Asphalt plant energy saving is a fundamental issue
Asphalt plant energy saving is a fundamental issue in asphalt plant operations and a decisive factor for the competitiveness of each and every company which produces asphalt, even though it is sometimes underestimated by the entrepreneur.The costs of both plant management and asphalt production tend to be considered as passive expenses for the company, and therefore insufficient attention is often paid to reducing costs as much as possible and optimising the company’s overall management margins.
The parameters which compete to form substantial savings are varied and their complex interaction need to be analysed on an individual basis since every work situation is different. Marini aims at partnering the client through advice on maximizing operational margins and state-of-the-art-solutions, plus in-depth analysis of every individual operation. The following text aims at providing some ideas for clients who want to get more out of their present plant performance.
The main factor regarding operative costs is without doubt the amount of fuel consumed by the dryer. Let’s take the following as an example: with a cost of natural gas fuel at 0.5 €/m³, an average consumption of natural gas per ton of finished product equal to 7 m³/t and an annual production of around 100,000 tons, the annual cost of drying the aggregates and heating them to the right temperature arrives at around € 350,000 per annum.
It is therefore evident that finding solutions to reduce dryer consumption can result in considerable savings – but how?
We must remember the importance of the moisture content in the aggregates/RAP. In fact, it is imperative for us to be aware that one percentage point of moisture is equivalent to approx 7 kWh/t of added energy consumption (almost 10%) for drying the materials.
So, in what way can the producer reduce and control the moisture content? First of all, it is important for the entrepreneur to consider the following: define what is the maximum moisture content when stocking up with aggregates (through well-designed contracts signed with the suppliers), purchase the right aggregates at the right moment, and, above all, ensure that the areas used for stock-piling are totally adequate – it is necessary to prepare a slightly sloping base for water drainage, to separate the stock piles with high dividers (to reduce the ground surface area occupied by the aggregates and so reduce moisture absorption in case of rain) and, above all, to sufficiently cover the sand and RAP stockpiles.
As well as the above points that every company should take into consideration, there are many other points of intervention, both on the plant itself and its operation (how the plant is used): correct and frequent burner calibration, optimum asphalt production temperature, ready checks of the temperature of bag filter gas emissions and reduction of excess oxygen during combustion.
Naturally MARINI is ready to offer advice and work closely with its clients when considering the above measures.
The specially designed ‘drying and filtering bar’, which has been carefully researched by MARINI and is now adopted on almost all its range, means that heat loss is reduced to a minimum and the main burner consumption is therefore optimised. A short, insulated fumes duct situated between the dryer and the filter avoids energy wastage and having to overheat the aggregates, and makes the air temperature in the filter more manageable. The position of the recovered fines hopper between the dryer and the bag filter helps keep the fines partially heated before being re-fed into the plant.
All Marini technical solutions are studied and selected with the aim of optimising energy savings.
Another factor that is hardly ever taken into full consideration is the cost of keeping the bitumen heated up to temperature in the storage tanks.
On many sites the ‘bitumen park’ is often old, with inadequately insulated tanks and ‘choked up’ heated coils, without mentioning the state of insufficient insulation on the bitumen pipes. And what is the result? Extremely high operational costs.
MARINI has conducted a study, compiled from many different site surveys, which reveals that almost all companies spend more than € 100,000 every year to heat bitumen (both with thermal oil tanks and old electric tanks).
It is therefore easy to imagine that a modern bitumen park could result in high energy savings with increased and improved insulation (200 or 300 mm thick), even on the lower parts. But that’s not all.
An innovative design for the insulation supports can result in a reduction of ‘thermal bridges’ and temperature loss on the outside, and also careful insulation of valves, pumps, pipes (with 100 mm rock wool) can halve the cost of bitumen management.
Final result: the replacement of an old bitumen park can usually pay itself off in just 5 to 6 years, then leaving the company with an ‘annual bonus’ of at least € 50.000, which increases market competition.
A MARINI team of experts can evaluate, together with site technicians, the specific requirements of each site and offer solutions for getting the best out of a bitumen park.
The relative costs of electric energy consumption can greatly vary depending on how the plant is used by the client.
If the work involves lots of starts and stops, the specific consumption per ton of asphalt could be considerably higher than plant which works in a continuous way.
And even if the cost of electrical power varies significantly in different nations and geographical areas, nevertheless the figures involved are extremely high.
The design of MARINI TOP TOWER plants has resulted in a reduction of electrical power because of the fewer screw conveyors, which, added to the benefits of softstart appliances on the main motors, means uncompromised savings.
Depending on individual circumstances, it could be worthwhile to use more efficient working solutions and our team is ready to work with the client to personalise the plants with the aim of optimising energy consumption.
Special kits can nowadays be integrated into plant software for monitoring costs. Entrepreneurs are therefore in a position to get to know their plant better and consequently intervene on their existing plants to optimise energy consumption, wherever possible, on their asphalt sites.