Since I have seen various estimates for the heating values of the fuel gas derived from the gasification of wood and of coal, to put my own mind at rest, I have worked-out from first principles what they should be according to quoted typical compositions for "wood gas" and "coal gas" (otherwise known as "town gas"), formed by heating coal in closed retorts in the absence of air. The strategy is different in the latter case, since bituminous coal will yield around 13% of its mass of town gas by simple heating, leaving around 65% of the original coal mass in the form of coke and the remaining 22% distilling over as coal-tar. Most usually, wood (or other biomass) is gasified by heating it in a stream of air, drawn either up or down the "gasifier" depending on its design as either "draw-up" or "draw-down" in which the process takes place, and consequently almost half the resulting gas is nitrogen. Apart from a few percent ash all of the wood is thus converted to gas, in contrast to coal as it is normally converted to town gas (see below).
WOOD GAS.
A composition is: N2, 50.9%; CO, 27.0%; H2, 14.0%; CO2, 4.5%; CH4, 3.0%; O2, 0.6%.
Per cubic metre (m^3) of gas, this amounts to:
270,000/24450 (volume of one mole of an ideal gas at 25 deg C and atmospheric pressure) = 11.04 moles CO, x 28 = 309.12 g.
140,000/24450 = 5.73 moles H2 = 11.46 g.
30,000/24450 = 1.23 moles CH4 = 19.68 g.
Given the molar enthalpies of combustion for these gases, we get:
11.04 x -283 (kJ/mol) + 5.73 x -286 + 1.23 x -890 = 3.12 MJ + 1.64 MJ + 1.09 MJ = 5.85 MJ/m^3.
Remaining (incombustible) gases:
509,000/24450 = 20.82 moles N2 = 582.90 g.
45,000/24450 = 1.84 moles CO2 = 80.98 g
6,000/24450 = 0.25 moles O2 = 8.00 g
Total mass of 1 m^3 of gas = 1,012.14 g. Hence the calorific value of wood gas is 5.85 MJ/m^3 or 5.85 x 1000/1012.14 = 5.78 MJ.kg.
TOWN GAS.
A composition is: H2, 51%; CO, 15%; CH4, 21%; C2H4 (ethene), 3%; CO2 + N2 = 10%.
Per m^3 of gas, this amounts to:
510,000/24450 = 20.86 moles H2 = 41.72 g.
150,000/24450 = 6.13 moles CO = 171.78 g.
210,000/24450 = 8.59 moles CH4 = 137.42 g.
30,000/24450 = 1.23 moles C2H4 = 34.44 g.
100,000/24450 = 4.09 moles CO2 + N2 = 151.33 g (assuming a 50:50 mixture).
Making a grand total of 536.69 g.
Again, using the molar enthalpies of combustion we derive:
20.86 x -286 + 6.13 x -283 + 1.23 x -1423 + 8.59 x 890 = 5.97 + 1.73 + 1.92 + 7.65 = 17.27 MJ/m^3. This translates to: 17.27 x 1000/536.69 = 32.18 MJ/kg.
Related Reading.
Wikipedia.
Thursday, February 12, 2009
Wednesday, February 11, 2009
Biomass Gasification.
World energy use in 2005 was 500 EJ or 5 x 10^20 J. Assuming that a calorific value of 15 GJ/tonne could be recovered, to provide that amount from biomass would require 33.3 Gt (billion tonnes) of biomass. Sums are often done assuming a given mass of "residue" from crops, but it is necessary for the good health of soil to return some of that chaff to the ground to preserve its organic carbon content, otherwise it becomes stripped and increased in mineral form, thus needing artificial fertilizers forever, or for as long as they can be provided.
Even at a yield of 10 tonnes/hectare of biomass residue, we need 3.33 x 10^9 hectares or 3.33 x 10^7 km^2 of land to produce it on, which at 33 million km^2 is over twice the area of arable land on earth (15 million km^2) and more than one fifth of the total land area of around 150 million km^2 (30% of the total 500 million km^2 of the surface of this blue planet). Clearly to provide all our energy from biomass is a very tall order, and it is obvious that we cannot simply substitute biomass in matching amount for fossil mass, as supplies of oil, gas and coal begin to wane. Since however, we will not need to convert overnight from fossil mass to biomass, and energy conservation will be forced on us by a simple lack of resources, biomass offers the potential to provide a significant proportion of the final energy bill, once we have made efforts to use less energy overall. Certainly it can make a significant contribution to the transitional period from the high energy status quo to a future civilization based on a more efficient use of energy and which furthermore is generated from renewable resources like biomass.
