Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 11

Energy (from whatever the sources – fossil fuel sources or renewable sources, often referred to as alternate sources) appears in many different forms, including electricity, light, heat, chemical energy, and motional (or kinetic) energy. An important scientific discovery in the 19^th century was that energy is conserved, which means that energy can be converted from one form to another but that the total amount of energy must stay the same.

Renewable energy can be derived from a variety of sources because the sources can be used and replaced without irreversibly depleting reserves or the sources (such as power from water systems, wind systems, and the sun) are consistently present in the Earth system, which makes these sources a valuable resource for the consistent production of energy. For this reason, renewable sources will continue to grow in importance as replacements for fossil materials used as fuels and as feedstocks for a range of products. Some renewable materials also have particular unique and beneficial properties which can be exploited in a range of products including pharmaceuticals and lubricants.

The concept is centered around a long-term vision that a significant proportion of the demand for energy and raw materials should be met through the commercial exploitation of science from crops, in a way which stimulates biodiversity and reduces greenhouse gas emissions and waste – particularly biodegradable waste going to a landfill site – and slows depletion of finite natural resources.

Fuels based on natural gas and crude oil are well-established products that have served industrial and domestic consumers for more than a hundred years. For the foreseeable future most of these fuels will still be largely based on liquid hydrocarbon derivatives. The specifications of such fuels will, however, continue to be adjusted as they have been and are still being adjusted to meet changing demands from consumers. Traditional refining of natural gas and crude oil underwent increasing levels of sophistication to produce fuels of appropriate specifications. Increasing operating costs continuously put pressure on refining margins but it remains problematic to convert all refinery streams into products with acceptable specifications at a reasonable return.

However, time is running out and natural gas and crude oil, once considered inexhaustible, is now being depleted at a rapid rate – the gas and oil from tight formations notwithstanding. As the amount of available natural gas and crude oil decreases, the need for alternate technologies to produce liquid fuels that could potentially help prolong the liquid fuels culture and mitigate the forthcoming effects of the shortage of transportation fuels that has been suggested to occur under the Hubbert peak oil theory. To mitigate the influence of the oil peak and the subsequent depletion of supplies, unconventional (or non-gas and crude oil) fuels are becoming a major issue in the consciousness of oil-importing countries.

In the near term, the ability of conventional fuel sources and technologies to support the global demand for energy will depend on how efficiently the energy sector can match available energy resources with the end user and how efficiently and cost effectively the energy can be delivered. These factors are related to the continuing evolution of a truly global energy market. In the long term, a sustainable energy future cannot be created by treating energy as an independent topic (Zatzman, 2012). Rather, the role of the energy and the interrelationship of the energy market with other markets and the various aspects of market infrastructure demand further attention and consideration. Greater energy efficiency will depend on the developing world market’s ability to integrate energy resources within a common structure.

However, the production of liquid fuels from sources other than natural gas crude oil (as well as coal and oil shale) has a checkered history. The on-again-off-again efforts that are the result of political maneuvering has seen to it that the race to secure self-sufficiency by the production of non-conventional fuels has never got much further than the starting gate! This is due in no small part to the price fluctuations in the price of natural gas and crude oil accompanied by the lack of foresight by various levels of government. It must be realized that for decades the price of natural gas and crude oil (and the resulting fuel products) has always been maintained at a level that was sufficiently low to discourage the establishment of an alternate fuels industry. However, it is close to the time when the lack of preparedness for the production of non-conventional fuels may set any national government on its heels.

On the other hand, alternate fuels, such as gasoline and diesel fuel derived from non-fossil carbonaceous sources, are making headway into the fuel balance. For example, naphtha – the typical starting liquid for automotive fuels – and biodiesel from plant sources is similar to naphtha and kerosene but may have differences that include a different distribution of the constituents. At this time, the potential for liquid fuels from various types of biomass is also seeing considerable interest.

Whatever the source of the fuels (gaseous, liquid, or solid) there is always the need for methods by which the fuels can be analyzed and specification derived. Typically, this aspect of non-fossil fuel technology is often omitted from many of the relevant works. In order to combat and mitigate such omissions, this encyclopedia contains articles related to product analysis that includes general descriptions of and references to the relevant text methods.

