C&D Recycling Line Design: Why Equipment Order Decides Your Recovery Rate

Two C&D recycling plants can own the same equipment list and produce completely different results. Sequence is one reason: each machine in a sorting line exists to make the next machine's job possible, and material placed in the wrong order gets contaminated, damaged, or lost to residue. The material itself is the other — arguably bigger — reason: every line is designed from its throughput, its composition, the client's needs, and the local market for the products. This article walks through the standard C&D sequence position by position, flagging where the right choice depends on what is actually in your debris.

Position 1: The primary stage — screen or shredder

The entire infeed stream enters the primary stage, fed by excavator or loader — either directly into a loading zone or via a steel apron conveyor that meters the surge of each bucket. On most lines that stage is a primary screen cutting at roughly 8 to 10 inches, answering the most basic question in C&D sorting: what can be processed mechanically, and what cannot?

The alternative primary stage is a shredder — and the whole stream goes through it, not just the big pieces. There is no oversize afterward: everything is reduced to machine-sortable size, and optical sorters, de-stoners, and screens handle the line autonomously with much less sorting labour. The price is twofold: a shredder generates significantly more fines (3-inch-minus) that must then be processed, and its maintenance cost is high. Most lines run the screen — the decision turns on labour availability, tonnage, and the products you intend to sell.

Position 2: Oversize to the manual A-line

On screen-based lines, everything above the primary cut — dimensional lumber, large rigid plastics, pipe, sheet metal — is simply too big for screens, separators, and sorters. It travels to an elevated manual sort line (the "A-line") where pickers recover wood, metal, plastics, cardboard, and any other recoverable material by hand.

Position 3: Ferrous off the primary unders

The fraction passing the primary screen meets a magnet — overhead self-cleaning or a drum magnet, depending on the layout — before any further processing. Pulling rebar, strapping, and sheet steel here protects every machine downstream and removes the most dangerous material before any manual station.

Position 4: Secondary screening around 3 inches

A secondary screen splits the stream at roughly 3 inches. On a trommel, that is a single cut, and the minus fraction gets its own fines screen further down the line. A dual-deck screen does both jobs in one machine: a hard top deck cutting around 3 inches over a flip-flow bottom deck cutting around 1 inch, delivering three fractions at once — 0–1, 1–3, and 3–8 inches. The exact cut points are per-project decisions driven by the material and the products, but the principle is constant: isolate the mid fraction, where most recoverable product lives.

Position 5: De-stoner — where the aggregate money is made

The 3–8 inch mids pass a de-stoner (dense-out), which drops the heavy fraction — stone, concrete, brick — away from the lighter wood and plastics. A well-fed de-stoner produces aggregate clean enough that final quality control is a light manual task: one picker can cover aggregate QC for an entire 150–200 TPH system. That single number is the strongest argument for putting density separation exactly here, after the secondary screen has classified the stream.

Position 6: Cleaning the lights before recovery

The light side of the de-stoner — wood, plastics, paper — heads to recovery, and the cleaner it arrives, the better every recovery stage performs. A fluff knife inserted here pulls out an ultralight fraction: film plastic, shingle debris, foam. Removing the ultralights before optical or manual sorting dramatically cleans the burden the sorters see. Wood recovery then happens either on a picking line or with an NIR optical sorter, which can take grade 1 and grade 2 wood together or as separate products.

Position 7: Eddy current — deliberately late

The eddy current separator recovers non-ferrous metals — aluminum, copper, brass. It is positioned this late for a mechanical reason: an eddy current is a comparatively fragile machine, and every stage upstream has reduced and disciplined the burden it must carry. An eddy current placed early in a C&D line takes heavy, sharp, unscreened material across its belt and rotor; placed late, it sees a light, clean stream and lasts.

Position 8: The fines line — where projects are made or broken

The minus fraction from the secondary screen is not residue — it is its own process line, and it carries a large share of the line's total tonnage. On trommel lines, a fines screen cuts near 1 inch; on dual-deck lines, the 0–1 and 1–3 inch fractions come straight off the screen. Either way, the true fines (minus 1 inch) drop out, and the 1–3 inch mids run a magnet followed by a second de-stoner, recovering aggregate that would otherwise ship out as waste.

The impact on overall recovery rate is hard to overstate. Because so much of C&D tonnage ends up in this fraction, pulling the aggregates out of it moves the plant-wide recovery number more than almost any other single decision — twice, in fact: every ton recovered is both a salable product and a ton of disposal cost avoided. Plants that treat the minus fraction as waste are frequently the difference between a project that makes its numbers and one that pays to landfill its own revenue.

The mass-balance discipline

Behind every layout decision sits a mass balance: tons per hour in, and a defensible estimate of what each stage removes. Skipping this step produces lines where a conveyor rated for the infeed chokes at a transfer point, or a screen sized for average flow blinds at peak. Before any steel is specified, insist on a stage-by-stage tonnage table for your actual material — not an industry average. C&D composition varies enormously by region and season; a line designed for someone else's debris will sort someone else's debris.

Common sequencing mistakes

Trying to sort primary oversize mechanically — above 8–10 inches, hands beat machines
Placing the eddy current early, where heavy burden shortens its life and recovery suffers
Skipping the fluff knife and feeding film and shingle debris straight into optical sorters
Treating the minus fraction as waste instead of running its own magnet and de-stoner line — the single most expensive mistake on this list
Choosing a shredder — or rejecting one — without costing the extra fines and maintenance against the labour saved

The full system logic, with the equipment used at each stage, is described on our C&D recycling systems page. For a layout built around your material and building, talk to engineering.