Solutions are needed for steel, cement and ammonia

Solutions are needed for steel, cement and ammonia
Solutions are needed for steel, cement and ammonia

When discussing how to reduce greenhouse gas emissions, and thus tackle climate change, we don’t often talk about steel, cement and fertilizers. Means of transport and electricity generation are much more mentioned, and it is understandable. Not only because they are two areas most familiar to most people, but also because reducing their impact on the environment is relatively easy: the solutions, however difficult to put into practice, are known. Finding a way to decrease the greenhouse gas emissions caused by the production of steel, cement and ammonia, three essential substances for our world, is much more complicated.

With steel we make machinery, appliances, means of transport, computers and many other things, in addition to the bars present in reinforced concrete; and cement is the fundamental ingredient for the construction of roads, large infrastructures and houses in much of the world (mixed with gravel, sand and water, cement gives concrete). Finally, ammonia is used to produce detergents, plastic and textile materials, and above all fertilizers, without which world agricultural production would not allow to feed the vast majority of people on the planet.

The problem is that these three substances contribute more to greenhouse gas emissions than do plastics or air travel.

There are different estimates on how many greenhouse gas emissions, in percentage, must be attributed to each different type of human activity: these are estimates that vary slightly depending on the sector in which the contribution linked to electricity production is counted.

According to those of the environmental research institute World Resources Institute, which allow us to make a fairly clear comparison, transport is responsible for 16 per cent of emissions (1.9 per cent to aviation) and the production of electricity and 31 per cent of its consumption in homes, offices, shops and clubs; to industrial activities as a whole, 29 per cent; to the production of iron and steel alone, 7 per cent; to the production of cement more than 3 per cent; and the chemical industry, for which ammonia is one of the main products, almost 6 percent. Furthermore, another 4 per cent of total emissions can also be attributed to ammonia, those due to the use of fertilizers in crops.

Because steel, cement and ammonia cause so many emissions
To produce steel, cement and ammonia emit greenhouse gases in two different ways.

The first is what most industrial productions have in common: to carry them out, energy is needed and that energy is produced, in most cases, by burning fossil fuels, the main source of carbon dioxide emissions (CO2), the main greenhouse gas. The second depends on the fact that, due to their chemical characteristics, the creation of these materials or their use generates greenhouse gas emissions in themselves.

Let’s start with steel, which is made of iron and carbon. To obtain it, iron ore must be smelted in the presence of coke, a type of coal. In smelting, iron ore releases the oxygen it contains, while coke releases carbon: part of the carbon binds to iron, creating steel, while the other binds to oxygen, generating CO2. To melt the iron ore then it is necessary to reach very high temperatures, around 1,700 ° C, and therefore a lot of energy is needed.

Workers at work in the blast furnace of the steel mill in Salzgitter, Germany, on March 2, 2020 (Maja Hitij / Getty Images)

Cement, on the other hand, is produced by burning limestone mixed with some other material. Limestone contains calcium (which is the fundamental element of cement), carbon and oxygen: combustion creates on the one hand calcium oxide, on the other carbon dioxide. Other CO2 it is emitted to produce the energy needed to reach the 1,450 ° C necessary for these reactions: to make cement, therefore, a greenhouse gas is emitted in two different ways.

Overall, if the cheapest fuel is used, i.e. coal, one ton of CO is emitted for every ton of cement produced.2. And billions of tons of cement are produced every year around the world.

On the other hand, 176 million tons of ammonia are produced every year, mostly used to obtain fertilizers: in fact, plants can obtain nitrogen from ammonia, a fundamental element for their growth.

To produce it, the so-called Haber-Bosch process is used, invented by the German chemist Fritz Haber in 1908: it involves obtaining hydrogen from natural gas, and then binding it to the nitrogen of the air, breaking the strong bonds that hold the nitrogen molecules together. using high temperatures (about 500 ° C) and pressures. Both operations require a lot of energy and therefore cause large emissions of carbon dioxide.

The Haber-Bosch process itself does not cause the creation of greenhouse gases, but the use of ammonia in fertilizers does. In fact, plants absorb only a small part of the nitrogen they contain, and the rest ends up pouring into water courses or arriving in the atmosphere as nitrous oxide (N2O), a less known gas than CO2 but which still contributes to the greenhouse effect.

