| WO2008136475A1 | 2008-11-13 |
ABDULLAH H. ET AL.: "Biochar as a Fuel: 1. Properties and Grindability of Biochars Produced from the Pyrolysis of Mallee Wood under Slow-Heating Conditions", ENERGY & FUELS, vol. 23, 24 July 2009 (2009-07-24), pages 4174 - 4181, XP008153751, DOI: doi:10.1021/ef900494t
PATENT ABSTRACTS OF JAPAN
PATENT ABSTRACTS OF JAPAN
| Claims 1. I claim to have invented with the fields of mechanical and chemical engineering, and within the scope of the general concept of using biochar for the smelting of metals, a manufacturing plant for the production of: a, "biochar-coke", a specially processed biochar formed into compacted blocks that can substitute directly for metallurgical coke as used in blast furnaces, the said production of biochar-coke taking advantage of the fact that pyrolysis of biomass produces biochar at temperatures approximating its plasticity temperature range, thus enabling energy efficient press-forming, and especially forging, of biochar into blocks with high mechanical strength and relatively large surface areas, both essential properties for a substitute for present coal-derived metallurgical coke in blast furnaces in the smelting of iron and other metals, and of b, the processing of granular biochar into a finer powder that can substitute at least in fart for pulverised coal presently used in pulverised coal injection blast furnaces, and of c, the mixing of biochar, ground iron ore, and possibly ground limestone, followed by forming this mixture into pellets of suitable size for the introduction into the top of a blast furnace. 2. A plant for the manufacture of biochar coke in which the forming of the biochar into blocks takes place in close proximity to the biomass pyrolysis reactor so that freshly pyrolysed hot biochar can be quickly transferred in an energy efficient manner to the area or areas for forming biochar into blocks of biochar-coke, the said areas for forming biochar into blocks and the pyrolysis reactor or reactors being arrayed around the area for biochar-coke forming so that hot biochar can be continually delivered to the biochar-coke forming machines while biochar is periodically removed from the pyrolysis reactor or reactors as soon as the pyrolysis is sufficiently complete, this happening via biochar being intermittently delivered in a staggered, synchronised manner from a plurality of pyrolysis reactors arrayed around a central biochar- coke forming mechanism, or conversely a plurality biochar-coke forming mechanisms arrayed around a large central pyrolysis reactor. 3. A plant for the manufacture of biochar coke in which biochar is removed from the pyrolysis reactor as soon as some portions of the charge of biomass has become sufficiently charred, thus prolonging the time during which fresh hot biochar can be removed at an approximately constant rate from a batch of biomass in a manner that avoids energy wasting over-pyrolysis of biomass, and at a rate of removal than can match the rate of utilisation by a nearby biochar- coke forming plant. 4. A plant for the manufacture of biochar coke in which the transfer of the fresh hot biomass from a pyrolysis reactor passes through thermally insulated conduits to a biochar-coke forming sub-plant, using screw feeds, augers, reciprocating rams, rotary pistons, conveyer belts of heat resistant materials, segmented chains, and the like, these transfer regions and the forming mechanism itself being enclosed in an essentially airtight structure, or enclosed and filled with a relatively inert hot gas such as flue gases from the pyrolysis reactor, or with re-circulating nitrogen or the like heated via a heat exchanger warmed by the said flue gases, thus reducing the oxidation of the hot biochar both before and directly after forming, the airtight enclosure having flaps or other valve structures allowing the entry of biochar and biochar-coke into and out of the said enclosure, the said biochar coke which after being removed from the enclosure, may be similarly cooled by said relatively non oxidative gases which have been cooled with fresh air inputs for combustion in the pyrolysis reactor via a suitable heat exchanger, thus also preheating combustion air, and so conserving energy. 5. A plant for the manufacture of biochar coke in which fresh hot biochar is press formed into blocks of biochar coke with relatively large surface areas, this being accomplished by press forming in either a slow manner or by faster forging, both these forming processes being via either rolling action, or by linear action such as forging or extrusion, the energy for the press forming being linked to the energy associated with the nearby pyrolysis plant generating steam, said steam being for the use in engines producing the rotary and reciprocating movements needed for press forming rollers, reciprocating forging dies, extrusion rams, and furthermore vibrating apparati which assist the release of biochar-coke blocks from the molds or dies as disclosed in later claims, any additional energy being required for steam production being supplied preferably from C02 neutral sources such as solar reflective power or biomass or crude bio-oil combustion, being resources ideally associated with a pyrolysis plant. 6. A plant for the manufacture of biochar coke in which the fresh hot biochar to be delivered to the biochar-coke forming apparatus is portioned out in approximately equal sized portions prior to entry into the individual biochar-coke block forming mechanisms using containers on a rotary delivery system or conveyer belt, with leveling out of any excess biochar in conjunction with a mass measuring device to give approximately uniform mass for each block as determined by optimisation for the type of press forming and dimensions and geometry of the biochar-coke blocks, the leveling of biomass also being performed by the action of a canister-scoop and its lid, the relative approach of the canister and lid being performed by movement of the canister and lid along convergent rails or the like, as they proceed through a conveying system removing hot biochar from a kiln as part of a production line, the inner surface of said lid also performing a dual function of being the upper die in the forging process of the subsequent claims. 7. A plant for the manufacture of biochar coke in which traditional drop forging and counter- forging and simultaneous multidirectional forging techniques are adapted to the forging of biochar-coke blocks with complex grooved surface contours and or pluralities of arrays of parallel holes in up to three dimensions, these processes including the forming of plurality of parallel holes using slow press forming or faster forging dies that pass through the pressed biochar blocks in a unidirectional contact manner thus giving a smoother surface to the potentially friable biochar-coke block, this being accomplished either by oscillating displacements in a direction normal to the generally downward movement of the forging die, and or the use of expandable hole forming dies, and or the release of the hole forming spear-like component of the die from its retaining base after being gripped by another retaining base on the other side of the press forming region, and or relying on differential cooling of biochar-coke and the die material, the differential cooling being either by gradual slow cooling of both biochar- coke and the die, or preferential active cooling of the die material. 8. A plant for the manufacture of biochar coke in which vibration of at least one of the press forming dies of the previous claims is accomplished through an eccentrically weighted rotary or reciprocating member producing small vibrations of the die, this vibratory movement being activated after the unidirectional piercing or bidirectional forging of the biochar coke by the press forming die either by bringing into physical contact the already vibrating member and the die, or by having a permanently fixed vibratory mechanism which is only caused to vibrate intermittently, these being synchronized with the movement of the press forming die such that the vibration takes place after the die pierces the biochar-coke and vibration stops before removal of the die from release biochar-coke. 9. A plant for the manufacture of biochar coke in which the cross section of the protrusion of array of elements of a press forming die are each of an elliptical, elliptoid or other regularly asymmetric cross section, individual protrusions being rotated through a small angle to make a larger hole in the compacted biochar-coke than accomplished by the otherwise straight impingement of the die on the biochar-coke, thus facilitating the release of the biochar-coke from the die and any surrounding mold. 10. A plant for the manufacture of biochar coke in which simultaneous forming of pluralities of arrays of parallel holes in three dimensions is accomplished through the drop forging or the like, of generally orthogonal arrays in two or three dimensions, of hole-piercing dies by the impact of another single piece die with its impact surface matching the arrays of the said arrays of piercing dies, thus producing in a single forging stroke a highly porous yet mechanically strong block of biochar-coke. 11. A plant for the manufacture of biochar coke in which a roller or rollers with gear teeth form deep grooves on at least one surface of biochar coke, the arc angle and pitch of the gear tooth profile being of sufficiently broad angle to allow the smooth release of biochar-coke from the rollers, and the rollers being frequently cleaned by brushes between contacts the hot biochar coke, this cleaning also being applied to the use of linear movement press forming such as forging as claimed previously. 12. A plant for the manufacture of biochar coke in which the biomass is selected for low sulfur phosphorus and other undesirable elements in metallurgical coke, and the pyrolysis conditions are adjusted such that the biochar has sufficiently high carbon content, thus assisting in the production of high quality metallurgical coke for the smelting of metals from their ores. 13. A plant for the manufacture of biochar into a carbon rich powder suitable for inclusion in present. pulverised coal injection technology blast furnaces, in which the biochar is introduced into the existing coal grinding apparatus and the length of time and pressure and spacing of the grinding rollers, wire brushes, rotary sieves, and the like, are adjusted to produce a carbonaceous powder able to directly substitute at least some if not all, the coal used in pulverized coal injection technology, said pulverising being done at either or ambient temperature with modified traditional coal pulverising, or at pyrolysis temperature in order to avoid the inefficiency of reheating for forging, in either case the fine biochar powder being allowed to fall through a low oxygen space and settle so that top layer of low density, high impurity ash, may be easily discarded from the biochar forging process. 14. A plant for the manufacture of biochar mixed with crushed iron ore, and optionally also crushed limestone, to produce pellets of suitable size for introduction into the top of a blast furnace, the already granular biochar having no need for additional crushing, the said mixture being moistened with water, and then pressed into pellets in a mold and then either dried in the mold or released from the mold for drying, the drying being accomplished by waste heat from associated pyrolysis plants or other carbon dioxide neutral energy sources such as focused thermal solar energy. Signed Enrol J Smith 20 May 2011 |
By Errol John Smith
Overview of topics covered
Background
Overview of blast furnace chemistry and production techniques
"Pulverised Coal Injection" used in conjunction with traditional metallurgical coke
"Green-coal", "Bio-coal", "Biochar-coal" not substitutes for "Biochar-coke"
Wood charcoal as a substitute for metallurgical coke?
