The invention is directed to an arrangement of two conduits, wherein the conduits are positioned parallel with respect to each other and wherein each conduit is provided with means suitable to remove solids from its surface and positioned along the length of one of the two sides of the conduit, wherein the means are one or more pairs of oppositely oriented nozzles, each nozzle having an outflow opening for gas directed, along the surface of the conduit, towards the outflow opening of the other nozzle of said pair, wherein the pairs of oppositely oriented nozzles of one conduit are arranged in a staggered configuration relative to the pairs of oppositely oriented nozzles of the other conduit.