Most biomass is simply burned to provide heat, and this can be done more efficiently in CHP (Combined Heating and Power) systems particularly in small-scale units. However, we need a more adaptable form of energy which is best provided in the form of liquid and gaseous fuels. In the latter aspect, synthesis gas or "syngas" is especially flexible, since not only can it be piped and burned directly, but also converted to methanol, other alcohols including ethanol and synthetic diesel using Fischer-Tropsch catalysis.
The simplest firm of gasification is done by pyrolysis, which usually involves heating biomass, e.g. wood, in a restricted supply (or the absence of) air. Thus, the cellulose, hemicellulose and lignin is decomposed to a mixture of solid (char), liquids (bio-oil) tar and a mixture of gases, mainly CO2, H2, CO and methane. The relative amounts of the different phases can be changed according to the temperature of the pyrolysis, the contact time with the heated zone, the pressure and the amount of oxygen present either in the diluted form of air or in some applications pure oxygen is used, but providing this adds-in its own contribution to the overall energy budget.
In terms of gasification, at temperatures >1000 degrees C, and short contact times of less than a second around 70% or more of the initial charge of biomass is converted to gas. There are gasifiers that work at lower temperatures say 400 degrees C and use more air, but provide a gas with a low thermal content of maybe 6 GJ/tonne which is around one fifth that of coal-gas (27 GJ/tonne) and about a tenth that of natural gas (methane, 55.7 GJ/tonne).
During WWII, cars and tractors were run using on-board wood-gasifiers, to cope with the fuel shortages in Europe, petrol and diesel being reserved for the military. The unit was called Gazogene. Full EROEI analyses are necessary to evaluate such gasification strategies, it is generally assumed that (as in making biochar by pyrolysis) the external heat source will come from biomass too. The beauty of using air/oxygen is that the gasification reaction becomes self-sustaining, i.e. the material effectively "burns" albeit in a controlled manner.
In addition to using biomass taken from fields, there is the option to use the technology to convert land-fill waste into useful fuel, as well as directly gasifying wet-biomass including algae which saves energy in drying the material prior to use as is normally necessary. In terms of converting algae to fuel, it may prove more efficacious to gasify the total mass directly rather than choosing a high-oil yielding variety, extracting the oil from it and then transesterifying that into biodiesel. The syngas could be used directly as a fuel or converted instead to synthetic diesel using FT rather than biodiesel. NB the calorific value of biodiesel is around 36 GJ/tonne compared with syn-diesel at 44 GJ/tonne, which is the same as for normal diesel.
The focus on biomass is of course that it is renewable, ideally carbon-neutral (on the grounds that the carbon content of the plant was taken from the air originally through photosynthesis), and is hence a better bet than fossil fuels which are being exhausted continually from their finite reserve and which contribute CO2 to the atmosphere.
I shall post more on this subject as I think more about it, but these are just some initial impressions.
Related Reading.
The figure of 500 EJ in 2005 from: http://en.wikipedia.org/wiki/World_energy_resources_and_consumption
There is another link at: www.sfpa.sk/dok/PDFI/MZeman.pdf (on slide number 6) that mentions 10,878 Mtoe which x 42GJ/t = 4.6 x 1020 J for 2005, and is thus also in the same ball-park.
Even at a yield of 10 tonnes/hectare of biomass residue, we need 3.33 x 10^9 hectares or 3.33 x 10^7 km^2 of land to produce it on, which at 33 million km^2 is over twice the area of arable land on earth (15 million km^2) and more than one fifth of the total land area of around 150 million km^2 (30% of the total 500 million km^2 of the surface of this blue planet). Clearly to provide all our energy from biomass is a very tall order, and it is obvious that we cannot simply substitute biomass in matching amount for fossil mass, as supplies of oil, gas and coal begin to wane. Since however, we will not need to convert overnight from fossil mass to biomass, and energy conservation will be forced on us by a simple lack of resources, biomass offers the potential to provide a significant proportion of the final energy bill, once we have made efforts to use less energy overall. Certainly it can make a significant contribution to the transitional period from the high energy status quo to a future civilization based on a more efficient use of energy and which furthermore is generated from renewable resources like biomass.
Most biomass is simply burned to provide heat, and this can be done more efficiently in CHP (Combined Heating and Power) systems particularly in small-scale units. However, we need a more adaptable form of energy which is best provided in the form of liquid and gaseous fuels. In the latter aspect, synthesis gas or "syngas" is especially flexible, since not only can it be piped and burned directly, but also converted to methanol, other alcohols including ethanol and synthetic diesel using Fischer-Tropsch catalysis.
