| OCR Text |
Show CONCLUSIONS The utilisation of low oxygen, high efficiency, high stability registers has allowed this NOx level reduction technique to be successfully employed on an existing boiler plant. 1. Low excess air performance does in its own application reduce NOx. 2. The high flame stability, which is a characteristic of these registers, has allowed the adoption of discrete flue gas recirculation as against the more usually employed method of overall dispersion of flue gas into the combustion air ducts. The resultant NOx reductions were achieved without detrimental combustion effects to the boiler as regards load, pulsation, vibration, or excessive temperatures either to the boiler fabric or the final steam temperature. 3. Modelling to produce equal air distribution between registers has allowed for optimum control of both combustion air flow and flue gas recirculation. 4. Indications are that the discrete mode of flue gas recirculation is more efficient than the previously employed mode as regards NOx reduction and allowed for lower overall excess oxygen levels to be obtained and with minimum increase in register draught loss. 5. The employment of simple variations on the geometry of a well proven nozzle also resulted in significant NOx reductions without incurring detrimental combustion effects. 5-34 |
