Bottom-unheading device and method for vertical vessels

An improved unheading device adapted for removal and replacement of a lower cover unit for flanged openings in a vertically oriented coking drum, comprising:

• (a) a cover unit adapted for being sealably attached by bolts to a flange of a lower flanged opening in a coking drum, said cover unit being attached to a supporting cradle means;
• (b) at least eight pivotable clamping means each pivotably attached to the vessel lower flange and including a detensioning means, said clamping means being substantially equally spaced around the perimeter of said cover unit, each detensioning means being adapted for connecting onto a lower nut for detensioning and removing the fastening bolts pivotably outward and upward so as to unfasten said cover unit from the coking drum lower flange;
• (c) a lifting frame means located below said cover unit and said cradle means, said lifting frame being supported from said coking drum and vertically movable by four equally-spaced vertically-oriented piston actuator means;
• and
• (d) carriage means supported partially by said lifting frame, said carriage means being adapted for lateral movement relative to the lifting frame by dual horizontally oriented piston actuators which are each attached to the carriage means forward end, said carriage means being supported at its forward end by a guide surface sliding on a support rail, whereby said cover unit can be lowered from the coking drum lower flange and moved laterally aside to permit coke removal through the lower opening in the coking drum, and then reconnected to the coking drum lower flange.