the dryer when you start it does fine soon as you walk away it throws the breakers whats causing this????

Try running it on air only or low heat to see if it still trips in the same amount of time. Also if the unit heats up on air only setting you have a grounded element.
Depending on the type of heating element you have, sometimes they loosen up, as it heats up it sags and touches the case/chassis tripping the breaker.

The above is not 100% because if you have a loose wire you could be removing power to this part of the circuit when you switch to low heat.
If it is the element often you can see the burn mark on the case.