How to improve the efficiency of your asphalt plant

In this article, N2P Design Engineer Peter Taylor explains several ways to improve the efficiency of your legacy asphalt plant, thereby reducing wastage and costs on diesel, gas and electricity – some involving automation and technology innovations, others not.

Tune your burners

The very first step to improving the efficiency in your asphalt plant is to improve the efficiency of your burner, and the very first step to doing that is to tune your burner.  

Why? Tuning your burner (calibrating and adjusting it) works in exactly the same way as tuning your car – if it’s not, you’re going to use a lot more fuel than you’d necessarily need.

How do you know if your burner isn’t tuned properly? Usually you’ll get a lot of smoke coming out of your stack. It similar to driving down the road behind a truck. If it’s not tuned correctly, you’ll get a lot of smoke pouring out from the exhaust.  If you’ve got the right amount of tuning, your plant will be burning nice and easily, and the smoke will be a lighter yellow colour.  

Part of this is to maintain good oil pressure, and clean nozzles. This is a very simple maintenance step that should not be neglected. When you do this, the diesel is atomised very finely – which means it burns efficiently and easily. Exactly what we’re aiming for.

Maintain the correct oxygen mix within the drum

You need a certain amount of oxygen coming into the burner to burn all the fuel. So, within an asphalt plant, we blow air into the front of the drum, providing lots of oxygen to help the fuel burn.  Then, at the back of the plant, we have a big main fan that sucks all the air out the back of the drum – creating a channel of heated air flowing through the drum.

The trick to improve efficiency within an asphalt plant is to get the airstream from the burner blower and the main fan to suck the exact same amount of air through.  

In a non-automated plant, this is achieved with a damper – a flat plate of metal, which you turn to an angle to slowly block off the ducting, restricting the air coming in. The problem with this is that your main fan is running at 100% of speed all the time – using a lot of power. This is akin to driving down the motorway with your foot hard on the accelerator, all while you’re pressing down on the brake to control the speed.

Highly inefficient. 

Our solution?

A far more efficient way to manage the air flowing through the drum is to put the main fan onto a variable speed drive.

The AC404 (designed for plant control and monitoring) can automatically control the speed of the main fan – to give you the correct amount of suction.

This offers two benefits:

  • Firstly, you’re only heating the air that you need to heat the stones. If you put in more air than you need, you’re just blowing excess air out the stack – and if you’re heating less waste air, you’re going to have a huge saving on your diesel and gas costs.
  • Secondly, if you’re sucking a lot of air out the back of your drum, you’re removing all the dust and fines from the aggregate. The baghouse will collect the dust and return it to your mix – but older plants that have a wet scrubber means dust and fines are wasted and build up in your ponds.

Keep your drum clean

In a drum, you’re trying to get heat into the stone and mix. In order to do that, there are lifters in the walls which lift the rocks up to the top of the drum and drop them down through the hot airstream.

If your drum is not very clean or well designed, or you’re running it very slowly, you end up with gaps in the “curtain” of stone falling down through the drum, and that leads to inefficiencies heating the aggregate.  Instead of having an even curtain, you’ll have a gap down one side – and instead of air going through stone and heating it, it will race down the side of drum where there is no restriction.

The key to heating aggregate efficiently lies in maintaining a clean drum and lifters. Aggregate can build up within a drum, so you need to climb inside and clean it out. This is a regular maintenance job that should not be missed.  To check if it’s time for a clean, take the temperature on either side of your drum, and see if you’ve got hotspots. If you’ve got build-up, you’ll find that one side of the drum is hotter.   

Minimise the moisture content of your aggregate

When you run the aggregate through the drum, the first third of the process is for combustion to burn off all the fuel, next third is your drying out and heating up all the stone, generally last stage you add bitumen and mix it all together. However, if you’ve got water on the rock, bitumen won’t stick to it, so you have to dry the stone – evaporating all the water off of it.

This is where it can become costly.

To illustrate just how expensive this can get, here’s some statistics on just how much fuel you need to burn to dry the aggregate.   At 6% moisture, 4 litres of fuel are required to dry one tonne of aggregate. That is a lot of fuel being used to dry your mix! Especially since, once dry, you’ll need an additional 3 litres of fuel to heat the aggregate up to 150*C.

Therefore, the dryer your aggregate, the less fuel you will need to dry it. 

Here are a few ways to minimise moisture content in your aggregate:  

  • Put covers over your fine aggregate to protect it from the rain, especially during winter, because fine aggregates made with dust and sand hold a lot of water.
  • Only take stock from the top of the aggregate where it’s dryer.
  • Store your aggregate on an angle, to allow the water to drain.

Leverage data-driven decisions to improve the efficiency of your burner.

Our MC404 has the capacity to look at the fuel that is being used by the burner. This will allow the operator to monitor the burner and show how many litres of fuel are being using per tonne of asphalt.  

If there’s a lot of fuel being used, you can see that you’re potentially having issues in these core four areas – burner needs clean out, drum is sucking too much air, lifters need cleaning, or you’ve got wet aggregate interfering with efficiency.  

Knowledge is power, and this technology helps you to identify issues faster, problem solve effectively, make the plant more productive – and allows you to see historically how improvements have had an effect.  

Improve the efficiency of your tanks

Next, we’re moving from the Plant, to the Bitumen Storage, where there are other efficiencies to be gained. Bitumen is stored at 150*C so to improve plant efficiency (and reduce electricity costs) you can place insulation around your storage tanks.

This is a smart and simple investment, because the more you spend upfront on insulation, the more you’ll save each year on heating costs – since the bitumen tanks will hold their heat better, and you’ll require less electricity to heat the bitumen and keep it at the correct temperature.

Reduce peak loading costs and tap into night-time efficiencies

The TC404 (which manages tank operations) has two capabilities that improve the efficiency of your tank.  

First, it can automatically turn off tank heating as soon as plant starts running.   Why? A lot of companies get charged for the power on the highest current for that month (known as “peak load”). So, if you’re running the plant and heating the bitumen simultaneously, you’re charged for that.

Secondly, the TC404 has a built-in time clock that can be set to heat the tanks at night, so that you get cheaper electricity rates.  This way you can utilise the cheaper power at night to heat the bitumen tank –which also reducing your peak load. 

Improve the efficiency of your plant

As you can see, a lot goes into improving the efficiency of your asphalt plant – but the rewards are great when it comes to cost-cutting. We offer operator training to help your employees run the plant efficiently. Click here to find out more.

Or, contact us to find out more about installing the AC404, MC404 or TC404 onto your site to benefit from the efficiency gains. We can add these systems onto any existing asphalt plant without an expensive rebuild. Our team has so much knowledge and can come up with a custom solution for your plant.

Free Guide: Optimising Your Asphalt Plant

Free Guide: Optimising Your Asphalt Plant





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