Over fire arrangement and method

An over fire air arrangement for a bubbling fluidized bed furnace, the furnace having opposing first wall and second wall and opposing first side wall and second side wall between the first and second walls for forming a furnace enclosure, the over fire air arrangement comprising:

• at least one first over fire air port provided to the first wall for supplying a first over fire air flow into the furnace,
• at least one second over fire air port provided to the second wall for supplying a first over fire air flow into the furnace,
• at least one first additional over fire air port provided to the first side wall in the vicinity of the first wall so that the at least one first additional over fire air port is arranged closer to the first wall than its distance to a vertical centre line of the furnace enclosure, the at least one first additional over fire air port being arranged to supply along the first wall a first additional over fire air flow into the furnace transversely to the first over fire air flow,
• at least one further first additional over fire air port provided to the second side wall in the vicinity of the first wall so that the at least one further first additional over fire air port is arranged closer to the first wall than its distance to a vertical centre line of the furnace enclosure, the at least one further first additional over fire air port being arranged to supply along the first wall a further first additional over fire air flow into the furnace transversely to the first over fire air flow,
• at least one second additional over fire air port provided to the first side wall in the vicinity of the second wall so that the at least one second additional over fire air port is arranged closer to the second wall than its distance to the vertical centre line of the furnace enclosure, the at least one second additional over fire air port being arranged to supply along the second wall a second additional over fire air flow into the furnace transversely to the second over fire air flow, and
• at least one further second additional over fire air port provided to the second side wall in the vicinity of the second wall so that the at least one further second additional over fire air port is arranged closer to the second wall than its distance to the vertical centre line of the furnace enclosure, the at least one further second additional over fire air port being arranged to supply along the second wall, a further second additional over fire air flow into the furnace transversely to the second over fire air flow,
• wherein
• at least one first secondary over fire air port provided to the first wall above the first over fire air port and above the at least one first additional over fire air port,
• at least one second secondary over fire air port provided to the second wall above the second over fire air port and above the at least one second additional over fire air port,
• the at least one first additional over fire air port, the at least one further first additional over fire air port, the at least one second additional over fire air port and the at least one further second additional over fire air port being in vertical direction above the at least one first over fire air port and the at least one second over fire air port and below the at least one first secondary over fire air port and the at least one second secondary over fire air port,
• at least one first secondary additional over fire air port provided to the first side wall in the vicinity of the first wall so that the at least one first secondary additional over fire air port is arranged closer to the first wall than its distance to the vertical centre line of the furnace enclosure, the at least one first secondary additional over fire air port being positioned in the vertical direction above the at least one first additional over fire air port and arranged to supply along the first wall a first secondary additional over fire air flow into the furnace transversely to the first over fire air flow,
• at least one further first secondary additional over fire air port provided to the second side wall in the vicinity of the first wall so that the at least one further first secondary additional over fire air port is arranged closer to the first wall than its distance to the vertical centre line of the furnace enclosure, the at least one further first secondary additional over fire air port being positioned in the vertical direction above the at least one further first additional over fire air port and arranged to supply along the first wall a further first secondary additional over fire air flow into the furnace transversely to the first over fire air flow,
• at least one second secondary additional over fire air port provided to the first side wall in the vicinity of the second wall so that the at least one second secondary additional over fire air port is arranged closer to the second wall than its distance to the vertical centre line of the furnace enclosure, the at least one second secondary additional over fire air port being positioned in vertical direction above the at least one second addition-al over fire air port and arranged to supply along the second wall a second secondary additional over fire air flow into the furnace transversely to the second over fire air flow, and
• at least one further second secondary additional over fire air port provided to the second side wall in the vicinity of the second wall so that the at least one second secondary additional over fire air port is arranged closer to the second wall than its distance to the vertical centre line of the furnace enclosure, the at least one further second secondary additional over fire air port being positioned in vertical direction above the at least one second additional over fire air port and arranged to supply along the second wall a further second secondary additional over fire air flow into the furnace transversely to the second over fire air flow, and
• the at least one first secondary additional over fire air port, the at least one further first secondary additional over fire air port, the at least one second secondary additional over fire air port and the at least one further second secondary additional over fire air port being in vertical direction above the at least one first secondary over fire air port and the at least one second secondary over fire air port.