Coke Physical Testing

Several tests are used to measure the physical properties of blast furnace coke. ASTM Stability and Hardness and the Coke Reactivity / Coke Strength After Reaction tests are the most common.

ASTM Stability and Hardness Tumbler Test
This test measures the resistance of coke to impact and abrasion during removal from the coke oven and transportation, as well as the abrasion that occurs during its descent in the blast furnace. Twenty two pounds of 3” by 2” sized coke is tumbled in a drum of specific dimensions for 1400 revolutions at 24 rpm. The coke is then screened and the percent + 1” = Stability and the cumulative percent + ¼” = Hardness. Most blast furnace operators want +60 stability coke.

Coke Reactivity Index (CRI) and Coke Strength after Reaction (CSR)
When coke descends in the blast furnace, it is subjected to reaction with countercurrent CO2 and to abrasion. These concurrent processes weaken the coke and chemically react with it to produce excess fines that can decrease the permeability of the blast furnace burden.

The CRI/CSR test measures coke reactively in carbon dioxide at elevated temperatures and its strength after reaction by tumbling. In the test, 200g of ⅞” x ¾” (19 x 22 mm) sized coke is reacted in a vessel in a furnace with CO2 gas for 2 hours at 1100°C. The weight loss after the reaction equals the CRI. The reacted coke is then tumbled in an I-shaped tumbler for 600 revolutions at 20 rpm and is then weighed. The weight percent of the + ⅜” coke equals the CSR. Most blast furnaces are looking for a coke with a >60 CSR value and <25 CRI.