Advanced Process Design of Nitric Acid Plants

Transcription

1 AspenTech Advanced Process Design of Nitric Acid Plants Ralph Grob and Paul Mathias Aspen Technology, Inc. 4 December 1998 Presented at: Nitric Acid Conference Valley Lodge, Magaliesburg 3-4 December, 1998

2 AspenTech AspenTech s Plantelligence TM Solution Enable the True Potential to be attained Design Model Determine the True Potential to be achieved Operate Manage Evaluate performance against True Potential

3 AspenTech The Opportunity : Enormous Economic Returns The Opportunity Industry Average Best Practices True Potential TM

4 Achieving True Potential AspenTech Core Competencies ERP Design Operate Models Manage Business Process Expertise IT Integration Manufacturing and Integrated Supply Chain Expertise Deep Process Knowledge Intelligent Field OCS Plantelligence Electronics, Computer Engineering, Network Communication

5 AspenTech 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.

6 AspenTech SEP TARGETED INDUSTRIES Inorganic chemicals Specialty chemicals Mining and metals

7 AspenTech Solids and Electrolytes Plus (SEP ) Process Simulator COMP1 Phase Equilibria Vapor-liquid-solid Vapor-liquid liquid-liquid-solid Reactor R1OUT VAP-A SEP1 Stream Structure PSD moments PSD Ions Databanks Ions Dilute electrolytes Solids Physical Properties C p, H, G, S U K POWDER1 Steady-state simulation AspenPlus Dynamic Simulation AspenDynamics Unit Operations crystallizer ion exchange dryers electrolytic cells GAS1 Process Models Fertilizers Caustics Metals Amines etc. Thermodynamic Models Zemaitis Chen Pitzer EOS

8 AspenTech 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

9 AspenTech SEP Models for the Fertilizer Industry NH 3 CO 2 Phosphate Rock Sulfur Potash Ore Nitric Acid Urea Sulfuric Potash Acid Potash Ammonium Nitrate Phosphoric Acid Diammonium Phosphate Box Code Red - Available Yellow - Under development White - Planned

10 AspenTech 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

11 AspenTech 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

12 AspenTech 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

13 AspenTech NITRIC ACID - PROPERTIES Pure water - cooling water and steam Modified RKS for polar nonelectrolyte mixtures Electrolyte NRTL Fine-tuned parameters - high, known accuracy

14 AspenTech Electrolyte NRTL and Chemistry High Accuracy for thermodynamic properties: Vapor-liquid equilibrium Enthalpy Density

15 AspenTech Partial Pressures of HNO 3 and H 2 O Over Aqueous Nitric Acid C Partial Pressure (bar) C x (HNO 3 )

16 AspenTech Txy Diagram for Aqueous Nitric Acid at 1 Atmosphere 400 Temperature (K) Bubble Point Dew Point x, y (HNO 3 )

17 AspenTech NITRIC ACID PLANT SECTIONS Gas-mixing Ammonia oxidation Nitric oxide oxidation Absorption Tail-gas treatment

18 AspenTech Nitric Acid Flowsheet Sections Front Section Air Compressor Liquid Ammonia Vaporizers Oxidation of NH 3 to NO NO Gas

19 AspenTech Nitric Acid Flowsheet Sections Middle Section NO Gas Oxidation of NO to NO 2 Dimerization of NO 2 to N 2 O 4 Condensation to form aqueous HNO 3 NO x Gas Nitric Acid Condensate

20 AspenTech Nitric Acid Flowsheet Sections Towers Section Water NO x Gas Nitric Acid Condensate Absorption of N 2 O 4 into water to form HNO 3 Turbine Expansion Degas Product Stream Exhaust Nitric Acid Product

21 AspenTech Countercurrent NO x Gas Cooler NO x Gas Coolant Out NO x Gas Coolant In 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

22 AspenTech Absorption Tower Several vapor and liquid phase reactions Rate-limited liquid-vapor mass transfer UA-limited heat transfer

23 AspenTech Rigorous Tower Model Reactions and Mass- Transfer Species Vapor Phase Interface Liquid Phase NO(G) mo NO(L) 2NO + O 2 o 2NO 2 N 2 O 4 (G) mo N 2 O 4 (L) N 2 O 4 + H 2 O mo HNO 3 + HNO 2 2NO 2 mo N 2 O 4 HNO 3 (G) mo HNO 3 (L) H 2 O(G) mo H 2 O (L)

24 AspenTech 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

25 AspenTech NITRIC ACID ABSORBER Four gas-phase reactions: 2NO + O 2 o 2NO 2 2NO 2 mo N 2 O 4 N 2 O 4 + H 2 O o HNO 3 + HNO 2 3HNO 2 o H 2 O + HNO 3 + 2NO

26 AspenTech Features of AspenTech s 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

27 AspenTech Features of AspenTech s 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

28 AspenTech 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?