By Leis Dartnell

Imagine that the world as we know it will die tomorrow. There has been a world-class cataclysm: a major flu, an asteroid impact, or a nuclear annihilation. The vast majority of people are dead, civilization is crumbling, and the survivors of the post-apocalyptic era find themselves in a post-apocalyptic world: cities are deserted, people are plundering each other, and the law of the jungle is the new law of survival.

Even if it sounds terrible, it's not the end of humanity and we'll always come back. As has been repeated countless times in history, sooner or later peace and order will be restored, and stable communities will gradually take shape and painfully rebuild the technological base from scratch. But here's the question: how far can such a society go? In a post-apocalyptic society, is there any chance to rebuild a technological civilization?

To be more specific, we have today consumed the vast majority of easily extractable oil, as well as a significant portion of the shallow and easily exploitable coal reserves. Fossil energy is both the core at which modern industrial society can be organized, and the key player in the birth of industrialization itself. And that's a unique role – even if we can do some degree without fossil fuels today (which we can't), whether we can get back to today's level of technology without fossil fuels at all, is another question.

So, is it possible to rebuild civilization on a planet without relying on fossil energy reserves to reach the possibility of a new industrial revolution? In other words, what if earthlings had never had oil and coal energy? Will our civilization inevitably stagnate in the pre-industrial era before the 18th century?

It's easy to underestimate how much the world is reliant on fossil fuels today. When we think of fossil fuels, we always think of their most intuitive uses for fuel-powered vehicles and thermal power generation provided by coal and natural gas. But we also rely on a wide range of industrial raw materials, and in most cases, extremely high temperatures are required to convert raw materials into usable products, such as glass and metal products, cement, fertilizers, etc. Most often, the thermal energy required for these manufacturing processes comes from fossil fuels: oil, coal, natural gas, and oil.

The problems don't stop there. From pesticides to plastics, a large number of chemical products needed to function in the modern world are organic matter derived from crude oil. As the world's crude oil reserves dwindle further, arguably the most wasteful application of these finite resources is to burn them down. For the sake of these precious organic compounds, people have to be very careful to conserve the remaining limited resources.

But this article isn't about what we should do now – probably everyone knows that people have to transition to a low-carbon economy anyway. What I am answering is a more theoretical, hopefully more theoretical question: Does the rise of a technologically advanced civilization necessarily depend on the availability of ancient and easily available energy sources? Is it possible to build an industrial civilization without fossil fuels? The answer is: maybe—but extremely difficult.

Sun and wind: how far can sustainable energy take us?

The first is a natural idea. Many alternative energy technologies are already well developed, for example, more and more roofs are equipped with solar panels for domestic or commercial use. A tempting question is whether Civilization 2.0 can pick up the legacy of its predecessors directly from the ashes and use renewable energy as a starting point for industrialization?

Well, in a very limited sense, it is possible. If you're a survivor of a post-apocalyptic world, you can indeed collect enough solar panels to live for a while and sustain an electrified lifestyle. Photovoltaic cells have no moving parts, require little maintenance, and are resistant to harsh environments. But they also wear out over time: moisture erodes its appearance, sunlight itself reduces the purity of the silicon layer, the electricity it provides drops by about 1% per year, and after a few generations, all the solar panels that have been handed down will be unusable. And then what to do?

It's hard to build a new solar panel from scratch. Solar panels use thin, ultra-pure silicon wafers, and while the raw material is just common sand, processing and refining silicon requires complex and sophisticated technology. This technical capability is more or less what we need to make modern semiconductor electronic components. It has taken a long time to develop this technology, and it is likely that it will take as long to restore it. So a society in the early stages of industrialization may not be able to produce photovoltaic solar energy.

However, starting with electricity may be the right way to go – most renewable energy technologies today produce electricity. In the course of our own history, the central phenomenon of electricity was discovered in the first half of the nineteenth century, much later than the early development of steam machinery. Heavy industry at that time already relied on internal combustion-based machinery, and since then electrical energy has played a major auxiliary role in the organization of our economic structure. But can this order be reversed? Does industrialization require that thermal machinery must come first?

On the face of it, it is not impossible for a progressive society to be able to build generators, then connect them to improvised windmills and waterwheels, and later develop wind turbines and hydroelectric dams. In a world without fossil fuels, we can envision an electric civilization that largely bypasses the history of the development of the internal combustion engine. Its transport infrastructure is supported by electric trains and trams for long-distance transport and urban transport. By "to a large extent" because we can't get around it entirely.

While electric motors may be able to replace coal-fired steam engines for mechanical applications, as we have seen, our society still relies on heat to drive many of the essential chemical reactions and physical transformations. How can an industrialized society produce key building materials like steel, bricks, stucco, cement and glass without coal?

You can, of course, use electricity to produce heat. We are already using electric furnaces and kilns, and modern electric arc furnaces are already being used to produce cast iron and recycled steel. The question is not whether electricity can be converted into heat, but that meaningful industrial production requires massive amounts of energy, and using only renewable energy sources as a source of heat, such as wind and hydro, would be quite stretched.

