IPRO 346- Design of a Coal Desulfurization Process to Improve the Environment Fall 2006

Transcription

1 IPRO 346- Design of a Coal Desulfurization Process to Improve the Environment Fall 006 Team Members: -Salil Benegal (CHEM) -Anthony Doellman (PHYS) -Greggory Kisiel (CHEM) -Andrew Keen (CHE) -James Maratt (CHE) -Amy McDowell (CHE) (team leader) -Adejoke Ogunride (CHE) -Oscar Olmos (CHE) -Myint Toe (CHEM) Advisor- Professor Mohammed Reza Ehsani

2 What is the problem? U.S. - Full of Coal Coal - Full of Sulfur Image 1- US Coal Bearing Areas 1 Sulfur Causes acid rain Alters ph of soil/water Damages man-made structures and buildings Increases difficulty and cost of producing steel In coke, promotes brittle steel Image - Illinois Coal Bearing Areas 1

3 Inorganic Sulfur Organic Sulfur Sulfur in Coal Mainly pyritic sulfur, a solid with the formula FeS in two types of crystalline formation: Pyrite & Marcasite Part of the chemical structure of the coal that cannot be removed by physical means

4 What is the solution? Objective: Desulfurize coal pre-combustion to fit EPA standards Produce coal for coking process Advantages to pre-combustion: Reduces environmental contamination Produces high purity coal for coke making Project Outline: Research Comparison Modeling Profitability analysis

5 EPA Standards EPA requires a removal of.5 lb SO/million BTU For our process of 70 tons/hr, this equals a total sulfur removal of 81%

6 What is coke? A solid derived from low ash, low sulfur bituminous coal Coal carbonization - process for producing metallugical coke used in steel making blast furnaces Used in steel making blast furnaces

7 Desulfurization Methods 3 types of methods: Biological Physical Chemical

8 Biological Methods Mix microorganism with coal in a batch process Different organism options for various removal rates and types of sulfur removed Advantages Low capital and operating costs Less energy use Disadvantages Sulfur removal rates are too slow Low removal percentages (50-60% total sulfur)

9 Physical Methods Flotation Method Flotation exploits the fact that coal has a specific gravity ~ whereas pyrite is >. By pulverization of coal particles, pyritic sulfur can be removed High Gradient Magnetic Separation Based on differing magnetic properties of coal and pyrite Ground coal slurry solution is run through a magnet Pyrite and ash are attracted to steel while coal passes through Up to 90% removal of pyrite

10 Physical Methods Advantage: Tend to be far more economical than their chemical or biological counterparts. Disadvantage: Act exclusively on inorganic forms of sulfur in coal

11 Chemical Methods Chemical Comminution Coal is treated with ammonia solution resulting in selective breakage for mineral liberation 80-90% less pyritic sulfur 50-60% less ash. No organic removal Magnex Process FeS + Fe(CO) 5 Minerals + Fe(CO) 5 Fe 1-x S +5CO Fe.Minerals + CO Magnex process uses a chemical reaction to convert weakly magnetic pyrite and nonmagnetic mineral into paramagnetic material No organic removal

12 Chemical Methods Molten Caustic Leaching Molten caustic leaching (MCL), uses strong bases at high temperatures to dissolve sulfur off of coal Common bases: NaOH, KOH Pyritic sulfur released at 150 C Organic sulfur released is released at 00 C Removal: 90-95% pyritic sulfur 70-90% organic sulfur 90-99% of ash.

13 HO (Steam) N Coal Bunker Grinder Mixer Heat Ex Cooler 100C Reactor Centrifuge Liquids NaOH, KOH 40C, 30min 300C, 98psig 1hr Cake, Coal (Alkalized) Desulfurized Coal/ Demineralized NaOH, KOH (5% of total use) Dryer Filter HO Mixer HSO4 (0.1M) Mixer Mixer HO Alkaline Sln. % coal Recovered= 80% %Sulfur Reduction=97% CaO 110C HO+Few Minerals Mixer HO Acidified Coal Centrifuge CaO Ca, Fe, Na, K, SO4 Dry Caustic Regenerator Evaporator Cost of processing coal = $1.05/ton Diagram 1: Molten Caustic Leaching Process Ca, Si, Al, S

