Landfill tends to predominate as a waste disposal mode because it is regarded as an effective but low-cost method of disposal, also for hazardous waste. Even where other methods are more suitable for environmental reasons, the higher capital and (short-term) running costs mean that they cannot compete without government intervention. However, such cost calculations take no account of the longer term. In the long run, landfill of hazardous materials may impose a larger financial burden than other methods because of the high cost of ensuring that the site remains secure for the time it takes for the waste to be rendered harmless.
Alternate Fuels – Solid Fuels
Solid fuels are those fuels that are solid under ambient conditions and remain solid under mild heating. Thus, examples of solid fuels from biofuel feedstocks include wood and wood-derived charcoal and dried dung, particularly cow dung.
Compared to gaseous fuels and liquid fuels, solid fuels are often cheaper, easier to extract, more stable to transport, and in many places are more readily available. Coal, in particular, is utilized in the generation of electricity because it is less expensive and more powerful than its gaseous or liquid fuel counterparts. However, solid fuels are also heavier to transport, require more destructive methods to extract/burn, and often have higher carbon, nitrate, and sulphate emissions. With the exception of sustainable wood/biomass, solid fuel (such as peat or coal) is typically considered to be non-renewable because it requires thousands of years to form.
Alternative Energy
Alternative energy is a term for any nontraditional energy form, source, or technology differing from the current popular forms, sources, or technologies. Currently, the term alternative energy is generally used in the context of an alternative to energy deriving from the widely-used fossil fuels and thus includes energy derived from such environmentally preferred sources as biomass, geothermal, ocean, solar, tidal action, water power, wave action, and wind power. Many definitions of alternative energy use this term interchangeably with renewable energy.
The term alternative energy is also used for energy derived from sources and technologies that do not involve the depletion of natural resources (such as fossil fuel sources) or significant harm to the environment. As such, the term alternate energy is used synonymously with the terms renewable energy and green energy or green power. The three terms have also been delineated differently even though, by most definitions, there is substantial overlap between energy forms, sources, and technologies that fit into these three categories, and alternative energy often is applied to energy without undesirable environmental consequences or with lessened environmental impact. Renewable energy generally refers most specifically to energy derived from sustainable natural resources that are constantly replenished within a relatively short time frame (such as deriving from such renewable natural resources.
Amine Washing
Amine washing (more correctly olamine washing) of a gas stream involves the chemical reaction of the amine with any acid gases with the liberation of an appreciable amount of heat, and it is necessary to compensate for the absorption of heat. Amine derivatives such as ethanolamine (monoethanolamine, MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA), di-isopropanolamine (DIPA), and diglycolamine (DGA) have been used in commercial applications (Table A-19). Amine washing is the primary process for sweetening sour natural gas and is quite similar to the processes of glycol dehydration and removal of natural gas liquids by absorption.
The primary process for sweetening sour natural gas is quite similar to the processes of glycol dehydration and removal of natural gas liquids by absorption. In this case, however, amine (olamine) solutions are used to remove the hydrogen sulfide (the amine process).
Table A-19 Amines (olamines) used for gas processing.
| Olamine | Formula |
|---|---|
| Ethanolamine (monoethanolamine) (MEA) | HOC2H4NH2 |
| Diethanolamine (DEA) | (HOC2H4) 2NH |
| Triethanolamine (TEA) | (HOC2H4)3N |
| Diglycolamine (hydroxyethanolamine) (DGA) | H(OC2H4) 2NH2 |
| Diisopropanolamne (DIPA) | (HOC3H6) 2NH |
| Methyldiethanolamine (MDEA) | (HOC2H4)2NCH3 |
In the process, the sour gas is run through a tower, which contains the olamine solution. There are two principal amine solutions used, monoethanolamine (MEA) and diethanolamine (DEA). Either of these compounds, in liquid form, will absorb sulfur compounds from natural gas as it passes through. The effluent gas is virtually free of sulfur compounds, and thus loses its sour gas status. Like the process for the extraction of natural gas liquids and glycol dehydration, the amine solution used can be regenerated for reuse.
As currently practiced, acid gas removal processes involve the selective absorption of the contaminants into a liquid, such as an olamine (Table A-19), which is passed countercurrent to the gas. Then, the absorbent is stripped of the gas components (regeneration) and recycled to the absorber. The process design will vary and, in practice, may employ multiple absorption columns and multiple regeneration columns.
Liquid absorption processes (which usually employ temperatures below 50°C (120°F) are classified either as physical solvent processes or chemical solvent processes. The former processes employ an organic solvent, and absorption is enhanced by low temperatures, or high pressure, or both. Regeneration of the solvent is often accomplished readily. In chemical solvent processes, absorption of the acid gases is achieved mainly by use of alkaline solutions such as amines or carbonates. Regeneration (desorption) can be achieved by the use of reduced pressure and/or high temperature, whereby the acid gases are stripped from the solvent.
Regeneration of the solution leads to near complete desorption of carbon dioxide and hydrogen sulfide. A comparison between monoethanolamine, diethanolamine, and diisopropanolamine shows that monoethanolamine is the cheapest of the three but shows the highest heat of reaction and corrosion; the reverse is true for diisopropanolamine.
The processes using ethanolamine and potassium phosphate are now widely used. The ethanolamine process, known as the Girbotol process, removes acid gases (hydrogen sulfide, and carbon dioxide) from liquid hydrocarbons as well as from natural and from refinery gases. The Girbotol process uses an aqueous solution of ethanolamine (H2NCH2CH2OH) that reacts with