Showing posts with label charcoal. Show all posts
Showing posts with label charcoal. Show all posts

Thursday, April 16, 2009

Subsistence Solar Heater

This is not particularly new technology but it is perhaps getting the marketing boost it needs. I also think that we can count on modern communications to keep the interest up in the natural market areas.

The value of this device is to displace a lot of charcoal out of the heating market. The device itself is up to the task of producing boiled water and that means hot beverages and also the production of stews. It may not seem like a lot, but if you are dependent on charcoal, that is most of your cooking energy on a given day A frugal cook is likely to be able to reduce charcoal use several fold.

Stripping forests for charcoal at the subsistence level that we are dealing with is never well done and is often unsustainable. We talk about the goats clearing of the forests of the Sahara. Before the goats finished the job, I am sure humanity hacked down the brush and trees for charcoal. It all goes on as if nothing has changed even today.

This is an incredibly simple device easily fabricated, packaged and shipped to the customers. Let us hope that this is enough to get it into the market place.

$6.60 Solar Cooker Wins Financial Times Climate Change Contest
Written by Megan Treacy
Thursday, 09 April 2009

In a beautiful marriage of high function and very low cost, a $6.60 solar cooker called the Kyoto Box won the Financial Times Climate Change Contest and $75,000 from Hewlett-Packard to get the idea into production.

The
Kyoto Box is made from insulating two cardboard boxes, one stacked inside the other, with straw or newspaper, placing foil inside the first box and then painting the inside of the second box black. An acrylic cover tops off the design.

The very simple and cheap design is already being produced in Nairobi and the maker Jon Bøhner hopes that it will cut down on the use of firewood for cooking, which would slow deforestation and reduce carbon emissions and indoor pollution throughout Africa. The box can boil 10 liters of water in two hours for cooking or for purifying.

Other simple designs that made it to the final round of the contest include a garlic-based feed supplement that would reduce the methane in cow "emissions" and a wheel cover for delivery trucks that would boost efficiency by decreasing drag.

Monday, March 23, 2009

Bronze

This is an excellent history of the bronze industry of the Bronze Age in Eurasia. Not unexpectedly, it fails to integrate the Bronze Age of the Americas at the same time. The acceptance of the reality of the Atlantic trade has not happened yet, no matter the climbing mountain of evidence. I suspect that every possible copper source around the globe that was accessible was exploited.

Again, if a Bronze age mining clan could exploit copper grades of a miserable eight pounds to the ton in Ireland and all the man hours of wood cutting, charcoaling, rock breaking, grinding, metal separation and smelting that that implied, then getting on an open boat to travel across the Atlantic was paradise.

Much of the conjectures that I have made earlier regarding the economic importance of copper are richly confirmed in this work. I have little to add.
There is a good comment linking the heroic image of the smith from Greek mythos to its clear Bronze Age origins. Arsenic was an occupational hazard that likely wreaked most in the trade. That also explains the popularity of tin. Not because the result was particularly better, but because the smith survived repeated exposure.

Anyway, this is a very complete survey and updates earlier work.

Bronze

Once skilled smelters could extract copper from sulfide ores, copper became much more plentiful as a metal. Eventually, however, smiths realized a new paradox: the most valuable product from these new ores was not pure copper, but a range of new substances that contained impurities.

In nature, chemicals are hardly ever pure. No wedding ring is pure gold, and no natural water is pure. Copper ores are never pure either, and all smelted copper contains impurities. The ancient smiths who exploited the first easy native-copper nuggets, and the dramatically colored surface malachite and azurite carbonate ores could select relatively pure ores for their smelters, and they did not have to worry too much about impurities in the copper that they produced. But as demand rose and the first early ore discoveries were worked out, they mined deeper, and began to reach copper sulfide ores that were more difficult to smelt and less pure.

The "copper" that began to come from the smelters now had relatively more impurities in it. Smiths were inadvertently smelting batches of metal that were not pure copper. Each batch was now an alloy, a metallic substance that is not a chemical compound, but a physical mix of two or more metals that may act as if it were a different metal. In our modern hardware stores, for example, we can buy solder (an alloy of tin and another metal [often antimony] which doesn't behave like either of them).

Almost all copper ores contain some small proportion of arsenic, tin, zinc, antimony, or nickel, which mixes at the molecular level with the copper during smelting‹in other words, a tremendous number of subtly different alloys can emerge out of a smelter after a mixture of ore has been smelted, even though the geologist has been skilled enough to select ores that are rich in copper. The alloys are still dominated by copper, but the alloy has a lower melting point than pure copper, which allows easier melting and casting. The castings are better quality, and the alloy is much harder than pure copper after it has been worked by hammering. Paradoxically, the less pure copper ore that was available, the greater the variety of alloy the smith would produce from his smelter. By trial and error, early metallurgists (smiths) would soon come to associate a particular mixture of ores in the furnace with a particular result. In time, a skilled smith would be able to have some control over the end product, producing not copper, not a random unknown alloy, but a specific alloy to suit the job at hand. The Bronze Age marks the time at which smiths became metallurgists, makers of magic, heroes, and gods. Bronze Age smiths were often buried with the tools of their trade: hammers, an anvil, knives and molds.

Bronze is any alloy that is 85-95% copper, with the other 5-15% made up of mainly of tin or arsenic, though other metals can be present in small amounts. It turns out that this range of chemistry produces an alloy that is harder than copper even though it melts at a lower temperature. A low amount of tin or arsenic does not improve the copper enough, and a higher amount makes the alloy so brittle that it is useless. Tin bronze is not too difficult to work, and melts at 950 degrees C rather than the 1084 degrees C of copper, making it easier to cast. Both bronzes make strong hard tools and weapons that retain an edge as well or better than stone, once they are strengthened by hammering. Other metal alloys were not available to bronze-smiths. Zinc (which alloys with copper to make brass) or nickel are rarer and much more difficult to smelt, and antimony/copper alloys are brittle.

In the Chalcolithic period in which copper and stone artefacts co-existed, we can see smiths producing bronzes, without realizing what they had done, and without using the bronze to its best advantage. For a long time, smiths used copper of greater or lesser purity without much discrimination. For example, many early Chalcolithic objects are made from copper with more than 5% arsenic. They were not made with the properties of arsenical bronze in mind, however, because there is no correlation between the object and the arsenic content: tools are made with low-arsenic copper and ornaments are made with high-arsenic copper. Probably arsenical copper was used only because arsenic lowered the melting point and made casting easier.

When and how were the mechanical properties of bronzes deliberately produced by smiths? I expect that at first, a skilled smith would be able to sense the different properties of each batch of metal that came from the smelter, and would keep the rough ingots arranged by property. He would quickly find that bronzes varied in hardness along a scale, with the optimal balance between softness and brittleness at 5­10% tin/arsenic. It's not that he had a chemical analysis, but he had a feel for hardness as he hammered the hot ingot. Once he was that far into the analysis, it would be an obvious step to combine two ingots at the ends of the scale to try to mix them into the best-quality alloy in between, and he would discover that the process worked as long as he melted then together completely. From that point, the smith with the best analytical skills (his touch with the hammer) would be able to produce the best artefacts.

