Baker Process has completed performance testing and optimising an Eimco Extractor Horizontal Belt Vacuum Filter (HBVF) at BHP Coal’s Saraji coal mine in Queensland’s Bowen Basin. Part of a new processing facility recently commissioned at the mine, the HBVF is, according to Baker Process, the largest Eimco filter of its type supplied to date to any Australian coal processing plant.
Baker Process (formerly Eimco) has been supplying HBVFs since 1962 and has installed more than 800 units worldwide. The company designed, built, installed and commissioned the Saraji machine, which will provide increased filtration capacity to dewater the additional fine coal produced by the mine’s new flotation plant. The new plant, valued at $18 million, comprises the HBVF, eight 4m-diameter Microcel flotation columns, four 1m-diameter dewatering cyclones and a range of ancillary equipment. The Microcel plant replaces Saraji’s conventional flotation cell facility and was designed, constructed and commissioned by project leader Taylor Woodrow Constructions, formerly Birtley Engineering.
According to Birtley general manager Graham Colliss, the Eimco filter is an integral part of the new plant. “The filter is performing to expectations and should make a significant contribution to the flotation plant achieving its goal of increasing the mine’s recovery rates,” he said.
The HBVF measures 4.2m in width, 31.4m in length and offers a filtration area of 103m². Under specified duty requirements, the unit is expected to produce dewatered cake throughput of up to 160 tonnes per hour with a moisture content of less than 22% w/w.
In operation, feed slurry with a moisture content of 75-80% w/w is distributed over the full width of the machine’s filter media: a belt filter-cloth overlaid on a perforated drainage belt. A vacuum pump, connected to a stainless steel pan mounted below the upper section of the horizontal belt loop, draws filtrate through the belts as concentrate is conveyed along the unit. The filtrate collects in the vacuum pan before being discharged. Cake is discharged at the end of the filter. During the return journey to the feed mechanism, the drainage belt and filter-cloth are separated and independently washed by a series of automatic, high-pressure spray heads. This prevents solids blinding and extends the life of both the belt and cloth.
The HBVF’s operating speed is determined by Saraji’s filter cake thickness throughput requirements. Designed for continuous operation, the machine is PLC-controlled and fitted with a variable speed drive capable of driving the belt at speeds from 0.2-0.6 m/sec.
Featuring a heavy-duty galvanised steel frame and stainless steel construction for virtually all other internal and external metal components, the machine is designed to resist corrosion caused by the aggressive media present in coal, thereby minimising maintenance requirements.
Saraji’s acting plant metallurgist Michael Taylor said the filter was operating reliably in an aggressive environment. “We don’t expect scheduled maintenance to be a problem, as the machine’s components are readily accessible,” he said.
Commenting on the HBVF’s contribution to the operation of the new processing facility, Taylor said: “The new plant was designed to provide a 4% increase in recovery rates. With the additional capacity provided by the Eimco filter, we’re actually achieving a yield increase of 4.5%.”
