The Riemann problem for a simplified chromatography system is considered and the global Riemann solutions are constructed in all kinds of situations. In particular, the zero rarefaction wave, the zero shock wave and the zero delta shock wave are discovered in the Riemann solutions in some limit situations, which have infinite propagation speeds. Furthermore, these zero waves are analyzed by introducing the so-called double Riemann problem with three pieces of constant states. More precisely, we take the approximations of zero waves and investigate wave interactions in details before the limits are taken.