LIQUID CHLORINE PUMPING
Liquid chlorine could be considered one of the top inventions mankind has ever created. Quietly, and without fanfare or accolades, Sodium Hypochlorite has allowed for the growth and expansion of industrialized society. Trailing only in importance to refined oil and cheap electricity, the discovery of sodium hypochlorite has created a base expectation of safe, clean water to cook with as well as quench the thirst of the mass of workers building society into the modern world.
Sodium Hypochlorite (Chlorine for purposes of this article) was discovered in 1785. Less “discovered” than “created”, when a French chemist named Berthollet passed Chlorine gas through sodium hydroxide and created a very stable liquid known then as Eau de Javel. What emerged was a stable saltwater-like liquid that kills everything that “exchanges with its environment”, i.e. LIFE.
Chlorine makes an effective disinfectant. But liquid chlorine was not an “overnight success” as far as sanitizing water systems. It took until 1911 to employ it as a water purification additive. Today, chlorine is employed worldwide to disinfect drinking water. That doesn’t mean it is easy to disperse!
Properties of Chlorine and Pump Basics
The liquid tends to “disassociate” itself and create two phases: Liquid and Gas. As long as the chlorine stays in liquid form, it is easy to pump accurately with a metering pump. Once the fluid is allowed to gas-off, the pump looses prime and it is very difficult, bordering on impossible, to pump chlorine until the pump is either manually or automatically re-primed.
Furrow Pump can offer a workable solution to the problem of gassing and loss of prime as well as designing and specifying a chlorine system. Keeping in mind even the smallest chlorine pumps don’t like to pump at a rate of less than 3-5 Gallons Per Day (GPD), there are several aspects to Chlorine pump sizing to keep in mind:
Most pumps don’t want to pump at a very low rate (less than 3-5 GPD). Dilute your chlorine to a strength where the pump has to WORK HARD to inject enough chlorine to maintain a residual. If the pump is working hard, it is more likely to remain primed.
The Golden Formula of Chlorine Delivery
The rule of 100-1-1 is crucial for all chlorine systems:
For every 100 Gallons Per Minute (GPM) you chlorinate to 1 PPM, you will pump 1 GPD. At 500 GPM, you will use 5 GPD, and it follows linear on all variables. As you can see, this relies on having an accurate estimate on the water flow rate.
Flood the Suction if You Can
As difficult as it may seem to take your chlorine feed from the bottom of the solution tank, the positive head pressure (Net Positive Suction Head Available or NPSHA) will always EXCEED the Net Positive Suction Head Required (NPSHR) of the pump. The likelihood of losing prime is diminished.
If you were to call Furrow Pump, these are some critical questions we would ask.
We start with the water flowrate. Nothing else is more important than the water flowrate.
50 gpm. Plug that into our Golden Formula (100-1-1) and we find that the chlorine demand will be around 0.5 GPD (one half of one gallon per day)! Very low and impossible to pump successfully out of a 55 gallon drum.
If you can’t pump the 12.5% chlorine the Golden Formula determines, then you will have to dilute
Dilute- If the pump cannot pump the very low demand using the powerful concentrated chlorine, you will have to dilute. We recommend diluting the chlorine to a level where you can operate the metering pump in the upper 75% of its capability. The more the pump works, the less you will work to keep it primed. In this case, the 0.5 gpd demand can be diluted 10-1 to produce a 5 gpd demand.
Once you determine you will have to dilute the chlorine 10 parts water and one part 12.5% chlorine, you chose how much space you can devote to the system.
The more space you devote, the more reliable the system will be.
By placing the pump on top of the tank, you will tighten up the footprint of the system. However, you are putting the pump in a situation called “lifetime lift” and you may pay the price with maintenance. By designing a “flooded suction” system and placing the pump on the floor or on a bracket on a nearby wall, the pump will have positive pressure on it and will lose prime less often.
How do we respond to our call-in application?
Our situation here really calls for a flooded suction tank with a pump on the wall and a pump that pumps 5 GPD in the upper part of its performance capability. Since most of the metering pumps cost the nearly the same regardless the size, we always recommend applying a pump that will work hard to pump the diluted chlorine. We also recommend devoting the space for the system to put the pump on the floor or the wall in a flooded suction situation.
What if the flowrate varies based on demand?
Furrow Pump has a water flowmeter for nearly every application and they connect directly to the pump. As the gallons per minute changes with demand, the pump cadence changes the speed of the pump. The chlorine dosage stays level almost no matter what the flowrate is.
What if I’m forced to lift my chlorine from a drum in concentrated form?
If your flowrate is higher than 500 gpm and your space is limited to the area of the chlorine drum, you may be forced into placing the pump on the top of the drum and lifting it out of the container. We have Automatic Priming Pumps that will assist in lifting the concentrated chlorine out of the barrel.