How could emissions of steel, cement and ammonia be reduced?
The main solutions proposed involve the use of two technologies that are still underdeveloped and expensive: the capture of carbon dioxide, which so far occurs only in a few experimental plants, and the use of “green” hydrogen as a fuel, that is, obtained thanks to energy sources that do not produce greenhouse gas emissions.

CO capture systems2 they would allow to retain the gas produced to obtain steel and cement before it diffuses into the atmosphere; the CO2 it would then be safely stored underground, for example. Hydrogen, on the other hand, is a very efficient fuel for industrial processes that require high temperatures and therefore could be used for the production of steel, cement and ammonia (in the latter case also as a raw material) avoiding the production of emissions.

As for steel, in addition to using the capture of carbon dioxide during the production phases in which it is emitted, an alternative method could be substituted for melting at 1,700 ° C in blast furnaces: electrolysis, already used to obtain aluminum from bauxite ores. It consists in passing electric current in a cell that contains a mixture of molten iron ore and other substances, but not coal: the current breaks down the mineral, allowing to obtain pure iron and, as a by-product, oxygen and not carbon dioxide. This process requires a lot of energy, which can be supplied by green hydrogen.

Some companies are already trying to make steel this way. On September 15, for example, the large Indian company Tata Steel announced that it will do so in its plant in IJmuiden, in the Netherlands; ArcelorMittal is also experimenting.

On the other hand, reducing the environmental impact of cement will be more complicated.

An initial reduction in production-related emissions could always be achieved by using green hydrogen as fuel instead of coal. Then, carbon dioxide capture systems could be used: according to a report by the International Energy Agency (IEA), they would allow emissions from cement production to be reduced by up to 55 percent by 2050. Part of the dioxide. on the other hand, carbon dioxide could be exploited for other uses, as the French company Vicat wants to try: recently it announced its intention to use 40 percent of CO2 resulting from its activities in a plant near Lyon to produce fuel for freight ships.

All these initiatives, however, will not make zero greenhouse gas emissions due to cement, an objective that could perhaps be achieved by changing the raw materials from which it is obtained. Various proposals have been made in this regard.

One involves the use of a type of clay instead of limestone: it would eliminate carbon dioxide emissions as a waste product and would require lower temperatures for industrial processes, therefore less energy.

Another proposal is to use magnesite instead of limestone: according to John Harrison, the Australian industrial chemist who first proposed this replacement twenty years ago, thanks to this material, which in turn would require lower temperatures, we would obtain a cement that absorbs the carbon dioxide present in the air. Normally used cement does, too, but less than chalk made from chalk, according to Harrison.

The problem with all the proposals to change the raw materials from which cement is made is that the initial costs for the producers would be very high, because they would require various experiments.

A farmer distributes ammonia-based fertilizer in a field near Gretna, Nebraska on April 6, 2015 (AP Photo / Nati Harnik, La Presse)

It should be easier to make ammonia using green hydrogen, as some companies are already doing. However, it would only be the first step to reduce the impact of this substance on the environment: a way should also be found to reduce the energy necessary to power the Haber-Bosch process, that is, to make the reactions necessary for the production of ammonia occur at temperatures. and lower pressures.

The bacteria present in the roots of plants succeed, but it takes too long to be used on an industrial scale, which is why a lot of research is done in the world of chemistry to find alternative solutions. For example, the Japanese company JGC is experimenting with the use of ruthenium, a rare metal, which it claims allows to reduce the pressure necessary for the synthesis of ammonia by three quarters. There are also those who do research to completely overcome the Haber-Bosch process, with other electrochemical processes.

To reduce the emissions caused by ammonia, however, it would also be necessary to intervene on the diffusion of nitrous oxide, so there are no capture systems such as those that are starting to be used for carbon dioxide.

The simplest solution would be to distribute fertilizers more efficiently – less than half of the ammonia spread in the fields reaches the roots of the plants – but to do so would require sophisticated technologies beyond the reach of most farmers. Some researchers would like to find a way to supply nitrogen to plants that does not involve the use of ammonia at all: by studying the genetics of some plants they would like to obtain crop varieties capable of “recruiting” nitrogen-fixing bacteria to supply it.

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