Another possible idea is to produce high temperatures directly from solar energy. Instead of relying on photovoltaic panels, solar concentrators can use giant mirrors to concentrate the sun's rays in a small spot. The heat energy concentrated in this way can be used to drive specific chemical or industrial processes, or to make steam to power generators. Despite this, it is still difficult for this system to produce the high temperatures required inside the molten iron blast furnace, for example. It is also clear that the energy efficiency of solar heat gathering is heavily dependent on the local climate.

Unfortunately, in order to produce the "white heat" required by modern industry, we really don't have many good options other than burning things.

But that doesn't mean we have to burn fossil fuels.

The Power of Burning: Can We Return to the Age of Timber?

Let's take a quick look back at the "prehistory" of modern industry. Charcoal was widely used to melt metals long before coal was used. It actually has advantages in many ways: it is hotter than coal, and there are far fewer impurities. In fact, coal impurities were one of the main factors that slowed down the industrial revolution – impurities released during combustion could contaminate the heated product. During the melting process, sulfur impurities can seep into the melted iron, making the finished product brittle and brittle, creating safety issues when used. It took a long time to figure out how to use coal in industrial production, and during this period of history, charcoal performed quite perfectly.

But then, we don't use charcoal. Looking back, it's a bit of a shame. As long as charcoal comes from sustainable sources, it is inherently carbon-neutral because it does not emit new carbon into the atmosphere – although this was not a cause for concern in early industrial civilizations.

However, the charcoal-based industry did not all die out. In fact, it has survived and is experiencing a resurgence in Brazil. Brazil is the world's largest producer of charcoal and the ninth-largest producer of steel due to its abundant iron ore reserves and scarce coal mines, and this is not a small workshop-style industrial production, so the Brazilian case provides an inspiring example of our thought experiments.

The trees used to make charcoal in Brazil are mainly fast-growing eucalyptus, which have been cultivated specifically for this purpose. The traditional method of charcoal making is to build a dome-shaped pile of naturally dried wood and cover it with turf or soil to block the air movement. Brazilian companies have greatly expanded this traditional technique so that it can be used for industrial production. The air-dried blocks are stacked in low, cylindrical masonry kilns and arranged in long rows for sequential loading and unloading. The largest production site can accommodate hundreds of these kilns, which are closed and ignited from above when the wood is inserted.

Charcoal production technology actually retains just enough air inside the kiln to react. There needs to be enough heat of combustion to produce enough heat to drive away moisture and volatile substances, and to pyrolyze the wood, but not so high that it burns the wood directly into a pile of ash. Kiln managers need to monitor the combustion status at all times, carefully monitor the smoke emitted from the kiln mouth, and adjust the whole process by opening or sealing the vents with clay at any time.

This tightly controlled, smoldering, low-temperature charcoal smelting method takes about a week. Similar methods based on this have been used for millennia, but the uses of the fuel thus produced are very modern. Charcoal made in Brazil is loaded out of the forest and transported to blast furnaces, where the ore is smelted into pig iron, which is the basic raw material for modern large-scale production of steel. These "Made in Brazil" are exported to countries around the world, where they are processed into cars, sinks, bathtubs and kitchen utensils.

About two-thirds of Brazil's charcoal comes from sustainable farming systems, so the modern use of charcoal has a reputation as "green steel". Unfortunately, the remaining one-third comes from unsustainable primary forest deforestation. Nonetheless, the case of Brazil does provide an example of how we can supply the raw materials needed for modern civilization beyond fossil fuels.

In addition, wood gasification may also be a relevant option. The use of wood to provide heat is as old as human history, and burning wood alone uses only one-third of its energy; Other energy is dispersed by the wind as the gases and vapors are released during combustion. Under the right conditions, even smoke is combustible. We don't want to waste it.

It is better to promote the pyrolysis of wood and collect the gas produced than mere combustion. If you light a match, you can observe this basic principle: the bright flame does not appear directly on the wood: it floats on the matchstick, there is a clear gap between the two, the flame is actually supported by the heat provided by the pyrolyzed wood, and the gas only burns when it is combined with oxygen in the air. It's fun to see a match up close.

In order to release these gases under controlled conditions, we have to roast wood in an airtight container. The oxygen is tightly controlled so that the wood does not catch fire directly. It undergoes a complex chemical molecular decomposition process called pyrolysis, and then this mass of high-temperature carbonized charcoal at the bottom of the container reacts with the decomposed products to produce combustible gases such as carbon monoxide and hydrogen.

The resulting "generator gas" is a versatile fuel: it can be stored or transported via pipelines, used in street lamps or heating systems, or used in complex machinery such as internal combustion engines. During the gasoline shortage of World War II, more than one million wood-gas vehicles around the world ensured the operation of private transportation. In occupation-time Denmark, more than 95% of farm machinery, trucks and fishing boats were powered by wood gas. About three kilograms of wood (depending on how dry and dense it is) contains about the same amount of energy as a litre of gasoline, while a gas-powered car uses energy in miles per kilogram of wood rather than miles per gallon. Wartime gas-powered cars could travel about 1.5 miles per kilogram of wood, and today's design is a further refinement of that.

