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    Mongabay, a leading resource for news and perspectives on environmental and conservation issues related to the tropics, has launched Tropical Conservation Science - a new, open access academic e-journal. It will cover a wide variety of scientific and social studies on tropical ecosystems, their biodiversity and the threats posed to them. Tropical Conservation Science - March 8, 2008.

    At the 148th Meeting of the OPEC Conference, the oil exporting cartel decided to leave its production level unchanged, sending crude prices spiralling to new records (above $104). OPEC "observed that the market is well-supplied, with current commercial oil stocks standing above their five-year average. The Conference further noted, with concern, that the current price environment does not reflect market fundamentals, as crude oil prices are being strongly influenced by the weakness in the US dollar, rising inflation and significant flow of funds into the commodities market." OPEC - March 5, 2008.

    Kyushu University (Japan) is establishing what it says will be the world’s first graduate program in hydrogen energy technologies. The new master’s program for hydrogen engineering is to be offered at the university’s new Ito campus in Fukuoka Prefecture. Lectures will cover such topics as hydrogen energy and developing the fuel cells needed to convert hydrogen into heat or electricity. Of all the renewable pathways to produce hydrogen, bio-hydrogen based on the gasification of biomass is by far both the most efficient, cost-effective and cleanest. Fuel Cell Works - March 3, 2008.

    An entrepreneur in Ivory Coast has developed a project to establish a network of Miscanthus giganteus farms aimed at producing biomass for use in power generation. In a first phase, the goal is to grow the crop on 200 hectares, after which expansion will start. The project is in an advanced stage, but the entrepreneur still seeks partners and investors. The plantation is to be located in an agro-ecological zone qualified as highly suitable for the grass species. Contact us - March 3, 2008.

    A 7.1MW biomass power plant to be built on the Haiwaiian island of Kaua‘i has received approval from the local Planning Commission. The plant, owned and operated by Green Energy Hawaii, will use albizia trees, a hardy species that grows in poor soil on rainfall alone. The renewable power plant will meet 10 percent of the island's energy needs. Kauai World - February 27, 2008.

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Tuesday, July 29, 2008

Bio-SNG pilot plant comes online in the Netherlands - further steps towards carbon-negative energy

Carbon-negative energy - the most radically green form of renewable energy - is beginning to enter the European discourse on clean energy and climate change in an ever more serious way. But there's more than dreaming of the concept, there's action too. The world's first pilot-scale biomass gasification plant that yields methane the carbon dioxide of which will be sequestered in the future, has come online in the Netherlands, bringing the concept closer to reality. This type of 'negative emissions energy' or 'carbon-negative biofuel' is capable of actively removing CO2 from the atmosphere, thus tackling climate change in the most drastic way. Carbon-negative forms of bioenergy allow us to consume energy while cleaning up the CO2 from the past.

The Energy Research Center of the Netherlands (ECN) has completed part of the technology that will make this fascinating concept real: an 800 kilowatt pilot-scale gasification plant based on its Milena gasifier technology, which uses an indirectly heated biomass gasification process with high cold-gas efficiency and a high methane yield. The plant is optimized for the production of Substitute Natural Gas from biomass (bio-SNG), also known as 'green natural gas', biomethane or simply 'renewable natural gas' (to distinguish it from biogas which is obtained from the anaerobic fermentation of biomass). The ECN has a dedicated website on Bio-SNG, which explains the production process in-depth. Its very many advantages as a biofuel are illustrated in the following conceptual map (click to enlarge):

The ECN, the Netherlands' largest energy research organisation, says that, because the large biogenic carbon dioxide stream that emerges during the green gas production will be stored in empty natural gas fields, the overall process will produce a CO2-negative result. In short, both the production of the fuel, as well as the carbon capture and storage (CCS) step will not only add no emissions, but will actually yield a fuel the combustion of which equals the removal of CO2 from the atmosphere over its lifecycle (as the biomass crops regrow and take more CO2 out of the air than is released during the combustion of the already 'carbon neutral' green gas the CO2 of which released during its production was sequestered). (Biopact hinted at applying CCS to high-carbon biomethane production a while ago.)

