System optimization and selection of coking coal drying process for coking process
0 likes793 views
The document discusses optimization strategies for coking coal drying processes, focusing on reducing moisture levels to enhance coke quality and productivity while mitigating dust issues. It outlines various drying technologies, energy consumption, and drying costs associated with different heat sources like flue gas. The text also compares advancements in drying techniques and provides insights into the design and operation of these systems in coking plants.
System optimization and selection of coking coal drying process for coking process
- 1. Solutions for Coal Drying System optimization and selection of coking coal drying process for coking process Delta Drying Technologies Ltd Add: Suite 219, Block B ，Qilu Software Park, No. 1 Shunhua Rd, Jinan, China Email: alexwong66@aol.com; oxtiger@139.com Website www:coaldryingtech.com Tel 0086-13953108165; 001-610-829-9317
- 2. History of CMC development For top charging coke oven •Coal Moisture Control (CMC) is a process to reduces the moisture of the feed for coke making from a normal 8 - 10% to around 6% with an aim to: •Reduce carbonization heat demand; •Increase productivity; •Enhance coke quality; •Increase usage of ratio of low-grade coking coal; •Reduce CO2 emission;
- 3. History of CMC development Dust issue with CMC project •Dust issue occurs during conveying and loading process due to lower moisture. Fine particles brought to pyrolysis process gas and tar oil have adverse effect on the operation of the following process; •According to study, percentage of fine coal liberation is closely related to coal moisture as below: 0% 20% 40% 60% 80% 100% 0% 2% 4% 6% 8% Percentage of Fine Liberation vs Moisture
- 4. History of CMC development • That is why final moisture is 6% or so in CMC, not even lower; • Dust issue still exists even with 6% or so moisture: moisture is reducing further in the process of falling during early stage of loading, therefore more fine is liberated. This is root cause for dust issue with top charging coke oven; • Dust issue was solved in DAPS and COPE21 processes: moisture is reduced to 2% or even 0% before charging. All fines can be liberated in this way, and then is collected by cyclone. Fine coal is heated close to its softening point and then briquetted by roll compactor. And fine issue can be fixed greatly in this way. • Low grade coking coal can be increased to 57% in SCOPE21 process mainly due to fine briquetting process, which is similar to stamping process in stamping coke oven;.
- 5. History of CMC development For stamping coke oven •For stamping coke oven, moisture should be controlled to the range of 8% to 12%, optimum moisture should be between 9% to 11%. Too low or too high moisture are unfavorable for stamping process; •If moisture is >12%, it would cause operational difficulty for chutes, gates, electromagnetic vibrating feeder, coal and coke crushing machines and coke oven management; •If moisture> 12% due to weather or supplying, coking coal must be dried to meet the process requirement on moisture;
- 6. History of CMC development • Japan is the home of CMC technology, three generations of CMC technologies has been developed; The first generation was rotary dryer with heating oil as drying medium; The second generation was rotary dryer with steam as drying medium; The third generation was fluidized bed dryer with low temp flue gas as drying medium; Japan also developed DAPS and SCOPE21 technologies which also Several coking plants in China also employed fluidized bed dryer in their CMC technology with success;
- 7. Comparison and Optimization of coking coal drying process Selection of drying technologies and heat source •Available heat source for CMC process in coking plants: Low temperature flue gas from coking oven, from 150C to 320C; Coking oven fuel gas orblast furnace fuel gas; LP steam from turbine (CDQ); •Dryers for CMC technologies: Rotary dryer; Steam rotary dryer Fluidized bed dryer;
- 8. • The following table is energy consumption and capital cost for CMC technologies with different heat source and different kind of dryer, for reference only: Comparison and Optimization of coking coal drying process Steam rotary dryer FBD with flue gas from coking oven Rotary dryer with flue gas from coking oven FBD with high temp flue gas Rotary dryer with high temp flue gas Fan power consumption kw/h 1100 2200 3000 600 1300 Steam consumption t/h 19.4 0.0 0.0 0.0 0.0 Coking oven fuel gas consumption m3/h 0 0 0 3500 3550 Steam consumption converted to kw kw/h 3460 0 0 0 0 Coking oven consumption converted to kw kw/h 0 0 0 6500 6600 Power price $/kw 0.12 0.12 0.12 0.12 0.12 Steam price $/t 24 24 24 24 24 Gas price $/m3 0.12 0.12 0.12 0.12 0.12 Power consumption 2 1.0 1.3 3.2 3.6 Capital investment 2 2.2 3.5 1.0 1.5 Drying cost 3.5 1.0 1.2 1.9 1.9
- 9. Comparison and Optimization of coking coal drying process • Above table is based on Inlet moisture 10.23% Outlet moisture 6.5% • Steam parameters: 250℃ @ 1.5Mpa, 175kwh power generation / t of steam; • Inlet flue gas temp for coke oven gas fluidized bed dryer is 950C; • Inlet flue gas temp for rotary dryer is 850C; • Inlet flue gas temp for coke oven flue gas fluidized bed dryer is 200C; • Heating value for coke oven fuel gas is 4200kcal/m3， 1.75kwh power generation / m3 of coke oven fuel gas; • From above table Lowest capital cost with coke oven fuel gas fluidized bed dryer; Lowest energy consumption with coke oven flue gas;
