Choosing the Right Freeze Dryer

Getting Started

Freeze drying is a manufacturing business that requires equipment with serious capitol costs. It is like most any manufacturing business in this way, which means it needs to be run with cool-headed deliberation.

Let's assume that you are already freeze drying, whether that be on a small scale using introductory equipment or have already established a manufacturing line with some large commercial size freeze drying machines, machines which can cost near a million dollars but have wide variance in list price among manufacturers. The task then is to determine which freeze dryer you should spend your money on. There are a number of factors you should consider.

Business Case

Your first task when choosing among any equipment for manufacturing is to analyze the business case, which requires that you calculate the total cost per unit of production as well as the per unit value of your product. In other words, divide the total annual gross profit potential of product by the total cost of the machine, installation, maintenance, and utilities. This needs to be a dollar amount in order to be meaningful. To do this, you need to know your input numbers, the revenue, the cost of materials, the cost of operation, etc. If you don’t know these numbers, then start small so you can learn as you go, then you can expand to meet more customer demand.

Throughput

The amount of product you can put through a production machine per unit time is called throughput. To determine the throughput of a freeze dryer is fairly simple but needs to be carefully accounted for when comparing machines. The factor that sets how much material you can run in a batch is the available area of the heated shelves. This is a set number for a given machine so ask for the OEM for the information. You should already know from experience how much of your product you can place per square foot of tray space, but if you don’t, then buy a baking tray that you can measure and subtract the empty weight from the loaded weight. Then tabulate for each machine that you are comparing the total amount of your product per machine load. You can do fresh frozen weight or dry weight, it will not affect the outcome of your comparison.

Cycle Time

For the default cycle time, which means the total time to run a batch from hitting the start button for one batch to hitting the start button of the next batch. It is really important to do it this way because it then includes your material handling time, which can be a significant portion of the total cycle time. For most machines, you should assume one load per day per machine unless your products have lower moisture content, like candy, ice cream, or equivalent. Next determine how many days per year you will operate your machine and then multiply that number of days, times the number of pounds per batch times the revenue or profit per pound. This gives you your expected total number of product cycles per year and can then be used to calculate your expected revenue and operating profit. Do not consider customer demand in these calculations. While they are important for your business growth case, they will not be helpful in selecting a machine. What you get from this exercise is the revenue and profit per day of operation as well as per year of operation. This is critical information in machine selection, in planning spare parts, in understanding the cost of maintenance, and a whole lot more.

Installation Costs

Buying a machine includes more than just the sale price of the equipment. Installation costs can be quite significant for large commercial freeze dryers. This number varies by machine so ask the OEM for their estimate. Add to that any costs you will incur building or providing facilities and footprint to that particular machine. Concrete pads, electrical installation, installation of sanitary walls, plumbing, conduit, etc. Are all expensive and real costs. During the calculation of these costs, you should work closely with each of the equipment manufacturers you are considering to determine how similar or different the costs will be. If this includes downtime of your other production machines during installation, that should be accounted for as well.

Labor Costs

The next big issue you should consider when comparing machines is labor. In some cases this might be your primary concern, but in most cases it's probably coming in a close second. I'm sure it's no secret that good employees are hard to find, lol maintaining your selection pool is as broad as possible is important when looking for employees. This is something that is particularly pertinent to freeze drying because handling product when loading and unloading your machines can create issues regarding the physical strength of the candidates. Let's be more specific, it is far easier for any person to lift and handle a single standard 18-in x 26-in aluminum baking tray than it is to lift and handle a 40 inch wide by 48-in long stainless steel product tray full of product. Some freeze dryers use small baking trays and standard, whereas others use very large trays as standard. If you choose a machine or build a machine that has oversized trays, you eliminate most female candidates, and many men with lower physical strength. Even if you can hire big strong men to lift and handle these trays, it creates working hazards that can turn into liabilities later on.

