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What are industrial fuels?

A Combustion File downloaded from the IFRF Online Combustion Handbook

ISSN 1607-9116

Combustion File No: 62

Version No: 1

Date: 22-April-02

Author(s): Peter Roberts

Source(s): Author

Referee(s): Neil Fricker

Status: Pubished

Sponsor: IFRF NET

1. What is a fuel?For the purposes of industrial combustion (CF32), a fuel is defined as a substance

containing carbon and hydrogen, which may combine within the industrial combustion

process, with the oxygen contained in a comburent, for example, atmospheric air see

CF61.

This rapid combination releases heat at relatively high temperature, which may then be

used for industrial process heating, including the generation of steam and high-pressure

hot water.

The combustion chemistry is very simplistically represented as:

2C + O2 2CO + Heat

2CO + O22CO2 + Heat

H2 + O2 H2O + Heat

Industrial fuels can contain other fuel elements, the most important of which is sulphur,

which when oxidised, can contribute significantly to the overall heat release in

combustion. However the use of high sulphur containing fuels is strongly restricted at

the time of writing, due to heavy limitations in the emission of sulphur dioxide see

CF121.

2. How did industrial fuels develop?

WoodNaturally the development of industrial fuels was dependent on the demands of

developing industrial processes. Almost certainly the earliest industrial fuel was wood,

or derived from wood - charcoal, fired in various open fires, ovens and kilns.

The development of metallurgical industries required charcoal, which also supplied the

carbon for ore reduction. Thus charcoal burning itself became an industry, eventually

consuming large tracts of forest. Later, raw wood became almost displaced as a fuel for

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large-scale industry, but it is again becoming important as a component of biomass fuel

or BioFuel, - see Section 3.

Coal and coal-derived fuelsWood was eventually replaced by coal, both in terms of an industrial fuel and as the

source of a reducing agent in metallurgical processes by the coal based product - coke.

Coal is a solid fossil fuel in the form of dark, compact, stratified rock-like mass ofdecayed plant debris interspersed with smaller amounts of inorganic matter and covered

with sedimentary rock, typically brown or black in colour.

Coal is a fossil fuelof widely varying quality, existing in below surface seams of

varying thickness, depth and extent. Initially, surface seam ends were outcropped,

progressing to deep mines with drift and/or vertical shafts, leading eventually to the

modern techniques of opencast mining. These days a large proportion of coal is traded

globally; the remainder is utilised close to the mine.

The origins and quality of coal is the subject of a separate Combustion File CF177, which

isthe basis of a developing coal knowledge resource within this Handbook. In modern

times coal is used mainly for:

Power generation and cement manufacturing, fired typically as a pulverised fuel,

and steam or hot water raising, fired as a pulverised fuel or as a crushed fuel in

fixed or fluidised beds.

As a raw material for the manufacture of metallurgical coke, a process giving a

by-product Coke Oven Gas a rich fuel gas that may be regarded as a

secondary fuel, and which is fired typically in integrated iron and steelworks.

Metallurgical coke is in turn used to fuel iron manufacturing in blast furnaces

which gives rise to a further by-product gas, a low grade secondary fuel known

as Blast Furnace Gas.

Coal can also be gasified, traditionally to Producer Gas and Water Gas, by passing

steam and/or air through hot coke beds. These processes either individually, or incombination, give a relatively low calorific value fuel gas. At various times and locations,

in the second half of the 20th century, there has been considerable RD&D to develop

commercially successful coal gasification processes. But the advent of plentiful supplies

of relatively cheap natural gas - see below has tended to prevent widespread

application, and to displace Town Gas as the coal derived gaseous fuel distributed in

urban areas for over a century.

Petroleum Fuels Liquid FuelsThe next set of fuels to become important in industry was essentially a variety of liquid

fuels. Liquid fuels are mainly oils, tars and pitches and are derived primarily from crude

petroleum, but also from oil shale by distillation, and from coal by carbonisation and

hydrogenation.

