Recycling Diaries...

01 April, 2007

As SB Waste in Wolverhapton continues its journey of upgrading its operations, Andrew Hewitt continues his diary offering readers advice and guidance on what he is learning from the process. This issue he looks at some of the plant the firm has chosen to meet its needs and reiterates the necessity of ensuring you have fully researched markets and potential future growth.

In the previous installment of my diary I left it open for us to progress to the major decisions that have to be made when building recycling plant. It is always worth stopping and thinking again about why you are expanding. For many companies plant is the biggest investment they make so you don't want to be rushed into anything by salesmen only interested in putting machinery on your site.

Firstly you need to determine the budget you have to work with. This will depend on how much and what type of waste you have coming through the gate. It also depends on how much you currently send to landfill and how much that costs the company in tipping fees, tax and haulage.

It’s not too difficult to work out if the new plant will increase the recycling capacity of the site by 25% and then determine the number of pounds saved each month. You can then set the payback time required for the plant – most people choose three years – and you’ve got a good indication of how much money can be spent.

A matter of size

As for picking the size of the plant, there are various calculations that can be made such as projecting turnover and forecasting future business. But please bare in mind it’s very easy to blind yourself with science. We followed a simple process to determine plant size.

Each individual business will know what waste is coming in on a day-to-day basis. If you know your catchment area and your customers and have a good idea of how much more efficient and competitive you can be with your new plant, you’ll know how the business can expand. Therefore it’s possible to determine what size of plant you need, as we did.

However, it is vital that the waste licence you have will either cover any increase in business or can be altered to do so. Otherwise you’re building in over-capacity that you can’t use. Why over-capacity? Because if a plant is built that runs at 100% from day one there’s no room to expand the business. The figures have already been done based on what’s happening today.

As long as the business doesn't contract the fact the new plant is only working at 40% capacity won't cause financial problems. It will, however, save a considerable amount of future investment in recycling plant as the business expands.

The limiting factor in any plant with a manual picking station is the picking station itself. It’s only possible to have a belt of a certain width. I wouldn’t go wider than 1,200mm because it’s impossible to reach comfortably into the middle to pick the waste – the HSE is getting tougher on back injuries.

The belt can’t travel too quickly or the pickers will not have time pick the waste. An average speed of 0.2mps is really the best you can do. There are guidelines on the HSE website with a number of other useful pointers: www.hse.gov.uk

Even working to these constraints, if the plant is designed properly, it’s possible to feed in 100m³ an hour at the start of the process, which is a lot of waste. If you want to process more than this then we have to look at another screen and splitting the waste stream – but this won’t be necessary for 95% of the waste companies who are currently looking for plant.

The next big question is do we shred the waste or not. There are pros and cons to weigh up on this one. Shredders are very expensive and a good one will eat 25% of the budget straight away. They are also very heavy on maintenance and running costs.

The upside is that if you get the right one, a good shredder will eliminate much of the pre-sorting required before feeding the waste on to the screen. It will deal with most of the material likely to cause blockages in the plant and make the material going into the picking station a great deal easier to deal with.

At SB we decided that a powerful, slow speed, high torque machine that ripped rather than shredded was needed so we could produce 400mm cubed material.

With the waste as <400mm cubed material it was a matter of figuring out how, and at what size, to screen the fines out. There are really only two possibilities: a trommell screen or a finger screen.

We decided that the finger screen would be best as the screening action is good. I suppose it’s my time with General Kinematics that leads me to think this way but the machine is tough and robust with so few moving parts it really chose itself.

We approached Blue Machinery to purchase a screen and a de-stoner (see below) but Blue was only interested in selling the complete plant. I’d known of another American company who produced a similar range of equipment but didn’t sell into Europe. We made contact and visited their factory in Oregon to see what they had to offer.

Action Vibratory Equipment have a very similar range of products to General Kinematics/Blue Machinery. They can supply screens, de-stoners and vibratory feeders and we came away from there the proud owners of a 12.1m long Taper-Slot finger style screen (see picture) and a 1.5m wide Dense-Out de-stoner – we will have the first operational models in the country by July.

As for the material size to screen we went for a 40mm cut. It’s a good size to screen if the material is wet, it gives a good material when re-screened at 40-15mm, and removing everything below 40mm makes life in the picking station much easier.

The next stage we saw as dealing with the fines or the <40mm material. This was simple. We set up the line exactly as with Thompson’s of Prudhoe in the North-West (see MQR Sept/Oct 06 ) and Irish Recycling Systems in Belfast.

The material goes under a Master Magnets overband magnet to remove any scrap metal, over a Pearson star screen to screen out at 12-15mm, and then through the Dense-Out to blow the paper, plastics and rags out of the 40-15mm stone – they are all plant I’d recommend.

The oversize material coming over the screen goes under another overband magnet and through a large blower. This is designed to remove the light material – paper, plastics, cardboard and rags – leaving the wood, stone, glass and heavy plastics to go into the picking station.

Which brings us back to the beginning of the article. As I said earlier, the plant is designed to remove as much material as possible before the picking station and we had already decided when we designed the plant that a second picking station is necessary to separate the paper, plastics and card because we know we will have sufficient quantities of each to make it worthwhile.

Every plant we’d visited that had this facility had a completely separate picking station to do this.

What we decided to do was separate the lights from the heavies with the blower and run the two picking lines parallel through an open plan picking station. This has two major advantages,

Firstly, any paper, plastic or card that the blower doesn’t remove can be picked off the heavies line and put straight into the right bay on the lights line. Secondly, depending which line is busiest, the pickers can easily move from one line to another. This will cut manpower by at least two to three people. This seemed to make so much sense we’re surprised we’d not seen it before.

And this is as far as we’ve got, so far. We’re busy working on the conveyors, the final layout, maximising the space available and making the plant as user friendly as possible. All of which we’ll tell you more about in the Hillhead May/June issue.

Next time: The critical issue of how to get the waste to the plant and the product away.

Andrew: 07773 715882