Theoretical Calculation of Calorific Values

THEORETICAL CALCULATION OF CALORIFIC VALUES

Dulong's formula

Dulong's formula for the theoretical calculation of calorific value is

GCV (or) HCV

where C,H,O and S represent the % of the corresponding elements in the fuel.

It is based on the assumption that the calorific values of C, H and S are found to be 8080, 34500 and 2240 kcal, when 1 kg of the fuel is burnt completely. However, all the oxygen in the fuel is assumed to be present in combination with hydrogen in the ratio H : O as 1 : 8 by weight. So the surplus hydrogen available for combustion is H – O/8

ஃ NCV (or) L C V = 

1. Problems based on calorific value

Problem 1

Calculate the gross and net calorific values of coal having the following compositions, carbon = 85%, hydrogen = 8%, sulphur = 1%, nitrogen = 2%, ash = 4%, latent heat of steam = 587 cal/gm. (A.U. June 2007)

Solution

(i) Gross calorific value (GCV)

(ii) Net Calorific Value (NCV)

Problem 2

Calculate the gross and net calorific values of a coal sample having the following composition C = 80% ; H = 7%; O = 3% ; S = 3.5% ; N = 2.5% and ash 4.4%.

Solution

(i) GCV

(ii) NCV

Problem 3

On analysis, a coal sample has the following compositition by weight; C = 85%; O  = 3%; S = 0.5% and ash = 3%. Net calorific was found to be 8400 kcal/kg. Calculate the percentage of hydrogen and gross calorific value of coal.

Solution

Problem 4

Calculate the net and gross calorific value of a coal sample having following composition:

C = 82%, H = 8%, O = 5%, N = 1.4% and ash = 3.6%.

Solution

 (i) GCV

Problem 5

Calculate the gross and net calorific value of a fuel having following composition 82% C, 8% H, 5% 0, 2.5% S, 1.4% N and 2.1% ash. (APJAKTU, July 2016)

Solution

We know that,

GCV = 1/100 [8080C + 34500 (H – O/8) + 2240S] kcal/kg

= 1/100 [8080 × 82 + 34500 (8 – 5/8) + 2240 × 2.5]

= 9225.97 kcal/kg

NCV = GCV – 0.09H × 587 kcal/kg

NCV = 9225.97 – 0.09 × 8 × 587 = 8803.3 kcal/kg

Problem 6

A coal sample has 80% of carbon, 9% of hydrogen, 6% of sulphur and remaining is ash. Calculate the HCV and LCV of the coal sample. (JNTU(H), June 2017)

Solution

(i) Higher Calorific Value (HCV)

(ii) Lower Calorific Value (LCV)