Crude petroleum (also known as crude oil or simply crude) is a liquid, light brown to

black in colour and varying considerably in viscosity depending upon origin. It occurs in

sedimentary rock strata and is a fossil fuel, derived over millions of years from the

decomposition of marine organisms, ocean bed plant life and land based organisms

carried into lakes and to the sea bottom. All industrial fuels derived from crude

petroleum are classed as fossil fuels. Crude petroleum is found regularly with natural

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gas - see below and also gives rise to a commercial gaseous fuel LPG, also described in

the following section.

Crude Oil was initially recovered seepage from near surface wells. As demand for

petroleum products increased towards the end of the 19th century, deeper and deeper

wells were identified and exploited through advancing exploration and drilling

techniques. In recent decades, land based production has been substantially augmented

by the development and exploitation of under-sea based oil fields.

Crude oil is processed to produce a whole range of domestic, automotive and industrial

fuels. The last group contains, petroleum distillate fuelslight fuels, and a range of

petroleum residual fuelsbroadly described as light, medium and heavy oils. These fuels

were relatively cheap and easier to transport and handle and fire than coal. Eventually at

the end of the 1940s petroleum residual fuels commenced to take over from coal-

derived fuels for the firing of industrial heating processes.

In 1974, the so-called oil crisis gave rise to a temporary loss of crude petroleum

supplies and also to a considerable rise in oil prices. This commenced the search for

alternative fuels, alternative supplies of crude oil or indeed liquid fuels alternative to

petroleum. In the 1980s research was carried out into the firing of very heavy residuals,the production of coal-water slurries, the development of bio-oils and so forth. The

application of these alternative fuels was however curtailed by the eventual reduction in

crude oil prices. Nevertheless it is strongly believed that the use of liquid, petroleum

based industrial fuels will remain important in the early decades of the present century

although their market share may decrease.

Natural Gas-Gaseous FuelsThe final range of fuels of industrial importance is gaseous fuels which are generally

the easiest fuels to handle and fire. At the time of writing, natural gas,a high calorificvalue, gaseous fossil fuel composed mainly of methane CH4, often found in association

with crude petroleum deposits, is the most abundantly distributed and fired. This gas is

also transported in bulk, in liquefied form LNG. A further industrial fuel derived fromnatural gas or from petroleum refining is LPG, a very high calorific gaseous fuel

composed primarily of propane and/or butane, distributed as a liquid prior to firing in

the gaseous state.

In the iron and steel manufacturing industry, coke oven gas (COG), blast furnace gas

(BFG) and basic oxygen steelmaking gas (BOS) are regularly used for associated

process heating e.g for the firing of reheating furnaces, Cowper stoves etc., and for

power generation. Similarly in the petro-chemical industries a variety of gaseous by-

product streams are used for the firing of associated processes.

Town Gas, usually derived from coal, is a medium calorific value gas formerly used

extensively for residential applications in the urban areas of mature economies, but now

largely superseded by Natural Gas.

3. Renewable Fuels

BackgroundThe combustion of fossil fuels effectively releases carbon, stemming originally from

decomposed plant and animal organisms, stored for millions of years as hydrocarbon

molecules in coal, petroleum or natural gas. This carbon is released as carbon dioxide. It

is presently believed that the massive increase in the combustion of fossil fuels

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commencing at the start of the industrial revolution has significantly increased the

concentration of carbon dioxide in the atmosphere.

Carbon dioxide is a so-called greenhouse gas which is said to contribute to the

phenomenon of global warming, exhibited as climate change. The Kyoto protocol,

requires the curtailment of carbon dioxide emissions from fossil fuel combustion which

can be achieved, among other ways, through:

Increasing the overall thermal efficiency of the use of fossil fuels;

Substituting fossil fuels by so-called renewable fuels in combustion processes;

Providing process energy from sources not requiring the conversion of any form

of fuel e.g. electricity produced form nuclear power stations, wind energy,

solar energy, etc. see CF78.