Loading Trays

In most cases, your material will need to be frozen prior to loading in your freeze dryer. Because of this material handling can also become a huge issue. If you have oversized trays, then you will need counter space large enough to hold those trays while they're being loaded or unloaded. Once those product trays are loaded, they need to be transported to the freeze dryer, which means if they're oversized you need to reserve extra footprint for moving those oversized trays from the freezer to the freeze dryer, which consumes valuable manufacturing floor space. Furthermore, it we'll also require that your freezer doors are large enough and that you reserve extra footprint inside your freezers for moving your product in and out of the freezer. If you spread your frozen product onto the trays right before inserting into the freeze dryer, you mitigate the footprint problem somewhat but then have a different problem, which is that you are extending your freeze trying cycle time by the amount of time it takes to load your shelves. If your total production cycle time exceeds 24 hours in a day. It is likely that you will lose one batch per week, because the cycle start time gets later everyday. This is particularly true if you are freeze drying product that has to be inspected by the USDA.

Cleaning

Cleaning the internals of the freeze dryer can become a very frustrating issue depending on the design of the freeze dryer and the frequency that cleaning is needed. Most freeze dryer designs have fixed shelves with one and a half to 2 in between shelves and deep corners and crevices that are very difficult to clean. In any facility wears, sanitation is critical or frequently inspected, cleaning of the freeze dryer internals can cause significant downtime. In cases like this, choosing a freeze dryer with removable shelves, like the TechSource Systems freeze dryers, can make cleaning a very simple process.

Refrigeration System

Proper design and specification of the refrigeration system on a freeze dryer is perhaps one of the areas where many freeze dryer brands fall short. The Cold plates in a freeze dryer act as cryogenic vacuum pumps. Remember that vacuum is created by removal of gases from a chamber, and water vapor is a gas. The key is that water vapor is a condensable gas and the most efficient way to pump condensable gases is to condense them. In fact, a cold plate in a freeze dryer. If properly cooled by the refrigeration system can pump hundreds of times faster than a sizable vacuum pumping system. The sizing of the refrigeration capacity is a straightforward engineering calculation. It it must be larger than the total heat load added to the system by the heated shelves. Theoretically it could be equal but there is no 100% efficient system. Therefore, it must be larger. How much larger depends on the thermal efficiency of the vessel and other cold surfaces. Better insulation means better thermal efficiency, which is not a surprising concept.

The refrigeration system in a freeze dryer is one of the most expensive components. This makes it one of the first targets for cost cutting by low cost equipment OEMs. This leads to a number of problems.

Undersized Refrigeration

If your refrigeration system is undersized and you will have difficulty maintaining your desired low pressure during processing. The pressure in your freeze dryer is critical to the entire freeze drying process. High pressure can lead to melt back. Essentially, if you deposit more heat on the surfaces of the Cold plates, then you are drawing out through the refrigeration. The surface of the cold plates will warm, meaning that the condensing pressure will rise, which in turn causes your chamber pressure to rise. Then the only way to maintain the desired pressure is to reduce the amount of heat going into your shelves. If you have a control system that controls heat based on system pressure, you will simply notice the cycle time getting longer.

An undersized refrigeration system will also be continuously operating at maximum power. Operating continuously at maximum power often leads to premature compressor failure due to overheating. It is common among freeze dryers to replace refrigeration condensers annually, which are expensive, both in capital cost and downtime.

Undersized refrigeration systems can also lead to premature vacuum pump failures. If less vapor is condensed, chamber pressure will rise, which causes the vacuum system to ingest more water vapor. If you are using an oil sealed vacuum pump, this means that you have to deal with frequent oil changes to maintain the pumps running properly or face a whole slew of problems, including inability to reach base pressure and premature vacuum pump failure. Vacuum pump failure, particularly while in process can be a very expensive occurrence. Loss of vacuum during processing can cause loss of that batch of product, a $15,000 to $25,000 loss. Furthermore, if you have a spare vacuum pump on the shelf, you could be back up and running the next day, but you have already lost an entire day of production. If you do not have a spare vacuum pump on the shelf, you could lose weeks or months of production, which is by far the most expensive of all.

