Agg-Net

The Aggregates & Recycling Information Network
Mobile Menu
From the organisers of
 

2020 / 2021 Edition

Order your copy here

Spin With Substance

Tony Blair may have been labelled the master of spin, but in the world of water recycling it takes a centrifugal decanter to deliver spin with substance. With grumbles being raised about plate presses in terms of lower than expected throughput and unexpected lime additions in clay processes, the first decanter has now been sold in the UK by Baioni and it promises to change the way aggregate producers recycle washing water. Now Duo is to release its own model of centrifuge at Hillhead. MQR has been finding out more.

At a time when the power of Tony Blair and his politics of spin is starting to decline, it appears there is another form of centrifugal force in the ascendancy, this time in the arena of water recycling.

But there is a major difference between the Blairite spin of old and the new dawn being enjoyed by the decanter recycling system. While with the Prime Minister’s end product there is often little to grab hold of, with the centrifuge you get spin with plenty of substance.

It seems only yesterday that the plate press was being voted in over the cumbersome belt press. Offering better throughputs, lower flocculent use and a drier end product, plate presses have left belt models in the equivalent of a political wilderness.

But rumbles of discontent are surfacing over plate presses and so the market is calling for elections. The main candidate announcing an intention to run against the plate press is the centrifugal decanter system. And it has some weighty backers.

First on the UK scene was Italian firm Baioni last year (see MQR March/April 2006). “It is smaller, quicker and cheaper than the plate press,” argues Baioni’s Graham Brain, “and as it is monitored by PC it can save energy by monitoring performance.”

Now Duo has also entered the fray by signing up a deal with Italian firm Gennaretti. But Duo’s Fintan McKeever is being a little more diplomatic about the potential of the centrifuge. He sees any election ending in a hung parliament. After all, Duo sells both products.

“I see the centrifuge as a complement to the plate press. There are pros and cons with both. For example, the centrifuge won’t give as dry an end product as the plate press so it all depends on needs,” he told MQR.

As with all matters in aggregates there is no right and wrong answer. It all depends on materials being processed. But even then there is disagreement between the two camps involved in centrifuges.

“The centrifuge will not operate well with free draining materials such as granite,” says McKeever. Not so retorts Brain: “There are granite operations in Italy using the centrifuge to great effect,” he says. And this is not the only area of contention.

“Centrifuges use more flocculent than plate presses,” says McKeever. “You dose once in the thickener tank and then again as the slurry is being pumped to the device in order to control consistency.”

Ah, says Brain, you may have to dose twice but it is of a lower level of flocculent. “Overall you use less flocculent even though you dose twice. Besides, many C&D waste recyclers find themselves having to use lime and extra flocculent to control the end cake because of clay. A centrifuge doesn’t have this problem,” he told MQR.

Frank Owen, recycling manager of GKL has just bought the first Baioni centrifuge operating in the UK. The probable need for a lime silo to feed into sludge entering a plate press is what pushed him towards opting for the spin dry option.

“For me it seemed the best solution. I offer a top soil from my Peterborough site and the material comes out ready to go into the top soil. I don’t need to worry about adding lime and the shovel driver can use it,” he told MQR.

The ease of use is just one the attractions of the centrifuge. A plate press requires bodies both for operational purposes and collection of material. A PC controlled centrifuge can be taken care of by the wheeled loader operator. But this is not the only advantage.

The real winner for many will be the price tag and throughput. If you have done any research into filter presses you know they can range from £200,000 for the smaller models to around £500,000 for the higher throughput models.

Prices for a centrifuge adapted to the quarrying and recycling industries range from below £20,000 for the smaller throughput machines up to £80,000 – the Gennaretti range is generally smaller than Baioni models but they do cross over.

But it is in terms of throughput that they really come into their own. The largest plate press in operation in the UK processes roughly 15m3 of sludge per cycle with a cycle taking anything up to an hour because of its size. The largest Baioni decanter processes 100m3 every hour and has an £80,000 price tag compared with about £500,000 for the press. It seems a no-brainer.

