You can go to Consulate General of China in Kolkata to apply for China Business Visa (F) because West Bengal is under its consular jurisdiction. The required documents for F visa are:
(i) Original passport which has more than 6 months left before it expires from the date of application and sufficient blank visa pages.

(ii) One completed Visa Application Form with a recently-taken passport photo;

(iii) Visa notification issued by the organization of International Conference

(iv) Covering letter from your university with the details of the visiting purpose.

(v) Photocopy of the personal data page of applicant's passport.