Substituting processed biochar for coal products in smelting,
Pulverised coal injection and metallurgical coke
Mimicking the physical and chemical properties of coal-derived metallurgical coke
Overview of present coke production
Coke-oven specific properties of coal-derived coke
Essential properties for all metallurgical cokes in conventional blast furnaces
Physical properties
Chemical properties
Forming biochar into metallurgical coke - general principles
Patentability and Prior Art
Marketability cost, etc
References
Claims, 1 - 14
Diagrams, Fig. 1- 3 Background
There is considerable environmental benefit in using specially processed biochar to substitute the carbon of both metallurgical coke and the coal in pulverized coal injection - two key products used in the primary production of iron in modern blast furnaces. At present about 6 to 7% of total anthropogenic C0 2 emissions are due to these fossil fuels - used mostly in smelting of iron but also of a few other metals including zinc. Coke and pulverised coal both have high carbon contents - coke is about 90% carbon. Coals vary from about 60% - 75% carbon (brown coal), and 75% - 91.5% (sub-bituminous to bituminous coals), to 91.5% - 98% (anthracite). Good quality biochars range from about 85% to 95% carbon, varying with biomass feedstock type, temperature and time of pyrolysis. See for example, table 2 of the Australian
Government's CSIRO, (Commonwealth Scientific and Industrial Research Organisation), 56 page review article, "Biochar, Climate Change and Soil, A Guide to Future Research", Feb 2009, at www.csiro.au/files files poei. df
The Inter-Governmental Panel on Climate Change audits of fossil fuel use include all coke used in blast furnaces under "fuels" since both the carbon oxidized for heat arid the carbon used to remove the oxygen from the iron oxide (chemical "reduction") both end up as atmospheric C0 2 . Even though the carbon used in the chemical reduction is not a heat producing "fuel", it is convenient to classify all carbon used in blast furnaces as "fuels". The limestone (CaC0 3 ) used in blast furnaces also releases C0 2 into the atmosphere.
Overview of blast furnace chemistry and production techniques
Carbon has two functions in blast furnaces:
1. Carbon is oxidised to produce the intense heat required for the endothermic chemical reactions involved, and to melt the iron ores, limestone, etc, into hot metal and slag.
C + 0 2 → C0 2 + heat energy
Coal-derived coke produces 29.6 mJ kg of heat energy in blast furnace combustion.
2. Carbon is involved in two types of reactions - each of which reduces the two common iron oxides (haematite and magnetite) to metallic iron.
Firstly, in the hot lower portion of the blast furnace the carbon dioxide reacts with carbon, (coke from the blast furnace charge and injected pulverised coal), to produce carbon monoxide.
2C + 0 2 → 2C0
This carbon monoxide is the main means for the reduction of haematite and magnetite into iron. Haematite
Fe 2 0 3 + 3CO→ 2Fe + 3C0 2
Magnetite
Fe 3 0 4 + 4CO→ 3Fe + 4C0 2
Secondly, at even hotter regions of the blast furnace some unoxidised carbon is also involved directly in the reduction of haematite and magnetite. At these elevated temperatures carbon monoxide, not carbon dioxide, is the product of this non dominant reaction. However this resulting CO can continue to produce further reduction of iron oxides, as above.
Haematite
Fe 2 0 3 + 3C→ 2Fe + 3CO
Magnetite
Fe 3 0 4 + AC→ 3Fe + 4CO In practice iron ores are not pure iron oxides, but contain other rocky materials, especially silicates, eg, Metal n Si0 2 . Pure silica, quartz, is Si 2 0 . Most silicate rocks do not melt at the temperatures of a blast furnace and need to removed as slag with the assistance of limestone. Firstly considerable heat input, (from the prior combustion of carbon as described above), breaks down the limestone to calcium oxide and releases further carbon dioxide.
CaC0 3 + heat energy→ CaO + C0 2
Calcium oxide is a basic oxide and reacts with acidic oxides such as silicon dioxide in the silicate minerals. Calcium oxide then reacts with silicon dioxide giving calcium silicate, or slag. CaO + Si0 2 → CaSi0 3
Calcium silicate has a lower meting temperature than other common silicates and is liquid at the temperatures in the center of a blast furnace and so flows downward with the molten iron. The mixture of molten iron and slag separate out at the very base of the furnace. Since molten iron is denser than the molten slag, the iron is tapped off below the slag. See diagram 1.
Note that overall the use of limestone as a flux in blast furnaces contributes considerably to anthropogenic carbon dioxide, a major greenhouse gas. However the release of C0 2 from the limestone itself, CaC0 3 , cannot be readily avoided. Limestone is already used as sparingly as possible in blast furnaces since the reaction, CaC0 3 + heat energy -→ CaO + C0 2 , relies on the combustion of carbon. Minimizing fuel costs already minimizes limestone use, whether the carbon is from a fossil fuel or renewable source. In addition limestone, though cheap is not free.
"Pulverised Coal Injection" used in conjunction with traditional metallurgical coke
Prior to the 1980's both the carbon for iron reduction and the carbon for combustion heat was provided by chunks of coke fed into the top of the blast furnace together with the iron ore and limestone. Sometimes petroleum fuel oil, and or natural gas, were introduced into the blast of air at the base of the blast furnace as additional fuels. The pipes introducing the blast of air into the base of the blast furnace as known as "tuyeres" _ Injecting petroleum and natural gas hydrocarbon fuels into the tuyeres of the blast furnace assists mainly in heating the blast furnace as very little un-reacted carbon is carried directly over into the blast furnace charge of ore etc to be significantly involved in the chemical reduction of the iron oxides higher up in the blast furnace. Carbon, generally in the form of coke, still had to be introduced into the top of the blast furnace together with the iron ore and limestone. Since the 1980's the expense of petroleum and natural gas compared to low grade coals, (i.e. coals not suitable for making . coke), has resulted in an increasing trend to use pulverized low grade inexpensive coals injected into the blast of air at the base of the furnace. Low grade coals tend to be softer and are easily pulverized by grinding with rollers, and then pneumatically injected into the tuyeres at the base of the blast furnace. This technology is known as "Pulverised Coal Injection".
Pulverised coal injection has required significant developments in blast furnace design including: 1, the faster flow of air in the tuyeres - so that the pulverized coal stays well mixed in the blast furnace air and does not settle due to gravity, 2, more aerodynamic contours of the tuyeres so that pulverised coal does not deposit in these conduits, 3, the thermal insulation of the pulverized coal storage bins that need to be situated in multiple small silos arranged around and near the blast furnace base, 4, the use of inert gas to move the pulverized coal into the base of the blast furnace to prevent premature combustion (or explosion) of the pulverized coal, 5, strict low humidity of the pulverized coal to prevent caking of pulverized coah 6, the late addition of high concentration oxygen into the flow of the pulverized coal and blast furnace air thus assisting in the efficient combustion of the pulverized coal despite the extra cooling effect of the higher flow rates of blast furnace air, the oxygen being introduced late in the tuyeres using hollow lances.
