Mineria

PROPERTIES OF COAL
PROXIMATE ANALYSIS, BOMB CALORIMETER

Objectives:
1. To carry out a proximate analysis of solid fuels and use this to determine their calorific values (CV). 2. To compare the CV determined in 1 with measured values through a calorimetric test and to recommend a best method of finding the CV

Reporting:
a) Tabulate results of the proximate analysis using the proformareport sheet and produce a calorific value plus an indication of errors. b) Tabulate the bomb calorimeter results using the bomb proforma report sheets. c) Compare the data in the attached table (properties of solid fuels), with sulphur, moisture and ash values you have measured to suggest a coal type for your sample. Compare the CV of this coal type with the CVs found in (a) and (b).

The ProximateAnalysis of Coal:
Determine the amount of moisture, ash, coke, 'fixed' carbon and volatile matter in a sample of coal, and calculate the calorific value of the sample from the results obtained. Method: Moisture. Add about 1gm of coal sample to a clean, dry crucible, which has been weighed previously, and place it in an oven at 373-376K for one hour. After cooling in a dessicator, re-weigh thecrucible and dry coal. Total % moisture = 100 (loss in mass)/(mass of coal) % Coke. Weigh a clean crucible without the lid and add about 1 gm of the coal sample. After re weighing, heat the crucible, with the sample covered by a lid (to avoid oxidation of the carbon), on a pipe clay triangle over a hot bunsen flame for 7 minutes. Cool in a dessicator and reweigh after removing the lid. (Note: 7minutes is prescribed in the standard procedure for this test to ensure comparability between different tests) % Coke = 100 (mass of residue)/(mass of coal) % Report the nature of the coke, for example: bulky and friable, dense and hard, porous, and so on. The nature of coke is compared to samples in a white display case marked ‘SPECIMENS OF COKE FROM DIFFERENT COALS’.

Ash. Now heat the cruciblecontaining the coke, without the lid, on a pipe clay triangle over a strong bunsen flame until all the carbon has burned away and only an ash residue remains. This usually takes about 1 hour, depending on the sample. Weigh the crucible and ash after cooling in a dessicator. % Ash = 100 (mass of residue)/(mass of coal used in the coke test) % Report on the nature and the colour of the ash.Calorific value. The calorific value (CV) of the coal can be estimated from the following relationship ascribed to Taylor and Patterson. CV = 4.1868 [ (82 x % FC) + (a x % VM) ] kJ/kg. where 'a' is a variable which varies with V 1 as shown in the following table, and V1 is the percentage volatile matter calculated on a dry, ash free basis : V1 = 100 (VM)/(VM + FC)

V1 a

5 145

10 130

15 11720 109

25 103

30 98

35 94

38 85

40 80

These values can be plotted and the curve used to determine the value of 'a' corresponding to the experimental results for V 1. (See reference: Fuel & Energy) The resulting calorific value should be compared with the values quoted in the literature for similar types of coal, and also with the results obtained with the bomb calorimeter. Withall the results, an estimate of the accuracy is required for example, %ash = 6.47 + 0.35%. In discussing the results for the calorific value, distinguish between 'gross' and 'net' values and explain their significance. Estimate the net value from your results.

Data Sheet.
Calorific Values of Solid Fuels (All kJ/Kg) 1: Dulong Formula: CV = 338.2 C + 1442.8 (H - 0/8) + 94.25 Grummell andDavies: CV = (15.22 H + 937) [C/3 + H - (O - S)/3] Taylor and Patterson: CV = 4.1868 [82FC + a VM] Where a is from the graph below and FC = Fixed Carbon; VM = Volatile Matter

2:

3:

150 140 130 120
o 110

100 90 80 70 0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0

% Volatile matter on a dry, ash-free basis (V 1)

In 1) and 2), H,C,O,S are percentages of those elements in the sample as determined by...