API STD 536:2017

This standard specifies requirements and provides guidance for the selection, design specification, mechanical description, operation, maintenance, and test procedures for post-combustion NOx control equipment and related mechanical systems and components used for fired equipment in petrochemical and general refinery service. This document covers the following methods of post-combustion NOx reduction for both new and retrofit applications: - Selective Non-catalytic Reduction (SNCR), and - Selective Catalytic Reduction (SCR). This standard is primarily intended for direct application to fired process heaters, reformers, and industrial and power boilers used in petrochemical and general refinery services. The same fundamental NOx control technologies and systems may also be applied to Fluid Catalytic Cracking Units (FCCUs), incinerators, gas turbine exhaust, and other exhaust gas process systems; however, SCRs may require additional considerations beyond the scope of this standard to address unique aspects, such as high particulate content and corrosive chemicals, in the flue gas stream. This document does not cover: - reduced NOx formation through combustion controls and design techniques such as low-NOx burners, flue gas recirculation (FGR), and staged combustion; or - non-selective catalytic reduction (NSCR) for the control of NOx and other pollutant emissions. For further guidance on post-combustion NOx control process selection and the application of SNCR and SCR systems, refer to Annex A. For further guidance on the process description of SNCR and SCR technologies and systems, refer to Annex B and Annex C, respectively. For further guidance on reactant storage, distribution, control, and injection systems, and general design considerations, including purchaser decisions for SNCR and SCR systems, refer to Annex D and Annex E, respectively.