Page 157 - Boiler plant and distribution system optimization manual

142 Boiler Plant and Distribution System Optimization Manual

Many boilers are unattended or are operated of its fuel just being ready to take the load if the
by a staff with many other jobs. With a computer- on line boilers encounter problems.
ized system, the boiler is monitored automatical-
ly which can mean a large savings in manpower
and energy. (Figures 10.36 and 10.37) 4. PROVIDE A STEAM FLOW (OR FEED-
WATER FLOW) METER FOR
Advantages/Disadvantages EACH BOILER
High cost and increased complexity are
drawbacks. Properly used and maintained, a mi- Flow meters do not save energy and they are
croprocessor can save a great deal of money by not necessary for producing steam but they are
reducing labor costs, identifying fuel wasting vital for managing an efficient plant. Once steam
problems, diagnosing plant and system problems leaves the boiler plant control is lost, it goes some-
and eliminating many service calls. where but does anyone have an accurate picture
Some of the features of the microprocessor of how it is used with no metering systems down-
based system are accuracy of data which can be stream. The American Society of Mechanical En-
stored and evaluated providing: gineers (ASME), in their boiler test code indicates
that a positive displacement feedwater flow me-
1. Continuous data sampling ter serves as a accurate substitute for a steam flow
2. Immediate alarms meter. In order to assess boiler performance you
3. Remote surveillance must know what the boiler is producing.
4. Accurate records
5. Energy and steam system modeling using
“what if” scenarios 5. MONITOR ExCESS AIR, CARBON
6. Typical days per month simulation with MONOxIDE AND COMBUSTIBLES
energy and cash forecasting
7. Production planning tool, economic hourly Monitor excess air, carbon monoxide and
plant operation combustibles either continuously or by regular
8. Optimal plant operating strategies checks with portable analyzers.

1. Excess air is an accurate indicator of chang-
3. PROVIDE A FUEL FLOW METER es in stack losses. The rule of thumb is that
FOR EACH BOILER AND EACH FUEL every 2% increase in Oxygen in the flue gas
represents a 1% loss in efficiency. (2% oxygen
Fuel flow meters do not save energy and is about 10% excess air).
they are not necessary for producing steam and
often are not installed but they are vital for man- 2. Carbon monoxide is incompletely burned
aging an efficient plant. If you know how much carbon which is unburned fuel. Every pound
fuel a boiler is using then you have a key to its of carbon monoxide has a value of 4,368.
real efficiency, especially when information is col- Btus which is 20% of the energy in a pound
lected over a long period of time. Boiler efficiency of natural gas.
testing can give you a snapshot of the operating
efficiency at specific loads, but a number of sig- 3. Unburned hydrocarbons are actually un-
nificant losses have different causes that are not burned fuel too, containing a lot of Btus. Ex-
measured in these tests. For example, if the boiler ample: with 5% oxygen in the exhaust gas a
is oversized for its demands, it can lose a lot of en- 2% hydrocarbon reading represents an 8%
ergy when it cycles frequently. Another example energy loss.
is the hot standby boiler that essentially wastes all