An interesting letter by T L Cardwell. Generally I would agree with most of it but unfortunately the writer does not substantiate most of his claims and he is not correct with all of them. For example he says:Thanks to Wand.
First coal fired power stations do NOT send 60 to 70% of the energy up the chimney. The boilers of modern power station are 96% efficient and the exhaust heat is captured by the economisers and reheaters and heat the air and water before entering the boilers.
Not true. The boiler efficiency of a modern black coal power station is about 88% and that includes the ‘recovered’ energy from reheaters and economisers. BTW that figure applies to the particular power station quoted by Cardwell.
The very slight amount exiting the stack is moist as in condensation and CO2.
I would say not true but it does not matter. I think he is talking about the heat and the moisture trapped in the exhaust gases. Well the moisture in the exhaust gas is the moisture from the fuel and the input combustion air. The moisture content for typical black coal for a NSW power station is about 8% and the relative humidity of the combustion air will vary with the local weather conditions but typically is about 50%. All the moisture is driven off in the exhaust gases at about 140 degrees C (exit temperature) which if allowed to cool would cause condensation. Actually because the exhaust gases are scrubbed to remove particulate matter, the exhaust gases from the stack of a power station appear to be almost invisible.
The 4% lost is heat through boiler wall convection. - Not true - see above.
Coal fired Power Stations are highly efficient with very little heat loss and can generate massive amount of energy for our needs. They can generate power at efficiency of less than 10,000 b.t.u. per kilowatt and cost wise that is very low. - An interesting way of expressing the efficiency of the power station and it won’t mean much to most people. Actually what he is saying is that the overall power station efficiency is better than 34% (10,000 BTU = 2.93 kWh - so for an input of 10,000 BTU or 2.93 kWh you deliver an output of 1 kWh). Actually the efficiency of a typical NSW black coal fired power station is about 37% sent out energy depending on load factors and utilisation. In case you are wondering what the difference is between this figure and a boiler efficiency of 88%, the additional losses are inherent in the power station steam cycle. Without going into a detailed thermodynamic analysis, simply not all the available energy can be captured from the steam and the exhaust steam needs to be cooled before it can be reused. There are later technologies such as a super critical power plant that will improve the overall efficiency of the power station to about 45%.
The energy balance of black coal power station may then be summarised as overall efficiency is 37% sent out, i.e., 37% of the input energy from the coal is converted to electricity that is transmitted to the electricity grid. The remaining 63% of the energy input is all dissipated as heat at the power station - some in the station auxiliaries, some as boiler losses mostly to air (approximately 12%) but the bulk of it (about 50%) is dissipated as waste heat through the power station cooling towers. Many NSW power stations use natural draft hyperbolic concrete cooling towers which required large quantities of fresh water. Wikipedia link for more information.. Often and erroneously (but what’s to stop a ‘good’ story) the MSW will use a photo of a typical cooling tower showing water vapour leaving the top with a suggestion that it is polluting the atmosphere.
So whilst Cardwell is strictly correct in that 60% of the heat is not sent up the ‘chimney’, the true picture is about 10% heat goes up the ‘chimney’ with 50% dissipated through the station cooling system.
Other technologies are available mostly with other (more expensive) fuels that can give higher energy conversion efficiencies but basically we are stuck with these ‘numbers’ because of the Physics of the processes. Actually the Physics of all the energy conversion processes indicates the folly of pursuing renewable energy technologies to the extent that we are. The problem with ‘renewable’ energy sources is that the energy sources are relatively weak, the energy conversion efficiencies are quite low and the energy supply is intermittent in nature. So all of them are problematic for providing electricity to an electricity grid because they all need back up from conventional power stations.
Cardwell is correct with his calculations of the volume that would be occupied by CO2 in his low ceiling height room. While his example attempts to illustrate the very small 0.04% very small component occupied by CO2 in the atmosphere, and the insignificant contribution from Australia to the world’s CO2, what he does not say is that CO2 levels are unimportant. If anything :
• CO2 is an essential component to life on the planet;
• CO2 is a plant food;
• Elevated levels of CO2 enhance plant growth;
• From the CRU - Hadley Centre ‘Climategate’ emails, the data used to show that the planet has warmed over the 20th century have been shown to have been fraudulently manipulated. Source data where available for selected locations in Australia and New Zealand show the manipulation that has been made. Also the variability in the data and the way in which it has been aggregated lead to doubt on drawing any conclusions about any temperature increase as any trend is really lost in the background noise. In any case, a temperature rise of a few degrees does not matter.
• On this basis alone, the theory of anthropogenic global warming has been disproved by the leaked emails.
Finally, my opinion is that the main driver of the climate on earth is the sun and the natural planetary cycles. Right now solar activity is at an historic low which has been accompanied by the shocking winter in the Northern hemisphere. No one knows or can predict when solar activity will resume and so I say if anything we should prepare for a period of cold winters. Apart from that the best that can be done with a proposed ETS and resources directed at mitigating carbon dioxide would be to abandon the exercise. It would better to devote resources to building our society rather than destroying it as an ETS would certainly do.
A final comment. CO2 is heavier than air with a molecular weight of 44 compared to 28.8 for air. If CO2 is stripped from the exhaust gases of power stations and concentrated by compressing and storing underground as seems to be a ‘preferred’ method, a potentially lethal gas storage system will have been established. When the CO2 leaks as it surely will one day, anyone in the vicinity will be likely asphyxiated before the CO2 can diffuse into the atmosphere. Very dangerous indeed.
Friday, January 15, 2010
Reply to letter in Rockhampton Bulletin
I received an email regarding the letter in the Rockhampton Bulletin from someone who knows the industry.