Page 199 - Boiler plant and distribution system optimization manual

184 Boiler Plant and Distribution System Optimization Manual

Example. Heavy rains have soaked the coal does this reduce the boiler firing rate?
supply and surface moisture is over 15%, (Ans. 5%)
how will this change the capacity and ef-
ficiency of a 200,000 pph (100 ton) boiler? h. Power used in pumps and fans varies with
____________ the cube of the rpm.
(Ans. efficiency will drop by 1.5%, capacity will Note: Tests have shown that power reduction
drop by 3,000 pph or 1.5 tons/hr) may vary with the square of the rpm when a
static head is involved.
e. A 10% change in wood/bark moisture
changes efficiency by 1.5% Example. Estimate the power demand re-
Example. Moisture has changed from 30% ductions produced by the following rpm
to 60%, how will this change efficiency and changes using the “cube” relationship.
output? ____________
(Ans. efficiency and capacity will drop by 4.5%) Reduction of rpm to 90% 80% 50%
Power Reduction —— —— ——
f. A 10% change in Bagasse moisture will
change efficiency by 3.0%. Ans. (90% Cubed—73% of original power)
Example. A new system to dry bagasse is be- (80% Cubed—51% of original power)
ing evaluated, it can reduce moisture from (50% Cubed—12.5% of original power)
50% to 15%, how will this change efficiency
and capacity? ____________
(Ans. Efficiency and Capacity change by 10.5%. REDUCING ExCESS AIR TO
Fuel savings if the original efficiency is 65% will IMPROVE EFFICIENCY
be 14%)
The purpose of this section is to show how
g. A 11°F condensate temperature change im- changing excess air changes heat losses.
proves efficiency by 1%.
Example. Condensate temperature drops 1. A Natural Gas boiler has a stack tempera-
from 195F [91C] to 160F [71C] during a cold ture of 600F [316C]. What will the efficiency
period. How has this changed system effi- increase and fuel savings be if the average
ciency? ____________ excess air is reduced from 90% to 15% (CO
2
(Ans. 3.2%) from 5.9% to 10.1%)?

Example. Condensate temperature suddenly As found efficiency 73.8%
rises from 160F [71C] to 200F [93C], estimate Net stack temperature
the amount of steam trap leakage if no make 600F-80F 520F [271C]
up water is being used. CO 5.9%
2
(Ans. 3.6% of system load)
Efficiency with reduced
Example. High pressure feedwater heater excess air 80.6%
temperature drops from 350F [177C] to 320F Net stack temperature
[160], how will this change boiler firing rate? 600F-80F 520F [271C]
(Ans . 2 . 7% more capacity will be needed to heat CO 2 10%
the feedwater)
Fuel savings ____%
Example. If an economizer raises the feed- (Ans.: 8.4%)
water temperature 55F [13C], how much