Aspen HNO3

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

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



The Opportunity : Enormous Economic Returns

Industry Average

Best Practices

True PotentialTM

The Opportunity



Core Competencies

Business Process ExpertiseIT Integration

Manufacturing andIntegrated Supply Chain

ExpertiseDeep Process

Knowledge

Intelligent FieldElectronics , Computer Engineering,

Network CommunicationOCS

ERP

DesignDesign

OperateOperate

ManageManage

Models



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.



SEP TARGETED INDUSTRIES

Inorganic chemicals Specialty chemicals Mining and metals



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



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



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



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



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



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



NITRIC ACID - PROPERTIES

Pure water - cooling water and steam Modified RKS for polar nonelectrolyte mixtures Electrolyte NRTL

Fine-tuned parameters -high, known accuracy



Electrolyte NRTL and Chemistry

High Accuracy for thermodynamic properties:

Vapor-liquid equilibrium Enthalpy Density



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



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



NITRIC ACID PLANT SECTIONS

Gas-mixing Ammonia oxidation Nitric oxide oxidation Absorption Tail-gas treatment



Nitric Acid Flowsheet Sections Front Section

Compressor

Vaporizers

Oxidation ofNH3 to NO

Air

LiquidAmmonia NO Gas



Nitric Acid Flowsheet Sections Middle Section

Oxidationof

NO to NO2

NO GasNOx Gas

Dimerizationof

NO2 to N2O4

Condensationto form

aqueousHNO3

Nitric AcidCondensate



Nitric Acid Flowsheet Sections Towers Section

Absorptionof N2O4 into

water toform HNO3

NOx GasExhaust

TurbineExpansion

Nitric AcidProduct

Nitric AcidCondensate

Water

Degas ProductStream



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



Absorption Tower

Several vapor and liquid phase reactions

Rate-limited liquid-vapor mass transfer

UA-limited heat transfer



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



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



NITRIC ACID ABSORBER

Four gas-phase reactions:

2NO + O2 2NO22NO2 N2O4

N2O4 + H2O HNO3 + HNO23HNO2 H2O + HNO3 + 2NO



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



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



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?

Documents

Aspen HNO3