At some point, a smith would connect the properties of the bronze ingot with the properties of the ores going into the smelter, which would save him a lot of work and charcoal blending ingot together. At this point the smith is truly master of his craft, and one can easily imagine that the best smiths would have routinely produced bronzes of much higher quality than normal. Smiths take on legendary or god-like form for the first time.
Arsenic ores are more common than tin ores, and make high-quality bronzes: there are no tin bronzes in Western Asia before 3000 BC. Arsenic bronzes do not cast as well, but are as hard as tin bronzes. The choice between arsenic and tin bronze may not have been easy, even when it became available. The choice may have depended on the ores available locally: arsenic/copper ores are common, while copper/tin ores are rare. We don't know accurately how often arsenate ores occur in copper deposits because the question is not important in modern mining. In this case, it is just possible that Chalcolithic miners were better informed than we are!

After 3000 BC, Cretan and Western Mediterranean bronzes were largely made with arsenic, Egyptian bronzes almost exclusively with arsenic, but Anatolian bronzes were made with both. We suspect that Anatolian bronzes were first made with tin extracted from the mineral stannite. It is difficult to distinguish tin-bearing stannite from the arsenic-bearing minerals arsenopyrite and enargite. Possibly the first use of tin ores stemmed from a simple mistake by prospectors searching for more arsenic-bearing ores.

Eventually smiths turned to tin ores even though they were more difficult to obtain than arsenic-bearing ores. Smelters work outside, so fumes can be dispersed in the wind, but a smith cannot help breathing in arsenic fumes as he heats, casts, and hammers hot arsenic-laced bronze. The symptoms of low-level arsenic poisoning develop slowly, usually over a period of years. The most obvious symptoms are gradual nerve damage in the limbs. Eventually smiths must have realized what was happening to them, and what was responsible; and eventually they recognized the danger of working with arsenic alloys. Except in Egypt, where arsenic was used until 2000 BC, tin bronze gradually became the alloy of choice, and the dominant metal of advanced civilizations in the Western World for 2000 years. The long agony of so many Bronze Age smiths has come down to us in legend, however: the Greek smith god Hephaestus and his Roman counterpart Vulcan were lame. This is not an occupational hazard of the Iron Age smiths that forged spears for the Greek hoplites and swords for the Roman legionaries. It reflects the centuries-old folk memory of their predecessors.

Bronze gave its name to the Bronze Age, a major innovative period in human history. Bronze artefacts are found at Ur and other Mesopotamian cities after about 3000 BC, then all over the Near East. A "bronze age" can only occur where copper and tin are both available, where the mining and smelting technology are developed, and where trade networks can disseminate the new technology and the new artefacts. Many regions did not have a bronze age, but changed directly from Chalcolithic to iron use.

The Source of Tin for the Bronze Age

Until 1984 we did not know the source of tin for the ancient bronze civilizations of the Near East. Now more than 40 ancient sites of tin mining have been discovered in the Taurus mountains of southern Turkey, only 40 km from the Cilician Gates, the main pass through the Taurus. The area has a great variety of metal ores, including placer deposits of gold and silver. But lead (as galena) is also present, and lead artefacts are known from Çatal Höyük. Cast lead figurines had become common by the late third and early second millenia, and silver was important from the late fourth millennium.

Cassiterite, the dominant tin ore, is tin oxide. It occurs as distinctive black grains in alluvial sands, and in some areas it is left behind as a resistant mineral after granite has weathered down to sand and clay. It is possible that its properties were examined closely by potters: kaolinite deposits often occur around old granite bodies, and cassiterite grains could be caught up in potters' clay. Since cassiterite melts at only 600 degrees C, it would be noticed, and perhaps accidentally smelted to tin.

An ancient tin mine was discovered in the Taurus at a site named Göltepe, which was a large village from around 3290 BC to 1840 BC. The mine has narrow steep shafts, and at least some of the underground work may have been done by children (several skeletons of children have been excavated from the mine). Cassiterite ore was then crushed at the surface, washed, and smelted with charcoal in rather small crucibles rather than the large furnaces characteristic of copper smelting sites. Goltepe has yielded many crucibles in which the tin was smelted into a slag that contained globules of pure tin, which had to be separated out by crushing and re-washing. The small scale of the crucible operations, and the crushing of the slag for multi-stage refining, make it difficult to detect the scale of the operations. But since over time the industry produced enormous deposits of slag in the district (600,000 tonnes in one pile), Göltepe was probably a major site for much of the Early and Middle Bronze Age. Some of the slag may date from more recent times, at least some of it is ancient, and some of it is very rich in tin.

The Taurus mountains, then, probably provided the tin for alloying into the earliest tin bronzes of the ancient Near East. There is no copper at Göltepe, and the tin was clearly exported to other centers for making bronze. However, other cities close by were centers that were famous for metal trading and metal working in the second millenium BC: Kültepe and Acemhüyük.

Metal traders and imperialists

After about 3500 BC, there was increasing use of several metals in Mesopotamia, not just copper and lead. Gold and silver were exploited as native metals. Silver was extracted from lead ores, possibly first as a by-product of lead, then as a desirable commodity in its own right. Bronze appeared in the region about 3000 BC.

The metal-working found in the royal tombs of Sumer (about 2650­2500 BC), whether it was done locally or was imported, is breath-taking in its beauty and skill. Riveting and soldering were invented, and by 2500 BC the value of tin was well known for soldering and brazing. Casting techniques were good enough to make human-sized statues and small lost-wax figurines.

Metal began to play a part in international relations, especially during Akkadian times (2350­2200 BC). About 2350 BC Sargon of Akkad invaded Anatolia from his lowland base. He set up a short-lived empire of secure trade routes, and he boasts that a single caravan carried about 12 tonnes of tin, enough to make 125 tonnes of bronze‹and to equip a large army.

After the fall of Akkad, the Assyrians ended as the dominant power in what is now northern Iraq. We have known for a long time that tin was brought in to Kültepe, in Anatolia, by Assyrian merchants and sold to local metal workers at prices that are recorded on local tablets as very high. A major trade in tin is recorded in Old Assyrian letters from about 1950-1850 BC. Tin shipments were sent on donkey caravans from the Assyrian capital, Assur, to Assyrian merchants living in Kültepe, who sold it to the local smiths, presumably for bronze-working in and around Kültepe. The shipments record well over a tonne of tin per year, enough to make about 10­15 tonnes a year of bronze.

This trade is subject to several interpretations, of course. The most likely is that foreign tin was imported to the processing area as local ores ran out, in the same way that South American tin was shipped to South Wales after the Cornish tin mines could no longer supply enough to the tinplate industry. (Today the British steel industry depends on imported iron.) Probably tin, the smaller and scarcer component of bronze, was shipped into Kültepe because the district was rich in copper, fuel, and technological skills, even after local tin ores were mined out. This policy would certainly make economic sense for the smiths of Kültepe, even if they had to import the tin to keep their bronze industry going. Presumably the Assyrians bought much of the bronze, though this is not recorded in the letters: the tin was sold in Kültepe for silver or gold. Kültepe by this time may have been very much a "smokestack" city, working bronze but with the profits skimmed off by the politically dominant Assyrians. (The letters indicate that the tin was marked up 75­100% between Assur and Kültepe, while transport costs were about 10% of the price in Assur.) Certainly any wealth from the industry did not support the same glittering power at Kültepe that is seen often in Bronze Age centers, though the Assyrian merchants in Kültepe were buried with gold and silver ornaments!. By 2000 BC Kültepe was an industrial city: political power was elsewhere.
Tin must have been a very important strategic metal, even though bronzes could also be made with arsenic, at great occupational hazard for the smelters and smiths. All around the Mediterranean, copper and tin mining were dramatically stepped up in this period.

