Production engineering question

[u/Comfortable_War_6457]

Hello people of Reddit, I work in production engineering at a chemical company, and we make phosphate based products. One of the improvements I’ve been wanting to make is lowering our phosphate grade in the final product, it’s been touching 53.5 % etc instead of around 52 %. Issue is that there are many different raffinates in our feed such as amber, purified acid, sludge etc in order to reach 52, and every time the feed is variable due to various conditions so it’s almost hard to predict what type of feed is going in. After we send an 8 am sample to the lab, it takes about 4 hours to breakdown everything in the product according to wt % etc. main thing that decrease phosphoric levels is sulfuric acid, but as it’s fed, it makes granule sizes smaller, making that an issue for the screens to send good amount of product. Though, do you guys have thoughts on how to decrease phosphoric levels immediately as the feed is variable.

[u/Patty_T]

lol do you work for a company called Mosaic and are talking about MAP? If so, and you’re in central Florida, good luck. The quality of matrix from the mines is getting worse and worse and allowing more contaminants into the final product just makes granulation worse and worse.

[u/Comfortable_War_6457 → u/Patty_T]

lol that’s close, a very similar company. Though that may be a case in Florida, though I’m not too sure up here in nc?

[u/Patty_T → u/Comfortable_War_6457]

It’s worth looking into trends of concentrations of your trace metals like aluminum and iron in the matrix feeding the phos acid plant and the concentrations of those same trace metals coming to your granulation plant. Generally speaking, these metallic complexes negatively affect granulation. The problem is that granulation is also affected by your reactor temperature, your mole ratio going to the granulator, the quality of your granule seed in the granulator (in terms of size. Seeding with dust will make producing good granules way harder), and your ammonia usage in the granulator (or your acid usage if you’re reverse titrating) on top of those trace metal contaminants, so it’s really hard to get a good granulation going once you go down the shitter

ETA: The rotational speed of your granulator also determines size - the slower you spin it, the bigger the granules get and vice versa. Our matrix was so bad I even considered putting a VFD on the granulator drive motor so that you can slow the speed down a bit if we were losing granulation but that’s not really a good solution worth the spend, more of a bandaid.

[u/kinnadian]

I don't have specific knowledge of your reaction so I'll just provide generic advice.

Have you researched or engaged consultants to advise alternate technology to reduce raw/product analysis times? Perhaps compromising accuracy to get a more frequent analysis (but still doing the less frequent analysis to confirm product spec). Something online would be ideal.

Can you monitor any process parameters to infer final product composition? Pressures, temperatures, offgas flow rates, densities, etc. If you find a correlation you can use this to tune in the process.

Have you modelled the reactor in Hysys or other to determine if you can predict final composition based on varied feed?

Can you use any recycle loops to modulate/buffer changes to raw input flows?

What tolerance is there to going under the spec? One analysis every 4 hrs, and being so close to the spec already, seems likely that you will go under the spec sometimes if you're targeting to go closer (but perhaps not picked up on an analysis due to frequency of sampling).

[u/Comfortable_War_6457 → u/kinnadian]

Hmm so we definitely can monitor all those process parameters, but I think the main issue would be that once the slurry is made out of all raffinates, it’s fed into a granulator and ammonia vapor is raked through. Now process conditions may be either too wet or too dry or pH levels are not adequate etc, so operators do make a lot of changes on the go, and that really messes with our ability to control the exact grade, because sometimes they may add more ammonia or larger slurry ratio, or high recycle feed ratio etc.

[u/thegof → u/Comfortable_War_6457]

Free, uncontrolled operator intervention can be the absolute bane of good process control. Now you're highly dependent upon the operator skill and experience, something also out of control. Are those (presumably) small and frequent adjustments documented? Is the lag time between what they are observing to causality long enough that they are adjusting due to something that already changed?

