6 replies to this topic

[raj1]

Can anyone explain me concept of HHV on fuel consumption in furnaces? We know HHV of hydrogen is higher than natural gas (85% methane). But for the same heat duty to acheive in furnaces, y should i require more hydrogen mass flow. HHV of hydrogen is ~ 62,000 Btu/lb and that to methane is 22,000 Btu/lb, hydrogen is almost 3 times higher HHV than natural gas. How come it requires more mass flow for the same duty to get acheive in furnace...pls clear my doubt.....

[Bobby Strain]

You should know the difference between HHV and LHV, and what the values represent. And by conducting a heat (energy) balance, clear your doubt.

 

Bobby

[breizh]

http://hydrogen.pnl....?canprint=false

 

Hi raj1 ,

 

Take a look at the document supplied then it should be crystal clear .

 

Good luck

 

Breizh

[Art Montemayor]

This topic is the stuff of basic, first-year chemical engineering stoichiometry.  I presume you are not a chemical engineer, so I'll take the liberty of reciting the basic definitions that my friends Bobby and Breizh are alluding to in order to allow you to study these definitions and extend your query if you have further questions or comments:

 

The Heating Value of a hydrocarbon fuel is the amount of heat produced by carrying out a complete combustion of that fuel and the heat released is measured as a unit of energy per unit mass or volume of substance (e.g., kcal/kg, kJ/kg, J/mol and Btu/m³).  The heat energy of combustion of hydrocarbon fuels is expressed by the Higher and Lower Heating Values (HHV and LHV).

 

The higher heating value (HHV) is also known as the gross calorific value and it is measured using a bomb calorimeter and defined as the amount of heat released when fuel is combusted and the resulting gaseous products have returned to a temperature of 25 °C.  The heat of condensation of the produced water vapor is included in the total measured heat.

 

The lower heating value (LHV) is also known as the net calorific value and is determined by subtracting the Latent Heat of Vaporization of the produced water vapor (resulting from the combustion of the fuel) from the higher heating value.

 

Since the Latent Heat of Vaporization of the produced water is never exploited (as in a steam boiler flue gas, for example) as transferred heat, it is the LHV that is the heat value used in combustion calculation processes.  This is obvious and common sense since the produced hot water vapor in an industrial combustion process exits the combustion process in the flue gas as a vapor - and not as a condensed liquid.

[raj1]

Thanks everyone for ur kind reply. I know very well.. to achieve same heat duty..natural gas requires less mass flow than hydrogen. But i have attached 1 excel spreadsheet below. It shows HHV and LHV of hydrogen is higher than natural gas...i.e almost 3 times more. I have attached it below for ur reference.

Attached Files

•  lower_and_higher_heating_values.xls   45.5KB   50 downloads

[Bobby Strain]

You are armed with the proper information to access the relative amounts of Hydrogen and Natural Gas to yield the same heat duty.

"I know very well.. to achieve same heat duty..natural gas requires less mass flow than hydrogen." This statement is inconsistent with the information that you present in the spreadsheet. So, what is the basis for this statement that you make?

 

Bobby

[raj1]

S bobby..you are correct...Actually i have done calculation in hysys..i defined wrong heating value. Which resulted in reverse effect...Anyway thank u every1 for ur guidance...