Field Report - Saturated steam table & tips

At the end of this article is a typical enthalpy table for saturated steam. You can use this type of chart to determine what the temperature is inside a dryer can at a given pressure.

Saturated steam is steam that is in equilibrium with heated water at the same pressure (it has not been heated past the boiling point for that pressure). Reducing saturated steam temperature while maintaining pressure will cause the steam to condense, even though the temperature may be well above the 212 °F boiling point at 1 atmospheric pressure.

Note that this is for saturated steam only. Superheated steam first has to be cooled to the saturated temperature before it can partake in the condensing process. This is why too much superheated steam in a dryer can actually reduce heat transfer to the sheet.

The mechanism to cool superheated steam is by convection, not a very fast way to bring the steam temperature down. There are instances of machines having to max out their steam pressures even at slow production rates and still not dry the sheet, only to find out that the steam temperatures were well above their saturation temperatures.

Steam should be at its saturation temperature for maximum heat transfer. Of course, the higher the pressure of the saturated steam, the higher its temperature will be, and the corresponding drying rate.

The can surface temperature is approximately 40 °F lower than the inside steam temperature if all is working properly. It should be noted however, that the enthalpy of condensation (the state change from vapor to liquid) is actually slightly lower as the pressure increases. This is why early dryer cans are efficient at increasing sheet temperatures because they use low pressure steam with high enthalpies of condensation.

Steam tips

  • Supply and return lines from low pressure sections must be sized large enough to handle the high volumes involved. Lines that are too small will not allow the cans to be vented properly.
  • You can check the approximate temperature of a dryer can using an infrared temperature gun on the cylinder heads. If the temperature is above that of saturated steam at the running pressure, there is a problem with the steam temperature controls.
  • Check the desuperheater for proper operation – the valve should not be wide open and condensate supply pressure needs to be sufficiently high. Desuperheater condensate supply pumps tend to be high pressure pumps subject to wear. Monitor condensate pressure periodically to provide baseline data.

Saturated steam enthalpy table

Gauge pressure (psig), Temperature (°F) Specific Volume Saturated Vapor (ft3/lb) Enthalpy
Saturated Liquid (Btu/lb) Evaporated (Btu/lb) Saturated Vapor (Btu/lb)
23 (inches vacuum) 134 145 102 1017 1119
20 (inches vacuum) 162 73.9 129 1001 1130
15 (inches vacuum) 179 51.3 147 990 1137
10 (inches vacuum) 192 39.4 160 982 1142
5 (inches vacuum) 203 31.8 171 976 1147
0 212 26.8 180 970 1150
1 215 25.2 183 968 1151
2 219 23.5 187 966 1153
3 222 22.3 190 964 1154
4 224 21.4 192 962 1154
5 227 20.1 195 960 1155
6 230 19.4 198 959 1157
7 232 18.7 200 957 1157
8 233 18.4 201 956 1157
9 237 17.1 205 954 1159
10 239 16.5 207 953 1160
12 244 15.3 212 949 1161
14 248 14.3 216 947 1163
16 252 13.4 220 944 1164
18 256 12.6 224 941 1165
20 259 11.9 227 939 1166
22 262 11.3 230 937 1167
24 265 10.8 233 934 1167
26 268 10.3 236 933 1169
28 271 9.85 239 930 1169
30 274 9.46 243 929 1172
32 277 9.10 246 927 1173
34 279 8.75 248 925 1173
36 282 8.42 251 923 1174
38 284 8.08 253 922 1175
40 286 7.82 256 920 1176
42 289 7.57 258 918 1176
44 291 7.31 260 917 1177
46 293 7.14 262 915 1177
48 295 6.94 264 914 1178
50 298 6.68 267 912 1179
55 300 6.27 271 909 1180
60 307 5.84 277 906 1183
65 312 5.49 282 901 1183
70 316 5.18 286 898 1184
75 320 4.91 290 895 1185
80 324 4.67 294 891 1185
85 328 4.44 298 889 1187
90 331 4.24 302 886 1188
95 335 4.05 305 883 1188
100 338 3.89 309 880 1189
105 341 3.74 312 878 1190
110 344 3.59 316 875 1191
115 347 3.46 319 873 1192
120 350 3.34 322 871 1193
125 353 3.23 325 868 1193

 

For more information on maintaining and optimizing your steam and condensate systems, contact your Valmet representative.