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

Tuesday, March 13, 2012

Coal-water-slurry- a new source of Hydrogen?

Dirty coal is still a popular choice for power generation around the world, irrespective of the status of the country, whether industrially advanced or backward. The abundant availability and cheap cost, makes coal more attractive from investor’s point of view; they care less for the environment, while Governments turn a blind eye to all the emissions and pollutions. It is a question of survival for millions of people who work in coal mines and industries. It is one of the toughest challenges many Governments are facing. Take for example India; about 65% of power generation still comes from coal. The import of coal increases year after year and there is no immediate solution in sight. Indian coal is a low grade coal with very high ash content. Each coal-fired power plant generates huge amount of fly ash and they stockpile them; supposed to be used in the production of Portland cement. It is a big business. China and Indonesia too uses coal as a major fuel for power generation. But they have come out with an innovative and pragmatic method of using coal. They use coal-water-slurry (CWS), a finely pulverized high grade coal (calorific value 5100-6100Kcal/kg) in water. They use some chemical additives that make the slurry a homogeneous fluid, similar to a Hydrocarbon such as Heavy fuel oil (HFO).The advantage with CWS is it can be easily pumped and injected into a furnace or boiler using ceramic nozzles, obviously to avoid erosion due the abrasive nature of coal, just like firing diesel or heavy oil. According to the literature, 1.8 -2.2 tons of CWS is equivalent to 1 ton of Heavy fuel oil (HFO) and it costs the same. It cost only US$ 62 million to retrofit an existing coal fired power plant with CWS system and the yearly savings are estimated at US$ 41 mil per year, an attractive rerun on investment. The beautiful aspect of this method is it generates Hydrogen rich Syngas according to the following chemical reaction. 2C + O2+2 H2O -------- 2H2+2 CO2, when the mixture is subject to gasification instead of mere combustion. The combustion efficiency is about 96-99% and the boiler efficiency of more than 90%. It generates less Sulfur dioxide and Nitrogen oxide emissions and good for the environment compared to conventional coal- fired power plants. It is a good technology that needs the attention of Governments especially India, China and Indonesisa.Even coal rich countries like US, Australia should focus on this technology apart from their persuasion such as carbon sequestration. In fact, this will open up new avenues for India and China to switch over to Hydrogen economy, without making substantial investments. The coal-water-slurry fluid has a property similar to a Hydrocarbon as shown below. Density 65-70% ,Viscosity 1000Cp, Size d< 50 microns, Ash content <7, Sulfur<0.5%. It is easier to handle a liquid than solid coal. Pulverised coal is pneumatically conveyed and fired in rotary cement kilns for so many years. There is nothing new about it. Similarly coal water slurry can be a game changer for the power industry if it is combined with Gasification and combined cycle. It will lead into Hydrogen based power generation industries using Fuel cell such as Molten Carbonate Fuel cell (MCFC). I believe there is a clear opportunity for the Governments and private industries to seriously look into CWS technology which I believe, is a ‘precursor’ for Hydrogen economy of the future.

Thursday, March 8, 2012

Hydrogen from Coal

Coal is an important fuel that helped industrial revolution. It is still a predominant fuel for power generation in many parts of the world. It is also an important raw material for number of chemicals and they directly compete with Hydrocarbons such as Naptha.It is abundantly available and it is cheap. We are still able to generate electricity at 5 cents per kwhr using coal. But, now we are entering into a new phase of energy generation and distribution, due to changing environmental and climatic issues of the twenty first century. We require completely a new fuel to address these issues; a fuel that has a higher heat content, which can generate more power per unit value of fuel, and yet, generates no pollution. It is a challenging job and the world is gearing up to meet these challenges. They affect the whole world because any issues concerning energy impacts each and every one of us. Many industrialized countries around the world are reluctant to sign an agreement that compels them to reduce their greenhouse emission to an acceptable level set by UN panel of scientists. Governments such as US, China and India are reluctant to sign such an agreement because their economy and growth depends upon cheap energy, made from coal. Such an agreement will be detrimental to their progress, and the leaders of these nations are not prepared to sign such an agreement. They also understand that world cannot afford to continue to use coal as they have used in the past. It is simply unsustainable. It is a precarious situation and they need to carefully plan their path forward. On one hand, they need to maintain their industrial and economical growth, and on the other hand they need to reduce their emissions and save the world, from catastrophic consequences of global warming. A simple analysis of the fuel will indicate that Hydrogen is a potential energy source for the future. It has energy content at least five times more than a coal for a unit value. Coal has an average heat content of 5000 kcal /kg while Hydrogen has an average heat content of 39,000 kcal/kg. Coal has a number of impurities such as ash, sulfur, phosphorous, other than carbon. Burning coal will emit greenhouse gases with toxic fumes that have to be removed. Therefore, these industrialized countries are now looking ways to generate Hydrogen from coal; that too at a cost which will be comparable to other current fuels such as natural gas. It is not an easy task because natural gas is formed by Mother Nature over several hundred thousand years. It is readily available and there is no manufacturing cost except processing cost. We are used to free energy from Mother Nature. This is the crux of the issue. Hydrogen is the most abundantly available element on earth; yet it is not available in a free form. It is available as a compound, for example, joined with oxygen forming water H2O molecule; or joined with Carbon forming Methane CH4 molecule.This Hydrogen should be separated in a free form, and this separation requires energy. How can coal, which is just a Carbon, generate Hydrogen? It requires an addition of water in the form of steam. When coal is gasified with air and steam, a mixture of Hydrogen and Carbon dioxide is generated, known as Syngas (synthesis gas). 2C + H2O+O2 ------- 2H2 +2 CO2 The syngas is separated into Hydrogen and carbon dioxide using various methods using their difference in densities. The Hydrogen can be stored under pressure for further use. Research work is currently under way to capture carbon dioxide for sequestering. Carbon sequestration is a method of capturing carbon dioxide and storing it in a place where it cannot enter the atmosphere. But the technical feasibility and economic viability of such a system is yet to be established. Carbon sequestration is a new concept and the cost of sequestration can potentially increase the cost of energy derived from Hydrogen despite the fact, Hydrogen has energy content five times more the carbon. However, there is no quick fix for our energy problems, and we have to reconcile to the fact that the energy cost will increase in the future but eventually reduce the greenhouse emissions. These developed countries should at least disclose to the rest of the world, how they plan to reduce their emissions and their action plans; such disclosure should be subject to inspection by UN panel. In the absence of any concrete mechanism, it will be impossible to stop the global warming in the stipulated time frame considering the fact that a number of coal/oil/gas fired power plants are already under implementation.