Though determining the feed rate for a volumetric feeder is not rocket science, there are some important things to consider when designing a continuous feed system. First, you need to know the desired solution concentration needed for the process. Second, you need the solution discharge rate in either gallons per minute or gallons per hour. Third, you need the rate of incoming water flow from the plant. The incoming water flow must be equal to or greater than your discharge rate. These three simple factors will determine the required rate the feeder needs to maintain in order to keep the desired solution concentration in suspension.
Let’s use an example of hydrated lime. The approximate bulk density is 35 pcf and your plant is looking for a solution concentration of 7%. You know that your discharge rate is 10 gpm and the available incoming water flow is also 10 gpm. With this information you can determine the capacity of the feeder.
See the equation below:
- (Water Flow) x (Weight of 1 Gallon of Water) = x
- (A) x (Desired Solution Concentration) = (Feed Rate in lbs. per Minute)
- You Can Multiply that by 60 to get lbs. per Hour or Divide by 35 to get Cubic Feet Per Minute.
Using the numbers from above we will work through the equation to determine the feed rate:
- 10 x 8.345 = 83.45 lbs. of Water
- 83.45 x 0.07 = 5.84 lbs. per Minute
Below are variations if you want to see the feed rate in a different unit of measure.
- 5.84 x 60 = 350.5 lbs. per Hour
- 5.84/35 = 0.167 Cubic Feet per Minute
- 0.167 x 60 = 10.01 Cubic Feet per Hour
With the known factors and quick calculation, the feeder must be capable of dispensing the hydrated lime consistently at 5.84 lbs. per min in order to keep the desired solution concentration in suspension.