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NITRIC ACID PLANT
(63% wt. HNO3)
Ammonia-Based Fertilizers
University of Illinois at Chicago
Department of Chemical Engineering
CHE 397 Senior Design II
January 24, 2012
Thomas Calabrese (Team Leader)
Cory Listner
Hakan Somuncu (Scribe)
David Sonna
Kelly Zenger
1
Today’s Agenda
 Big Picture – Fertilizer Plant
 Supplier
 Customers

Nitric Acid Plant Design Basis
 Starting Reagents
 Products
 Environmental Concerns






Process Block Flow Diagram
General Process Overview
Catalysts
Useful Energy Recovery
Pressure and Temperature Effects
NOx Emission Control
2
BIG PICTURE-FERTILIZER PLANT
Ammonia (Liquid)
Supplier (603.5 TPD)
INTERNAL
AIR (10820 TPD) CUSTOMER
2571.2 TPD
HNO3 (63 wt%)
OUTSIDE CUSTOMERS
717.8 TPD HNO3 (63 wt%)
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Design Basis

Produce 3,289 TPD of 63% wt. nitric acid solution (~14M)
 Starting Reagents



Ammonia (NH3) - 603.5 TPD
Excess Air – 10,819.5 TPD
Excess Oxygen (O2) from Air – 2,272.0 TPD
 Products



63% wt. Nitric Acid Solution (HNO3) - 3,289.0 TPD
Water (H2O) – 1,216.9 TPD
Useful Heat
 Environmental Concerns


Oxides of Nitrogen (NOx) (<200 ppm)
Nitrous Oxide (N2O) (<200 ppm)
4
572 TPD NH3 (g)
from Ammonia Plant
Ammonia
Filtration
Mixing
Catalytic
Reactor
(Oxidation of NH3)
NO (g)
10,322 TPD Air
Air
Filtration
Air
Compression
Heat Recovery
(Oxidation of NO)
1,843 TPD
Steam
to CHP
Atmosphere
Gas Expander
Nox
Compressor
Hot Tail Gas
NOx (g)
NO2 (g)
Bleacher
Column
Absorption
Column
(Strip Dissolved NOx)
(Formation of HNO3)
607 TPD
Process Water
Cold Tail Gas
3,289 TPD
63% wt. HNO3
718 TPD
to Market
2,571 TPD to
Ammonium Nitrate
General Process Overview


Primary Chemical Reactions (Ostwald Process)
 Oxidation of Ammonia to Nitrogen Monoxide
4NH3 (g) + 5O2 (g)  4NO (g) + 6H2O (g)
 Oxidation of Nitric Oxide to Nitrogen Dioxide
2NO (g) + O2 (g)  2NO2 (g)
 Reaction of Nitrogen Dioxide to Nitric Acid
3NO2 (g) + H2O (l)  2HNO3 (aq) + NO (g)
Side Chemical Reactions
 Simultaneous to Oxidation of Ammonia
4NH3 (g) + 3O2 (g)  2N2 (g) + 6H2O (g)
4NH3 (g) + 4O2 (g)  2N2O (g) + 6H2O (g)
6
Materials of Construction
Material
Pros
Cons
Steel and aluminum
Cheap, can be used at low
temperatures
At elevated temperatures
forms oxides and nitride
films on surface of metal.
Stainless Steel
Operating performance, less
maintenance. Required for
elevated temperatures. Corrosion
resistant.
Higher capital cost
compared to basic metals
Hastelloy
(Nickel alloy)
Highly corrosion resistant. Can be
operated at high temperature and
high stress
More expensive than
stainless steel. Degradation
due to handling.
Monel
(Nickel Alloy)
Can be operated at high
temperatures. Corrosion resistant
Much more expensive than
stainless steel
7
Energy Recovery Methods



Heat from Oxidation in Catalytic Reactor
Heat from Absorption
Mechanical Energy from Tail Gas Expansion
8
Energy Recovery Methods

Net Energy Exporter






Little effect from single/dual-pressure and other considerations
Steam (standard)




