Cycles carbon

The most actively cycled reservoir of carbon is atmospheric C02 (it constitutes 0.034% of the atmosphere). Carbon dioxide dissolves readily in water and is in direct equilibrium with dissolved inorganic forms of carbon (H2C03, HCO, and CO7-, see Section 6.2.1.3). Once there, it may precipitate as solid calcium carbonate (limestone). Corals and algae encourage this reaction and build up limestone reefs in the process, but a much larger portion in the deep sea equilibrates only at the slow rate of 

Example 7.1 Determine the oxidizing and reducing agents in reaction (7.1). 

H2 — H2O + [CH2O] hydrogen loses electrons therefore, it is a reducing agent. 

C02 - [CH20] carbon gains electrons it is an oxidizing agent. 

If glucose is used as the substrate for respiration, the reaction is the following  

Residence time (x) for reservoir 1 and reservoir 2 at steady state condition is 

The carbon content of important reservoirs earbon content (in units of lO g) 

---

It has been detected spectroscopically in great abundance, especially in the hotter stars, and it is an important component in both the proton-proton reaction and the carbon cycle, which account for the energy of the sun and stars. 

One of the things that environmental scientists do IS to keep track of important elements in the biosphere—in what form do these ele ments normally occur to what are they transformed and how are they returned to their normal state Careful studies have given clear although compli cated pictures of the nitrogen cycle the sulfur cy cle and the phosphorus cycle for example The carbon cycle begins and ends with atmospheric carbon dioxide It can be represented in an abbrevi ated form as... 

Renewable carbon resources is a misnomer the earth s carbon is in a perpetual state of flux. Carbon is not consumed such that it is no longer available in any form. Reversible and irreversible chemical reactions occur in such a manner that the carbon cycle makes all forms of carbon, including fossil resources, renewable. It is simply a matter of time that makes one carbon from more renewable than another. If it is presumed that replacement does in fact occur, natural processes eventually will replenish depleted petroleum or natural gas deposits in several million years. Eixed carbon-containing materials that renew themselves often enough to make them continuously available in large quantities are needed to maintain and supplement energy suppHes biomass is a principal source of such carbon. 

Carbon. Most of the Earth s supply of carbon is stored in carbonate rocks in the Hthosphere. Normally the circulation rate for Hthospheric carbon is slow compared with that of carbon between the atmosphere and biosphere. The carbon cycle has received much attention in recent years as a result of research into the possible relation between increased atmospheric carbon dioxide concentration, most of which is produced by combustion of fossil fuel, and the "greenhouse effect," or global warming. Extensive research has been done on the rate at which carbon dioxide might be converted to cellulose and other photosyntheticaHy produced organic compounds by various forms of natural and cultivated plants. Estimates also have been made of the rate at which carbon dioxide is released to soil under optimum conditions by various kinds of plant cover, such as temperature-zone deciduous forests, cultivated farm crops, prairie grassland, and desert vegetation. 

The efficiency of the weathering of rocks in using carbonic acid produced in the carbon cycle is affected by various hydrologic, environmental, and cultural controls. The fact that the principal anion in fresh surface water worldwide almost always is bicarbonate attests to the overriding importance of this process. Exceptions are systems in which evaporite minerals are available for dissolution by groundwater or where human activities are major sources of sulfate or chloride inflow. 

Feedbacks within the Marine Segment of the Carbon Cycle... 

The harmful effects of air pollutants on human beings have been the major reason for efforts to understand and control their sources. During the past two decades, research on acidic deposition on water-based ecosystems has helped to reemphasize the importance of air pollutants in other receptors, such as soil-based ecosystems (1). When discussing the impact of air pollutants on ecosystems, the matter of scale becomes important. We will discuss three examples of elements which interact with air, water, and soil media on different geographic scales. These are the carbon cycle on a global scale, the sulfur cycle on a regional scale, and the fluoride cycle on a local scale. 

Figure 8.1 Diagrammatic model of the global carbon cycle. Questions marks indicate that no estimates are available. Figures are in units of lO tonnes of contained carbon but estimates from various sources sometimes differ by factors of 3 or more. The diagram is based on one by B. Bolin modified to include more recent data. ...

B. BOLtN, The carbon cycle. Scientific American, September 1970, reprinted in Chemisiry in the Environment, pp. 53-61, W. H. Freeman, San Francisco, 1973. 

Schlamdinger, B., and Marland, G. (1996). The Role of Forest and Bioenegy Strategies in the Global Carbon Cycle. Biomass and Biocncrgy 10(5/6) 275-300. 

Like all matter, carbon can neither be created nor destroyed it can just be moved from one place to another. The carbon cycle depicts the various places where carbon can be found. Carbon occurs in the atmosphere, in the ocean, in plants and animals, and in fossil fuels. Carbon can be moved from the atmosphere into either producers (through the process of photosynthesis) or the ocean (through the process of diffusion). Some producers will become fossil fuels, and some will be eaten by either consumers or decomposers. The carbon is returned to the atmosphere when consumers respire, when fossil fuels are burned, and when plants are burned in a fire. The amount of carbon in the atmosphere can be changed by increasing or decreasing rates of photosynthesis, use of fossil fuels, and number of fires. 

NOTE Condensate system corrosion was an inevitable result of old-style, carbonate cycle internal softening programs, commonly employed in HRT, economic, locomotive, Lancashire, and similar boilers. 

The most popular form of internal treatment for many years dates from the nineteenth century and is based on a combination of soda ash and caustic. This traditional program, the so-called carbonate-cycle or carbonate treatment, utilizes the addition of sodium carbonate to the BW to deliberately form carbonate sludges that can be removed by BD, rather than permit sulfate scales to develop. If sulfate scales do form in the boiler, the removal process is difficult and very time-consuming, and obviously, boiler operating efficiency will continue to decrease as the sulfate scale increases in thickness. 

Sludge conditioners are required. Originally these were based on starches and lignins, but modem carbonate cycle treatments use carbonate-polymer programs, where the polymer (such as a phos-phinocarboxylic acid) provides a combination of threshold effect, crystal distortion, and sludge dispersion to minimize scaling and prevent sludge deposition. 

With high-hardness waters, the carbonate-cycle form of precipitation treatment is often preferred to the phosphate-cycle because it forms a less bulky and less dense sludge. The disadvantages of hard-water carbonate-cycle precipitation treatments include ... 

The principal carbon-cycle reaction chemistries are shown in the following equations, together with reactant molecular weights. 

Table 10.2 Carbonate-Cycle Program. BW Carbonate Reserve Requirements by Pressure and Sulfate Concentration...

In summary, the carbonate-cycle program provides preferred precipitation and coagulation reactions to prevent hard scale from forming. Key functions are ... 

For more details on carbonate-cycle control limits, see Table 10.3. These control limits are for non-highly rated boilers and assume that modem polymeric sludge conditioners are employed (i.e., not starches, agar, etc., which tend to form colloidal suspensions and may be difficult to remove by BD). 

Table 10.3 Carbonate-Cycle Coagulation and Precipitation Program. Recommended BW Control Limits for Non-Highly-Rated FT Boilers Employing Hard or Partially Softened FW...

---