A high temperature gas cleanup system, which consisted of three cyclone separators in series, has operated satisfactorily through 500 hours in a 1 Mwt PFBC pilot test unit. The total collection efficiency of this system was 99-99.3%. The fly ash concentration in cleaned gas stream reduced to values below 2 x 10(-4) kg/m3 (N) and there are no particles larger than 10mum. The second stage cyclone is the newly developed PHI 240mm PV type cyclone separator with dimensions optimized. Its measured cut size is 1.2mum and the resistance coefficient considering pressure drop about 12. The third stage multicyclone separator consists of three PHI 100 EPVC - I type cyclone tubes and its collection efficiency of 8mum particle is about 99.5%.