Dear Paul O
>It is so inefficient to burn dirty coal or coal of a high moisture content. Please define a ‘dirty coal’. I have used many coals and they all made my hands dirty. I know you mean they burn badly in devices they are not suited for, right? >Some say that there is no such thing as a bad fuels, just bad stoves. I can certainly say that from personal experience of designing coal stoves and advising coal stove designers. >Just ask anyone in the coal industry if there is any such thing as a bad coal. Let us hear from them what a ‘bad coal’. I would like to know. >They will immediately point to many things that could make coal unfit for >combustion. Combustion in what? Good grief. If you build a device to burn anthracite and load lignite into it there will be all sorts of smoke and CO. If you put diesel into a gasoline engine you get a similar result – for very obvious reasons. Is anyone surprised? >They will point to things such as moisture content, ash content, sulfur >content, grindability, ash fusion temperature, grain size, MAF calorific >value, volatile matter content, fixed carbon content and much more. Those are all issues that can be addressed when designing a combustor. When trying to make a short, hot, small, fan powered multi megawatt combustor, they are very careful to pick a coal to match exactly. Europeans think they are really good at burning coal – centuries of experience, right? They bring their power station combustors to South Africa and show them off. They all fail. None of them work. Why? Lots of South Africans build coal burners that work really well. They also have years of experience: designing combustors that work with their local coal! Quelle surprise. The new power station Eskom is building right now can burn coal with 40% ash. A European ‘coal expert’ will tell you that is a ‘lousy, unburnable coal’. It works fine if you have a clue what you are doing. >Imagine how inefficient the coal industry would be if it had to design power >stations around each type of bad coal presented to it. Imagine trying to design a biomass stove that was tuned to each type of fuel that happened to be available…oh wait…that is exactly what is happening on this list! What a surprise, again. Is that not exactly what you are doing? >If we prepare fuels correctly, designing stoves is so easy. Really? If you have unprepared fuel, but you know its characteristics really well, designing a stove to burn it cleanly is easy. Why do ethanol stoves stink? Have you ever smelled a Clean Cook stove? That is a highly prepared fuel. Everyone thinks designing an ethanol stove is really easy because ‘the fuel is clean’. Rubbish. There is no such thing as a ‘clean fuel’ and the proof is buy an ethanol stove and light it in a closed room. Measure the CO. Fuels do not a clean burn make, it is a match between the stove and the fuel and the operational method. >We focus far too much on designing stoves and surely not enough on preparing >fuels. This is the big mistake that most funding organizations make in their >promotion of clean cook stoves. We do not focus enough on how to design good stoves and hope that preparing the fuel will compensate for our collective ignorance. Commercial companies burn all sorts of things very well. Sometimes it involves fuel selection or preparation. But it always involves a careful balance of the combustor and the fuel properties. The Japanese are burning kerosene with no flame at all. Eskom is burning coal with 40% ash. The Brits are burning car tires super clean and recovering the metals from the gas stream. The Mongolians are burning 30% moisture lignite with 50% volatiles cleaner than a Philips fan stove. Read the literature: all four are heavily criticised as being ‘dirty fuels’. There are thousands of negative references as people who have little idea what they are talking about parrot each other’s ignorance. Of course power stations are built to deal with the available coal types. Just like a TLUD rice hull gasifier. It is a one-trick pony. Nothing wrong with that. Regards Crispin
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