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Using a Steamroom To Sterilize Pallets of Styrofoam Seedling Container Blocks
Steam generated by a 9.5-horsepower (about 400,000 British thermal units per hour) propane boiler (figure 10) flows through a 1-inch black pipe installed along the bottom of two sides of the room (figure 11). The steam pressure was reduced from the standard 40 pounds per square inch at the boiler to 10 pounds before the steam entered the room. Holes 1/16-inch in diameter were drilled in the pipe every 6 inches to release the steam. Galvanized steel sheets installed behind the pipes protected the foam insulation from the steam.
![[photo] Steam boiler used to heat sterilization room.](images/fig10.jpg)
Figure 10—A 9.5-horsepower steam boiler was
used to heat the sterilization
room.
![[photo] Pipe in sterilization room distributing heat.](images/fig11.jpg)
Figure 11—Black pipe distributes steam in the
sterilization
room. The pipe runs along the bottom of
the side
walls. Steam leaves the pipe through holes
(1/16 inch in
diameter) drilled into the pipe.
Remote electronic controls set the temperature inside the room. Although the temperature probe to the electronic controller could be placed anywhere in the room, we put it in the middle styroblock of a group of styroblocks on a pallet to ensure that the interior styroblocks were heated thoroughly. An electric water feed valve, chemical feeder, blowdown tank, and a water softener were added, as were relief valves and miscellaneous plumbing, including plumbing for the propane supply. Converting the room from cold storage to a styroblock sterilization room cost about $24,000.
The time required to heat the room to sterilization temperature (160°F) depends on the boiler size, room volume, and starting temperature. With an initial temperature of about 40°F, it takes about 15 hours to bring the sterilization room at Lucky Peak Nursery up to 160°F. Reheating the room for additional loads will not take as long. The walls, ceiling, and concrete floor will retain heat, which should reduce reheating time considerably. It is advantageous to fill the room with as many styroblocks as possible per load. The room holds about 4,000 styroblocks. The blocks should remain in the room for several hours at 160°F to ensure sterilization.
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