Lesson3 Coal Assay

Coal assay techniques are specific analytical methods designed to measure the particular physical and chemical properties of coals.

煤质分析技术是专门用来测量煤的特定物理和化学性质的特定分析方法。

These methods are used primarily to determine the suitability of coal for coking, power generation or for iron ore smelting in the manufacture of steel.

煤质分析主要用于确定炼焦、发电或炼钢过程中铁矿石冶炼用煤的适用性。

Chemical Properties of Coal

煤的化学性质

Coal comes in four main types or ranks: lignite or brown coal, bituminous coal or black coal, anthracite and graphite.

煤主要有四种类型:褐煤,烟煤,无烟煤和石墨。

Each type of coal has a certain set of physical parameters which are mostly controlled by moisture, volatile content (in terms of aliphatic or aromatic hydrocarbons) and carbon content.

每种类型的煤都有一组特定的物理参数,这些参数主要由水分,挥发分(就脂肪烃或芳族烃而言)和含碳量控制。

Moisture: Moisture is an important property of coal, as all coals are mined wet.

水分:水分是煤炭的重要属性,因为所有煤炭都是湿法开采的。

Groundwater and other extraneous moisture are known as adventitious moisture and are readily evaporated.

地下水和其他外来水分称为外在水分,很容易蒸发。

Moisture held within the coal itself is known as inherent moisture and is analysed.

煤中所含的水分称为内在水分,可以被定量分析。

Moisture may occur in four possible forms within coal.

煤中的水分有四种可能的形式。

  • Surface moisture, water held on the surface of coal particles or macerals.

煤颗粒或其显微组分表面的水分。

  • Hydroscopic moisture: water held by capillary action within the microfractures of the coal.

吸湿性水分:通过毛细作用保持在煤的微裂缝中的水分。

  • Decomposition moisture: water held within the coal’s decomposed organic compounds.

分解水分:煤中分解的有机化合物中的水分。

  • Mineral moisture, water which comprises part of the crystal structure of hydrous silicates such as clays.

矿物水分,是由含水硅酸盐(如粘土)的部分晶体结构组成的水。

Total moisture is analysed by loss of mass between an untreated sample and the sample once analysed.

总水分通过分析未处理样品和分析后样品之间的质量损失进行计算。

This is achieved by any of the following methods:

可通过以下任一方法实现:

  • Heating the coal within a solution of toluene.

在甲苯溶液中加热煤

  • Drying in a minimum free-space oven at 150°C within a nitrogen atmosphere.

氮气气氛下,在150°C的最小自由空间烘箱中干燥。

  • Drying in air at 100~ 105°C and relative loss of mass determined.

在100~105°C的空气中干燥,并测定相对质量损失。

Methods 1 and 2 are suitable with low-rank coals but method 3 is only suitable for high-rank coals as free air drying low-rank coals may promote oxidation.

方法1和2适用于低变质程度煤,但方法3仅适用于高变质程度煤,因为自由空气干燥可能促进低变质程度煤的氧化。

Inherent moisture is analysed similarly, though it may be done in a vacuum.

固有水分的分析类似,但是它需要在真空中进行。

Volatile Matter: Volatile matter in coal is the components of coal, except for moisture, which is liberated at high temperature in the absence of air.

挥发分:煤中的挥发分是煤的组成部分,水分除外,水分在没有空气的情况下在高温下释放出来。

This is usually a mixture of short and long chain hydrocarbons, aromatic hydrocarbons and some sulphur.

挥发分通常是短链和长链烃、芳香烃和一些硫的混合物。

The volatile matter of coal is determined under rigidly controlled standards.

煤的挥发分是在严格控制的标准下测定的。

In Australian and British laboratories this involves heating the coal sample to (900±5) °C for 7 minutes in a cylindrical silica crucible in a muffle furnace.

在澳大利亚和英国的实验室中,在马弗炉中的圆柱形二氧化硅坩埚中将煤样加热至(900±5)°C 保持7分钟。

American Standard procedures involve heating to (950± 25) °C in a vertical platinum crucible.

美国标准步骤是在立式铂坩埚中将煤样加热至(950±25)°C。

These two methods give different results and thus the method used must be stated.

由于这两种方法得出的结果不同,因此测定挥发分必须说明所使用的方法。

Ash: Ash content of coal is the non-combustible residue after coal is burnt.

灰分:煤的灰分是煤燃烧后的不燃残渣。

It represents the bulk, mineral matter after carbon, oxygen, sulphur and water (including from clays) has been driven off during combustion.

它相当于燃烧过程中碳、氧、硫和水(包括粘土中的水)排出后的大块矿物质。Analysis is fairly straightforward, with the coal thoroughly burnt and the ash material expressed as a percentage of the original weight.

灰分分析相当简单,煤完全燃烧,灰分物质以原始重量的百分比表示。

Fixed Carbon: The fixed carbon content of the coal is the carbon found in the material which is left after volatile materials are driven off.

固定碳:煤中的固定碳含量是挥发物质被赶走后,在物质中发现的碳。

This differs from the ultimate carbon content of the coal because some carbon is lost in hydrocarbons with the volatiles.