The simplest firm of gasification is done by pyrolysis, which usually involves heating biomass, e.g. wood, in a restricted supply (or the absence of) air. Thus, the cellulose, hemicellulose and lignin is decomposed to a mixture of solid (char), liquids (bio-oil) tar and a mixture of gases, mainly CO2, H2, CO and methane. The relative amounts of the different phases can be changed according to the temperature of the pyrolysis, the contact time with the heated zone, the pressure and the amount of oxygen present either in the diluted form of air or in some applications pure oxygen is used, but providing this adds-in its own contribution to the overall energy budget.
In terms of gasification, at temperatures >1000 degrees C, and short contact times of less than a second around 70% or more of the initial charge of biomass is converted to gas. There are gasifiers that work at lower temperatures say 400 degrees C and use more air, but provide a gas with a low thermal content of maybe 6 GJ/tonne which is around one fifth that of coal-gas (27 GJ/tonne) and about a tenth that of natural gas (methane, 55.7 GJ/tonne).
During WWII, cars and tractors were run using on-board wood-gasifiers, to cope with the fuel shortages in Europe, petrol and diesel being reserved for the military. The unit was called Gazogene. Full EROEI analyses are necessary to evaluate such gasification strategies, it is generally assumed that (as in making biochar by pyrolysis) the external heat source will come from biomass too. The beauty of using air/oxygen is that the gasification reaction becomes self-sustaining, i.e. the material effectively "burns" albeit in a controlled manner.
In addition to using biomass taken from fields, there is the option to use the technology to convert land-fill waste into useful fuel, as well as directly gasifying wet-biomass including algae which saves energy in drying the material prior to use as is normally necessary. In terms of converting algae to fuel, it may prove more efficacious to gasify the total mass directly rather than choosing a high-oil yielding variety, extracting the oil from it and then transesterifying that into biodiesel. The syngas could be used directly as a fuel or converted instead to synthetic diesel using FT rather than biodiesel. NB the calorific value of biodiesel is around 36 GJ/tonne compared with syn-diesel at 44 GJ/tonne, which is the same as for normal diesel.
The focus on biomass is of course that it is renewable, ideally carbon-neutral (on the grounds that the carbon content of the plant was taken from the air originally through photosynthesis), and is hence a better bet than fossil fuels which are being exhausted continually from their finite reserve and which contribute CO2 to the atmosphere.
I shall post more on this subject as I think more about it, but these are just some initial impressions.
Related Reading.
The figure of 500 EJ in 2005 from: http://en.wikipedia.org/wiki/World_energy_resources_and_consumption
There is another link at: www.sfpa.sk/dok/PDFI/MZeman.pdf (on slide number 6) that mentions 10,878 Mtoe which x 42GJ/t = 4.6 x 1020 J for 2005, and is thus also in the same ball-park.
Friday, February 06, 2009
Yorkshire Carbon Capture Project gets Go-Ahead.
Mike O'Brien the British Minister for Energy has given consent to build a 900 MW power station at Hatfield in Yorkshire, which it is claimed developers are hoping to convert to carbon-capture technology "at a later date". This is a milestone on both fronts, since there is on the one hand a loud voice of objection from environmentalists who are against using coal because of its contribution to carbon emissions and secondly if carbon capture (CC) is added-on, that will be a first, and it is an "if". A new plant in Kent was approved a while ago, but without CC, on the grounds that the technology is unproven and expensive, so whether the Hatfield power plant is retro-fitted with CC remains to be seen.
Mr O'Brien is quoted as saying: “It is essential to replace older polluting power stations that are reaching the end of their lives with new stations that operate more efficiently."
What is clear is a shift of emphasis by the government, who while being aware of the anthropogenic carbon/greenhouse effect/global warming/climate change theories, are also well informed that the U.K. has an energy supply problem, to put it mildly. Hence avoiding people freezing in the winter and keeping the lights on in general here, is of more immediate concern than GW, the connection of which to wholesale climate change is a matter of model and debate. Thus, coal appears as a useful indigenous fuel, especially as we are running out of our other indigenous fuels - gas and oil, from North Sea fields that are likely to be almost dry in 6 years time.
How much accessible coal we have depends on how it is accounted, but there is enough for some decades in all likelihood, and much longer if underground coal gasification (UCG) is implemented on a grand scale. Uzbekistan has been running a UCG plant since the 1940's. Indeed, the National Coal Board ran an experimental UCG plant in Derbyshire in the 1950's but rejected the technology on the grounds it was too expensive compared to cheap solid coal that we were still producing to the tune of around 150 million tonnes/year.
The Hatfield plant is not a standard coal-fired power plant, which simply burns finely powdered coal, but rather uses coal that has been gasified, and it is the gas that is burned. It is termed a Combined Cycle plant and it was approved along with two more, one at Pembroke in South Wales (2 GW) and another at Kings Lynn in Norfolk (1 GW). Powerfuel, the company which bought the Hatfield colliery in 2006 plans to construct the "world's first large scale integrated gasification combined cycle (IGCC), near zero carbon emissions powers station with carbon capture capability." The grand total of 4 GW worth of electricity from the three new power stations is enough to power 4 million homes.
