Page 137 - Boiler plant and distribution system optimization manual

122 Boiler Plant and Distribution System Optimization Manual

Class III—Post-Flame treatment of interruption of steam service in facilities such as
pollutants, slag and soot hospitals if the active boiler goes down for some
• Soot removal reason. Because none of this the fuel us used to
• Control slag build up provide steam to the facility it is essentially wast-
• Corrosion reduction ed with zero efficiency. When you consider fuel is
• Particulate collection enhancement being used to just keep a boiler hot 24/7 year in
• Sulfur oxide scavengers and year out, this represents a substantial savings
to eliminate this type of energy loss and wear and
tear on the boiler. Flash boilers have proven to be
21. SHUT OFF BOILERS DURING WEEKENDS quite dependable and relatively efficient.
AND SUMMER MONTHS WHEN
NOT NEEDED
23. ECONOMIzER OPERATION
For long layup periods consider the wet lay
up or dry lay up options suggested by the manu- An economizer is a simple device that gets
facturer. hardly any notice and is not expected to have any
problems. One problem that could occur with
high sulfur fuels is “cold end corrosion” where the
22. CONSIDER THERMAL MASS tubes are attacked by acids having a dew point in
WHEN PLANNING BOILER OPERATIONS the range of water inlet temperatures to the econ-
omizer. The sulfur in the fuel forms SO and SO
3
2
which combines with water to form sulfuric acids
Low feedwater temperatures will cause this prob-
lem to accelerate.
The economizer also comes equipped with
bypass piping in the event it springs a leak or
some other problem. On rare occasion the bypass
valve has been left open. This could cause exhaust
temperatures to go up as high as 200F and bring
efficiency and capacity down by as much as 5%.

Section 10-2

Figure 10.18—The fire Tube type boilers with big Combustion Systems
drum capacity contain many thousands of pounds of
water which must be heated to operational tempera- CHECkLIST – 2
tures at a safe rate of about 100F per hour to avoid COMBUSTION SySTEMS
unusual stresses on the boiler. This takes time on the
order of 2 to 3 hours and wastes all the energy in-
vested in this action until the boiler can be brought 1. Fuel selection
on line. The smaller flash boilers can be producing 2. Oxygen trim
steam in 5 to 15 minutes using far less energy and 3. Carbon monoxide trim
time to get started. 4. Control system linearity
5. Characterizable fuel valve
In many applications a large stand-by boiler 6. Over fire draft control
is kept on hot standby status to insure there is no 7. Cross limiting controls