All these developments have seen the proportion of pulverized coal increase steadily so that now in the latest technology blast furnaces pulverized coal injection forms 40% - 50% of the total carbon inputs. The Claudius Peters company is an example of this well developed technology. See www.claudiuspeters.com/_apps/dynamic/library videos/309%20PCI.pdf .
Pulverised coal suitable for pneumatic injection into the base of a blast furnace is necessarily small particles, and small particles have a relatively large surface area on a per mass basis. This is advantageous in rapid intense combustion, but combustion of small particles rapidly depletes the carbon from being used to produce carbon monoxide or act directly in reducing iron oxides deeper in the blast furnace. Iron reduction requires some residence time for contact between iron oxides and carbon monoxide or carbon. Therefore pneumatic injection of pulverized coal can never be the sole way of introducing carbon for iron reduction.
In addition, fluid dynamics imposes a limit to how much coke can be replaced by pulverized coal, (or powdered biochar), via pneumatic injection into the base of the blast furnace. This route is suitable mainly for heating - not for the reduction of iron. Again, increasing the amount of pulverized coal injected at the base of the furnace such that after combustion there is excess carbon for iron reduction has limited scope beyond present levels of 40 - 50%.
Furthermore, the amount of carbon injected without excessive cooling from blast furnace air required to mobilize the pulverised carbon is near its limit. Adjusting the residual injected carbon would be difficult to control. Finally, the main region for carbon to be in prolonged contact with iron ore is in the centre of the charge of ore and limestone, not at its lowest surface.
Consequently, the main route for introducing the carbon for iron reduction is from the top of the blast furnace, mixed in with the iron ore and limestone. Entry via the top of the blast furnace require relatively large and heavy pieces of carbon as small light pieces of carbon introduced via the top of the furnace will get blown back by the strong updraft of blast furnace air. Inescapably there has to be large amounts of large pieces of carbon introduced from the top of the furnace.
Another possible way to introduce suitably heavy pieces of carbon into the top of the blast furnace is to mix pulverized carbon with ground iron ore and form suitably sized pellets which can be introduced via the top of the blast furnace. The pellets need to be of sufficient size and density so that they will not be blown back up in the blast of furnace air. As will soon be discussed, biochar would not need pulverising as it is already in a fine granular form that can be easily mixed with ground iron ore forming such pellets. The resistance to air flow through such a charge of iron ore carbon pellets and limestone would be greater than the air flow through chunks of coke, iron ore and limestone. Coke's special properties of high macro and micro- porosity and consequent very large chemically active surface area, its structural strength and resistance to crumbling even under high temperatures and pressures, synergistically enable it to produce an overall large scale porosity of the whole blast furnace charge that allows high flows of blast furnace gases without extreme pressures and risks of blockages from aggregation.
For this reason the traditional large chunks of coke, (40 - 100mm), or a suitable sized chunks of a biochar substitute, will probably remain an important component of the blast furnace charge introduced at the top of the furnace. This will continue to be true even with a trend to include pelletised mixtures of iron ore and pulverised carbon, (due to the limits outlined above), and especially true in older furnaces which use traditional non-pelletised iron ore. "Green-coal", "Bio-coal", "Biochar-coal" not substitutes for "Biochar-coke"
So called "green-coal" etc are C0 2 neutral emission substitutes for thermal coal, not substitutes for chunks of metallurgical coke. They are similar to coal briquettes made from coal "fines", compacted (not at particularly elevated temperature), and often using tar and moisture as binders. Coal and coke fines are otherwise difficult to utilise. Coal briquettes are still sometimes used in industry but have gone out of vogue for domestic heating dues to their high rate of smoke and noxious fumes production. "Green-coal", "bio-coal", "biochar-coal", "biochar- briquettes", etc, are a more environmentally friendly form of briquettes and are being
increasingly used for heating and cooking in some developing countries which do not have their own coal reserves and for which importing coal is too expensive. The touted benefits are low cost, appropriateness of technology, and being neutral C0 2 emission neutral. This last factor which actually be negated by the all too often non-closed pyrolysis of biomass systems in developing countries in which un-burnt methane (a potent green house gas) may leak in significant quantities. Another advantage is that that the high purity compressed carbon is a quite dense form of energy storage and easy to transport. However simply burning dried biomass in the cooking stove etc requires less overall biomass than pyrolysing the biomass, compacting it into briquettes and burning them in a cooking stove, (hopefully a stove of a design that doesn't release methane - relevant for both simply dried biomass and biochar-briquettes).
Small very compact cylindrical biochar briquettes have been produced as a way of safely and compactly transporting high purity carbon from a pyrolysis plant to a blast furnace, where the pellet are duly ground for use in pulverized coal injection system. Note that this is not direct substitution for chunks of coal-derived coke. See recent work of the Dutch "Ingenia" company; W.Robert van der Waal, et al, "A multi-purpose pellet (MPP) facility and real options portfolio management (ROPM) in response to value chain changes of biomass resources",
www.ingenia.nl/Flex/Site/Download. aspx?ID=5905, and the Ingenia website.
Wood charcoal as a substitute for metallurgical coke?
It may be noted that chunks of wood charcoal have been used for smelting of iron for several millennia prior to the conception of coal-derived coke in 1603, its use as general heating fuel in 1642, and use in iron smelting in 1709. Even in modern large scale blast furnaces with their high mechanical pressures wood charcoal is still being used to a substitute considerable amounts coal-derived metallurgical coke, most notable in countries such as Brazil which have large forestry industries. However in order for such chunks of wood charcoal to be large enough and mechanically strong enough to substitute for coke in modern blast furnaces, similarly large pieces of quite dense timber needs to be pyrolysed. Such qualities of timber are almost always better off used for construction and manufacturing - both from an economic perspective and environmental perspective, especially as may often be the case, when the timber is being harvested in a non-sustainable manner. The economics of wood charcoal are "favorable", it would seem, mainly in places where cheap quality non-sustainable timber from is cheaper than locally available or imported coal. From both an environmental and economic perspective it is better to use diverse inexpensive sources of biomass for pyrolysis and biochar-coke production.
Torrified wood is a form of very low temperature slow-pyrolysis wood that is of a suitable size for use in blast furnaces. Torrification of wood is performed at a temperature low enough that the structure of the wood is largely retained, and is thus stronger than traditional charcoal, hence more suitable for use in modern large blast furnaces with their very heavy pressures from overburden of iron ore and limestone. Nevertheless the main limitation is the same as for wood charcoal, see above. See Patrick Bergmann & Jacob Kiel, "Torrefaction for biomass upgrading", 14 th European biomass conference and exhibition, Paris, France, 17-21 October 2005", (ECN- RX— 05-180), pp.1-8, at www.ecn.nl/docs/library/report/2005/rx05180.pdf , and also J. Kiel "Torrefaction for biomass upgrading into commodity fuels", Energy Research Centre of the Netherlands, (ECN), Berlin, 2007,
www.ieabcc.nl/meetings/task32_Berlin_ws_systemjDerspectiv es/03_Kiel.pdf
Substituting processed biochar for coal products in smelting,
Pulverised coal injection and metallurgical coke
Coke derived from coal is a significant use of fossil fuels and replacing such coke with a carbon neutral biochar-coke derived from biomass, and thus ultimately from renewable plant photosynthesis, would significantly reduce atmospheric C0 2 . In the recent past a few people in internet chat-rooms and websites interested in biochar have suggested the possibility of using biochar as a substitute for metallurgical coke. However these vague suggestions have not researched or solved the technical difficulties associated with the practical, efficient, economical conversion of biochar into a chemically and physically adequate coke substitute that can be used in present industrial scale blast furnaces. It would be very advantageous to have a biochar derived coke substitute that did not involve changing present blast furnace design. Blast furnaces have a working life of up to several decades. The major retrofitting of conventional blast furnaces to use unprocessed biochar injection is feasible - but not an economic option.
As discussed previously pneumatic injection cannot be the only carbon source. Nevertheless pneumatic carbon injection could use about 40 - 50% of total carbon input as minimally processed biochar powder that is introduced into the base of the blast furnace, entrained in the blast furnace air input in a manner very similar to present pulverized coal injection. There would be very little if any change to present pulverized coal injection plants as biochar could be fed into the same grinding mills that pulverise low grade soft coals. If anything, pulverising the already granular powder of biochar would require less time in grinding and energy than the soft coals or coal fines now used for pulverised coal injection. Present pulverized coal injection plants would not require retrofitting to use biochar, providing a smooth transition of technologies.
