coalgas

Coal gas, sometimes written as coalgas, refers to a flammable gas produced by the gasification or destructive distillation of coal. Once manufactured in gasworks and distributed through urban pipelines, it was used primarily for lighting, and later for cooking and heating in many cities.

Production involves heating coal in the absence or with limited supply of air, or gasifying coal with steam and limited oxygen, to drive off volatile components. The resulting gas is a mixture dominated by hydrogen and carbon monoxide, with methane, carbon dioxide, and nitrogen also present. Small amounts of other hydrocarbons and sulfur-containing compounds may be present. Because of toxicity and flammability, the gas often required purification to remove tar, sulfur compounds, and ammonia, and was odorized to aid leak detection.

Historically, coal gas powered street lighting and home illumination in the 19th and early 20th centuries. With the introduction and expansion of natural gas and improvements in gas-cleaning technology, coal gas declined in many regions during the mid-20th century and was largely replaced by natural gas by the 1960s–1970s. Some places still operate manufactured gas systems for niche applications or as part of legacy infrastructure, but most modern gas networks rely on natural gas or synthetic gases.

Byproducts of coal gas production, such as coal tar and light liquids, were important industrial commodities, while gasworks sites often left legacy environmental contamination requiring remediation. The term coalgas today is largely historical, though it may appear in discussions of energy history or in reference to older urban infrastructure.