Timna: Bronze Age mining and smelting

The Chalcolithic copper mining district at Fenan in the southern Levant was expanded in the Bronze Age‹major workings began some time between 3000 BC and 2000 BC. The most famous sites are in the Sinai desert, and at Timna near Eilat, but others stretch from the southern Sinai to northern Israel and Jordan. There are more than 300 sites near Timna alone, and over 400 in the Sinai Peninsula.

The Timna workings are some of the best-studied industries of the Early Bronze Age, typical of the entire desert copper-mining and smelting operations, even though the quantities mined were small, even by the standards of the time. The miners at Timna were digging for nodules of malachite in fairly soft sandstone. They used hafted stone hammers, digging vertical shafts connected by galleries. The shafts and galleries were rather haphazard, presumably following rich ores without any overall plan. The ore preparation sites contain broken pieces of malachite copper ore, granite mortars and pounding stones, other stone tools, and pottery shards. The smelting furnaces were not on the valley floor, but high on the ridges, so that the wind would help raise the furnace temperatures by forced draught. Pieces of slag are scattered round the furnaces, some containing little blobs of metallic copper created in the furnaces. The furnaces themselves are bowl-shaped, with a clay layer lining a sandstone cavity about 80 cm (nearly 3 feet) high. The fuel was collected from the desert acacia trees in the region, and fuel shortage was probably the main reason for the rather small production from Timna.

Experiments show that the Timna furnaces reached temperatures between 1180° to 1350°, which could only have been achieved with some forced draught other than natural wind currents. Perhaps goatskin bellows were used. Charcoal makes a hotter fire than wood, and may have been used also. The Timna furnaces produced rather impure masses of metal that needed further cold working by hammering, or a further firing to produce much purer copper ingots. (Later technology, with larger furnaces and hotter fires, allowed smelting to be carried out in one step.)

At Fenan, which was mined for copper in Chalcolithic times (Chapter 3), Bronze Age workings began around 2000 BC. The Fenan miners now followed the ores far underground, in inclined shafts that were as much as 15 to 20 m underground and at least 55 m long. The ore-bearing layers were carefully mined on a chamber-and-pillar system, with pillars left to support the roof. The best ore was separated from waste rock underground by lamplight, and the waste either packed into old galleries, or piled up into artificial support pillars, with the addition of large boulders dropped down from the surface from the bed of the wadi. These methods exploited the ore efficiently, avoiding the labor of carrying too much material up out of the mines.

Bronze Age production at Fenan has been studied only superficially. Fenan production was large, and it must have been a strategically important area. The copper was eventually worked into very finely executed objects, many of them ornamental pieces that presumably had high value. Copper objects were traded and hoarded at this time all over the region from Anatolia to Egypt and Mesopotamia.

Timna under Egyptian management

The best documented history of technological advance in early smelting methods comes from Egypt, where pictorial images flesh out the written record. The Egyptians brought new technology to the malachite workings at Timna around 1300-1100 BC, where the local Midianites worked at least eight large mining centers along the Timna cliffs, using bronze tools. It's clear that Egyptian copper- and gold-mining technology had its roots in mining methods that were originally designed to mine for turquoise in the Sinai peninsula.

The smelting centers nearby were highly organized, with areas for ore crushing, storage pits for ore, charcoal, and iron oxide flux. Scores of furnaces were clustered close together, this time on the valley floor rather than on the ridges, because the Egyptians now relied entirely on bellows to pump air through the furnaces. Each furnace was sunk into the desert sand, and was lined with cement. Each had one or more complex tuyères in it, nozzles to which a bellows were connected.

The copper was sent off to Egypt to be made into bronze: tin bronze by this time. Copper and tin ingots were melted together in the right proportion, and the molten bronze used to make the desired objects. These were sometimes as large as temple doors. The Sinai mines were not the major source of copper for ancient Egypt, however: there was extensive trade with Cyprus, too.

Cyprus

Cyprus has extraordinary copper deposits that were mined in ancient and classical times: the name for the metal in all Western European languages is derived from the Latin aes cyprium which means "Cypriot copper."

Once smelting of sulfide ores became economic from about 1600 BC, Cyprus became a vital link in the trade of Eastern Mediterranean Bronze Age cultures for 500 years, serving not just as a convenient island in the center of many trade routes, but producing large quantities of copper for export. Every major copper body mined in the early 20th century in Cyprus had already been discovered and mined in ancient and/or classical times. Altogether, Cyprus has more than 40 slag heaps containing more than 4 million tonnes of historic slag, showing the massive scale of the industry over time.
Homer says that his heroes wore Cypriot bronze armor in the Trojan War (about 1100 BC?). The Cypriots used copper and bronze to pay debts and tribute: for example, about 1470 BC the ruler of Cyprus paid tribute to Pharaoh Tutmose III with 108 ingots of copper. The ingots weighed about 30 kg (65 pounds), and were poured into molds that resemble ox-hides‹a rectangle with four projecting corners. The size of the ox-hide ingots means that furnaces had reached much larger size than those at Timna a few centuries before: the ingots are ten times as big. The shape is probably convenient for pouring and handling, rather like the "pigs" of later iron-workers, but it may also refer to the bull-worship of the region. Ox-hide copper ingots have been found all over the Mediterranean shoreline, reflecting two facts: first, that most large-scale trade was shipborne; and second, that copper ingots were an acceptable form of currency. A shipwreck from about 1300 BC, discovered at Ulu Burun, near Cape Gelidonya on the Turkish coast, was carrying a tonne of copper ingots and several dozen small tin ingots, new bronze tools, and scrap metal, and a blacksmith's forge and tools. Thus the cargo of one ship could have equipped the army of one of the small Mycenean city-states: 50 suits of bronze-sheathed armor, 500 spear points, 500 swords. This ship was also carrying enough valuable gift goods (ivory scepters, shell rings from the Red Sea, and a complete ostrich egg) that excavators are beginning to suspect it may have been carrying a diplomatic mission along with its cargo of strategic weaponry (probably not a new concept in international politics).

Copper and bronze were precious enough that old artefacts were recycled. (A Middle Babylonian document says that if a slave escaped with his copper chains, the guard responsible would be charged twice that amount in copper. In other words, the chains were valued as much as the slave.) Smithies were often as much recycling centers for old bronze tools as they were centers for alloying new copper and new tin into bronze. Archeological sites often contain as much scrap bronze as they do new ingots.

Copper and Bronze in Central Europe

Trade in copper was not confined to the Mediterranean, of course. About 2500 BC copper began to be produced from centers in Germany and the Carpathians. By 2000 BC, the bronze industry had percolated throughout Europe, and regional smiths made their own distinctive products. Deep gallery mines in the Alps, in Bohemia, and in the Carpathians produced copper ores, and bronze really began to displace stone for the first time in everyday tools during this period. The best studied are mines in the Mitterberg region of Austria, which had systematic galleries 150 m long that followed ore bodies, interconnected in some places by galleries that must have been for better air circulation, for the sake of fire-cracking as well as the health of the miners. Wood and clay dams kept water from flooding the working faces, but even so, there were water problems, and many pieces of wooden buckets have been found. Many thousands of tonnes of copper were produced during the thousand years of the Bronze Age in this part of Europe: some of the slag heaps have up to 500 tonnes of slag, and there are hundreds of them. Copper ingots were mass-produced, and were cast into characteristic shapes, rings or curved bars. Thousands of them have turned up in ancient copper hoards, many hundreds of kilometers away from the mines.

