Training Manual on Energy Efficiency - APO Asian Productivity ...

<strong>Training</strong> <strong>Manual</strong> on Energy Efficiency for Small and Medium Enterprises
2.6.6 Adopt automatic blowdown controls
As a first choice, ensure maximum condensate recovery, since condensate
is the purest form of water, and this would help reduce dependence on
make-up water and also blowdown requirements. Uncontrolled, continuous
blowdown is very wasteful. For optimizing blowdown, automatic controls can
be installed, which can sense and respond to boiler water conductivity and
pH. Relate blowdown to TDS limits/Conductivity of boiler and feed water TDS/
Conductivity, by online monitoring.
2.6.7 Optimize boiler steam pressure
Wherever permissible, operating a boiler at lower steam pressure (a lower
saturated steam temperature, higher latent heat of steam, and a similar
reduction in the temperature of the flue gas temperature) helps to achieve fuel
economy. In some cases, the process demands are not continuous, and there
are periods when the boiler pressure could be reduced. Pressure could be
reduced in stages, and no more than a 20% reduction should be considered.
Care should be taken that adverse effects, such as an increase in water
carryover from the boiler owing to pressure reduction, do not negate any
potential savings.
2.6.8 Variable speed control for fans, blowers, and pumps
Generally, combustion air control in boilers is achieved by throttling dampers
fitted at forced and induced draft fans. Though dampers are a simple means
of control, they are an inefficient means of capacity control as they lack
accuracy, giving poor control characteristics at the top and bottom of the
operating range. If the steam demand characteristic of the boiler is variable,
the possibility of replacing an inefficient damper and throttling controls by
electronic Variable Speed Drives should be considered for reducing auxiliary
power consumed in boiler fans and pumps.
2.6.9 Effect of boilder loading on efficiency
Optimum boiler efficiency occurs at 65%–85% of full load. As the steam
demand falls, so does the value of the mass flow rate of the flue gases through
the tubes. This reduction in flow rate for the available heat transfer area
helps to reduce the exit flue gas temperature by a small extent, reducing the
sensible heat loss. However, at below 50% load, most combustion appliances
need more excess air to burn the fuel completely, and this would increase the
sensible heat loss. Operation of a boiler at low loading should be avoided.
2.6.10 Boiler replacement
If the existing boiler is old and inefficient, not capable of firing cheaper
substitute fuels, over or under-sized for present requirements, not designed
for ideal loading conditions, or not responsive to load changes, replacement by
a more efficient one needs to be explored.
- 18 -