As the same time biochar may be introduced into the top of the blast furnace via two
complementary means: 1, mixed with ground iron ores (and possibly limestone) formed in suitable size and weight pellets, and, 2, as chunks, of carbon mimicking traditional lightweight strong porous metallurgical coke. These two approaches will discussed in turn.
1. Pellets formed from unprocessed biochar mixed soft pellets that are mixed with the charge of iron ore and limestone, moistened and then press formed in a mold and dried would produce a more dense and virtually non porous material compared to metallurgical coke. These soft pellets would be susceptible to crumbling and so producing blockages. Their density would also result in a greater resistance to air flow. The overall pressure and flows of the blast furnace air would have to be considerably greater than in conventional blast furnaces to overcome the increased resistance to air flow. Blast furnace design would have to adapt to such increases in pressure and flow of blast furnace air. Such structural and materials challenges could be solved with modern engineering, but at considerable cost if adequate safety is to be maintained. A small but significant proportion of pellets could probably be used in present furnaces without retrofitting.
2. Biochar-coke that mimics the essential physical and chemical properties of conventional coal derived coke can fully and directly substitute present metallurgical coke as part of the long term practical option, as well as being the only practical short term transitional option. Biochar-coke with identical (or even superior) properties to conventional coal derived coke would enable a seamless transition with blends of biochar-coke and coal derived coke, facilitating the complete transition from coal derived coke to all biochar-coke. The practical manufacture of biochar into a substitute for metallurgical coke is an important mechanical and chemical engineering problem to be solved. The present provisional patent application explores and addresses the key issues involved in this problem, and claims novel, inventive and practical solutions to the problem.
Mimicking the physical and chemical properties of coal-derived metallurgical coke
Coke is like a hard gritty sponge, the sponge like character giving it a considerable lower density than solid rock-like coal. The bubbly texture ultimately comes from the bubbling release of volatiles during the formation of semi-coke (475 - 600°C), this sponge like structure being hardened during the next phase of coke stabilisation (600 - 1100°C). Coke stabilisation removes any (small) last traces of hydrocarbon volatiles and encourages fusing of C-C bonds linking graphene-like and fullerene-like sheets into 3-D lattices/networks, these very large molecular structures improving mechanical strength. Improving physical properties, not chemical properties is the main function of coke stabilisation. The inclusion of trace hydrocarbon or even carbohydrate and other minor oxygen containing functional group volatiles is not a problem with the elemental composition of semi coke.The chemical and physical properties of present coal derived metallurgical coke are in part merely related to the present means of production in coke ovens, and in part necessitated by the final use required in conventional blast furnaces. These two areas will be discussed in turn after an overview of present coke production.
Overview of present coke production.
Coke is a highly porous solid with a high concentration of carbon. The chemical properties of the best coke for blast furnace use, "Grade Γ coke, is specified on a by weight basis as:
Fixed Carbon 88 % min.
Ash 10.5% max.
Volatile Material 1.5% max.
Sulfur 0.6% max.
Phosphorous 0.035% max.
Moisture 5% max.
(The physical properties of coke will be discussed later.)
Coal derived coke is produced when an appropriate blend of coal is heated in a low oxygen environment such that volatile matter is released and the remaining components, (fixed carbon, ash, sulfur, phosphorous, nitrogen, oxygen, etc), fuse to form a homogenous porous solid. The low oxygen environment prevents combustion of the solid fixed carbon and volatile hydrocarbons. The volatile hydrocarbons are removed and either burnt to produce heat for the coke oven, or condensed into useful byproducts such as coal tar, light oils, benzene, ammonia, etc. After formation from coal, the hot coke is traditionally cooled rapidly with water, (or sometimes with cool gases in more recent coke ovens), before being exposed to the normal oxygen concentration of the atmosphere. At ambient temperature the rate of further oxidation of the "fixed" carbon is very slow.
The common "beehive", (or "slot"), style of coke ovens has an array of numerous large firebrick lined vertical slots for containing and heating coal thus forming coke. The slots are filled with a charge of premixed coal blends and sealed at either end with doors, and at the top and bottom with solid walls. The coal and coke filled slots alternate with slot like spaces for combustion of various fuels. Heat is transferred from the combustion slots to the coal and coke slots through the adjacent vertical walls of the "beehive". After the coke has formed, large rams push the hot coke along the slots and out the opened doors at the end of the slots into containers which are quickly taken to a nearby site for quenching. See diagram 2. The heating of the coke transforms the coal into coke via the following series of chemical and physical changes. Heat is transferred from the hot walls of the slot into the coal charge. From about 375°C to 475°C, the coal forms plastic layers near each wall. From about 475°C to 600°C, the volatile materials are released, in particular tars and aromatic hydrocarbon compounds. This is followed by a re-solidification of the plastic mass into "semi-coke". Semi- coke is a porous high carbon material. But it is mechanically soft and weak and thus not useful as metallurgical coke in conventional blast furnaces. Coking coals are blended to have between 26 - 29% of volatiles prior to coking. This amount of volatiles helps give the suitable porosity after coking.
During the plastic stage, the plastic layers of coal move inwards from each heating wall towards the center of the charge of coal, trapping the released gas and volatile material and creating a buildup of gas pressure which must be balanced mechanically by the heating wall. When the plastic layers have met at the center of the charge of coal, the entire process of carbonisation into semi-coke is complete - though not strong enough for use in conventional blast furnaces.
From about 600°C to 1100°C is the coke stabilisation phase. This is involves contraction of the coke mass, the structural development of coke into a more porous substance being assisted by the final release of any residual hydrogen. The carbon and residual ash are fused at this stage resulting in a homogenous hard strong material. Finally, the red-hot coke is gas or water quenched prior to transfer to the blast furnace.
The properties related to present coke-oven practicalities do not necessarily have to be mimicked by biochar-coke, however they are worth reviewing as application some of these principles recur in some of the proposed techniques of biochar-coke production.
Coke-oven specific properties of coal-derived coke:
Firstly, coal blend for coke production are selected so that input coal contains about 26-29% of volatile components. On heating the released volatiles exert a predictable and not too high pressure on the coke oven walls. This is largely irrelevant in biochar-coke as the volatiles have already been extracted to give crude pyrolytic bio-oil and syngas.
Secondly, in "by-product" coke ovens some effort is taken to maximise the use of the volatiles. Again this is largely irrelevant in the production of biochar-coke as are there are negligible volatiles remaining in biochar. In biochar pyrolysis the volatile substances have already been used in the formation of syngas and crude pyrolytic bio-oil.
Thirdly, the final coke should be able to contract sufficiently to allow the coke to be pushed from the oven. If coke becomes jammed in the large slot cavities of present large coke ovens batteries it is a considerable problem, and risks the breakage of the oven walls if excessive force is used by rams to remove the coke charge - and at worst the cooling and possible replacement of that portion of the coke ovens. These problems do not occur with the proposed methods of biochar-coke production in which individual lumps of coke are extruded, press- formed, forged etc. Occasionally having to manually or semi-automatically remove a lump of biochar-coke adherent to a mold etc does not necessitate the shutting down of the whole production process and is acceptable. Essential properties for all metallurgical cokes in conventional blast furnaces:
Physical properties
The physical properties: size, surface area, tensile strength, compressive strength, impact toughness and resistance to abrasion vary in importance depending on the stage in the iron production process.
The size of coke used in present blast furnaces ranges from about 40mm to 100mm. There is usually a limit set on the amount of smaller sized coke. For example, "Grade coke has very little coke less than 25mm. For further practical discussion of the sizing of coke see the 2007 McGraw-Hill Encyclopedia of Science and Technology article on "Coke", (Vol.4, p.387-389).
