English (United Kingdom)Russian (Russe)
Nitric acid

CEAMAG MONO PRESSURE PROCESS


CEAMAG offers the mono pressure process, suitable for small size and middle size Nitric Acid plants. Two processes can be contemplated :


  1. The mono pressure process operating at 600 kPa
  2. The mono pressure process operating at 800 kPa

In the first process, the plant efficiency is better, whereas in the second process the investment is lower. The final choice will depend upon the choices of the Customer, and optimisation according to local conditions.


Both technologies are well proven in numerous plants of the same type. The processes offer high stream factor, low cost operation, stable and safe process, an optimized heat recovery efficiency and low maintenance cost.


The process description hereinafter corresponds to the case at 600 kPa. Differences in the process flow diagram will concern mainly the heat exchanger train between the Ammonia Converter R101 and the condenser E109 as well as inter-stage coolers for the Air Compressor.


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” type having the advantage of a better overall efficiency.


Air compressor


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 evolves a big amount of heat. Temperature after the 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:


  1. Production of HP steam, 2.8 to 4.0 MPa at about 420°C. The pressure level and superheating will depend about the choice of turbine and Customer requirement,
  2. Re-heating of tail gas from the Absorption Column C101 before entering in the Denox Reactor R102 and then in the expander K103.

In general, the heat recovery train will include a Superheater E104 after Pt gauzes, a Steam Evaporator E105, an Economiser E106, two Gas/Gas Heat Exchangers E107 and 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 NOx Condenser E109 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 Condenser E109 is introduced under the first oxidation tray at the bottom of the Absorption Column.


The Absorption column is composed of two main sections:


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

Absorption column


Between the two sections, an accumulation tray recovers the Nitric Acid production stream and drives the stream to the Bleaching section, located in the bottom of the Column. 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 is 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 concentration of NOx of about 1500 ppm.


Re-heating of tail gas and Denox Reactor


At the outlet of the Absorption Column, the tail gas is first re-heated in First Tail Gas Heater E110, by means of hot secondary air, and then passes through the Gas/gas Heaters E108 and E107. The ammonia necessary for the reduction of NOx is injected in the tail gas stream under flow control and analysis of the tail gas. After the Denox Reactor, the hot tail gas is sent to the Expander K103, and then directed to the stack.


Typical CEAMAG Process Flow Sheet



Typical expected figures

 
Reactor  pressure
600 kpa abs
Reactor Pressure
800 kpa abs
Acid Quality (%HNO3)
58 - 62
58 - 62
Specific Consumptions    
Ammonia : kg/t
Including NH3 for Denox
287
289
Platinum loss: mg/t - Gross
140 – 150
200
Net with recovery gauzes
45 – 50
50 – 60
Steam Export : kg/t    
With a steam turbine
~600
~300 – 400
NOx emission : ppm (*)
50 - 200
50 - 200

(*) Depending upon requirement