The fixed-bed workhorse — screened granules in a vessel, treating a continuous flow to a steady outlet. Backwashed while in service, and reactivated once it is spent.
How much gets removed depends on how long the stream and the carbon actually stay together.
Contact time, bed depth and flow speed are designed together, not as three separate numbers. Shorten any one of them and the active zone of the bed shifts toward the outlet, letting contaminants through sooner — no matter how much capacity the carbon still has left. That's why a bed is sized against real test data on the actual stream, not a catalogue capacity figure.
900–1,100
mg/g Iodine
Typical iodine number across the granular range, coal and shell.
The bed is designed once and lived with for years.
The stream is tested against candidate grades to work out real capacity and how breakthrough will behave. This is what turns a catalogue number into an actual bed size.
Contact time, bed depth and flow speed are fixed together against the design flow, with mesh size chosen for the pressure drop the installation can handle and the internals already in place.
The bed runs with outlet quality monitored, and is backwashed on pressure drop or on a schedule to clear fines and re-settle. Backwash rate comes from the granule density, not copied from another plant.
Spent carbon is flushed out and either reactivated or disposed of. Planning that route at design time is why hardness and density are part of the original spec.
Feedstock and grain size are chosen against the duty and the vessel.
Bituminous · 8x30, 12x40
A wide pore range and high mechanical strength for heavily loaded, coloured streams, and for beds that will go through several reactivation cycles.
Coconut · 8x30, 12x40
Very high micropore volume, very low ash and very high hardness — for trace-level polishing and drinking-water duty where the outlet target is tight.
4x8 · 4x10 · extrudates
Coarse grains and pellets chosen for low pressure drop in deep vapour-phase beds, released on CTC activity rather than iodine number.
What each property actually governs once the bed is running.
Micropore capacity — the figure most specs lead with. On its own it says nothing about how the granule will behave hydraulically.
The single most important mechanical choice. It sets pressure drop, how much the bed expands on backwash, and the length of the active zone.
Governs how much fine dust builds up over the service life, and whether the granule survives flushing, transport and thermal reactivation.
Fixes how much carbon a vessel holds, and so the bed life. It also sets the backwash rate needed for proper expansion.
How tightly sized the grains are. A narrow size range settles cleanly on backwash and keeps pressure drop predictable across the run.
Determines how much of the delivered tonnage is actually carbon — the figure a fill quantity should be checked against.
By balancing speed against pressure drop. A finer grain shortens the active zone and improves outlet quality, but costs more pressure drop and can exceed what the underdrain can hold back. In practice the vessel internals and available pump pressure narrow the choice before the carbon does.
For most liquid duties, ten to twenty minutes is the working range, with dechlorination running much shorter and tough trace organics running longer. The figure is confirmed by testing on the actual stream.
Based on pressure drop rather than the calendar, though a minimum schedule keeps the bed from settling too tight. The backwash rate has to lift the fine dust without carrying grains out over the weir, and is calculated from granule density and water temperature.
Yes, provided the grade was chosen with that in mind. Thermal reactivation restores most of the original capacity, with some yield lost each cycle — a hard, dense granule is what makes several cycles worthwhile. Carbon that has adsorbed certain contaminants may be excluded from reactivation for regulatory reasons.
By sampling at the outlet and, where fitted, at points partway down the bed, against a set breakthrough level. Sampling partway down gives early warning before the outlet actually shifts — which is what makes a planned changeout possible.
Send us your stream analysis, vessel dimensions and design flow. We will come back with the grade, bed size and changeout interval your duty actually needs.