Oxidation reaction: 1,600 Btu/lb of pure nitric acid
Absorption process: 370 Btu/lb
Tail gas turbine: 325 Btu/lb (~80% of mechanical energy used)
Total: 1,955 Btu/lb (967-1,217 Btu/lb at 50-65% efficiency)
Augmented with natural gas at startup
Combined Heat & Power (CHP)
Generate high pressure steam and run through turbine
Offsets power purchase from the grid
9
Which Catalyst?
Platinum-Rhodium
Cobalt Oxide (Co3O4)
Cost ($/short ton
$3 - $4
of HNO3 produced)
$0.50 - $0.75
Lifespan
3-4 months
12 months
Downtime
 4 hours to replace gauze at
end of lifespan
 Remove Rhodium Oxide
buildup (every 3-4 weeks)
None
Conversion
Efficiency
93% - 96%
95% - 98%
Operating
Parameters
24-95 psi, 1490-1724 °F
0-95 psi, 1549 °F
Use
Very common, industry standard New, commercial use
Drawbacks
Cost, lifespan, and greater N2O
formation
Minimal data available,
new reactor design,
deactivation to CoO
10
Why are Pressure and
Temperature Important?
Cost
Catalyst Life
NH3 Oxidation
NO Oxidation
Absorption of
NO2
Low Pressure
(0-25 psig)
Lowest Cost
Shorter than Dual
Increased Oxidation
Rate
Decreased Yield
Less Absorption
High Pressure
(90-120 psig)
Increased Cost
Shorter than Dual
Reduced Oxidation
Rate
Increased Yield
Improved
Absorption
Dual Pressure
Highest Capital and
Materials Cost
Longest Catalyst Life
Increased Oxidation
Rate, Best
Conversion
Increased Yield
Improved
Absorption
Increased
Temperature
-
-
Increased Yield
Decreased Yield
Improved
Absorption
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Controlling NOx Release

Primary Methods-reduce N2O formed during ammonia
oxidation

70-85% efficiency
Add an “empty” reaction chamber between the catalyst bed and the first heat
exchanger (increase residence time)
 Modify the catalyst used during the ammonia oxidation


Secondary Methods-reduce N2O formed immediately after
ammonia oxidation (Selective Catalytic Reduction)

Up to 90% efficiency

Secondary catalyst is used to promote N2O decomposition by increasing the
residence time in the ammonia burner
2N2O (g)  2N2 (g) + O2 (g)

12
Controlling NOx Release

Tertiary Methods-reduce N2O from or to the tail gas
(Non-Selective Catalytic Reduction)
 80-98+% efficiency
 A reagent fuel (e.g. H2 from an ammonia plant purge) is
used over a catalyst to produce N2 and water
 Alternatively, following SCR the tail gas is mixed with
ammonia and reacts over a second catalyst bed to give N2
and water
13
Thermodynamic Models for HNO3 (63 wt%) Plant
Up-stream of HNO3 (63 wt%) Plant – Soave-Redlich-Kwong (SRK)
 The SRK property method uses the Soave-Redlich-Kwong (SRK) cubic equation of state for all
thermodynamic properties with option to improve liquid molar volume
 Mixture Types
 Use the SRK property method for non-polar or mildly polar mixtures.
 This property method is particularly suitable in the high temperature and high pressure regions
 Range
 It can be expected reasonable results at all temperatures and pressures.
 The SRK property method is consistent in the critical region.
 Therefore, unlike the activity coefficient property methods, it does not exhibit anomalous
behavior. Results are least accurate in the region near the mixture critical point.
Down-stream of HNO3 (63 wt%) Plant - ELECNRTL
 It can handle very low and very high concentrations
 It can handle aqueous and mixed solvent systems
 The solubility of supercritical gases can be modeled using Henry ‘s Law
 The Redlich-Kwong equation of state is used for all vapor phase properties
 Mixture Types
 Any liquid electrolyte solution unless there is association in the vapor phase
 Range
 Vapor phase properties are described accurately up to medium pressures.
Aspen Database
Summary
 Produce 3,289 TPD of 63% wt. Nitric Acid
 Key Equipment

Ammonia Evaporator, Air Compressor, Catalytic
Reactor, and Absorption Column
 Competing Processes
Platinum-Rhodium Alloy or Cobalt Oxide
 Single or Dual Pressure System
 Energy Recovery
 Materials of Construction

15
Looking Ahead

Problem areas to be addressed









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Catalyst decision
Single or dual pressure plant decision
Material balance
Thermodynamic model
Method of pollution control
Equipment material
Finalized Material and Energy Balances
Rough Economics
Hand Calculations
Additions to Report
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References





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
ASPEN Thermodynamic Database.
Available and Emerging Technologies for Reducing Greenhouse Gas Emissions from the Nitric Acid
Production Industry. U.S. Environmental Protection Agency. 2010.
<http://www.epa.gov/nsr/ghgdocs/nitricacid.pdf>.
Bell, B. Platinum Catalysts in Ammonia Oxidation. Platinum Metals Rev. 4. 1960.
Best Available Techniques for Pollution Prevention and Control in the European Fertilizer Industry,
Production of Nitric Acid. EFMA. 2000. <http://www.efma.org/PRODUCT-STEWARDSHIPPROGRAM-10/images/EFMABATNIT.pdf>.
Cobalt Oxide Catalyst. Catalyst Development Corporation. 2003. <http://www.cobaltoxide.com/>.
Pratt, Christopher, and Robert Noyes. Nitrogen Fertilizer Chemical Processes. Pearl River: 1965.
Ullman’s Encyclopedia of Industrial Chemistry. Volume A17. VCH.
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Questions?
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