Nitric acid mono pressure process

 

CEAMAG offers the mono pressure process suitable for small and middle size Nitric Acid plants.

The chosen operating pressure may vary between 600 to 800 kPa abs. The final choice would depend on optimization according to local conditions and customer requirement.

A Lower pressure at Ammonia conversion reactor improves the ammonia conversion efficiency, whereas a higher pressure tends to lower the investment.

The technology is well proven in numerous plants of the same type. The processes offer high stream factor, stable and safe process easy to operate, an optimized heat recovery efficiency and low maintenance cost.

Ammonia evaporation

Liquid ammonia is received from Battery Limits and feeds the Ammonia Evaporator E101, Necessary heat for evaporation is brought by cooling water coming from the absorption Column C101 and NOx Condenser E109. A small amount of liquid is extracted from the bottom of E101 and sent to the Auxiliary Ammonia Evaporator E103 in order to maintain the water and oil concentration in E101. At the outlet of E101, ammonia gas is superheated in Ammonia Superheater E102.

Air compression

The atmospheric air necessary for the process is compressed by the Air Compressor K102. The compressor is driven by the power coming from the expander K103 and complementary power coming from the steam turbine K101. Compressor can be either horizontal train or “Bull Gear”.

Before entering in the Air Compressor, atmospheric air is filtered by Air Filter F101. The efficiency of filtration will result in protection of compressor itself, and will prevent damages of Platinum gauzes. The total flow is divided in process air sent to the Ammonia Converter R101 and secondary air sent to the Bleaching section of the Absorption Column C101. As an option for small size plants, the steam turbine can be replaced by an electrical motor.

Ammonia / Air Mixing and reaction

Gaseous ammonia is injected in the process air stream under ratio control. Appropriated safety controls and trips systems insure the safe operation of the plant, outside the explosion limits of the Ammonia/Air mixture. In order to insure a proper mixing and good conversion on the Platinum gauzes, the mixture passes through the Ammonia/Air Mixer M101. The reaction of Ammonia with the oxygen of air on platinum catalyst evolves a big amount of heat. Temperature after the Platinum gauzes is about 890°C.

Heat Recovery System

In order to recover the heat generated by reactions of ammonia in air and NOx gas oxidation, the heat recovery is designed for two purposes:

  • Production of HP steam, ~2.8 to 4.5 MPa at about 420°C. The pressure level and superheating will depend upon the choice of turbine and Customer requirement,
  • Re-heating of tail gas from the Absorption Column C101 before entering in the DeN2O Reactor and then in the expander K103.

In general, the heat recovery train will include:

  • The Steam Superheater E104,
  • The Waste Heat Boiler E105,
  • The Process Gas Cooler E106,
  • The Economizer E107,
  • The Cooler Condenser E108.

The exchangers train and the equipment lay-out are optimised for a maximum recovery of oxidation heat, taking into account of investment cost.

NOx Gas Condensation, NOx Absorption and Nitric acid production

After passing through the Heat recovery system, the NOx gas arrives in the Cooler Condenser E108 were part of NOx gas and water are condensed to form week acid. The week acid is then sent to the Absorption Column C101, to the tray having the same concentration. The NOx gas leaving the Cooler Condenser E108 is introduced under the first oxidation tray at the bottom of the Absorption Column C101.

The Absorption column is composed of two main sections:

  • The first bottom part is composed of oxidation trays, in order that NOx gas in sufficiently oxidized in NO2 and N2O4 before absorption,
  • After the oxidation trays, the section starts with absorption trays, where the Nitric Acid is formed.

Between the two sections, an accumulation tray recovers the Nitric Acid production stream and drives the stream to the Bleaching Column C102, located in the bottom of the Absorption Column C101 (the Bleaching Column may be a separate item, depending upon local conditions and plant capacity).

The last two trays on the top of the Absorption Column receive the process water necessary for achieving the absorption of NO2 and N2O4 species to form Nitric Acid. The last tray is fed with demineralised water and the tray before may be fed with process condensates coming from the Ammonium Nitrate plant via a tank in which nitric acid is introduced under pH control, in order to maintain the process condensate always in acidic pH. The heat evolved by absorption reaction and the oxidation of NOx gas is removed via coils installed above trays. The tail gas leaving the column has a NOx concentration of about 1000 ppm.

Re-heating of tail gas, DeN2O and DeNOx Reactors

At the outlet of the Absorption Column, the tail gas is first re-heated in Tail Gas Heater E109, by means of LP steam. The tail gas is then heated in the Expander Inlet Cooler E110, before passing through the Process Gas Cooler E106, in which heating is finally adjusted for getting the required temperature for the N2O abatement.

After re-heating, the tail gas passes first on a catalytic bed for N2O abatement (R102). After reduction of N2O gas, the tail gas is directed to the second catalytic bed (R103) for reduction of NOx species. The ammonia necessary for the reduction of NOx is injected in the tail gas stream under flow control before entering in DeNOx reactor R103.

After outlet of the DeNOx Reactor R103, the hot tail gas is sent to Expander inlet Cooler E110 in which its temperature is adjusted for optimization of power recovery at the Expander K103.

After the Expander K103, the tail gas is sent to atmosphere through the tail gas Stack.

Optional Steam export / co-generation

The heat recovery system can be easily adapted to local needs and conditions for using of the reactions heats:

  • Steam turbine may be replaced by electrical motor for optimization of steam export optimization,
  • Coupled with a steam turbine consuming the full available produced steam, an electrical power generator may be installed when export of steam is not required.

Depending on the case and temperature finally obtained at outlet of the expansion turbine, an economizer can be installed at the expander outlet for recovery of part of available heat (to a point that avoids deposit of nitrite salts on cold points).

 

Main figures
1 Acid Quality (%HNO3) 58 - 62
2 Specific Consumptions  
Ammonia : kg/t
Including NH3 for DeNOx
284+2
Platinum loss: mg/t - Gross 140 – 150
Net with recovery gauzes 45 – 50
3 Steam Export : kg/t
With a steam turbine
~550
4 N2O / NOx emissions EFMA – BAT (*)

(*) Compliance with local requirement