14.1 Gaseous Chlorine Feed Systems (Subclass 11)
Key Takeaways
- A modern chlorinator is a vacuum-operated system in which ejector water flow creates the vacuum that opens the regulator, so a loss of ejector water pressure stops chlorine feed and is the most common cause of a sudden residual loss.
- Withdrawal from a 150-pound cylinder is limited to roughly 40 pounds per day at about 70 degrees F, and from a ton container to roughly 400 pounds per day as gas, because the container absorbs heat from the room to vaporize the liquid.
- Exceeding the withdrawal rate causes frost on the container and reliquefaction downstream, which floods the regulator with liquid chlorine and can destroy the feed equipment.
- An evaporator is used where demand exceeds gas withdrawal capacity, drawing liquid chlorine from the container and vaporizing it under controlled heat with a pressure-reducing valve ahead of the chlorinator.
- Automatic switchover manifolds change from an empty to a full container without interrupting feed, but they must be exercised and the reserve bank verified, since a switchover into an empty bank silently ends disinfection.
The Vacuum Principle
Every current gas chlorination installation is a vacuum-operated, solution-feed system, and understanding why is worth several examination questions. Chlorine gas is never pushed under pressure to the point of application. Instead:
- Motive water flows through an ejector (also called an injector), a venturi that creates a vacuum.
- That vacuum is transmitted back through the vacuum tubing to the vacuum regulator mounted directly on the container valve.
- The vacuum opens the regulator inlet, allowing gas to flow. Gas passes through the rotameter (a V-notch variable orifice flow meter) where the operator sets the feed rate.
- Gas is drawn to the ejector, dissolves in the motive water, and the resulting chlorine solution is piped to the diffuser at the point of application.
The safety consequence is fundamental: if any part of the system loses vacuum, the regulator closes and gas flow stops. A broken vacuum line leaks air inward, not chlorine outward. Pressurized chlorine exists only between the container valve and the vacuum regulator, which is why the regulator is mounted at the container.
Containers and Withdrawal Rates
| Container | Net chlorine | Handling | Typical maximum gas withdrawal at about 70 degrees F |
|---|---|---|---|
| 150-pound cylinder | 150 lb | Upright, secured by chain at two thirds height, moved with a hand truck | About 40 lb/day |
| One-ton container | 2,000 lb | Horizontal on trunnions, lifted only with an approved lifting beam and rated hoist | About 400 lb/day as gas |
Withdrawal is limited because vaporizing liquid chlorine absorbs heat, and the only heat source is the room air around the container. Pull faster than the container can absorb heat and three things happen in sequence: frost forms on the container, the internal pressure falls, and liquid chlorine carries over into the vacuum regulator, where it re-evaporates and can rupture equipment or drive corrosive liquid into the rotameter. The remedy is more containers manifolded together, never heating a container with a torch, heat blanket or steam, which is prohibited and dangerous.
A ton container has two valves. Positioned with the valves vertically aligned, the upper valve draws gas and the lower valve draws liquid. Drawing liquid when the system is set up for gas is a serious error.
Evaporators
When required feed exceeds the gas withdrawal capacity of a reasonable container bank, an evaporator is installed. Liquid chlorine is drawn from the container into a water bath heated to a controlled temperature, typically around 180 degrees F, where it vaporizes. Downstream components include a pressure-reducing and shutoff valve, a gas filter and the vacuum regulator. Key operator points:
- Water bath temperature and level alarms must be functional; low temperature allows liquid carryover.
- The cathodic protection anode in the water bath is a maintenance item.
- Never bypass the pressure-reducing valve, and start the evaporator and allow it to reach temperature before opening the liquid valve.
Troubleshooting a Chlorinator
| Symptom | Likely cause | Check |
|---|---|---|
| Feed stops entirely, vacuum lost | Loss of ejector motive water pressure or flow | Booster pump, strainer, water supply pressure |
| Feed stops, vacuum present | Empty container, closed container valve, plugged regulator inlet filter | Container weight, valve position |
| Rotameter float bouncing or erratic | Moisture in the gas, dirty tube, fluctuating ejector water pressure | Clean tube, check water pressure regulation |
| Cannot achieve full feed rate | Undersized ejector, high back pressure at the diffuser, plugged diffuser | Back pressure, clean diffuser |
| Frost on container, falling feed | Withdrawal rate exceeds container capacity | Manifold additional containers |
| Chlorine odor at the regulator | Leaking connection, failed lead gasket | Ammonia vapor test, replace gasket every container change |
Two habits prevent most failures: use a new lead gasket on every container connection, never reusing one, and test every new connection with an ammonia vapor swab, which produces a visible white cloud at a leak. Never spray liquid ammonia on the joint.
Weight-Based Accountability
Chlorine feed is verified by scale weight loss, not by the rotameter alone. The daily weight loss in pounds, compared against the calculated pounds fed from flow and dose, is the check that catches a plugged diffuser, a leaking connection or an inaccurate rotameter. A container that loses more weight than the calculated feed indicates a leak somewhere in the pressurized section.
Where Safety Requirements Attach
Chlorine room engineering controls, the toxicological profile, leak response and Chlorine Institute emergency kits are covered in the workplace safety section. For this subclass, remember the operating interfaces: the room ventilation and chlorine gas detector interlocks, the outward-opening door with a viewing window and outside light and ventilation switches, self-contained breathing apparatus stored outside the room, and the requirement that no operator enter a room with a suspected leak alone.
A gas chlorination system suddenly stops feeding and the vacuum gauge reads zero, while the chlorine container is more than half full and its valve is open. What should the operator check first?
Frost has formed on a 150-pound chlorine cylinder and the achievable feed rate is falling during a period of high demand. What is the correct response?
Why is scale weight loss used to verify chlorine feed rather than relying on the rotameter setting alone?