If you’re one of the many asphalt plants across New Zealand and Australia operating without automation, and relying purely on the knowledge of your operators, you might want to rethink your approach. We asked our Designer Engineer Peter Taylor to explain how getting the plant timing controls right can make a big difference to your plant’s efficiency.
Technology isn’t uncommon in asphalt plants, but it’s not being used to its full potential.
Most asphalt plants in Australia and New Zealand have some form of computer component that controls the asphalt mix designs – we’ll call this your “cake mix” – and controls how much of each material goes in to make the perfect asphalt recipe. (How good this automation is varies hugely; but it’s safe to assume that there would be some sort of automation involved.)
However, when it comes to your “cake mixer”– made up of the conveyer belt, hot belt, burner, and drum – there’s far less automation present and higher dependence on the skills and experience of your operators. Unfortunately, specialised training is sparse. “Plant operators are unfortunately given very limited formal training,” says Peter Taylor, Senior Design Engineer at N2P Controls.
Given that an asphalt plant costs up to $8M, can waste in excess of $25K materials per day, and cause damaging mix inconsistencies without proper optimisation, this is a problem.
In this article we explain why wastage and mix inconsistencies occur and share two ways to solve it (one that involves automation, and one that doesn’t).
How An Asphalt Plant Works
To create asphalt, you put different-sized materials – anything from 40mm stone to a very find dust
or sand – and combine them with liquid bitumen within a drum.
Most of the raw ingredients get added into the drum by the slinger or cold feed, and a third of the way down the drum is where the bitumen pipe flows into the drum.
To make perfect (or usable) asphalt, you want dust and heavy materials to get to the bitumen pipe at the same time. That way all the ingredients are coming together at the same time, in the right proportions – and your mix is in spec. Voila!
However, physics isn’t really on our side here, and dust and fine materials get blown through the drum very quickly, since they are so light … while heavy materials like 40mm stone take longer.
This is where time delays – otherwise known as “start and end delays” – become important, because they change time at which different materials are released into the drum, to ensure that they are coming together at the right time, to create the right mix.
Time Delays Minimise Wastage
Without time delays that control when each different material is released into the drum, you’ll end up with a whole lot of dust at the start of each run that’s contaminated and unable to be used again, and you’ll have wastage at the beginning and end of each run where your mix isn’t quite right yet.
What happens to that mix that isn’t quite right? Unfortunately, it usually it gets dumped. Some plants can recycle it, but most don’t, and it gets thrown in a rubbish pile somewhere. Not only does that have an environmental impact, it has a significant financial impact too.
A tonne of asphalt is sold for $250 to $300, so if you’re losing 2 tonnes every single time you start a machine (that’s a minimal amount) – that’s $500 to $600 worth of waste. And that’s just when you start your machine ONCE or twice a day. Imagine if you start and restart your machine 10X a day (not unknown in the industry). That’s $25K to $30K of wastage in a single day. Ouch! With time delays, you can reduce that wastage significantly.
Keep Your Mix Consistent
This isn’t the only wastage that time delays prevent.
Everyone can see the waste at the beginning and end of a run – it’s very obvious. However, there’s another far more insidious issue that comes into play here too.
Asphalt plants running all day won’t run at the same speed consistently; they’ll speed up or slow down – and if you change your plant rate, the timing delays aren’t right, and it affects your mix quality. Eventually it comes right, but there’s a significant chunk of time where the mix is out of spec.
This isn’t unknown in the industry, says Peter. “I’ve been told by one operator that they were taught ‘never to take an asphalt sample after changing a plant rate, and to always wait 10 minutes before you do’” – and that’s because they’re making out of spec mix. If it’s tested, it won’t be accepted.
But because people avoid testing immediately after a rate change, the non-compliant mix goes out the machine, into a silo, it isn’t sampled, and nobody sees that. Just because it’s invisible though, doesn’t mean it isn’t impactful.
When that mix is out of spec, and doesn’t comply, it can fail; and when it fails you will have to dig up a stretch of road and replace it. This isn’t just costly in terms or labour and materials. It’s also costly to your reputation.
The Problem with Manual Asphalt Operations
Time delays are calculated according to the differential between the time fine particles travel down the drum vs. heaver materials, to ensure the “perfect” compliant asphalt.
However, manual asphalt operations rely completely on a plant controller to have a “rule of thumb” when creating a mix, and when they adjust the speed of the plant. Obviously, this doesn’t always work out – it relies on operator experience, and “a good guess”. There’s a lot of money at stake here to rely on guesswork.
There are two solutions to this pervasive problem: Education or Automation.
Training operators to do better estimations
In practice the perfect recipe isn’t always easy to achieve without automation or very accurate estimations.
However, if an operator is able to better what they’re doing, and why, then they are far better equipped to make changes and try and improve it; thereby minimising waste and improving your mix all-round. This is where targeted education and training come in.
At N2P Controls, we offer a half day on site training, customised to your business. This training will cover the following with approximate timings:
- Feeder setup and operation – mechanical (1.5hrs)
- How to improve their manual estimates (2hrs)
- Plant operation, including typical safety interlocks (0.5hrs)
- Plant walkaround (1hrs)
Automation of asphalt plant
More and more people are coming to realise the value of automating not just their mixers, but the entire plant. Automation will ALWAYS be more efficient and accurate than manual operation and even the most educated guesswork.
With automated plant systems you’re going to produce a more consistent mix and less wastage and manage your mix more efficiently. Not only that, but you can test your mix at the touch of a button, leading to better quality control.
Our Solution- Introducing the MC404
Our MC404 control module is designed to ensure you make great mix, every time, and has great reporting features to allow you to drive efficiency from your plant.
All our control modules come with full documentation including, PLC code, functional descriptions, process flow diagrams, electrical wiring diagrams, commissioning sheets, and operational manuals so you can be sure your team will understand how to use the technology, removing the “guesswork” from the process. Better still, the reporting that this module provides demonstrates the both the efficiency and profitability gains within the plant.
If you are considering adding automation to your plant, so you can have less wastage and lower costs, a more reliable and consistent mix, and better quality-control, click here to contact us.
Check out the other blogs in our asphalt explainer series, where we discuss how to improve health and safety in your asphalt plant and how to improve efficiency and reduce costs.