Interview with Ed Graf

The inventor of a new technology called air-dried-tissue (adt) gives his thoughts on its advantages, its configurations and its super-fast future

Air dried tissue, or ADT, is a simple yet potentially groundbreaking new technology for making tissue. The first installation of this configuration is up and running on a small scale at a confidential mill in the United States. We interviewed Ed Graf, the inventor and patent holder for the ADT configuration, to learn where the technology came from, how it’s working so far, and where it might be going in the future. Join us to take a look.

Perini Journal

What is ADT and what advantages does it offer over other tissue making configurations?

Ed Graf: ADT is a new way of making tissue and toweling that grew out of existing papermaking, though not specifically tissue making, technology. Conventional tissue making involves drying the sheet on a Yankee dryer with the moisture being driven up from the heated surface of the Yankee and being met by high velocity air being impinged on the sheet.

I started thinking about this and asked: What happens if we put air on both sides of the sheet? This means we would be impinging the sheet from both sides with hot air that is devoid of moisture. We theorized that this could both pull the moisture from the sheet and also, at the same time, create a slight fiber rise or bulk. We ran some very simple trials and it worked. 

Traditionally, a Yankee dryer renders unidirectional drying. Instead, we wanted to explore if we could get bidirectional drying which we felt could give advantages in terms of energy, bulk and, very importantly, sheet breaks/runnability. We accomplish this using a carrier belt which takes the sheet through an air flotation dryer, meaning that if there is any sheet break the carrier belt will self thread the sheet without any lost time. This also helps reduce grade change times.

Before we go into further details, can you tell us about your background?

Ed Graf: I worked for the large paper machine builders for about 30 years. I started in research and development at Beloit Corporation for five years, then went to Voith as chief engineer of technical services working mainly on wet end developments and equipment, as well as Yankee dryers. Following that, I was at Escher Wyss as vice president of product development, followed by Black Clawson as a technology manager and then back to Voith in application engineering and director of product development. Then, in 2005 I started on my own.

So when did you start thinking about this ADT process?

Ed Graf: I had been thinking for a long time that there must be a better way to both dry the sheet and get bulk, rather than the very large, complex and energy intensive drum that is used in the TAD process. Air flotation dryers caught my attention, as I knew that they were used both for heat setting forming fabrics for papermaking, as well as for drying clay coatings on lightweight coated (LWC) printing papers machines. I thought we could modify that process but instead of floating the sheet, which would be impossible due to its low grammage and strength, we could put it on a belt that is made out of heat resistant plastic. We bias the air to give a slight push toward the belt, so it does not blow off the belt. We do it in a way so that part of the sheet is lying on the belt, and part of it has been lifted off, so you get very high air and moisture exchange. The result of this slight disruption of the sheet is both increased bulk and increased softness.

As I conceived it, ADT requires a smaller and therefore much less expensive building structure. For example, we may be able to run ADT completely without a Yankee dryer, although that is not what we did in the first machine. So, if you have no Yankee, you do not need an overhead crane. The heaviest component would then be the headbox and that can be installed with portable cranes. In fact, you don’t even need a basement if you don’t want it because you could simply put two pits in the floor; one for the pulper and one for the fan pump. With no Yankee and no boiler, this takes out a tremendous amount of infrastructure and therefore cost.

So are you the inventor of this concept alone, or was there a team involved?

Ed Graf: I’m the sole inventor and have two patents that have been applied for and granted for this technology and configuration. I started working on this idea in August of 2005, I consulted with trusted industry friends and by late 2010 we had installed our first ADT machine. It’s presently running well at a location in the United States, which I am unable to disclose due to my agreement with the company.

Air flotation dryers which are similar to the ADT configuration have been used on lightweight coated (LWC) printing papers machines for a long time. So the basic technology was around, but it had never been used for tissue. We, of course, had to make some modifications. I spoke to a company which is a world leader in this type of technology, in Green Bay, Wisconsin USA, and they were pleased to do the modification so that it would run on tissue. We now have the one installation running and have had serious projects with several other, smaller, companies. Unfortunately, however, those companies were so small that they were unable to raise the funding, so those projects have not gone through. It’s not because they didn’t like the technology, and decided on something else. They simply could not raise the capital. However, there has been, and continues to be, much interest in this technology due to the advantages it offers. Interest is clearly heating up in the ADT technology, as gauged by the number of inquiries and phone calls I have had in recent months about possible ways to apply it.

So, specifically, what are the advantages?

Ed Graf: We can quite simply make a bulky towel sheet that is very similar to TAD but with energy savings that are 17% lower for the overall process in terms of energy per ton. Of course, the quality of the sheet depends on the quality of the fibers used. Furnish does play an enormous role. But, all things being equal, we can make a TAD-like sheet with a lot less energy.

How do you get such energy savings?