The sometimes rough initial transport from the coke ovens and conveyer belt transport to the top of the blast furnace require considerable mechanical strength of the coke - but this is not at elevated temperatures. The required mechanical properties of coke at room temperature is usually measured by the Micum Index which indicates the strength of coke against both impact and abrasion. The Micum Index test mimics both abrasion and impact typical of the conditions encountered in transport to the top of the blast furnace and the conditions in the lower temperature regions of the blast furnace. For example, the M 40 Micum Index test is performed taking a representative 50kg sample of coke that is unable to pass through a sieve of 63mm square holes. This 50kg sample is rotated inside the Micum drum which is a mild steel drum of size 1m internal diameter. The coke is rotated in the drum for 4 minutes at a rate of 25 revolutions per min. After rotation, the coke is taken out and screened through standard round holes of 40mm diameter. The percentage coke not passing through the 40mm holes is designated as the M 40 Micum Index. The minimum Micum Index for blast furnace use is 80%. The M 10 and M 20 etc Micum Indices are similarly determined.
In the upper portion of the blast furnace, termed the granular zone, the coke is mixed with dense iron ore pellets and fluxes such as limestone. The coke needs to maintain its structural integrity and bulk porosity enabling the large volumes and high flow rates of hot blast furnace gases, (at about 400°C), to escape. If the light porous coke becomes broken into finer particles these tend to compact and impede the blast of gas rising from the hotter lower regions of the blast furnace.
The region below the granular zone is termed the cohesive zone. Here the iron ore and limestone become molten and the carbon of the still solid coke reduces the iron oxide to molten iron and produces molten slag at about 1800°C. These liquids then flow downwards through a core of hot porous still solid coke. The coke must still maintain significant structural integrity to allow good gas flow despite these extreme temperatures and forces of the blast of hot gas from below, balancing the tons of overburden consisting of iron ore, limestone and coke above.
The next lower central core of coke forms the hearth where the oxidation of the coke provides the heat for the other regions above it. A very high pressure blast of hot air (at entry about 1000°C), and other combustible gases enters from below the core of coke. This region is for heat production, (reaching about 1800°C), not primarily for the reduction of iron oxide, however the reducing state of the carbon monoxide and carbon is maintained as the liquid iron flows through it. Coke must have high compressive and strength and maintain its porosity despite the elevated temperature in this region. The required mechanical properties of coke for the hot regions are usually measured by the Coke Strength after Reaction test. The CSR test consists of taking of representative 10 kg sample of coke of size greater than 25 mm and crushing it. From this crushed coke sample is taken another smaller representative sample of 200g of coke that can pass through a 21 mm but not 19mm sieve of square holes. This 200g sample of coke is re-coked by heating at 1100°C under 1atm pressure of carbon dioxide for 2 hours. The coke is cooled under nitrogen. The reacted coke is gently placed in a steel drum and subjected to 600 revolutions. The percent of material removed from the drum that is does not pass a sieve of 10mm square holes is known as the coke strength after reaction (CSR). Coke suitable for blast furnace use has a minimum CSR value of 62%.
The high macro and micro porosity of coke is important as it gives the relatively high surface area which is important both for high rates of chemical reaction of reduction of iron oxide to metallic iron, and the high rates of oxidation and combustion of coke giving the high
temperatures required to melt the iron and slag. In our discussion porosity is considered under mechanical properties because it will be addressed by mechanical solutions in the production of biochar-coke. (Porosity could have been considered under physico-chemical properties, a subset of chemical properties discussed next. Porosity of present coal-derived coke is actually a physico-chemical process.)
It has been found that for present blast furnace use, the optimal density of coke, measured as the specific gravity, (relative density compared to water), is about 0.77. This compares with anthracite, the highest grade coal, which has a specific gravity of 1.3 to 1.4. If biochar-coke was just as strong as coke, but even less dense and with greater surface area it would probably be even better than the best of present metallurgical coke. Whether this is possible has to be determined by careful optimisation of the various proposed means of biochar-coke production.
Chemical properties
Just as the "Micum Index" and "Coke Strength after Reaction" are tests developed to measure the relevant mechanical properties of coke, chemical tests have been developed to measure the relevant chemical properties that affect the quality and efficiency of the iron produced.
As discussed above, the chemical properties specific to present cbke oven technology are largely irrelevant to biochar-coke. However the chemical properties related to the blast furnace itself are very relevant and important for biochar coke. As stated previously "Grade 1" blast furnace coke is specified as:
Fixed Carbon 88 % min.
Ash 10.5% max.
Volatile Material 1.5% max.
Sulfur 0.6% max.
Phosphorous 0.035% max.
Moisture 5% max.
Forming biochar into metallurgical coke - general principles.
These chemical composition specifications cited just above compare very favorably with biochar. This implies that if optimally treated, biochar has the potential to produce metallurgical coke of the highest quality. There may be larger amounts of hydrogen in biochar coke produced at 500°C, (and below), compared to fully coked coal at 1000 to 1100°C. This hydrogen would be in the form of numerous possible hydrocarbons amongst the mostly carbon matrix. Relatively low temperature (500°C) biochar-coke would release small amount of hydrogen on heating to temperatures about 2000°C at the centre the blast furnace. The hydrogen would burn to produce more heat, and or act as a reducing agent removing oxygen from iron oxide and producing water. A little extra hydrogen can be a good thing in blast furnace smelting of iron.
Therefore the remaining challenge in manufacturing metallurgical quality biochar coke is not to mimic the elemental chemical composition, but to mimic the physical properties of metallurgical coke in an energy efficient manner - and to do so without compromising the chemical qualities. Biochar produced by slow pyrolysis involves the heating of biomass to about 500° which is very conveniently close to the plastic range for coal (375°C to 475°C). This temperature range for coal's plasticity would be very similar to the temperature range of biochar's plasticity given the chemical similarity of the 2 materials. For coal the range 475°C to 600°C involves the release of volatile material, and since slow pyrolysis heats the biomass at about 500° for about 1 or 2 hours this allows time to release the volatiles which are condensed to form crude pyrolytic bio- oil. Meanwhile residual gaseous volatiles (syngas) is burned to provide heat for the whole process. Coal derived coke is further heated under some pressure to about 1000 to 1100°C to change the soft semi-coke into hard porous metallurgical coke. This same heating could be done to biochar that had been pressed or otherwise formed into suitable sized blocks. However considerable high temperature energy would be needed to heat the biochar from 500°C to 1000 - 1100°C.
An alternative to the energy intensive process of coking at 1000 to 1100°C may be to take advantage of the plasticity already present in biochar at 500°C and use a rapid forging process instead of merely the low and slow pressure forming of biochar into blocks, and then heating the blocks to 1000 to 1100°C. The forging process generally produces much stronger materials than other process such as slow pressing and or machining. This advantage is because the single sudden forging impact gives a single breakage and slippage of intermolecular bonds into their final orientation - rather than repeated breaking and reforming of such bonds until the final form is reached, with each formation and breakage of bonds requiring a similar energy input to overcome the activation energy of breaking the inter-molecular (or even intra-molecular) bonds involved. The total energy required for this repeated process in non-plastic temperatures (i.e. cold pressing), or with slow pressure forming techniques, even at plastic temperatures, are considerably more than a rapid (near) single step process of fast hot forging.
Note that we are not generally speaking of the covalent and ionic electron bonds, but the attraction between inter and intra-molecular bonds of macromolecules due to Van der Waals forces etc. The final density and mechanical strength of the pressure formed product increases with the peak pressure applied. If the same total energy is applied to slower press forming and compared to the sudden intense pressure of forging one would achieve a higher peak pressure with forging process.
Forging is usually the most energy efficient means of producing a mechanically strong product. Other techniques do not achieve the same microscopic flow and texture that follow the outer contours of the object of manufacture. Matching the fine grained microscopic structure with the lines of force experienced within a material are an essential key to making mechanically strong lightweight materials. The strength advantages justify the extra energy needed to heat a metal to forging temperature. How much more energetically advantageous is forming an object if it is already at a forging temperature When compared to other means of formation. The cost effective advantages of forming mechanically strong metal objects with forging (compared to cold machining), are well recognized in making engineering tools where strength is paramount.
