Energy from Waste

Paul Breeze

• Publisher: Academic Press
• Year: 2017
• ISBN:
  9780128095133
• Topic: Technologie et ingénierie
• Subtopic: Ressources d'alimentation

Energy from Waste is a concise, up-to-date and accessible guide on how to create power from both urban and industrial waste. The book explores the types of waste that, instead of going to landfill, can be converted to energy, also discussing the most up-to-date technologies for doing so. The book contains a strong emphasis on the related environmental impacts and economic factors involved in the various methods of generating electricity, making this a valuable and insightful read for those involved in the management and conversion of waste, including energy engineers, managers and technicians.

• Explores both urban and industrial waste, its composition and how it is collected, enabling readers to better understand which power generation technologies can be used to convert it into power
• Discusses the most up-to-date technologies, along with the impacts they have on the environment, including solid residue, chemicals and dust from the flue-gas treatment (and the flue gas itself)
• Evaluates the economic impact of converting energy from waste and implementing and managing waste plants

Chapter 1

An Introduction to Energy From Waste

Abstracts

Human societies generate large volumes of waste. These include agricultural wastes and industrial wastes, but the most important type of waste in modern societies is municipal solid waste. Some of this waste can be recycled but there is usually a residue. In the past, this has been buried but today it is often burned to generate electricity, as well as to reduce its volume. Power generation is typically carried out by using the heat to raise steam and drive a steam turbine. Other methods include gasification and pyrolysis of waste. The earliest recorded waste to energy plant was built in Sweden in 1904. In Europe, it has been common to combine waste combustion with district heating. More recently, waste has become a valuable resource. There was around 13 GW of waste to energy capacity across the globe in 2014.

Keywords

Waste-to-energy; municipal solid waste; MSW; agricultural waste; waste combustion; waste gasification; waste pyrolysis

Human activity generates a range of waste materials. Some of these can be reused or recycled, but there are always residues that have no further value in their current form. Often, these residues can be exploited in a combustion plant to generate electrical power, or as a feedstock that is used to make a liquid or gaseous fuel. Where this is possible, it provides both a means of disposal and an additional useful product.

Agriculture produces some of the largest volumes of waste. Many crops, such as cereals, sugar cane or rice leave waste material behind when harvested. Provided it is economical to collect, this type of waste is easily combustible and can be used in power plants designed specifically for the purpose. The raising of animals, too, produces waste. This is not always flammable but can often be converted into biogas using a process called anaerobic digestion. Forestry, like agriculture, produces waste that, if collected, can easily be used to generate electrical power. The paper industry, which relies on forestry, generates several types of waste that have traditionally been used to generate power and heat with the energy used to power the industrial plant producing the paper. Other industries produce specialized wastes, and these can sometimes be converted into energy. Often, however industrial wastes must be disposed of using special techniques, particularly if they are hazardous.

The most ubiquitous and socially most important source of waste, however, is municipal waste, the waste that is produced by households and individuals as they go about their lives. Waste of this type is produced in all societies, but modern advanced societies produce far more than older rural societies. Urban waste, in particular, is produced in massive volumes and its collection and disposal is both costly and time consuming. Some of this waste, such as paper, glass, and metal cans, can be recycled. This involves sorting the waste either before or after collection. Organic residues can be allowed to decompose naturally and then be returned to the soil to provide nutrients. However, there will always remain a significant residue. Exploiting this to generate energy offers a cost-effective and convenient method of disposal.

In the past, the combustion of residual waste, often without electricity or heat generation, has been used as a means of reducing the volume of waste for disposal. The residual ash is then buried in a landfill site. Such processes are wasteful of energy and today this will not be considered appropriate in many jurisdictions and may contravene local regulations. Across the European Union (EU), for example, there are strict rules about how waste must be treated and combustion without energy generation would be considered one of the least desirable options.

Combustion technologies that are capable of utilizing the energy released from the waste to generate electricity and heat offer a much more environment-friendly solution. However today, there are additional considerations to take into account related to atmospheric emissions and global warming. Some waste may be biological in origin; wood, paper, and agricultural products might fit into this category. These can be considered to be renewable. Their combustion, while producing carbon dioxide, does not add to the atmospheric load because they are part of a short biological cycle in which more, similar material will soon be grown and this will reabsorb carbon dioxide from the atmosphere. On the other hand, plastics are often made from fossil-fuel-based materials and so when these are burnt in a combustion plant they add to the atmospheric load of carbon dioxide. This must be taken into consideration when assessing energy from waste projects in regions such as the EU.

There are several ways of generating energy from waste. The simplest and most widely used is to burn the combustible material in a combustion boiler, generating heat that is used to raise steam and drive a steam turbine generator. Power generation depends on the quality of the waste and (its energy content, or calorific value), but the efficiency is generally relatively low at around 25% to 30%. It is possible to raise the efficiency if heat from the plant can be used as well as electricity. This depends on being able to site a power from waste plant close to users of heat, which is not always possible, but where heat can be used, efficiency can be increased to over 40%.

Two more advanced techniques for dealing with waste are pyrolysis and gasification. Both are high temperature techniques that can ensure destruction of complex; sometimes, hazardous organic molecules within the waste. Pyrolysis can produce gaseous or solid byproducts that can be burnt to generate energy or used in other processes. Gasification normally produces a low energy content gas which can also be burnt to generate energy. The gas can be used either in a conventional steam generating boiler or may be used as fuel for a piston engine or gas turbine.

Whatever the process, the generation of power-from-waste is a very specialized industry. The plants must include extensive environmental controls to ensure that they do not release any toxic materials into the environment and are consequently expensive to build. The cost of electricity from a power to waste plant will be high when calculated using the normal economic model for the cost of electricity. Against this the economics of a waste to energy plant does not normally depend entirely on the value of the electricity it produces; plant operators are generally paid for the waste that they process and this helps balance plant economics. In a sense electricity and heat are valuable byproducts and disposal of the waste is the main object. Increasingly, however, waste is being considered as a useful energy resource that should, where possible, be utilized in the most energy-efficient way possible. This is particularly relevant to the advanced economies that produce the most waste.

Waste to Energy: A Historical Perspective

The combustion of waste probably has a long, unrecorded history but municipal combustion or incineration of waste can be traced back to 1874 when the first incinerator, known as a destructor, was built in Nottingham, United Kingdom, by a company called Manlove, Alliott and Co. The earliest US incinerator was constructed 1 year later, in 1885, when a unit was built on Governors Island, New York. A further 200 were built across the United States in the next two decades, although by 1902 half of these had been abandoned or dismantled. It is likely that similar units were in use in many European countries by, or soon after the turn of the 20th century. Meanwhile ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Chapter 1. An Introduction to Energy From Waste
• Chapter 2. The Politics of Waste
• Chapter 3. Waste as a Resource
• Chapter 4. Waste to Energy Technologies
• Chapter 5. Landfill Waste Disposal, Anaerobic Digestion, and Energy Production
• Chapter 6. Traditional Waste Combustion Technologies
• Chapter 7. Advanced Waste-to-Energy Technologies: Gasification, Pyrolysis, and Plasma Gasification
• Chapter 8. Waste to Energy Plants and the Environment
• Chapter 9. The Economics of Energy From Waste
• Index