Payback for a Typical 500-MW Coal-Fired Unit
A 500-MW coal-fired unit with two APHs with 10% air leakage has combined fan power consisting of primary, secondary and induced draft fans for each APH. Fan curves show that with increases of APH leakages of 10%, fan power requirements increase by 13% (1.12 MW). The table below shows a simple payback for APH brush seal installation of $100K in just days. This payback does not consider the additional saving realized by increased efficiency in the air quality control system, reduced load on installations with bag filtration systems and lower dust emissions at the stack. All these savings can be directly the result of lower flue gas velocity achieved by reducing air leakage in the APH system.
- A 500-MW plant can save up to $1.5 million in fuel costs annually!
- Rotary air preheaters (APHs) are particularly critical to the efficient operation of coal-fired power plants, delivering up to 12% of the heat transfer used in the steam generation process. A useful rule of thumb is that for every 20° C decrease in the APH gas outlet temperature, boiler efficiency increases by about 1%. In a 500-MW plant, that translates into a $1.5 million in fuel savings. In addition to lowering fuel costs, an optimally operating APH reduces fan power consumption, also increasing net plant capacity.
Reducing air leakage in APHs results in lower flu gas velocity and reduces the pressure losses in downstream air-quality control system. This can mean lower dust emissions at the stack and, for plants with fabric filters, higher air-to-cloth ratios may mean less bag cleaning and longer bag life.
The savings calculation is based on the following:
85% capacity factor
10,550 kj/kWh heat rate
Coal heat content of 5,500 kcal/kg at $80/ton
Electric sale price - $30/MWh off peak (75% of operating hours); $150/MWh at peak