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Achieving True Potential
AspenTech
1998 AspenTech All Rights Reserved.
Advanced Process Design of Nitric Acid Plants
Ralph Grob and Paul MathiasAspen Technology, Inc.
4 December 1998
Presented at:Nitric Acid ConferenceValley Lodge, Magaliesburg3-4 December, 1998
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
AspenTechs PlantelligenceTM Solution
OperateOperateModel
ManageManage
DesignDesign Determine the True Potentialto be achieved
Enable the True Potentialto be attained
Evaluate performance against
True Potential
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
The Opportunity : Enormous Economic Returns
Industry Average
Best Practices
True PotentialTM
The Opportunity
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Core Competencies
Business Process ExpertiseIT Integration
Manufacturing andIntegrated Supply Chain
ExpertiseDeep Process
Knowledge
Intelligent FieldElectronics , Computer Engineering,
Network CommunicationOCS
ERP
DesignDesign
OperateOperate
ManageManage
Models
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Solids and Electrolytes Plus Industry-specific layered product.
- Specialized property and equipment models- Molecular and stream attributes (e.g., PSD)- Standard, proven process simulations
Expertise in targeted industries.- We know, understand your technology- Technology transfer, consulting and support
Long-term commitment to customer success.
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
SEP TARGETED INDUSTRIES
Inorganic chemicals Specialty chemicals Mining and metals
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Solids and Electrolytes Plus (SEP) Process Simulator
Reactor SEP1
R1OUT
COMP1
VAP-A
POWDER1
GAS1
SteadySteady--state simulationstate simulation AspenPlusAspenPlus
Dynamic SimulationDynamic Simulation AspenDynamicsAspenDynamics
Stream StructureStream Structure PSD momentsPSD moments PSDPSD IonsIons
Unit OperationsUnit Operations crystallizer ion exchange dryers electrolytic cells
DatabanksDatabanks Ions Dilute electrolytes Solids
Physical PropertiesPhysical Properties Cp, H, G, S
Phase EquilibriaPhase Equilibria Vapor-liquid-solid VaporVapor--liquidliquid--liquidliquid--solidsolid
Process ModelsProcess Models Fertilizers Caustics MetalsMetals AminesAmines etc.etc.
Thermodynamic Thermodynamic ModelsModels ZemaitisZemaitis Chen Pitzer EOSEOS
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Core Capabilities of SEP Technology
Comprehensive strength of Aspen Engineering suite
Focus on engineering science of systems containing solids and electrolytes
Expertise in process engineering of target industries - inorganic chemicals, metals and mining
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
UreaDiammonium
Phosphate
NH3
CO2
Phosphate Rock
Sulfur
Potash Ore
NitricAcid
PotashSulfuricAcid
Potash
AmmoniumNitrate
PhosphoricAcid
S EP Models for the Fertilizer Industry
Box CodeRed - AvailableYellow - Under developmentWhite - Planned
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Benefits of Process Modeling Gain a deeper understanding of the
process Investigate process enhancements,
safety Improve control Improve environmental compliance Reduce energy costs Utilize wide range of raw-material blends
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Benefits of Nitric Acid Modeling MARKET FORCES
80% into fertilizer industry - demand is cyclical OPERATIONAL CHALLENGES
Emissions limitations are critical when demand is high Yield is critical when demand is low Ammonia oxidation is sensitive to temperature, pressure,
reactor space velocity - catalyst losses must be minimized Absorber must be optimized for off design and normal
conditions, and within NOx emissions limits CAPITAL PROJECTS
Debottleneck absorber Add air compression, new columns Evaluate piping changes to reduce side reactions, improve
yields Add advanced or multi-variable control
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Challenges of Nitric Acid Modeling
Multiple reactions occur in most equipment, including pipes, gas coolers, heat exchangers and condensers
Performance is flow rate and pressure sensitive Special physical properties are needed for nitric acid