Bronze in China

The earliest well-dated bronze object in China is a knife from Gansu province, from about 3000 BC; it had been cast in a mold. There are smelting sites nearby with malachite ore, slag, and corroded copper. Somewhat later, the Qijia Culture of north China was producing a good number of copper and bronze awls, knives, sickles, and adzes, using casting techniques followed by cold-hammering to harden them. In 1976 copper and bronze artefacts were found in Gansu province associated with the Xia Dynasty, which on other evidence is dated from 2200 BC to 1760 BC. All the evidence, then, suggests an independent Chinese discovery of bronze (tin is comparatively abundant in China).

Bronze became widespread in the central plain of China in early Shang times. The Shang dynasty ruled from its capital at modern Anyang, in Henan province, for 300 years until its collapse in 1122 BC. Anyang was close to the most abundant deposits of lead, copper, and tin in China, and bronze-making apparently spread from here to the rest of China. Shang metallurgists had discovered that a small percentage of lead in the bronze made casting easier. They produced ceremonial cast bronze cups and bowls of all sizes up to massive cauldrons, intricately decorated with raised or incised relief designs taken from nature. The largest Shang cauldron weighs 875 kg (nearly a ton), and is the largest metal casting from anywhere in the world from the second millenium BC.

Casting large objects is not easy. It requires large crucibles and efficient furnaces, and casting the largest objects requires coordinated melting in many crucibles that resembles a modern factory.

A problem with the quality of the Shang bronzes is that they are so impressively large, leading some scholars to feel that somewhere else there must be an earlier bronze-working culture still to be discovered. However, the Shang metallurgical tradition probably arose very quickly from pottery making. The Chinese made porcelain in Neolithic times: pottery kilns found near Xi'an were designed to maintain temperatures as high as 1400 degrees C as early as the 6th millenium BC, more than enough to melt copper. Many of the ritual Shang cups and crucibles, including their ornamental relief, are shaped in direct continuity with earlier clay objects. Shang metallurgists did not use stamping, or engraving, or hammering in their work: they simply cast their works of art. Probably, then, the Shang used casting methods almost exclusively because their pottery industry was so advanced they could readily reach the high sustained temperatures that made smelting and casting comparatively easy. The Western tradition of hammering metalwork and the Chinese tradition of casting it (at least from Shang times onward) are in stark contrast. .

The Chinese became more sophisticated bronze metallurgists than their Western counterparts. The famous terracotta army of the Emperor Qin, made for him about 220 BC and buried with him, have weapons that are basically bronze, but they have been deliberately alloyed with metals such as titanium, magnesium, cobalt, and so on, no doubt after empirical trial and error, to give superior hardness and penetrating power. This weaponry, combined with technological advances such as fast-loading crossbows, united China under the Qin dynasty and defended it against invaders.
Other Chinese bronzes, designed for other purposes, have lead alloyed to improve casting fidelity and to make polishing easier. These alloys were used to make bronze mirrors and bells. In 1978, 64 bronze bells were found in the tomb of a nobleman named Yi, dating from about 450 BC. The largest bell weighs 203 kg (about 450 pounds), and is 1.5 m (over 4 feet) tall. The bells together allow a complete 12-tone scale to be played by a team of five to seven musicians.

Overall, the Chinese bronze industry was very large: an enormous mine dating from around 400 BC has been excavated at Tonglushan: it covered an area of 2 km x 1 km, and had deep timbered underground galleries.

Mining, Smelting, and Fuel

Once copper smelting developed from pottery-making, the use of wood fuel accelerated. By the time the Bronze Age was well under way, wood was being consumed around the Eastern Mediterranean on a scale that could not possibly be sustained on a long-term basis. Mining, smelting, metal-working, ship-building, pottery-making, and construction industries all had massive appetites for fuel, and almost all domestic fuel was also wood.

As cities developed around the seasonally dry eastern Mediterranean, they had to build large cisterns for water supply; most often their construction demanded large quantities of cement and plaster. Mediterranean private and public buildings all contained large quantities of cement, plaster, brick, and terracotta, all of which required far more wood for production than the equivalent amount used directly for construction. The effects on local fuel supplies would have been increasingly severe.

Egypt, which has practically no trees, was trading with Byblos (on the Lebanese coast) for cedar for shipbuilding, temple construction, and furniture-making as early as 3000 BC. But perhaps the most famous documentation of the shortage of wood around the ancient Mediterranean is the Epic of Gilgamesh, the earliest epic poetry that has survived. Gilgamesh was a Sumerian, king of Uruk around 2700-2500 BC. He conquered Kish, Uruk's great rival city, thus gaining power over all of southern Mesopotamia. Apparently the first epics about him were written in Sumerian around 2000 BC. We do not have the originals, but we have copies made by scribes in Old Babylonian times for their libraries. They were separate stories, and the welding of these separate pieces into an Epic was an Akkadian literary innovation, not a Sumerian one. This means that the central theme of the Gilgamesh epic may date to 1500 BC rather than Sumerian times, but it is still illuminating.

Stripped of sex and violence, the Gilgamesh epic is about deforestation. Gilgamesh and his companion go off to cut down a cedar forest, braving the wrath of the forest god Humbaba, who has been entrusted with forest conservation. It's interesting that Gilgamesh is cast as the hero, even though he has the typical logger mentality: cut it down, and never mind the consequences. The repercussions for Gilgamesh are severe: he loses his chance of immortality, for example. But the consequences for Sumeria were even worse. It's clear that the geography and climate of southern Mesopotamia would not provide the wood fuel to support a Bronze Age civilization that worked metal, built large cities, and constructed canals and ceremonial centers that used wood, plaster, and bricks. Most timber would have to be imported from the surrounding mountains, and deforestation there, in a climate that receives occasional torrential storms, would have led to severe erosion and run-off. The loss of Gilgamesh's immortality may be a literary reflection of the realization that Sumeria could not be sustained.

Theodore Wertime suggested that massive deforestation of the eastern Mediterranean began about 1200 BC, for construction, lime kilning, and ore smelting. Probably it began earlier in the drier regions further east. King Hammurabi's laws (around 1750 BC) carried the death penalty for unauthorized felling of trees in Mesopotamia. The problem may have been even worse in intensive metal-working regions like Anatolia. Metal smelting and forging had been going on in Anatolia for at least 3000 years by 1200 BC.

At any rate, most likely the Bronze Age saw a westward spread of a timber crisis. By 800 BC an extensive new use (ornamental and roof tiles) added to the burden, and around 500 BC the rise of the classical civilizations brought the final intolerable strain on the forests immediately round the Mediterranean. Eratosthenes, writing of the Late Bronze Age, say 1200 BC, reports that Cyprus was so heavily forested at that time that even smelting copper and silver, and felling trees for shipbuilding, had made little inroads on the forest. Farmers were even encouraged by gifts of land to clear the forest for agriculture. But soon after this a boom in mineral production, and a major improvement in the technology of tree-felling tools (as well as military weapons) both allowed and encouraged major forest clearing.

