There is nothing built-in to robotframework to support parallel execution. It can be done but you'll have to do some work. For example, the simplest is to create a shell script (or batch script, or powershell script...) that simply calls robot 20 times in 20 processes, waits for them to complete, and then consolidates the logs.
When I googled on "robotframework parallel", the first hit took me to a library named Parallel, which advertises:
Library for executing tests in parallel from inside of a robot test case.
There is also pabot, which is "A parallel executor for Robot Framework test cases." This one has been discussed in the robotframework-users group here, among other places.
However, since you mentioned using chrome, I assume these use the selenium library. There is a limit to how many browsers you can have open on a machine, and the limit is below 20. So, you'll have to either run these tests on more than one machine, or set up a selenium grid that these tests can leverage so they aren't all opening browser windows on the same machine.
There's a wiki page showing a possible solution using grid here: Use Selenium GRID with Robotframework