Hardgrove index
The Hardgrove Index ( HGI for short , from English "Hardgrove Grindability Index") is a measure of the hardness of coal during grinding . The hardness is in the unit of degree (° H) specified, for example 40 ° H or 55 ° H . The larger the Hardgrove Index, the easier the coal is to grind (the higher the grindability).
The grindability is an important parameter for the processability of the coal and the dimensioning of the coal mills . Since the grindability depends on various influencing variables, which are not yet fully known in detail, it is determined empirically with a test mill as described below .
The index is named after Ralph M. Hardgrove (* 1891 in Massillon, Ohio , † October 29, 1978 in Jacksonville, Florida ,) who developed the determination method in the 1930s for Babcock & Wilcox in the USA.
The procedure has established itself internationally today and is standardized according to the American ASTM standard D 409, DIN 51742 and the international ISO standard 5074.
Measurement method
Fifty grams of air-dry coal with a grain size of 0.6 to 1.2 mm are filled into the mill and the grinding body is loaded with a weight. After sixty revolutions of the grinding media, the crushed coal is placed on a test sieve. The Hardgrove index H is calculated from the sieve passage D:
The method only supplies relative values, since the setting of the test mill is carried out with a reference carbon whose Hardgrove index is set equal to 100.
Individual evidence
- ↑ Archive of THE WESTFIELD (NJ.) LEADER newspaper from November 9, 1978 ( memento of the original from October 14, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF, English; 404 kB).
- ↑ HARDGROVE GRINDABILITY INDEX ( Memento of the original from October 4, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. - Detailed information on the HGI from the Australian Coal Industry's Research Program (PDF, English; 538 kB).
- ↑ The STOCK® Gravimetric Feeder on asme.org ( Memento of the original from September 16, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , with photo by R. Hardgrove (PDF, English; 794 kB).
