Scope

This test method covers the determination of the gross calorific value of coal and coke by an isoperibol bomb calorimeter using electronic temperature sensors and automatic calorimeter controllers.

Terminology

Calorific Value

The heat produced by combustion of a unit quantity of a test specimen under specified conditions.

Discussion

It is expressed in this method in calories per gram (cal/g), and can also be expressed in British thermal units per pound (BTU/lb), or in the International system of Units (SI) in Joules per gram (J/g), when required.

Calorimeter

As used in this test method - not only the bomb and its contents but also includes the bucket, electronic sensing devices, ignition leads, water, and the stirrer when using water.

Calorimeter Jacket

The insulating medium surrounding the calorimeter.

Isoperibol

Term used in combustion calorimetry meaning constant temperature jacket (environment).

Microprocessor

A central processing chip within the electronic controller section of the apparatus.

Corrected Temperature Rise

The temperature change of the calorimeter caused by the process that occurs inside the bomb, that is, the observed temperature change corrected for various affects.

Energy Equivalent, Heat Capacity, or Water Equivalent

The energy required to raise the temperature of the calorimeter one arbitrary unit. This is the quantity that when multiplied by the corrected temperature rise, and then adjusted for extraneous heat effects and divided by the mass of the sample, determines the gross calorific value.

Summary of Test Method

Calorific value is determined in this test method by burning a weighed sample of coal or coke under controlled conditions, in an atmosphere of oxygen, in a calibrated microprocessor controlled isoperibol calorimeter. The calorimeter is calibrated by burning a specified amount of benzoic acid. The calorific value of the test specimen is computed from microprocessor temperature readings made before, during and after making proper allowances for heat contributions by other processes. The microprocessor may record these temperatures in either of two modes: a full-temperature method and a temperature extrapolation method.

Significance and Use

When mutually agreed upon between the buyer and seller, the gross calorific value can be used to compute the total calorific content of the shipment of coal, represented by the sample, for commercial purposes.

The gross calorific values can be used to determine whether the coal meets the regulatory specifications and requirements for industrial fuels.

The gross calorific value can be used for evaluating the effectiveness of any beneficiation process or for research purposes.

The gross calorific value is required to classify coals according to procedures specified in Classification D 388.

Apparatus and Facilities

Test Space

A room or area free from drafts that can be kept at a reasonably uniform temperature for the time required for the determination. The apparatus shall be shielded from direct sunlight and radiation from other sources. Thermostatic control of room temperature and controlled relative humidity are desirable.

Combustion Bomb

Constructed of materials that are not affected sufficiently by the combustion process or products to introduce measurable heat input or to alter the end products. The bomb shall be designed so that all liquid combustion products can be completely recovered by washing the inner surfaces. There shall be no gas leakage. The bomb shall be capable of withstanding a hydrostatic pressure test of 20 MPa (3000psi) at room temperature without stressing any part beyond its elastic limit.

Balance

A laboratory balance having the capability to accurately weigh the sample to the nearest 0.1mg. The balance shall be checked periodically to determine its accuracy.

Calorimeter Vessel (Bucket)

Made of a suitable metal with a tarnish-resistant coating, with all outer surfaces highly polished. It shall be of such construction that the environment of the calorimeter's entire outer boundaries are maintained at a uniform temperature.

Jacket

A double-walled air, or water-filled jacket. The calorimeter shall be insulated from the jacket by an air space or an equally satisfactory isolating medium or both. The sides, top and bottom of the calorimeter vessels shall be positioned approximately 10mm from the inner thermal construction as possible. The jacket shall be capable of maintaining the temperature constant to within +-0.1 Deg C of room temperature at a calorimeter temperature 2 Deg C below, and 2 Deg C or more above room temperature throughout the determination. When a water-filled jacket is used, it shall have a device for stirring the water at a uniform rate.

Temperature Sensing Device

Thermometers with a precision equal to or better than 0.0001 Deg C. Platinum resistance or other electronic temperature sensors can be used if properly calibrated.

Temperature Measuring Accessories

(that measure in Degrees Celsius) Equivalent temperatures may be recorded in ohms or other arbitrary units instead of degrees. Consistent units shall be used in standardization as well as in the actual calorific value determination. If arbitrary units other than degrees Celsius are used, the temperature interval shall not vary so as to cause an error greater than 0.001 Deg C.

Sample Holder

An open crucible of platinum quartz, or base-metal alloy. The base-metal crucibles should be heat-treated for 4h at 500 Deg C to ensure they are completely oxidized.

Ignition Wire

Such as Chromium Alloy, iron, platinum, or palladium wire that can ignite the sample. It shall be of same length and diameter, or mass, for all calibrations and calorific value determinations.

Firing Circuit

6-24V AC or DC, required for ignition purposes. A variable transformer connected to an alternating current lighting circuit or batteries can be used.

Isoperibol Calorimeter, Microprocessor Controlled

An electronically controlled calorimeter with a central processing unit capable of measuring temperatures, igniting the sample, and calculating the results.

Reagents

Standard Benzoic Acid

Use pellets made from Benzoic Acid calibrated against the standard material of the National Institute of Standards and Technology. The value of heat of combustion of Benzoic Acid, for use in calibration calculations, shall conform, with the certified value.

Hazards

In addition to the safety hazards statement given, and the equipment manufacturer's installation and operating instructions, special precautions are recommended for safe calorimeter operations by consulting with the calorimeter equipment manufacturer or his certified representative prior to and following the installation.

The mass of the coal or coke sample and the pressure of the oxygen admitted to the bomb must not exceed the bomb manufacturer's recommendations.

Inspect the bomb parts carefully after each use. Check the bomb for thread wear on any closures; if an inspection reveals any wear, replace the worn parts or return the bomb to the factory for testing or replacement of the defective parts. It is good practice to replace the o-rings and seals, inspect screw cap threads, and hydro-statically test the bomb as per the manufacturer's recommendation.

Equip the oxygen supply cylinder with an approved type of safety device, such as reducing valve, in addition to the needle valve and pressure gauge used in regulating the oxygen to the bomb. Valves, gauges, and gaskets must meet industry safety codes. Suitable reducing valves and adapters for 3-4 MPa (300-500 psi) discharge pressure are obtainable from commercial sources of compressed gas equipment. Check the pressure gauge annually for accuracy or after any accidental over-pressures that reach maximum gauge pressure.

During ignition of a sample, the operator's body shall not be permitted to be directly exposed to the calorimeter.

Exercise extreme caution not to exceed the bomb manufacturer's recommendations and avoid damage to the bomb when combustion aids are used. Do not fire loose fluffy material such as un-pelleted benzoic acid unless thoroughly mixed with the coal sample.

Do not fire the bomb if the bomb has been dropped or turned over after loading or if there is evidence of gas leakage when the bomb is submerged in the calorimeter water.