I got rank AIR 47415 OBC NCL in JEE Main 2018. Am I eligible for civil engineering in NITS?

Predict engineering colleges you can get on the basis of your JEE Rank. Use Shiksha JEE College Predictor: https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=cconnect&utm_medium=CR_JEECP&utm_campaign=7489993.

You have a very low chance of getting admission into NITs due to your rank. I would recommend you check out other institutions like UPTU etc. Depending on your state and look towards securing an admission there.

In NITs, there's very low chance because rank that you have mentioned is category rank and not the overall rank. It is very hard to get any NIT. And if you tried to some state govt. college based on the counselling of state government, then there is a chance that you may get.