煤气化工艺中煤渣、煤灰的利用

1、AilWUhl?匸As*HcmBH*品 rfcanHridfAkr qpdhkiRAirSlennlift in*cjO；Coal Gasification ash and Applications1. Gasifier ash deposition and agglomerationStltO中弄他古卑HlJ4 M ：5肚徑Figure I.Gasification-based energy production system concepts(Sandeep Tandon, 2008 Asia Clean Energy Forum)Con ceptually, coal gasificat

2、i on is a relatively simply process. A carb on aceous fuel-usually coal, petroleum coke, or heavy oil-is co-fed with water and oxygen in a reducing atmosphere at high pressure (up to 1,000 psig) to produce the desired products of carb on mono xide (CO) and hydrogen (H 2). Sulfur in the form of H 2S

3、and some amount of CO 2 is also produced and removed in the process. This gaseous mixture is commonly referred to as synthesis gas or syngas. Commercial gasifiers differ widely in the way in which they produce ash, either a dry ash, an agglomerated ash, or slag may result. The Lurgi and other fixed-

4、bed gasifiers operate by passing air or oxyge n and steam un der pressure up through a bed of coal, which is fed to the top of the bed through a lock hopper. Coal and char move to the bottom as they are gasified, and the dry ash is removed through a bottom grate. Alter natively, a fixed-bed gasifier

5、 can be desig ned to operate at high temperatures, produc ing a bottom slag that is tapped through a hearth, i.e., the British Gas Lurgi (BGL) process. Fluidized-bed gasifiers, including the US Kellogg Rust Westinghouse (KRW) and In stitute of Gas Tech no logy (IGT) processes and the Germa n Win kle

6、r process, operatein a gasification mode using steam and air or oxygen in a fashion resembling PFBC (pressurized fluidized-bed combustion). Fluidized-bed gasifiers may produce either a dry ash or a fused agglomerated ash, depending on the design, the operating temperatures, and the fusion temperatur

7、e of the ash. Entrain ed-flow gasifiers, in cludi ng Dow, Texaco, and Shell desig ns, all operate at very high temperatures and produce a vitreous slag. Integrated gasification comb in ed-cycle (IGCC) systems directly link these various types of gasifiers with a gas turbin e-steam turb ine cycle to

8、achieve high conversion efficie ncy.劇 hCCflF I?(a)GasEnirninsd Flow(b)Figure 2.(a)Fluidized-bed gasifier; (b)Entrained-bed gasifier (up-flow)(1999 Energy & Environmental Research Center Topical Report)In a dry-ash fixed-bed gasifier or grate-type combustor, bed temperatures are maintained below the

9、fusi on temperature of the ash, and the bulk of the ash is con solidated on the grate discharge. In very high-temperature slagging gasifiers and combustors, all of the physical transformations described are operative, but the consolidation of ash and slag depends on reactor configuration. In a fixed

10、-bed slagg ing reactor (e.g., the BGL gasifier), virtually all of the in orga nic react ion products are recaptured in the relatively cool desce nding fuel bed and con solidated into the slag discharge. (Steven A. Benson, et.al. Fuel Processing Technology 44(1995) 1-12)In an entrain ed-flow reactor

11、(e.g., Texaco, Dow, and Shell gasifiers or cycl on e-type combustors), slag is partially separated by imp in geme nt or cycl onic acti on, while a (pote ntially small) fracti on is carried forward with the hot gas. Hot mineral matter is deposited on the wall as slag. The slagging behavior is a criti

12、cal for protecting the refractory-lined walls of the gasifier from the harsh environment within the gasifier. I nadequate slaggi ng can lead to excessive refractory wear.Figure 3.Gravity induced flow of a viscous slag layer down a solid surface.(Michael J. Bockelie, et.al. Reaction Engineering Inter

13、national)Coals with low ash content are preferred for both econo mical and tech ni cal reas on s. If gasifier operati ng con diti ons are kept con sta nt, an in crease in coal ash content will lead to a decrease in gasificati on efficie ncy and an in crease in slag product ion and disposal. However,