In a later application of the technology, the biomass-based gas can be reformed into hydrogen, which, unlike methane, is a fully decarbonised fuel. When the CO2 out of this process is then again sequestered, the energy generated by the biohydrogen will be carbon-negative in the most radical way.

'Negative emissions energy' is the greenest form of renewable energy imaginable: depending on the technology, it can take up to 1000 tons of CO2 out of the atmosphere per GWh of electricity generated (that is: its carbon balance is -1000 tons CO2). Mildly carbon-positive renewables like wind (+30 tons CO2eq/GWh) or solar PV (+100 tons CO2eq/GWh) emit small amounts of CO2 to the atmosphere over their lifecycle. In short, carbon-negative energy is capable of tackling climate change far more drastically than any other type of (renewable) energy.

The Netherlands is certainly one of the pioneers in 'bioenergy with carbon storage' (BECS) - as the concept is sometimes called - because it has large depleted natural gas fields that can be used to sequester CO2. This potential is now increasingly being coupled to the idea of storing biogenic CO2, instead of CO2 from fossil fuels. The motivation behind this reasoning is simple: if expensive carbon capture and sequestration (CCS) infrastructures are going to be built in any case, then we better use them to store CO2 from carbon-neutral fuels - that is biomass - because this allows us to remove CO2 from the atmosphere, instead of merely 'reducing emissions' from power generation.

Negative emissions energy is not only gaining a foothold amongst an a tiny avant-garde of renewable energy experts, or solely in the Netherlands. No, it is gradually penetrating the wider discourse of climate scientists and renewable energy technologists at large. An important breakthrough in spreading the concept came most recently, when the Bellona Foundation analysed carbon-negative energy's potential role in mitigating climate change - the first major environmental think tank to do so. Its results were stunning: in a scenario that aims for an 85% reduction of CO2 emissions by 2050, carbon-negative energy was the second most important 'wedge', capable of meeting 23% of that target, coming only after energy efficiency (25%). All other renewables combined (wind, solar, hydro, etc) only contribute around 10%. In short, the promise of BECS is enormous.

Another advocate of carbon-negative bioenergy is NASA/Columbia University's Dr James Hansen, who wants humanity to aim for a future in which atmospheric CO2 levels are to be reduced to 350ppm. This will mean we will have to design energy concepts capable of actively taking CO2 out of the atmosphere. Dr Hansen lists BECS as one of the options, alongside biochar, another negative emissions technology that works by sequestering carbon in soils.

The pilot biomass gasification plant now up and running in the Netherlands brings us a first step closer to Hansen's goals.

Let's zoom in on it a bit more.

From the lab...
The lab-scale MILENA has been operated during a large number of tests under different conditions. Parameters that have been varied are biomass fuel, gasification temperature, bed material, inertisation gas and supplementary fuel to combustor (simulating tar recycle). The aim of the experiments was to find the optimum conditions for the highly efficient production of a CH4-rich product gas:
:: :: :: :: :: :: :: :: :: :: :: :: :: :: ::

Biomass fuels
Two different types of fuels were used in the tests: clean beech wood and grass. Beech wood was fed as small particles and grass was fed as milled pellets. From lab to pilot the fuel has changed: Biomass Magazine quotes Dr Christiaan van der Meijden, a researcher with the center’s Biomass, Coal & Environmental Research division, as saying that the primary feedstock for the pilot plant currently is waste wood. But “we plan to test other biomass fuels, as well, [such as] sunflower husks,” he adds.

