ASARCO Inc., El Paso, Texas facility is over a hundred years old and is one of the oldest in the nation for copper smelting. However, the old is combined with the new in helping this facility meet strict environmental requirements. The El Paso facility, situated in a valley inhabited by nearly two million people, was originally built to handle ore from Mexico. The facility consists of two sulfuric acid plants, a 1972 Lurgi and a 1978 Monsanto.
According to Fred Scott, acid supervisor at the El Paso facility and a 31-year veteran of the sulfuric acid industry, state emission standards are going to get more stringent.
“The amount of sulfur dioxide that facilities are allowed to emit into the atmosphere is going to get a lot stricter,” he said. “Some of the new sulfuric acid plants have bigger preheaters that can take the entire capacity of the plant as they can heat up all of their beds, leaving virtually no tail gas.”
Currently, if a plant’s sulfuric acid emissions exceed 600 parts per million, it is shut down. Scott said this is a big concern because the materials and cost of operations are going to be astronomical.”The size of the equipment, the amount of catalyst in the beds and the maintenance are going to be very critical,” Scott explained. “If you lose a heat exchanger due to a few leaking tubes, for example, the amount of tail gas is going to shut your plant down.”
There are some simple tests that can be run across heat exchangers to determine leaks. However, these conventional tests are not perfect and have been known to miss leaks.With the help of the latest in acoustic emission monitoring equipment, heat exchanger leaks can now be found quickly and precisely with very little downtime.
“With the acoustic emission monitoring equipment, we can check 2,000 tube units in 15 minutes and determine which tubes are leaking and need to be plugged,” Scott explained. “But in order to enter the exchanger, it must be cooled to ambient temperature which can take from 24-hours to 36-hours.”
Because it takes such a long time to cool down a heat exchanger, Scott said they brought in VIP International to save the downtime with its high temperature entry process.
With VIP’s process, a heat exchanger only needs to be cooled to 550 degrees Fahrenheit from its original 850 degree temperature. VIP is the only company providing this service to sulfuric acid plants.
Scott said it takes approximately six hours to cool a heat exchanger to 550 degrees, at which time a VIP International crew was able to locate and plug leaking exchanger tubes while the plant was still hot.”VIP’s process saves us a lot of time,” Scott said. “On a recent turnaround, VIP used the acoustic emission equipment to spot leaks immediately and we did not have to pressure test each tube. With this acoustic emission equipment, you can pick up the sounds of leaking tubes and have them all identified within 20 minutes,” Scott added.VIP’s high temperature entry was used to eliminate the exchanger cooling process, which can take several days. Once the exchanger was cooled, a very time- and cost-consuming pressure test was required to check for leaking tubes, sometimes up to 2,000 of them.
“The advantage of VIP’s high temperature entry and the use of acoustic emission equipment is that it flat out saves time and money,” David “Hoss” Maddry, VIP International vice president, said. “Another advantage of VIP’s acoustic emission leak detection program is that we can detect leaks in the tube sheet also.”
To check a leaking tube sheet conventionally requires pressure testing the whole vessel or using a dye penetrant, a time consuming process. Maddry explained conventional methods result in lost time and production, while VIP’s methods limit downtime and are more efficient at locating tube and tube sheet leaks.
In addition to dealing with 550 degree temperatures and the need to expedite tube leak repair, VIP technicians must also systematically inspect and identify nearly 2,000 tubes per vessel entry.”We have to have good communication in order to perform our mission well,” Mark Thompson, VIP superintendent on the ASARCO turnaround, said. “In order to remove confusion when dealing with a few thousand tubes, we make a concise blueprint of the vessel.”
Using the blueprint, VIP crews identify a reference point within the vessel to easily coordinate tube leak identification. Thompson explained that the crew in the vessel inspects each tube and delays their findings to a console operator who relays that same information to a man on the top of the exchanger. The man on top of the exchanger, who also has a blueprint of the vessel, then plugs any tubes that have been found to be leaking.
To do such an astronomical task is not easy. Through the use of proper equipment and a high degree of training, VIP International crews are able to enter high temperature vessels safely.
Stanley “Bubba” Miller, operations manager of VIP International, was a co-developer of high temperature entry in 1981.
“We originally developed this capability so we could repair broken or fallen grates as well as doing emergency catalyst screening in high temperatures,” Miller said. “Normally it takes 24 to 48 hours to cool a convertor to ambient temperature, but it only takes four hours to cook it so we can enter. From there it was a natural fit to move into another high temperature scenario,” he added.
With the combination of technology – acoustic emission monitoring equipment and high temperature entry capabilities – VIP International is able to save sulfuric acid plants time and money.
“VIP has definitely found a better way to find exchanger leaks and cracks,” Scott said.