14、 each tech no logy has slightly differe nt coal ash requireme nts depe nding on their desig n. There is a minimum ash content required for the SCGP (Shell Coal Gasification Techno logy) (8 wt%), the BBP ( 1 wt%) and the Hitachi gasifiers because of a slag self-coating system on the wall of the gasif

15、iers, which has to be covered by slag to function and minimize heat loss through the wall (Figure 4).Figure 4.The Prenflo gasifier(Andrew J. Minchener. Fuel 84 (2005) 2222 -2235)2. Properties and applications of gasifier ash1The chemical, mineralogical, and physical characteristics of gasifier ash h

16、ave been investigated ,23and the characteristics of ash produced from the Shell pilot-scale testing and Texaco testing have been reported. Slag and ash samples have been characterized from eight gasifiers. The types of materials examined included coarse ash or slag and cyclone dust. The materials we

17、re found to be non hazardous, but the physical characteristics and chemical compositi ons varied sig ni fica ntly as a function of process configuration, operation, coal feed composition, and coalhandling. Theeleme ntal compositi ons of the slags produced in gasificati on systems were similar to the

18、 bottom(1)Eklund, A.G., 1986. Coal gasification environmentaldata summary: Solid wastes and tarby-products.EPA/600/7-86/0ISc,April. (2) McCarthy, G.J., Keller, L.P., Stevenson, R.J., Galbreath, K.C. and Steinwand, A. L., 1985. Characterization of a lignite ash from the METC Gasifier, I. Mineralogy.

19、In: G .J. McCarthy and R.J. Lauf (Eds.), Proceedings of the Fly Ash and Coal Conversion By-Products: Characterization, Utilization, and Disposal I Symposium. Materials Research Society, Pittsburgh, PA. (3) Stevenson, R.J. and Larson, R.A., 1985. Characterization of a lignite ash from the METC Gasifi

20、er II.Scanning electron microscopy. In: G .J. McCarthy andR.J. Lauf (Eds.), Proceedings of the Fly Ash and Coal Conversion By-Products: Characterization, Utilization, andDisposal I Symposium. Materials Research Society, Pittsburgh, PA.2Mahagaokar, U., Krewinghous, A.B. and Kiszka, M.B., 1990. Shell

21、Coal Gasification Project: Gasification of six diverse coals.EPRI report, GS-7051s.Electric Power Research Institute, 1990. Cool water coal gasification program final report. EPRI GS-6806, Project 1459. ash from conventional coal combustion systems. The bulk compositions of cyclone dust samples were

22、 found to be similar to conventional coal combustion fly ash. The mineralogical examination of slags indicated that many of the same high-temperature silicate minerals are present in the slag samples, along with reduced iron-bearing compounds. The key difference in coal gasification ash and slag com

23、pared to combustion ash is the lack of sulfur. Sulfur is present in small quantities in the ash, usually in the form of a sulfide. In addition, the other ash species in the system may also be in reduced form. The entrained-flow slagging gasifiers recycle all fly ash back to the vitreous slag. Slag s

24、amples produced in the Shell process were shown to be depleted in several trace elements. The fine fly slag contained carbon and a higher level of trace metals and other volatile inorganic components.The characteristics and subsequent utilization potential of residues from new coal use technologies

25、will be determined by the uniquely different thermal transformations of the coal ash, new process provisions for sulfur and NOx control, and new particulate collection methods (hot gas cleaning). In many new technologies, the sulfur is captured along with the ash residues, producing large volumes of

26、 high-calcium and high-sulfur residues. These residues do not exhibit properties at all similar to those for conventional CCBs such as fly ash, bottom ash, or boiler slag, and they are not generally suitable for use in the same applications. The classification of these typically high-calcium and hig

27、h-sulfur residues by application is necessarily speculative at this time, but some general observations can be made.Fly ash from pressurized combustors that do not introduce calcium for sulfur capture should be similar to conventional pulverized coal-fired fly ash and would have applications in the

28、same types of cement replacement uses. High-strength vitreous slags from entrained-flow gasifiers would be suitable for most applications where fine aggregate (e.g., sand) is customarily used, which can include concrete products, asphalt filler, controlled low-strength material (CLSM), roofing granu