But care is needed in terms of a direct price comparison. Firstly, both presses and decanters do not stand alone. Flocculent tanks, buffer tanks, thickeners, support structure and electrics all need to be taken into account.

Models such as the Baioni decanter will optimise power use by PC and an electric inverter motor but still centrifuges demand much more power than the small amount needed to squeeze plates together in a press.

But then a decanter could demand fewer support set up costs. The largest Baioni model only weights in at 6,500kg and measures only 470cm x 130cm x 265cm. The smallest Diemme press from CDE weighs 58,000kg and is 1,261cm long, demanding much more concrete, steel and construction costs.

McKeever believes there is a rule of thumb you can follow: “This won’t always be the case but my advice is if you are processing a free-draining material such as granite, a dry cake is OK and you don’t want the trouble of flocculants, then go for a plate press.

“If you want a smaller capital outlay, have levels of clay in the water, don’t mind a wetter cake, don’t mind a slightly higher power bill and want high throughput then go for a centrifuge,” he says.

But, as with any good election process, there is always another opinion. Brain says he finds it difficult to envisage any situation in the quarrying and recycling sectors where a plate press would out-do a centrifuge.

“A filter press give an inconsistent product and has a lot of downtime during cycles. A centrifuge can operate 24/7 and you can use two in conjunction.

“In fact, if you wanted to process 200m3 an hour you could have a 100m3 and join it to a smaller model to reach the 200m3 figure because of the way they work in tandem.

“Also, after 2-3months plate filters become less efficient and have a lower flow rate. Not so with decanters. The spiral in the decanter needs replacing about every two years but even then the machine compensates for spiral wear.

“Baioni stopped making belt and filter presses two years ago because it could see the potential in the decanter. We currently have 60 installations across Europe and growing. I think the positives of the decanter far outweigh those of the press,” he told MQR.

If the battle for votes over spin or press hasn’t made it to you yet, it will soon. With the first decanter now having been sold in the UK by Baioni, and others in the pipeline, recyclers now have a UK-based operation at which to see it in action – it will be up and running around the end of March.

MQR has also heard that both models could be showing at Hillhead this year but this is far from confirmed. We’ll let you know. If so, go and have a look and make up your own mind. After all, it is a democracy.

Baioni: 01789 268583

CDE: 028 8676 1414

Duo: 02476 405100

Frank (GKL): 07773 395426

www.gennaretti.com

The brief lowdown on spin

By summer this year there will be a choice of two ranges of centrifuge on the market for the sector: Gennaretti from Duo and Baioni.

Duo is keeping its specificatons close to its chest at the moment. We know it will be showing a 15tonnes an hour model at Hillhead and that its range goes up to a 30tonne an hour model. It contains hard wearing metals in the spiral drum, says Duo, and will only need maintenance every 6,000-10,000hours.

Much more is known about the Baioni model and its specs are impressive.There are eight models in the range with throughput rates of 1m3 to 100m3 an hour. Power needs range from 5.5kW in the smallest model to 90/30kW in the 100m3 machine. Weight ranges from 1,000 to 6,500kg.

Some of the adaptations made to ready the Baioni models to the quarrying and recycling industries include the use of a tungsten carbide screw (see picture below) which moves the spun material to the outlet for stockpiling. While the outlet itself has been fitted with ceramic discs (numbered 5 below) to take into account the extra abrasion from solids. The feed tube leading in (number 1) can be adjusted inwards or outwards to allow for a wetter or drier product. It can run 24 hours a day, seven days a week with the spiral needing replacing every two years. It takes two-three hours to replace. Baioni is currenlty looking for a UK?manufacturer to produce new spirals and sharpen blunted ones. The range comes with a remote control option.

Share this page

Add new comment

Filtered HTML

  • Web page addresses and e-mail addresses turn into links automatically.
  • Allowed HTML tags: <a> <em> <strong> <cite> <blockquote> <code> <ul> <ol> <li> <dl> <dt> <dd>
  • Lines and paragraphs break automatically.

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.