- 10. Comparison and Optimization of coking coal drying process Effect of price of available heat source on CMC process • Energy price (power, steam and fuel gas) varies greatly among different plants and this price difference has a great effect on drying cost; • The following table is drying cost comparison between coke oven flue gas (150C to 320C) and coke oven fuel gas fluidized bed dryer with $0.12 and $0.06/kwh power price (solid line is $0.12/kwh and $0.12 and dotted line is $0.06/kwh ); • The horizontal axis is the temperature of the flue gas of a low temperature oven; the ordinate is drying cost comparison between coke oven flue gas (150C to 320C) and coke oven fuel gas fluidized bed dryer (solid black line is equal operating cost for two heat sources);
- 11. Comparison and Optimization of coking coal drying process Effect of price of available heat source on drying cost for CMC process (1 USD = 6.2 RMB) 0% 25% 50% 75% 100% 125% 150% 175% 200% 150 200 250 300 1RMB /m3 0.8 RMB/m3 0.6 RMB/m3 0.4 RB/m3 0.2 RB/m4 1RMB /m3 0.8 RMB/m3 0.6 RMB/m3 0.4 RB/m3 0.2 RB/m4
- 12. Selection of lignite coal pre-drying technologies DDT high temperature flue gas fluidized bed dryer process •High temp flue gas fluidized bed dryer has been developed based on conventional low to medium temp (650 C and below ) to utilize high temp flue gas (900 C to 1000 C ) ; •The inlet flue gas temp was only about 450 C in the original design in the early stage, and it was gradually increased with the increase of production. The highest inlet flue gas was reached 750 C in operation nowadays; •DDT has developed air distribution with independent Intellectual Property Rights which made it possible to increase inlet flue gas to 1000 C;
- 13. Optimization of drying system for CMC technology Features of high temperature flue gas fluidized bed dryer •Inlet flue gas temperature can be as high as 950C; •Small equipment dimension, low capital investment and low energy consumption due to higher inlet flue gas temperature; •Larger capacity: up to 500t/h water evaporation per unit; •Coarse coal (up to 50mm) can be dried; •Can be designed and operated in slight positive system pressure, oxygen concentration can be controlled to 2.5% or less, which makes sure that drying system is free of coal dust explosion; •Fine can be separated from coarse coal and then briquetted with BCB process without dust issue
- 14. • Fine coal briquetting (Binderless Coal Briquetting, BCB process; Hot briquetting process, HBP): (1), Fine coal collection fine coal is collected by cyclone after dryer. Fine coal dusting issue is mainly caused by fines 150 mesh or less; 150 mesh or less fines only accounts for 35% or so from cyclone; (2), Fine heating Fined coal is heated close to its softening point with vertical indirect heating (3), Fines screening Fine coal is then screened after heating. According to the mechanism of pressing granulation, occupied state and void ratio of fines are determined by its size distribution; larger bonding interface between fines are necessary for fine briquetting and finer coal would have higher strength of product. Screening before briquetting is necessary: the amount of fines to briquetting process is reduced; strength of product is increased, which is particularly important for lignite coal as it will experience multi loading and unloading for long distance transportation; (4), Fine briquetting: Fine coal passed screen is briquetted after screening with roll compactor; Features of BCB / Hot briquetting Binderless and low cost Fines are heated up to close its softening temperature and therefore power consumption for briquetting can be reduced to minimum; Optimization of drying system for CMC technology
- 15. Optimization of drying system for CMC technology • DDT provides different drying process for different customers to chose according to their situations and remands: Coke oven flue gas fluidized bed dryer; Coke oven fuel gas fluidized bed dryer; Coke oven flue gas & Coke oven fuel gas combined fluidized bed dryer; Modified SCOPE21 technology
- 16. Optimization of drying system for CMC technology CMC process with coke oven flue gas
- 17. Optimization of drying system for CMC technology CMC process with coke oven fuel gas CMC process with coke oven flue & coke oven fuel gas combined
- 18. Optimization of drying system for CMC technology Modified SCOPE21 process
- 19. Optimization of drying system for CMC technology Coke oven flue gas & Coke oven fuel gas combined fluidized bed dryer •For existing fluidized bed dryer, inlet flue gas temp has to be increased in order to accommodate to the increase of coal inlet moisture •The relationship between inlet flue gas temp and water evaporation Outlet moisture % 10 10 10 10 10 10 10 10 10 Inlet moisture % 13 14 15 16 17 18 19 20 25 Inlet flue gas temp C 250 300 340 385 430 480 525 580 850 Water evaporation t/h 3.5 4.7 5.9 7.1 8.4 9.7 11.1 12.5 20
- 20. Optimization of drying system for CMC technology Modified COPE21 technology •For top charging coke oven; To replace fluidized bed dryer with high temp fluidized bed dryer; Fluidized bed dryer can be designed as two layer: first layer for drying and second layer for coarse coal preheating due to high inlet temp; To replace pneumatic fine preheater with vertical indirect fine preheater; Fine coal is screened before briquetting;
- 21. Optimization of drying system for CMC technology Comparison between modified SCOPE21 process and SCOPE21 process •Double layer fluidized bed dryer (drying & coarse coal heating) vs Single layer fluidized bed dyer (drying only); •High flue gas temp vs low flue gas temp; •Low exhaust temp vs high exhaust temp; •Fine coal indirect preheating vs fine coal direct preheating; •Low capital cost vs high capital cost; •Short flow sheet vs long flow sheet; Large temp differential vs smaller temp differential; Smaller flue gas flow rate vs large flue gas flow rate; Inlet flue gas temp for drying C Exhaust temp for drying C Temp differential for drying C Inlet temp for fine preheating C Exhaust temp for fine preheating C Temp differential for fine preheating C SCOPE21 650 400 250 450 360 90 Modified SCOPE21 950 75 875 700 400 300