Fossil Substitute FuelsThis an important area of development and is introduced in CF23, which considers the

developing role of biomass.

Generally this set of fuels is based on plant forms, including

Plants from wood to straw, that can be grown and harvested as a fuel (so-called

energy crops);

Waste residues from plant processing piths, bagasse etc.,

In addition to biomass, a further developing area includes fuels derived from municipal

(domestic, commercial and industrial) wastes so-called Refuse Derived Fuels RDF

and sewage sludges. With the increasing prohibition of landfill and river and sea dumping

as a means of disposing of these wastes, recycling of waste products including the

development of potential industrial fuels streams is a developing area, and one of

interest to industry as a source of fossil replacement fuels.

There has been considerable research in the last decade into the firing of such fuels,

either in the co-firing mode or in combustion equipment specifically designed for thefiring of these fuels with built-in heat recovery.

Co-firing essentially means the mixing, for example of an RDF with a coal, in combustion

equipment designed for coal preparation and firing. The heating process can be steam

raising for power production of a cement kiln.

The essential point is that the amount of waste for disposal is reduced and that the

calorific value of the RDF or other waste fuel streams is released in a controlled manner

at a point where it can be easily utilised, reducing the need to fire a specific fossil fuel.

4. ConclusionsFor the foreseeable future, fossil fuels will continue to provide the bulk of the

industrial fuel supply. Gradually developing fossil substitute fuels, based on biomass and

recycled wastes will contribute a relatively small but nevertheless significant portion of

the industrial fuel supply.

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Glossary termsBasic oxygen steel making gas (BOS gas) Low to medium calorific value gaseous by-

product from oxygen blown steel-making process

BioFuel Fuel derived from biomass

Biomass - Biomass comprises all growing organic matter, such as plants, trees, grasses,

peat and algae. Biomass is renewable fuel from organic origin, residues from forestry,

agriculture and energy crops

Bio-oils Liquid fuels processed from biomass materials, for example wood chips, which

are being developed as an automotive or industrial fuels

Blast Furnace Gas (BFG) A low calorific value fuel gas produced as a by-product from

the reduction of iron ore using coke in a blast furnace

Carbonisation This process, referring to the carbonisation of coal, is achieved by

decomposition of the coal through the application of heat, out of contact with air, where

the prime product is a solid residue coke with liquid and gaseous distillation by-

products

Carbon Dioxide CO2 A principle product of combustion of carbon containing fuels; a

greenhouse gas

Charcoal The char product of wood pyrolysis, formerly extensively used as a fuel and

reducing agent in metallurgical production processes

Coal - A solid fossil fuel in the form of dark, compact, stratified rock-like mass of

decayed plant debris interspersed with smaller amounts of inorganic matter and covered

with sedimentary rock

Coke A dark porous solid fuel, mainly carbon, formed as a pyrolysis or carbonisation

product of coal, produced either as by-product of Town Gas production or as the main

product of Coke Ovens metallurgical or hard coke. Optimum Coke properties depend

upon the end-use which include presently, the main energy supply and ore reducing agentin blast furnaces, and in former times a domestic and industrial smokeless fuel and a

basic fuel for gas producers

Coke Oven Gas (COG) A medium calorific value fuel gas produced as a by-product

from the pyrolysis of coal in coke ovens, which have as the main product, metallurgical

coke similar in quality to traditional town gas

Comburent The agent, which supports the combustion of a fuel or combustible, usually

air or oxygen. Although this term is not found in English dictionaries, it has been

adopted (probably adapted from the French comburant) by the IFRF and is used

throughout this handbook. There is no convenient English equivalent

Combustion - The act or process of burning; in which principally the carbon and hydrogencomponents of the material being burned are oxidised releasing heat

Crude Petroleum A liquid fossil fuel, also known as crude oil, that occurs naturally in

sedimentary rocks and consists mainly of hydrocarbons

Crude Oil A liquid fossil fuel, also known as crude petroleum, that occurs naturally in

sedimentary rocks and consists mainly of hydrocarbons

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Fuel A fuel is the generic term describing the material - solid, liquid, gaseous, emulsion

etc. - which contains the carbon and/or hydrogen consumed in the industrial combustion

process

Fossil fuel - Organic fuels obtained from organic matter natural maturation during long

periods of time (coal, oil, natural gas).

