Zero Liquid Discharge Plants 1

[pollok]

Just wondering if there are any other power plant folks out there who are ZLD. We are going through a lot of growing pains at my plant. Nalco has us switching from ferric sulfate as our primary coagulant in our clarifiers to a polymer coagulant that they sell. Has anyone else seen a similar situation?

 

[cub3bead]

Ferric sulfate is a commodity chemical and the polymer is a proprietary chemical that is a lot more costly.

Some questions to ask yourself before implementing the recommendation: Were you getting good results with the ferric previously? Are there any specific plant desires not to use ferric? Are there any regulatory reasons to switch? Has the polymer been demonstrated to deliver superior performance?

You mentioned ZLD, have you considered all possible impacts on your water balance with this change? The moisture content of your dewatered sludge will likely change, is this a plus or a delta on your water balance?

Finally, what is the bottom line impact on your plant? Is the switch economically justified?

I hate answering a question with more questions but without a lot more information it is hard to answer your question.

 

[saxon]

pollok, "ZLD" is a bit of a misnomer. The reality is, there are always some system losses that occur (leakage, evaaporation, windage and drift loses, etc.) which can be quite substantial, that disrupts the over all material balance. A more accurate description would be "Minimal Liquid Discharge".

Hope this helps.
saxon

 

[pollok]

cub3bead,
Thanks for the reply. Your questions answering questions is what I was looking for. I was trying to voice my concerns over this move to our management but was shut out. Your questions are similar to the ones I had, particularly what is the overall impact. From what I've heard from others with ZLD experience, they say the focus should be on your waste treatment end and then work backwards through your upstream chemistry. I appreciate the help.

 

[cub3bead]

Coming up with a design basis for a zero liquid discharge facility is not as strainght forward as most would assume. You are always balancing operational flexibility against capital cost. But once a water balance is set for a facility any changes to the process can have serious impacts unless these changes are carefully considered.

I have always tried to incorporate a lot of flexibility in my designs because when you get into operations things don't always follow the plan and you have to make adjustments to keep the plant on line.

One coal fired power plant project had a client set design basis of 65% annual capacity factor. We questioned the client at length about this and were told to proceed on that basis. Guess what? For the past 18 years the plant has operated at 85% capacity factor. The only thing that saved this client from major capital expeditures to expand the ZLD system is my leaving room in the cooling tower chemistry to increase the cycles of concentration from 6 to 10 which was enough to allow them to operate the plant at a higher capacity factor.

My best advice is at the end of the day you are responsible to management for operating your plant not the chemical vendor.