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. Ed Graf, the inventor and patent holder for the ADT configuration, speaks about 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.
What is ADT and what advantages does it offer over other tissue making configurations?
ADT is a new way of making tissue and toweling that grew out of existing paper making, 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?
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?
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.
