I was surprised that there were no how to's for charcoal productions without the need for kilns, drums etc, so thought this might be of interest to some as a trial technique. It is not very efficient by way of volume of charcoal to volume of biomass to start, but can be useful if you have quantities of garden waste such as prunings, bark, leaves etc. This type of stuff normally goes into green waste, or needs chipping to compost or use as mulch as it is too big for compost bin.
This is a process I have used which requires only an open fire or fire pit, shovel or rake and water (hose or steel buckets with water). It is a minor modification of the techniques used when cooking using the camp oven - which only uses coals instead of flame. Instead of transferring the coals to the oven pit, they are wetted down to stop burning, and create charcoal.