Increased Absorption
One solution was suggested in a brain storming session hosted by the Hunter Technology group in Newcastle in 1990. This was to increase absorption of carbon dioxide in economic crops near to large point sources.
The principal greenhouse gas, carbon dioxide, is naturally absorbed in nature.
The planet has an existing, very large solar collector, plant life. From this collector almost all our existing energy requirements are originally derived. Solar energy is consumed reducing carbon dioxide back to carbon rich compounds.
Carbon dioxide and water are combined through photosynthesis in the leaves of plants to produce sugar and other carbohydrates used by the plant for tissue growth, and in doing so release oxygen. This is a highly complex process involving a large number of processes but can be simplified to the following equation.
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If the process of carbon dioxide absorption by trees and crops could be accelerated, then much of the lost plant growth could be replaced, additional crops could take up additional industry produced carbon dioxide, and problems associated with the burning of fossil fuels would be reduced.
The only long term and practical solution to carbon dioxide consumption from the gases must be biological. Chemical gas scrubbers to remove carbon dioxide require more energy input and therefore increase fossil fuel consumption. The scale of any biological solution and the need for energy input, preferably solar, precludes the possibility of large structures (such as glass houses) through which the gas is processed (unless this problem becomes so acute that large sums can be expended for environmental reasons alone).
Hundreds of millions of years ago when the carbon dioxide level was higher in the atmosphere due to volcanic activity, the rate of plant growth was far higher than it is today. In the carboniferous period, large amounts of plant growth were laid down to become coal and this process continues on a smaller scale today, where peat and other organic materials are being absorbed.
Within the limits indicated (less than 0.05%), many plants try to absorb all the carbon dioxide they can get, provided they also have sufficient water and other trace nutrients.
It can be seen from the above equation that if fully absorbed, the 44 million tonnes of carbon dioxide produced by NSW power stations each year would produce in excess of 31 million tonnes of additional plant carbohydrate production. About 18,000 megalitres (ML) of additional water would be required. This is significant but well within the water resources of the Hunter region (potential ground water resources of the Hunter exceed 278,000 ML per average year).
Solar input is also adequate over the area contemplated (as much as 500 sq kilometres in areas near the five major Hunter power stations would be treated). The area treated would become a huge biological solar collector.
In practical terms the carbon dioxide would be distributed over a very large area in the open. Not all carbon dioxide produced would be absorbed. Although carbon dioxide is 1.53 times heavier than air and would be distributed over a very wide area, there would be losses due to wind and diffusion. The distribution system would also need to avoid areas of high loss or natural build up and monitor and cut supply if excessive losses or build up occur. Different rates may be required for different types of vegetation.
The gas could add very significantly to economic crop production. The most probable crops to be accelerated initially would be C4 plants with a leafy canopy or dense foliage that will serve to contain the carbon dioxide and include trees, high grasses (wheat corn, sugar etc), sunflower and grapes. A number of aquatic plants may also have potential. Some of these might be genetically modified to absorb more CO2.
In areas where water is relatively plentiful, the soil is fertile and sunlight is adequate for agricultural growth, such as the Hunter, the introduction of additional carbon dioxide to crops will increase plant growth. This new growth can be used to produce additional building materials for an expanding world population, for food and fibre production.
The absorption of carbon dioxide would, of course, have to happen in rural areas and would have to be associated with large sources of carbon dioxide, such as power stations and steel plants. Here coal has an advantage over oil used in transportation. Unlike oil, most coal is burnt in large stationary power stations and industrial plant and this may give coal an advantage as the energy source of the future.
The catch to the idea of using crop growth and solar energy to absorb coal-sourced carbon dioxide is that carbon dioxide from industrial furnaces is often hot and dirty and contains trace gases that are harmful to crop growth. Cleaning the gas and delivering it to the crops so that it is not blown away may also be difficult and costly. But this may be a small cost to pay (like the cost of sewage treatment plants) for the benefits to the environment and to the future of the coal industry that such cleaning technology may provide.
If ways can be found to clean the carbon dioxide so it can be used for agricultural purposes, the location of major coal burning plants in a region may become a major asset to the local agricultural industries.