The great silver mines of Laurion, near Athens, required not only the fuel to smelt the ores, but the fuel to build and maintain the water cisterns. Wertime estimated on the basis of 3500 tonnes of silver and 1.4 million tonnes of lead production for classical Athens over perhaps 300 years, that the Laurion mines had consumed 1 million tonnes of charcoal and 2.5 million acres of forest. It is, in fact, quite likely that the mines declined, not because they were exhausted of ore, not because the miners had reached the water table, but because the fuel costs had risen to the point that they were uneconomic to run. It is clear that deforestation, accompanied by soil erosion, was already a severe problem in Attica, the region surrounding Athens. Plato wrote that the region is a mere relic of the original country.... What remains is like the skeleton of a body emaciated by disease. All the rich soil has melted away, leaving a country of skin and bone. Originally the mountains of Attica were heavily forested. Fine trees produced timber suitable for roofing the largest buildings: the roofs hewn from this timber are still in existence.

Shipbuilding timber had to be imported from the Balkans and southern Italy to build the great Athenian fleet that beat the Persians at the Battle of Salamis in 480 BC. Timber was a vital strategic commodity during the Peloponnesian War between Sparta and Athens. In 422 BC the Spartans conquered the Athenian trading cities on the coast of Macedonia. This alarmed the Athenians greatly, because it cut off their gold supplies and their ship-building timber, which had been shipped down the coast from the inland forests of Macedonia. By 415 BC Alcibiades of Athens was arguing for a major expedition to try to seize control of Sicily because of the supplies of timber there‹and the failure of this expedition was the critical point at which Athens lost control of the war and went down to defeat.

[A similar situation faced the British during the war against Napoleon. Napoleon had ordered an embargo on trade with the British, and in 1801 the French armies controlled Denmark. The Danes controlled seaborne trade with the Baltic Sea, because all ships had to pass by Copenhagen on their way out through the Kattegat into the North Sea. The Baltic trade was vital for the British because it provided them with their only supply of fir trees for ships' masts for the Royal Navy. (The American colonies, with their vast forests, had been lost in 1783 or 1776, depending how you like to count it.) The British fleet bombarded Copenhagen, destroyed the Danish fleet, and opened that vital strategic route. History might have taken a very different turn if the British had failed. It was close. Admiral Nelson ignored orders to withdraw (by putting his telescope to his blind eye) and pressed home the critical attack on the Danish fleet.]

The crisis in wood continued to plague Athens. By 313 BC the only available ship timber in or close to Greece itself was in the far northern forests of Thrace and Macedonia: overseas supplies had to come from the Black Sea coasts, southern Turkey, Lebanon, or Italy. By the 4th century BC it was no longer economic to transport charcoal overland and uphill to the mines at Laurion: instead, the ore was smelted down on the coast, and charcoal was shipped in on barges. Even then, an increase of lead content in the slag shows that the smelting was being done with minimum fuel.

The island of Elba was once called Aethaleia, "the smoky island," because of the massive smelting industry there. But the Romans had to give up smelting ores from Elba on the island itself in the first century BC because they ran out of wood: they had to ship ore to Populonia on the mainland to continue the industry. By late medieval times, even the productive forests of Germany could usually support iron smelting for only three months a year.

The Rio Tinto mines in Spain probably needed 260 tonnes of wood a day even in Roman times. Fuel shortage may have been the single most serious constraint on copper production as early as the Bronze Age in some areas.

Copper smelting needs a great deal of fuel, especially if the ore supply is dominantly sulfide. About 300 kg of charcoal are needed to produce 1 kg of copper by smelting 30 kg of sulfide ore. A tonne of charcoal needs somewhere between 12 and 20 cubic meters of wood.

Archaeologists have estimated that the Bronze Age copper mines at Mitterberg, in the Austrian Tyrol near Salzburg, must have employed about 180 miners and smelters to produce about 20 tonnes of copper a year. Then one has to add the woodcutters, carpenters, charcoal burners, and carters who cut, carried, and processed the wood needed for the gallery timbers, the firing of the working face, and the fuel for the furnaces, and then add the farmers that fed all these. This was a very large-scale operation.

In copper smelting we find, perhaps, the first major environmental effect of mining. The Mitterberg copper mine probably required about 19 acres of forest to be felled each year, just for the smelters. Even with efficient natural regeneration of the forest, this is a sustainable harvest from perhaps 2 square miles of forest. In fact, however, the cleared land was probably used not for re-growth but at least partly for agriculture, to support the mining community.
On a time scale longer than 10 years, however, a Bronze Age copper mining operation must have caused local deforestation on a large scale, and ever-increasing costs for hauling the wood to keep the industry going.

The problem may not have been so great in the Alps, where there were smaller populations, and where the forest regrew comparatively quickly. But in the drier Mediterranean countries, there was an irreversible change in the vegetation and landscape. On Cyprus, the magnificent pine forest that once covered the island was cleared in a comparatively short time, mainly for charcoal for smelting. Cyprus has a classic Mediterranean climate with a long dry season, and winter rains on steep deforested slopes quickly degrade the soil by washing it downhill. Seedlings have difficulty in re-establishing the forest, especially after clear-cutting, and the soil quickly degrades to the point that pine forest cannot recover even by deliberate planting. Certainly the Mediterranean island of Seriphos has been deforested for a long time, although there are large copper slag heaps on the tops of the ridges, evidence of former forest and former massive wood consumption.

The tremendous tonnage of ancient copper slag on Cyprus suggests that the Cypriot copper industry collapsed around 300 AD simply because the island ran out of cheap fuel. The slagheaps suggest a total production of perhaps 200,000 tonnes of copper, and that in turn suggests that fuel equivalent to 200 million pine trees were cut to supply the copper industry, forests 16 times the total area of the island. Even given that high-altitude Cypriot forests can regenerate quickly in the right conditions, this suggests that wood fuel was a critical constraining factor on the Cypriot copper industry, and must have been a persistent problem on the island for other industries too.

The landscape of Cyprus today (and Greece, and Turkey, and Lebanon, and in fact most of the Mediterranean seaboard) is quite unlike its appearance 5000 years ago. The magnificent cedar forests of Lebanon were felled largely for timber for buildings and ships, but copper smelting must take most of the blame in Cyprus. This Mediterranean ecological disaster used to be blamed on the Arab introduction of goats to the region several centuries AD, but the change was much earlier. There are secondary effects of deforestation, of course: hillsides are exposed to greater run-off, and erosion can be greatly accelerated. Part of the story of the later Bronze Age seems to be the silting of coastal ports and cities. The city of Tiryns, for example, spent a great deal of effort just before its end building a diversion structure to keep floods out.

Page last updated April 1999.


Monday, December 22, 2008

Post 1492 Reforestration

Without a doubt, an explanation for the Little Ice Age is a priority item on my personal to do list. Here we are introduced to a factor that I certainly have overlooked and may turn out to be valid. We do not know the real extend of pre Columbian agriculture except to recently recognize that slash and burn was not part of the program.
The early explorers in North America found woodlands and small tracts but that was a century after Columbus and several centuries after a previous economic high. A die off could have progressed generation by generation penalizing organized high density populations whose remnants merged with less organized groups.

The few reports we have out of the Amazon is saying the same thing. The real question is what size of population was necessary to create the warmer original regime as per this theory. Viewed in reverse, it quickly becomes much less convincing and sounds more like an argument in favor of today’s global warming theory.