29、les, and brick or other ceramic products. Agglomerated ash, such as that obtained from high-temperature fluidized-bed gasifiers, is similar to bottom ash from conventional boilers and would be used in similar applications in road base and aggregate. Dry ash from fixed-bed gasifiers will be intermedi

30、ate between fly ash and bottom ash and incorporate some reduced chemical phases; the most likely uses are in high-volume fill and specialty manufactured products. As previously noted, calcium sulfide produced by in situ sulfur capture in some gasifiers must be oxidized to sulfate prior to use or dis

31、posal. Additional research is needed to characterize many of these materials for regulatory classificati on and optimum ben eficial use.Research to date has not adequately addressed the utilizati on pote ntial of these materials, but they have bee n show n to be environmen tally acceptable for many

32、use applicati ons and disposal by1conventional methods . More work is needed to achieve high levels of utilization and to reduce the Ian dfill ing that would otherwise be required.3. Coal ash use in Integrated Coal Gasification Combined Cycle (IGCC) systemMore than 43 million tonnes (metric) of coal

33、 fly ash (FA) are produced annually in the Europea n Union. Although the main proport ions of these FAs are produced by Pulverized Coal Combusti on (PCC) process, small amount of FA are gen erated from the In tegrated Coal Gasificati on Combi ned Cycle (IGCC). I n the PCC pla nts the 80% of coal com

34、bustion by-products are produced as FAs and 20% as slag. Conversely, most of the gasification by-products are obtained as slag (around 90%), and a small proportion (around 10%) is collected as FA. Apart from these differe nces, the PCC and IGCC processes gen erate FAs with differe ntmin eralogicalco

35、mpositi ons. The PCC FAs are made up of alu mino sillicate glass (52-90% for Europea n FAs), with Ca, Fe, Na, K, Ti, Mn impurities, and variable minor amounts of quartz, mullite, lime, hematite, magnetite, gypsums and feldspars, as well as traces of sillimanite, cristobalite-trydimite, wollastonite,

36、 and Fe-Al spinels. IGCC FAs are characterized by a predominant aluminosilicate glass matrix and a wide variety of fine crystalline reduced species (mainly sulphides).Integrated Gasification Combined Cycle (IGCC) plants produce a large volume of solid byproducts, just like pulverized coal combustion

37、 (PCC) plants. It is estimated that a 425 net MW IGCC pla nt burning 10% ash coal will produce about 450 to 500 tons per day of solid byproducts. These can be separated into two fractions: a coarse vitreous fraction (FRIT) and a carb on aceous fines fraction (CFF). The CFF fraction, which has a high

38、 heati ng value, is gen erally recycled through the gasifier as a fuel source to improve coal utilization. The FRIT fraction may be used as an abrasive, in cement-concrete applications, or as road sub base material. The physical and chemical properties of such solid byproducts are differe nt from fl

39、y ash and bottom ash produced Sutton and Stehouwer, 1992; Weber and others, 1993; Beeghly and others, 1993GOO VHAtKfOxyo&n _J fHfln 厂 召胎l圖sufjhorH i!.dBoiler feed-qiTKirigFuel 佃Gas turblFEfrom PCC pla nts. Therefore, developme nt of gasificatio n byproducts utilizatio n strategies that are econo mic

40、 and environmen tally sound is esse ntial for the commercializatio n of IGCC tech no logy.sjpnurn&cowsrr |Sj phurFigure 5.Simplified flowsheet of IGCC plant(E.Furimsky.Oil&Gas Science and Technology -Rev.lFP, 54 (1999) 597-618)The studies completed indicate that IGCC byproducts vitrified coarse frac

41、tion (FRIT) has properties very similar to glass and has potential for development into glass fibers, and associated materials such as rock wool, substrates for solar energy absorption, obscuring material for military applicati ons, and decorative tiles for the exter nal/i nternal surfaces of buildi

42、 ngs. The FRIT also has potential to be used as an insulating material for steel beams, partly due to its high melting temperature of 1600oC. The idea is to insulate steel beams in high rise buildings with this material. In the eve nt of a fire, the FRIT would in crease the time it would take for th

43、e steel beams to reach their softening temperature limit and could conceivably prevent building collapse.Most operators currently recycle the fines fraction, with much higher heating value, into the gasifier. The ash content of this carb on aceous fraction even tually gets con verted to the FRIT fra