Their intention is to do this in two stages: first an 800 MW combined cycle gas turbine (CCGT) plant will be fabricated which burns coal that has been gasified into "syngas" (a mixture of CO + H2), and then this will be "upgraded" to an IGCC facility of 900 MW capacity running on coal from the Hatfield colliery. Richard Budge, CEO of Powerfuel, stressed the advantages of having a power producing facility in the north of England that runs on a secure fuel source based in the U.K. - i.e. coal. The first stage at Hatfield is expected to cost around £900 million and the second around £1 billion.
That carbon then has to be "removed for sequestration", i.e. put somewhere safe for hundreds to thousands of years, usually in rock-formations. Where, I wonder? Or, perhaps feed it to algae and turn it into liquid fuels? In that latter case, the carbon would end up in the atmosphere when the fuel was burned but it might be argued that there would be a trade-off against the oil that would otherwise be used as a fuel instead.
Related Reading.
[1] "Green Light for 900MW carbon capture coal plant in Yorkshire." http://newenergyfocus.com/do/ecco.py/view_item?listid=1&listcatid=32&listitemid=2223§ion=Carbon
[2] "First 'clean coal' power station gets go-ahead," by Robin Pagnamenta: http://business.timesonline.co.uk/tol/business/industry_sectors/natural_resources/article5670940.ece
Mr O'Brien is quoted as saying: “It is essential to replace older polluting power stations that are reaching the end of their lives with new stations that operate more efficiently."
What is clear is a shift of emphasis by the government, who while being aware of the anthropogenic carbon/greenhouse effect/global warming/climate change theories, are also well informed that the U.K. has an energy supply problem, to put it mildly. Hence avoiding people freezing in the winter and keeping the lights on in general here, is of more immediate concern than GW, the connection of which to wholesale climate change is a matter of model and debate. Thus, coal appears as a useful indigenous fuel, especially as we are running out of our other indigenous fuels - gas and oil, from North Sea fields that are likely to be almost dry in 6 years time.
How much accessible coal we have depends on how it is accounted, but there is enough for some decades in all likelihood, and much longer if underground coal gasification (UCG) is implemented on a grand scale. Uzbekistan has been running a UCG plant since the 1940's. Indeed, the National Coal Board ran an experimental UCG plant in Derbyshire in the 1950's but rejected the technology on the grounds it was too expensive compared to cheap solid coal that we were still producing to the tune of around 150 million tonnes/year.
The Hatfield plant is not a standard coal-fired power plant, which simply burns finely powdered coal, but rather uses coal that has been gasified, and it is the gas that is burned. It is termed a Combined Cycle plant and it was approved along with two more, one at Pembroke in South Wales (2 GW) and another at Kings Lynn in Norfolk (1 GW). Powerfuel, the company which bought the Hatfield colliery in 2006 plans to construct the "world's first large scale integrated gasification combined cycle (IGCC), near zero carbon emissions powers station with carbon capture capability." The grand total of 4 GW worth of electricity from the three new power stations is enough to power 4 million homes.
Their intention is to do this in two stages: first an 800 MW combined cycle gas turbine (CCGT) plant will be fabricated which burns coal that has been gasified into "syngas" (a mixture of CO + H2), and then this will be "upgraded" to an IGCC facility of 900 MW capacity running on coal from the Hatfield colliery. Richard Budge, CEO of Powerfuel, stressed the advantages of having a power producing facility in the north of England that runs on a secure fuel source based in the U.K. - i.e. coal. The first stage at Hatfield is expected to cost around £900 million and the second around £1 billion.
The initial CCGT station will employ gas turbines provided by General Electric, which are proven in their purpose, and it is planned that its construction will start in 2009 and finish in 2012, by when a connection to the national grid will have been implemented. The stage-two gasification technology is licensed from Shell and will capture 90% of the carbon emissions so that the fuel will be essentially hydrogen.
That carbon then has to be "removed for sequestration", i.e. put somewhere safe for hundreds to thousands of years, usually in rock-formations. Where, I wonder? Or, perhaps feed it to algae and turn it into liquid fuels? In that latter case, the carbon would end up in the atmosphere when the fuel was burned but it might be argued that there would be a trade-off against the oil that would otherwise be used as a fuel instead.
Related Reading.
