Building on its long history in ANNA industry, Stamicarbon is introducing its dual pressure nitric acid process. The dual pressure nitric acid technology of Stamicarbon is designed to guarantee high energy recovery. This is achieved by a proper selection of the heat exchangers position downstream the ammonia burner. The main feature of the process is the high tail gas temperature, up to 480°C. This is accomplished by locating the last tail gas heater close to the Pt/Rh gauzes in the ammonia burner vessel where higher process temperatures are encountered.
The high tail gas temperature has several advantages. On the one hand, the N 2 O decomposition can be performed in a tertiary abatement system without the addition of an external reducing agent like natural gas. On the other hand, more power can be generated by the expansion turbine, decreasing the amount of work to be realised by the steam turbine. Besides this, the expanded tail gas still contains valuable heat that can be exchanged in a tail gas/tail gas heat exchanger, allowing a lower temperature in the stack and therefore, more heat recovery in the system. All these advantages are translated into higher steam export and therefore, more energy recovery.
A thoughtful heat exchangers distribution also allows to minimise the well-known condensation/re-evaporation effect and hence, corrosion. This allows the use of common materials of construction which reduce the manufacturing cost of the heat exchangers considerably.