Company will incur variable costs, will start expensing interest costs and depreciation will go up as well. So I am not sure if costs will be at the same level.
I am also skeptical of ramping up additional capacity in the near term. In the past they took a long time to utilize the new capacity. I know a lot has changed since last 2-3 years so future growth may not look like the past.
Source: Capitaline.
Looking at past utilization numbers, to me it looks like they have some spare capacity even without the new capacity.
This is partly correct and perhaps one of the few bright points in the story. Growth in imports is mainly driven by demand rather than prices. In 2015-16 though imports dropped while demand picked up allowing domestic producers to sell more. GHCL might just be able to sell all it can make albeit at lower margins. Market might already have priced in some drop in margins.
Source: Alkali Manufacturers Association of India.