Coiled Nichrome wire 220 volt
This is may not the answer that you expect, but your construction becomes very complicate. I will not tuch the the practices that using for wood drying, the safety matters etc, because I have no idea. I hope you are aware about this issues.

The kiln surface, the wall material and the temperature you want to rise, after a rough calculation requires an electric power of around 20kW. So first check if your electric company service can supply this 90A in a single phase.

Second, because of this current, you can not use a single nichr wire. The key factor here is the surface loading that you have to optimize. In the temperature range of 600~700 degr Celc. use a maximum factor of 4.5W/cm2 for a reasonable element life. This value is also affectd by the bonding method of the wire.

To obtain this value of surface load, needs a heating strip follow by a complicate calculations. However, you need also a slow temperature increase, that means a higher resistance element and consiquently a thin wire, or more precisely many thin wires connected in parallel.

As you can understand, all the above factors needs a very carefull design and this is the job of a specialist.