Crushing plant (stone and aggregate)

01

Plan the crushing stages and screen circuits

EPA's AP-42 section 11.19.2 (Crushed Stone Processing, 2004) describes the process flow: quarried stone “normally is delivered to the processing plant by truck and is dumped into a bin”, a feeder or screens (grizzly) remove material that does not need primary crushing, and jaw, impactor or gyratory crushers are “usually used for initial reduction”, with a product AP-42 says is “normally 7.5 to 30 centimeters (3 to 12 inches)”. A scalping screen sends oversize to the secondary crusher — AP-42 says cone crushers are “commonly used” there, “although impact crushers are sometimes used” — which AP-42 says “typically reduces material to about 2.5 to 10 centimeters (1 to 4 inches)”; undersize can be sold as base material. [1]

The tertiary circuit has a sizing screen and a tertiary crusher — AP-42 says tertiary crushing is “usually performed using cone crushers or other types of impactor crushers” — whose output AP-42 says is “typically about 0.50 to 2.5 centimeters (3/16th to 1 inch)”, returning to the screen in closed circuit. Some plants make manufactured sand of up to 0.5 cm (3/16 in.) using a fines screen and a cone crusher or hammermill, with washing where product specifications require it. [1]

Editorial calculation: taking stone from a 30 cm primary product to a 2.5 cm tertiary product is an overall reduction of 30 / 2.5 = 12:1 across the secondary and tertiary stages, and to 0.5 cm sand 60:1; ask the supplier for the reduction ratio and closed-side setting planned at each stage. [1]

Give the supplier the rock type and hardness (for example granite, basalt, limestone), abrasiveness and moisture, maximum feed size, required products and proportions (including manufactured sand), capacity in t/h and hours per day, plant type (stationary, semi-mobile, mobile), site layout and power, dust and noise limits, and stockpile and loading needs.

02

Size capacity, product split and dust control

SBM describes a 200 t/h basalt crushing plant in Ethiopia producing 0–5 mm sand and 5–13–31 mm aggregate, combining secondary impact crushing with sand making, using a feeder tunnel under the 5–13 mm stockpile as a buffer for sand making, and allowing the product ratio to be shifted from 5–10 mm aggregate toward 0–5 mm manufactured sand; the client also needed steel structures, conveyors, cables and control cabinets. [2]

AP-42 notes that crushing, screening, size classification, material handling and storage can all be significant sources of particulate (PM and PM-10) emissions if uncontrolled. [1]

Editorial calculation: at 200 t/h for an assumed 10 operating hours a day, a plant produces about 2,000 t a day; ask the supplier for the design capacity at your closed-side settings and rock, not only nameplate capacity, and for the dust control (water sprays, enclosures, filters) included. [2]

In the United States, plants covered by NSPS Subpart OOO (40 CFR 60.670–60.676) built or modified on or after 22 April 2008 must keep fugitive emissions to 7% opacity at screens, transfer points, bins and similar equipment and 12% at crushers without capture systems, with water sprays inspected periodically and a repeat test within 5 years where no sprays are used. Where a capture system feeds a control device, the stack limit is 0.032 g/dscm (0.014 gr/dscf); building openings around enclosed equipment are held to 7% opacity, and truck dumping into a hopper or crusher is exempt. Earlier plants (1983–2008) have 10% and 15% opacity and 0.05 g/dscm. [3]

Editorial note: for a US site, ask the supplier which transfer points get water sprays and which get capture hoods and filters, so the 7%/12% opacity and 0.032 g/dscm limits can be met at start-up testing. [3]

A mobile-plant case shows the operating figures to ask about. Metso's case study on a Lokotrack LT220D cone plant used by a Norwegian contractor (published 2015) reports 25% more capacity and fuel use of 34 litres per hour, a 40% fuel saving against the earlier LT1100 cone plant, and 25–30 t/h more output, with an expected 60,000–70,000 litres of fuel saved a year; the unit is about 10 t lighter than its predecessor. In its first ten months it ran more than 2,500 hours and crushed and screened about 250,000 t, making 0–4, 4–8, 8–11, 11–16 and 8–16 (16–22) mm products, with a separate mobile screen adding 0–2, 2–5 and 5–8 mm grades, on 12-hour days with a one-hour service break. [4] Editorial calculation: 250,000 t over 2,500 hours is about 100 t/h on average, and 34 L/h over 100 t/h is about 0.34 L of fuel per tonne; ask suppliers for fuel or power per tonne on your rock, not only rated capacity. [4]

03

Nine listings, from single crushers to complete aggregate lines

The suppliers reviewed list jaw, cone, impact and sand-making crushers, screens and mobile or stationary plants; ask each for a flow sheet with tonnages and product sizes, crusher and screen models, installed power, steel structures and conveyors included, and dust control.

04

Feeder, primary crusher, screens, cone or impact stages, sand making and dust control

The stage rows follow the AP-42 flow sheet; SBM's basalt plant adds the conveyors, steel structures and control cabinets that client also had to buy.

05

Flow-sheet data: sizes, capacity, crushing ratio, power and dust

Only the product-size, capacity, crushing-ratio and dust rows carry source values; the other ten rows have none in the sources reviewed, so ask for them with the flow sheet.

06

Send the rock, product and site data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Rock: [type; hardness; abrasiveness; moisture]
Feed: [max size; t/h]
Products: [sizes; split; sand]
Plant: [stationary; semi-mobile; mobile]
Site: [layout; power; water]
Environment: [dust; noise limits]
Scope: [structures; conveyors; controls; installation]

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