Thermal Analysis Application Brief - TA Instruments

1 Thermal Analysis & Rheology(inert or reactive) and the weight change is recorded. Toobtain a complete proximate Analysis in a single TGAexperiment, the system is programmed to hold initially at200oC in nitrogen, then to jump to 900oC and hold for aspecified period of time in nitrogen before switching tooxygen. Recent advances in TGA instrumentation havemade proximate Analysis even easier to perform. Theseinclude: Automated gas switching - with a Gas Switching Accessory, the purge gas change at 900oC can be built into the multisegment experiment method so that the Thermal Analysis Controller automati- cally makes the switch. Hi-ResTM TGA and the "abort" segment - histori- cally the time that the TGA remained at a specific set of conditions to ensure that the associated weight loss was complete was operator - selected based on experience.

2 In fact, the time was usually set to allow a "safety" margin which ensured that the weight loss was complete. With the new TGA "abort" segment, the Thermal Analyst Controller can be programmed to automatically proceed to the next experimental step when a weight loss is this study, five coal samples representing the majorclasses of coal were evaluated. 40-45 mg samples were used,and nitrogen and oxygen purge gases at 60cc/min wereintroduced at appropriate times in the 1 illustrates the typical TGA profile obtained. Thethree weight loss steps correspond to moisture, volatiles andNumber TA-129 Thermal Analysis Application BriefSummaryProximate Analysis is an important quality control parameterfor coal and coke.

3 Thermogravimetric Analysis (TGA)which measures weight changes in a material with tempera-ture provides a convenient method for performing a proxi-mate Analysis usually in less than 20 Analysis covers the determination of moisture,volatile matter, fixed carbon, and ash in coals and cokes, andis used to establish the rank of coals, to show the ratio ofcombustible to incombustible constituents, or to provide thebasis for buying/selling, and otherwise evaluating coal forvarious purposes. Thus, it is important to both the suppliersand users of coal to have a rapid, accurate, and reliableprocedure for obtaining the proximate , the various proximate Analysis determina-tions involve heating the sample to constant weight underASTM specified conditions.

4 These determinations, how-ever, are time consuming and require a significant amountof laboratory equipment. An alternative method for proxi-mate Analysis is thermogravimetric Analysis (TGA). Al-though this Thermal Analysis technique also involves heatingthe sample to constant weight under specified conditions, itdoes, because of smaller sample sizes and rapid temperatureand atmosphere control, substantially reduce the analysistime as well as the equipment necessary for TGA, the sample contained in the pan of a sensitiveanalytical balance is heated under a flowing atmosphereProximate Analysis of Coal and CokeWt. %MoistureMoistureAsh ContentAsh ContentCoal Sample(ASTM)(TGA)(ASTM)(TGA) carbon respectively.

5 The remaining weight at 900oC inoxygen is ash. A summary of the results obtained is shownin Tables 1 & 2. Also shown in the tables are the ASTM -determined values for Analysis OF COAL BY TGACOMPARISON TO ASTM METHODSTABLE 1Wt. %VolatilesVolatilesFixed CarbonFixed CarbonCoal Sample(ASTM)(TGA)(ASTM)(TGA) Analysis OF COAL BY TGACOMPARISON TO ASTM METHODSTABLE 2 This general TGA procedure is also useful for the proximateanalysis of cokes. Since the two quantities of primaryinterest to the users of coke are the fixed carbon and ashcontents (the percent moisture and volatiles are usually low),the procedure used for coal is modified slightly to accommo-date this fact.

6 Using only the isothermal temperature of900oC and varying the atmosphere from N2 to O2, a two stepweight loss curve is obtained. The first weight loss corre-sponds to moisture and volatiles, the second to fixed carbonand the residue is ash. A complete proximate Analysis forcoke can be obtained in less than ten more information or to place an order, contact:TA Instruments , Inc., 109 Lukens Drive, New Castle, DE 19720, Telephone: (302) 427-4000, Fax: (302) 427-4001TA Instruments , Paris, France, Telephone: 33-1-30489460, Fax: 33-1-30489451TA Instruments , Gent, Belgium, Telephone: 32-9-220-79-89, Fax: 32-9-220-83-21TA Instruments GmbH, Alzenau, Germany, Telephone: 49-6023-30044, Fax: 49-6023-30823TA Instruments , Ltd.

7 , Leatherhead, England, Telephone: 44-1-372-360363, Fax: 44-1-372-360135TA Instruments Japan , Tokyo, Japan, Telephone: 813-5434-2771, Fax: 813-5434-2770 Thermal Analysis & RheologyA SU B SIDIARY OF WAT E R S CORPORATIONI nternet: (min)WEIGHT (%)FirstDerivativeFigure 1 Sample Size:40-45 mgProgram:200 C Iso N 900 C Iso N 900 C Iso O222 PROXIMATE Analysis OF COAL