Clean Electricity Through Advanced Coal Technologies

Handbook of Pollution Prevention and Cleaner Production

Nicholas P Cheremisinoff

• Publisher: William Andrew
• Year: 2012
• Print ISBN: 9781437778151
• eBook ISBN: 9781437778168
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Coal power is a major cause of air pollution and global warming and has resulted in the release of toxic heavy metals and radionuclides, which place communities at risk for long-term health problems. However, coal-fired power plants also currently fuel 41% of global electricity.Clean Electricity Through Advanced Coal Technologies discusses the environmental issues caused by coal power, such as air pollution, greenhouse gas emissions and toxic solid wastes.This volume focuses on increasingly prevalent newer generation technologies with smaller environmental footprints than the existing coal-fired infrastructure throughout most of the world. These technologies include fluidized-bed combustion and gasification. It also provides an overview of carbon capture and sequestration technologies and closely examines the 2008 Kingston TVA spill, the largest fly ash release ever to have occurred in the United States.Each volume of the Handbook of Pollution Prevention and Cleaner Production covers manufacturing technologies, waste management, pollution issues, methods for estimating and reporting emissions, treatment and control techniques, worker and community health risks, cost data for pollution management, and cleaner production and prevention options.- Discusses the environmental impact of coal power, including air pollution, greenhouse gas emissions and solid toxic wastes- Focuses on newer coal technologies with smaller environmental footprints than existing infrastructure- Provides an overview of carbon capture and sequestration technologies

1

Air Pollution

Chapter Outline

1.1 Overview

1.2 The National Emissions Inventory

1.3 Criteria Air Pollutants

1.3.1 Carbon Monoxide

1.3.2 Lead

1.3.3 Nitrogen Dioxide

1.3.4 Particulate Matter

1.3.5 Ozone

1.3.6 Sulfur Dioxide

1.3.7 NAAQS

1.4 Comparing Emissions

1.4.1 National Emissions Inventory

1.4.2 Toxics Release Inventory

1.5 Mercury Releases

1.1 Overview

Nearly 50% of the electricity generated in the world uses coal as the primary fuel. The function of the coal-fired thermal power plant is to convert the energy available in the coal to electricity. Coal power plants work by using several steps to convert stored energy in coal to usable electricity. The conversion from coal to electricity takes place in three stages.

Stage 1 involves the conversion of energy in a boiler. Coal is burned in the boiler furnace to produce heat. Carbon in the coal and oxygen in the air combine to produce carbon dioxide and heat.

Stage 2 is a thermodynamic process. The heat from combustion of the coal boils water in the boiler to produce steam. In a modern power plant, boilers produce steam at high pressures and temperatures. The steam is then piped to a turbine. The high-pressure steam impinges and expands across a number of sets of blades in the turbine. The impulse and the thrust created rotate the turbine. The steam is then condensed and pumped back into the boiler to repeat the cycle.

In Stage 3 rotation of the turbine rotates the generator rotor to produce electricity based on Faraday’s Principle of electromagnetic induction.

In practice, to effect these three stages of conversion, many systems and subsystems have to be in service. Also involved are different technologies, such as combustion, aerodynamics, heat transfer, thermodynamics, pollution control, and logistics. As an example, consider the following: for a coal-fired power plant of capacity 500 MW, about 2 million tons of coal are needed each year to produce the continuous power. Also, coal combustion in the boiler requires roughly 1.6 million cubic meters (m³) of air in an hour to be delivered by fans into the furnace. For this same size plant, the ash generated from the combustion of coal is around 200,000 tons per year. Electrostatic precipitators (ESPs) capture most of this ash without dispersing it to the atmosphere. Pollutants from coal power plants include carbon dioxide, sulfur dioxide, nitrogen oxide, and particulate matter (PM). Thermal power plants are the largest producers of carbon dioxide.

The boiler for typical 500 megawatt (MW) units produces around 1,600 tons per hour of steam at a temperature of 540–600°C. The steam pressure is in the range of 200 bar. The boiler materials are designed to withstand these conditions with special consideration for operational safety. Heat transfer from the hot combustion gases to the water in the boiler takes place due to radiation and convection. The electrical generators carry large electric currents that produce heat and are cooled by hydrogen and water. The steam leaving the turbine is condensed, and the water is pumped back for reuse in the boiler. To condense all the steam requires around 50,000 cubic meters per hour of cooling water to be circulated from lakes, rivers, or the sea. The water is returned to the source with only an increase of 3–4°C to minimize negative impacts to the environment. In addition to the cooling water, the power plant also requires around 400 cubic meters per day of fresh water for making up the losses in the water–steam cycle.

