I have been reading a bit about Kanban and i am slightly confused on the topic of Requirements. 

In my current project we use Scrum. At the beginning of a Sprint, we have a session where the BA does a walkthrough of the Story and describes it as best she can. We then take the story, review it, discuss it and prepare a questions for the BA for the next Sprint planning session. On the next session, the BA answers all the questions and the session finishes with us having understood the requirements (well most of the time). 

The next step is that we then produce a technical design and develop the solution/story. 

With Kanban, everything i read suggests there is no Sprint Planning in Kanban. My question is at what point (In kanban) do the techies and the business folk sit down together to discuss the requirement for the story? Doesnt the Product Manager or BA provide a walkthrough of the Story in Kanban?

With Scrum, the BA is usually avaialble throughout the Sprint to support the development and i assume it is the same with Kanban. It is not clear for me though how with Kanban, the techies understand the Story if there is no sprint planning.