Apparatus for separating solids from flue gas in a circulating fluidized bed (CFB) boiler includes plural vertical, impact type particle separators made of cooling tubes located within the CFB in a plurality of staggered rows. One embodiment employs a plurality of stacked, slip fit elements having apertures which accept the cooling tubes. The slip fit elements cooperate with one another to form a collecting channel, typically U-shaped, which separates particles from flue gases conveyed across the particle separators. Shiplap joints in between the individual slip fit elements prevent gas and solids from leaking therebetween and allow for thermal expansion. Alternatively, the impact type particle separators include cooling tubes connected to one another to form a unitary structure. Pin studs welded to the cooling tubes and covered with a coating of refractory; ceramic tiles; metal or ceramic spray coatings; metal or ceramic castings; weld overlay; and/or shields provide erosion resistance.