What is the optimal forced air flow on the kiln shell? How does this impact on the refractory life? What is the interval in the shell temperature when I should turn on and turn off a fan?

I would say the optimum forced air flow on the kiln shell is zero. The higher the air flow then the higher is the loss of energy through the shell. This means greater heat requirements in the kiln and more penetration of salts into the refractory and therefore a negative impact on refractory life. However, as the refractory lining wears switching a fan onto the shell can be useful to try to build coating. I would suggest switching the fans on at above 350 degrees C.

We have a hot spot at 22m on our kiln, would it be possible to use a jet of water to cool the shell in this area?

People sometimes do that. However, it causes a significant blemish on the shell and when the water is switched on a significant thermal shock and potential contraction. In general it is better to use fans and/or stop the kiln and repair the refractory lining. If you put a fan close to the shell you may induce the thin section of the lining to coat over and bring the shell temperature down.