Page 227 - Boiler plant and distribution system optimization manual

212 Boiler Plant and Distribution System Optimization Manual

Fuel energy used to form steam Actual condensate 120F 88 Btu/lb
with 80% efficient boiler 1100 Btu/lb Energy loss 74 Btu/lb
Fuel energy loss includ-
Fuel Energy invested ing boiler (80% Eff) 93 Btu/lb
in making steam
(180 + 180 + 1100 = 1460 Btu/lb) 1460 Btu/lb Fuel energy used to make original steam with
80% efficient boiler using condensate @

Fuel energy used to make original steam with 1190 – 162
194F [162 Btu/lb] —————— 1285 Btu/lb
80% efficient boiler
.8
(1189 Btu/lb – 162 Btu/lb)/80% = 1283 Btu/lb
93 Bu/lb
1460 – 1283 Fuel Loss = ————— = 1285 Btu/lb
Fuel Loss = ————— = 13.7% 7.2%
1283

Comment: a 74 F Temperature drop of the condensate
Comment: A 144F temperature loss (194 – 50F) cost a
cost a 7 .2% fuel loss, about 1% per each 10 .3 degrees .
13 .7% fuel loss, about 1% per each 10 .5F .
Example 4. Derive the “Rule of Thumb” relation-
ship about how boiler feedwater temperature
Example 2. What is the total loss involved in
influences boiler efficiency. How many degrees
steam leaks?
must the feedwater or condensate change to cause
approximately a one percent change in boiler sys-
Replacing Lost Steam
tem efficiency?
City Water SOP 18 Btu/lb
Heat in 100 psig steam 1190 Btu/lb
Given for water
Net Heat 1172 Btu/lb
1 Degree F = 1 Btu/lb
Fuel energy used to make
100 PSI steam 1190 Btu/lb
replacement steam with
150 F Condensate 118 Btu/lb
80% efficient boiler 1465 Btu/lb ——————
1070 Btu/lb
Fuel energy used to make original steam with 1% of 1070 Btu/lb = 10.7 F
80% efficient boiler using condensate @

1190 – 162 Rule of Thumb: “A 1% increase in efficiency oc-
194F [162 Btu/lb] ————— 1285 Btu/lb
.8 curs with each 11°F rise in condensate return or
feedwater input temperature.
1465 Btu/lb =
Fuel Loss —————— = 114% Example 5. What is the efficiency of recovering 5
1285 Btu/lb psig flash steam per pound?
100 psi steam 1190 Btu/lb
Fuel energy invested to
Example 3. Assume the condensate should be re- make 100 psig steam
turning to the plant at 194F, it has been returning with 80% boiler 1487 Btu/lb
at 120F instead. What losses are involved? Heat in 5 psig steam 1156 Btu/lb

Fuel energy saved by
Heat in 100 psig steam 1190 Btu/lb recovering steam in a
Hot condensate 194F 162 Btu/lb 80% boiler system 1445 Btu/lb