“Up to 30 percent of a cement plant’s electricity needs can be generated using waste heat recovery systems.”
Concrete is the most widely utilized construction material on the planet, and has been so for centuries. The advantages of including it in building projects are well-known and simple: It’s strong and highly durable, and the ingredients – gravel, sand and water – are found just about anywhere.
Cement and concrete’s carbon emissions
Despite the obvious benefits of using concrete in construction projects, there’s one major downside to the concrete and cement industries: Their carbon footprint is enormous. In fact, cement production is thought to contribute as much as 5 percent of global CO2 emissions, according to the Cement Sustainability Initiative.
A large part of these emissions is unavoidable. When limestone – a critical component of cement – is heated up, it converts to calcium oxide and releases carbon dioxide. This transformation accounts for about half of the CO2 emissions released during cement production, according to the Cement Industry Federation. Another 35 percent of the emissions created is a byproduct of burning fuels to keep the cement plant operable. The remaining 15 percent is due to electricity used throughout the plant.
Although cement creation contributes to global pollution in a major way, the need for concrete outweighs any notions that production should be cut back. Relying on alternative construction materials has not yet proven to be more environmentally friendly, according to Cement Science. Additionally, transporting alternative materials to certain construction sites is far more complicated than logistics to do with concrete.
Compared to the production of steel and other materials, cement and concrete use relatively low levels of energy, Cement Science pointed out. The biggest reason the cement industry contributes such a large portion of CO2 emissions is its popularity. In 2016, 4,200 million metric tons of cement was produced globally, with 85.9 million metric tons being made in the U.S., according to Statista.
Waste heat recovery systems market increases
Growing concerns about climate change and the negative impact of carbon emissions have encouraged many companies to develop ways to lower their carbon footprints. Various governments’ dedication to green production practices have led to tighter regulations. And more consumers voicing their support for companies that make an effort to lower their own emissions has motivated production plants to explore new ways to make their operations more environmentally friendly.
These trends have fuelled the growth of the waste heat recovery system market, which is expected to grow 6.9 percent annually between 2016 and 2021, according to a report from MarketsandMarkets. By 2021 the market is expected to be valued at $65.87 billion.
MarketsandMarkets found that the largest driver of this growth is the cement sector. The global cement industry is projected to grow 9 percent a year until 2021. Massive construction efforts around the world, particularly in Indonesia, India and China, are some of the biggest reason for this.
As the need to reduce carbon emissions becomes more pertinent to the cement industry, and as the need for cement in global construction projects continues to be at a high level, it’ll become more important for manufacturers to invest in waste heat recovery systems.
Waste heat recovery in the cement making process
The first time a cement producer employed a heat recovery system to reduce operation costs was Japan’s Kawasaki Heavy Industries, which outfitted its Sumitomo Osaka Cement plant with a waste heat recovery system in 1980, according to a report from the International Finance Corporation. Since that time, more cement companies have enjoyed the benefits of waste heat recovery. “Up to 30 percent of a cement plant’s electricity needs can be generated using waste heat recovery systems.”
The typical process by which cement is made includes raw materials (usually limestone, sand, shale or chalk) being collected in a rotary kiln, which heats the materials to around 2,640 degrees Fahrenheit. At this temperature, the materials undergo chemical reactions that result in a product called clinker, which looks like small dark rocks. After the clinker is cooled, it’s ground to a fine powder along with additives like gypsum. This powder is the final product – cement.
Reaching 2,640 degrees requires a lot of energy. Kilns are powered by heat sources like coal or natural gas. Rock and sand can be preheated prior to moving into the kiln, which cuts down on the energy required to heat up the materials. The hotter the shale, chalk and other materials can get prior to entering the kiln, the faster the cement-making process will be and the more energy efficient the plant runs.
Preheaters in cement operations are typically systems of large cyclones that utilize exhaust gas leaving the kiln. Some systems have as many as six cyclones. Materials successively pass through each one, getting hotter as they go before finally reaching the kiln. Each cyclone takes advantage of heat escaping the kiln.
Using heat from the kiln to prepare raw materials for production is an excellent way to increase energy efficiency, but it’s not the only method of utilizing waste heat in a cement operation. Aside from the kiln, heat escapes from the preheating cyclones as well as the system used to cool the clinker before it’s ground into cement. These sources of heat can be directed to other parts of the plant where heat is needed, including the general HVAC system. It can also be used to generate electricity to decrease the plant’s reliance on the grid and lower utility costs. Nearly one-third of a plant’s electricity needs can be generated using waste heat recovery systems, the IFC explained.
A high-quality heat exchanger is the key to an effective waste heat recovery system in a cement plant. If you’re seeking out new ways to reduce your operational expenses, investing in a shell and tube heat exchanger to begin recovering otherwise wasted heat is an excellent place to start. To learn about the best way to incorporate a waste heat recovery system in your plant, reach out to the engineers at Enerquip.