Model 4
1500 - 6000 MBTU/hr
Rev. 03-08
Section B2-17
Parameter
Boiler Water Limit
pH
8.3 - 10.5
Iron
0.1 ppm
Ox ygen
0.1 mg/liter
Specific Conductivity
2000 µ mho/cm
Suspended Solids
300 ppm
Total Hardness
0 ppm as CaC O
3
Table B2-13. Feedwater makeup rates
Table B2-14. Water quality parameters
Boiler Size
Gallons/Minute
1500
2.5
2000
3.3
2500
4.1
3000
5
3500
5.8
4000
6.6
4500
7.5
5000
8.3
6000
9.9
Blowdown
As steam is produced, unwanted solids are left behind in the boiler water and
become concentrated within the vessel. If these constituents are allowed to adhere
to the heat transfer surfaces, they will impede the flow of energy into the water.
Their removal requires proper blowdown that will include bottom and possibly
surface blowoff. For proper TDS control, surface blowoff with a TDS monitoring
device is recommended. Local codes will dictate the manner of treating the
blowdown affluent.
Boiler Stacks
General
- The Model 4 boiler operates with a positive vent pressure and a vent gas
temperature that is non-condensing. Therefore, the stack must be a positive
pressure design.
Proper design and installation of the flue gas venting is critical to efficient and safe
operation of the burner. The vent should be designed with proper supports and
clearances from combustible materials. Use insulated vent pipe spacers where the
vent passes through walls and roofs.
The design of the stack and breeching must provide the required draft at each boiler
stack connection. Although constant pressure at the flue gas outlet is not required,
it is necessary to size the breeching and stack to limit flue gas pressure variations.
Consideration of the draft must be given where lengthy runs of breeching or
unusually high stacks are employed. Please note: the allowable pressure range for
design of the stack and breeching is negative 0.25" w.c. (-62 Pa) to a positive 0.25"
w.c. (+62 Pa) for proper light offs and combustion.
NOTE:
This pressure range does
not pertain to the boiler room; that is, the boiler room must be neutral or slightly
positive, never negative when using air from the boiler room for combustion.
When two or more Model 4 boilers are connected to a common breeching/stack,
one should evaluate the affects of pressure variations that may occur during boiler
sequencing while boilers are firing. It may be determined that some type of
mechanical draft system be employed to ensure proper draft at each boiler is
maintained.
Combustion Air
- The burner for each boiler must be supplied with adequate volume
of uncontaminated air to support proper combustion and equipment ventilation. Air
shall be free of chlorides, halogens, fluorocarbons, construction dust or other
contaminants that are detrimental to the burner or boiler heating surfaces.
Combustion air can be supplied by means of conventional venting, that is, with
combustion air drawn from the area immediately surrounding the boiler (boiler
