Coal Industry
Water run-off from coal mining operations is acidic and
must be collected and treated prior to contact with surrounding
water sheds. Anhydrous ammonia is typically used
as a reagent to increase the pH. Values of coal run-off water
have been known to be as low as 2.05 pH.
Under atmospheric conditions, anhydrous ammonia is a
vapor. Stored in a tank under pressure, it is a liquid. Specially
engineered systems can feed either liquid or vaporous anhydrous
ammonia. Depending on the system design criteria,
each form has its particular advantages and disadvantages.
When feeding anhydrous ammonia in vapor form, an electrically
heated vaporizer must be used. Ammonia is easier to
measure and control if applied as a vapor.
Run-off water is collected or pooled. The pH of this effluent
is measured and then compared to the control setpoint. If
the pH is below the acceptable level, the pH controller controls
a valve to allow the reagent to be added to the effluent
and mixed until the optimum pH value is reached. After the
collected water is appropriately treated, it is discharged.