煤气化工艺中煤渣煤灰的利用Word文件下载.docx

1、Figure 1.Gasification-based energy production system concepts（Sandeep Tandon, 2008 Asia Clean Energy Forum）Conceptually, coal gasification is a relatively simply process. A carbonaceous fuel-usually coal, petroleum coke, or heavy oil-is co-fed with water and oxygen in a reducing atmosphere at high p

2、ressure （up to 1,000 psig） to produce the desired products of carbon monoxide （CO） and hydrogen （H2）. Sulfur in the form of H2S and some amount of CO2 is also produced and removed in the process. This gaseous mixture is commonly referred to as synthesis gas or syngas. Commercial gasifiers differ wid

3、ely in the way in which they produce ash, either a dry ash, an agglomerated ash, or slag may result. The Lurgi and other fixed-bed gasifiers operate by passing air or oxygen and steam under pressure up through a bed of coal, which is fed to the top of the bed through a lock hopper. Coal and char mov

4、e to the bottom as they are gasified, and the dry ash is removed through a bottom grate. Alternatively, a fixed-bed gasifier can be designed to operate at high temperatures, producing a bottom slag that is tapped through a hearth, i.e., the British Gas Lurgi （BGL） process. Fluidized-bed gasifiers, i

5、ncluding the US Kellogg Rust Westinghouse （KRW） and Institute of Gas Technology （IGT） processes and the German Winkler process, operate in a gasification mode using steam and air or oxygen in a fashion resembling PFBC （pressurized fluidized-bed combustion）. Fluidized-bed gasifiers may produce either

6、 a dry ash or a fused agglomerated ash, depending on the design, the operating temperatures, and the fusion temperature of the ash. Entrained-flow gasifiers, including Dow, Texaco, and Shell designs, all operate at very high temperatures and produce a vitreous slag. Integrated gasification combined-

7、cycle （IGCC） systems directly link these various types of gasifiers with a gas turbine-steam turbine cycle to achieve high conversion efficiency. （a）（b）Figure 2.（a）Fluidized-bed gasifier; （b）Entrained-bed gasifier （up-flow）（1999 Energy & Environmental Research Center Topical Report）In a dry-ash fixe

8、d-bed gasifier or grate-type combustor, bed temperatures are maintained below the fusion temperature of the ash, and the bulk of the ash is consolidated on the grate discharge. In very high-temperature slagging gasifiers and combustors, all of the physical transformations described are operative, bu

9、t the consolidation of ash and slag depends on reactor configuration. In a fixed-bed slagging reactor （e.g., the BGL gasifier）, virtually all of the inorganic reaction products are recaptured in the relatively cool descending fuel bed and consolidated into the slag discharge. （Steven A. Benson, et.a

10、l. Fuel Processing Technology 44（1995） 1-12）In an entrained-flow reactor （e.g., Texaco, Dow, and Shell gasifiers or cyclone-type combustors）, slag is partially separated by impingement or cyclonic action, while a （potentially small） fraction is carried forward with the hot gas. Hot mineral matter is

11、 deposited on the wall as slag. The slagging behavior is a critical for protecting the refractory-lined walls of the gasifier from the harsh environment within the gasifier. Inadequate slagging can lead to excessive refractory wear. Figure 3.Gravity induced flow of a viscous slag layer down a solid

12、surface.（Michael J. Bockelie, et.al. Reaction Engineering International）Coals with low ash content are preferred for both economical and technical reasons. If gasifier operating conditions are kept constant, an increase in coal ash content will lead to a decrease in gasification efficiency and an in

13、crease in slag production and disposal. However, each technology has slightly different coal ash requirements depending on their design. There is a minimum ash content required for the SCGP （Shell Coal Gasification Technology） （8 wt%）, the BBP （ 1 wt%） and the Hitachi gasifiers because of a slag sel

14、f-coating system on the wall of the gasifiers, 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） 22222235）2. Properties and applications of gasifier ashThe chemical, mineralogical, and phys

15、ical characteristics of gasifier ash have been investigated, and 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 sla

16、g and cyclone dust. The materials were found to be nonhazardous, but the physical characteristics and chemical compositions varied significantly as a function of process configuration, operation, coal feed composition, and coal handling. The elemental compositions of the slags produced in gasificati

17、on systems were similar to the bottom ash from conventional coal combustion systems. The bulk compositions of cyclone dust samples were found to be similar to conventional coal combustion fly ash. The mineralogical examination of slags indicated that many of the same high-temperature silicate minera

18、ls are present in the slag samples, along with reduced iron-bearing compounds. The key difference in coal gasification ash and slag compared 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

19、 in the system may also be in reduced form. The entrained-flow slagging gasifiers recycle all fly ash back to the vitreous slag. Slag samples 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 o

20、ther volatile inorganic components.The characteristics and subsequent utilization potential of residues from new coal use technologies will be determined by the uniquely different thermal transformations of the coal ash, new process provisions for sulfur and NOx control, and new particulate collecti

21、on methods （hot gas cleaning）. In many new technologies, the sulfur is captured along with the ash residues, producing large volumes of 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

22、 slag, and they are not generally suitable for use in the same applications. The classification of these typically high-calcium and high-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

23、introduce calcium for sulfur capture should be similar to conventional pulverized coal-fired fly ash and would have applications in the 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.

24、, sand） is customarily used, which can include concrete products, asphalt filler, controlled low-strength material （CLSM）, roofing granules, and brick or other ceramic products. Agglomerated ash, such as that obtained from high-temperature fluidized-bed gasifiers, is similar to bottom ash from conve

25、ntional boilers and would be used in similar applications in road base and aggregate. Dry ash from fixed-bed gasifiers will be intermediate 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. A

26、s previously noted, calcium sulfide produced by in situ sulfur capture in some gasifiers must be oxidized to sulfate prior to use or disposal. Additional research is needed to characterize many of these materials for regulatory classification and optimum beneficial use.Research to date has not adequ

27、ately addressed the utilization potential of these materials, but they have been shown to be environmentally acceptable for many use applications and disposal by conventional methods. More work is needed to achieve high levels of utilization and to reduce the landfilling that would otherwise be requ

28、ired.3. Coal ash use in Integrated Coal Gasification Combined Cycle （IGCC） systemMore than 43 million tonnes （metric） of coal fly ash （FA） are produced annually in the European Union. Although the main proportions of these FAs are produced by Pulverized Coal Combustion （PCC） process, small amount of

29、 FA are generated from the Integrated Coal Gasification Combined Cycle （IGCC）. In the PCC plants the 80% of coal combustion 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 coll

30、ected as FA. Apart from these differences, the PCC and IGCC processes generate FAs with different mineralogical compositions. The PCC FAs are made up of aluminosillicate glass （52-90% for European FAs）, with Ca, Fe, Na, K, Ti, Mn impurities, and variable minor amounts of quartz, mullite, lime, hemat

31、ite, magnetite, gypsums and feldspars, as well as traces of sillimanite, cristobalite-trydimite, wollastonite, 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 Gasificatio

32、n Combined Cycle （IGCC） plants produce a large volume of solid byproducts, just like pulverized coal combustion （PCC） plants. It is estimated that a 425 net MW IGCC plant 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 carbonaceous fines fraction （CFF）. The CFF fraction, which has a high heating value, is generally recycled through the gasifier as a fuel source to improve coal utilization. The FRIT fraction may be used