Higher and lower heating values

Given a 2.0 MWac fuel cell cycle operating on 700 Ib/hr of methane, what is (a) the HHV thermal input of the methane gas, (b) the LHV thermal input, (c) the HHV electric efficiency, (d) the LHV electric efficiency, and (e) the HHV Heat Rate Assume the higher and lower heating value of methane as 23,881 and 21,526 Btu/lb respectively. 

Heating values are expressed as higher or lower heating values (HHV or LHV). Both higher and lower heating values represent the amount of heat released during combustion. The difference between the HHV and LHV is simply whether the product water is in the liquid phase (HHV), or the gaseous phase (LHV). 

For gaseous ammonia at 25 °C and 1 atm, and for liquid ammonia at — 33 °C, 1 atm, the exergies in Gcal/MT (MT = metric tons) NH3 are shown in Table 6.2 together with the higher and lower heating values, which are the first law values of ammonia. 

The difference between higher and lower heating value is the heat of evaporation of water (at 25°C) ... 

For definition of higher heating value (HHV) and lower heating value (LHV), see Section 1.5, Chapter 1. 

In all cases the heat of combustion of the solvent to be destroyed needs to be known. In almost every case the water generated in the destruction will be discharged as water vapour and so the lower or net calorific value is the appropriate one to use and it is the one quoted here. The only common solvent which has no hydrogen to convert to water and therefore has identical higher and lower calorific value is carbon disulphide. 

The proximate analysis of charcoal is 20-25% volatile matter, 70—75% fixed carbon, and 5% ash. Charcoal briquets have lower heating values than charcoal lumps, because of additives in the briquets. The higher heating value of lump charcoal is - 28 kJ/kg (12,000 Btu/lb). The higher heating value of briquets is 23 to 25 kj/kg ( -- 9,900-10,800 Btu/lb). 

The calculation of the turbine firing temperature (Ttit) is based firstly on the fuel injected into the turbine and the fuel s lower heating value (LHV). The lower heating value of the gas is one in which the Fl20 in the products has not condensed. The lower heating value is equal to the higher heating value minus the latent heat of the condensed water vapor. 

Definition of Absolute Temperature.— The temperatures of two bodies are proportional to the quantities of heat respectively taken in and given out in localities at one temperature and at the other, respectively, by a material system subjected to a complete cycle of perfectly reversible thermodynamic operations, and not allowed to part with or take in heat at any other temperature or, the absolute values of two temperatures are to one another in the proportion of the heat taken in to the heat rejected in a perfect thermodynamic engine working with a source and refrigerator at the higher and lower of the temperatures respectively. ... 

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