这与煤的最终含碳量不同,因为一些碳随挥发物在碳氢化合物中损失。

Fixed carbon is used as an estimate of the amount of coke that will be yielded from a sample of coal.

固定碳被用来估计从煤样中产生的焦炭量。

Fixed carbon is determined by removing the mass of volatiles determined by the volatility test, above, from the original mass of the coal sample.

固定碳的测定方法是从煤样的原始质量中去除上述挥发性试验测定的挥发物质量。

Chemical Analysis

化学分析

Coal is also assayed for oxygen, hydrogen and sulphur content.

煤也要化验氧、氢和硫的含量。

Sulphur is also analysed to determine whether it is a sulfide mineral or in a sulfate form.

硫也被分析以确定它是硫化物矿物还是硫酸盐形式。

This is achieved by dissolution of the sulfates in hydrochloric acid and precipitation as barium sulphate.

这是通过在盐酸中溶解硫酸盐并沉淀为硫酸钡来实现的。

Sulfide content is determined by measurement of iron content, as this will determine the amount of sulphur present as iron pyrite.

硫化物含量通过测量铁含量来确定,因为这将确定以黄铁矿形式存在的硫含量。

Carbonate minerals are analysed similarly, by measurement of the amount of. carbon dioxide emitted when the coal is treated with hydrochloric acid. Calcium is also analysed. The carbonate content is necessary to determine the combustible carbon content and incombustible (carbonate carbon) content.

Chlorine, phosphorus and iron are also determined to characterise the coal’s suitability for steel manufacture.

An analysis of coal ash may also be carried out to determine not only the composition of coal ash, but also to determine the levels at which trace elements occur in ash. This data is useful for environmental impact modelling and may be obtained by spectroscopic methods.

Physical and Mechanical Properties

Relative density: Relative density or specific gravity of the coal depends on the rank of the coal and degree of mineral impurity. Knowledge of the density of each coal ply is necessary to determine the properties of composites and blends. The density of the coal seam is necessary for conversion of resources into reserves.

Relative density is normally determined by the loss of a sample’s weight in water. This is best achieved using finely ground coal, as bulk samples are quite porous.

Particle size distribution: The particle size distribution of milled coal depends partly on the rank of the coal, which determines its brittleness, and on the handling, ·crushing, milling it has undergone. Generally, coal is utilised in furnaces and coking ovens at a certain size, so the crushability of the coal must be determined. It is_ necessary to know this data before coal is mined, so that suitable crushing machinery can be designed to optimise the partide size for transport and use.

Float-sink Test, Coal 1s usually washed by passing it over a bath of liquid of known density. This removes high-ash content particles and increases the salability of the coal as well as its energy content per unit volume. Thus, coals must be subjected to a float-sink test in the laboratory, which will determine the optimum particle size for washing, the density of the wash liquid required to remove the maximum ash content with minimum work. Float-sink testing is achieved on crushed and pulverised coal in a process similar to metallurgical testing on metallic ore.

Abrasion Testing: Abrasion is the property of the coal which describes its propensity ‘and ability to wear away machinery and undergo autonomous grinding. While carbonaceous matter in coal is relatively soft, quartz and other mineral constituents in coal are quite abrasive. This is tested in a calibrated mill, containing four blades of known mass. The coal is agitated in the mill for 12,000 revolutions at a rate of 1,500 revolutions per minute. The abrasion index is determined by measuring the loss o°f mass of the four metal blades.

Special Combustion Tests

Specific Energy: Aside from physical or chemical analyses to determine the handling and pollutant profile of a coal, the energy output of a coal is determined using a bomb calorimeter which measures the specific energy output of a coal during complete combustion. This is required particularly for coals used in steam-raising.

Ash Fusion Test: The behaviour of a coal’s ash residue at high temperature is a critical factor in selecting coals for steam power generation. Most furnaces are designed to remove ash as a powdery residue. Coal which has ash that fuses into a hard-glassy slag known as clinker is usually unsati factory in furnaces as it requires cleaning. However, furnaces can be designed to handle the clinker, generally by removing it as a molten liquid.

Ash fusion temperatures are determined by viewing a moulded specimen of the coal ash through an observation window in a high temperature furnace. The ash, in the form of a cone, pyramid or cube, is heated steadily past l ,000°C to as high a temperature as possible, preferably 1, 600″C. The following temperatures are recorded:

Def ormatio11 temperature, this is reached when the corners of the mould first become rounded.

Softening (sphere) temperature, this is reached when the top of the mould takes on a spherical shape.

Hemisphere temperature: This is reached when the entire mould takes on a hemisphere shape.

Flow (fluid) temperature: This is reached when the molten ash collapses to a flattened button. on the furnace floor.

Crucible swelling index (Free Swelling Index): The simplest test to evaluate whether a coal is suitable for production of coke is the Free Swelling Index test. This involves heating a small sample of coal in a standardised crucible to around 800°C. After heating for a specified time, or until all volatiles are driven off, a small coke button remains in the crucible. The cross-sectional profile of this coke button compared to a set of standardised profiles determines the Free Swelling Index,

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