In the event, strong reforestation was taking place, as is happening today in the East.

I am inclined to think that expanding forests will absorb more of the incoming solar energy and thereby add to the Earth’s total heat.

In any case, this is a factor that is quite real whose effect may be measurable and needs to be accounted for. The problem is that we have a very poor understanding of the impact.

We know that the Bronze Age saw the stripping of the Sahara coinciding with the end of the two millennia climate optimum that was warmer than the present. This is explained easily by understanding that the Earth lost the ability of the Sahara to absorb and hold heat. Since then we have had a well frozen Arctic and a cooler regime in Europe with some warm pauses.

That is why I am a little hesitant to assign an extended little ice age to this cause, but the carbon ratios and the decline in atmospheric CO2 certainly points at a contemporaneous shift in biomass size independent of the weather.

New World Post-pandemic Reforestation Helped Start Little Ice Age, Say Scientists

ScienceDaily (Dec. 19, 2008) — The power of viruses is well documented in human history. Swarms of little viral Davids have repeatedly laid low the great Goliaths of human civilization, most famously in the devastating pandemics that swept the New World during European conquest and settlement.

In recent years, there has been growing evidence for the hypothesis that the effect of the pandemics in the Americas wasn't confined to killing indigenous peoples. Global climate appears to have been altered as well.

Stanford University researchers have conducted a comprehensive analysis of data detailing the amount of charcoal contained in soils and lake sediments at the sites of both pre-Columbian population centers in the Americas and in sparsely populated surrounding regions. They concluded that reforestation of agricultural lands—abandoned as the population collapsed—pulled so much carbon out of the atmosphere that it helped trigger a period of global cooling, at its most intense from approximately 1500 to 1750, known as the Little Ice Age.

"We estimate that the amount of carbon sequestered in the growing forests was about 10 to 50 percent of the total carbon that would have needed to come out of the atmosphere and oceans at that time to account for the observed changes in carbon dioxide concentrations," said Richard Nevle, visiting scholar in the Department of Geological and Environmental Sciences at Stanford. Nevle and Dennis Bird, professor in geological and environmental sciences, presented their study at the annual meeting of the American Geophysical Union on Dec. 17, 2008.

Nevle and Bird synthesized published data from charcoal records from 15 sediment cores extracted from lakes, soil samples from 17 population centers and 18 sites from the surrounding areas in Central and South America. They examined samples dating back 5,000 years.

What they found was a record of slowly increasing charcoal deposits, indicating increasing burning of forestland to convert it to cropland, as agricultural practices spread among the human population—until around 500 years ago: At that point, there was a precipitous drop in the amount of charcoal in the samples, coinciding with the precipitous drop in the human population in the Americas.

To verify their results, they checked their fire histories based on the charcoal data against records of carbon dioxide concentrations and carbon isotope ratios that were available.

"We looked at ice cores and tropical sponge records, which give us reliable proxies for the carbon isotope composition of atmospheric carbon dioxide. And it jumped out at us right away," Nevle said. "We saw a conspicuous increase in the isotope ratio of heavy carbon to light carbon. That gave us a sense that maybe we were looking at the right thing, because that is exactly what you would expect from reforestation."

During photosynthesis, plants prefer carbon dioxide containing the lighter isotope of carbon. Thus a massive reforestation event would not only decrease the amount of carbon dioxide in the atmosphere, but would also leave carbon dioxide in the atmosphere that was enriched in the heavy carbon isotope.

Other theories have been proposed to account for the cooling at the time of the Little Ice Age, as well as the anomalies in the concentration and carbon isotope ratios of atmospheric carbon dioxide associated with that period.

Variations in the amount of sunlight striking the Earth, caused by a drop in sunspot activity, could also be a factor in cooling down the globe, as could a flurry of volcanic activity in the late 16th century.

But the timing of these events doesn't fit with the observed onset of the carbon dioxide drop. These events don't begin until at least a century after carbon dioxide in the atmosphere began to decline and the ratio of heavy to light carbon isotopes in atmospheric carbon dioxide begins to increase.

Nevle and Bird don't attribute all of the cooling during the Little Ice Age to reforestation in the Americas.
"There are other causes at play," Nevle said. "But reforestation is certainly a first-order contributor."

Tuesday, January 8, 2008

Early Terra Preta Production

As my long time blog readers know, terra preta is a man made soil located in the Amazon by the Indians up to the time of the conquest for at least a thousand years. Besides the substantial 15% content of powdered charcoal we have an additional persuasive content of apparent broken pottery shards throughout.

The Indians were able to produce powdered charcoal while consuming a lot of low grade pottery in the process. This is many tons of charcoal per acre. The manufactured soil retains fertility without significant assistance in an environment were its only competitor is low productivity slash and burn. High density settlement resulted and was almost certainly responsible for the legends of El Dorado. The Spaniards were about a generation too late and the knowledge was lost.]

Reconstructing the production protocol was tricky but is is really very simple.

It was and still is impossible to use wood economically to produce the powdered charcoal. I say impossible because the direct costs of harvesting wood is well known and the cost of producing charcoal is also well known. That implies that wood charcoal which also has to be fine ground must have a cost base approaching that of sawn wood. The sunk cost is far too high to ever use as a soil additive. This is borne out even in Africa were we see charcoal been made to take advantage of its direct cash value as fuel.

That leaves us with dry crop residue as a source material and a very productive one to boot. In the time and place, and this is almost still true today, the only crop that fitted the volume need to make the process practical is and was corn. Today bagasse could also be used. The important factor is tonnage per acre. Corn is good for ten tons per acre. Most other crops simply fail to produce enough plant material. Additionally, corn waste or stover must be removed and burned regardless.

Since it must be gathered and burned in any event, the question is how to convert this feedstock into a ton or two of powdered charcoal or more reasonably into biochar retaining both the charcoal content and some remaining plant material.

Here, the nature of the corn root itself helps out hugely. It form a flat disc, not unlike the base of a floor lamp. This dirt ball can be treated almost like a brick. It permits the building of tightly packed stacks whose outer wall is formed be tightly packed root discs loaded with mud. It is no big trick to build a vertical wall of these root discs to act as the outer shell of what is a temporary earthen kiln. It was actually a brilliant innovation by some Indian a couple of thousands of years ago.

This earthen kiln is then fired by the process of dumping a charge of glowing wood coals on the top of the stack, directly into the packed dry corn stalks, and covering it immediately with the sun dried earthen platter that carried the coals. You would then cover the top with additional dirt to maintain the integrity of the earthen kiln and let the coals do their work.

The coals will drive a chimney into the stack and all the combustion will take place inside the covered chimney. This nicely minimizes any unnecessary energy loss and maximizes combustion which goes into reducing the balance of the stover. The earthen wall even filters out any errant heavy gases as they try to escape. I suspect that it is only with the recycled gas systems of today that we can do better.

This task would be done after the corn had fully ripened and dehydrated which occurs just after harvest. The corn stalks dry out then and are still pretty impervious to wetting by rain.

Once the burn is complete the next day, one would rake out any unburned roots to throw into the next kiln and then take baskets of the soil - charcoal mixture back into the field to produce the hills for the next crop. The only tool used would be the earthen ware pottery and a strong back. Today I would use a metal garbage can lid.

This process produces enough material to salvage the field in tropical conditions for an immediate crop during the next season. Once this was understood, it became practice and was intensively employed long past its actual necessity for many thousands of acres in the Amazon.