Hydrogenation - This process, referring to the hydrogenation of coal, is achieved byautoclaving the coal with hydrogen at high temperature and pressure, and distilling the

product to produce liquid fuels

LNG Acronym for Liquefied Natural Gas, a state of natural gas used for bulk

transportation or for motor vehicle fuel. LNG is a cryogenic fluid with a boiling point of

circa minus 165oC at atmospheric pressure. Methane at room temperature does not

liquefy at any pressure.

LPG Acronym for Liquefied Petroleum Gas, a very high calorific value gaseous fuel

composed primarily of a mixture of butane and propane, sold and transported in liquefied

form and evaporated prior to firing. LPGs liquefy at ambient temperatures and low

pressures (a few bar)

Methane CH4 Main component of natural gas; methane is a strong greenhouse gas

Natural Gas A high calorific value, gaseous fossil fuel composed mainly of methane,

typically found in association with crude petroleum deposits

Oil Shale - A petroleum containing shale; a black or dark brown type of shale from which

petroleum can be extracted by distillation

Petroleum Distillate Fuels Relatively light liquid fuels obtained from the fractional

distillation of crude petroleum

Petroleum Residual FuelsHeavy products from distillation and other petroleum

refining processes which may be fired as a liquid fuel

Producer Gas A relatively low calorific fuel gas produced by blowing a mixture of airand steam through a bed of coal or coke

RDF - Acronym - Refuse Derived Fuel -recycled municipal solid waste, which has been

processed prior to combustion to increase the calorific value of the waste. It is

produced by mechanically removing the non-combustible materials such as metal and

glass and then processing the remaining waste into coarse (c-RDF) or densified RDF (d-

RDF) pellet or briquette. The removal of organic waste is preferred as it has high

moisture content.

Solar Energy - Energy that comes from the sun, directly and in real time.

Town Gas A medium calorific value fuel gas produced traditionally through the

pyrolysis of coal in retorts, for distribution in a town or city, as a residential, tertiary(commercial) or industrial fuel, with coke and tars as by-products similar in quality to

coke oven gas

Water Gas A low to medium calorific fuel gas produced by blowing steam and air,

individually through coke in the air cycle the coke is heated up from 900C to over

1000C and the product discarded in the steam cycle blue water gas is produced

Wind Energy- Energy that comes from the movement of air

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Wood - A hard fibrous substance, the chief component of shrubs and trees and found

beneath their bark. Wood was an important fuel, in former times, and a building

material. In recent times, wood is being revived as a fuel within the group BioFuels.

Waste wood from building demolition is also used in this way

Keywordsfuel; gas; gaseous; industrial; coke oven; blast furnace; natural; town; producer; water;

petroleum; crude; oil; liquid; solid; coal; coke; RDF; biofuel; biomass; sewage sludge;

Kyoto; tars; fossil; carbon, hydrogen; methane; greenhouse; calorific value; substitute;

alternative; LNG; LPG; BFG; COG; BOS; wood; straw; bagasse; energy; crops;

Related Combustion FilesCF23 What is biomass?

CF32 What is industrial combustion?

CF61 What are industrial comburents?

CF78 What are Renewable Energy Sources - RES?

CF121 How do I find information on EU air quality regulations, directives and decisions?

CF177 What is coal?

SourcesAuthor

AcknowledgementsNone

File Placing[Fuels and Comburents]; [Introduction to Fuels]; [Basics]

[Power Generation]; [Fuels]; [Introduction]

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