A multi-bed selective catalytic reduction system comprising a gas input duct, a first ammonia injection grid assembly located downstream from the gas input duct, a first selective catalytic reduction catalyst assembly located downstream from the first ammonia injection grid assembly, a second ammonia injection grid assembly located downstream from the first selective catalytic reduction catalyst assembly, a second selective catalytic reduction catalyst assembly located downstream from the second ammonia injection grid assembly, and an exhaust stack located downstream from the second selective catalytic reduction catalyst assembly. By passing a combustion waste stream through two sets of ammonia injection grid assemblies and selective catalytic reduction catalyst assemblies, the multi-bed selective catalytic reduction system removes more nitrogen oxide emissions from the waste stream, uses less ammonia to do so, and results in less ammonia emissions than systems with only one ammonia injection grid assembly and selective catalytic reduction catalyst assembly.