A storage tank is purged continuously with a stream of nitrogen. The purge stream leaving the

tank is saturated with the product stored in the tank. A major part of the product lost in the

purge could be recovered by installing a scrubbing tower to absorb the product in a solvent.

The solution from the tower could be fed to a stage in the production process, and the product

and solvent recovered without significant additional cost. A preliminary design of the purge

recovery system has been made. It would consist of the following:

A small tower $0\mathrm{.}5m$ diameter, $4\mathrm{.}0m$ high, packed with $25mm$ ceramic saddles, packed

height $3\mathrm{.}0m,$

A small storage tank for the solution, $5m3$ capacity

The necessary pipe work, pump, and instrumentation

All the equipment can be constructed from carbon steel.

Using the following data, evaluate how long it would take for the cost savings to pay for

the capital cost of installing the recovery system:

Cost of product $$5$ per $lb$

Cost of solvent $$0\mathrm{.}5$ per lb

Additional solvent make$-$up $10k\frac{g}{d}$

Current loss of product $0\mathrm{.}7k\frac{g}{h}$

Anticipated recovery of product $80\%$

Additional utility costs, negligible

Other operating costs will be insignificant.