U.S. Treasury Secretary says there are many strong candidates for Fed chair.  
The selection process will start this fall.  
Trump may nominate a new Fed chair early to limit Powell's influence.  
Powell's term has 11 months left.  
Sources say Trump could pick a successor by September or October.  
He’s reportedly angry at Powell and might move faster.  
Possible candidates include ex-Fed official Kevin Warsh and White House adviser Kevin Hassett.  
Others in the mix: ex-World Bank head Malpass