Gasification temperatures
The gasification temperature influences the product gas composition, the amount and composition of the tar in the gas, and the conversion of the fuel in the gasifier. Which is why research into optimal temperatures has been key. The gasifier temperature is measured at the outlet of the gasifier. A thermocouple placed in the gas stream is used for this measurement. The heat loss in the upper part of the installation is relatively high. This causes a rapid decrease in gas temperature at the outlet. In previous experiments, the temperature was measured in the settling chamber, were there was a direct contact between thermocouple and circulating sand, this temperature measurements gives an better indication of the gasifier temperature, but the thermocouple broke down. The average difference in measured gas temperature was 26.5°C. The gasification temperature is defined as the measured gasifier outlet temperature +26.5°C.

By varying the reactor wall temperature (trace-heating) and adding additional fuel to the combustor (both the use of recycled product gas and recycled tar were simulated by oil for practical considerations) the temperature in the reactor was varied. The air to fuel ratio for the combustor was held at a fixed value (typical between 3 and 6 vol% dry of oxygen in the flue gas).
In the MILENA pilot plant, as in a commercial demo plant, the gasifier temperature is not a control parameter but a result of the temperature in the combustor, which is set by the amount of char that is fed to the combustor. The concentration of methane typically decreases with increasing the temperature.

The total amount of tar produced in the gasifier without the use of catalytic bed material is relatively high and varies a lot. Increasing the temperature does not decrease the total amount of tars in the gas. Heterocyclic components, like phenol, pyridine and cresol (class 2 tars) decrease in concentration with increasing temperature. Heavy poly-aromatic hydrocarbons (4-5 rings PAH’s, i.e. class 5 tars) increase in concentration with increasing temperature. The heterocyclic tar components are the least stable and therefore readily broken down. The heavy poly-aromatic hydrocarbons are formed from lighter tars (i.e. via polymerization). This behaviour is also observed in bubbling fluidized and circulating fluidized gasifier.

Effect on fuel conversion
The fuel conversion (or carbon conversion) in the gasification section of the installation varies between 70 and 90%. The unconverted fuel (char) is send to the combustor were it is completely combusted and produces the heat for the gasification reactor. Resultantly, the fuel conversion in an indirect gasifier system is essentially 100%. The amount of char going to the combustor determines the temperature in the gasifier, so the fuel conversion in the gasification reactor determines the temperature in the combustor and the gasifier. This makes the carbon conversion in the gasification section an important design parameter.

Carbon conversion is defined as the amount of carbon in the product gas divided by the amount of carbon in the fuel or 100% minus the amount of solid carbon leaving the gasifiers divided by the amount of carbon in the fuel. The last method was used to calculate the carbon conversion in this report. The amount of solid carbon leaving the gasifier was calculated from the amount of air fed to the combustor and the measured oxygen concentration in the flue gas. Part of the carbon leaves the system with the product gas in the form of dust and is not returned to the combustor in the lab-scale installation. The product gas contains approximately 10 g/mn3 of dust. An estimated 20 wt% of this dust is bed material (sand). Normally 5 mn3/h of gas is produced; this results in a char loss of 40 gram/h. Corresponding to approximately 10% of the char that is produced in the gasifier.

Carbon conversion is influenced by fuel particle size, fuel type, temperature, and residence time in the gasifier. The particle size cannot be varied in a range that is useful for commercial application, because the size of the feeding system and the reactor is relatively small in the lab-scale set-up. For all test fuel particles of 0.7 2.5 mm were used. For commercial applications particles up to several cm are foreseen. Tests in the pilot-scale plant must generate the required carbon conversion fuel size relations.

The carbon conversion generally increases with increasing temperature. This makes the process self-regulating, if the temperature in the reactor lowers, the amount of char produced increases and the amount of heat produced in the combustor increases. Resulting in an increase in gasification temperature.

Recycle of tar to the combustor
Tar recycle was simulated by the supply of oil to the combustor, because it was not possible to feed relatively small quantities of tar in the lab-scale set-up. A cooled nozzle was fabricated to feed the oil in the bed (near the bed wall). The temperature in the bed was increased by the combustion of the oil. The increased combustion reactor temperature resulted in an increased gasifier temperature.

