Hardgrove Grindability Index

http://www.bing.com/search?srch=106&FORM=AS6&q=HARDGROVE+GRINDABILITY+INDEX&adlt=strict

hi, HGI means it is the measure of the ease with which coal can be pulverised. One of the methods of measuring it is HGI Number. Higher this number easier in coal pulverisation. Which type of coal you are using whether it is indian or foreign. If you are knowing the HGI number then we can discuss more....

Hi, Natarajan. Thank you. We have coal mills designed for HGI 50 coal. But now we are reciving coal of HGI 47 to 50. Our mill wear increases probably due to this. We use ball and race type pulveriser and the ball material is Nihard 4, race material is cast manganese steel. In respect to this I want to know the defination of HGI and the procedure of testing and any measuring table or graph.

Suranjan-

The HGI is an empirical measure of grindability obtained by performing a tightly controlled procedure using a specific apparatus. It would violate copyright law for someone to post the standard test procedure here, but it can be obtained at:

http://www.astm.org/Standards/D5003.htm

hi suranjan, Normally Indian bituminous coals having HGI from 45 to 60. So i think HGI might not be the only reason for your mill wear.. Mill wear also depends on the period of service and wearing property of the material.. Revise the material property of Nihard 4 and cast manganese steel. I don't know the procedure of testing...

HGI is a measurement (or empirical indication) of the difficulty of grinding a product.
It was designed for coal, but is now applied to a variety of mineral products in order to properly dimension a grinding installation (i.e. a mill).

It is not directly related to a product abrasiveness. A product may be easy to grind, but very abrasive and vice-versa.

It is indeed much used as coal specification. Coal HGI ranges from ±40-80 or even 90. The higher the HGI, the easier to grind.

A change from 47 to 50 in HGI is very negligeable.
If there is more wear with your new coal, check the chemical composition: it may have more impurities which cause the wear.

A change in HGI would rather affect the performance of your installation: if it is designed for a coal HGI 50, it is dimensioned for a specific throughput. Using coal with a (much) higher HGI should increase production, but only if the whole installation is sufficiently dimensioned to deal with a higher throughput (air flow etc...).

HGI testing machines are available in India. I hope you have one- else how do you know the HGI?

We prefer YGP index for ours, but both are basically empirical.

Nihard-4 is now ourtdated technology. Of course I am not very familiar with the E type mills (Ball and race) but we are now at least a couple of generations ahead than that in Raymonds as well as Tube Mills.

Try alternate materials especially under poor coal conditions. Your HGI do not look good.

There are too many other factors that too affect the wears - %V, %Moisture, Ash, Pyrites,Coal Type, ...

All these are only partially reflected in the indexes.

Indeed, ball and race type mills are not designed for products with a HGI much lower than 50 (some suppliers decline responsibility if such coal is grinded in their mills): since mechanical pressure is applied with the balls, if the product is too hard to grind, there won't be enough product between the ball and the lower rotating race. This will create vibrations that may cause damage to the mill and the installation as a whole.

For such products with a low HGI (below 45-50), Roller (pendulum) Mills are much more appropriate. Raymond in the USA and Poittemill in Europe are the main suppliers of such mills.

For abrasive products, alloys more resistent than manganese steel may be used (e.g. chromium alloys).

Good evening. Thank you to all. Actually we are more worried about mill and PF pipe wear and coal quality. Our boiler is designed for Indian bituminious coal of CV-5000kcal/kg, VM-30%, ash- 25% but we are now receving coal with about 42% ash content, VM- 17 to 23%, and CV- 4250 Kcal/kg(ADB) low sulpher coal with HGI 47-50. I want some more suggestion to prevent mill wear. We also thinking about material of mill.

Try Hichrome balls (but you have to change the races too correspondingly)

The ash content looks to be a bit too high, but that may be expected in the coals available in India. in fact the 5000 KCal/Kg coal is the one that looks a bit surprising.

I don't have much experience in E Mills, being involved in Bowl and Tubes where we can, and do, a lot of material as well as profile modifications to improve wear properties as well as mill output. But those will not be useful for your case and may be the better option will be to try hichrome balls.

UD15

Thank you all very much. You all have given me many valuable input. We have thought regarding materials and converted the metallergy to Nichrome alloy with 13.4-13.8% Cr for E70/62 mills and Hichrome alloy with 16.4% Cr, 0.65%Cu for 10.9E10 mills from Nihard4 and cast manganese steel and lined our PF pipes with ceremic liners at mostly affected areas and till date it works good. Thank you again for your valued suggestions. I welcome further input form you to prevent PF lekage to zero level.

Suranjan Chattopadhyay

Hi

Basically its a machine that is used to determined the grindability value of the coal.

Hrdgrove was a scientist who design a machine to determine the grindability value of coal or other raw materials while drawing a graph or index.it gives us the pulverized coal that may further use in the power sectors. The HGI is commonly applied to specifications for coal to be used in the iron making, cement and chemical processes.

Here are several different "standard" methods for the determination of HGI (e.g. - AS1038 Part 20:2002, and ASTM D409-2006), which can lead to significantly different results. Further, HGI is an empirical measure and not a physical proprty of coal; as such the results of any standard test have relatively low repeatability for a given coal sample.
In general, the higher the HGI value, the more readily a coal can be reduced to smaller particle sizes