Dusseldorf is indeed about 147 feet above sea level. However I am not sure where you are getting your altitude of 2900 ft (by the way, it is not flight level FL290, which would be 29,000 feet). Are you referring to the height which you intercept the glideslope? In that case you would not add the 147 feet, although it wouldn't make much of a difference if you had. At 2900 feet, you should intercept the glideslope around 5-6 miles out I believe.