Electricity has often been characterized as the foundation of advanced countries and societies. It unquestionably is the basis by which societies maintain human life and sustain and grow economies. But the dependence on coal-fired technologies is a dirty business that has global implications on long-term sustainability. In the United States alone, there are more than 440 power plants larger than 25 MWs located in 46 states and Puerto Rico that burn coal to generate electricity. The National Emissions Inventory shows that 84 of the 187 hazardous air pollutants (HAPs) identified by the U.S. Environmental Protection Agency (EPA) pose a threat to human health and the environment. These plants release about 386,000 tons of hazardous air pollutants annually, accounting for roughly 40% of all hazardous air pollutant emissions from point sources. In fact, coal-burning power plants release more hazardous air pollutants than any other point source category. These plants are the largest point source category of hydrochloric acid, mercury, and arsenic releases to air.¹ Additionally, coal-fired plants are major sources of emissions for criteria air pollutants (CAPs) such as sulfur dioxide, oxides of nitrogen, and particulate matter.

1.2 The National Emissions Inventory

The U.S. EPA’s National Emission Inventory (NEI) can be found at http://www.epa.gov/ttn/chief/net/1999inventory.html. The EPA’s Emission Factor and Inventory Group (EPA/OAR/OAQPS/EMAD/EFIG) prepares a national database of air emissions information with input from numerous state and local air agencies, from tribes, and from industry. This database contains information on stationary and mobile sources that emit criteria air pollutants and their precursors, as well as hazardous air pollutants (HAPs). The database includes estimates of annual emissions, by source, of air pollutants in each area of the country, on an annual basis. The NEI includes emission estimates for all 50 states, the District of Columbia, Puerto Rico, and the Virgin Islands. Emission estimates for individual points or major sources (facilities), as well as county-level estimates for area, mobile, and other sources, are available currently for years 1985 through 1999 for criteria pollutants, and for years 1996 and 1999 for HAPs. Data from the NEI are used for air dispersion modeling purposes, regional strategy development, regulation setting, air toxics risk assessment, and tracking trends in emissions over time. For emission inventories prior to 1999, criteria pollutant emission estimates were maintained in the National Emission Trends (NET) database, and HAP emission estimates were maintained in the National Toxics Inventory (NTI) database. Since 1999, criteria and HAP emissions data are being prepared in a more integrated fashion in the NEI, which takes the place of the NET and the NTI.

1.3 Criteria Air Pollutants

Six criteria air pollutants (CAPs) are tracked on the NEI. They are carbon monoxide, lead, nitrogen dioxide, particulate matter, ozone, and sulfur dioxide.

1.3.1 Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless gas emitted from combustion processes. Nationally, and particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources.

CO can cause harmful health effects by reducing oxygen delivery to the body’s organs (such as the heart and brain) and tissues. At extremely high levels, CO can cause death. Exposure to CO can reduce the oxygen-carrying capacity of the blood. People with several types of heart disease already have a reduced capacity for pumping oxygenated blood to the heart, which can cause them to experience myocardial ischemia (reduced oxygen to the heart), often accompanied by chest pain (angina), when exercising or under increased stress. For these people, short-term CO exposure further affects their body’s already-compromised ability to respond to the increased oxygen demands of exercise or exertion.

The EPA first set air quality standards for CO in 1971. For protection of both public health and welfare, the EPA set an 8-hour primary standard at 9 parts per million (ppm) and a 1-hour primary standard at 35 ppm. In a review of the standards completed in 1985, the EPA revoked the secondary standards (for public welfare) due to a lack of evidence of adverse effects on public welfare at or near ambient concentrations. The last review of the CO National Ambient Air Quality Standard (NAAQS) was completed in 1994, and the agency chose not to revise the standards at that time.

The Clean Air Act (CAA) requires the EPA to set national ambient air quality standards for “criteria pollutants.” Currently, carbon monoxide and five other major pollutants are criteria pollutants; the others are ozone, lead, sulfur oxides, nitrogen oxides, and particulate m...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• About the Author
• 1. Air Pollution
• 2. Solid Wastes
• 3. Old and New Generation Technologies
• 4. Carbon Capture and Sequestration
• 5. The TVA Ash Spill
• Recommended Sources
• Glossary
• Index