Fuel gas

Fuel Gas

Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Many fuel gases are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources of potential heat energy or light energy that can be readily transmitted and distributed through pipes from the point of origin directly to the place of consumption.

Fuel gas is contrasted with liquid fuels and from solid fuels, though some fuel gases are liquefied for storage or transport. While their gaseous nature has advantageous, avoiding the difficulty of transporting solid fuel and the dangers of spillage inherent in liquid fuels, it also has limitation. It is possible for a fuel gas to be undetected and collect in certain areas, leading to the risk of a gas explosion. For this reason, odorizers are added to most fuel gases so that they may be detected by a distinct smell.

The most common type of fuel gas in current use is natural gas. Types

There are two broad classes of fuel gases, based not on their chemical composition, but their source and the way they are produced: those found naturally, and those manufactured from other materials.

Manufactured fuel gas

Manufactured fuel gases are those produced through an artificial process, usually gasification, at a location known as a gasworks. Manufactured fuel gases include:

Coal gas

Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. Town gas is a more general term referring to manufactured gaseous fuels produced for sale to consumers and municipalities.

Coal gas contains a variety of calorific gases including hydrogen, carbon monoxide, methane and volatile hydrocarbons together with small quantities of non-calorific gases such as carbon dioxide and nitrogen. Prior to the development of natural gas supplies and transmission systems (during 1940s and 1950s in the US and the late 1960s and 1970s in the UK), virtually all fuel and lighting gas used in both the United States and Great Britain was manufactured from coal. Gas was often supplied to households via a municipally owned piped distribution system. Originally created as a by-product of the coking process, its use developed during the 19th and early 20th centuries tracking the industrial revolution and urbanization. By-products from the production process included coal tars and ammonia, which were important chemical feedstock for the dye and chemical industry with a wide range of artificial dyes being made from coal gas and coal tar. Facilities where the gas was produced were often known as a manufactured gas plant (MGP) or a gasworks. The discovery of large reserves of natural gas in the North Sea off the UK coast during the early 1960s led to the expensive conversion or replacement of most of the nation's gas cookers and gas heaters, with the exception of Northern Ireland, from the late 1960s onwards.

The production process is distinct, both physically and chemically, from that used to create a range of gaseous fuels known variously as manufactured gas, syngas, hygas, Dowson gas, and producer gas. These gases are made by partial combustion of a wide variety of feed stocks in some mixture of air, oxygen, or steam, to reduce the latter to hydrogen and carbon dioxide although some destructive distillation may also occur. Water gas

Water gas is a synthesis gas, containing carbon monoxide and hydrogen. It is a useful product but requires careful handling due to its

flammability and the risk of carbon monoxide poisoning. The gas is made by passing steam over a red-hot carbon fuel such as coke:

H 2O + C → H

2

+ CO (ΔH = +131 kJ/mol)

The reaction is endothermic so the fuel must be continually re-heated to keep the reaction going. In order to do this, an air stream, which alternates with the vapor stream, is introduced for the combustion of carbon to take place.

O 2+ C → CO

2

(ΔH = ?393.5 kJ/mol)

Theoretically to make 6 L of water gas, 5 L of air is required.

Or alternatively to prevent contamination with nitrogen, energy can be provided by using pure oxygen to burn carbon into carbon monoxide.

O

2

+ 2 C → 2 CO (ΔH = ?221 kJ/mol)

In this case 1 L of oxygen will create 5.3 L of pure water gas. Producer gas

Producer Gas is a generic term referring to:

?Wood gas: produced in a gasifier to power cars with ordinary internal combustion engines.

?Town gas: manufactured gas, originally produced from coal, for sale to consumers and municipalities.

?Syngas: used as a fuel source or as an intermediate for the production of other chemicals.

In old movies and stories, when describing suicide by "turning on the gas" and leaving an oven door open without lighting the flame, they were talking about coal gas or town gas. As this gas contained a significant amount of carbon monoxide, the gas 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 gassy odor added to it for identifying leaks.