[1] "Green Light for 900MW carbon capture coal plant in Yorkshire." http://newenergyfocus.com/do/ecco.py/view_item?listid=1&listcatid=32&listitemid=2223§ion=Carbon
[2] "First 'clean coal' power station gets go-ahead," by Robin Pagnamenta: http://business.timesonline.co.uk/tol/business/industry_sectors/natural_resources/article5670940.ece
Thursday, February 05, 2009
Thinking Positive - Carbon Capture.
Whenever anyone mentions carbon capture there are two opinions - essentially for and against. "For", in service of the carbon-induced global warming/climate change theory and "against" as in "it's pointless" since the impact of using fossil fuels will be attenuated by inevitable cuts in their use according to peak oil, peak gas and a potential peak coal that was recently calculated using a Hubbert Linearization to arrive by 2028. I am not sure about the realities of the "for" case, in terms of how the Earth systems will respond exactly to GW (and nobody will know until the vast experiment is completed in reality) but in regard to the "against" I agree that global warming is the least of our worries in the immediate term, and running short of supplies of oil and gas will launch a cataclysm of social disintegration if we have no alternative - plan B - in place.
The two concepts might be combined however, at least assuming there is enough time, and that the EROEI stacks-up. For the moment, however, let's think positive and assume that it does. Proposals for geoengineering always make me uneasy, including the idea of "seeding the ocean". Principally, my disquiet stems from a feeling that all aspects of nature are interconnected and by messing about with one thing, an unforeseen calamity might ensue elsewhere - the butterfly effect, to use a well-known phrase.
However, if phytoplankton could be caused to bloom, say in the Southern Ocean, 1 Gt (billion tonnes) of carbon could be captured annually. It is claimed that regenerative agriculture might sequester around 3 Gt of carbon each year (although there is some dispute about this), and that by 2050, biochar production could account for another 1 Gt of carbon annually. In principle - and this is where the link comes in - the carbon in the soil can stay there and improve its quality, but if the other kinds of captured carbon could be harvested, it might provide a useful potential source of biomass/fuel. Growing algae on a local level - a "village pond" you might call it - could provide energy to replace fossil fuels for local communities, without impacting on arable land.
Since we emit 7 Gt/year of carbon from fossil fuels, the sum comes out something like (in Gt): 7 - 3 - 1 -1 = 2 Gt left to worry about. A cut in fossil fuel use by 50% through biomass curbs that to 1 Gt. Photosynthesis already absorbs around 3 Gt of carbon/year into oceanic phytoplankton and land-based plants, and if localised algal production cuts emissions from oil by another 1 Gt (assuming that we need 1 Gt less since we have that from algal biomass), the combined scheme is carbon negative by -3 Gt/year.
Hence in 40 years this would have cut 120 Gt of carbon from the atmosphere, which would reduce the concentration of CO2 by around 50 - 60 ppm.
Now this is an extrapolation of sums I have seen done and on paper it looks pretty rosy, implying that we can eke-out our oil, gas, coal and nuclear and at the same time bring down the carbon-content of the atmosphere to pre-industrial levels by the end of this century.
What is rarely mentioned let alone costed-in is the lead-in time, the energy costs, the EROEI, the materials, the engineering and so on... that's when it begins to look less rosy.
For example, while I like the idea of biochar, the stated goal by the International Biochar Initiative (IBI) is that we could have 1 Gt/year of carbon being drawn from the atmosphere by 2050. O.K. let's assume that's 40 years time and that there is currently (in Gt terms) about zero biochar being produced currently. Even if we assume a linear growth in the technology, that "wedge" (if you draw a straight line on a piece of graph paper from 0 - 1 Gt on the y-axis up to 40 years on the x-axis) that only accounts for 20 Gt of carbon, or a reduction of about 10 ppm, which is neither here nor there, and the biomass production and processing would be simply colossal when viewed en mass.
That said, if that level is achieved by, and sustained beyond 2050, 1/7th of all carbon (14%) captured per year is significant, and could be a higher proportion if fossil fuel burning has by then been significantly curbed, either deliberately or because we have less of them available. The main benefit of biochar is likely to be in terms of improving soil quality, if it is employed as a soil-amending agent, and thereby reduces demand on water and nutrients like N and P to grow crops. The latter is likely to be particularly significant in parts of the world where the soil is poor, e.g. Africa and Asia. In the U.K. soil tends to be very rich - too rich sometimes - but even here, the incorporation of biochar into the soil would attenuate problems from run-off waters that contain too much phosphate and nitrate.
Regenerative agriculture is somewhat contested in terms of its carbon capture potential, and there is little evidence that we can "seed" the oceans in a practical fashion, or recover the plankton on any significant scale. Indeed, if massive amounts of phytoplankton were to grow through seeding, the emissions of sulphur compounds (H2S, dimethylsulphide etc.) which are oxidised to particulate "sulphate" matter in the troposphere, would have the effect of further seeding cloud formation. This might help to cool the planet through reflecting more sunlight back into space, which sounds good in GW-terms, but it would surely affect rainfall and how the earth-systems distribute water around the planet.
