How to have survey respondent take the survey multiple times and keep a common ID for all responses?

Not possible.
You options are either to use an authenticator (read support pages) or to manually set a cookie based on their response id and use that to keep a track of the respondents.

Thanks Ahmed for the response.
I would also like to add that during session 1 of the day the respondents see only Block 1, and during session 2 of the day, they see only Block 2 of the survey. Is there no way that a respondent data is collected at different time points, still retaining the common identity of the respondent?

Thanks for the help!
Ank

As I mentioned earlier, this is technically not possible.
You'll have to use workaround, and therefore, the answer I've given earlier is the only generic answer I'm able to provide.
Your setup will depend upon various factors like what types of links are you using, what all identifiable information are you collecting, what is you survey setup etc.