Ref https://en.wikipedia.org/wiki/Cooling_tower and this maker (one of many many) https://jcequipments.com/dry-cooling-tower-india.html
A dry tower simply does not use any water running over the outside of the heat exchanger that is transferring heat from the fluid to the outside air. Wet or more correctly, evaporative, cooling towers are only needed if one must produce fluid temps lower than ambient outside air temps. One company that already does the whole package for miners is https://www.engineeredfluids.com/for-crypto-currency

The temps I stated are the chip temps. Because miners are normally using air cooling and have rather limited sized heatsinks inside of them that is what sets the typical ambient air temp restrictions. Any sort of liquid cooling massively increases the effectiveness of a heat sink.

Well, BitFury's farms ARE all liquid cooled.
Why don't others do it? Aside from the time it takes to remove fans and plug in a fan simulator (to keep cgminer happy) for each miner, no idea. Seems a no-brainer to me especially if you are putting miner containers into remote areas.

Ya the fluids used to cool the miners are not cheap but still, I see no downside to it.

As for sizing the cooling tower, easy: determine how much power you are feeding the miners ( I read somewhere a typical small well can support up to around 250kw), convert to BTU's (1kw = 3412.142 BTU's), know the maximum outside air temp where the miners & towers are located, use say 60C as maximum desired fluid outlet temp from the tower and give that info to the cooling tower manufacturer.  While they will also need to know the flow rate the coolant moves at (depends on the size of miner tanks and thermal characteristics of the fluid used) they can then provide the correctly sized tower to do what you need.

Oh, and here is an announcement from a Canadian company that is doing flare gas powered mining: https://www.globenewswire.com/news-release/2018/01/22/1298376/0/en/Cryptocurrency-Mining-Operation-Launched-by-Oil-and-Gas-Producer-Iron-Bridge-Resources.html
and
https://www.jwnenergy.com/article/2018/1/junior-producer-leverages-cheap-natural-gas-mine-cryptocurrencies-rock-bottom-prices/