Arrangement and Method for Heave Compensation of Tools Provided with Vertical Rack Gearing in a Derrick

Abstract

An arrangement and a method is for heave compensation of a working unit. At least one driving unit is arranged in a vertically displaceable manner in a tower by the driving unit being in engagement with a pitch rack arranged vertically in the tower, the pitch rack being hung off in a vertically displaceable manner in a heave compensator.

1 . An arrangement for heave compensation of a working unit, thereby compensating heave motion of a floating surface installation on which the working unit is installed, the working unit comprising at least one driving unit and being arranged in a vertically displaceable manner in a tower by said at least one driving unit being in engagement with a pitch rack arranged vertically in the tower, wherein the pitch rack is hung off in a vertically displaceable manner in a heave compensator arranged in an upper tower portion, the pitch rack depending from the heave compensator. 
     
     
         2 . The arrangement according to  claim 1 , wherein the heave compensator comprises at least one rotary actuator taken from a group comprising hydraulic motors and electric motors. 
     
     
         3 . The arrangement according to  claim 1 , wherein the pitch rack is provided with two opposite rows of teeth, and the heave compensator comprises at least one rotary actuator in engagement with each of the rows of teeth. 
     
     
         4 . The arrangement according to  claim 1 , wherein a rotary actuator is connected to a mechanical or hydraulic transmission via a remote-operated clutch. 
     
     
         5 . The arrangement according to  claim 1 , wherein the tower comprises several parallel pitch racks, whose vertical displacements are synchronized by the pitch racks being interconnected by a mechanical or hydraulic transmission for generating the cooperating displacements of the pitch racks via at least one associated rotary actuator. 
     
     
         6 . The arrangement according to  claim 1 , wherein the tower comprises several parallel pitch racks whose vertical displacements are synchronized by each pitch rack being connected to an electronic position-monitoring system connected to a control system for the heave compensator for the generation of displacement of each pitch rack via at least one rotary actuator connected to each pitch rack or group of pitch racks. 
     
     
         7 . A method of heave-compensating a working unit, thereby compensating heave motion of a floating surface installation on which the working unit is installed, the working unit comprising at least one driving unit and being arranged in a vertically displaceable manner in a tower by said at least one driving unit being in engagement with a pitch rack arranged vertically in the tower, the method comprises the steps:
 a) arranging a heave compensator in an upper portion of the tower;   b) hanging off the pitch rack in the heave compensator;   c) registering a heave movement in the tower via a control system connected to the heave compensator;   d) displacing the pitch rack vertically via the heave compensator in order thereby to neutralize the heave movement of the tower.   
     
     
         8 . The method according to  claim 7 , wherein the method further comprises:
 e) hanging off several pitch racks in the same heave compensator; and   f) moving the pitch racks synchronously by
 f1) connecting the pitch racks to a mechanical or hydraulic transmission, and moving the pitch racks collectively, or 
 f2) connecting each pitch rack to an electronic position-monitoring system connected to a control system for the heave compensator, and displacing each pitch rack individually. 
   
     
     
         9 . (canceled)