Homegrown Oxidizers, Part Five
WSM

Is that all there is?

We’ve built and run single batch cells and even set them up to run fairly consistently. We’ve improved efficiency by controlling the pH to where we approach the “sweet spot” of ideal precursors to get more chlorate for the current consumed. But the big question is, “Can we run a system continuously the way industry does?” The short answer is, yes!

The Continuous System Theory

System Design

Because of the complex steps and details involved in moving from a batch cell to a continuous system, one of us has commented, “It’s amazing how complicated a simple concept can get!”

A great deal can be learned from studying the layout of commercial chlorate plants, and a lot of this information is available for free on the internet and from patent searches (also found on the internet for free).

There are several details that need to be decided when planning the design of a continuous system. Even though much of what we learned from running batch systems is directly applicable to a continuous system, there are many new steps that need to be considered as we make this quantum leap in technology.

In deciding the details of a continuous potassium chlorate system, things to consider include:

• What is the end goal, what do we hope to accomplish with the system?
• The most efficient use of resources
• What materials should we use for the best effect?
• To use several separate tanks or minimize tankage?
• To use heat controllers or not
• What form of pH control?
• How to move liquids; pump or gravity feed?
  

There are many more things to consider, and these are but a few. For economy and simplicity, let’s make our continuous system tanks of hard PVC materials; pipe for the cylindrical parts and flat sheet for the ends. Other shapes of PVC are available and simplify some of the more complex designs. Remember to keep anything that will contact the cell’s liquor (fluids) compatible to minimize problems (leaks, contamination etc.).

01 Basic Cell Setup 5-25-14.pdf
The diagram above is a design drawing based on a multi-tank system and outlines some fundamentals to keep in mind.

Temperatures are critical to think about so as to prevent crystallization of the potassium chlorate before it gets to the crystallizer and again in pumps and other vital components (where it would foul the systems). Sometimes compatible heaters are required in strategic locations to prevent crystal growth in sensitive locations (float switches and tubing, for instance). Other times it’s desirable to heat a separate tank of water and pump the heated liquid through jackets (surrounding delivery tubes) designed to keep system liquor (loaded with dissolved chlorate) warm enough to discourage crystal growth in those tubes, until the liquor is delivered into the crystallizer.

We’ve decided to build a system that is gravity fed from the reaction chamber (RC) to the crystallizing chamber (CC) and design special components to assist in fluid handling.

Liquid level controller


An electric fluid level controller based on relays and float switches (which will be connected to the terminal block on the left side of the panel). The electrical outlet powers a pump that delivers salt solution to the RC.

The idea is to keep the reaction chamber fluid level constant and gravity feed the chlorate-rich liquor to the crystallizer, where the chlorate will drop out of solution due to the cooler temperatures there. The crystallizer fluid levels will vary within preset bounds which are determined by fluid additions to the RC, all controlled by float switches in the “heat well” in the crystallizer.


Heat well for the crystallizer

03 Thermal Well for the Crystallizer Return Intake.pdf

This top view of a shallow crystallizing chamber (CC) shows the “heat well” in the upper right hand corner and the RC overflow pipe in the bottom center. The heat well contains a submersible diaphragm pump (represented by the small square with a circle in it) and the “start” and “stop” float switches (represented by the two small circles above the pump).

Not shown is a compatible heating element, used to keep the heat well at the higher reaction chamber (RC) temperatures to prevent crystal growth in the heat well components. The heat well walls have openings below the fluid surface, to allow the depleted liquor to enter, where it’s drawn into the pump intake and also moves the fluid level controller float switches.


Submersible diaphragm pump

To move depleted liquor from the crystallizer back to the reaction chamber without causing temperature problems, we’ve designed a submersible diaphragm pump that runs on compressed air from a fish aquarium air pump. To control the pump air supply, we use a repeating timer and a pneumatic valve that causes the diaphragm to “breathe”, moving the fluid in controlled pulses.

The movement of the fluids isn’t required to be fast, but continual; and this design accomplishes the goal efficiently. If required, the compressed air can be heated by running it through a coil of tubing in a hot water bath before it goes to the pump in the heat well.

This design was perfected by the collaboration of two enthusiasts who offer their efforts to further research into continuous oxidizer production by amateur electrochemists (and amateur pyrotechnists, working to be self sufficient).



A working prototype submersible diaphragm pump made entirely of PVDF (Kynar) polymer and Viton B rubber components.

05 Submersible Diaphragm Pump Design 5-31-14.pdf
Our design for a compatible and submersible diaphragm pump, showing a side view and a bottom view.



Jacketed liquor tube with hot water reservoir

06 Heat Exchanger Diagram.doc


Protected thermal sensors

To ensure proper operation of our continuous system, we monitor the temperatures of various sections while they run. Liquid filled glass thermometers can work but add the potential of contamination if they break, so we opt for electronic sensors with panel mounted displays.

Since most electronic sensors are not compatible with the cell liquors they would be exposed to, they need to be protected. Whether the sensors are bought with Teflon or Kynar coverings or compatible shrink tube materials (Teflon [PTFE], Kynar [PVDF], or Viton B synthetic rubber) are properly applied to protect the sensors, the goal of a compatible thermal sensor in the highly corrosive liquor will be met.


A Teflon (PTFE) covered PT100 thermal sensor connected to a temperature controller system.

Price can be a serious drawback to these devices, but through careful searches online we’ve found sources of supply in China for the sensors and digital display panel meters; both as low as $10 each.

At these bargain prices we can monitor the temperatures of several parts of the continuous chlorate system simultaneously.


The Next Challenge: Built it and Run it…