But in fact, "Wood Gas" has a lot to do in addition to driving cars. In fact, it is suitable for any of the aforementioned manufacturing processes that require heat, such as supplying energy to kilns that make lime cement bricks. The generator sets of Wood Gas can easily provide power for agricultural and industrial equipment, as well as various pumps. Sweden and Denmark are world leaders in the use of sustainable forests and agricultural waste, which they use to run steam turbines in power stations. Once the steam is used in the Combined Heat and Power Plant (CHP), it is transported to nearby towns and factories for heating, enabling the CHP plant to achieve 90% energy efficiency. Such plants demonstrate the excellent industrial prospects of completely eliminating the dependence on fossil fuels.

But how much wood do we have to work with?

So is this considered a solution? Can we rebuild the new society on the basis of wood and renewable energy? Perhaps, if the population is rather small. But there's a conundrum here. These alternative options are premised on the survivors' ability to build efficient steam turbines, combined heat and power plants, and internal combustion engines. Of course we know how to make these things, but if civilization is destroyed, who knows if all this craft knowledge will disappear with it? If even the knowledge is gone, how much chance will it be for future generations to be able to rebuild it?

In our own history, the first successful application of steam engines was for coal mine pumping. It's a fuel-rich environment, so it doesn't matter if the original design was extremely inefficient. The growing production of coal is first used to melt the iron feedstock and then shape the iron. Iron components were used to make more steam engines, which were eventually used to excavate mineral deposits or to power blast furnaces in iron foundries.

And, apparently, machine builders also used steam engines to make more steam engines. It is only after the steam engine is built and put into use that subsequent engineers can begin to improve its efficiency and energy savings. Various methods of reducing volumetric weight and using it for transportation or factory production were subsequently developed. In other words, there was a positive feedback loop at the heart of the Industrial Revolution: the production of coal, iron, and the steam engine all supported each other.

In a world where there are no off-the-shelf coal mines, there may be no chance to test the extravagant prototypes of the steam engine, even though they will become more mature and efficient over time. How hopeful is it that a society will be able to fully understand thermodynamics, metallurgy, and mechanical mechanics to make more complex, precise and efficient internal combustion engine components without experimenting with the simpler steam engine external combustion engine, the steam engine with separate boilers and cylinder pistons?

In order to reach the heights of modern technology, we consume a lot of energy, and it will take a lot of energy to start all over again. Without fossil fuels, the world of our future will need a frightening amount of wood.

In a temperate climate like the UK, one acre of broadleaf trees can produce four to five tonnes of biofuel per year. If fast-growing varieties such as willow or miscanthus are cultivated, yields can be quadrupled. The trick to maximizing timber production is to use the "dwarf forest method": cultivating trees that grow from their own stumps, such as ash or willow, which can be cut down again in 5-15 years. This ensures a continuous supply of timber without the fear of cutting down all the surrounding trees and causing an energy crisis.

But here's the trouble: the technology of working in the woods was well developed in pre-industrial England. It has not been able to keep up with the rapid pace of society. The core problem is that forests, even if well managed, are in conflict with other land uses – mainly agricultural land. The double dilemma of development is that as the population grows, people need more farms to provide food and more wood to provide energy, and the two needs are competing for the same land.

In our own history, things have developed like this: from the mid-16th century onwards, Britain responded to this dilemma by mining coal massively – essentially by tapping the energy of the ancient forests beneath the ground without reducing agricultural output. An acre of grove produces the equivalent of 5-10 tonnes of coal in a year, but the latter can be dug directly from the ground much faster than waiting for the grove to regrow.

It is this limitation of heat supply that will become the biggest problem in trying to industrialize in societies without fossil fuels. This is true in our post-apocalyptic world, or in any hypothetical world that does not take advantage of fossil fuels. For a society to industrialize without these conditions, it would have to concentrate its efforts on a specific and extremely advantageous natural environment – not the coal-filled islands, as in 18th-century England, but in Scandinavia or Canada, where both the hydroelectric energy provided by the rapid flow of water and the sustainable heat provided by the vast vegetation.

Still, the Industrial Revolution without coal reserves was very difficult, to say the least. Today's use of fossil fuels is actually growing, and many of the reasons for concern are too familiar to be repeated. It is imperative to move towards a low-carbon economy. But at the same time, we should also know how these accumulated thermal energy reserves have supported us step by step to get to where we are today. Without them, one might have taken the hard path of slowly advancing mechanization using renewable energy and sustainable biofuels, which might or may not have succeeded – but it may not. We would do well to hope that the future of our own civilization is optimistic, because we may have exhausted all the resources needed for any successor society to follow in our footsteps.

Author: Leis Dartnell ()

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