What I can see is that production of biochar and algae on a local level, as part of a programme of lower-energy living could offer some benefits. There is also (for once) the advantage that there are a lot of people on the planet. Hence if a community of 2000 people could catch and sequester 200 tonnes of biochar per year (100 kg/person), 7 billion of us in total could sequester almost 0.8 Gt/year (close to the IBI projection of 1 Gt/year by 2050). However, it is the curbing of energy use that really counts. Back to the village algae-pond. As a total area, we would need around 3200 km2 of ponds to fuel Britain (more of which could be turned to other purposes than personalised transport through relocalisation), that suggests that each village pond would need to be:
3200 km2 x 100 ha/km2/60 million x 2000 = 10.7 hectares for each 2000 person community. It's big but it doesn't sound impossible when broken down like this. The real problem is how to process the algae either by extraction of its oil/transesterification or bulk thermal gasification. It might be simpler to just grow the algae (and other biomass), dry it out and burn it as a source of thermal energy.
All of the above is going to take an awful lot of engineering, hence energy and time, but let's not depressed about the details, and look at those "happy sums" again.
Related Reading.
[1] http://ergobalance.blogspot.com
[2] http://en.wikipedia.org/wiki/Carbon_sequestration
[3] http://en.wikipedia.org/wiki/Carbon_sink
The two concepts might be combined however, at least assuming there is enough time, and that the EROEI stacks-up. For the moment, however, let's think positive and assume that it does. Proposals for geoengineering always make me uneasy, including the idea of "seeding the ocean". Principally, my disquiet stems from a feeling that all aspects of nature are interconnected and by messing about with one thing, an unforeseen calamity might ensue elsewhere - the butterfly effect, to use a well-known phrase.
However, if phytoplankton could be caused to bloom, say in the Southern Ocean, 1 Gt (billion tonnes) of carbon could be captured annually. It is claimed that regenerative agriculture might sequester around 3 Gt of carbon each year (although there is some dispute about this), and that by 2050, biochar production could account for another 1 Gt of carbon annually. In principle - and this is where the link comes in - the carbon in the soil can stay there and improve its quality, but if the other kinds of captured carbon could be harvested, it might provide a useful potential source of biomass/fuel. Growing algae on a local level - a "village pond" you might call it - could provide energy to replace fossil fuels for local communities, without impacting on arable land.
Since we emit 7 Gt/year of carbon from fossil fuels, the sum comes out something like (in Gt): 7 - 3 - 1 -1 = 2 Gt left to worry about. A cut in fossil fuel use by 50% through biomass curbs that to 1 Gt. Photosynthesis already absorbs around 3 Gt of carbon/year into oceanic phytoplankton and land-based plants, and if localised algal production cuts emissions from oil by another 1 Gt (assuming that we need 1 Gt less since we have that from algal biomass), the combined scheme is carbon negative by -3 Gt/year.
Hence in 40 years this would have cut 120 Gt of carbon from the atmosphere, which would reduce the concentration of CO2 by around 50 - 60 ppm.
Now this is an extrapolation of sums I have seen done and on paper it looks pretty rosy, implying that we can eke-out our oil, gas, coal and nuclear and at the same time bring down the carbon-content of the atmosphere to pre-industrial levels by the end of this century.
What is rarely mentioned let alone costed-in is the lead-in time, the energy costs, the EROEI, the materials, the engineering and so on... that's when it begins to look less rosy.
For example, while I like the idea of biochar, the stated goal by the International Biochar Initiative (IBI) is that we could have 1 Gt/year of carbon being drawn from the atmosphere by 2050. O.K. let's assume that's 40 years time and that there is currently (in Gt terms) about zero biochar being produced currently. Even if we assume a linear growth in the technology, that "wedge" (if you draw a straight line on a piece of graph paper from 0 - 1 Gt on the y-axis up to 40 years on the x-axis) that only accounts for 20 Gt of carbon, or a reduction of about 10 ppm, which is neither here nor there, and the biomass production and processing would be simply colossal when viewed en mass.
That said, if that level is achieved by, and sustained beyond 2050, 1/7th of all carbon (14%) captured per year is significant, and could be a higher proportion if fossil fuel burning has by then been significantly curbed, either deliberately or because we have less of them available. The main benefit of biochar is likely to be in terms of improving soil quality, if it is employed as a soil-amending agent, and thereby reduces demand on water and nutrients like N and P to grow crops. The latter is likely to be particularly significant in parts of the world where the soil is poor, e.g. Africa and Asia. In the U.K. soil tends to be very rich - too rich sometimes - but even here, the incorporation of biochar into the soil would attenuate problems from run-off waters that contain too much phosphate and nitrate.