44、ction duri ng the recycle gasificati on step.Praxis Engineers, Inc (2000), with funding from the Electric Power Research Institute, (EPRI), the U.S. Department of Energy (USDOE), and Illinois Clean Coal Institute (ICCI), demonstrated that slag can be used as aggregate in ceme nt -con crete and aspha

45、lt, roofi ng shin gles, and abrasive materials. Char can be easily separated from slag using physical separation techniques. The removal of char enhances slag properties for use in con struct ion applicati ons. Praxis also dem on strated that lightweight and ultra lightweight aggregate could be prod

46、uced from slag todevelop con struct ion materials with enhanced sound and in sulati on properties. They also reported that the energy requirements for producing synthetic lightweight aggregate (LWA) using slag are significantly lower than using clays or perlite.The vitreous slag and fly ash wastes p

47、roduced in Puertollano IGCC power plant exhibit expa nding properties whe n they are heat treated at high temperatures in oxidiz ing con diti ons due to degass ing the glassy phase in the form of bubbles that are released to the viscous liquid phase at temperatures near the softening point (Figure 6

48、). This foaming process is simultaneous to the devitrification for crystalline phases growth, and the consequenee of both processes is the conversion of the slag and the fly ash in a porous lightweight ceramic or glass-ceramic material being mullite, hercynite and anorthite the main developed crysta

49、lline phases in the fly ash andMullite in the slag.CRUDE1(a)LI4W- FA2 Twq steps of heatingLWA- FA1: one step of heating(b)(C)Figure 6.(a) External view of particles of fly ash before and after being transformed into LWA; (b) Inner view ofLWA particles; (c) SEM inner view of a fly ash LWA(M onica Ain

50、eto, et.al)Chen et.at produced full-size fire bricks containing up to 20% of the coal slag from a gasificati on pla nt in In dia na at a ben ch-scale facility. These bricks have color and texture similar to those of regular fired bricks and their water absorpti on properties met the ASTM specificati

51、 ons for a severe weathering grade. The surface of a slag containing brick is rougher than that of a regular brick as see n in Figure 7. Some specific con struct ion applicati ons may ben efit from the added surface rough ness of the slag-c ontaining bricks. (2009 World of Coal Ash Conferen ce)Figur

52、e 7.A close view of the surfaces of the conventional brick and a brick containing slag.Wabash River IGCC dem on stratio n pla nt reported that coal ash was con verted to a low-carb on vitreous slag, which is impervious to leachi ng and may be used as aggregate in con struct ion or as grit for abrasi

53、ves and roofing materials . Most of the solid byproducts were marketed beneficially.The production of such materials was however small.Charah Environmental of Madisonville, Kentucky, in cooperation with the University of Kentucky, demonstrated for the IGCC byproducts from TECO Energy Demonstration P

54、lant in Florida, that the by-products can be separated into three fractions: vitreous material or frit, carbon rich- char and fines.Chugh and Patwardhan (2002) demonstrated a physical separation technique to separate slag from char based on size separation and flotation techniques. These studies wer

55、e performed for TECO IGCC byproducts.Under DOE Cooperative Agreement DE-FC26-04NT42204, Norton (2004) of Mississippi State University studied incorporation of gasifier slag for enhancement of structural foam glass materials . The author demonstrated that the addition of the slag significantly increa

56、ses the compressive strength of the foamed glass. Norton, Palmer, and Ramsey (2006) completed a study to enhance structural foam materials through incorporation of gasifier slag (FRIT). The project concluded that 1) the addition of small amounts of FRIT results in significant increase in abrasion re

57、sistance and a moderate increase in mechanical strength, 2) the process allows improved abrasive resistance at no additional cost, and 3) improved materials could create an insulation market for the buildings industry. The authors suggest development of stronger materials for protective armor. The f

58、oamed nature of glass can provide an energy absorbing barrier for impacting weapons.The University of Kentucky is currently performing a study to evaluate separation of different fractions from IGCC byproducts for large volume utilization. The DOE contract number for this project is (DE-FC26-04NT42203). More specifically, the investigators are demonstrating separation of about 100-tons of byproducts, from Polk Power Station in Florida an