Apparatus and methods for size-specific detection of particles entrained in fluids are provided. A particle size selector separates particles entrained in a sample fluid stream using a curved channel. Shroud fluid streams are interposed between the sample fluid stream and walls of the channel. Centrifugal forces arising from fluid flow through the curved channel separate differently-sized particles into different transverse sections of the channel. A detector downstream from the particle size selector specifically detects particles in one or more transverse sections of the channel.

Processes and systems for pyrolysing a hydrocarbon. In some examples, the process can include mixing a cooled hydrocarbon effluent and a cooled de-coking effluent to produce a combined effluent. The combined effluent can be introduced into an inlet conduit of a separator under conditions that provide >80 wt. % of the plurality of coke particles with a Stokes number of >10. From a first exit conduit of the separator >55 wt. % of the plurality of coke particles in the combined effluent can be removed, and from a second exit conduit of the separator a coke-lean hydrocarbon effluent that includes <45 wt. % of the plurality of coke particles in the combined effluent can be removed. The first exit conduit and the second exit conduit can be coupled to the inlet conduit.