Regenerative agriculture is somewhat contested in terms of its carbon capture potential, and there is little evidence that we can "seed" the oceans in a practical fashion, or recover the plankton on any significant scale. Indeed, if massive amounts of phytoplankton were to grow through seeding, the emissions of sulphur compounds (H2S, dimethylsulphide etc.) which are oxidised to particulate "sulphate" matter in the troposphere, would have the effect of further seeding cloud formation. This might help to cool the planet through reflecting more sunlight back into space, which sounds good in GW-terms, but it would surely affect rainfall and how the earth-systems distribute water around the planet.
What I can see is that production of biochar and algae on a local level, as part of a programme of lower-energy living could offer some benefits. There is also (for once) the advantage that there are a lot of people on the planet. Hence if a community of 2000 people could catch and sequester 200 tonnes of biochar per year (100 kg/person), 7 billion of us in total could sequester almost 0.8 Gt/year (close to the IBI projection of 1 Gt/year by 2050). However, it is the curbing of energy use that really counts. Back to the village algae-pond. As a total area, we would need around 3200 km2 of ponds to fuel Britain (more of which could be turned to other purposes than personalised transport through relocalisation), that suggests that each village pond would need to be:
3200 km2 x 100 ha/km2/60 million x 2000 = 10.7 hectares for each 2000 person community. It's big but it doesn't sound impossible when broken down like this. The real problem is how to process the algae either by extraction of its oil/transesterification or bulk thermal gasification. It might be simpler to just grow the algae (and other biomass), dry it out and burn it as a source of thermal energy.
All of the above is going to take an awful lot of engineering, hence energy and time, but let's not depressed about the details, and look at those "happy sums" again.
Related Reading.
[1] http://ergobalance.blogspot.com
[2] http://en.wikipedia.org/wiki/Carbon_sequestration
[3] http://en.wikipedia.org/wiki/Carbon_sink
Monday, February 02, 2009
It's a Gas.
A new study concludes that half of all households in the U.K. could be heated by biogas, as generated from waste food or sewage. The gas itself is methane, and would be piped to the national (gas) grid in sufficiency to provide 15% of all energy from renewable sources by 2020. In the longer run, it is concluded by Ernst and Young, such biogas could provide up to half of Britain's domestic gas heating... yes, things begin to get a bit nebulous in these quotations. I believe that 40% of Britain's total energy is provided by natural gas (for heating and electricity generation), about another 35% for transport, mostly cars, and roughly 40% of the total amount of energy goes for space-heating, so that might equal 20% of the grand total?
In any case it is a good portent. We do need to focus on renewable sources, but the engineering involved will be massive. As I have alluded before, the jury is still out regarding anthropogenic climate change, but either way, fossil fuels are in limited supply and so the same action - of using less of them - satisfies both agenda.
Sir Richard Budge ("King Coal" as he is dubbed deservedly) is a man to be admired. He has opened a formerly closed (Thanks Maggie!) coal mine in Yorkshire - a scene of dispute of the worst industrial strife in British history; ignoring the Tonypandy riots in South Wales - and adjacently, has planned to implement a combined-cycle power station, which generally gets 56% of the thermal energy recovered rather than the 36% that is dictated by the thermodynamic Carnot Cycle limits, and is also "clean". This, at any rate is his intention.
His company, Powerfuel, has requested planning-permission to build a 900 MW plant, with low-emissions, i.e. "clean-coal", fuelled from the Hatfield colliery, which he unsealed in 2009, funded by Russian investors. I use the world "unsealed" deliberately because Margaret (Maggie) Thatcher's government inaugurated the sealing of the mines with concrete as a demonstration of force against the trade unions who, although I am a socialist, were asking for trouble... sadly it is the population of this country in general that paid the price for both the union militants and Thatcher's unabating worship of monetarism - a kind of academically discredited economic policy that has brought the world to the pivot of bankruptcy.
As I note, it is a combined cycle (IGCC) - that's Integrated, Gasification, Combined Cycle - plant, which first gasifies the coal dust and converts it to synthesis gas (a mixture of H2 and CO) which is burned at high efficiency. The consequent CO2 is separated out and can then be "sequestered" in some way - possibly it could be fed to algae and the resulting yield used in a thermal gasification process to provide more "syngas".
