The very nature of cement production – the combustion and the reactions – generates an enormous amount of heat. When you consider that cement clinker is formed at a temperature of 1450 °C, and that it also needs to be cooled, it’s easy to see why so much excess heat is wasted.
With average energy prices set to increase by around 80 percent in 2022, there is both a financial and environmental incentive to find ways to lower energy costs. The most obvious place to start is by using less energy, and one of the best ways to do that is through more energy efficient technologies – such as waste heat recovery.
In this blog post, we’ll take a look at waste heat recovery, what it is, how it works, and the benefits it brings for both the environment, and cement factory operations.
What Is Waste Heat Recovery?
Waste heat recovery (WHR) is the process of recovering as much heat as possible from an industrial plant’s production processes, and optimising its re-usage to minimise the amount of heat being distributed into the surrounding environment, including the air, or bodies of water such as rivers.
Whilst there are existing opportunities to recover heat and re-use it within the cement manufacturing process, in some cases, a large proportion still gets wasted. However, there are a number of feasible ways to optimise waste heat recovery, and leverage the potential of this wasted heat on an industrial scale.
It goes without saying that the stacks on an industrial facility release emissions, in the form of hot gases, into the atmosphere. Due to the temperature of these emissions, energy is lost. So it’s logical to recover this energy and harness it through a waste heat recovery system.
For cement production, this is a win-win situation because what’s good for the environment is also good for the plant’s operating expenses due to the reduction in energy consumption.
How It Works In Cement Production
Over the past decade, the cement industry has seen a gradual increase in waste heat recovery systems, as more and more plant owners see the economic and environmental benefits.
In some countries, such as China, it’s become mandatory for new cement plants to install adequate waste heat recovery systems in order to be awarded a licence to operate.
In simple terms, WHR systems consist of a heat recovery boiler where the hot gas transfers its thermal energy into a liquid (water or oil) and a turbine system where thermal energy converted into electrical energy.
Traditional cement plants have two waste heat recovery locations. The one is the preheater gas conditioning tower, and the other is the clinker cooler outlet. In such plants without WHR, hot gas (over 350 ºC degrees) is cooled down by means of water or air, in order to have lower temperature (i.e. 150 ºC degrees) to release atmosphere.
There are currently two waste heat recovery turbine systems available on the market. Variables such as budget and operating conditions determine which technology is most suited to a cement plant:
- Steam Rankine Cycle: Water is pumped through pipes, and the recovered heat (hot gas) turns the water into steam. This pressurised steam is then sent through the blades of a turbine to generate electricity.
- Organic Rankine Cycle: Instead of using water, this type of waste heat recovery system uses an organic fluid, such as hydrocarbons. The key difference is that whilst water has a relatively high boiling point, other organic fluids become a gas at a much lower temperature.
Similar to existing non-renewable energy sources, only about a quarter of the fuel’s energy can be converted into electricity, but this still enables cement plants to recover a significant proportion of wasted energy.
In countries such as Türkiye, which uses around 45,000 megawatts per hour, around 40% of that energy is currently generated by coal power plants. That means any reduction at all in energy usage by cement plants also results in a reduction in CO2 emissions.
The Benefits Of Waste Heat Recovery
Within the context of a cement plant, there are a number of benefits to harnessing wasted heat:
- Generate Electricity And Steam: Recovering waste heat reduces steam consumption in the plant and frees up a larger portion for generating electricity.
- Reduce Fuel Consumption: Reducing the demand for electricity from the grid has a direct cost saving on cement production.
- Lower The Cost Of Cooling: Recovery and reusing heat reduces the need, and therefore the cost, of cooling.
- Reduce Greenhouse Gas Emissions: Using less fuel as a result of waste heat recovery inevitably leads to reduced emissions, especially if the originating energy source is a fossil fuel power plant.
Engineering Systems For Recovering Heat
For every new cement plant or upgraded production line, feasibility is always the most important consideration. However, as energy prices continue to rise, energy demand increasingly outstrips supply, and more and more governments tighten up their regulations around emissions, energy efficiency is likely to become a key market differentiator, even to the point of determining whether a facility can do business at all. That’s why so many cement plant owners are including waste heat recovery as part of their invitations to tender.
Sintek has over a decade of experience in handling the engineering and construction of cement plants. Find out more about our services in Europe. Read about us.
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