With the high price of petroleum, U.S. producers must maximize every dollar from a barrel of crude oil. Every 42-gallon barrel produces 45 gallons of petroleum products. Most of the petroleum is refined into gasoline (47 percent) followed by heating oil/diesel fuel (20 percent) and jet fuel (8 percent). After that, the percentages decrease significantly as refiners produce liquid and gas distillates for industry and construction. One of these is petroleum coke.
During the petroleum refining process, distillates are separated from residual oil after it goes through a vacuum distillation unit. These lighter grade petroleum products—such as hydrocarbon gases, naphtha and light and heavy gas oils—are separated from the oil in a coker unit. After distilling the desired petroleum byproducts, the remaining carbonaceous solid residue is petroleum coke, which has to be cut out of the coker unit with high-pressure water.
Petroleum coke (often abbreviated as petcoke), is more than 90 percent carbon and releases 5 to 10 percent more carbon dioxide than coal when burned. Petcoke, depending upon the grade—either high or low in sulfur and metals—is used as inexpensive fuel in offshore power generation, coal fired boilers or in the steel and aluminum industries. U.S. refineries produced more than 61.5 million tons of petcoke in 2011—enough to fuel 50 average coal plants each year.
Oil refineries usually store petcoke onsite awaiting pending sales or ship it to other companies that store and sell it. PABTEX, L.P., an affiliate of Kansas City Southern Industries, located in Port Arthur, Texas, is a major bulk-commodity handling facility and vessel-loading terminal. It specializes in exporting petroleum coke and receives petroleum coke by train from one of several refineries in the area. On its 29 acres of outside storage, PABTEX can store 500,000 tons of petcoke before transferring it to shipping terminals for transport to global end users.
When the raw petcoke is transported to PABTEX’s terminal in bottom dump railcars, a system of shakers breaks the petcoke into smaller chunks that are easier to transport on a conveyer system. Below the shakers is the open conveyer shaft that is 70 to 80 feet below the ground.
Because rainwater often fills the conveyer shaft, a large sump was sunk into the bottom of the shaft to ensure that water could be pumped into an existing retention pond. With the shakers directly above the bottom of the conveyer shaft, pieces of petroleum coke fall into the shaft and eventually wash into the sump.
Todd Wilkes, the maintenance supervisor of Savage Gulf Services, which operates PABTEX’s Port Arthur terminal, had tried several submersible pumps in the conveyer shaft sump. However, coke is similar to coal fines when pumped—very abrasive and easily separates into a slurry. Because most submersible pumps are cast iron, they cannot hold up in this demanding service. Petcoke is too abrasive, and without an integral agitator, solids settle-out and clog the pump.
A 15-horsepower, high-head, hard metal agitator submersible slurry pump was suggested by Tim Weber, sales manager of industrial fluid handling distributor, Saladin Pump, as a solution for Wilkes’ problematic sump application.
Heavy-duty submersible slurry pumps with agitators have been applied to many similar abrasive applications—such as lime slurries, mill scale coal runoff sumps, wash-down sumps and ash transfer. Its success can be attributed to two important features:
- Optimum wear resistance—all wetted parts are constructed of abrasive-resistant, 28-percent chrome iron (600 Brinell, 57 Rockwell C) for maximum wear life. In addition, a replaceable hardened wear plate is located on the suction side, where erosion would cause a loss of pump performance.
- Maximum solids-handling capability—an integral agitator fluidizes settled solids into a slurry, making them easier to pump with less chance of clogging. The semi-open impeller handles abrasive solid concentrations as high as 70 percent by weight.
The submersible slurry pump achieves maximum service life because of numerous design features, such as:
- Class H motor insulation and built-in amperage (full load amp) and temperature overload protection
- Double silicon carbide mechanical seals in a separate oil filled seal chamber
- Heavy-duty lip seal—additional protection for the mechanical seals
- Stainless steel shaft and shaft sleeve, which provides maximum wear and corrosion protection
- Pump volutes cast from hardened ductile iron (300 Brinnell hardness), which is twice as abrasive resistant as standard ductile iron with extra thick walls where pumped slurry enters the discharge
Another key feature of the submersible slurry pump is its top-discharge design. Slurry pumps are considered utility pumps, and they are frequently dragged from one site to another. Other pumps have side-discharge connections that can break off or be damaged as it is pulled and pushed into place.