All of these issues, whether failures of compressors, frequent oil changes, or vacuum system failures, will cost you what you would have paid for the more expensive freeze dryer many times over but you will still be stuck with the cheaper less reliable freeze dryer. Either way you will spend the money, so you might as well get the best freeze dryer and enjoy, The durability and production for decades after.

Vacuum System

The vacuum system is one of the four critical parts of a freeze dryer. While it is true that the ice banks can pump the condensable gases at hundreds of times faster than a vacuum pumping system, The Cold plates cannot pump non condensable gases, which include the air that you pump out at the beginning of the process as well as other non-condensable gases that evolve from your product during the process. The good news is that most vacuum pumps that are sold today will pump the non-condensable gases just fine. The bad news is that once the chamber is pumped down, very little of the gases that are being pumped are in fact non-condensable gases. So what ends up in the vacuum pump? Mostly water vapor, but sugars, fats, fatty acids, lipids, waxes and other stickies are also going to end up in the vacuum pump. Therefore, the right vacuum pump is one of the most important choices that face and OEM when building a freeze dryer. Naturally, the best pump is one of the most expensive pumps. In this regard, there is clearly one that stands above the rest in the field, namely the Leybold Screwline SP 630, an all aluminum dry screw pump. The good news here is that most of the reputable OEMs are already equipping their freeze dryers with this pump. However, you may have a legacy freeze dryer that still uses an oil filled vacuum pump, whether it be rotary vane or piston. If that's the case, you should contact us about upgrading to the right vacuum pump. It will be one of the best decisions you make for your freeze-drying business. There are plenty of reasons to choose this pump, so we encourage you to research it or contact us for more information.

Vacuum Chamber

The vacuum chamber is often taken for granted in a freeze dryer, but it is obviously one of the critical components of a freeze-drying system. There are several factors which create advantages and disadvantages between freeze dryer models. Some are cylindrical which use thinner walls and therefore less materials due to their geometry but take up a larger footprint for equivalent manufacturing capacity. There are rectangular chambers that require reinforced walls which uses more materials but have a smaller footprint for equivalent manufacturing capacity. There are some systems that are designed for mobile product shelves that allow for easy loading and unloading. There are models that have sophisticated overhead rail systems to move heated product shelves in and out of the freeze dryer. The choices are many. Make sure that you take the time to choose the one that works best for your operation. At TechSource we have developed in patented rolling product racks with removable heated shelves. There are several reasons for this choice. You can read about them here.

One of the most important issues to consider is quality of the vacuum chamber, which is often overlooked. The leak tightness of the chamber over time can make a huge difference. The more your chamber leaks, the harder it is to maintain the proper pressure for processing your product. Small leaks can be found using a vacuum helium leak detector and subsequently sealed, but the leak that is difficult to fix is at the chamber door. Other than changing the seal on the main door, there is little you can do. Unfortunately, the chamber door seal is not always easy or cheap to replace. Make sure when you are selecting a freeze dryer that you carefully consider how the chamber door is constructed, how it is sealed, and how you change the seals once they wear out.

Machine Controller

Finally, the machine controller and software are critical parts of good freeze dryer design. Carefully consider whether the control software matches what you want to do with your freeze dryer both now and in the future. If you want changes at some point in the future and you are not allowed access to the proprietary software, you will be unable to maintain the flexibility of your business. These are critical issues that you should ask for more information about from any OEM, regardless of how reputable.

In Summary

Clearly, there are many factors to consider when choosing a freeze dryer for your business. At TechSource Systems, we highly encourage you to thoroughly investigate several equipment OEMs before you make your choice. This is a large and expensive piece of capital equipment, and it merits a trip to the manufacturing facility and in-depth discussions with the OEMs to determine how each of the potential failure points are handled.