When forming hot biochar it would be wise to have enclosed transferring conduits for hot biochar and the forming mechanism being filled with a non oxidising atmosphere. A practical means of doing this would be to have an air-tight enclosure around the relevant hot sections. This enclosure may be filled with some of hot flue-gases from the combustion of syngas in the pyrolysis reactor. Similarly, cooled flue-gases, for example after passage through a heat exchanger that preheats ambient temperature combustion air prior to use in the pyrolysis reactor, may be used to cool the biochar-coke that has been formed. Another practical consideration in using fresh hot pyrolysis biochar to produce metallurgical coke is that pyrolysis does not always produce a steady supply of hot biochar. Indeed, the most useful method for producing large amounts of inexpensive biochar is "slow pyrolysis". This technique often produces large batches of biochar every 1 or 2 hours rather than continuously. A pressure forming process for producing suitable sized pieces of biochar-coke would ideally operate with a steady rate of hot biochar production matching the rate of usage by press forming. This problem is best solved by beginning to remove biochar from the slow pyrolysis reactor as soon as at least part of the biomass has been sufficiently charred. Thus a roughly constant rate of removal could continue till the biomass batch has been fully charred. If the pyrolysis reaction chamber is well insulated, then the external heating of pyrolysis chamber could then be turned off, or at least left with a very low rate of heating, while the remaining biochar is removed at a sufficiently hot temperature for the plastic formation by forging, (or slower press forming as the case may be). This approach would give intervals of relatively constant supply of hot biochar followed by intervals of non supply. The inefficiency of such an intermittent process could be overcome merely by having several pyrolysis reactions chambers operating in a staggered manner. Such out of phase operation would be more feasible with quite large scale biochar-coke forming plants having capacity for a number of pyrolysis reactors of optimal individual size. The location of the biochar-coke apparatus would be approximately equidistant from each pyrolysis reactor - at the centre of a cluster. The optimal number of pyrolysis reactors in such a cluster is determined by the fraction of time that fresh biochar can be produced compared to the whole cycle of pyrolysis, not just the 1 or 2 hours for pyrolysis, but including the time for filling with biomass, cleaning and maintenance.
The best region for removal of hot biochar from a pyrolysis reactor would probably be those portions of the biomass batch which have been in longest contact with the hottest region of the pyrolysis chamber. If the reaction chamber is heated from below, then this region this would likewise be near the lower portion of the pyrolysis chamber. An auger, gravity feed ram pump, equal double rotary piston pump, or the like, made of suitable mechanically strong, hard and friction resistant, temperatures resistant materials may be used to slowly and steadily remove hot biochar from the base of the pyrolysis chamber. If the most suitable region to remove biochar is not at the base of the reaction chamber then the height at which the removal takes place may be suitably altered. The possibility of a spatially adjustable removal system may be considered necessary, guided by visual monitoring - or by an automated feedback based on the depth or weight of the solid biochar in the base of the reaction chamber. A fully sealing positive displacement pump mechanism would have the advantage of removing biochar without significant release of pressure inside the pyrolysis chamber.
Further similar sealing could be incorporated by have a scoop for the biochar and a sealing lid. The action of scooping up biochar, leveling it, and sealing it with a lid could be combined with a simple mechanism in which a canister and lid are moved on rails or the like through an automated transit through the batch of hot biochar. Combining this lid with the forging die such that a close though not tight fitting lid can be placed on the canister containing loosely compacted hot biochar, and later be transferred to the forging region when a forging blow presses the lid into the biochar could potentially be advantageous. The inner surface of the container lid can double up as one of the forging dies. The container itself can be in the shape of a cylindrical scoop with a closed base at one end. (The the inner surface of the base of the container would be less suitable for doubling up as a forging die since this would impede the scoop action.) Suitable linkages such as hooks and holes on the canister and its conveying system may be part of the production line. The scoop may be automatically attachable to a conveyor belt (or chain link system) that enters into the pyrolysis kiln on a track that passes through the bulk of the mature hot biochar. The track guides have a shape that slides the scoop laterally as the conveyor belt system moves the scoop longitudinally. When the scoop has traversed it predetermined path, the lid that fits into the cylindrical scoop which was likewise being moved by another parallel track approaches and seals the scoop. This sealed canister continues out of the pyrolysis kiln and into is automatically detached from the conveyer belt system and slid into an insulated and low oxygen storage awaiting transfer to the next available forging process. The lid for the canister could have the appropriate prongs etc formed on its inner surface. The process of forging would continue as described elsewhere.
This automated sealing of canisters could also be adapted to continuous feed systems such as augers, etc.
The duration of high pressure to the forging canister may be extended beyond typical metal forging if it is found that brief forging pressure does not produce a mechanically strong enough material. The molecular structure may need some time to readjust and align bonds, that is, to fuse into a more dense structure.
A wide variety of engineering ceramic and cermets or metals with temperature resistant coatings or inserts may be used in the construction of the hot biochar pump. A survey of suitable materials at a variety of elevated temperatures is included as an appendix to the author's previous provisional patent application, "Negative Carbon Dioxide Emissions
Automotive Engine".
The distance from pyrolysis chamber to slow press forming or more rapid forging process would need to be as short as possible, well insulated and possibly actively heated perhaps sharing the same combustion as the nearby pyrolysis reactor(s), or at least have a thermal jacket of flue gases. Focused solar energy could also be utilised directly or indirectly in keeping this transit region for the biochar at a temperature required to give it sufficient plasticity for slow pressure forming or rapid forging of the biochar.
If the forging involves a moving die and a stationary die then there may be a considerable vibration associated with the impact of forging and measures such as use of shock resistant materials in the foundations of the forging region may need to be used to prevent such vibrations being transmitted to other nearby mechanisms and contributing to metal fatigue etc. However if single, or small number of blocks of biochar are only ever forged in each impact, then the amount of energy expended in any individual forging impact would not be very great. This is especially true since small amounts of hot biochar require much less impact than the typical forging of metals for machine parts and tools etc. Using a counter-forging approach when two or more forging dies move in a way that absorbs the net energy within the dies, and which cancels out net impulse to the environment is probably an unnecessary complication given the materials being worked, although counter-forging may still be considered as an option.
An area of special consideration relates to the ease of removal of formed biochar coke from its mold as the biochar cools. The thermal contraction properties of forged biochar as it cools are not easy to predict and may need to be determined empirically for each forging process contemplated. The variables could include the exact physico-chemical nature of the biochar, (biomass source and preparation, length and temperature of pyrolysis, degree of de-volitisation, etc), the pressure and duration of the slow pressure forming or rapid forging, and the geometry of the block of biochar, (especially given the wide variety of means of producing high surface area biochar-coke blocks).
Nevertheless there are only three eventual outcomes for changes from the size of the biochar at the instant of hot forming to its ambient size: either the biochar-coke can shrink, stay the same size, or expand. In other words the cooling biochar will either spontaneously loosen release from its mold, or it will not - or it will in some parts and not in other parts. For this reason a quite wide variety of slow press forming and rapid forging techniques will be considered. The best outcome may be determined empirically by optimisation of each techniques and comparison of the result biochar-coke blocks in terms of performance in a blast furnace, energy consumption and cost etc.
Classification of the geometries of blocks of biochar coke can be considered topologically. Note that it is not practical to produce hollow structures via slow pressure of rapid forging techniques. This limits the options to blocks that have a finite number of convex and or finite number of concave regions, i.e indentations, and with finite whole numbers of holes or fenestrations. Three dimensional objects with no holes and a plurality of both convex and concave surface regions are important.
Slow pressure continuous gear tooth profiles may be pressed into hot biochar. The biochar may be formed between one geared wheel moving and a relative flat surface, or the biochar may be formed between two geared wheels rotating at the same speed with a suitable distance of separation between the two rotating wheels. These two gear wheels may be either in phase or out of phase. The choice of gear tooth profile would be determined by ability of the tooth to clear the press-formed biochar as the gear tooth profile rolls forward - otherwise the gear tooth could damage the still relatively soft hot compacted biochar. As well as simple spur gears with their grooves being parallel to the axis of rotation, one could use oblique or herringbone gears. In addition to uninterrupted straight grooved gears, one could have gears that are a series of gear profile shaped spikes that produce rows of gear profile shaped holes in the press-formed biochar. With all these above means of rotary dies the press formed biochar one may include raised portions designed to cut off the press-formed biochar into suitable length blocks. These raised portions would be of a height that nearly meets with the opposing surface or die and may be introduced at regular interval around the circumference of the rotary die.
