UA5 C3 Liquid and Solid Emissions Obj 1.docx
Transcript
Many, if not most, industrial processes produce solid or liquid wastes. Some of the categories used to describe industrial waste include: • Organic and non-organic • Solid, semi-solid, and liquid • Hazardous and non-hazardous Power Engineers use significant amounts of water to generate steam and...
Many, if not most, industrial processes produce solid or liquid wastes. Some of the categories used to describe industrial waste include: • Organic and non-organic • Solid, semi-solid, and liquid • Hazardous and non-hazardous Power Engineers use significant amounts of water to generate steam and operate related processes. To protect equipment, chemicals are added to the water to prevent corrosion and scale deposition. Water is also used for cooling systems. Chemicals are added to prevent the growth of bacteria and algae. Wastewater treatment processes produce contaminated organic sludge that needs further treatment. All chemical liquids and chemically treated water must be disposed of according to local regulatory requirements. Many mines and other industrial processes produce residual waste solids called slags. For example, steel manufacturing produces blast furnace slag. The power industry, by burning solid fuels such as coal and wood waste, produces fly ash, bottom ash, and slag. Solid waste can contain hazardous components, depending on the source materials. For example, fly ash can contain arsenic, cobalt, and vanadium. Liquid wastes often contain hazardous solids either in solution or suspension. These liquids require cleaning, through filtration or deposition, before they can be reused or released into the environment. The recovered hazardous solids must be disposed of safely. Power Engineers must be familiar with the waste materials produced by the processes they are responsible for, so that they can be safely handled and disposed. This chapter will examine the effects of liquid and solid waste on the environment and the different options for disposal. 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. 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.
