Fluid catalytic cracking regeneration with reduction of nitrogen oxide

An FCC catalyst regeneration technique in which the catalyst is regenerated in a dense bed regenerator. Regeneration effluent gases are collected from different parts of the regenerator vessel in a common collection zone and passed through the catalyst separation cyclones from the common collection zone. The cyclones may be arranged with their inlet horns adjacent one another in the common collection zone or a cyclone inlet manifold with a common inlet may be connected to the cyclone inlets. The inlet port to the manifold may be extended to form an elongated vertical duct through which regeneration effluent gases and entrained catalyst pass from the dilute phase of the dense bed to the cyclone so that mixing of the effluent gases is promoted to ensure combustion in residual quantities of oxygen present in the effluent gases before the gases enter the cyclones. Improved operating flexibility is obtained together with a reduced likelihood of cyclone damage as a result of localized high temperature excursions. In addition, the NOx level of the regenerator stack gases is reduced.