Question

A 30.75kg of coal contains 24% phosphorus, 28% pyrites,0.01% Nitrogen, 8% Oxygen and moisture as basic impurities. It is desired that this Coal will be used in the metallurgical industry, production of electricity through combustion and synthesis of ammonium compounds for fertilizer production.
(a) Explain the analytical method used in estimating the percentage amount of impurities?
(b) Is this coal sample suitable for the purposes stated above?
(c)Explain the coal cleaning scheme unit operations.

Answer 1

(a)

There are mainly two methods such as Ultimate and proximate coal analysis, which are used to determine the quality of coal.

Ultimate Analysis:

This method provides elemental analysis (i.e. % of carbon, hydrogen, Sulphur, nitrogen, ash, oxygen) of the coal. The analysis is comparatively costly and the process is slow. It is used to find the calorific value of the coal.

Proximate analysis:

Proximate analysis of coal is an assay of the quantity of the coal. It determines moisture content, volatile matter, ash and fixed carbon content. The analysis is cheap and the process is fast. It is used for classification, the gradation of coal and predicting its industrial use.

(b)

For fertilizer production: Amount of phosphorous and nitrogen content should be more in coal.

For metallurgical Industry: Ash, Sulfur, phosphorus content should be less

For electricity production: Lignite is used for the production of electricity.

Composition of Lignite

%C	%H	%O	%N	%S	%ash
42	7	43	1	1	6

(c)

In the initial preparation phase of coal cleaning, the raw coal is unloaded, stored, conveyed, crushed, and classified by screening into coarse and fine coal fractions. The size fractions are then conveyed to their respective cleaning processes. Fine coal processing and coarse coal processing use similar operations and equipment to separate the contaminants. The primary difference is the severity of operating parameters. The majority of coal cleaning processes use upward currents or pulses of a fluid such as water to fluidize a bed of crushed coal and impurities. The lighter coal particles rise and are removed from the top of the bed. The heavier impurities are removed from the bottom. Coal cleaned in the wet processes then must be dried in the final preparation processes. Final preparation processes are used to remove moisture from coal, thereby reducing freezing problems and weight and raising the heating value. The first processing step is dewatering, in which a major portion of the water is removed by the use of screens, thickeners, and cyclones. The second step is normally thermal drying, achieved by any one of three dryer types: fluidized bed, flash, and multi-louvered. In the fluidized bed dryer, the coal is suspended and dried above a perforated plate by rising hot gases. In the flash dryer, coal is fed into a stream of hot gases for instantaneous drying. The dried coal and wet gases are both drawn up a drying column and into a cyclone for separation. In the multi-louvered dryer, hot gases are passed through a falling curtain of coal, which is then raised by flights of a specially designed conveyor