Using xiànzài and zhèngzài in a single sentence I saw sentence xiànzài wǒ zhèngzài xué hànyǔ. And I can understand it as "I'm learning Chinese now". What bothers me is would it be any different meaning if I just say xiànzài wǒ xué hànyǔ? Or even wǒ zhèngzài xué hànyǔ? 

P.S. I'm also assuming that zhèngzài can be replaced with zài without changing in meaning, am I right?
"现在", "正在", "在" all have the meaning of "now", but have slightly differences. "现在" is more like "nowadays", "正在" and "在" are equivalent to me, they are all like "-ing" in English. "现在我正在学汉语" sounds like "Nowadays I'm learning Chinese".  "我正在学汉语" means "I'm learning Chinese". "现在我学汉语" is weird, it's like "Nowadays I learn Chinese".  And you are right, as a Chinese, "正在" and "在" are equal to me if you want to use them to express "-ing".