Unit A-5 Plant Operations & Environment PDF

Unit A-5 • Introduction to Plant Operations and the Environment Objective 1 Describe the sources and effects of solid pollutants from energy plants. Sources of Solid Pollutants One of the main sources of solid pollutants from energy plants is derived from the fuel that is burned. Coal, wood-based...

Unit A-5 • Introduction to Plant Operations and the Environment Objective 1 Describe the sources and effects of solid pollutants from energy plants. Sources of Solid Pollutants One of the main sources of solid pollutants from energy plants is derived from the fuel that is burned. Coal, wood-based fuel (hog fuel), biomass, and municipal solid waste are solid fuels. When they burn, they produce ash as a residual product. Ash is the non-combustible component of a fuel. When ash is so light that it travels with flue gas, it is called fly ash. Larger ash particles that cannot be carried in a flue gas stream, fall and become bottom ash. In a coal furnace, ash can be heated to the point where it melts and becomes slag. Fly ash that enters the atmosphere is often referred to as particulate. Particulates are typically described as solid or liquid matter small enough to be suspended in the atmosphere. The type of fuel determines both the type of ash and the quantity of ash produced. Analysis of different coals can show ash content of up to 20 percent by mass. Some will end up as bottom ash and slag; the rest is fly ash. In comparison, the ash from wood-based fuels consists of only 0.5 to 2 percent of the total dry mass. Some flue gas desulfurization (FGD) processes result in byproducts that have economic value such as sulfur, sulfuric acid, or gypsum. However, the more common type of flue gas desulfurization process results in no usable product. This sludge must be disposed of properly. Soot is another particulate. It may form when combustion is incomplete. Soot is different from ash because it contains a significant percentage of carbon residue. The figure below shows where in the process these solid pollutants are produced in a coal-fired plant. Figure 1 – Sources of Solid Waste in a Coal-Fired Plant 3-4 4th Class Edition 3 • Part A Liquid and Solid Emissions • Chapter 3 Adverse Effects of Solid Pollutants Particulates form a special type of hazard to humans. They are easily inhaled and can become lodged in the lungs. The smaller the particulate matter, the more damage they can cause. Larger particles can be filtered out in the nose and throat. However, the smallest particles can find their way to the deepest parts of the lungs. From there, these nanoparticles can pass from the lungs to other organs in the body. Adverse health effects associated with particulates include asthma, lung cancer, and cardiovascular diseases. Particulate matter can also affect the environment. It can reduce visibility, change the pH of lakes and streams, increase the effects of acid rain, and damage forests and crops. Solid fuels can also contain trace elements such as uranium, mercury, arsenic, and heavy metals. These elements do not burn off. Instead, they are left behind with the ash. The amount of these elements leads to debate on whether or not coal ash should be considered a hazardous waste. 4th Class Edition 3 • Part A 3-5