14 Chemical Methods Oxydesulfurization Uses high temperature and pressure along with steam and air to remove sulfur from coal Takes place in a fluidized bed reactor Removes 70-90% of total sulfur in coal Main advantage is the use of air over chemicals

15 Process Flow Diagram Diagram : Oxydesulfurization Process

16 Simplified Process Flow Diagram Diagram 3: Simplified Oxydesulfurization Process

17 Main Reactor (Fluidized Bed) Pressurized gaseous medium of air and steam passes through coal particles Oxygen binds with sulfur on coal and is removed as SO Image 3: Fluidization Regimes- Perry s Handbook, Ch17 pg 4 Image 4: Fluidization Graph - Kunii & Levenspiel Fluidization Engineering

18 Calculations U mf - Minimum fluidization velocity Calculated using correlation by Wen and Yu Takes into account particle size distribution and spherocity U mf Re mf f d p P h 150(1) gu Re d 7 1 4d p 3 Calculated Values: U mf 33cm /s Re 6.4 Ar 1.06x10 7 P 1.49psi Re ( * Ar) Ar Reactor Size: d 3 p ( ) g f A s r 4.6m h 8m f weight * gravity pressure m Perry s Handbook, Ch17 pg 4

19 Calculations (Kinetics) Pyritic Sulfur FeS FeS FeS FeS r r r r O FeSO 7 O H O 15 1 O H O 4 15 O H O 4 FeSO FeSO FeSO FeSO K K K K p p p p 4 C C C C S Fe FeS FeS FeS FeS Fe 1 SO 3 Fe SO O 3 4 H 4 4H H Modeled as a batch reactor: SO 4 % Desulfurized Pyritic Sulfur = 99.5% dc dt ps K 4 p C s r FeS r ifes 4K p C FeS i1 J 46.5X10 6 K p 1.14X10 4 *exp kmol RT

20 Calculations Elemental sulfur S 3 O HO H SO 4 r 5S 1 r 5O 3 r 5 H O 1 r H r SO 4 dc dt elems K p C s Modeled as a batch reactor: % Desulfurized Elemental Sulfur = 94.7%

21 Inorganic Sulfur & Elemental Sulfur Concentration (Kgmol/m^3) Vs Time (s) SO4-- Produced Pyritic Sulfur Elemental Sulfur Graph 1: Inorganic and Elemental Sulfur Change in Concentration Over Time

22 Organic Sulfur Organic Sulfur (kgs/kgcoal), SO production (kgso/kgcoal) Organic Sulfur SO Produced Graph : Organic Sulfur and SO Change in Concentration Over Time

23 Calculations Oxidation of Carbon dc c dt K 0 K 0.88X X10 exp RT 6 J kmol mol 3 m. s % C _ recov ered mol m mol m * % Coal Loss (mol/m^3) Time (s)

24 Economic Analysis Production Basis: 554,400 tons/year clean coal Cost of Cleaning Coal (includes cost of raw coal) Total Sales Pre-tax Earnings Total Cleaning Cost Total Sales $88/ton $98/ton $10/ton $48,90,410/year $54,070,90/year

25 Economic Analysis Total Cost of Equipment $6,656,840 Total Capital Investment $14,346,75 Pre-tax Earnings $5,167,879 Return on Investment 3% Payback Period years

26 Safety Analysis Critical aspects: High pressure considerations for reactor design Operating pressure maintenance to prevent combustion Fluidized bed effluent is harmful to operators Bleed valve on fluidized bed necessary to unload coal safely Non-critical aspects: Water cleansing and disposal Periodic acid neutralization in the entire system to prevent corrosion in points of accumulation

27 Feasibility of Process Method is feasible, but not mainstream Meets EPA Standards 86% sulfur removal Necessary for higher quality steel production Successful ash and sulfur removal drastically improves product quality Solid state of coke makes forms of post-combusion undesirable Organic sulfur removal can still be improved without significant changes in operating conditions

28 Acknowledgements Professor Mohammed Reza Ehsani Professor Javad Abbasian

29 Questions?