Sootblower isolation wall box

A method of sealing a lance tube for cleaning internal surfaces of a combustion device, and wherein a fluid cleaning medium flows through the lance tube during a cleaning cycle and is ejected from the lance tube within the combustion device, the lance tube being retractable into and withdrawn from the combustion device through a cleaning port, the method comprising the steps of:

• providing a wall box at the cleaning port having a clamping seal assembly having a plurality of movable seal assemblies, each of the movable seal assemblies having a seal element movable in a radial direction relative to the lance tube through the action of an actuator, the seal element engageable with the outside surface of the lance tube in a sealing position and withdrawable from the outside surface of the lance tube in a released position, the seal element movable between the sealing and retracted positions through the action of the actuator, wherein the plurality of seal assemblies are arranged in a housing with an internal chamber having a cylindrical wall and with a circular jaw plate mounted within the internal chamber with a clearance gap between the jaw plate and the cylindrical wall, each of the plurality of seal assemblies being formed of at least one piston retained by the jaw plate and each piston coupled with one of the seal elements and configured to move the one of the seal elements radially with respect to the jaw plate, and the jaw plate being radially movable within the internal chamber and self-centering around the lance tube,
• withdrawing the seal elements from contact with the outside of the lance tube during the cleaning cycle by moving the seal elements to the released position, and
• at the conclusion of the cleaning cycle, actuating the actuator for moving the seal elements into the sealing position in contact with the outside surface of the lance tube.