Is there any daily quota for VOA applicant ?

It is true that some applicants arriving at the later stage on certain days are returned back because it is simply impossible to process all the applications within the opening hours of Luohu visa office. So, you should arrive early to be perfectly certain that your application will be processed during that very day. The alternative is to take a ferry from Hong Kong to Shekou port in Shenzhen where you do not have to worry about the quotas, but you have to be aware about the Shekou visa office opening hours: 9:00 - 13:00 & 14:30 - 16:30. Have a nice visit to Shenzhen.