A method for processing a chemical stream, the method comprising: contacting a feed stream with a catalyst in an upstream reactor section of a reactor system, wherein the reactor system comprises the upstream reactor section and a downstream reactor section, and the contacting of the feed stream with the catalyst causes a reaction which forms an intermediate product stream; passing at least a portion of the intermediate product stream and the catalyst from the upstream reactor section to the downstream reactor section; introducing a riser quench fluid into the downstream reactor section, the upstream reactor section, or a transition section between the downstream reactor section and the upstream reactor section and into contact with the at least a portion of the intermediate product stream and the catalyst in the downstream reactor section, the upstream reactor section, or the transition section to slow or stop the reaction of the intermediate product stream with the catalyst to form a product stream, the riser quench fluid having a temperature less than a temperature of the intermediate product stream; separating at least a portion of the catalyst from the product stream in a catalyst separation section downstream of the downstream reactor section; passing at least a portion of the product stream and the riser quench fluid to a product processing section; introducing a product quench fluid into the product processing section to provide cooling to the product stream, remove at least a portion of the riser quench fluid from the product stream, or remove entrained particulate solids from the product stream in the product processing section, wherein the product processing section comprises a quench tower; and separating at least a portion of the riser quench fluid from the product stream in the product processing section, wherein the riser quench fluid introduced to the downstream reactor section, the upstream reactor section, or the transition section comprises the at least a portion of the riser quench fluid separated from the product stream. contacting a feed stream with a catalyst in an upstream reactor section of a reactor system, wherein the reactor system comprises the upstream reactor section and a downstream reactor section, and the contacting of the feed stream with the catalyst causes a reaction which forms an intermediate product stream; passing at least a portion of the intermediate product stream and the catalyst from the upstream reactor section to the downstream reactor section; introducing a riser quench fluid into the downstream reactor section, the upstream reactor section, or a transition section between the downstream reactor section and the upstream reactor section and into contact with the at least a portion of the intermediate product stream and the catalyst in the downstream reactor section, the upstream reactor section, or the transition section to slow or stop the reaction of the intermediate product stream with the catalyst to form a product stream, the riser quench fluid having a temperature less than a temperature of the intermediate product stream; separating at least a portion of the catalyst from the product stream in a catalyst separation section downstream of the downstream reactor section; passing at least a portion of the product stream and the riser quench fluid to a product processing section; introducing a product quench fluid into the product processing section to provide cooling to the product stream, remove at least a portion of the riser quench fluid from the product stream, or remove entrained particulate solids from the product stream in the product processing section, wherein the product processing section comprises a quench tower; and separating at least a portion of the riser quench fluid from the product stream in the product processing section, wherein the riser quench fluid introduced to the downstream reactor section, the upstream reactor section, or the transition section comprises the at least a portion of the riser quench fluid separated from the product stream.