The Blood Furnace is located in the Hellfire Peninsula in the Outland of World of Warcraft. The specific location is as shown in the picture below:
The Blood Furnace is a copy in World of Warcraft and is located on the upper right side of Hellfire Citadel. The demon Magtheridon is imprisoned here. Illidan's servants used the blood of Magtheridon to create a race of fel orcs with greater fighting capabilities. The demon's blood was drawn out, refined in the furnace, and finally injected into the orcs. Illidan's most powerful teams emerged from this.