Lower heating value determination

Figure 27-11 gives the theoretical air requirements for a variety of combustible materials on the basis of fuel higher heating value (HHV). If only the fuel lower heating value is known, the HHVean be calculated from Eq. (27-6). If the ultimate analysis is known, Eq. (27-7) can be used to determine HHV. 

A fuel cell system for automobile application is shown in Figure 1.5 [41]. At the rated power, the PEMFC stack operates at 2.5 atm. and 80°C to yield an overall system efficiency of 50% (based on lower heating value of hydrogen). Compressed hydrogen and air are humidified to 90% relative humidity at the stack temperature using process water and heat from the stack coolant. A lower system pressure is at part load and is determined by the operating map of the compressor-expander module. Process water is recovered from spent air in an inertial separator just downstream of the stack in a condenser and a demister at the turbine exhaust. 

The cost of transporting wood chips by truck and by pipeline as a water slurry was determined. In a practical application of field delivery by truck of biomass to a pipeline inlet, the pipeline will only be economical at large capacity (>0.5 million dry t/yr for a one-way pipeline, and >1.25 million dry t/yr for a two-way pipeline that returns the carrier fluid to the pipeline inlet), and at medium to long distances (>75 km [one-way] and >470 km [two-way] at a capacity of 2 million dry t/yr). Mixed hardwood and softwood chips in western Canada rise in moisture level from about 50% to 67% when transported in water the loss in lower heating value (LHV) would preclude the use of water slurry pipelines for direct combustion applications. The same chips, when transported in a heavy gas oil, take up as much as 50% oil by weight and result in a fuel that is >30% oil on mass basis and is about two-thirds oil on a thermal basis. Uptake of water by straw during slurry transport is so extreme that it has effectively no LHV. Pipeline-delivered biomass could be used in processes that do not produce contained water as a vapor, such as supercritical water gasification. 

We also need to determine how many additional tons have to be mined due to the lower heating value of the Western coals. 

To calculate a lower heating value of a fuel from a higher heating value or vice versa, you must determine the moles of water produced when one mole of the fuel is burned. If this quantity is designated n, then... 

During the quarter-load operation part, the heating value was not determined regular intervals because gas measurements were made down through the char bed. At 07 20 hours the producer gas was sampled and analysed and the lower heating value was calculated to be 5.1 MJ/Nm. At this point in time the model calculation showed a lower heating value of 4.9 MJ/Nm. ... 

The second observation is explicitly made by the two authors in their paper. All correlations between chemical availability and lower heating value in terms of either atomic or mass ratios were based on values calculated for dry fuels with no moisture content. However, in applying those equations to fuels whose heating values do not appear on available tables, it is quite possible that the experimental determination of such value would be achieved by burning moist fuel in a calorimeter without first drying the substance. Care should then be exercised not to use the heating value of moist fuel in formulae derived for dry fuels. Nevertheless, the lower heating value of the dried fuel (LHV) can be established in terms of that of the wet fuel (LHV)W by means of the relation... 

If the chemical composition of the tar is known, the procedure to compute its chemical availability is entirely parallel to that used for coals and chars. After estimating the tar s lower heating value and determining its atomic ratios, the corresponding formula from table II is applied. 

Three properties of the simulated test fuels that need to be matched are the isentropic coefficient, molecular weight, and lower heating value (LHV). These properties need to be closely approximated to reproduce the fuel pressure versus heat release relationships. The Wobbe number may also be calculated to determine similarity in fuels. The chemical properties that need to be matched are the adiabatic flame temperature, inert content, olefins and hydrogen content, and the LHV. These properties need to be closely approximated so that the combustion process produces similar flame heights, pollutant emissions, and flue gas temperatures. 

First, let s calculate the total amount of heat released (or firing rate) from the flame. The total heat release (HR) is calculated by multiplying the fuel flow rate, rh, by the lower heating value (LHV) of fuel. Knowing the LHV of propane is 21,500 Btu/lb the heat release can be determined ... 

Gasification determines to a large extent the cost of indirect liquefaction. Also, the thermal efficiency of gasification contributes largely to the overall thermal efficiency of the entire process. The thermal efficiency is defined as the lower heating value of the products divided by the lower heating value of the feed... 

First a 5 kW combined methanol steam reformer-catalytic combustor was built. The reactor was composed of modules ofthree types of plates forming a stack. Instead of microchaimels, fins served as mechanical support and improved heat transfer. A total of 225 plates were incorporated into the reactor. The reactor was designed for a maximum operating pressure of 4bar and 350 °C maximum reaction temperature. The experimental results presented were determined at a partial load of the device [1-2 kW for the lower heating value (LH V) of the hydrogen produced]. At a S/C ratio of... 

At 85% utihzation, then stack efficiency is 50.9%. A lOkWe fuel-ceU system therefore requires 19.65 kW [lower heating value (LHV) Hz] hydrogen. Using the LHV of hydrogen, that is, 241.8kJmoH, a molar flow of 0.0813mols is determined. 

The lower heating value of a chemical substance is defined as its standard enthalpy of formation. The lower heating value of any fuel CJ-iyOz is easily determined by the following formula [13] ... 

In a catalytic reactor, a certain bio-mass stack is converted into a biofuel gas mixture that contains 50% methane, 45% carbon dioxide, and 5% hydrogen by volume. Determine the lower heating value of this bio-fuel gas mixture. 

No seciu-ed results on efticiency improvements could be demonstrated because of incomplete data over the testing period with regard to gas analysis and densities to determine the lower heating value, the latter being necessary to have accurate corrected efficiencies and turbine inlet temperature by heat balance calctdations. 

Boilers. Boiler efficiency will determine how much fuel is used, an important operating cost parameter. Pin the supplier down on just what efficiency is quoted and whether the basis is higher or lower fuel heating value. 

For non-Newtonian liquids and suspensions, an apparent viscosity is determined using correlations which include power input and the Reynolds number. Scale-up comparisons based on heat generation data only were determined by comparison of results from RC1 experiments and from a 675-liter reactor [208]. In the experiments, a Bingham plastic fluid was used to determine the film heat transfer coefficient. This presents a worst case because of the low thermal conductivity of the Bingham plastic. Calculated inside film heat transfer coefficients determined in the RC1 tests were about 60% lower than the values determined in the pilot plant reactor, even though substantial effort was made to obtain both geometric and kinematic similarity in the pilot reactor. 

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