Ash Fusion Temperatures
Home Up Ash Fusion Temperatures Ultimate Analysis Chemical Fractionation Ash Chemistry Heating Value

 

 


 

 

Ash Fusion Temperatures
Home Up Ash Fusion Temperatures Ultimate Analysis Chemical Fractionation Ash Chemistry Heating Value

 

Ash fusion temperatures give an indication of the softening and melting behavior of fuel ash. These temperatures are widely cited in fuel specifications for boilers despite a relatively poor record of correlating with slagging or fouling behavior. Reasons for the poor predictive behavior include:

Fusion temperatures are based on fuel ash whereas deposits commonly are enriched and depleted in several elements relative to the fuel. Fusion temperatures are measured over short time periods while heating ash at a rate of 8 +/- 3 C (15 +/- 5 F) per minute whereas ash deposits typically accumulate for hours and are formed during cooling relative to the bulk gas temperature. Fusion temperatures do not account for either boiler design or boiler operation, both of which strongly influence slagging and fouling behavior. Fusion behavior changes when samples are allowed to stand at a given temperature. Fusion temperatures generally significantly decrease if the samples equilibrate at a given temperature for an hour or so.

Fusion temperatures at one time were also quite subjectively measured, but this criticism has been addressed by the development of automated techniques for performing the measurements that require no intervention by the operator. Despite the shortcomings, fusion temperatures are valuable guides to the high-temperature behavior of the fuel inorganic material.

Fusion temperatures typically are measured at four defined points under both reducing and oxidizing conditions. These are defined as follows:

Name is the temperature at which
Initial deformation temperature (IT) the point of cone begins to round
Softening temperature (ST) also sometimes called the spherical temperature the base of the cone is equal to its height
Hemispherical temperature (HT) the base of the cone is twice its height
Fluid temperature (FT) the cone has spread to a fused mass no more than 1.6 mm in height

Generally, a temperature under reducing conditions should be equal to or lower than the corresponding temperature under oxidizing conditions.  The difference in these temperatures generally increases with increasing iron content in the ash.  As is apparent from the definitions above, fusion temperatures should also monotonically increase in order of IT, ST, HT, FT.  Ash fusion temperatures from some of the coals investigated in the MFC are indicated below.

Ash Fusion Temperatures (F)
Fuel Name Initial Deformation, Reducing Hemispherical, Reducing Spherical, Reducing Fluid, Reducing Initial Deformation, Oxidizing Hemispherical, Oxidizing Spherical, Oxidizing Fluid, Oxidizing
Beulah Lignite 1107.936508 1176.031746 1190.396825 1199.206349 1254.518519 1292.851852 1296.074074 1309.148148
Black Thunder 1160.555556 1177.777778 1188.888889 1210 1178.888889 1200 1209.444444 1242.777778
Blind Canyon 1192.037037 1230 1298.333333 1449.444444 1215.740741 1240.555556 1315.555556 1468.148148
Decker 1124.259259 1172.592593 1182.962963 1200.925926 1278.333333 1347.222222 1355.740741 1368.148148
Eagle Butte 1217.037037 1234.259259 1238.580247 1244.938272 1195.617284 1212.407407 1220.617284 1231.481481
Eastern Kentucky 1620.416667 1637.638889 1644.166667 1648.888889 1626.666667 1646.666667 1648.888889 1648.888889
Gascoigne Wood Coal 0 0 0 0 0 0 0 0
Hanna Basin 1196.388889 1229.166667 1246.388889 1281.111111 1246.111111 1268.611111 1287.222222 1344.444444
Illinois #6 (1) 1059.666667 1090.333333 1154.222222 1252.777778 1240.944444 1254.833333 1285.277778 1365.833333
Illinois #6 (2) 1085.666667 1117.333333 1183.444444 1291.666667 1256 1276.777778 1264.666667 1341.777778
Kentucky #11 1076.111111 1109.444444 1181.111111 1268.333333 1267.685185 1290 1317.777778 1341.296296
Kentucky #9 1081.778 1116 1187.889 1281.889 1272.556 1323.111 1353.944 1385.389
Pittsburgh #8 (1) 1047.222222 1082.222222 1178.888889 1222.222222 1336.666667 1372.222222 1381.111111 1388.888889
Pittsburgh #8 (2) 1153.703704 1242.222222 1305.925926 1360.37037 1355.555556 1381.851852 1399.074074 1428.888889
Pittsburgh #8 (3) 1084.62963 1104.259259 1137.592593 1229.259259 1308.333333 1342.037037 1368.888889 1394.444444
Pittsburgh #8 (4) 0 0 0 0 0 0 0 0
Pocahontas #3 1191.111111 1248.518519 1277.592593 1331.111111 1296.666667 1312.962963 1337.037037 1363.703704
Roland 1130.185185 1155.925926 1166.296296 1197.592593 1166.851852 1191.481481 1205.37037 1243.703704
San Miguel Lignite 1286.975309 1347.716049 1415.555556 1514.753086 1281.049383 1333.641975 1413.08642 1516.728395
Upper Freeport 1191.790123 1269.320988 1302.037037 1336.358025 1339.259259 1378.395062 1397.96 1429.135802
Wyodak 1182.5 1212.083333 1224.444444 1253.194444 1178.888889 1206.666667 1221.666667 1251.527778