Hardgrove test

The development of a continuous grinding index was the focus of work in the late 1970s (59). The laboratory test equipment used is similar to that for the Hardgrove test but permits classifying the product and recycling the oversize material. An improved correlation is obtained that may, however, need to be corrected for the relative sizes of the test grinding balls versus those used in commercial-scale equipment. The continuous grinding index is especially useful for lower rank coals. 

This approach is considered more flexible than other approaches, such as the Hardgrove, which are defined only for a given feed and product size. In addition the Hardgrove test requires only a small fraction of the coal to pass a given screen size and so may only reflect surface fracturing. 

Heating value of the product (SRC) is ca 37 MJ/kg (16,000 Btu/lb). Sulfur contents have been reduced from 2—7% initially to 0.9% and possibly less. Ash contents have been reduced from 8—20% to 0.17% (102). These properties permit compliance with EPA requirements for SO2 and particulate emissions. The SRC is primarily intended to be used as a boiler fuel in either a soHd or molten form (heated to ca 315°C). The soHd has a Hardgrove index of 150 (103). Boiler tests have been successfully carried out using a utiHty boiler. 

Other Tests. The so-called tumbler tests are usually used for testing material like coke, coal, iron ore pellets or tablets. They can be divided into drum tests and ball mill type tests. The latter type is used to derive both the Hardgrove Index and the Bond s Work Index, which are often used to classify the material friability as described in Sec. 3. They are generally more suited to coarse material. The Hardgrove Grindability test requires an initial size range form 595 to 1190 microns. 

Other important chemical and physical tests performed to characterize coal include (I) Heating value (Btu content) (2) sulfur forms (31 ash fusibility temperatures (4) ash analysis (5) trace elements (6) free swelling index and (7) hardgrove grindability. 

ASTM D-409. Standard Test Method for Grindabifity of Coal by the Hardgrove-Machine Method. 

ASTM D-5003. Standard Test Method for the Hardgrove Grindability Index (HGI) of Petroleum Coke. 

Standard tests consisted of proximate, ultimate, higher heating value, ash composition, ash fusibility temperatures, Hardgrove grindability, and screen analyses. Special bench scale characterization tests consisted of micro-proximate analysis and micro-ultimate analysis (C, H, N) micro-proximate and micro-ultimate analyses were performed on particulate samples collected from varying stages of combustion in the DTFS and CMHF. In addition, selected samples of SRC and chars from partial combustion or pyrolysis of the SRC were submitted for Thermo-Gravimetric analyses. 

In the test method (ASTM D-5003), the coke sample is crushed to produce a high yield of particles passing a No. 16 sieve and retained on a No. 30 sieve. These particles are reduced in the Hardgrove grindabiUty machine according to the test method for coal (ASTM D-409). The quantity of particles retained on a No. 200 sieve is used to calculate the Hardgrove grindability index of the sample. Both this test method and the test method for coal (ASTM D-409) produce the same results on petroleum coke samples. 

The Hardgrove Grindabilify Index (HGI) is an empirical measure of fhe work required to crush coal based on the generation of 200 mesh coal on air—dried test sample ground in a small ball-and-race mill for 60 rpm. The HGI of 58 is located at the top side of the scale showing the low hardness value of the petroleum coke. 

The hardgrove grindability index (HGT). This indicates the ease with which the coal can be ground to fine powder. HGI is the test most directly related to the maceral and maceral group composition but is also dependent on rank and mineral content. 

ASTM. 2011b. Standard Method of Test for Grindability of Coal by Hardgrove Machine Method (ASTM D409). Annual Book of ASTM Standards, Section 05.05. American Society for Testing and Materials, West Conshohocken, PA. 

Hardgrove Grindability Index The weight percent of coal retained on a No. 200 sieve after treatment as specified in ASTM Standard Test Method D409. 

Size reduction is carried out on the samples for analysis, depending on the specific analysis or test (i.e., <0.212mm for chemical analysis, <4.75mm for Hardgrove [Pg.762]

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