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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.