I want to take some time and provide a “layman's description” of the Separation chemical process currently being used in Pretreatment. A lot has been said about this pilot test and again, I'd like to know that everyone has at least a relative understanding of this chemistry as we attempt to determine if this method is best suited for our operation. To reiterate my previous statement: “The temporary-built installation is solely for the purpose of qualifying a chemical process.” Should we find that the economics are unreasonable, we will attempt to prove-out alternatives that might work better for us, both economically and operationally. Consider it an ongoing process…until we achieve success and sustainable reliability.
The floc-tube/Separation chemistry program was selected to test first because of various results that would be realized with a permanent system: 1.) inexpensive to implement (present chemical costs notwithstanding) 2.) reduced manual operation (vs. typical cold lime softening), and 3.) ability to reach 15 cycles in cooling tower without significant additional capital equipment (eg. third clarifier unit and/or RO filtering).
The people who expect cold-lime softening results will probably be more agreeable with Separation chemistry. One goal of developing a custom chemistry was to get away from the dry chemicals that require being "slaked" in the system and in addition to its inefficiencies; we weren't keen on a cold lime process that actually contributed hardness to the cooling tower water. With Separation chemistry, we've replaced the lime with sodium hydroxide and the mag-ox with magnesium sulfate; however the ferric sulfate is now being used in an entirely different way. It's also important to understand how the floc-tube fits in and how each reaction is occurring independently of the other. Noting the location of the original cold lime injection points, we used to make "chemical soup" in the reaction zone and hope for the best. With Separation chemistry, we can inject neat feed chemicals based solely on flow rates and pH, and since the reactions occur prior to the clarifier inlets we can do this independent of clarifier operation. Should we ultimately find that the H2O Tech Services process is economically infeasible, we would be more inclined to continue testing with a neat-feed, separation chemistry program rather than returning to straight cold lime softening.
How we use the chemicals:
1.) Sodium Hydroxide - Addition of Sodium Hydroxide will soften the water by precipitation of calcium and magnesium carbonates, provided the pH of the solution is greater than pH 9, and that this pH is maintained. The solubility of silica is dramatically different across the pH spectrum. It's relatively pH-independent below pH 9, but as you increase above pH 9, solubility will be greatly enhanced. For the separation chemistry to work properly, performing both softening and silica removal, our pH needs to be maintained at pH 11.
2.) Magnesium Sulfate - This product is base fed to allow some background magnesium to form complexed magnesium silicate. Its only purpose is to accomplish this.
3.) Ferric Sulfate - Ferric is the coagulant we are using. Ferric, aluminum and calcium are very good at complexing with semi-soluble compounds. In this way it is used to remove phosphorus, nitrogen, color and other items including silica (silicates). The dosage of ferric will go up exponentially as the removal of the soluble target is increased in efficiency. therefore it's pretty easy to get 50 percent removal but after this point the dosage requirement for ferric increases proportionally to get to the target of 70-75 percent removal. In this way, the ferric is controlling the silicate removal “efficiency”.
4.) All the products are followed by an anionic flocculant . This is what makes the larger particle or floc you see up top and helps settle the particles in a larger agglomerate to the bottom of the clarifier.
H2O expects to start injecting their proprietary product, Purefloc, into the north RW tank early next week. This particular isolated microbe (don't be daunted by the term “microbe”, it's simply a small organism that's too small to be seen with the naked eye, therefore requiring a microscope to see it) has been identified to absorb primarily silica as its “food source”. Bacteria are found everywhere and many have useful purposes in our lives….converting the sugar in hops into ethanol, for instance. And of course they produce other helpful products like insulin but that's not important here. There are more than 500 different species of bacteria found in the human mouth and about a billion bacteria cells in a single teaspoon of topsoil, all with their own unique purpose in life. This isn't exactly rocket science but the isolation process is rather cutting edge.
Ultimately, this product will lower our current chemical usage in a few different ways. First, the microbe in the Purefloc will adsorb the silica in the water in a linear fashion. To obtain the same silica removal, our pH can then be lowered and less sodium hydroxide would be required. ‘Softening' of the water would still be a necessary function so expect to have a continued need for this chemical.
Because the silica will be absorbed directly into the microbe, magnesium sulfate, which now provides the extra background magnesium will decrease or perhaps in time, may not be needed at all. Resident amounts of magnesium already in the source well water will actually be beneficial to the removal process.
Ferric sulfate use will also decrease because we'll be able to obtain the removal we need less dependant on that exponential portion of the solubility curve. Also the ratio of silica to microbe is > 2:1, therefore the coagulation efficiency (charge neutralization) of the ferric sulfate will increase and less will be needed. Remember, ferric is not used as a pH adjustment chemical, only as the coagulant for the silicates in the water. If pH is controlled on the front end of the system, we won't have a need to greatly adjust pH on the backend of the process.
I have realized this has been an awful lot of work to establish the test, prove out even a temporary system, and just simply get to the end game. We've been plagued with equipment failures, costly chemicals, blinded filter presses, carryover, high ferric levels, dirty floors, rusty towers…you name it. I've seen charts showing severe degradation of condenser efficiencies and charts that indicate completely the opposite, finger pointing, blaming, strong feelings, and apathy. Truth is though people, we're doing “ something ” and in my mind, that's everything. The “better ideas”….though quite prevalent, were not ones we could implement with a trial operation and in the short period of time we needed for ADWR requirements. Had we not moved from concept to prototype on this particular Separation chemistry program, I'm quite certain the cold lime softening system would still be in quasi-operation today…or perhaps not. Given our track record, I would've been surprised to make it through the summer without an outage just to pump out the sludge in the cooling tower basins.
A fundamental philosophy at Mesquite Power is that neither I nor Joe would ever support inaction over someone making a decision they felt was the best they could make at the time, given the information they had at the time. It has to be well understood that any event that may create a carryover condition will require you to decide if the chemical system needs to be shutdown or not. It's always better to run straight raw water through the clarifiers than to forward any pretreatment chemicals into the circ water system. If you don't believe you can re-establish the failed component within a very short period of time, shut down the chemical feeds to the floc tube. Our permanent designed system, regardless of the chemistry program chosen, will include a bypass line for the raw water around the clarifier units as a means of mitigating this occurrence in the future.
We should have preliminary results within a short period of introducing the Purefloc next week. With experience and luck, we'll have the mechanics of the system working properly and the testing will proceed on track. I only ask that you remain open-minded and focus on a successful launch of the new product. All of us were all here at least once before when technology changed before our very eyes.