Rotary Dryers,
Tarmac’s Direct Fired Rotary Dryer is specifically engineered for fast site installation, safety, efficiency, and lower critical emissions. This article is the second in our series about Tarmac rotary dryers, and covers dryer drives, shell support and insulation. You can read the first article HERE. Next time Ron will discuss burner efficiency.
Drive options for Direct Fired Dryers
Tarmac offers two drive options for all dryers: trunnion drive and wrap chain drive.
- Wrap chain drive allows for over half of the sprocket teeth engaged with the roller bushing drive chain, which causes less wear to both the sprocket and the drive chain. The first photo below shows a wrap chain drive dryer.
- Trunnion drive uses (2) drive trunnions for small dryers and (4) drive trunnions for larger dryers. Drives are either Nord drives or shaft mounted reducers and motors for larger dryers. The center photo below shows a (4) trunnion drive dryer. If the customer is worried about fine abrasive dust sticking to the sprocket and chain, the trunnion drive method eliminates this wear point.
Wrap Chain Drive 
Trunnion Drives with shaft mount reducer 
Twin thrust rollers are on each side of a dryer tire.
The photo on the right shows the thrust roller package. This helps keep the dryer centered on the trunnions and used with both dryer drives.
Tarmac tire to shell support method:
Tarmac supports the dryer tire from the dryer shell using Leaf Springs. These are welded to the inner side of the dryer tire and then welded to the dryer shell. The dryer shell expands when the drying process is taking place due to increased temperatures of the dryer shell. The Leaf Springs flex into compression when the dryer shell expands then as the dryer shell cools the Leaf Springs return to a normal flex.
This is a great improvement over solid blocks or support methods under the tires that do not allow the dryer shell to expand. The result of not using Leaf Springs is dimpling or an indent on the dryer shell where each solid block attaches to the dryer shell. You must weld shims in place multiple times per year when a dryer shell dimples. The left photo below shows the leaf springs installed. The right photo shows a rigid tire support that has been repaired with shims.
Tarmac Dryer Tire with welded leaf springs 
Solid dryer supports repaired with shims
Dryer Shell Insulation
Dryer shells radiate heat from the outer shell surface to ambient air. Also, weather and rain can cool shells. Tarmac offers dryer shell high temperature insulation which saves fuel. The fuel savings is related to the amount of fuel or BTUs created within the dryer to the number of BTUs radiating from the shell. Tarmac shell insulation can provide 20% to 30% fuel savings.
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