efficiently in separation chamber 1 whose separation principle can be referred to as lt lt gravity separation gt gt whereas the finer particles are removed more efficiently in plate precipitation device 20 the performances of the separation chamber can be compared with those of a conventional horizontal gravity separator in order to obtain a 100 removal efficiency for 30 micron diameter sand grains a conventional horizontal gravity separator with the same height and width as the separation chamber described in the example above of the present invention must be about 48 m long which is 11 times as great as the 4 5 m length of the separation chamber of the present invention if it was decided that the height the width and the length of a conventional horizontal gravity separator should have the same value it has been calculated that these three dimensions would then be 9 4 m the performances of the separation chamber can also be compared with those of inertia separators of complex design which can reach a 90 removal efficiency for 30 micron sand grains but at the cost of a pressure drop that is much higher than the 180 pa measured in the separation chamber high performance cyclone collectors can nearly reach a 100 removal efficiency for 30 micron sand grains but also at the cost of a pressure drop much above 180 pa the total thermal sand removal efficiency obtained with the combination according to the invention of the order of 99 5 is matched by no other known mechanical separator in the variant illustrated.