D-1300Thermal Drying

How it works

1. Why anyone bothers — A tonne of cake at 22 % dry solids is 780 kg of water you are paying to cart away. Dry it to 92 % and the same solids weigh a quarter as much, stop smelling, stop rotting and become a fuel. Everything after this is the price of that.
2. The water left is the hard water — Dewatering takes the water between the particles, and stops when only the water inside the cells is left. No press, no centrifuge and no amount of polymer will take that — it has to be boiled, and boiling is 2.26 MJ for every kilogram.
3. The sticky phase — Between roughly 40 and 60 % dry solids the cake is neither pumpable nor free-flowing: it is glue. It climbs screws, welds itself to heating surfaces and stops dryers dead. Watch the band on the scale below — every machine here has to carry the cake through it.
4. Two ways through it — A convective belt dryer never enters the band: it mixes dried granulate back into the wet feed until the mixture is already past 60 %. A conductive dryer drives straight through on torque, which is why its gearbox is the most expensive part of it.
5. The off-gas decides the project — Convective drying needs about four kilograms of air for every kilogram of water, and all of it leaves humid and smelling of sludge. Conductive drying makes a vapour stream you can condense. On a site with houses nearby that single difference usually settles the choice before the fuel bill is opened.
6. The product is a fuel — Dry solids from undigested sludge carry 20–24 MJ/kg; digestion burns off the volatile fraction and leaves 10–13. Coal is 25–30. From undigested sludge the granulate can carry more energy than the dryer burned to make it, which is the whole argument for drying rather than landfilling; from digested sludge it usually cannot. Move the calorific value and watch the bars on the right cross.
7. Convective belt — Large works making a granulate for sale. Gentle, low temperature, and it steps around the sticky phase by mixing dried product back into the feed. Hot air driven through a moving bed.

Design parameters

The panel opposite runs the same correlations as the D-1300 design sheet, so the animation and the calculator cannot disagree. Every parameter below is live — drag one and the picture responds.

The full D-1300 design calculation — governing equations, accepted envelopes and the worked sizing — is in the design calculator workbook. Everything on this page stays free.