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A manufactured gas plant converts substances like coal or oil into gas that can be used for things such as lighting, heating and cooking. The raw material being converted is often referred to as a feedstock. These plants were most common from the late 1800s to the mid 1900s, when the use of manufactured gas was largely replaced by natural gas. During the years they were in operation, the gas created in a manufactured gas plant was often known as city gas, as it was piped throughout the local city for use by homes and industry.
In order to create gas, a manufactured gas plant relied on either carbonization or gasification. Many types of plants existed that operated on these two different principles. The carbonization of coal is the result of a process typically known as coking, where coal is heated to create coke that can then be used for other purposes. In a manufactured gas plant, this coke would still typically be produced, though the main goal would be to capture the off gases for distribution to the nearby urban area.
Gasification is a process used at a manufactured gas plant to produce gas from a feedstock by inducing a chemical reaction. This type of gas is often known as producer gas, and included variants such as blue water gas (BWG) and carbureted water gas (CWG). These gasses were typically manufactured by passing air through a heated bed of coal, though the process differed depending on whether BWG or CWG was being produced.
In addition to providing gas for home and industrial use, manufactured gas plants often created a number of useful byproducts. Plants that carbonized coal produced large amounts of coke, though coal tar was also a common byproduct. Coal tar could then be distilled to yield creosote, phenols and other useful chemicals.
The use of manufactured gas dropped off sharply with the introduction of natural gas. Cities often had pipe networks for their local manufactured gas, and these networks were often switched over to use natural gas instead.
Very few manufactured gas plant sites remain intact, with one notable exception being Gas Works Park in Seattle, Washington, in the United States. Most former manufactured gas plants were dismantled, the soil remediated, and the land repurposed. Since manufactured gas plants could produce a large amount of toxins, this could be a long and expensive process. A site like Gas Works Park has undergone efforts to clean the soil, but retains the old gas plant structures as the centerpiece of a public park.
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