In order to satisfy specific needs with regard to the type of feedstock to be processed, as well as to the nature of the product, the various standard test methods and specifications are a means of describing and/or recommending the rules and conditions for how materials and products should be manufactured, defined, measured, or tested. There are various standards organizations, such as the ASTM International (formerly known as American Society for Testing and Materials). Thus, it is appropriate that in any discussion of the physical properties of fuels from non-fossil fuel sources and, accordingly, where appropriate, the various ASTM test numbers have been cited in the text.

However, although not mentioned in the text, several other countries have standard test methods for fuel identification – examples are Germany (identified by the prefix DIN), the European countries (intended to be used in the European Union and identified by the prefix EN), the International Standards Organization (identified by the prefix ISO) and the United Kingdom (identified by the prefix IP and the prefix BS) – these test methods are not referenced in this encyclopedia but are available through the use of an internet search engine to which the reader is referred for further details and comparison of the test methods.

Following nomenclature and definitions presented in the United States Energy Policy Act of 1992 (Section 301), in the context of the present book, alternate fuels (alternative fuels) are defined as

Methanol, denatured ethanol, and other alcohols; mixtures containing 85 percent or more (or such other percentage, but not less than 70 percent, as determined by the Secretary, by rule, to provide for requirements relating to cold start, safety, or vehicle functions) by volume of methanol, denatured ethanol, and other alcohols with gasoline or other fuels; natural gas; liquefied petroleum gas; hydrogen; coal-derived liquid fuels; fuels (other than alcohol) derived from biological materials; electricity (including electricity from solar energy); and any other fuel the Secretary determines, by rule, is substantially not natural gas or crude oil and would yield substantial energy security benefits and substantial environmental benefits.

It is this definition that is used to guide the contents of this book and show that sources that are “substantially not petroleum” are available as sources of fuels.

However, it must be recognized that the forms of energy from renewable sources vary according to the source. For example, biomass and waste can be combusted directly or they can be converted to gaseous fuels and liquid fuels by conversion and refining of the gases and the liquids. The encyclopedia would be missing important articles if there was not some mention of the methods and processes by which gases and liquid products from renewable sources can be prepared for sales. Accordingly, the technologies for refining the gases and liquids into usable fuels and other (petrochemical-type) products are derived from the current natural gas industry and the crude oil industry. Hence the reason for inserting the relevant refining-related articles into the encyclopedia.

In addition, there is a fundamental attractiveness about harnessing such forces in an age which is very conscious of the environmental effects of burning fossil fuels, and where sustainability is an ethical norm. Currently, the focus of many countries is on both adequacy of energy supply long term and also the environmental implications of particular sources. In that regard the near certainty of costs being imposed on carbon dioxide emissions in developed countries at least has profoundly changed the economic outlook of clean energy sources.

However, there is the need to understand that all energy sources have some impact on the environment. Renewable energy sources do substantially less harm to the environment than do fossil fuels (coal, natural gas, and crude oil) by most measures, including air and water pollution, damage to public health, wildlife and habitat loss, water use, land use, and global warming emissions. However, renewables such as biomass as well as sources such as wind, solar, geothermal, and hydropower also have environmental impacts, some of which are significant and must not be ignored. This encyclopedia also presents information related to those aspects of environmental science and engineering that are susceptible to changes caused by renewable energy sources in addition to the environmental effects caused by the use of fossil fuels. It is for these reasons that articles related to the discharge of pollutants into the environment are included.

In fact, when the benefits of developing renewable energy sources are considered, it is equally important to acknowledge that there can also be disadvantages. While all renewable energy sources – wind, solar, geothermal, hydroelectric, and biomass – can provide substantial benefits for the climate and the economy, all energy sources have some impact on the environment and even renewable sources such as biomass, wind, solar, geothermal, biomass, and hydropower also have environmental impacts, some of which are significant. The exact type and intensity of environmental impacts varies depending on the specific technology used, the geographic location, and a number of other factors. By understanding the current and potential environmental issues associated with each renewable energy source, effective measures can be taken to avoid or minimize these impacts as they become a larger portion of the electric supply.

However, there is a variety of environmental impacts associated with the use of alternative energy sources which can include land use and habitat loss, water use that should be recognized and mitigated. They include land use issues and challenges to wildlife and habitat. The exact type and intensity of environmental impacts varies depending on the specific technology used, the geographic location, and a number of other factors. For example, sources of biomass resources for producing energy are diverse, ranging from energy crops (like switchgrass), to agricultural waste, manure, forest products and waste, and urban waste. Both the type of feedstock and the manner in which it is developed and harvested significantly affect land use and life-cycle global warming emissions impacts of producing power from biomass.