Extrusion of biochar may be used to give relatively large surface areas to a volume of biochar. The simplest shapes for extrusion are non hollow cross sections. These would include shapes with the star-like radiation of sheets of biochar radiating out from a central region. However such thin section although stronger than isolated thin sheets, would probably not be mechanically strong enough to survive the extremes of blast furnace operation. Hollow sections may be extruded given that quite soft non-compacted biochar may be introduced upstream to the internal dies. Any arrangement of holes may be used though most suitable are symmetrical arrays such as triangles, squares, hexagonal arrays, and concentric arrays of variable numbers of holes. The outer shape could be circular to give the greatest strength, although rectilinear, and oval shapes are also quite strong and their irregularity may give advantages in air flow around them when immersed in the dynamic environment of a blast furnace.
The above methods of gear tooth press forming and extrusion of biochar may be contrasted with pressure techniques in which pressure forming dies move in straight lines. Furthermore gear tooth and extrusion forming are generally slow pressure forming techniques and not able to be performed under the extremes and rapid pressures of forging. The following "forging" techniques may also be done slowly as well as rapidly, although generally a more energy efficient and mechanically stronger product will result from more rapid higher pressure forming as discussed above.
Firstly, recall that rotating gear teeth press forming involves the gear tooth profile moving smoothly away from the compacted biochar with a rolling motion that starts with a separation of the two surfaces, (i.e. the biochar and gear tooth), at very low angles, thus not damaging the fresh surface of the newly compacted biochar. However with the simplest approach to forging the die moves towards the biochar and then moves away from it in the opposite direction from which it approached. There is not a gentle rolling action at low angles, but a movement of the two parallel surfaces, (i.e. the biochar and forging die), moving apart. This creates a suction-like effect which pulls the surface of the biochar in the opposite direction to which it was compacted, thus de-compacting the fresh surface of the newly compacted and still somewhat hot and slightly soft biochar. This change in direction while still in contact or very close proximity to the biochar could have the effect of crumbling the surface of the biochar as the die is released, partly undoing the structural benefit of the compaction of the biochar. Note that forging of metals does not suffer from this potential problem because metals in general are malleable and ductile. Powdered carbon in the form of hot biochar is neither malleable nor ductile, and may crumble relatively easily in this simplest form of forging in which the compacting force changes directions. In practice this may not be a problem, but several solutions to this potential problem will now be proposed in case it is a major drawback.
The forging of holes now described allows an alternative form of forging than that given above. It allows the use of a piercing forge die which only has one direction of movement as the die traverses the biochar. The surface compaction is therefore left in its peak compaction since the die that formed it slides past at the peak pressure. Each hole is forged by a die that is tapered at each end with the full diameter being at a length in the middle. This advancing taper forms an initial indentation that is opened out to the full diameter and compresses the biochar as it advances. The trailing taper allows the two surfaces of the biochar and die to separate at a shallow angle without a change of relative movement.
There are two approaches to automating such a piercing forging process. Firstly, the die stays the same size and is pulled all the way through the block of biochar allowing the biochar block to be removed out of the path of the die, there are several variants of this a reciprocating movement, best accomplished by horizontal movement of the die, and a unidirectional movement of the die, requiring the die to be moved back into it previous position, either by bringing it up in between before the next block of un-compacted biochar is introduced, or bring it to initial position via a path that does not intersect with a more continuous introduction of biochar into the forging area.
Secondly, it would be possible to have each tapered die contractible by have an expansile section at full diameter section. The die is fully expanded in piercing the hole and in compacting the biochar. When the fully expanded portion of the die has fully passed through the biochar the full diameter portion of the die is then contracted and then retracted back through the biochar without touching the freshly compacted biochar on the internal diameter of the hole. The expansion and contraction of the full diameter portion of the die could be most practically accomplished by mechanical means, or though thermal expansion. The use of piezoelectric materials may just be feasible, though not very practical.
An elliptical cross section die element could be rotated slightly after forging, to produce a hole with a small clearance on the die for most of the circumference of the hole. Removing the die in the opposite direction from which it came would involve friction only with the portions of the ellipse still in contact with the biochar, and possible produce loosening of the surface of the biochar only for this small segment, an acceptable compromise. The mechanics of producing a die with numerous elements with elliptical cross section that can be rotated, may be addressed by having the elliptical cross sectioned prongs having solid flanges at one end, these flanges being fitted into an array of holes in the die, and these flanges transferring the impact of forging to the rest of the die housing. Beyond the flanges on the other side of the member pierced with the numerous holes, the prongs would continue and have gears mounted on them such that the individual prongs could all be rotated individually by the movement of a rack and pinion or other hear wheel with very large diameter.
Alternatively there could merely be a single tooth-like projection on each prong rather than a full gear wheel, and this projection could be operated by a lever with suitable sized notch formed in it. With a full circle of gear teeth the prongs could be turned through either a full circle, or oscillated through a suitable arc. However the single projection and notched lever would be best be operated with oscillations through a small arc. Care would have to be taken with choice of materials and clearances between the prongs and its supporting die plate such that the prongs did not deform and jam in their supporting holes. At the temperatures used conventional lubricants would be of little use.
With the above methods of piercing forging the "lower" die or mold may include an array of holes that correspond to the projection on the "upper" die. These holes are to allow the projections of the upper die to penetrate with a small clearance. In this way any overshoot of the upper die would not result in direct die to die impact and excessive wearing, burring or fracturing of either dies. This would also allow some variability in how compact the biochar becomes. There would be a small variation in thickness of the final blocks of biochar-coke but this would be inconsequential in the final use as blast furnace coke.
The forging of holes is particularly relevant with biochar-coke as one is trying to make a highly porous, relatively high exposed surface area, yet mechanically strong substance. A block of biochar-coke forged with an array of multiple small holes accomplishes these goals very well. See claim 10 for an approach to forging three dimensional orthogonal hole arrays in one impact.
The selection of the number, size and geometrical type of array the forged holes and the density of the biochar coke after compaction offers a wide scope of possible solutions to manufacturing metallurgical coke. Optimising these variables starts with determining the optimal density of forged biochar-coke from an energy efficiency perspective. This in turn includes firstly the temperature at which the fresh biochar is forged, more plasticity and greater final strength requiring more energy to heat the biochar to a greater temperature and maintain that temperature, and secondly the mechanical energy required operate the forging process. A graph of energy used in heating and strength of final product, together with a graph (on a independent axis) of the mechanical energy used in forging, would have a relative plateau the edge of which plateau would be the locus of energy efficient density of biochar-coke production.
Improving the carbon content of the biochar may take advantage of the fact that sulfur etc is concentrated in the ash portions, and ash is of a different density than the rest of the biochar. Very fine grinding of the biochar may separate the micro-particles of ash of the surface of the carbon rich portion. See electron microscopy images in, Malone, S., "Characterization of Sulfur in biochar", National Renewable Energy Laboratory, (US Dept of energy), University of Colorado at Boulder, Jan 2010, http://digitalcommons.calpoly.edU/star/9. Extremely fine grinding of biochar existing coal grinding apparatus may be performed by adjusting the length of time and pressure and spacing of the grinding rollers in pulverized coal technology, or by using intermeshing wire brushes, high speed rotary sieves, and the like. This may be done at either or ambient temperature with modified traditional coal pulverising, or at pyrolysis temperature in order to avoid the inefficiency of reheating for forging, in either case the fine biochar powder being allowed to fall through a low oxygen space and settle so that top layer of low density, high impurity ash, may be easily discarded from the biochar forging process. Traditional ash removal from coal, dissolving the ash in alkali, etc, generally takes place room temperature, not pyrolysis or forging temperature, but may also be used to purify biochar, however this would require reheating to forging temperature
Patentability and prior art
The claims of novelty centre on the use of CO 2 emission neutral biochar in specific systems for metal smelting as a direct substitute for 1 , metallurgical coke, using modified forging techniques being newly applied to hot biochar, fresh from the slow pyrolysis reactor, and 2, substitution of coal in pulverized coal injection and pelletised iron ore and coke mixtures.
With forging the energy efficiency of forming fresh hot biochar into biochar-coke is important.
As stated previously I am not aware of any specific proposals or similar attempts to manufacture metallurgical quality coke from biochar that take advantage of fresh biochar being at the plasticity needed for forging, (with either fast or slow pressure), to give the requisite strength for metallurgical coke, and that simultaneously uses such pressure forming to introduce a relatively great surface area that largely functionally mimics the porosity of coal derived coke.
