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Showing posts with label clean coal technology. Show all posts
Showing posts with label clean coal technology. Show all posts

Sunday, August 19, 2012

Colloidal Coal Water Fuel by Nanotechnology for power generation

Coal is still the dominant fuel used for power generation due to its low cost and abundant availability despite its emission problems and global warming issues. Companies around the world are trying to improve the efficiency of coal fired power plants and reduce emissions by various methods. The idea is to prepare an ultra clean coal with very low ash content in the form of coal-water slurry that can be directly injected into a diesel engine. Direct firing of coal requires micronising to less than 20-30 microns for diesel engine and less than 10 microns for turbines and producing a coal water slurry with at least 50% w/w coal content. The thermal and combustion efficiency of coal water fuel seems to be matching to that diesel engine at up to 1900rpm according to literatures. Still more research is required on engine modification and engine nozzle to handle coal water slurry because of its abrasive nature. If coal can be converted into a fluid like a diesel or Fuel oil then it can substitute diesel at reduced cost. However the Carbon problem needs to be addressed by ongoing research on sequestration. Nanotechnology is an emerging field that offers hope to produce Colloidal coal water fuel that resembles fuel oil that may be suitable for direct injection into diesel engine with little modifications. The colloidal suspensions of coal in water (CCW) are produced using a proprietary wet-combination device. These suspensions are a new material with new properties. “First, the colloidal fraction plus water is a pseudo fluid good for transport, handling and suspension of large particles. Second, the surface area per unit volume of coal available for chemical reaction and burning is greatly increased and finally, CCW may be milled with a third fluid, seeding the mixture with submicron coal. The colloidal nature of the majority of particles provides for very good features such as outstanding long-term stability, in contrast to regular coal water slurries (CWS) which rapidly sediment under storage. Moreover, the very small particles create an increased reactivity to combustion because small particles with large surface area react faster than large particles with the same volume.” A company based in Panama has conducted experiments using colloidal coal water fuel and published the following information. CCW suspension preparation and properties Characterization “The colloidal dispersions are prepared in two stages: first by a bench mill and then by our wet- comminuting device. The bench mill was manufactured by IKA®- Group. After grinding, samples were sieved using mesh size sieves 40 (400 μm), 70 (212 μm) or 140- (106 μm) and the passing particles were retained and used to prepare coal suspensions with various water contents (30 to 50 %), surfactants and other type of additives. These mesh sizes are not foreign to coal fired power plants. It is noteworthy that a preliminary formulation study is first necessary in order to determine the type and concentration of additives that are best suited to improve coal particle wetting and reduce viscosity. The additives were mostly surfactants and viscosity controlling agents and every type of coal tested usually required a specific formulation. In general, it was found that nonionic surfactants were good wetting agents, in concentrations varying from 0.1 to 0.6 w/w %. Some of the additives used to reduce viscosity by decreasing particle interactions, before or after the wet comminuting process, were amines. The suspension formulation previous to the wet-comminuting instance was very simple since what was basically required was a good wetting agent or a combination of two wetting agents. The idea was to have a uniform mixture with as low viscosity as possible. Particle size of coal samples was determined by direct observation in an optical microscope, or by sieving using five or six different sieves ranging from 20 to 400 μm, or using a laser diffraction apparatus made by Microtrac Corporation, Nanotrac model, having a measurement range from 8 nm to 6.5 μm. Neither of these methods was sufficient to obtain a complete characterization of the particle size distributions, but a combination of the three allowed for a good assessment of what really was in the suspension, before and after the wet-comminuting process. In our study, the percentage of mass passing the 635 mesh size sieve (< 20 μm) was used as an indicator of wet-comminuting process efficiency (generation of colloidal particles), given that microscopic observations generally showed that particles between 8 to 20 μm were very scarce. The preparation of the colloidal suspension of coal was centered in a technology that is totally based on fluid mechanics principles. As mentioned above, a preliminary suspension was prepared in a tank with low agitation and the appropriate water and surfactant contents. This suspension is then fed into a device that spins a film of the fluid to the walls of a cylindrical vessel at very high speed and under cavitations free conditions. The resulting flow field induces a “particle trap” region where coal particles are locally concentrated above their nominal value and under very high shear. Particles are then milled to very small sizes by a wet-comminuting mechanism. Friction heating is controlled by a chilled water jacket around the vessel.
A schematic view of the set up is shown in the attached figure. The energy consumed by the wet-comminuting device was evaluated by monitoring the power (voltage and amperage) during the process. The latter has two components, the power required to drive the motor shaft and mechanical seal, and the net power consumed by the fluid during comminuting. It was found that the net power divided by the mass flow rate, in terms of kWH/ton depended on coal content and viscosity of the preliminary slurry, exhibiting values of 30 to 80 kWh/ton. The energy consumed by the motor shaft and seal would account for 50 to 80 % of the total power consumed. Using the method described above, 100 gallons of CCW were prepared, using an Eastern bituminous coal that was previously grinded to 200 mesh. Several properties of this sample were characterized.” Colloidal coal water fuel has certain distinct advantages over conventional coal water slurry for power generation using conventional diesel engine and turbines. Further research and development work is needed before it can be expanded for large scale production. But it offers a hope to improve the efficiency of existing coal fired power plants and reduces emissions.

