If a balance calculation is performed for a steam boiler at a specified load based on the incoming and outgoing material and energy flows, the proportion of energy that cannot be used quickly becomes evident. Fuel, combustion air, feed water and electrical output, e.g. for pumps and fans, is supplied.
The variables in the balance calculation that are removed are, in addition to the useful thermal energy in the steam, proportional losses for the flue gas, surface blowdown or bottom blowdown and thermal losses due to radiation and conduction.
The losses can be minimised by taking suitable measures. When selecting the optimisation measures, priority should be given to those which offer the best cost-benefit ratio. However, this cost-benefit sequence of measures depends on the specific system and also largely on the mode of operation of the overall boiler system. The following table provides an overview of the measures for increasing efficiency. Most of these measures can be combined.
Energy saving measures
Potential savings
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Economiser
≤ 7 % fuel
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Condensing heat exchanger
Air preheating
≤ 2.5 % fuel
Feed water cooling
≤ 1.8 % fuel ≤ 3 % fuel at 4-pass boiler
Brine expansion and heat recovery
≤ 2 % fuel, freshwater, waste water
Oxygen and/or CO burner control
≤ 0.5 % fuel
Speed control, fan
≤ 75 % electricity costs
Exhaust vapour heat exchanger
High-pressure condensate system
≤ 12 % fuel, freshwater
Automatic and continuous water analysis
≤ 0.5 % fuel, chemicals, personnel costs
Optimisation of control parameters, regular service, maintenance, cleaning
≤ 3 % fuel, extended service life, process reliability
Osmosis water preparation
≤ 3 % fuel, freshwater, chemicals