Keywords: reburn, low-NOx systems, staged combustion
Experience on coal reburn in a utility boiler
Reburning is an in-furnace combustion modification technology for the reduction of NOx. By staging the introduction of the fuel, an environment is created where NOx generated by the combustion of the main fuel supply is subsequently consumed by the hydrocarbon radicals arising from the reburn fuel under reducing conditions. ENEL has retrofitted unit No. 4 of Vado Ligure power station with coalover-coal reburn technology, with the target of 65% reduction of NOx emissions (425 mg/Nm³ of NOx @ 6% O2, with American Ashland coal). This retrofit represents the first application of the technology to a utility boiler in Europe, and it has been undertaken by a consortium of European companies, research centres and universities, as listed in the following ENEL (Italy), Mitsui Babcock Energy (United Kingdom), Ansaldo (Italy), Electricity Supply Board (Ireland), PowerGen (United Kingdom), Instituto Superior Tecnico Lisbon (Portugal), Electricidade de Portugal, Howden & Sons (United Kingdom), Electricité de France and University of Stuttgart (Germany), with the support of the European Community through the Thermie Programme. Results from the experimental campaign show that it has been possible to achieve NOx emissions in the order of 350 mg/Nm³ (@6% O2), burning a variety of coals, with carbon in ash ranging from 5 to 8%. Calculations performed on the experimental data show that the impact on boiler operation is also minimised, with a negligible change on the boiler heat transfer pattern.