How can I run grunt with global path?

Question

When I run 'grunt' at commend line, error occurred 'enable to find local grunt.' Because, in my directory there is no grunt module. I want to run grunt with global path and not contain node_modules in my project folder. The more adding node_modules in my project the slower running a project. In my project, there is only Gruntfile.js except for any other node_modules. How can I run grunt and grunt sub modules with global path? I can't find solution about this problem anywhere.