SOME products — and specialty chemicals certainly fall into this category — require extremely well controlled transportation and handling to ensure quality levels and the safety of equipment and personnel around them. Organic peroxides are one such class of chemicals.
These chemicals have a wide range of uses, most particularly as catalysts and process initiators within the plastics industry. Probably the simplest possible example would be the catalysts used to start the hardening of the epoxy resin for fiberglass boat repair. Many others have much more exotic uses. In nearly every case, these chemicals are inherently unstable, breaking down into simpler compounds with little or no outside intervention, because the chemical bonds forming them are weak.
Organic peroxides decompose at predictable rates. Stored at the correct temperature, they remain useful for extended periods. Potential problems arise when the storage temperature is too low or too high. Stored at excessively low temperature, some peroxides separate and form solid precipitates. Allowed to become too warm, the rate of decomposition accelerates, which generates heat. As a chemical engineer explains it: “These compounds do not explode, but they do undergo catastrophic decomposition.”
Small amounts for big jobs
As is the case with most catalytic agents, it doesn't take a lot of organic peroxide to get a chemical reaction started. Unlike the basic feedstocks for plastics, which are transported in highway, rail, or marine container tanks, organic peroxides are usually packaged in gallon jugs, four jugs to a case. A standard refrigerated trailer is the most common mode of transport for highway delivery. However, like most things in the chemical industry, organic peroxides are transported worldwide, requiring the use of refrigerated marine containers.
It is at this point that concern for product quality and container ship safety becomes most noticeable. Peroxides can be transported in standard marine containers, but the value of the product is such that manufacturers want a higher level of protection than usually offered by an ordinary refrigerated container. In addition, shipping lines require that containers stuffed with peroxides be loaded aboard the vessel in a location that makes tipping them overboard possible if the refrigeration unit malfunctions.
No one, however, wants to throw away a whole container load of valuable product along with the container itself. A solution to this problem previously experienced in the chemical industry and one refined further for international shippers is to provide trailers or containers with backup refrigeration.
The latest of these refinements is a specially modified line of containers sold by Refrigerated Container Services, a part of the RCS Group in LaPorte, Texas. Primarily, RCS is a container maintenance and storage company with locations in California, Florida, New Jersey, South Carolina, and Mexico as well as headquarters near the Port of Houston. At the end of a trip, container operators deliver empty containers to RCS for cleaning, maintenance, and storage. Containers are thoroughly cleaned, the refrigeration unit inspected and serviced, and the container placed on ready standby until needed again by the carrier. Local cartage companies deliver empty containers to RCS locations and move them to shippers for cargo stuffing before delivering them to the port for vessel loading.
Two refrigeration units
In response to requests from chemical shippers, RCS has developed a container design to ensure proper temperature maintenance for organic peroxides. The company refers to its design as a Dual TS-500 container, because it uses two Thermo King TS-500 truck refrigeration units for cooling. Ten of the containers are currently in service, and more are under construction. So far, RCS has built the modified containers from both 40-ft and 20-ft marine boxes.
The Dual TS-500 container is actually a modification of a standard refrigerated marine container purchased from any one of a number of manufacturers worldwide. Of the containers already in service, the 40-ft boxes are high cube versions 9'6" tall, and the 20-ft boxes are standard specification containers 8'6" high. Built to standard ISO specifications, the containers have 63 mm of foam in the sidewalls, 95 mm in the ceiling, 80 mm in the floor, and 60 mm in the rear doors. In approximate English dimensions, that is 2½ inches in the walls, 3¾ inches in the roof, 3 inches in the floor, and 2⅓ inches in the doors.
In addition to mounting a pair of refrigeration units on the nose, modification of a container at RCS involves cutting away the front wall from a standard container and rebuilding it slightly more than three feet back from the front edge of the stacking frames. This provides the space to mount the refrigeration units, which extend 37 inches out from the front wall completely within the area protected by the steel stacking frames.
Inside the containers, RCS retains the stainless steel wall liners and three-inch T-section cross-flow floor. Unlike marine refrigeration units, the TS-500 units have an evaporator housing that protrudes 30 inches into the cargo space. With one unit mounted on top of the other, these two evaporator sections are surrounded by a stainless steel plenum to capture evaporator outlet air and direct it to the rear of the container through a standard highway air delivery chute. Without the plenum, evaporator outlet air from the lower unit would strike the front edge of the load and recirculate through the return air opening without reaching the rear of the container. An open bulkhead built of tubular stainless steel prevents damage to the evaporator plenum and provides a pressurized return air cavity. The evaporators, plenum, and bulkhead take up four feet of container interior space.
RCS chose the TS-500 truck units for this application, because, with scroll compressors, the unit offers the highest capacity available to fit into the limited space on the container nose. Capacity of the TS-500 is 18,000 Btu/hr at 0° F when running on diesel power and 17,000 Btu/hr at the same temperature running on electric power. In operation, both units run simultaneously at start up to provide rapid container cool down. After the thermostat set point is reach, the units run one at a time in tag team sequence.
A new floor is installed between the rebuilt front bulkhead and the lower front frame. This floor supports a 59-gallon tank for diesel fuel and a battery box for each of the two refrigeration units. Two electric fuel pumps move fuel from the tank to the units when they are running under their own power. Standard procedure is to use diesel power only during highway transportation or if electric power aboard ship is interrupted. Running on diesel power, 59 gallons of fuel will supply one unit for approximately three days in the Cycle Sentry start/stop mode. A stainless steel spare parts bin is mounted on top of the fuel tank. Typically, the spares box contains fuel pumps, fuel filters, fuel solenoids, belts, a complete unit control panel, and parts and service manuals for the refrigeration units.
Two monitoring systems are installed on the containers and refrigeration units. For refrigeration monitoring, the units have Thermo King's DAS digital data logger. Some have GPS locators. To make data extraction without a computer possible, the containers also mount conventional analog Partlow temperature recorders that inscribe temperature data on a paper disk.
Containers are tested for thermal integrity before and after modification to ensure that they meet international standards. Delivery takes 10 to 15 weeks if RCS has a box in stock when an order is received.