VLE and heat of mixing calculations Many recycle streams for heat and power integration Absorption tower has rate-limited and equilibrium
vapor and liquid reactions, rate-limited mass transfer, and cooling coils on most trays
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
NITRIC ACID - PROPERTIES
Pure water - cooling water and steam Modified RKS for polar nonelectrolyte mixtures Electrolyte NRTL
Fine-tuned parameters -high, known accuracy
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Electrolyte NRTL and Chemistry
High Accuracy for thermodynamic properties:
Vapor-liquid equilibrium Enthalpy Density
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Partial Pressures of HNO3 and H2O Over Aqueous Nitric Acid
0.0001
0.001
0.01
0.1
1
0 0.2 0.4 0.6 0.8 1x (HNO3)
P
a
r
t
i
a
l
P
r
e
s
s
u
r
e
(
b
a
r
)
60C
100C
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Txy Diagram for Aqueous Nitric Acid at 1 Atmosphere
350
360
370
380
390
400
0 0.2 0.4 0.6 0.8 1
x, y (HNO3)
T
e
m
p
e
r
a
t
u
r
e
(
K
)
Bubble Point
Dew Point
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
NITRIC ACID PLANT SECTIONS
Gas-mixing Ammonia oxidation Nitric oxide oxidation Absorption Tail-gas treatment
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Nitric Acid Flowsheet Sections Front Section
Compressor
Vaporizers
Oxidation ofNH3 to NO
Air
LiquidAmmonia NO Gas
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Nitric Acid Flowsheet Sections Middle Section
Oxidationof
NO to NO2
NO GasNOx Gas
Dimerizationof
NO2 to N2O4
Condensationto form
aqueousHNO3
Nitric AcidCondensate
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Nitric Acid Flowsheet Sections Towers Section
Absorptionof N2O4 into
water toform HNO3
NOx GasExhaust
TurbineExpansion
Nitric AcidProduct
Nitric AcidCondensate
Water
Degas ProductStream
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Countercurrent NOx Gas Cooler
Problem Two streams exchange heat with countercurrent
flow One stream has two reactions
Solution Model with RPLUG and specify a countercurrent
coolant Use a design-spec to determine the exit
temperature of the coolant
NOx GasCoolant InCoolant Out
NOx Gas
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Absorption Tower
Several vapor and liquid phase reactions
Rate-limited liquid-vapor mass transfer
UA-limited heat transfer
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Rigorous Tower Model Reactions and Mass-Transfer Species
Vapor Phase Interface Liquid Phase
2NO + O2 2NO2
2NO2 N2O4
NO(G) NO(L)
N2O4 (G) N2O4 (L)
HNO3 (G) HNO3 (L)
H2O (G) H2O (L)
N2O4 + H2O HNO3 + HNO2
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
NITRIC ACID ABSORBER
Rate-based mass transfer, chemical reaction
Bulk vapor and liquid on each tray perfectly mixed
Optimum set of 4 gas-phase reaction
Mass-transfer through gas and liquid films
Estimated heat transfer to cooling coils Negligible heat loss to surroundings
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
NITRIC ACID ABSORBER
Four gas-phase reactions:
2NO + O2 2NO22NO2 N2O4
N2O4 + H2O HNO3 + HNO23HNO2 H2O + HNO3 + 2NO
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Features of AspenTechs Nitric Acid Plant Model Simultaneous rate-limited and equilibrium
reactions are modeled in pipes, heat exchangers, and condensers
Property models were developed using Aspen Plus electrolyte capability
Compressors modeled using performance curves
Pressure drop calculated for each piece of equipment based on volumetric flowrate
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
Features of AspenTechs Nitric Acid Plant Model
Model is segmented for simulation of part of plant or entire plant
Rigorous and efficient absorber model for accurate absorber and plant simulations
Special summary report of nitric acid concentration and production rates, cooling water usage, power requirements, and flue gas composition
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AspenTechAchieving True Potential
1998 AspenTech All Rights Reserved.Plantelligence
USES OF NITRIC ACID PLANT MODEL
Verification of plant design
Day-to-day analysis of equipment performance
Plant optimization - Optimize cost function subject to equipment performance and operating constraints
Debottlenecking studies - is tower or compressor limiting?
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