However, not that it matters much, as I have already made the point, Dr John Theon, who was apparently James Hansen's boss - the main climate change/anthropogenic CO2/global warming protagonist - has come clean that he isn't convinced that this theory is right. I keep an open mind on this - I am not a specialist in atmospheric chemistry, but I am a well qualified physical scientist and I can understand many original papers when I read them and do the sums - but Theon alleges that data has been "cherry picked" to fit the whole picture, and that the "models" which is all they are, a mathematical "fit" inside a computer may give particular results according to a given algorithm; i.e. other models will give different predictions. Theon says, "They have resisted making their work transparent so that it can be replicated independently by other scientists. This is clearly contrary to how science should be done. Thus there is no rational justification for using climate model forecasts to determine public policy."
Now, the latter is an extremely significant point. We are projected to invest billions of whatever currency prevails in carbon capture and sequestration, and yet it is not absolutely clear whether letting that element in the form of its most highly oxidised state - CO2 - into the atmosphere will fry the planet or not. But, burning less carbon in the form of fossil fuels is paramount, because we are going to run out of cheap and readily availabile amounts of them sooner not later. Either line of argument (resource considerations or global warming) takes us to the same conclusion.
Related Reading.
[1] http://www.theregister.co.uk/2009/01/28/nasa_climate_theon/
[2] http://business.timesonline.co.uk/tol/business/industry_sectors/natural_resources/article5627318.ece
[3] http://www.theherald.co.uk/news/environment/display.var.2486272.0.Half_of_UKs_homes_could_be_heated_by_biogas_from_waste_study_finds.php
In any case it is a good portent. We do need to focus on renewable sources, but the engineering involved will be massive. As I have alluded before, the jury is still out regarding anthropogenic climate change, but either way, fossil fuels are in limited supply and so the same action - of using less of them - satisfies both agenda.
Sir Richard Budge ("King Coal" as he is dubbed deservedly) is a man to be admired. He has opened a formerly closed (Thanks Maggie!) coal mine in Yorkshire - a scene of dispute of the worst industrial strife in British history; ignoring the Tonypandy riots in South Wales - and adjacently, has planned to implement a combined-cycle power station, which generally gets 56% of the thermal energy recovered rather than the 36% that is dictated by the thermodynamic Carnot Cycle limits, and is also "clean". This, at any rate is his intention.
His company, Powerfuel, has requested planning-permission to build a 900 MW plant, with low-emissions, i.e. "clean-coal", fuelled from the Hatfield colliery, which he unsealed in 2009, funded by Russian investors. I use the world "unsealed" deliberately because Margaret (Maggie) Thatcher's government inaugurated the sealing of the mines with concrete as a demonstration of force against the trade unions who, although I am a socialist, were asking for trouble... sadly it is the population of this country in general that paid the price for both the union militants and Thatcher's unabating worship of monetarism - a kind of academically discredited economic policy that has brought the world to the pivot of bankruptcy.
As I note, it is a combined cycle (IGCC) - that's Integrated, Gasification, Combined Cycle - plant, which first gasifies the coal dust and converts it to synthesis gas (a mixture of H2 and CO) which is burned at high efficiency. The consequent CO2 is separated out and can then be "sequestered" in some way - possibly it could be fed to algae and the resulting yield used in a thermal gasification process to provide more "syngas".
However, not that it matters much, as I have already made the point, Dr John Theon, who was apparently James Hansen's boss - the main climate change/anthropogenic CO2/global warming protagonist - has come clean that he isn't convinced that this theory is right. I keep an open mind on this - I am not a specialist in atmospheric chemistry, but I am a well qualified physical scientist and I can understand many original papers when I read them and do the sums - but Theon alleges that data has been "cherry picked" to fit the whole picture, and that the "models" which is all they are, a mathematical "fit" inside a computer may give particular results according to a given algorithm; i.e. other models will give different predictions. Theon says, "They have resisted making their work transparent so that it can be replicated independently by other scientists. This is clearly contrary to how science should be done. Thus there is no rational justification for using climate model forecasts to determine public policy."
Now, the latter is an extremely significant point. We are projected to invest billions of whatever currency prevails in carbon capture and sequestration, and yet it is not absolutely clear whether letting that element in the form of its most highly oxidised state - CO2 - into the atmosphere will fry the planet or not. But, burning less carbon in the form of fossil fuels is paramount, because we are going to run out of cheap and readily availabile amounts of them sooner not later. Either line of argument (resource considerations or global warming) takes us to the same conclusion.
Related Reading.
[1] http://www.theregister.co.uk/2009/01/28/nasa_climate_theon/
[2] http://business.timesonline.co.uk/tol/business/industry_sectors/natural_resources/article5627318.ece
[3] http://www.theherald.co.uk/news/environment/display.var.2486272.0.Half_of_UKs_homes_could_be_heated_by_biogas_from_waste_study_finds.php
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