Producer gas

Producer gas is fuel gas that is manufactured from material such as coal, as opposed to natural gas. It can be produced from various fuels by partial combustion with air, usually modified by simultaneous injection of water or steam to maintain a constant temperature and obtain a higher heat content gas by enrichment of air gas with hydrogen. In this respect it is similar to other types of "manufactured" gas, such as coal gas, coke oven gas, water gas and carburetted water gas. Producer gas was used primarily as an industrial fuel for iron and steel manufacturing, such as firing coke ovens and blast furnaces, cement and ceramic kilns, or for mechanical power through gas engines. It was characteristically low in heating value but cheap to make, so that large amounts could be made and burned.

Adler Diplomat in WW II with wood gas generator

In the USA, producer gas may also be referred to by other names based on the fuel used for production such as wood gas. In the UK, producer gas is generally referred to as suction gas. The term suction refers to the way the air was drawn into the gas generator by an internal combustion engine.

Wood gas is produced in a gasifier and used to fire kilns, but the gas generated contains distillates that require scrubbing for use in other applications. Depending on the fuel, a variety of contaminants are produced that will condense out as the gas cools. When producer gas is used to power cars and boats[1] or distributed to remote locations it is necessary to scrub the gas to remove the materials that can condense and clog carburettors and gas lines. Anthracite and coke are preferred for automotive use because they produce the smallest amount of contamination, allowing smaller, lighter scrubbers to be used.

Producer gas is generally made from coke, or other carbonaceous material[2] such as anthracite. Air is passed over the red-hot carbonaceous fuel and carbon monoxide is produced. The reaction is exothermic and proceeds as follows:

Formation of producer gas from air and carbon:

C + O₂ → CO₂, +97,600 calories

CO₂ + C → 2CO, –38,800 calories

2C + O₂ → 2CO, +58,800 calories

Reactions between steam and carbon:

H₂O + C → H₂ + CO, –28,800 calories

2H₂O + C → 2H₂ + CO₂, –18,800 calories

Reaction between steam and carbon monoxide:

H₂O + CO → CO₂ + H₂, +10,000 calories

CO₂ + H₂ → CO + H₂O, –10,000 calories

The average composition of ordinary producer gas according to Latta was: CO₂: 5.8%; O₂: 1.3%; CO: 19.8%; H₂: 15.1%; CH₄: 1.3%; N₂: 56.7%; B.T.U. gross per cu.ft 136 [3][4] The concentration of carbon monoxide in the "ideal" producer gas was considered to be 34.7% carbon monoxide (carbonic oxide) and 65.3% nitrogen.[5] After "scrubbing", to remove tar, the gas may be used to power gas turbines (which are well-suited to fuels of low calorific value), spark ignited engines (where 100% petrol fuel replacement is possible) or diesel internal combustion engines (where 15% to 40% of the original diesel fuel requirement is still used to ignite the gas [6]). During World War II in Britain, plants were built in the form of trailers for towing behind commercial vehicles, especially buses, to supply gas as a replacement for petrol (gasoline) fuel.[7] A range of about 80 miles for every charge of anthracite was achieved.[8]

In old movies and stories, when describing suicide by "turning on the gas" and leaving an oven door open without lighting the flame, the reference was to coal gas or town gas. As this gas contained a significant amount of carbon monoxide it was quite toxic. Most town gas was also odorized, if it did not have its own odor. Modern 'natural gas' used in homes is far less toxic, and has a mercaptan added to it for odor for identifying leaks.

Various names are used for producer gas, air gas and water gas generally depending on the fuel source, process or end use including:

• Air gas: a.k.a. “power gas,” “generator gas” or “Siemens’ producer gas.” Produced from various fuels by partial combustion with air. Air gas consists principally of carbon monoxide with nitrogen from the air used and a small amount of hydrogen. This term is not commonly used, and tends to be used synonymously with wood gas.
• Producer gas: Air gas modified by simultaneous injection of water or steam to maintain a constant temperature and obtain a higher heat content gas by enrichment of air gas with H₂. Current usage often includes air gas.

• Semi-water gas: Producer gas.

• Blue water-gas: Air, water or producer gas produced from clean fuels such as coke, charcoal and anthracite which contain insufficient hydrocarbon impurities for use as illuminating gas. Blue gas burns with a blue flame and does not produce light except when used with a Welsbach gas mantle.

• Lowe’s Water Gas: Water gas with a secondary pyrolysis reactor to introduce hydrocarbon gasses for illuminating purposes. [9][10]

• Carburetted gas: Any gas produced by a process similar to Lowe’s in which hydrocarbons are added for illumination purposes.

• Wood gas: produced from wood by partial combustion. Sometimes used in a gasifier to power cars with ordinary internal combustion engines.

Other similar fuel gasses

• Coal Gas or Illuminating gas: Produced from coal by distillation.

• Water gas: Produced by injection of steam into fuel preheated by combustion with air. The reaction is endothermic so the fuel must be continually re-heated to keep the reaction going. This was usually done by alternating the steam with an air stream. This name is sometimes used incorrectly when describing carburetted blue water gas simply as blue water gas.

• Coke Oven Gas: Coke ovens give off a gas exactly similar to illuminating gas, part of which is used to heat the coal. There may be a large excess, however, which is used for industrial purposes after it has been purified.

• syngas, or synthesis gas: (from synthetic gas or synthesis gas) can be applied to any of the above gasses, but generally refers modern industrial processes, such as natural gas reforming, hydrogen production, and processes for synthetic production of methane and other hydrocarbons.

• City (Town) gas: any of the above-manufactured gases including producer gas containing sufficient hydrocarbons to produce a bright flame for illumination purposes, originally produced from coal, for sale to consumers and municipalities.

Uses and Advantages of Producer Gas:

• It is used in furnace. When furnaces are big, no scrubbing etc. is required. When furnace is small, scrubbing is necessary to avoid chocking of small burners. In gas engines, it is used after scrubbing.
• There is no loss due to smoke and convection current.
• Quantity of air required for the combustion of producer gas is not much above the theoretical quantity while burning solid fuel far more than theoretical quantity is required. So in case of solid fuels, the larger quantity of exhaust gases takes away sensible heat and thus there is loss of heat.
• Producer gas is more easily transmitted than solid fuel.
• Gas-fired furnaces can be maintained at a constant temperature.
• With gas, an oxidising and reducing flame can be obtained.
• Heat loss due to converting solid fuel into producer gas can be made in an economic way,
• Smoke nuisance can be avoided.
• Producer gas can be produced even by the poorest quality of fuel.