Las Coloradas, located on the northern edge of the Yucatán Peninsula, Mexico is home to salinity concentration ponds belonging to Industria Salinera de Yucatan SA de CV (ISYSA), a solar salt extraction mining operation that harvests up to 750,000 t of salt a year at this site. The salt harvesting process begins with water flowing from the Ría Lagartos estuary into a 20 km chain of ponds connected by pumps and canals. The first stop is a string of 26 evaporation ponds where the water is held until evaporation begins, thus increasing its salinity. As the water reachs optimal temperature and salinity, ISYSA uses a series of pumps to move the water to 15 crystalliser ponds.
The salt harvesting operation kicks into gear as soon as the salt crystals are exposed. ISYSA harvests salt twice a year with the first and largest harvest beginning around March or April and the second around September or October. Once kicked off, the salt harvesting operation runs 24/7. The harvesting is completed as quickly as possible to avoid rainfall. Rain, or even worse, a hurricane, can significantly set harvest back by dissolving salt crystals and adding fresh water to the ponds.
In the harvesting phase, the operation begins by using a motor grader to push salt into 250- to 350 mm-high windrows. The grader operator leaves about 2.5 cm of salt on the bottom of the pond to avoid mixing dirt from the pond bed with the harvested salt. A heavy-duty conventional farm tractor follows, pulling a special salt harvester capable of picking up the salt windrows and conveying the salt into a hauler, harvesting 300 t of salt an hour. The unit works by scooping salt from the salt windrows onto a conveyor which transfers the material into a bottom dump trailer pulled by a conventional off-highway truck/tractor.
Three custom-engineered tractor trailers constantly rotate between the salt harvester and the raw salt processing plant, ensuring continuous salt harvesting and as little harvesting downtime as possible. When a trailer is filled to about 60 to 70 t the harvester briefly stops, the loaded trailer pulls away and the next trailer is pulled into position before the salt harvester resumes operation. The bottom dump trailers dump the salt into a hopper connected to a salt washing and processing plant. The processing plant rinses the salt using saturated salt brine to prevent any harvested salt from dissolving. Connected conveyors then dump the salt into massive piles that rise up to 14 m above the landscape.
This harvesting process has improved considerably over the years. Until 2013 ISYSA used five on-highway bottom dump trailer trucks with capacities of 13 t or 26 t. The trucks’ low capacity slowed salt harvesting production. Using the five trucks, just 4,000 t of salt could be harvested on a really good day, with the first harvest of the year taking about five months to complete. Salt harvester idle time was high as the trucks filled up quickly and the salt harvester was constantly stopping and starting.
Because much of the harvested salt is meant for human consumption, it is also very important that there are no harvesting equipment fluid leaks or equipment contaminants lost in ISYSA’s salt harvesting process. Thus, the first shift every day carefully cleans and inspects harvesting equipment for any issues. With the exposure to the extremely corrosive salt environment, the previous on-highway bottom dump trailer trucks required regular repairs, particularly involving the pneumatic door cylinders. The previous trucks were down for maintenance up to 30% of the time.
ISYSA management realised that adding new efficiencies to the process was important for the future of their operation. They also wanted to limit the environmental impact by reducing needless idle time while using tractors that are more efficient and decrease emissions. ISYSA management knew that the long-term success of the salt mine relied on finding a more efficient trucking solution. That solution required higher capacity bottom dump tractor trailers that could handle the desired salt production. Management sought out Philippi-Hagenbuch, Inc in 2012 and requested a solution to double their salt production and minimise maintenance issues. The Peoria, Illinois-based manufacturer designs and builds such custom equipment for off-highway haul trucks.
The two companies worked together to assess ISYSA’s needs and design a suitable bottom dump trailer. The trailer needed a 70 t load capacity. Trailer components would also have to be able to withstand the corrosive salt environment and require only minimal maintenance. Additionally, the tractor trailer needed to be fairly narrow and have a lower load height than a typical 70 t capacity bottom dump trailer to accommodate ISYSA’s existing salt harvester. Following initial design discussions, PHIL representatives visited Las Coloradas to see ISYSA’s salt harvesting and processing plant firsthand and to determine the full design-scope and engineering requirements for the fully customised project to become a reality.
