igcc

Aspen Plus IGCC Model Contents TOC \o "1-3" 1 Introduction 1 2 Components 1 3 Process Description 2 4 Physical Properties 3 5 Chemical Reactions 3 5.1 Coal Gasification 4 5.1.1 Coal Decomposition 4 5.1.2 Coal Gasification 4 5.2 Fuel Gas Combustion 5 6 Simulation Approaches 6 7 Simulation Results 8 8 Conclusions 9 1​ Introduction This model simulates an Integrated Coal Gasification Combined-Cycle Power (IGCC) process. The model includes the following features: ​ A set of chemical species including conventional, solid and nonconventional for this process. ​ Typical process areas including: coal crushing and screening, gasification, power generation, and the main streams connecting these units. ​ The specification for nonconventional solid components. ​ Definition of property model parameters with user data. 2​ Components The table below lists the components modeled in the simulation. Components Component ID Type Component name Formula H2O CONV WATER H2O N2 CONV NITROGEN N2 O2 CONV OXYGEN O2 COAL NONC NO2 CONV NITROGEN-DIOXIDE NO2 NO CONV NITRIC-OXIDE NO S CONV SULFUR-RHOMBIC-MONOCLINIC S SO2 CONV SULFUR-DIOXIDE O2S SO3 CONV SULFUR-TRIOXIDE O3S H2 CONV HYDROGEN H2 CL2 CONV CHLORINE CL2 HCL CONV HYDROGEN-CHLORIDE HCL C SOLID CARBON C CO CONV CARBON-MONOXIDE CO CO2 CONV CARBON-DIOXIDE CO2 ASH NONC ARGON CONV ARGON AR H2S CONV HYDROGEN-SULFIDE H2S COAL and ASH are specified as nonconventional solid components. The only properties calculated for nonconventional components are enthalpy and density. Aspen Plus includes special models for estimating these properties for coal and coal-derived materials. See item 4 Physical Properties for more details. Since there are conventional solid and nonconventional solid components in this process, you must select the stream class as MCINCPSD type on Setup | Specifications form. 3​ Process Description Figure 1 shows the process flowsheet which includes: coal sizing and screening, gasification, and power generation. _____________________________________________________________________ Figure 1: IGCC Process Flowsheet The large coal particles (no less than 1mm), are delivered to the three stage coal crushing and screening area for particle reduction. After crushing, more than 93 % of the coal particles are less than 0.18mm and no particles are larger than 0.36mm. Water is mixed with coal feed to aid conveying and crushing The water phase is separated from the coal before it enters the gasification area. The small coal particles (containing 15 wt% moisture), are mixed with pure O2 separated from air. This mixture reacts in the gasification furnace to produce crude coal gas (1148 ℃, 3.0Mpa). A dust wiper is used to remove the ash generated in the gasification furnace, before the crude coal gas is fed into the power generation system. The hot coal gas is cooled from 1148 to 200 ℃ in the boiler to generate superheated steam (500 ℃, 4.0Mpa). The steam is passed through a two stage steam turbine which drives a generator to produce electrical power. Corrosive components such as S, SO2, SO3, CL2, H2S and solid carbon are removed from the cooled coal gas. The clean gas is then mixed with air and burned in a combustor. The gas is at very high temperature (2059 ℃) and at medium pressure (2.85Mpa). It is passed through a gas turbine, and then used to provide further heating of the steam to the second stage of the steam turbine. The gas turbine provides power to the feed air compressor and to an electrical generator. Process summary Area Purpose Coal Crushing and Screening Reduce coal particle size Coal Gasification Decompose coal to produce coal gas Power Generation Generate electrical power by utilizing the coal gas 4​ Physical Properties The global property option used in this model is PR-BM. This option set is used for the gasification and downstream unit operations. The SOLIDS property option is used for the coal crushing and screening section. The enthalpy model for both COAL and ASH is HCOALGEN and the density model for both components is DCOALIGT. The HCOALGEN model includes a number of empirical correlations for heat of combustion, heat of formation and heat capacity. You can select one of these correlations by specifying an option code in the Properties | Advanced | NC Props form, the table below lists the specification of this model: Model Parameter COAL ASH Code Value Correlation Code Value Correlation Enthalpy Heat of Combustion 6 User Specification 1 Boie Standard Heat of Formation 1 Heat-of-combustion-based correlation 1 The same as those of COAL Heat Capacity 1 Kirov 1 Enthalpy Basis 1 Elements in their standard states at 298.15K and 1 atm 1 The heat of combustion for COAL, is specified on the Properties | Parameters | Pure Component form. Select the object HEAT and click the Edit button to view or change the value of the parameter HCOMB. The density method DCOALIGT is specified on the Properties | Advanced | NC Props form. This model is based on equations from IGT (Institute of Gas Technology). The Aspen Properties User Guide, Chapter 6 gives more details on this. 5​ Chemical Reactions The chemical reactions in this process are very complicated. This model uses a relatively simple approach to represent the reactions. In this model, some trace reaction products such as COS, CS2 are not considered. The reactors are modeled with the built in models RStoic, RYield and RGibbs. The table below lists the reaction units and corresponding Aspen Plus models: Reaction Unit Reaction Type Aspen Plus Model Coal Decomposition Yield RYield Coal Gasification Equilibrium RGibbs Fuel Gas Combustion Fractional Conversion RStoic Reactions in each reactor and their specifications in Aspen Plus model are listed as follows: 5.1​ Coal Gasification 5.1.1​ Coal Decomposition Component Bass Yield H2O Mass 0.2 ASH Mass 0.2 C(CIPSD) Mass 0.1 H2 Mass 0.1 N2 Mass 0.1 CL2 Mass 0.1 S Mass 0.1 O2 Mass 0.1 Since the reaction products include conventional solid C and nonconventional solid ASH, you should specify the PSD for these two components and Component Attributes for ASH. Note: The component yield of the coal decomposition product depends on the coal ULTANAL attributes, not on the yield specification. 