Fuels used in catering industry: Types of fuel used in catering industry; calorific value; comparative study of different fuels,
Types of fuel used in catering industry.
FUEL
The combustible substances which on burning in air produces large amount of heat that can be used economically for domestic and industrial purposes are called fuels. eg. wood ,coal, CNG, petrol etc.
COMBUSTION OF FUEL
The term refers to the exothermal oxidation of a fuel, by air or oxygen occurring at a sufficiently rapid rate to produce a high temperature, usually with the appearance of a flame.
TYPES OF FUEL
PRIMARY FUELS – fuels which occur naturally such as coal, crude petroleum and natural gas. coal and crude petroleum
SECONDARY FUELS – fuels which are derived from naturally occurring ones by a treatment process such as coke, gasoline, coal gas etc.
Calorific value comparative study of different fuels.
CALORIFIC VALUE
The calorific value of a fuel is defined as the quantity of heat (expressed in calories or kilo calories) liberated by the complete combustion of unit weight (1 gm or 1 kg) of the fuel in air or oxygen, with subsequent cooling of the products of combustion to the initial temperature of the fuel.
The calorific value of a fuel depends upon the nature of the fuel and the relative proportions of the elements present, increasing with increasing amounts of hydrogen. moisture if present, considerably reduces the calorific value of a fuel. the calorific value may be theoretically calculated from the chemical composition of the fuel.
HEAT UNITS:
B.T.U. (British thermal unit)
C.H.U. (centesimal heat unit)
Cal (Calorie) etc.
1 Kcal = 2.21 CHU = 3.97 BTU.
1BTU = 0.556CHU = 0.252 Kcal
HEAT TRANSFER
Heat can be transferred by Convection, Conduction and Radiation.
GROSS CALORIFIC VALUE
The gross calorific value (or the higher heating value) is the quantity of heat liberated by the complete combustion of unit weight of the fuel with subsequent cooling of the products of combustion to the initial temperature of the fuel.
NET CALORIFIC VALUE
Under normal working conditions, water vapors produced during combustion are not condensed and escape as such along with the hot gases. Hence lesser amount of heat is available, which is called Lower or net calorific value.
Net calorific value= Gross calorific value – Latent heat of water vapours
NCV = GCV-weight of hydrogen x 9 x Latent heat of water vapours
*Latent heat of water vapors is 588 kcal/kg
CHARACTERISTIC OF GOOD FUEL
High calorific values
Moderate ignition temperature
Low moisture content
Low smoke and ash
Moderate rate of combustion
Should not produce harmful and toxic products
Low cost
Easy storage & transportation
Easily controllable
Calculation of amount of fuel required and cost.
Calculation of amount of fuel required and cost
Comparative fuel cost
Fuel cost can be calculated by using a formulae by arriving at the cost of a useful “therm”.
1 Therm = 100,000 BTU
Coke:- If coke cost Rs. 12000 per ton or Rs. 4/- per lb then
1 therm cost = Cost per lb x 100000 / 12000 = (4 x 100000 / 12000) = Rs. 33.33
A useful therm is the amount of heat output put to good use. Generally coke is considered as 60% efficient fuel. So, one useful therm costs = Cost per therm x 100 / 60 = Rs. 33.33×100/60 =
Rs. 55.55
Gas:- To change cu.ft to therm, the heating power or calorific value of the gas to be known. This is generally shown on the gas cylinders.
Cost of Therm = Calorific value x Hundred of cu. ft / 1000 = A
Generally gas is calculated on 80% efficient.
So, one useful therm cost = Cost per therm x 100/80 = A x 100/80
Electricity:-
1 unit of electricity produces 3412 BTU. Electricity is calculated as 100% efficient.
So, 1 therm costs = Cost per unit (B) x 100000 / 3412 = B x 100000/3412
Oil:- 1 gallon produces 165000 BTU. Oil is calculated as 75 % efficient.
So, 1 therm costs = Cost per gallon x 100000 / 165000 = C
So, one useful therm costs = Cost per therm x 100/75 = C x 100 / 75
