CHEN 4470 – Process Design Practice

Dr. Mario Richard EdenDepartment of Chemical Engineering

Auburn University

Lecture No. 3 – Modeling Gasification Systems in Aspen Plus

January 17, 2013

Gasification in Aspen Plus

Components

Feedstock used in this example is Montana Sub-Bituminous Coal

Note: NOT an exhaustive list.

Stream Classes

Used for models where you have both conventional (carbon) and nonconventional (coal/biomass + ash) solids present, but no particle size distribution

Properties

The first parameter (6) indicates that you want to enter the heat of combustion information yourself, rather than have Aspen estimate it.

Properties

Properties

Enter a new pure component parameter here. Since we are entering the heat of combustion for the coal/biomass, it is classified as nonconventional

Properties

From feedstock information for Montana Sub-Bituminous Coal

Feed Specification

Simple basis: 1000 kg/hr

Note that the coal is located in the NC substream!

Feed Specification

Note: PROXANAL values for FC, VM, and ASH sum to 100!

Moisture is added separately.

Feed Specification

Note: ULTANAL values sum to 100!

Values taken from feedstock description

Feed Specification

Note: SULFANAL values sum to ULTANAL value for sulfur!

Sulfur breakdown from feedstock description: 45% pyritic, 45% organic, 10% sulfate

Pyritic: 0.45*1.22 = 0.549Organic: 0.45*1.22 = 0.549Sulfate: 0.10*1.22 = 0.122

Coal Decomposition

First reactor (RYIELD) serves to convert/decompose the coal/biomass into its constituent parts, i.e. H2, O2, N2, H2O, S, C, and ASH.

This is NOT a true stand alone reactor, but an integral part of the gasification reactor. The decomposition reactor serves to convert the nonconventional solids into true components and ash.

Coal Decomposition

Coal Decomposition

Yield distribution is entered as mass yield of component per total mass of feed and calculated from the ultimate analysis data:

mH2 = (1 – XMoisture)*XH*mFeed = (1 – 0.105)*0.0489*1000 kg = 44 kg → yield H2 = 0.044

mO2 = (1 – XMoisture)*XO*mFeed = (0.895)*0.1304*1000 kg = 117 kg → yield O2 = 0.117

mN2 = (1 – XMoisture)*XN*mFeed = (0.895)*0.0149*1000 kg = 13 kg → yield N2 = 0.013

mH2O = XMoisture*mFeed = 0.105*1000 kg = 105 kg → yield H2O = 0.105

mS = (1 – XMoisture)*XS*mFeed = (0.895)*0.0122*1000 kg = 11 kg → yield S = 0.011

mC = (1 – XMoisture)*XC*mFeed = (0.895)*0.6684*1000 kg = 598 kg → yield C = 0.598

mASH = (1 – XMoisture)*XASH*mFeed = (0.895)*0.1251*1000 kg = 112 kg → yield ASH = 0.112

Coal Decomposition

Note: It is necessary to specify that the ASH component is 100% ash in PROXANAL.

Coal Decomposition

Note: It is necessary to specify that the ASH component is 100% ash in ULTANAL.

Coal Decomposition

Note: It is necessary to specify that the ASH component is 0% sulfur in SULFANAL.

Coal Gasification

Second reactor (RGIBBS) serves to convert the decomposed coal/biomass into synthesis gas by reacting it with oxygen. The stream labeled GASFEED does not exist in reality. It serves as a means of transferring the constituent elements of the decomposed coal/biomass to the actual gasification reactor.

It is necessary to link the two reactor blocks by a heat stream in order to take the energy required for the decomposition into account!

Coal Gasification

Simple basis: 1000 kg/hr

You will need to identify the optimal oxygen feedrate along with temperature and pressure

Coal Gasification

Coal Gasification

Important: The elementary carbon formed (if any) needs to be specified as a pure solid.

Solids Removal

The SSPlit subroutine allows for splitting the feed according to the individual substreams, i.e. It enables separating the solids that are ”carried” in the NC and CISOLID substreams to be separated from the gaseous products in the MIXED substream

Solids Removal

A Few Results

Stream: SYNGAS Stream: ASHSubstream: MIXED Substream: NC Mole Flow kmol/hr Mass Flow kg/hr HYDROGEN 15.6820753 COAL 0 OXYGEN 4.47E-15 ASH 112 NITROGEN 0.46290993 Total Flow kg/hr 112 WATER 11.2474944 Temperature C 1005.92981 SULFUR 8.55E-09 Pressure bar 30.3975 CO 34.8003674 Vapor Frac 0 CO2 14.797821 Liquid Frac 0 H2S 0.34304247 Solid Frac 1 METHANE 0.18950623 Enthalpy kcal/kg 55.4111977 C 0 Enthalpy Gcal/hr 0.00620605 AMMONIA 0.00230474 Entropy Total Flow kmol/hr 77.5255214 Density kg/cum 3486.88409Total Flow kg/hr 1888 Average MW 1Total Flow cum/hr 273.345722 Temperature C 1005.92981 Pressure bar 30.3975 Vapor Frac 1 Liquid Frac 0