Nitrogen dilution

The product gas from an indirect gasifier contains small amounts of nitrogen. The nitrogen comes from air that is fed with the fuel, nitrogen that is used as purge gas, fuel-bound nitrogen, and gas transport from the combustor. Nitrogen in the product gas increases in N2 concentration in the final SNG product. Experiments were performed to minimise the nitrogen dilution resulting from the use of nitrogen as inertisation gas of the biomass feeding bunkers. The fuel bunker was purged with CO2 and the nitrogen purge of the feeding screw was replaced by a CO2 purge. A CO2 purge is a realistic option for commercial plant, as CO2 is removed in the SNG upgrading, therefore CO2 is available and a CO2 dilution of the product gas is not a problem.

The compositions for a typical product gas produced in the lab-scale MILENA gasifier with and without a CO2 purge are shown in the table above (click to enlarge). The argon in the gas results from the steam generator; argon is used as carrier gas. The nitrogen content can be as low as 1.2 vol% in the dry product gas, which results in a calculated N2 content in the SNG of approximately 2.5 vol%.

...to the pilot and demonstration plant

In a first step, the green gas produced by the pilot-scale plant will be used to fuel one type of several natural-gas-powered consumer automobiles currently available in Europe. Natural gas is one of the fastest growing automotive fuels in the EU, because of its increasing cost-advantage compared with diesel or gasoline.

The next step will be to begin construction of a 10-megawatt demonstration plant in 2009. “Several industrial parties are interested and involved in parts of the development,” van der Meijden told Biomass Magazine. “We have not licensed the Milena technology yet.” However, he added, the technology will become commercially available after the demonstration.

This demo plant - the next phase of the concept - will initially produce gas for a boiler. Later, it will include an oil gas scrubber tar removal system developed by the ECN to recycle tar for combustion to produce green gas. Ultimately, the plant will be equipped with a gas cleaner to produce substitute natural gas at grid specifications. “The technology to have the gas on specification for gas grid injection or use as [biobased compressed natural gas] should be ready for commercialization in 2015,” van der Meijden said.

By that time, the first Dutch carbon capture and storage infrastructures and technologies should be out of their current experimental phase, and allow the CO2 generated during the production of the green gas to be sequestered in empty gas fields.

In the final step, the biobased gas can be reformed directly into hydrogen, when fuel cell vehicles become more widely available. Alternatively, the green gas can be fired in natural gas plants equipped with pre-combustion, oxyfuel or post-combustion carbon capture infrastructures, so that all the carbon from the green gas can be trapped and stored permanently in the empty offshore gas-fields that are widely present in the Netherlands.

This is the moment when fully 'negative emissions' energy becomes available. This is the slightly strange moment when using this energy means that you take CO2 from the past out of the atmosphere. No longer will you be reducing carbon-emissions to 'zero', as you would when using energy from wind or solar. You will be going 'beyond zero'.

Picture: the 800 kilowatt-hour pilot-scale gasification plant which uses Milena gasifier technology developed by the ECN.

Map: Bio-SNG's very many advantages. Credit: ECN.


Biomass Magazine: Dutch biomass gasification process comes on line - August 2008 Issue

Energy Center of the Netherlands: Biomass, Coal & Environmental Research.

Energy Center of the Netherlands: dedicated website on Bio-SNG.

Biopact: Carbon-negative bioenergy making headway, at last - June 06, 2008 [see references in that article].

Biopact: Pre-combustion CO2 capture from biogas - the way forward? - March 31, 2007


Blogger brutontom said...

Hi folks,
Thanks for the technical update. A cost-effective technology for doing anything less than 1MW with biomass is really needed.
I have to ask you to use the correct terms for power generation. A very common error in all kinds of publications is confusing power generation (kW) with output (kWh).
"an 800 kilowatt-hour pilot-scale gasification plant " is a scientific impossibility - please just remove the word hour.

10:20 AM  

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