5.1.2​ Coal Gasification Component Valid Phases H2O Mixed N2 Mixed O2 Mixed NO2 Mixed NO Mixed S Mixed SO2 Mixed SO3 Mixed H2 Mixed CL2 Mixed HCL Mixed C PureSolid CO Mixed CO2 Mixed ARGON Mixed H2S Mixed Coal gasification is modeled using the Gibbs free energy minimum method in the RGibbs model. This determines the equilibrium composition of the products resulting from the many reactions that can occur. 5.2​ Fuel Gas Combustion Rxn No. Specification type Stoichiometry Fraction Based Component 1 Frac. Conversion 2 CO + O2 --> 2 CO2 1 CO 2 Frac. Conversion 2 H2 + O2 --> 2 H2O 1 H2 At very high temperature, it is assumed that components H2 and CO burn completely. 6​ Simulation Approaches Unit Operations – The major unit operations are represented by Aspen Plus models as shown in the following table (excludes reactor units): Aspen Plus Unit Operation Models Used in the Model Unit Operation Aspen Plus Model Comments / Specifications Coal Crushing Crusher Rigorous simulation of PSD Coal Particles Screening Screen Rigorous simulation of the separation efficiency of the screen Dust Removing Sep Simplified simulation of gas/solid separation by fixed split fraction specification Coal gas Purifying Sep Simplified simulation of removing components from gas by fixed split fraction specification Air Compressor Compr Calculates power required Boiler Heater Simplified simulation of the generation of HP steam in a boiler Turbine Compr Calculates power produced Streams - Streams represent the material and energy flows in and out of the process. For the nonconventional solid components in the coal feed stream FEEDCOAL, the specification of PSD and component attributes is required. The values used are: PSD Specification: Interval Lower limit Upper limit Weight fraction 1 0.000000000 0.000044013 0 2 0.000044013 0.000063002 0 3 0.000063002 0.000087996 0 4 0.000087996 0.000124990 0 5 0.000124990 0.000176990 0 6 0.000176990 0.000249990 0 7 0.000249990 0.000353870 0 8 0.000353870 0.000499870 0 9 0.000499870 0.000707130 0 10 0.000707130 0.001000050 0.1 11 0.001000050 0.002000100 0.1 12 0.002000100 0.004000000 0.2 13 0.004000000 0.008000000 0.35 14 0.008000000 0.016000000 0.25 Component Attributes: PROXANAL ULTANAL SULFANAL Element Value Element Value Element Value MOISTURE 15 ASH 9.2 PYRITIC 0.6 FC 45.1 CARBON 67.1 SULFATE 0.1 VM 45.7 HYDROGEN 4.8 ORGANIC 0.6 ASH 9.2 NITROGEN 1.1         CHLORINE 0.1         SULFUR 1.3         OXYGEN 16.4     Design-Specs, Calculator Blocks and Convergence - The simulation is augmented with a combination of flowsheeting capabilities such as Convergence, Design Specs and Calculator Blocks. The following tables outlines the key flowsheeting capabilities used in this model: Design Specs Used in the IGCC Model Spec Name Spec (Target) Manipulated Variables BFWFLOW Sets the temperature of steam from BOILER-B to 500 ℃ BFW (Boiler Feed Water) mass flow THRSG Sets the temperature of gas EXHAUST2 from HRSG-A to 350 ℃ BFW2 (Boiler Feed Water) mass flow XCESSAIR Set O2 mass fraction of stream TOTURB to 0.005 AIR2 mass flow Calculators Used in the IGCC Model Name Purpose REYIELD Transfers the component yield from wet coal basis to water free coal basis. Uses Excel to perform this calculation. The Excel file is embedded in the file with extension .apmbd. 7​ Simulation Results The Aspen Plus simulation main flowsheet is shown in Figure 2. Figure 2. IGCC Flowsheet in Aspen Plus No errors occur in the simulation. Warnings occur due to physical property parameters PC and Freeze Point of carbon being outside the normal range. Key simulation results are shown in the following table: Key Stream Simulation Results: Flowsheet Variable Value Unit Feed Coal Feed 10800 kg/hr Water for crushing 12600 kg/hr O2 for Gasification 6159 kg/hr Air for Combustion 54240 kg/hr BFW for Boiler 40462 kg/hr Product Power 25931.6 kW Waste Water for Crushing 12600 kg/hr ASH 845 kg/hr Acid Water 136 kg/hr Exhaust Gas 90503 kg/hr Key Process Simulation results: Process Variable Value Unit Coal Moisture before entering into Gasification furnace 15% Coal Particle Size < 0.354 mm Gasification Furnace Temperature 1144 ℃ Combuster Temperature 2057 ℃ Air/fuelgas mole Ratio in combustor 2.29 8​ Conclusions The IGCC model provides a useful description of the process. The simulation takes advantage of Aspen Plus’s capabilities for modeling solid components. This includes tracking component attributes and particle size distribution, and estimating properties for coal. The model may be used as a guide for understanding the process and the economics, and also as a starting point for more sophisticated models for plant design and specifying process equipment.