It must be realized that the transfer from non-renewable energy source to renewable energy sources is not without some risk. Just as chemicals from non-renewable energy sources can enter the environment, chemicals from renewable energy sources can also enter the air, water, and soil when they are produced, used, or disposed. The impact of these chemicals on the environment is determined by the amount of the chemical that is released, the type and concentration of the chemical, and where it is found. Some chemicals can be harmful if released to the environment even when there is not an immediate, visible impact. On the other hand, some chemicals are of concern as they can work their way into the food chain and accumulate and/or persist in the environment for many years.

The final concentration of a chemical (or a mixture of chemicals) in various environmental systems (such as the atmosphere, water, and the land) depends on environmental emission rates and environmental distribution and fate of the chemical. Thus the first step in environmental risk assessment is always to quantify the emissions of a chemical into the atmosphere, the water, and the land.

Many chemicals, in fact all chemicals, that enter the environment should be categorized and ranked using hazard assessment criteria. This would not only ensure that truly pressing environmental issues are identified and prioritized, but would also maximize the use of limited resources. In the case of soluble chemicals, surrogate data such as persistence and bioaccumulation have been used, in combination with toxicity, for the purpose of hazard categorization. However, for insoluble or sparingly soluble chemicals such as metals and metal compounds, persistence and bioaccumulation are neither appropriate nor useful. Unfortunately, this is not always recognized by regulators or even by scientists.

The use of persistent, bioaccumulative and toxic (PBT) criteria for chemicals was developed to address the hazards posed by synthetic organic chemicals. In fact, the criteria and test methods to evaluate persistence (i.e., the lack of degradability of a chemical) and bioaccumulation (the dispersion of a chemical through knowledge of the water-octanol partition coefficient) were developed to be used in combination with toxicity in order to reduce the importance given to the use of toxicity data alone. These test methods were based on an understanding of the chemistry of chemicals of concern at the time and of the biological interactions that the chemicals would have with the surrounding biota. Specifically, it was realized that if some chemicals exerted high intrinsic toxicity under standardized laboratory test conditions but did not persist or bioaccumulate, the environmental hazard of such chemicals would be lower.

As mentioned above, persistence is measured by determining the lack of degradability of a substance from a form that is biologically available and active to a form that is less available. This applies to many substances – metals and metal compounds tend to be in forms that are not bioavailable. Only under specific conditions would metals or metal compounds transform into a bioavailable form. Thus, rather than persistence, the key criterion for classifying metals and metal compounds should be their capacity to transform into bioavailable form(s). Furthermore, although bioavailability is a necessary precursor to toxicity, it does not inevitably lead to toxicity. Although metals and metal compounds stay in the environment for long periods of time, the risk they may pose generally decreases over time. For example, metals introduced into the aquatic environment are subject to removal/immobilization processes (e.g., precipitation, complexation and absorption).

Similarly, the use of bioaccumulation has significant limitations for predicting hazard for metals and metal compounds. Generally, either bioconcentration factors (BCFs) or bioaccumulation factors (BAFs) are used for this purpose. A bioconcentration factor is the ratio of the concentration of a substance in an organism, following direct uptake from the surrounding environment (water), to the concentration of the same substance in the surrounding environment. A bioaccumulation factor considers uptake from food as well. In contrast to organic compounds, uptake of metals is not based on lipid partitioning. Further, organisms have internal mechanisms (homeostasis) that allow them to regulate (bioregulate) the uptake of essential metals and to control the presence of other metals. Thus, if the concentration of an essential metal in the surrounding environment is low and the organism requires more, it will actively accumulate that metal. This will result in an elevated bioconcentration factors (or bioaccumulation factor) value which, while of concern in the case of organic substances, is not an appropriate measure in the case of metals.

The primary determining factor of hazard for metals and metal compounds is therefore toxicity, which requires consideration of dose (indeed, the fundamental tenet of toxicology is the dose makes the poison). Historically, it has been the practice to measure the toxicity of soluble metal salts, or indeed the toxicity of the free metal ion. However, in different media, metal ions compete with different types or forms of organic matter (e.g., fish gills, suspended solids, soil particulate material) to reduce the total amount of metals present in bioavailable form. Toxicity of the bioavailable fraction (i.e., as determined through transformation processes) is the most appropriate and technically defensible method for categorizing and ranking the hazard of metals and metal compounds.

