How to Troubleshoot an Off-Spec Spray Drying Run

TL;DR

When a production run drifts off-spec, Hendrik Grobler says Advanced Powder Dynamics does not treat it as a reformulation problem. The team evaluates the process in real time, starting with exactly which specification is failing, using a problem toolbox to correct issues without shutting down the dryer, then checking the liquid side and raw material lots before considering rebatching or reformulation. For ongoing contract spray drying, APD qualifies two to three suppliers per ingredient and needs materials at least two to three weeks before a run.

• An off-spec run is treated as an opportunity to evaluate the process in real time, not as an immediate reformulation exercise.
• Troubleshooting starts by pinning down the failing parameter: moisture content, flowability, solubility, color, density, water activity or yield.
• Operators work from a problem toolbox of immediate actions that can be applied without shutting down the dryer.
• If the dryer side checks out, the team looks at batching sequence, formulation, ingredient lot numbers, supplier changes, viscosity and liquid temperatures before rebatching.
• Raw materials are tested by lot before each campaign, and product is released only after testing.
• APD qualifies two to three suppliers per product, needs materials two to three weeks before a run, and relies on client forecasting to have equipment and workforce available.

What happens when a spray dried product goes off-spec mid-run?

Hendrik Grobler: I will not go into too much technical detail, although we have a very specific process to address these issues. The short answer is when something goes wrong on the powder specification requirements during a production run, we do not see this as a reformulation option. We see this as an opportunity to evaluate the process in real time and determine the action that we should take to rectify that.

The first thing that we do is determine what actually is the problem. Out of spec product, or the product looks a little off, is not enough to determine what is wrong. We look at specifications. Is it moisture content? Is it flowability? Is it solubility? Is it color? Is it the product density? What exactly is the problem? And then it could be yield. We are not achieving the yield requirements. What is causing that? Is it static? Is the product building up in the drying chamber? Are we overwhelming the system? Is it the hygroscopicity of the material? We look at environmental conditions, anything that could influence what exactly caused that problem.

Our teams are well trained, and they have what we refer to as a problem toolbox, which gives them immediate action opportunities if they run into specific issues. The moisture content, the water activity or the density is out of spec: what do you do? They have an immediate action process that they can follow without shutting down the dryer, without running around looking for the managers. We prepare well in advance to prevent these kinds of problems. But if they do occur, we have a process to evaluate and to determine what is the problem and how we’re going to address that.

When does troubleshooting move from the dryer to the liquid side?

Hendrik Grobler: If there’s nothing that we can find on the drying process side, then we will go to the liquid side. We would determine that they followed the correct batching sequence, that they followed the right formulation. Is there anything that changed on the ingredient side from the previous time that we ran it? Lot numbers different, supplier differences. Anything there that could have influenced the final product. Is the viscosity the same, did we use the same temperatures on the liquid side? And only at that stage will we consider shutting the dryer down to rebatch or reevaluate the formulation.

The bottom line for us is that if there are any issues during a production run, we don’t look at reformulation immediately. We look at what we can do in real time to address the issues so that we can produce a high value, in-specification product for the customer.

Why do spray drying runs need constant correction?

Will West: When I hired my first employee in this business almost a decade ago, he warned me that in this industry, something always goes wrong in manufacturing, and it’s largely true. We’re running very high volumes of material through physical equipment, and it’s formulated, and there’s heat, and there’s movement, and there are controls. It’s foolish to think that everything is going to work precisely the first time every time.

There are always things that are off one way or another, because we try to perform to very high specifications, and we monitor things with a high degree of refinement. We’re generally trying to fit things into very narrow performance windows and keep them in very narrow performance windows, which means there’s usually room for tweaking to keep them in those fine corridors of flow and performance and particle engineering and outcomes. There are almost always some corrective actions to guide the outcome where we’re trying to get it to go.

Hendrik’s point is the right one. It’s less an issue of reformulation. It’s usually an issue of understanding whether or not we have all of the right inputs and exactly the right tolerances within the right processes. Are we operating exactly the process? Is the machinery and the equipment being operated within the right tolerances, with lots of people checking and monitoring the software to make sure that all of the measurements and the tolerances are right continuously, batch after batch, day after day? It’s a lot of supervising the process in place within quality standards, with lots of things that can start to gradually go outside the lines, and we have to bring them back inside the lines.

Only after exhausting all the other possibilities do we really think about reformulation. But there are also times when the formulations themselves are speculative, and we try to control that on the front end by doing good work with the client. If they don’t already have a proven formulation, we do our best work based on hundreds of other projects to create that formulation. If we need to create one, then we test it at small scale before going up to larger scale over time.

How are raw material problems caught before product ships?

Will West: We test before each campaign. We’re testing raw materials that come in, and we test by lot, but that doesn’t mean that you can’t have things within a lot, even though the lot was tested, that prove to be bad for whatever reason and don’t perform. So you have to chase that down later. We do have procedures for all of that.

If you have things that show up on testing after the fact, then you have to chase them down. That’s also part of our process: to make sure that anything that is released is only released after testing, so we catch it before it goes out the door.

How does a CDMO protect supply continuity for recurring production?

Hendrik Grobler: It’s important for APD to demonstrate to the customer that we have a plan in place if anything goes wrong, and that is on the supply chain side and on the process and equipment side. Whether the customer provides their raw ingredients or the feed product or whether APD provides ingredients, we communicate with the customer lead time expectations prior to production campaigns. We ensure that they understand that they should have properly vetted ingredient suppliers that can provide ingredients in a timely manner, with proven delivery times and proven good quality products.

The same with APD: we have a vendor qualification program for at least two to three suppliers for each product, so that if one supplier cannot provide the products, then we have a backup. It’s critically important that we have the lead times communicated to the customer so that they understand that we need the product at least two to three weeks before we even start a production run. That could prevent any delays for starting the production run.

Then it’s redundancy on APD’s side with regards to the dryer, dryer backup and utilities. What do we do if we have a utility breakdown? Do we have redundancy on the critical equipment, the auxiliary equipment? Do we have a qualified preventative maintenance program? Do we have spare parts? Do we have a trained technical team that can address issues when they occur or can change out equipment if that is required?

It is also important if we have recurring customers with multiple campaigns per year and specific purchase order requirements. For example, a customer needs a thousand kilograms dry per month. How would we ensure that if anything happens on the supply chain side or on the dryer side or the equipment side, we can still comply without them having issues with their volume requirements? APD has developed a specific program for that. We have a supply chain manager that communicates to the customer the importance of lead times and qualifying and vetting suppliers. We have a full technical department that’s trained and understands the equipment. They understand that we have to have backup equipment, whether it’s just a mixer or a blender, and if something goes wrong on the dryer side, that we have the spare parts so that we can address the issue and continue the campaign.

Ulli Lindauer: I’d like to add something here, which comes from the exact opposite end of this continuum. If a client wants to make sure that supply chain continuity for them can be properly managed, the single most important thing that they can provide to their partner, us, for example, is forecasting. Having been on both sides of this equation, it is critically important that the manufacturing partners, be it a spray dryer, be it dynamic atomization, particle engineering, have a good sense of what volumes are coming when, so that equipment and workforce are available to actually process the project.

Edited for length and clarity from a recorded conversation with Hendrik Grobler and Will West and Ulli Lindauer.