One cannot give a detailed answer without more specifics but the major source of failure is fretting of the support against the tube caused by bouncing of the bed and augmented by the abrasive particles of the bed.  This can be eliminated by welding the tubes to a support of the same alloy.  For a cylindrical coil I would drill holes in flat bars with the same pitch as the coil.  The bars should probably be two to four times the thickness of the tube wall.  Thread the coil through the support bars and weld all around the tube on both sides of the support bar.  The support bars can then be bolted to the sides, top and/or bottom of the vessel.    

I would prefer U formed slots since the operation of passing the coil through all holes is very difficult. same material is to be used because of thermal expamsion between welding and use. The bars have also to be so that free expansion is possible for the ccoil.

You can split the hanger and weld it back together when you weld it to the coil.  I worry about insufficient weld area if you just use a U slot.  Don't make the support too unconstrained as there can be a lot of vibration in a fluidized bed.

thanks for your answer.Regarding the details,this is for a big size CFBC boiler,where tube is around 40 mm , longitudinal pitch near 100 mm and transverse pitch is 120mm.there are more than 30 coils inside the chamber.arrangement will be similar to this http://www.faqs.org/patents/imgfull/20140150735_01

Comments are qualitative. I would prefer some more indications in which direction the quantitative analysis has to be pushed. We do not know if the "coils" are horizontal or vertical. We do not know what is understood by "fluidising envirionment ". there are still too many unknowns. If we look at the above mentioned patent then it is not a "coil" but a "serpentine" which has to be supported and the problem is TOTALLY different since the "coil" is a 3D structure and the one in the patent is basically a 2D structure. the supports have to be different and are to be designed so that neither in the vertical plane nor in the horizontal plane excessive vibrations have to occur however the supports have to consider the fact that they are assembled at environmental temp (20...30°C) and they will work at 85.°C. So that important deformations will occur supports have not to induce in the tubing stresses which could lead to buckling or excessive bending and creep.

Attached link will give you fair idea regarding tube profile in a fluidised bed heat exchanger and the operating environment . problem is regarding support of the tubes so as to allow their expansion while preventing vibration.http://www.sciencedirect.com/science/article/pii/S0032591012000204.