The relative proportion of hazardous constituents present in any collection of chemicals (crude oil-derived products included) is variable and rarely consistent because of site differences. Therefore, the extent of the contamination will vary from one site to another and, in addition, the farther a contaminant progresses from low molecular weight to high molecular weight the greater the occurrence of polynuclear aromatic hydrocarbons, complex ring systems (not necessity aromatic ring systems) as well as an increase in the composition of the semi-volatile chemicals or the non-volatile chemicals. These latter chemical constituents (many of which are not so immediately toxic as the volatiles) can result in long-term/chronic impacts to the flora and fauna of the environment. Thus, any complex mixture of chemicals should be analyzed for the semi-volatile compounds which may pose the greatest long-term risk to the environment.

Heavy metals are common chemical pollutants. The most common heavy metals found at contaminated sites, in order of abundance are Pb, Cr, As, Zn, Cd, Cu, and Hg. Those metals are important since they are capable of decreasing crop production due to the risk of bioaccumulation and biomagnification in the food chain. There is also the risk of superficial and groundwater contamination. Knowledge of the basic chemistry, environmental, and associated health effects of these heavy metals is necessary in understanding their speciation, bioavailability, and remedial options. The fate and transport of a heavy metal in soil depends significantly on the chemical form and speciation of the metal. Once in the soil, heavy metals are adsorbed by initial fast reactions (minutes, hours), followed by slow adsorption reactions (days, years) and are, therefore, redistributed into different chemical forms with varying bioavailability, mobility, and toxicity (Shiowatana et al., 2001). This distribution is believed to be controlled by reactions of heavy metals in soils such as (i) mineral precipitation and dissolution, (ii) ion exchange, adsorption, and desorption, (iii) aqueous complexation, (iv) biological immobilization and mobilization, and (v) plant uptake (Levy et al., 1992). The toxicity of metals varies greatly with pH, water hardness, dissolved oxygen levels, salinity, temperature and other parameters.

The specific type of metal contamination found in a contaminated soil is related to the operation that occurred at the site. The range of contaminant concentrations and the physical and chemical forms of contaminants will also depend on activities and disposal patterns for contaminated wastes on the site. Other factors that may influence the form, concentration, and distribution of metal contaminants include soil and groundwater chemistry and local transport mechanisms.

Finally, in order to evaluate the impact of a chemical that has been released to the environment, the chemical must be characterized in terms of the transport and transformation in that system (atmosphere, water, or land) and the potential for the transport of the chemical from one system to another or from one system to the other two. The assessment should focus on areas with which a released chemical is most likely to have contact. For a meaningful characterization, the environment must be viewed as a series of interacting compartments and it must be determined whether a chemical will remain and accumulate in the local area of the origin of the chemical. The potential for the chemical to be physically, chemically, or biologically transformed in the system of its origin (such as by hydrolysis, oxidation, or other transformation; Chapter 8) or be transported to another system such as by volatilization or by precipitation. The chemical could also be transferred by deposition and runoff to surface water that provides drinking water.

Each of these scenarios defines a pathway from the air emission to contact with a person, and each pathway has an associated route of contact. The true potential for exposure cannot be quantified until the pathways and routes that account for a substantial fraction of the intake and uptake for the receptor population have been identified. The likelihood of any pathway depends on the chemical properties of the substance released, where and how it is released, and environmental conditions. Sometimes the exposure increases along a pathway (such as bioaccumulation), but more often the exposure may decrease.

Thus, characterizing transportation pathways begins at the source of the agent release. In some situations, the source may be obvious and can be defined and characterized from air or soil concentrations. In many cases, such as contamination of water supplies, sources and emissions may be multiple and poorly characterized. However, classification of a potential transportation route should, as much as possible, be based on the released volume, duration of the release, and the rate of emission.

In order to fully understand the impact of a released chemical on the environment, the potential for chemical transformation of the spilled chemical which may occur as a result of biotic or abiotic processes, can significantly reduce the concentration of a substance or alter its structure in such a way as to enhance or diminish its toxicity or change its toxic effect. For example, for many airborne organic compounds, transformation processes, such as photolytic decomposition and oxidation/reduction reactions, can result in conversion to other compounds. For organic chemicals, the half-life of the chemical for any given transformation process provides a useful index of persistence in environmental media. For example, the photochemical half-life can vary from day to night, and specific information on the rates and pathways of transformation for individual chemicals of concern must be obtained directly from experimental determinations or derived indirectly from information on chemicals that are structurally similar to the released chemical.