In searching for prior art one must remember that the term "char" in the context of the petroleum industry refers not to bio-char but to the solid carbonaceous residue remaining after the distillation and refining of petroleum products. This "char" is still a fossil fuel which
unambiguously distinguished it from biochar which is a renewable carbon source. Only rarely is the term "char" used to refer to biochar, and such instances can be clearly determined by the individual contexts.
Because of the importance of efficient iron production there have understandably been many previous attempts to make cheaper and or stronger coal derived coke. In more recent decades due to environmental concerns with fossil fuels such as coal has aroused some interest in including carbonaceous waste products such as used automobile tyres and the like, as part of the coal mix that is introduced into conventional coke ovens. Including coal "fines" which are too small to be coked unless compacted into suitable sized briquettes has also been a subject of industrial research because of the economic advantages of using a wider range of coal products for coking. Since coal fines may still have a high quality elemental composition they can be mixed with a proportion of low quality other coals. The means of forming briquettes sufficiently strong to be introduced into a coke oven, (but not strong enough for blast furnace extremes), has involved the use of adhesive binders such as petroleum based pitch etc. It has also been found that water and sufficient pressure are also able to bind certain mixtures of coal and other carbonaceous products, this last fact may be usefully applied in a new context in the press forming of biochar, iron ore and possibly limestone pellets as discussed previously. Marketability
The iron smelting industry is very large and growing. The amount of coke used for primary iron production is likewise very large, at least 400 million tonnes per year. To quote the Inter- Govemmental Panel on Climate Change, (IPCC), Fourth Assessment Report, Climate Change 2007, Working Group III, Mitigation of Climate Change,7.4.1 , Iron and Steel: "Global steel industry C0 2 emissions are estimated to be 1500 to 1600 MtC0 2 (410 to 440 MtC), including emissions from coke manufacture and indirect emissions due to power consumption, or about 6 to 7% of global anthropogenic emissions (Kim and Worrell, 2002a)."
Biochar-coke economics, Cost of coal-derived coke
Biochar-coke will be competing with coke made from high quality coal. At present the price for bulk metallurgical coke is mostly between US$400 to US$500 per tonne. (March 201 1 prices from the global online trade and industry advertising agency
www.alibaba.com/products/metallurgical_coke ranged from $380 to $600 depending on quality and transportation costs.)
High quality coking coal is usually bought by steel manufacturers who convert it themselves into coke on site at their own iron smelting plants. High quality coking coal for bulk export costs about US$220 per tonne, compared to lower quality thermal coal (also known as steaming coal) at US$95 per tonne. As bulk metallurgical coke usually sells for $400 to $500 per tonne, (range $380 - 600), it is usually cheaper, more convenient and more reliable for steel manufacturers to make their own coke from high quality coal, (at$220 per tonne), on site at their own blast furnace plant.
Bulk prices for thermal coal were about US$95 per tonne for 2010 settlements, (up 60% from 2009). In contrast early in 2010 BHP, a very large Australian coal exporter, settled contracts for coking coal at $200 per tonne with JFE (JeiefuT HOrudingusu Kabushiki-gaisha), the 5 th largest steel manufacturer in the world. JFE doubtless negotiated a very competitive price based on very large volumes. Prices for coking coal are expected to settle at US$220 per tonne in 2010- 2011. (The Reserve Bank of Scotland cited by Zac Leman in NEXT, Daily market analysis for 10 March 2010).
Cost of biochar-coke
Several published analyses of biochar and biocrude mass production have shown that the cost of biochar, hence biochar coke, depends mainly op the cost of the initial biomass. Unlike other biofuel approaches, slow pyrolysis can easily use all types of biomass - all lingo-cellulosic agricultural and forestry wastes, wild grasses, wild algae (not just oil producing but less prolific algae), fresh water weeds and saltwater weeds, sorted municipal waste, animal manure and human sewerage, selective sustainable harvesting of natural ecosystems (cultivating natural biodiversity as energy crops). Some well adapted natural plants are able to use less arable land and so avoid the food versus fuel dilemma of other biofuels.
Numerous slow pyrolysis pilot plants and rapidly developing associated technologies are improving the financial viability of slow pyrolysis. Present estimates of the cost of manufacturing biochar vary widely from $100 to $400 depending on feedstock cost, type of slow pyrolysis plant, transport, C02 offset credits etc. Such analyses are large and complex and will be covered in some detail in subsequent solution reports. With the present rate of development, and especially the use of prolifically growing wild algae feeding off smokestack C02 (not slow growing genetically engineered oil rich algae species), the lower price range is quite realistic in the near future. A conservative guess at the cost of the final forging biochar-coke may be double the cost of biochar. The energy for forging and physical manipulation of the forging dies can be supplied by excess heat from the pyrolysis plant producing steam, a simple but effective way to lift a drop forge die. With biochar at the lower end of the price spectrum, (eg $150 per tonne), biochar coke may be producible at $300 per tonne, quite competitive with even average quality coal-derived coke.
The possibility for adjusting the size of the chunks density and fenestration size etc of the forged biochar coke to exceed the physical and chemical characteristics of the even the best coal- derived coke. "Designer biochar-coke" could command a price at the high range of present coke, ($500-600 per tonne).
Niche markets
Niche markets for very high quality coke exist in zinc and copper smelting. Very low sulfur phosphorous and ash are possible with careful choice of low impurity cellulosic biomass for slow pyrolysis. Having very low impurities is more important in these non ferrous smelting processes because there is less capacity for secondary smelting as exists in primary high carbon "pig iron" production. Pig iron is converted to steel in the basic oxygen furnace, a process which removes both the excess carbon of pig iron and other impurities.
With pulverised biochar injection the cost of biochar needs to compete with high quality coal marginally less than coking coal ($220 per tonne). The cost of pulverizing coal would be an additional small cost, a cost which biochar would not incur since it is already in a powdery form, (although mass transit of completely un-compacted biochar powder does require care to make explosive carbon dust.) As mass production of biochar is just approaching these costs, perhaps of $250 per tonne, biochar injection has not yet been widely used in iron smelting . The development of financially profitable would assist the mass production of biochar in general, and so lower the price of biochar for injection, enabling it to compete with pulverized coal injection.
We have not mentioned the very important synergy of biochar as a soil enhancer, including several innovative uses which will be presented in a subsequent package of solution reports. However if biochar is used for biochar-coke less biochar is available for use as a soil enhancer. The optimal balance of uses of biochar will also be discussed in subsequent solution reports.
Comparative Benefits / Advantages
The main advantage of biochar coke is that is it almost C02 emission neutral, (if plant operation uses heat from pyrolysis to do the mechanical work of production, however transport costs of biomass to the pyrolysis plant and transport of coke to the blast furnace is C02 emission positive at present given the widespread dependence on transport on fossil fuels.)
It is likely that bulk biochar-coke can be produced more cheaper than coal-derived coke.
There do not appear to be any direct competitors to direct substitutes for coal-derived coke in modern large blast furnaces. The usually soft wood charcoal and terrified wood is not scalable or environmentally sustainable, and more expensive than the cheapest forms of biomass that can be pyrolysesd. Pulverised biochar injection has been proposed by others but the technology is very recent and opportunities for forging process, but is limited to supplying only about 45% of the total carbon need in iron smelting blast furnaces. References
Clark, J., "The Blast Furnace wwwxhemguide.co.uk/inorganic/extraction/iron. html
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Lehmann, J., "Biochar Science and Policy", Cornell University, 2009, p.26, (power point presentation).
www.anzbiochar.org/AP%202009%20presentations/Lehmann%20Bi ochar%20IBI%20AustralAsi a%20May2009s.pdf
Leman, Z., "NEXT", Daily market analysis for 10 March 2010
Malone, S., "Characterization of Sulfur in biochar", National Renewable Energy Laboratory, (US Dept of energy), University of Colorado at Boulder, Jan 2010,
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McLaughlin, H., "All Biochars are Not Created Equal, and How to Tell Them Apart, Version 2 (October 2009), which supersedes the digital reprint issued at the North American Biochar Conference, Boulder, CO - August 2009. www.biochar-international.org/node/1029
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Wikipedia articles on coal, coke, alloy steel
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