Posts Tagged ‘Combustion’

Man-made global warming is just presumption

December 18, 2013

Presumptions, presumptions everywhere but no evidence to be seen.

  1. There is a presumption among the global warming orthodoxy – but no evidence – that increasing carbon dioxide concentrations in the atmosphere causes significant warming of the Earth’s surface.
  2. There is a presumption that carbon dioxide emissions from human activities (primarily by the increase in fossil fuel combustion since the 1950’s) is the primary cause of the increase of concentration in the atmosphere. This presumption is based on the assumption that the oceans and the forests absorb just as much carbon dioxide as they emit. This balance is an assumption and is based on the argument that pre-industrial concentrations of carbon dioxide in the atmosphere were largely constant. The actual emissions from the forests and the oceans are each an order of magnitude greater than man-made emissions of carbon dioxide. The margin of error in the estimates of amounts of carbon dioxide emitted (and absorbed) by the oceans and the forests is greater than the emissions from fossil fuel combustion. The emissions due to volcanic activity are not well understood just as the rate at which ¬†carbonate sediments are laid down by the oceans is unknown (which in turn affects the concentration of what is dissolved in the oceans and therefore how much gets absorbed by the oceans from the atmosphere). Carbon dioxide released or absorbed by tectonic activity is unknown. There is a presumption based on some limited evidence that approximately 40% of what is released by fossil combustion is accumulating as atmospheric concentration. There is no presumption, however,¬†that increasing carbon dioxide concentration in the atmosphere must lead to an increased absorption rate.
  3. Fossil fuel combustion and man-made carbon dioxide emissions as well as the atmospheric concentration have been increasing at least since about 1950. For the last 17 years this increase has continued but global temperatures have not increased. For the last 10 years the global temperature has shown a slight decline. It is therefore presumed that the original presumption still holds and that the extra heat is presumed to be hidden in a variety of places ¬†(the deep oceans for example) other than at the Earth’s surface. There is no presumption that these observations are fundamentally in conflict with the original presumption.
  4. It is entirely logical that warming of the earth will cause the ice caps to melt and sea levels to rise just as global cooling will cause the ice sheets to expand and the sea levels to fall. It is presumed by the “establishment” that observed short-term reductions of ice extent are not due to natural variation but are proof that man-made global warming prevails. But when ice extent increases – as is happening currently – it is presumed to be due to natural variability and not relevant to the underlying trend due to man-made global warming.
  5. It is postulated by the establishment that extreme weather events are more likely to occur due to man-made global warming (and are not due to natural variability). But when extreme weather events show a decline – as they are doing currently – then any such decline is presumed to be due to natural variability.
  6. A preponderance of “cold records” being broken – rather than “heat records” is presumed to be proof of man-made global warming causing extreme weather events.

Presumptions do not a science make – especially when the evidence available increasingly conflicts with the presumptions.

Composition of exhaust gases from humans and from fossil fuels

April 13, 2013

It occurred to me when carrying out some combustion calculations that what humans breathe out is pretty close to the flue gas from a gas-fired, gas turbine combined cycle plant.

In a gas turbine combustion chamber, fuel is burned typically at an excess air level of about 200% (the amount of oxygen available in the combustion air compared to that which is needed for complete oxidation of the fuel). This means that about one third of the oxygen available is used and converted to carbon dioxide and water while about 2/3ds just passes through (i.e of the 21% oxygen in air, about 6-7% is “consumed” and about 14 -15% passes through unused). In coal-fired plants the excess air levels are usually only about 25% which leads to about 15 -16% of the incoming 21% oxygen being consumed with about 5% passing through. The amount of oxygen actually consumed depends on the fuel composition and the oxygen demands of the elements which are oxidised during the combustion process. Carbon, hydrogen and sulphur (giving CO2, H2O and SO2) are the main oxygen consumers. All the other constituents of air pass through – heated up of course – but otherwise unchanged. Minute quantities of the fuel- nitrogen and the nitrogen in the incoming air can – depending upon the combustion temperature – be “fixed” to create the nitrogen oxides – nitrous oxide (N2O) and nitrogen dioxide (N2O). The higher the combustion temperature the greater the “fixing”. Too low a combustion temperature – for example with very wet fuels and bio-mass – can give “incomplete combustion” with some carbon monoxide (CO) and even some dioxins and hydrocarbons with a particularly poor combustion process. Internal combustion petrol engines essentially run at stoichiometric conditions (zero excess air) and there is no oxygen in the exhaust. However combustion is never quite complete and around 1% carbon monoxide is usually present (which is why suicide by exhaust fumes becomes possible). Diesel engines on the other hand have 10% oxygen in the exhaust when idling and this reduces to 1 or 2% when fully loaded.

All fuels essentially contain carbon and hydrogen as the main energy releasing elements when oxidised. Most industrial combustion processes happen fast and speed of combustion – which is desirable for complete combustion – has to be tempered by the need to keep temperatures at levels which can be handled by the materials used. The human use of the same elements of carbon and hydrogen for the release of energy however is by a relatively slow oxidation processes. Not all the water produced leaves the human body with our expelled breath since some part of it leaves in liquid form with urine. But from the composition of the waste gas we breathe out it seems that the carbon/hydrogen ratios in our food intake cannot be so very different to the natural gas burned in gas turbines (and not very surprising considering that plant-life is the ultimate source of both).

exhaust gas compositions

 

Since human exhaust gases emit the same concentration of carbon dioxide as gas turbine, combined cycle power plant perhaps we should penalise every human as well?

 


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