When I first made this hypothesis on the likely protocol, I did a literature search of the Archeological data on the Terra Preta soils looking for the pollen data. Remember that corn is not your first choice of a crop plant on a rain forest soil. I was gratified to discover that the two principal crops were corn and cassava which also produces a lot of biomass but no usable root ball. This confirmed that the protocol had legs.

I am quite prepared to work with someone who wishes to run field tests at no charge since I personally think that this will revolutionize all subsistence farming generally as they can be the first adopters. Larger acreages will need kiln equipment at the least and this will be capital intensive.

And it would be great to get this going where the crop cycle is currently multiple years through slash and burn. I think particularly of the Philippines were I have had fifteen year fallow periods reported. The same must be true for a lot of land in Africa and elsewhere. The more interesting question is the fertility increases in soils now been exploited.

Monday, September 24, 2007

Developing biochar protocols

In reviewing my posts on terra preta and the comments since generated by the expanded participation around the terra preta website in particular, I realize that this is a good time to share with everyone the thought processes that led to the corn culture hypothesis. This will also serve to air my response to the many nagging questions that I see recurring on the site.

I proceeded by developing my understanding of the constraints under which the farmers operated and investigating possible solutions. This approach should also inform other researchers looking at alternative solutions which may be out there.

It is fairly trivial to determine the time and place that the original terra preta soils were created. Archeology has pushed the time line back to 2500 years ago and to as recently as 500 years ago. It was clearly linked to an agricultural civilization with all the archaeological evidence lined up behind it. Although The apparent beginning coincided with the late European Bronze Age, I an unaware of any Archaeological evidence to suggest that we are dealing with a technology level that was any thing other than late stone age. That could still imply very limited access to some copper tools but nothing that would likely leak into the agricultural economy. Even the late European Bronze age I suspect had trouble using their only form of portable wealth to help their farmers.

So we can be fairly sure that our farmer worked with what tools could be made out of wood and stone. This is sufficient to girdle trees and to painfully do some wood cutting. So slash and burn becomes practical as does a limited wood processing industry. My best informant on this is the eighteenth century state of woodworking on the Pacific Northwest which then blossomed into the artistic explosion we know with the advent of steel axes. Cutting and splitting wood was possible but clearly not easy.

I then investigated traditional open air charcoal making which deforested much of the Eastern woodlands in the nineteenth century. Nothing like checking with the real experts who were relying on a thousand year old tradition. What is immediately evident, is that high yield charcoal making in open air is dependent on limiting air flow through the maximizing of packing ratio and the uniformity of that ratio. This is perhaps obvious but the fact that the packing ratio needs to be better than 75% is not obvious.

Packing ratio is a mathematical concept that measures the amount of open space to solid as a ratio. For example, a bucket of balls has a best packing ratio of 51%. This is not obvious.

Cutting hardwood to length and splitting out four inch blocks, which are then tight packed achieves both a 75% plus packing ratio but also good heat circulation. This is why the high yields were achieved.

To replicate the same packing ratio and heat transport with any biomass is a tall order. Most biomass is often almost unpackable, such as woodland waste or any branched crop. The simple jumbling together of waste ensures a lousy packing ratio and heat transport problems. In fact, it is fair to say that charcoaling woodland waste was also not very convenient without steel tools to cut the wood to length to get the needed packing ratio.

Once one realizes that the jungle is not a viable source for high volume ongoing biochar production, one must retreat to their crops. Recall that these fields are created first by the process of slash and burn which produces only a little charcoal which likely burns in the next cycle of slash and burn.

Again the packing ratio has a lot to say. Most of the burn happens just on the ground or above it. There is a lot less heat penetration of the soil than you would suppose. Recent comments on prairie grass misses this effect, since prairie grass has a packing ratio of possibly less than 20%, most of the heat is dumped into the atmosphere. I learned this lesson by attempting to roast a potato under a mound of better fuel than prairie grass. (the neighbors all came out to see the 'barn' burn:)).

If we want to produce biochar at all we have to grow the feedstock and then tightly pack it in order to get the necessary conditions in place. This limits us quickly to stalk plants that have a natural theoretical packing ratio of 77%.

Most grain crops seem to lend themselves to this except for their low volume on a per acre basis. Modern crops such as sugar cane would be possible if we did not use the cane. some other plants can be obviously used in this way. However, we very quickly are forced to consider corn simply because its non edible part consisting of the stalk represents a ten ton per acre source of biomass and a potential one to two ton source of char per acre.

This very high per acre yield is very necessary to the farmer because he has to see that he is visibly changing the seed bed and not expending a huge effort on haulage. Even today, this is the one crop producing enough bio mass to make terra preta practical.

The antique farmer had a waste product that he had to pull out of the ground and build into a waste stack to begin with so that he could raise the next crop. It was a likely ten ton stack since that was as far as he wished to haul this material. He then simply burned it as farmers do to this day. Even without proper packing some char was produced. It was not a big leap to optimize the packing and eventually to optimize the biochar production from this base.

I had reached these conclusions before I queried google scholar and ran down the pollen profile of the terra preta soils which immediately confirmed the predominance of corn pollen. Cassava also showed up which is also suitable for packing.

I will develop the rest of the story in my next post, but it can be found piecemeal in my earlier posts.


Wednesday, September 5, 2007

Global Corn Culture

I have become progressively more comfortable with the production of biochar using some form of corn stack. As each new issue is addressed, the genius of the Amazonian Indians becomes more apparent and appreciated. The difficulties of providing a mechanical assist also seem readily surmountable.

I am far less comfortable using various oven designs and pressure chamber converters to achieve largely the same end with a marginally better yield, yet with an order of magnitude jump in handling costs. My best design concept of the two lung incinerator, while maximizing yield will also demand to be fed year round in order to be possibly economic. And that also applies to pyrolyzers and the like. This means that a minimal 1000 ton per day operation will require at least a 1000 square miles of supply area and all the trucking that goes with that. Tom Miles is certainly not wrong on this.

My single farm modified container will only operate for around a month during the appropriate season and very little in between. It must be cheap and I do not know if that will actually be achievable. The second lung and its controls could turn out to be commercially crippling, principally because an expensive high grade fire brick must be used.

I keep coming back to the simplicity of carefully field stacking corn stover to produce the biochar. We know that this will yield a mix of char and soil representing a twenty percent yield with only a small increase in handling effort. With equipment we can actually build windrows, even driving on top of them to compact the stack properly before covering with dirt and igniting.

The only drawback, which seems to make some folks hysterical is that we lose the volatiles into the atmosphere. Most of this is CO2, while the rest is in the form of a wide range of organic molecules, similar to that produced from a forest fire or slash and burn agriculture. The heavy end falls back onto the soil, while the lights are typically degraded sooner or later in the upper atmosphere. Methane and probably ethane even end up in the troposphere above our atmospheric circulation system.

Unlike forest fires and their like, this process sequesters a great deal of carbon. Which returns us to the whole point of the exercise. Adding charcoal to the soil appears to vastly improve and stabilize the majority of soils. Right now we do not know were it does not work.

This is because charcoal is a strong acid, yet is insoluble. That allows it to grab nutrients year after year and recycle them back to the plants. A minimum amount of maintenance ensures maximal fertility anywhere once the initial effort is made to create the soils.

