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Fuel Characteristics. Source: USEPA, APTI, 2012, Combustion Source Evaluation Student Manual. Source: USEPA, APTI, 2012, Combustion Source Evaluation Student Manual. Heating Value.

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slide4

Heating Value

Heating values are determined by burning a small sample (typically one gram) in a calorimeter that measures the amount of energy released.

A British Thermal Unit (BTU) is the amount of energy required to heat one pound of water one degree Fahrenheit.

Source: USEPA, APTI, 2012, Combustion Source Evaluation Student Manual.

slide5

The energy released when burning a pound of fuel should be equally unambiguous, but unfortunately there are two different definitions commonly used. The difference has to do with the water vapor generated by burning hydrogen in the fuel and whether or not this water vapor condenses.

  • The higher heating value (HHV) assumes that all the water condenses, which means that the flue gas is cooled to room temperature. This is what happens in the laboratory test apparatus that measures heating value.
  • In real combustion systems, the flue gas is almost never cooled below the water dew point, so the uncondensed water vapor carries energy with it up the stack. If one excludes the heat of condensation from the definition, you have the lower heating value (LHV).
  • The difference is 1030 BTU/lb of water generated by combustion.

Source: USEPA, APTI, 2012, Combustion Source Evaluation Student Manual.

slide6

HHV is used for emission calculations and is nearly always the value used in any regulatory context, but it also is used by people who operate boilers and furnaces. HHV is generally used by anyone selling fuel because no vendor would voluntarily use the lower value to characterize his fuel.

  • On the other hand, engine and turbine manufacturers use LHV. The argument for this approach is: “since the heat of condensation is never available, we will exclude it from all calculations”. A resulting benefit is that their reported engine efficiency is higher (more impressive) when they use the lower heating value.

Source: USEPA, APTI, 2012, Combustion Source Evaluation Student Manual.

slide7

為什麼不同燃料的HHV和LHV2的差值不同

Source: USEPA, APTI, 2012, Combustion Source Evaluation Student Manual.

slide8

一個火力發電機組,發電量為400MW,使用的煤其低位發熱量(LHV)為30000J/g,能源轉換效率為0.4,請問此電廠每天要燒多少煤?(1MW=106J/s)一個火力發電機組,發電量為400MW,使用的煤其低位發熱量(LHV)為30000J/g,能源轉換效率為0.4,請問此電廠每天要燒多少煤?(1MW=106J/s)

slide9

假設泥煤(peat)中碳(C)含量佔其質量的67%,其熱值(heating value)為28400kJ/kg;天然氣中C佔74%,熱值為54400kJ/kg,依此條件計算,當釋出能量相同時,泥煤排放的CO2是天然氣的幾倍?

slide11

Ultimate Analysis

  • An ultimate analysis is usually performed for the benefit of an air emissions assessment.
  • The ultimate analysis presents the elemental composition of the fuel as determined by ASTM D3176. The elements include, but are not necessarily limited to the following:
  • • Carbon • Nitrogen
  • • Hydrogen • Sulfur
  • • Oxygen • Chlorine
  • In addition to these elements, the ultimate analysis usually includes data on ash and moisture levels. The moisture levels presented in ultimate analyses usually represent moisture present on a “moisture free” basis after being gently oven dried.

Source: USEPA, APTI, 2012, Combustion Source Evaluation Student Manual.