Experienced operators (and engineers) are priceless, but many/most are just "good". Few (of both types) are good at being able to substitute directly for the process controls due to the need to factor in the time based elements. Try to isolated those parameters that are most sensitive. Ensure any changes to those are documented and the result of those changes is also monitored and documented. Th act of documenting may help ensure that changes are more intentional rather than casual.

[u/carpenterfeller]

I deal with variability in feedstock at work, and the AI answer is right about a holding tank. That can mitigate short term variability.

Your grade should depend on what your customers require. If we have issues with a product, there are some customers that can handle certain issues when others cannot.

I would definitely consider looking at a holding tank if that's feasible.

[u/Comfortable_War_6457 → u/carpenterfeller]

Hmm so a follow up question for me may be, if operators were to make manual changes after it’s fed from holding tank such as amount of ammonia, recycle feed, moisture addition, what would your thoughts be on that?

[u/carpenterfeller → u/Comfortable_War_6457]

I don't know your process, but I would say none of that should be affected, unless retention time somehow affects your feedstock. Any of those changes could be made similarly to how you change them now, just using lab information from samples from the holding tank. Any fast changes in feedstock should just be muddled by having more of the previous feed held up.

Are the issues cause by operators making poor choices? If anything they change causes issues, changing your process would not be the answer.

[u/AutomaticPianist4308]

As a generic “process engineering” approach I would run as advanced of a DOE as possible (without it costing a ridiculous amount) and begin to create regression trees/ models to help predict how different amounts of raffinate in feed/ h2so4 affects phosphate amount. This is all assuming you can study the raffinate amounts in the feed. You could also create correlations/ classifications for the feed raffinates based on the “various conditions” you mention if you measure them.

I have no knowledge of the chemistry behind your process but I like to also always compare experimental data to any engineering correlations that predict what the phosphate amount should be based on known inputs (like reaction kinetics or something along those lines).

[u/MuddyflyWatersman]

I'm just going to say that look regardless of a specification........ customers expect to keep receiving the same thing that they have been receiving....... changes need to be carefully considered. I've known people that have been fired because of things that were not even on product specifications..... but were a problem for the customer.... you do have to be smart about things it's expected

[u/Admirable-Access8320]

Not sure how this legit got it from GPT but used my own flavor of prompting.

1. Equalize first – Route all raffinate streams into a well-mixed hold tank with level time ~1–3 hours. – This smooths spikes before they hit the granulator.
2. Measure in real time – Inline density or Coriolis on each feed, plus conductivity. – Add a fast PAT probe: NIR or Raman for acid strength and phosphate speciation. – Install an inline titrator for “acid number” – gives a 2–5 minute proxy while the lab takes 4 hours.
3. Blend smart – Use mass-flow control on each stream and target a calculated P2O5 setpoint with a soft sensor. – Feedforward trim of sulfuric acid based on the analyzer prediction, with PID feedback from the inline titrator.
4. Decouple grade from granule size – Split H2SO4 addition between conditioner and granulator to reduce local over-acidification. – Compensate granule size via recycle ratio, seed rate, moisture, and drum speed. – Run a quick DOE to map “acid trim vs size” so control has hard limits.
5. Tighten supplier QA, but pragmatically – Keep lots segregated by supplier and assay. – Use certificates as guardrails, not crutches. Reject or derate out-of-spec lots.
6. Close the loop operationally – SPC charts on inline signals. – Alarms on predicted grade drift, not just lab results.

Net: equalization + inline analytics + feedforward trim lets you hit 52 percent without shrinking granules into dust. Supplier fixes are gravy. Process control is the steak.

[u/Comfortable_War_6457 → u/Admirable-Access8320]

Hmm now a holding tank is an interesting thought, I’d like to think that all those streams are already fed into a blend tank which feeds into the reactor, but an issue would be that operators make a lot of changes in ammonia feed, or moisture or pH etc, which may mess with the wt % or final product? But let me explore a holding tank? Thanks btw