Energy Efficiency Technologies - Annex III

Willnow, Klaus

2013

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Understanding and comparing generating efficiency across power generation assets is a very challenging problem due to differences in technology, operation, fuel, size, and age. Even what in concept would seem very straightforward, such as monitoring fleet generating efficiency to produce realistic improvement targets, is a more difficult task than one might think at first glance. The reasons are many and include factors such as the simple fact that it is not easily measured, asset diversity (as noted above), and normal asset degradation. From the perspective of producing improvement targets, even a comparison of a unit to its own historical or design performance is a challenge due to changes in operation, modifications made to address environmental regulations, normal degradation, changes in fuel quality/sourcing or equipment upgrades. Comparison of a particular unit to its “peers” is further challenged by the large diversity of plant design configurations and the non-standard protocols for plant data, instrumentation and performance calculations. Unit-level performance calculations tend to be highly customized, resource-intensive and not well suited for producing centralized performance metrics. One important factor to consider when comparing generating assets is to ensure that all metrics of efficiency are compared on an equal footing. The United States and a minority of other countries typically refer to boiler and plant efficiency on a higher heating value (HHV) or gross calorific value (GCV) basis, which for a combustion unit signifies that the latent heat of vaporization of moisture from the fuel is recovered. Whereas most of the world refers to boiler and plant efficiency on a lower heating value (LHV) or net calorific value (NCV) basis. Neither metric is “right” or “wrong,” but it is important to understand the differences when assessing generating asset efficiency. The primary metric of unit efficiency used in the industry is the heat rate of the unit, which is a ratio of the energy required to produce a unit of electricity – such as how many Btu/hr of fossil fuel are required to produce 1 kW of electricity at the generator terminal. Design heat rates vary significantly based on plant type. Actual heat rates may vary by as much as 10-15% from factors including normal degradation, fuel source, how well it’s operated, etc. As an example, the heat rate of a large coal plant may be reduced by 3-4% by switching from a bituminous fuel to a low sulfur sub-bituminous coal. This efficiency loss, when coupled with the expected increases in unit auxiliary power which are coincident with using a lower-quality coal, can result in a reduction in the plant efficiency of 5% or more! A combustion turbine based plant burning natural gas may perform 1-3% better than the same plant design burning oil. Another factor affecting many coal plants is the addition of emissions equipment such as Selective Catalytic Reduction (SCR) systems and flue gas scrubbers which may hurt performance by as much as 1-2% in exchange for reducing SO2 emissions. One of the large hurdles to CO2 sequestration is the huge impact on unit performance of as much as 50%. In the following chapters the different technology options based on thermal power generation will be described assuming the efficiency definition based on LHV. Components and processes influencing the overall plant performance will be discussed by its technological potential. Furthers factors like degradation and different operation modes are not considered.

Eficiencia energética; Energía termal; Nivel mundial;