Atmospheric air is filtered and compressed to about 9.5 kg/cm2. Intercooling in the air compression system is adjusted to produce hot compressed air at 232 degrees C.
Primary air, about 80 percent of the total compressed air, passes through a compressed air filter and enteres the ammonia-air mixer where air is mixed with the required amount of ammonia supplied to contractor's batterly limits at 14 kg/cm2 (min.) and 32 degrees C. The ammonia-air mixture flows from the mixer to the burner assembly which contains a set of platinum-rhodium gauzes. The oxidation of ammonia to nitric oxide takes place at the gauze. The resulting hot gases leave the gauze at approximately 900 degrees C and flow around the tubes of the turbine gas heater and through the tubes of the burner gas boiler, generating steam.
The cooled product gases leave the boiler and flow through a catalyst recover filter, tail gas heater, boiler feedwater heater, nitric gas cooler and water cooled weak acid condenser. Acid collected in the latter unit flows to the proper tray of the absorption tower while the uncondensed process gas flows directly to thel lowerpart of the tower where it is mixed with air from the bleaching section.
Hot secondary air from the air compression system (the remaining 20 percent of the compressed air) is cooled by exchange with tail gas and flows to the bottom section of the absorption tower to "bleach" the product acid before mixing with the process gas.
Make-up water is pumped from the condensate tank to the top of the absorption tower, and the acid produced in the absorber passes through the bottom bleaching section where it is stripped of nitrous acid by the warm secondary air. The product acid lows to the nitric acid storage tank under system pressure. The absorption tower is designed to recover almost all the nitrogen oxides present, yielding a tail gas containing about 250 ppm by volume.
The tail gas flows through the tail gas mist separator at the top of the absorption tower and then through a reheating cycle.The gas is first heated by the bleaching air in the bleach air cooler, by steam in the tail gas preheater and by exchange with the process gas in the tail gas heater and turbine gas heater.
The hot tail gas then enteres the power recovery turbine of the air compression system, furnishing most of the normal compression power. The remaining power required is furnished by a steam turbine.