Ed Graf: Well, if we step back and look at how things are done today, with the Yankee dryer in the center, what we know is that at higher speeds it is actually the hood that is doing the drying and evaporation work, not the Yankee itself. Today’s modern hoods are very efficient in terms of the ratio of energy going in versus mass of water evaporated out.

What is the actual configuration of your first machine?

Ed Graf: It uses a current technology headbox, followed by the wet end which is the standard crescent former configuration. A very small Yankee dryer follows, with this section being used to transfer the sheet and bring it to approximately 75% dryness. From there it goes into the ADT unit which is, in reality, a modified air flotation dryer section with a direct fired multifuel design. Fuel used in ADT can be natural gas, propane or even fuel oil. A Maxon burner was used in the first installation. 

The ability exists to “ramp up” and “ramp down” the drying rate within the air flotation dryer section in a much more controllable manner since heating in multiple zones can be done very flexibly. Finally, the reel on this machine is a conventional surface wind device and was one of the few items that was used/rebuilt. An alternative would be to use a newer center wind design with a digitally programmed “turn up” sheet transfer. The mechanics of this new reel concept are simplified over current designs. Narrow machines may also utilize expandable core shafts so that a winder may not be necessary and the rolls may be directly sent to converting. As an option, a slitter section could possibly also be integrated into the reel to allow production of a number of narrow finished rolls.

I am a little confused. Do you need a Yankee dryer or not?

Ed Graf: That’s a very good question. Some of our trial work indicates we can actually remove the Yankee dryer entirely and just run the sheet via the former, through a modified press section and straight into the ADT unit. I’m just guessing it will be possible, and perhaps energy usage would go up somewhat, but if you wanted bulk you would certainly get bulk. And you would save enormously on capital cost by eliminating the need for a boiler, the Yankee itself, and even the crane in the machine hall.

For nominal 110 inch or 2.7 m wide machine, the ADT unit costs about half of what a TAD drum does. Not only is the unit less expensive but the headroom, meaning ceiling height of the building, is much lower. You do not need a very tall building.  

Can ADT replace TAD?

Ed Graf: We think so. We believe the quality can match TAD while consuming less energy. You get a very nice bulked-up sheet because you’re not restraining it with the Yankee surface. We get “fiber rise” which means the fibers are sticking up from the surface, which you certainly do not want on a printing paper, but for tissue it can be a strong advantage for bulk and softness characteristics. This is because the fibers can rise from the free surface.

So how do you ideally see ADT expanding its applications in the tissue and towel business?

Ed Graf: We think the most financially efficient way to utilize ADT is, if a mill has an existing tissue machine with the Yankee dryer and the creping doctor, they can add ADT after that. That simply means moving the reel to provide space for the ADT unit. That immediately makes it into a swing machine that can make both tissue and toweling grades, with rapid grade change times. Additionally, because the ADT dryer has been added, a 20% increase in towel production tonnage, over the machine’s original production tonnage will be realized.

What are the fastest speeds you think you could reach?

Ed Graf: We have published that we can reach 7000+ ft/m which is 2120+ mpm. In this case, it is without a Yankee dryer, because you are speed limited by the material strength of the iron. In Yankees, the combination of the high pressure inside and the centrifugal forces can blow the Yankee apart. So maybe you don’t need a Yankee, and the doctor. There can be other ways to put topography into the sheet.

What else are you thinking about these days?

Ed Graf: I certainly have some exciting ideas but I don’t want to talk about them publicly yet. I prefer to under-promise and over deliver. However, I can say that I am fairly sure that tissue machines today are generally far too complicated for what they are trying to accomplish; there may be easier and simpler ways to do this. Ideally we could run much faster than the top speeds of today. For exam-ple, there are things I’m working on to make the wet end go much faster, and if you put that together with the ADT dryer, you can imagine the sheet would run extremely fast without a complicated Yankee or drum. 

What are the other parts of your business?

Ed Graf: My day job is providing consultancy services on headboxes. I have done design and operational work on headboxes for both paper machines and tissue machines for more than 40 years, and have numerous patents in that area, and having won more than 50 patents in total. In addition to the ADT project, my main work is with headbox technology and troubleshooting mainly in North America and Europe.

In the long run, where do you think we are going with paper machine technology?

Ed Graf: I think I have partially answered that already but I would say simply “wider and faster while moving away from Yankees and TAD drums”. Specifically, with iron Yankee dryers we are at the limit as far as face width is concerned at about 300 inches or 7.6 m. Perhaps steel Yankees can be wider but I’m not sure. On the other hand, ADT-type dryers for other applications have been built in widths over 400 inches, which is 10 m. So we could quite easily build an ADT dryer for tissue that wide, as that technology is well proven. Put that together with an equally wide headbox that is designed to run superfast and you get an idea of what the future might hold for tissue. *

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