Production of Silicon and Carbon Dioxide Treatment Simulation Using Aspen Plus
Process Description
This report will focus on the production of molten silicon through the reaction between silica sand and carbon from a coke fuel. Molten silicon is implemented in many semiconductor industries because of its high storage capacity, which is ten times bigger than molten salts [1]. The following reactions are the key reactions in molten silicon production [2]:
2SiO2(l) + 4C(s)-> SiO(g) + SiC(s) + 3CO(g)
SiO(g) + SiC(s) -> 2Si(l)+ CO(g)
2CO(g) + O2(g) -> 2CO2(g)
ELECNRTL is appropriate for the silicon production process because silicon is produced by reducing SiO2. The intermediate reduction product is SiO, which reacts with SiC to product Si. Therefore, reduction furnace is used when performing the set of silicon production reactions. The carbon dioxide produced from the reaction gets treated with sodium hydroxide later in the process.
Two major chemical components, SiO2 and C, dominates the silicon production process. Before the two components are put into the reactor, natural gas is combusted to heat up the chemicals. Sand and coke are supplied at standard state conditions, whereas natural gas and air are injected at 2atm. The four inlet streams are specified below:
| Stream | SAND | COKE | N-GAS | AIR |
| Flow Rate (kg/hr) | 7382 | 3071 | 363.68 | 7965 |
| Temperature (degrees C) | 25 | 25 | 25 | 25 |
| Pressure (atm) | 1 | 1 | 2 | 2 |
Sand and coke are used as pure sources of SiO2 and C, respectively. The information of natural gas compositions is assumed to become 84 percent methane, 8 percent ethane, 3 percent propane, 2 percent butane, and 3 percent pentane; all other compositions are neglected for this simulation [1]. The n-tane components are combusted to produce some amount of water and carbon dioxide:
CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g)
C2H6(g) + 7/2O2(g) -> 2CO2(g) + 3H2O(g)
C3H8(g) + 5O2(g) -> 3CO2(g) + 4H2O(g)
C4H10(g) + 13/2O2(g) -> 4CO2(g) + 5H2O(g)
C5H12(g) + 8O2(g) -> 5CO2(g) + 6H2O(g)
The amount of carbon dioxide and water produced from the reactions are shown below:
| Component | Water | Carbon Dioxide |
| Flow Rate (kg/hr) | 783.83 | 1011 |
| Temperature (degrees C) | 1446.04 | 1446.04 |
The two carbon dioxide streams emitted from H-101 and R-101 are combined and sent to a heat exchanger after going through E-101 and E-102, the cooling blocks. The purpose of producing quench fluids is to prevent the heat exchanger from being damaged by the heat generated from the hot streams. This process is economically beneficial to the production company as the implementation of high heat resistance material on a heat exchanger is not feasible. The following reactions are the chemical reactions of treating carbon dioxide:
CO2(g) + H2O(l) -> H2CO3(s)
2NaOH(s) + H2CO3(s) -> Na2CO3(s) + 2H2O(l)
When treating carbon dioxide, adding a small percentage, about 3%, of moisture is important as carbon dioxide reacts with the moisture to form carbonic acid, which in return, reacts with the hydroxide to form . (CARBON SCRUBBER REFERENCE)
Through the combustion reaction, Si and carbon are heated up to 1500. The combustion process is essential to maximize the yield of silicon produced by preventing Si from reacting with carbon [2]:
Michael Gyuhan Kyoung, Art Samanthai
-Natural Gas Composition Reference
https://www.e-education.psu.edu/fsc432/content/natural-gas-composition-and-specifications
-Carbon Dioxide Scrubber Reference
https://www.pwperkins.com/how_decarbite_works.html
-Carbon Dioxide Generated Reference
https://www.ipcc-nggip.iges.or.jp/public/gl/guidelin/ch2ref1.pdf