It's a little difficult to get acquainted at first however from jack's blog

For a lower cost to enter It is recommended to purchase an entry fee reduction by acquiring the Ring of Charos (a) RuneScape Gold. However, avoid using the pay option in foreman at the Blast Furnace foreman as it can void the benefits of the ring. You can gain this ring at the end of The Creature of Fenkenstrain questline.

Bringing Ice Gloves to the Blast Furnace will assist when you're using the bar dispenser because they will cool the bars quickly enough for you to take. This will cut down on time, instead of getting buckets of water each time to cool your bars (and it will save space in your inventory too).

Before beginning how to get to the Blast Furnace itself be aware that it's only available across the four worlds 352, 355 3, 358, 386 and 387. Once you've sat down with the Giant Dwarf and proceeded into Keldagrim You must turn north and work your way over the bridge. Once you've crossed it, continue heading south until are able to see an Blast Furnace icon on the map. Go inside the marked building then walk down the stairs and you'll find the furnace.

Once you've finished this and you'll be much more able to visit in the future. You can take advantage of the Grand Exchange shortcut on the northwest wall, take an excursion in the minecart that runs through Ice Mountain Dwarven Mines, or play the minigame group searcher that will let you enter the building.

It's a little difficult to get acquainted at first however, the minigame that comes with the Blast Furnace is simple. To use the furnace take these steps: Deposit your ore onto the conveyor belt Old School RS Gold. Go down the ramp by a bucket of water or gloves that are ice. Cooldown your bars and bank them.