I suspect that, while terra preta soil manufacturing was the dominant culture in the Amazon, that there is no reason for it to be a continuously applied system in most soils. After all we know that a season's corn production will generate around a ton of charcoal per acre which is actually a lot already. Fifty tons per acre is likely the maximum that you would ever want in the soil.

Thus doing corn with terra preta in normal field rotation is very plausible everywhere. Europe and North America are the most glaring examples that I am familiar with, and I am very sure that this will be another green revolution in both India and China. Fifty years of effort and all crop lands will be well on the way to be terra preta soils and their permanent fertility will be secure. I can tell you that from a farmers perspective, that this is almost too good to be true. Fertility has been foremost on their thoughts forever.

Even more exciting, this looks like a method to restore fertility in despoiled lands were past practice has destroyed fertility and with it the soil's water holding ability. Mesopotamia particularly leaps to mind. Why should the Garden of Eden be covered with blowing salt ladened dust and treeless hillsides.

I am hopeful that the simple restoration of irrigation, can allow a corn crop to be nursed into full growth. Remember that the root practically lies on the surface, so working the top three inches of soil with biochar should quickly restore these soils. The important question is whether the charcoal will progressively sequester the salts and as a result to gently sweeten the soils. If it does not, there are still practical options because of the soil improvement brought on. They will simply take longer to have effect.

Monday, August 6, 2007

Heat Distribution and Terra Preta soils

As could be expected, we are now seeing a range of tests been done in the creation of terra preta. this is generating discussion on the terra preta web site that you can link to from here. Most of these tests, so far are using some form of commercial charcoal as would be expected.

In earlier posts, I have described the corn stover protocol that I suggest was used as the only practical means available to the populations. What I have not discussed are some of the likely derivative benefits of the approach.

The most important characteristic of corn stover is that it will produce a fine grained product. There will be almost no lumps to breakdown, although there will be remnant roasted plant fiber that will be slowly degraded by bacteria in the soil.

The covering of dirt maintained while the stack is burning is still porus to air. This permits a steady supply of oxygen to the burn but at a low level. We anticipate that the average temperature will be around 380 to 400 degrees. This is hot enough to drive off the volitiles and char most of the carbon. It is not hot enough to do more to the stover than properly carbonize most of it.

However for the stack to reach a general average of 400 degrees, the volitiles must burn at much higher temperatures. That means that we will have a distribution of high temperature carbon products within the stack that will include high temperature activated charcoal. This is one of the benefits of the stack method that is hard to replicate in a carbonizing device were one gets a little too efficient.

I know that the agricultural carbonizer design that I posted on earlier posts separates the volatiles and burns them at 2000 dgrees before throwing the heat back into the fuel to produce more volatiles. More direct combustion within the fuel may well be called for.

I think that we need to sample the production of dirt covered burn stacks and measure not just the carbon output but the distribution of types by size and if possble, activity. then we can use better production methods and blending to match the terra preta profile.




Tuesday, July 17, 2007

Terraforming - 1 - agricultural lands

I began this blog to open discussion on the need to progressively terraform the earth. And core to that proposition is the modification of global agricultural practice to achieve that end. It is easy to establish the objective of sequestering CO2 when the linkage to global warming is in your face, valid or not. For the first time in human history a long term weather prediction seems to be holding up.

We have discovered now useful corn carbonization in particular is going to be for pure carbon sequestration. What is just as important, this form of sequestration will also support and restore long term fertility to the soils. I do not know if this will be the whole story, but it certainly switches agriculture from an extractor of nutrients and carbon through clearing practices into a force for nutrient and carbon sequestration.

The next zone of improvement that needs implemention is the true application of agricultural protocols to woodlands in general. It has always been a long cycle economic problem that society has chosen to ignore. It seemed easier to let nature take its course regardless of the degradation visited on the land by the owners. We have spoke earlier of the need to create a long term partnership with local agencies and landowners that is mandated by legislation and funded on a very long term basis to create mutual wealth. It takes political will, yet is likely the best economic solution for all stakeholders and we can expect that the carbon content will be optimized inside of 1oo years.

Fundamentally all the lands under direct human agricultural use where sufficient moisture is available can be brought under these two specific protocols with a major improvement in fertility and carbon uptake. And they should be.


Monday, July 16, 2007

pyrolysis

I have read a lot of comment of the role of pyrolysis and how it produces gases and liquids while leaving char behind. Obviously the higher the temperature the more complete the process that could well include substantial reforming of complex molecules into simpler compounds. This is well worth the trouble if the fuel and the end markets for the liquids, gases, heat, and char are located in the same industrial setting.

As soon as we lose any of that closeness for any component, we lose efficiency in a hurry. I say this because even if one has a market for the lighter components, then you will need to shift unto other components of the fuel in order to support the process. The point I am making is that a lot of the fuel gets used to produce process heat.

Agricultural charcoal is in the position of been located at the source and application sites of the process protocol. Thus all the light fractions and as much of the process heat as possible needs to be used in the process itself.

This will also turn out to be the best protocol for an industrial sized plant as well. The secondary gases and liquids are potentially a red herring that can generate poor design when the only thing that matters is burn efficiency.

The interesting question for the shipping container design is what might the net efficiency be? I ask this because it will be possible to avoid any combustion in the main chamber as an operating option. The 2000 degree exhaust gas from the second burner can bring the core temperature of the shipping container up to the needed 400 t0 500 degree level.

Yields of obviously inefficient and messy systems run around 20 percent. It may be thus possible to exceed this by an additional twenty percent . The theoretical 80 percent yield may even be possible if it turns out that the volatiles produce enough fuel to complete the job.

This is a major potential payoff for both agricultural charcoal yields and the direct sequestering of carbon, and well worth the small additional capital investment in a charcoaling system.


Thursday, July 12, 2007

Nutrient Accumulation

Now that we understand the corn carbon protocol and how it is able to deliver powdered charcoal into the soil to form Terra Preta soils, we can make a couple of observations.

Corn charcoal will form a powder requiring very little additional work. Wood charcoal is lumpy and must be crushed to a fine powder for it to be of much value. In the soil, is is important to maximize the available surface area of the charcoal.

This powdered charcoal is activated carbon and will both absorb and adsorb. This means that it will grab and hold nutrients which can then be accessed. In fact the soil will begin to accumulate nutrients in the top layer were it is needed.

The normal nutrient cycle sees the nutrients drawn from the overall soil mass which in forests can be twenty to thirty feet thick. They are very mobile and tend to migrate deep into the soils. Dying vegetation releases these nutrients back on the surface so that they can once again begin this cycle. Charcoal in the surface layer changes this dramatically because a portion of these nutrients are grabbed by the charcoal.

Thus, over hundreds of crop cycles we can expect the nutrient load to be shifted into the surface layer. Obviously this is dramatically true in respect to tropical soils were the most need exists today. And temperate soils are also amenable to this type of soil enhancement and this sets the stage for large scale industrial organic agriculture, hugely minimizing the need to replenish nutrients with select chemicals.

A really interesting experiment would be to soak the powdered charcoal in nitrogen fertilizer to see how long it has an effect on the crops. In other words, what is the decline curve? It is currently measured in weeks.

The corn carbon protocol appears capable of preventing unused nutrients from escaping into the subsoil. This is a revolution that compares to the invention of the plow and for the same reason. the plow recovered nutrients and returned them to the seed bed. This prevents them from even escaping the seed bed