CHEN 4470 – Process Design Practice

1. Gasification in Aspen Plus CHEN 4470 – Process Design Practice Dr. Mario Richard EdenDepartment of Chemical EngineeringAuburn University Lecture No. 3 – Modeling Gasification Systems in Aspen Plus January 17, 2013

2. Components Feedstock used in this example is Montana Sub-Bituminous Coal Note: NOT an exhaustive list.

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

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

5. Properties

6. 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

7. Properties From feedstock information for Montana Sub-Bituminous Coal

8. Feed Specification Simple basis: 1000 kg/hr Note that the coal is located in the NC substream!

9. Feed Specification Note: PROXANAL values for FC, VM, and ASH sum to 100! Moisture is added separately.

10. Feed Specification Note: ULTANAL values sum to 100! Values taken from feedstock description

11. 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

12. 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.

13. Coal Decomposition

14. 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

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

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

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

18. 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!

19. Coal Gasification Simple basis: 1000 kg/hr You will need to identify the optimal oxygen feedrate along with temperature and pressure

20. Coal Gasification

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

22. 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

23. Solids Removal

24. A Few Results