Page 173 - Boiler plant and distribution system optimization manual

158 Boiler Plant and Distribution System Optimization Manual

steam system can require up to 100% make 21. DIRECT CONTACT
up feedwater. The actual requirement for HOT WATER HEATER
makeup water can vary widely. (Figure 10.54)
2. It minimizes losses associated with steam
traps, valve stem and packing gland leakage, Cost
blowdown and flash losses associated with High
open condensate receivers.
3. It can pack more usable heat into a given vol- Potential Savings
ume than a steam system and needs smaller High 15% Range
diameter piping.
4. Water temperatures can be lowered during Description
low heat demands reducing pipe insulation 12%-15% of the waste energy in the exit flue
losses. Boiler exhaust temperatures are low- gas is stream formed from the combustion of hy-
ered by this also. drogen in the fuel and other moisture. For every
pound of hydrogen that is burned with the fuel,
Disadvantages nine pounds of water is formed which escapes
Circulating pumps must run continuously. out of the stack as vapor carrying with it a great
Return water temperature must be maintained deal of energy. This flue gas moisture is usually
above a certain limit to avoid thermal stress and accepted an inevitable energy loss energy loss as
piping system noise and damage. it is difficult to recover the latent heat from this
vapor, this method successfully recovers this en-
ergy. (Figure 10.23).
20. PULSE COMBUSTION UNITS (Figure 53)

Figure 10.53—Gas fired Pulse Combustion units operate very efficiently because
they condense the latent heat energy usually in combustion exhaust producing very
high operating efficiencies. They are practical for hot water circulating systems and
hot water heaters. They don’t need special exhaust systems but do produce water
that must be drained away somehow.