High Pressure Filtration

With the successful application of the Tube Press on fine china clays, further test work and product development was carried out on many mineral and mineral by-product applications. A laboratory size Piston Press was designed to test the wide variety of samples and determine filtration characteristics for each. Testing pressures of 2000 PSI (140 bar) enable optimum filtration pressures to be determined. Of the various minerals tested, coal fines were among those identified as having excellent characteristics whereby higher filtration pressures than currently achievable with existing systems resulted in greater moisture reduction in the cake products.

Australian Coal Washery Trials Test

The Tube Press has proven that coal fines can be processed to achieve acceptable moisture content levels and produce a hard, surface dry filter cake. The saleable filter cake product can be added to the coarser clean coal product, reducing the volume of disposable refuse, returning clean process water to the plant, and increasing overall plant product output.

Bench scale tests on ultra-fine waste coal slurry were conducted for an Australian coking coal producer, at Clough Mining Services Perth, Australia laboratory.

Trials Tube Press Test Description

Slurry feed at the Australian coal washery used for the Tube Press tests came from classifying cyclone overflow processing the fine coal flotation concentrate. On each series of tests, two different Tube Press filtration cycles were evaluated to determine the minimum achievable moisture content:

Cycle 1 filtration without air purge

Cycle 2 filtration with air purge

The Typical Tube Press cycle for both cycles consisted of the following steps:

Series 1 – Test Results

Feed size (one sample) of fine coal feed to the Tube Press is shown in Figure 2.

Cycle 1 – Filtration Without Air Purge

Slurry feed concentration variations did not aid test results and certainly contributed to moisture levels averaging higher than that sought. Tube Press throughput, however was adequate.

Cake Moisture Content,
Average) 22%
Range: 20.1 – 23.8

Solids Throughput, Kg/Hr (lbs/hr)
Average: 810 (1785)
Range: 690-1050 (1520-2315)

Cycle 2 – Filtration With Air Purge

Again, variations in feed solids in the slurry affected test results, but the use of air purge enabled a low filter cake moisture (15.5%) be attained. Extended HP times to achieve the low moisture reduced the filter cake production rate to 750 Kg/Hr (1655 LBS/Hr).

Further tests with adjusted cycle times increased filter cake production rates to 1016 Kg/Hr (2240 LBS/Hr), while cake moisture was maintained below 20%.

Cake Moisture Content,
Average: 16.5
Range: 15.2-18.1

Solids Throughput, Kg/Hr (lbs/hr)
Average: 750 (1655)
Range: 440-1016 (970-2240)

Series 2 – Test Results

The Series 2 test work conducted at the Australian coal producer was required due to plant operation modifications, which resulted in a change in fine coal sizes in the Tube Press slurry.

Cycle 1 – Filtration Without Air Purge

The fine coal feed tested for this series was easily dewatered to moisture contents below 20%.

Cake Moisture Content,
Average: 19.2%
Range: 18.6 – 19.7

Solids Throughput, Kg/Hr (lbs/hr)
Average: 1520 (3350)
Range: 1308-1804 (2885-3980)

Cycle 2 – Filtration with Air Purge

Since moisture contents of less than 20% were achieved without air purge, these tests were conducted strictly to identify the lowest moisture level attainable with one air purge cycle. A moisture content of 13.4% was achieved, but solids throughput was only 964 kg/hr (2125 LBS/Hr), due to the extended HP times.

Cake Moisture Content,
Average: 15.0
Range: 13.4 – 19.1

Solids Throughput, Kg/Hr (lbs/hr)
Average: 1226 ((2705)
Range: 964-1460 (2125-3220)

Effect of Varying Feed Solids Concentration

The Series 2 tests were conducted using a feed tank to maintain an even percent feed solids to the Tube Press. This also enabled the feed solids concentration to be varied by controlled addition of dilution water to the feed tank. Maintaining cycle times, a series of tests were run to observe filter cake moisture contents and Tube Press throughput. The results are shown in Figure 5.

Discussion of Test Results

The Tube Press tests were conducted on coal samples of different sizes, yet with the range of -35 micron (-400 mesh) coal ranging from 63 to 96%, the Tube Press was capable of producing filter cake products in a series of tests that were less than 20% moisture.

Special Process Features

The standard Tube Press cycle described above can be extended to permit the use of either an air purge cycle, a cake wash cycle, or both. Air purge can be used to further reduce the cake moisture content. Cake wash is typically used if removal of soluble salts or maximum recovery of valuable filtrate from the filter cake is desired

Denver Laboratory Piston Press

Laboratory test work is conducted with a bench scale model of the Tube Press, which can operate at pressures ranging from 8 to 275 bar (250-4000 psi). Sample charges are typically 200 – 400 ml per test. The Piston Press tests establish moisture content and cake characteristics, as well as filtration rates for particular slurries.

Denver Tube Press Trials Test Unit

Piston Press tests assume that the slurry tested is typical of plant feed requiring processing. To confirm Piston Press tests in the production environment, a mobile 200 series Tube Press, 1.8 m (5.9 ft) long, complete with all ancillary pumps and controls, is available for pilot testing.