Rinker Materials, Florida's largest producer of building materials and one of the leading U.S. manufacturers, decided to make a major investment back in 1992. The company purchased a pneumatic ship unloader from Fuller-Kovako Corp. for unloading cement from cargo ships at its terminal in Port Everglades, Florida.

Previously, Rinker had contracted with chartered vessels that employed onboard pneumatic systems. However, for nearly six years, Rinker used the unloader to successfully convey nearly 3 million tons of cement. Downtime had been non-existent during frequent periods of continuous operation, and only routine maintenance has been required.

According to Scott Maguire, terminal manager for Rinker Materials, "When we need this unloader to perform, we really need it. Unloading a cargo ship full of cement is a six-day, around-the-clock operation. The faster we go, the less we have to pay in docking fees, and the sooner we can fill product orders."

The ship unloader owes much of its performance record to its conveying system, whose key components include four vacuum pumps and two compressors. One of the vacuum pumps is a standby unit. The dependability of the compressors is most critical, in that the failure of either will cut capacity in half and double unloading time.

To supply the pressure and the vacuum, Rinker's ship unloader uses single-stage, rotary screw compressors from Aerzen USA. Because the rotors do not require any lubrication oil, there is no possibility of air contamination within the compression system.

The compressors used in Rinker's unloader are intended for at least five years of continuous operation before needing a first scheduled servicing. Typical field experience with these compressors shows continuous operation is well over five years.

"This has been Rinker's first experience with Aerzen compressors," said Maguire. "The only maintenance requirements have been routine oil and filter changes. Clearly, their performance had been a major contributor toward the ship unloader's considerably lower-than-anticipated operational costs."

Maguire also noted that Rinker maintains a clean plant environment, however, the process of transferring any powder such as cement creates airborne dust that can contribute to machinery problems. These compressors are widely used in cement plants and engineered for the harsh conditions typically found in these facilities.