Fly Ash Hopper - Calculate force acting on the access door.

We are a mechanical engineering company; our project is to install access doors to a steel construction 'fly ash' hopper for use in the power station sector. The doors require automation for open and closing with electrical actuator drives. We must identify the forces applied/ acting on the access door in Nm to allow us to select the appropriate rated actuator. Calculation based on the scenario where the hopper is full of fly ash materials. The question: Calculate the force acting on the access door in the horizontal plane, force newton meters [Nm]. The door opening is 600mm x 600mm and constructed from 6.0mm thick carbon steel. Need to simulate if hopper was full of fly ash materials to the level of 2,100mm. Note; for fly ash without close compaction, the bulk density (mass per unit volume including air between particles) can vary from 540 to 860 kg/m3 (34 to 54 lb/ft3), whereas with close packed storage or vibration, the range can be 1120 to 1500 kg/m3 (70 to 94 lb/ft3). Calculate to upper range as assumed worst case scenario that materials are compact. See attached sketch and dimensions.