Due to the ever increasing population in the southeastern US, road building and maintenance will generate a steady demand for aggregate.
Due to the ever increasing population in the southeastern US, road building and maintenance will generate a steady demand for aggregate.

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According to one of the largest producers of stone aggregates in the US aggregates are being used more to protect our environment. When aggregate company Midsouth Aggregates needed to replace a submersible pump that pumped quarry water to a stone washing tower, they also looking to increase discharge flow. BJM’s was confident that its 6 in KZN hard iron submersible pump could do the job.

Midsouth Aggregates, headquartered in Birmingham, Alabama USA, produces aggregates by quarrying naturally occurring rock deposits. Granite and limestone are extracted by carefully controlled blasting, then are crushed and graded to produce stones of different sizes to be used in various applications. From concrete, wall board and roofing tiles to the roads we drive on and the bridges we cross – all use aggregates.

Midsouth Aggregates supplies aggregate products to the Alabama, Georgia, Tennessee and Florida Departments of Transportation, the US Army Corps of Engineers and the Federal Aviation Administration. Due to the ever increasing population in the southeastern United States, road building and maintenance will continue to be a top priority and will generate a steady demand for aggregate.

The challenge

A Midsouth Aggregates plant in north central Alabama needed to replace a submersible pump that pumped quarry water to a stone washing tower. The plant also wanted to increase the discharge flow of the pump. The existing pump had a 4 in discharge. The new pumping conditions were 1000 GPM, 50 feet of vertical lift and 500 feet of horizontal run to the water tower. The manufacturer of the existing pump would have to use a pump with an 8 in discharge in order to meet the new conditions; BJM could accomplish the job with a 6 in KZN.

Aggregate from bedrock deposits are classified as hard, medium-hard and soft. After it's harvested, quarry rock is processed, which involves crushing, screening and cleaning. Massive stones are sent along a vibrating feeder from the feed bin to a jaw crusher for rough crushing. The smaller rock is then transferred by conveyor to a cone or impact crusher for secondary crushing. The fine crushed stones are transferred to a vibrating screen for separation by size. Stones that meet the specific requirements of the finished product are transferred to a finished products pile. The remaining stones are sent back to be crushed again. Dust removing equipment is often used as an additional environmental protection.

The solution

Scott Morrow, a dynamic fluids transfer distributor specializing in pumping equipment, suggested a BJM Pumps submersible built specifically for hard-to-handle rock slurries. Midsouth Aggregates didn't have any experience with BJM submersibles, so Morrow provided information on the BJM KZN hard metal slurry pump. Specifically, Scott suggested the BJM KZN220-30 HP high head, hard metal agitator slurry pump.

Quality features

Because of BJM's wide experience in pumping coal slurries, line slurries and a variety of abrasive products found in wash down sumps, Midsouth Aggregates decided to give the pump a try. The quality features built into BJM’s KZN slurry pump series were also factors in the decision and include the following:
• Optimum wear resistance. All wetted parts are constructed of abrasive resistant 28% chrome iron (600 Brinell, 71 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% by weight.

Numerous design features

Also weighing into the decision was the fact that the KZN slurry pump achieves maximum service life because of numerous design features such as:
• Class H motor insulation and built in amperage (FLA) and temperature overload protection;
• Double silicon carbide mechanical seals in a separate oil filled seal chamber;
• Heavy duty lip seal that provides additional protection for the mechanical seals;
• Stainless steel shaft and shaft sleeve that provide maximum wear and corrosion protection;
• Pump volutes cast from hardened ductile iron (300 Brinell hardness), which is twice as abrasive resistant as standard ductile iron with walls that are extra thick at the point where pumped slurry enters the discharge.

Another key part of the pump construction is the semi-open impeller. Also made of 28% chrome, the slurry impeller must have the ability to work in tandem with the agitator to pass the aggregate through the pump and out the discharge. The agitator’s ability to keep solids suspended in the fluid being pumped, as well keep the suction clear of clogs greatly aids the pumping action.

Additionally, Midsouth Aggregates liked the BJM vertical top discharge feature of the KZN220 agitator pump. The existing submersible pump in Midsouth Aggregates' application was a side discharge 90° elbow pipe that had a high wear area on the 180° turn. BJM’s vertically positioned top discharge KZN promotes optimum wear resistance along the discharge path as well as use of the fluid being pumped for natural cooling of the pump's internal motor functions. BJM’s vertical design also allows for the sump to be pumped down to within inches of the bottom.

Further, the vertical discharge and the 22.75 in diameter of the KZN220 creates a space saving footprint and allows installation in the tightest of manholes.

Conclusion

Midsouth Aggregates' Alexander City quarry plant manager Shane Horton mentioned that the BJM KZN220 has been in operation for more than three years. “We start the pump when the day begins and shut it down when we leave at the end of the day," he said. The pump's ability to pick up silt-laden water from a groundwater pond and pump it to the rock screen washing tower has provided trouble-free operation.

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