Rotary Dryers,
Attention to the fine points is important. Tarmac’s Direct Fired Rotary Dryer is specifically engineered to assure fast site installation, safe operation, efficient operating burners, and lower critical emissions. This article is the first in a series highlighting the fine points that make Tarmac rotary dryers stand out. Today we will cover Parallel Flow vs. Counter Flow, Pre-assembly, and safety. Next time will be drive options and shell support (read that article HERE). Our last article in the series will cover burner efficiency.
Two types of Direct Fired Dryers
Tarmac builds two types of direct fired dryers, Parallel Flow and Counter Flow. We match the correct burner size to each dryer to assure quality production.
PARALLEL FLOW
Tarmac uses Parallel Flow dryers when the product size is small and travels down the dryer easily at higher interior dryer shell gas velocity. These dryers have higher gas discharge temperature to material temperature than counter-flow dryers. They are therefore less efficient. See parallel flow dryer drawing below.
COUNTER FLOW
Counter Flow Dryers are used when the product size is larger or the size is mixed from large to small. In these dryers, product moves down-hill against the gas flow. These dryers are more efficient and have lower gas discharge temperatures compared to the material discharge temperature (cool material enters the dryer and cools the gas flow as it leaves the dryer). The counter flow dryers are also used when the material temperature is over 400° F and the gas flow needs to be from 350 – 375° F maximum. 350 – 375° F is a safe gas temperature operating range for baghouse bags. See counter flow dryer drawing below.
PRE-ASSEMBLED FOR FAST INSTALLATION
Before shipping, full assembly of the drying plant at the shop is standard. We Pre-assemble the dryer shell, trunnions, and thrust rollers in order to ship from the factory completed and assembled on a frame. If you have not purchased a dryer frame you cannot receive an assembled dryer package. Tarmac supplies a dryer frame from the burner, between the trunnions, and back to the gas discharge plenum. This allows the dryer to ship with the frame, drive package, and burner which reduces installation days and freight costs, see photo to the left. Adding legs under the frame eliminates the cost and time of pouring large piers under the dryer. See Photos below to center and right showing structural legs. Photo to the right is final assembly with walkways, hand rails, pre-assembled burner fuel train.
Dryer safety: walkways and handrails
Rotary dryers need daily and weekly maintenance on components. Trunnions need daily grease and weekly adjustment. Managers must check burners for heat damage to wiring and instruments. Dryer interiors need to be inspected for worn or loose flights. For this reason, Tarmac offers bolt on walkways around the dryer with stairways (not caged ladders) up to access the walkways. Tarmac strongly urges you to purchase walkways for safety and to ease access to maintenance areas.
In conclusion, Tarmac International, Inc.’s team will help you determine the dryer that will work best for you, parallel flow or counter flow. Our dryer product line is assembled and shipped to you with a frame allowing the pre-assembly of the dryer shell, drive system, burner, and blower. You can purchase structural legs to delete the costs for pouring piers above grade to support the Dryer Assembly. Other options include walkways on all 4 sides of the dryer to facilitate safe maintenance.
CLICK HERE to request a call. Let’s talk about what fine points you need in a dryer.
CLICK HERE to take a look at some of the dryers we have working around the world.