Despite these environmental impacts, renewable energy technologies compare extremely favorably to fossil fuels, and remain a core part of the solution to future energy requirements. Renewable energy is going to be an important source for power generation in the near future because the resources again and again produce useful energy. Wind power generation is considered as having lowest water consumption, lowest relative greenhouse gas emission, and most favorable social impacts. It is considered as one of the most sustainable renewable energy sources, followed by hydropower, photovoltaic, and then geothermal. As these resources are considered as clean energy resources, they can be helpful for the mitigation of greenhouse effect and global warming effect.

However, by understanding the components of the environment and the current and potential environmental issues associated with each renewable energy source, the reader can understand the means to effectively avoid or minimize these impacts as they become a larger portion of energy supply. For this reason, this encyclopedia is an all-inclusive work that also presents not only the environmental components but also the various environmental aspects of the generation and use of renewable energy. Other issues arise that are similar to those produced by the use of fossil fuels – contamination of the atmosphere, water, and the land – but the degree of the contamination is not the same.

However, it would be a serious omission if recognition of some of the potential properties and effects of renewable fuels such as biogas and bio-oil and were omitted from this work. For example, biogas and bio-oil could cause harm to the environment is used without any form of treatment. The gas needs to be cleaned of objectionable environmentally harmful constituents and the bio-oil (from whatever the source) needs to be processed to provide useable products. Accordingly, it has been necessary to include options for gas cleaning and options for bio-oil refining (such as hydrotreating and hydrocracking) so that the reader may understand the conditioning of these products into environmentally benign use.

The dynamics are now coming into place for the establishment of an alternate energy industry and it is up to various levels of government not only to promote the establishment of such an industry but to lead the way, recognizing that it is not only supply and demand but the available and variable technology. The processes for recovery of the raw materials and the processing options have changed in an attempt to increase the efficiency of energy production.

In addtion, there are several interrelationships between conventional fuels and alternate fuels, especially in the areas of fuel production and fuel refining. Accordingly, it has been found necessary to include segments for the conventional fuel industries that are applicable to the alternate fuels industries. As ready reference, the articles in this encyclopedia have been assembled to assist the reader to understand the options that are available for the production of alternate energy, especially alternate fuels, and such processes from the conventional fuels industries and also from the unconventional fuels are, where they are applicable to renewable fuels, also included.

The Scrivener Encyclopedia of Renewable Energy was compiled because the need was recognized for an extensive work on the nature of renewable energy sources. This will be a convenient-to-use encyclopedia that will be a suitable companion for the researcher, teacher, and manager. Also, in order for help the reader understand the nature of renewable energy sources (Table 1), the encyclopedia contains segments that will allow the reader to compare renewable energy sources with the (to date) more conventional fossil fuels resources and how the conventional processing units that will be necessary to process renewable energy sources that are in the form of gases, liquid and solid.

Table 1 Simplified categorization and nomenclature of the various energy sources.

Conventional Energy Sources Natural gas Crude oil Heavy crude oil Coal*

Non-conventional Energy Sources Extra heavy crude oil Tar sand bitumen Coal* Coal gas Coal liquids Shale oil

Renewable Energy Sources Biomass Waste Hydrogen Hydroelectric energy** Geothermal energy Nuclear energy Ocean Energy** Solar energy Tidal energy** Wind energy

*When used as a solid fuel for combustion processes and without any modification other than cleaning, coal is often considered to be a conventional energy source. **Often grouped together under the name “hydrokinetic energy” – hydroelectric energy may also be included in this group.

The encyclopedia also contains a section on further reading for those readers who require further information on any of the subjects.

Finally, the temperature scales used in this work are the Centigrade (Celsius) scale and the Fahrenheit scale. Generally, when the temperature is below 100°C the conversion to the exact temperature in degrees Fahrenheit is presented immediately following in parenthesis. On the other hand, when the temperature is above 100°C the conversion to the nearest 5° Fahrenheit is presented immediately following in parenthesis.

Dr. James Speight

Laramie, Wyoming, USA

February 2021