In 2013, PHIL delivered three custom engineered bottom dump tractor trailer trucks to ISYSA. To fit ISYSA requirements and to match with the existing salt harvester, these 70 t capacity trailers were 12.9 m long; 4 m wide; 3 m high; included a struck volume of 46.6 cubic metres; and a 2:1 heaped volume of 57.4 cubic metres. The trailers also initially featured long goosenecks designed for proper weight distribution with the three tractors ISYSA ordered to pull them.
To minimise the effects from the corrosive salt hauling environment and to protect the salt hauling areas of the bottom dump trailers, PHIL used a unique Duracorr stainless steel plate. Additionally, SSAB’s Hardox® 450 high-strength steel was used for the overall trailer structure, consequently minimising overall bottom dump trailer weight. Lowering trailer weight and associated ground pressures in the drained salt ponds was yet another important ISYSA concern to prevent risks of the equipment getting stuck in the soft pond beds.
In order to achieve a 70 t capacity and a low load height, PHIL designed the trailers with vertical side walls instead of common inward sloping side walls. A teepee-shaped structure lengthwise in the center of the trailer accommodated full-trailer-width clamshell doors, which facilitate even and quick “full” trailer-width material dumping.
A single hydraulic cylinder controls the trailer’s clamshell doors as opposed to the typical two pneumatic cylinders featured on ISYSA’s old trucks. The single cylinder opens both doors in unison, minimising trailer rocking that can happen as a result of opening only one door at a time. The doors also feature an over-centre door locking system which minimises forces on the door’s hydraulic control cylinder when the trailer is loaded.
“It wasn’t long before ISYSA noticed big improvements resulting from the new bottom dump trailers. Daily production doubled to a steady 8,000 t per day with the three new trailers. In addition, the first harvest of the year now takes only about three months as opposed to five months with previous equipment.”
“Philippi Hagenbuch has always been a custom solution provider,” said LeRoy Hagenbuch, Philippi-Hagenbuch Co-Founder and Chief Engineer. “These trailers are a great example of our custom engineered approach. ISYSA had a need they wanted to solve. They looked at other manufacturers, but no one was willing or able to develop a solution. We understood their problem and worked closely with them until we could deliver exactly what they were looking for.”
The mine’s maintenance department also took a liking to the new equipment. PHIL built the trailer with all vulnerable parts sealed from the corrosive environment. The single door cylinder and hoses are protected and require no greasing or maintenance. The trailers use rugged 75 mm pins surrounded by 12 mm wall bearings for all door pivots. In addition, the trailers have sealed, oil-cooled disc brakes and an oil brake control line, both of which minimise the risk of leaks.
“Maintenance is minor on the PHIL trailers, especially compared to the pneumatic cylinders on the old equipment. Those previous trucks had a number of mechanisms that often broke down,” said Mario Guzman, Jefe de Transporte. “We went from the equipment being broken for 30% of the time to excellent up-time with the new bottom dump trailers.”
Though happy with the new bottom dump trailers, ISYSA did have problems with the used trailer tractors they had originally chosen for this project. The used tractors required a lot of maintenance and were not the ideal choice for the environment. When management looked into purchasing new Caterpillar tractors, they again reached out to PHIL for help customizing the new tractors to work with their PHIL Bottom Dump Trailers. PHIL agreed, developing and sending the Las Coloradas operation kits to install fifth wheel hitch arrangements on their new Caterpillar tractors’ chassis. The kits PHIL supplied also included components to modify the length of the bottom dump trailer tongues to optimize weight distribution on the updated truck-trailer-chassis combination.
ISYSA management said the improved production speed and reduced maintenance from the new tractor trailers have helped ensure a fast return on their equipment investment. Instead of having to scramble to keep up with the salt harvest and stay ahead of weather issues, crews now periodically finish harvesting salt ponds faster than others can be drained. This has led plant management to look for further ways to increase salt production.
