Water gas is a manufacturing gas historically valued as a fuel and a chemical building block in industrial processes. It is produced by a high-temperature reaction between steam and a carbon-rich material like coke or coal. Historically, its development influenced the town-gas industry, providing a combustible gas for lighting and heating. While modern processes have largely replaced its direct use as a primary fuel, its underlying chemistry remains fundamental to industrial gas production.
Chemical Composition and Properties
Water gas is defined by its primary constituents, which are a mixture of hydrogen (\(H_2\)) and carbon monoxide (\(CO\)). The ideal composition is an equimolar or roughly equal proportion, meaning the gas is typically close to 50% hydrogen and 50% carbon monoxide by volume. This specific combination is sometimes referred to as “blue water gas” because of the non-luminous blue flame it produces when burned.
The presence of hydrogen gives water gas a high calorific value, making it a clean-burning fuel that produces relatively low particulate emissions. This high energy content was an advantage over other fuel gases used in the past, such as producer gas, which contains a large amount of inert nitrogen. The mixture is highly toxic due to the significant concentration of carbon monoxide, a colorless and odorless poison. This danger, combined with its lower heat content compared to natural gas, led to its replacement as a residential fuel once natural gas became widely available.
Industrial Generation Process
The manufacturing of water gas involves a process called gasification, where steam is passed over a bed of incandescent carbonaceous material, such as coke or coal. This reaction requires maintaining the carbon bed at an extremely high temperature, typically between 900 and \(1000^\circ C\). The fundamental chemical reaction that occurs is carbon reacting with water vapor to form carbon monoxide and hydrogen (\(C + H_2O \rightarrow CO + H_2\)).
This steam-carbon reaction is endothermic, meaning it absorbs heat from the carbon bed to proceed, causing the temperature to drop rapidly. If the temperature falls too low, the reaction slows down or stops, making the production process inherently cyclical. To counteract this heat loss, the process operates in alternating phases known as the “blow” and “make” cycles.
During the “blow” cycle, a blast of air is introduced into the generator, which combusts some of the carbon to produce heat (\(C + O_2 \rightarrow CO_2\)). This exothermic reaction rapidly reheats the carbon bed back to the required high temperature for the steam reaction. The waste gases from this phase are vented, as they contain significant amounts of inert nitrogen from the air.
Once the carbon bed is sufficiently hot, the “make” cycle begins, and the air blast is replaced by a stream of steam. The steam reacts with the hot carbon to produce the water gas mixture of hydrogen and carbon monoxide. After a short period, the endothermic reaction cools the bed down again, requiring the process to switch back to the “blow” cycle to restore the heat.
Primary Industrial Applications
Water gas holds a dual commercial utility, serving both as a direct fuel source and as a precursor for more complex chemical synthesis. As a fuel, its clean-burning properties made it valuable in industrial heating applications, such as glass making and welding, before more energy-dense alternatives became common. The mixture’s high flame temperature makes it effective for processes requiring intense heat.
Beyond its role as a fuel, water gas is highly valued as a form of synthesis gas, or syngas, which is a foundational ingredient in the petrochemical industry. The hydrogen content can be further enriched and purified through a catalytic process called the water-gas shift reaction. This purified hydrogen is then channeled into large-scale production of ammonia, which is utilized extensively in fertilizer manufacturing.
The carbon monoxide and hydrogen mixture is also a feedstock for synthesizing various organic compounds. Most notably, it is used in the synthesis of methanol, a solvent and fuel additive intermediate in the chemical industry. Water gas is also a starting material for the Fischer-Tropsch process, a series of catalytic reactions that converts the gas into liquid hydrocarbons, including synthetic diesel and gasoline.