After I had more time to think about this, this is my final suggestion. In a simplified way.
The Problems:
- Scrap smelter refines slow
- Scrap metal takes up a lot of POB space, because 2 Scrap = 1 BA
The Suggestions:
- Increase the smelt speed, so that the space taken up by Scrap Metal is made free faster (kind of like Ore refineries).
- If the devs are happy with the current smelter speed (I can understand not wanting to allow making 1 trillion BA a day), make the smelting 1 to 1. 1x Scrap metal refines into 1x Basic alloy.