber |
| (vi) Fuel choice | In general, oil-fired furnaces show lower NOX emissions than gas-fired furnaces due to better thermal emissivity and lower flame temperatures |
| Special furnace design | Recuperative type furnace that integrates various features, allowing for lower flame temperatures. The main features are:
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| Electric melting | The technique consists of a melting furnace where the energy is provided by resistive heating. The main features are:
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| Oxy-fuel melting | The technique involves the replacement of the combustion air with oxygen (> 90 % purity), with consequent elimination/reduction of thermal NOX formation from nitrogen entering the furnace. The residual nitrogen content in the furnace depends on the purity of the oxygen supplied, on the quality of the fuel (% N2 in natural gas) and on the potential air inlet |
| Chemical reduction by fuel | The technique is based on the injection of fossil fuel to the waste gas with chemical reduction of NOX to N2 through a series of reactions. In the 3R process, the fuel (natural gas or oil) is injected at the regenerator entrance. The technology is designed for use in regenerative furnaces |
| Selective catalytic reduction (SCR) | The technique is based on the reduction of NOX to nitrogen in a catalytic bed by reaction with ammonia (in general aqueous solution) at an optimum operating temperature of around 300 – 450 °C. One or two layers of catalyst may be applied. A higher NOX reduction is achieved with the use of higher amounts of catalyst (two layers) |
| Selective non-catalytic reduction (SNCR) | The technique is based on the reduction of NOX to nitrogen by reaction with ammonia or urea at a high temperature. The operating temperature window must be maintained between 900 and 1 050 °C |
| Minimising the use of nitrates in the batch formulation | The minimisation of nitrates is used to reduce NOX emissions deriving from the decomposition of these raw materials when applied as an oxidising agent for very high quality products where a very colourless (clear) glass is required or for other glasses to provide the required characteristics. The following options may be applied:
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