In the UK, producer gas, also called suction gas, specifically means a fuel gas made from coke, anthracite or other carbonaceous material. Air is passed over the red-hot carbonaceous fuel and carbon monoxide is produced. The reaction is exothermic and proceeds as follows:

2C + O

2 + 3.7

3 N

2

→ 2CO+ 3.73 N

2

The nitrogen in the air remains unchanged and dilutes the gas, giving it a very low calorific value. The concentration of carbon monoxide in the "ideal" producer gas was considered to be 34.7% carbon monoxide (carbonic oxide) and 65.3% nitrogen.[1] 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 40% - 15% of the original diesel fuel is still used to ignite the gas [2]). During the Second World War 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.[3]A range of about 80 miles for every charge of anthracite was achieved

Syngas

Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide. The name comes from its use as intermediates in creating synthetic natural gas (SNG)[1] and for producing ammonia or methanol. Syngas is also used as an intermediate in producing synthetic petroleum for use as a fuel or lubricant via the Fischer–Tropsch process and previously the Mobil methanol to gasoline process. Syngas is combustible and often used as a fuel of internal combustion engines.[2][3][4]It has less than half the energy density of natural gas.

Production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal,[5] biomass, and in some types of waste-to-energy gasification facilities.

Wood gas

Wood gas is a syngas fuel which can be used as a fuel for furnaces, stoves and vehicles in place of gasoline, diesel or other fuels. During the production process biomass or other carbon-containing materials are gasified within the oxygen-limited environment of a wood gas generator to produce hydrogen and carbon monoxide. These gases can then be burnt as a fuel within an oxygen rich environment to produce carbon dioxide, water and heat. In some gasifiers this process is preceded by pyrolysis, where the biomass or coal is first converted to char, releasing methane and tar rich in polycyclic aromatic

Biogas

Biogas typically refers to a mixture of gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from regionally available raw materials such as recycled waste. It is a renewable energy source and in many cases exerts a very small carbon footprint.

Biogas is produced by anaerobic digestion with anaerobic bacteria or fermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops. It is primarily methane

(CH

4) and carbon dioxide (CO

2

) and may have small amounts of hydrogen

sulphide (H

2

S), moisture and siloxanes.

The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.[2]

Biogas can be compressed, the same way natural gas is compressed to CNG, and used to power motor vehicles. In the UK, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel.[3] It qualifies for renewable energy subsidies in some parts of the world. Biogas can be cleaned and upgraded to natural gas standards when it becomes bio methane.

Blast furnace gas

Blast furnace gas (BFG) is a by-product of blast furnaces that is generated when the iron ore is reduced with coke to metallic iron. It has a very low heating value, about 93 BTU/cubic foot, because it consists of about 60 percent nitrogen, 18-20% carbon dioxide and some oxygen, which are not flammable. The rest is mostly carbon monoxide, which has a fairly low heating value already. It is commonly used as a fuel within the steel works, but it can be used in boilers and power plants equipped to burn it. It may be combined with natural gas or coke oven gas before combustion or a flame support with richer gas or oil is provided to sustain combustion. Particulate matter is removed so that it can be burned more cleanly. Blast furnace gas is sometimes flared without generating heat or electricity. Blast Furnace Gas is generated at higher pressure and at about 100 °C (212 °F)-150 °C (302°F) in a modern Blast Furnace. This pressure is utilized to operate a generator (Top-gas-pressure Recovery Turbine - i.e. TRT in short), which can generate electrical energy up to 35 kwh/t of pig iron without burning any fuel. Dry type TRTs can generate more power than wet type TRT.

Auto ignition point of blast furnace gas is approximate 630 °C (1,166 °F)-650 °C (1,202°F) and it has LEL (Lower Explosive Limit) of 27% & UEL (Upper Explosive Limit) of 75% in an air-gas mixture at normal temperature and pressure.

Higher concentration of carbon monoxide makes the gas hazardous.