Wednesday, May 23, 2012

Liquid coal- a novel fuel to reduce greenhouse gas

Coal is the single largest fuel currently used for power generation all over the world due to its abundant availability and established infrastructure and technology. However greenhouse gas emission poses a significant challenge in continuing the usage of coal as prime fuel. Currently Natural gas is favored as fuel for power generation and number of LNG plants have been set up in many part s of the world. Coal seam methane gas is another potential source that competes with natural gas .Basically, Methane is the major constituent of such gases and they are suitable for both combustion as well as for gasification for power generation.Countries who are endowed with large deposits of coal such as Australia, South Africa, Indonesia have advantages in clean coal technologies and in reducing their greenhouse gas emissions. There is an opportunity for coal fired power plants to continue their operations if they can solve the greenhouse gas emission and other pollution problems associated with coal. Number of companies are now re-evaluating clean coal technologies such as IGCC and carbon capture and reuse. As we have seen in previous articles, Hydrogen is the key in developing clean coal technology of the future. That is why gasification technology such as IGCC (Integrated Gasification and Combined Cycle) is gaining importance over combustion technologies because, that is the only way we can introduce a Hydrogen molecule in the combustion by way of ‘Syngas’.By introducing Hydrogen, we not only improve the thermal efficiency but also utilize the heat of combustion to the maximum by combined cycle while reducing GHG emission. It also facilitates the usage of existing and known power generation technologies such as steam turbine and gas turbine as well as new technologies such as Fuel cell and Hydrogen turbines. Coal in the form of pumpable liquid (CWS –coal water slurry) is another key milestone in developing a clean coal technology. Countries like China and Indonesia have been using coal water slurry for power generation successfully. Finely powerdered coal is mixed with water in the ratio of 60:40 along with dispersant such as Lignosulfonate as additives to make a finely dispersed, viscous liquid that resembles heavy petroleum oil, ready for combustion. It is easier to handle pumpable oil than a solid coal. A novel products called ‘colloidal coal water’ (CCW) is a finely dispersed colloidal coal in water with additives such as surfactants and dispersants with specific formulating agents leading to certain rheological properties is a key development in clean coal technology. The coal water slurry currently used does not have long term stability and storage properties like colloidal coal water fuel. The work is under development and it is expected that such finely dispersed colloidal coal water mix resembling a liquid hydrocarbon may be named as ‘liquid coal’ for all practical purposes will become a low cost fuel in the future power generation. This ‘colloidal coal liquid’ can be easily gasified or used as liquid fuel for combustion equipments such as boilers and also serve as precursor for a number of chemical product synthesis as downstream products. The emitted Carbon dioxide can be captured cryogenically and separated in a pure form for potential application such as ‘Natural Refrigerant’ and to synthesize number of chemical products. Clean coal can become a commercial realty provided we re-evaluate the coal preparation, gasification methods and to contain emitted carbon into an useful product of commerce.

Saturday, April 21, 2012

Carbon capture or Carbon recycle?

We live in a carbon constrained world where carbon emission is considered as the biggest challenge of the twenty first century. We unearthed fossil fuel which Nature buried for millions of years and burnt them for our advantage to generate power and to run our cars. Scientists pointed out that the unabated emission of greenhouse will cause the globe to warm with dire consequences.This came as an ‘inconvenient truth’ to industries and Governments around the world. However, economic consequences of stopping fossil fuels outweiged the impact of global warming. Governments were in a precarious situation and were unable to take a concrete policy decision. Popular Governments were not willing to risk their power by taking ethical decisions and opted for popular decision to maintain their growth. Then the financial crisis became an issue, which has nothing to do with greenhouse emission or global warming. Yet, the economic and industrial growth stumbled in many developed countries and unemployment skyrocketed. Governments are caught in a situation where they need to take a balanced view between an ethical decision and economic decisison.The overwhelming evidence of global warming and their consequences are slowly felt by countries around the world by natural disasters of various sizes and intensities. Some scientists suggested that there was nothing wrong using fossil fuels; we could continue with greenhouse emission without risking the economic growth by capturing the carbon and burying them underground. Carbon sequestration and clean coal technologies became popular and more funds were allocated to them than renewable energy development.Countires like India and China were not in a hurry to discontinue fossil fuels but continued to make massive investments on coal fired power plants. They neither try to capture carbon nor bury them, but continue to emit carbon claiming that it is their turn of economic growth and right to emit carbon emission. The chief of UN panel on climate change headed by an Indian has no say in the matter.Politicians push scientists into the background whenever the truth is inconvenient to them. How feasible in the carbon sequestration technology and what is the cost? Even if we can come up with a successful technology of capturing carbon and burying them underground, there will be a cost involved. This cost will invariably be passed on to the consumer which will eventually increase the cost of energy. Constraining carbon emission without incurring a cost can only be a dream. Capturing carbon emission is nothing new; Carbon dioxide is absorbed by solvents like MEA (Monoethanolamine) in many chemical industries. The absorbed carbon dioxide can be stripped free of solvent and the solvent can be recycled. This carbon dioxide can be treated with Ammonia to get Urea, a Fertilizer. But the source of Hydrogen can come only from renewable energy sources. That is why ‘Renewable Hydrogen ‘is the key to solve global warming problem. We can produce Urea from “captured Carbon” and ‘Renewable Hydrogen’ so that we can reduce a substantial quantity of greenhouse emission. Carbon recycling is a sustainable solution than Carbon capturing and burying. Countries like India who depend upon import of Urea for their agriculture production should immediately make Carbon recycling into Urea production mandatory. It is a win situation for everybody in the world.