Chemical injection and control system and method for controlling chloramines

1. A method of automatically controlling chloramine concentration in a body of water contained in a reservoir, the method comprising:

a) determining residual chloramine concentration in a first water sample obtained from the body of water;

b) automatically engaging a supply of chlorine to add chlorine to the body of water when:

i) the residual chloramine concentration in the first water sample is determined to be below a pre-determined residual chloramine concentration set-point; or

ii) the residual chloramine concentration in the first water sample is determined to be below a first chloramine concentration percentage of a pre-determined residual chloramine concentration set-point;

c) determining residual chloramine concentration in a second water sample obtained from the body of water after step b); and

d) automatically engaging a supply of ammonia and the supply of chlorine to add both ammonia and chlorine to the body of water if:

i) the residual chloramine concentration in the second water sample is determined to be below the residual chloramine concentration in the first water sample; or

ii) the residual chloramine concentration in the second water sample is determined to be below a second chloramine concentration percentage of the pre-determined residual chloramine concentration set-point,

wherein a controller, in operable communication with an analyzer and one or more computer-readable storage mediums containing programming instructions, automatically executes steps a)-d),

wherein the programming instructions comprise algorithm I for causing the controller to execute step b) i), or algorithm VIII for causing the controller to execute step b) ii):

Algorithm I: y<x=add chlorine only, where y is the residual chloramine concentration determined in the first water sample and x is the residual chloramine concentration set-point; and

Algorithm VIII: y<[(a)(x)]=add chlorine only, where y is the residual chloramine concentration determined in the first water sample, a is a percentage selected within a range of 99% to 80%, and x is the residual chloramine concentration set-point;

wherein the programming instructions further comprise algorithm II for causing the controller to execute step d) i) and after chlorine only was added to the body of water, or algorithm IX for causing the controller to execute step d) ii) and after chlorine only was added to the body of water:

Algorithm II: w<y=add both chlorine and ammonia, where w is the residual chloramine concentration determined in the second water sample and y is the residual chloramine concentration determined in the first water sample; and

Algorithm IX: w<[(b)(x)]=add chlorine and ammonia, where w is the residual chloramine concentration determined in the second water sample, b is a percentage selected within a range of 99% to 80%, and x is the residual chloramine concentration set-point.

2. The method of claim 1 , wherein the supply of chlorine is added to the body of water in step b) when (i) the residual chloramine concentration in the first water sample is determined to be below the pre-determined residual chloramine concentration set-point and the programming instructions comprising algorithm I cause the controller to engage the supply of chlorine, and

wherein the supply of chlorine and the supply of ammonia are both added to the body of water in step d) when (i) the residual chloramine concentration in the second water sample is determined to be below the residual chloramine concentration in the first water sample and the programming instructions comprising algorithm II cause the controller to engage the supply of chlorine and the supply of ammonia.

3. The method of claim 1 , wherein the supply of chlorine is added to the body of water in step b) when (i) the residual chloramine concentration in the first water sample is determined to be below the pre-determined residual chloramine concentration set-point and the programming instructions comprising algorithm I cause the controller to engage the supply of chlorine, and

wherein the supply of chlorine and the supply of ammonia are both added to the body of water in step d) when (ii) the residual chloramine concentration in the second water sample is determined to be below the second chloramine concentration percentage of the pre-determined residual chloramine concentration set-point and the programming instructions comprising algorithm IX cause the controller to engage the supply of chlorine and the supply of ammonia.

4. The method of claim 1 , wherein the supply of chlorine is added to the body of water in step b) when (ii) the residual chloramine concentration in the first water sample is determined to be below the first chloramine concentration percentage of the pre-determined residual chloramine concentration set-point and the programming instructions comprising algorithm VIII cause the controller to engage the supply of chlorine, and

wherein the supply of chlorine and the supply of ammonia are both added to the body of water in step d) when (i) the residual chloramine concentration in the second water sample is determined to be below the residual chloramine concentration in the first water sample and the programming instructions comprising algorithm II cause the controller to engage the supply of chlorine and the supply of ammonia.

5. The method of claim 1 , wherein the supply of chlorine is added to the body of water in step b) when (ii) the residual chloramine concentration in the first water sample is determined to be below the first chloramine concentration percentage of the pre-determined residual chloramine concentration set-point and the programming instructions comprising algorithm VIII cause the controller to engage the supply of chlorine, and

wherein the supply of chlorine and the supply of ammonia are both added to the body of water in step d) when (ii) the residual chloramine concentration in the second water sample is determined to be below the second chloramine concentration percentage of the pre-determined residual chloramine concentration set-point and the programming instructions comprising algorithm IX cause the controller to engage the supply of chlorine and the supply of ammonia.

6. The method of claim 1 , wherein, if the residual chloramine concentration in the second water sample is determined to be at or above the residual chloramine concentration in the first water sample but below the pre-determined residual chloramine concentration set-point, the programming instructions cause the controller to continue to engage the supply of chlorine and the addition of chlorine only to the body of water is maintained.

7. The method of claim 1 , wherein, if the residual chloramine concentration in the second water sample is determined to be at or above the pre-determined residual chloramine concentration set-point, the programming instructions cause the controller to stop engaging the supply of chlorine and the supply of chlorine to the body of water is stopped.

8. The method of claim 1 , wherein the supply of chlorine and the supply of ammonia are added to the body of water during step d) until a subsequently obtained water sample is determined to be at or above the pre-determined residual chloramine concentration set-point and the programming instructions cause the controller to stop the supply of chlorine and the supply of ammonia into the body of water.

9. The method of claim 1 , wherein the first chloramine concentration percentage is higher than the second chloramine concentration percentage when both the first and second chloramine concentration percentages are utilized to control the chloramine concentration.

10. The method of claim 1 , wherein a feed rate of at least one of the chlorine and ammonia are determined by reservoir water volume and dwell time.

11. The method of claim 1 , wherein, if it is determined that the body of water has a residual chloramine concentration at or above the pre-determined residual chloramine concentration set-point after step b), the method further comprises:

e) determining residual chloramine concentration in a subsequent water sample obtained from the body of water; and

f) automatically engaging the supply of ammonia and the supply of chlorine to add both ammonia and chlorine to the body of water if:

i) the residual chloramine concentration in the subsequent water sample is determined to be below the pre-determined residual chloramine concentration set-point; or

ii) the residual chloramine concentration in the subsequent water sample is determined to be below a third chloramine concentration percentage of the pre-determined residual chloramine concentration set-point,

wherein the controller, in operable communication with the analyzer and the one or more computer-readable storage mediums containing programming instructions, automatically executes steps e) and f).

12. The method of claim 1 , wherein determining the residual chloramine concentration in the first and second water samples comprises measuring a total chlorine concentration in the first and second water samples.

13. The method of claim 1 , wherein the chlorine and ammonia are both automatically added to the body of water to provide a weight ratio of chlorine to ammonia of 5:1.

14. The method of claim 1 , wherein the chlorine and the ammonia are added to the body of water by a chemical dosing assembly that comprises chemical treatment flow tubes and a water motive tube, and wherein the chlorine and the ammonia are added to the body of water by the chemical treatment flow tubes in an area above the water motive tube to form a high energy mixing zone.