ChE/T/323     ENERGY RESOURCES AND THEIR UTILIZATION Introduction -Survey of different sources of energy and their utilization. Fossil Fuels - coal, crude petroleum and natural gas.Processed Fuels - Charcoal, coke, water gas, producer gas, refinery gas, LPG and synthetic petrol.Nuclear Fuels - Sources of nuclear fuels and introduction to nuclear reactions.Solar Energy-. Effective utilization of solar energy for room heating, water heating and other industrial processes.Energy from Biodegradable Materials - Survey of bio-degradable materials, Methods of processing the materials with special reference to gobar gas plant.Energy utilization - Thermodynamic and economic aspects of utilization:. Design of burners stokers, and furnaces for. combustion of various conventional fuels.Waste Heat Recovery - Analysis of waste heat systems and efficient methods of heat recovery.

Energy sources

What are sources of energy and where are they used for? Which different sources of energy do we know?What are the pros and cons of different sources of energy?

What are sources of energy and where are they used for?An energy source is a system which makes energy in a certain way, for instance a hydro-electric station. A hydro-electric station uses the current of the river for the making of electricity.

Which different sources of energy do we know?How many energy-sources do we know, below are the most important sources.

Nuclear powerNuclear power is a form of energy which arise from a reaction between atomic nucleï. Mostly this form of energy comes out of nuclear fission. To explain how this process works, we give a little explanation about the structure of atomic nucleï. Atomic nucleï exist out of neutrons and protons. these little parts (neutrons and protons) are held together in the center of the atomic nucleus through a special energy, called binding-energy. In a process in which the atomic nucleï collide with each other, they fall apart and the loose parts come out of the atomic nucleus. The energy which kept the parts together is not necessary anymore and this energy comes 'free'. At the technique of nuclear fission, atomic nucleï collide with each other in a central boiler to become as much energy out of it as possible. The so called 'binding-energy' falls apart and this energy comes out of the atomic nucleus. This energy is used for heating up water and this water becomes steam. Through the steam a turbine can be driven and so electricity is a fact. The speed in which the atomic nucleï collide is controlled by special rods. These rods can pull atomic nucleï towards them and so there become less atomic nucleï which can collide and then there is less binding-energy to come 'free'.

Fossil energy

Fossil energy is generated through the burning of fossil remains. At this burning the fossil fuel is used as a source of heat to make steam out of water. This steam is used for the working of a turbine. With the help of a generator, this turbine can make electricity. Examples of fossil fuels are oil, natural gas and coal. These fossil fuels are remains of dead materials of plants and animals. These plants and animals died over a million years ago and under the pressure of the earth's surface and through the decay of this material their came a process of compression. Carbon is the main part of these fossil fuels, the more carbon, the heavier the fuel.

Alternative energy

Alternative energy is a form of energy without waste-matters. It is also a form where the source, which delivers the energy, is endless. Some alternative energy-sources are sun-, water- and wind energy. By all these forms of alternative energy, existing energy (like water, wind and sun) is used for the making of electric energy. For instance, a hydro-electric station makes use of the fall between a lake and a river. They build a flood control dam between the lake and the river. And in the one outlet of the dam they build a turbine. This turbine activates a generator and the water energy is transformed into electric energy.

What are the pros and cons of different sources of energy?

The three different kinds of energy-sources have their own pros and cons. In this part we give a few of them.

Nuclear power

For the generation of nuclear power little raw material is needed to generate a lot of electric energy. This is an advantage, because the supply of the raw material will be enough for quite a time. A very big disadvantage is that the raw material for nuclear power, uranium, is very radio-active. Also the used rods and other used materials stay radio-active for ages. at a nuclear power plant as Tsjernobyl we have seen how dangerous this type of energy-generation can be. This is the major reason why environmental groups (like Greenpeace) are against this form of energy-winning.

Fossil energy

The big advantage of fossil energy is that, to generate the energy from the raw material is easy and cheap. Disadvantage is that during the process of combustion a lot of toxic materials comes into the air which causes extra pollution of the atmosphere, these materials also increase the effect of global warming. Another disadvantage of fossil energy is that the supply of fossil fuels is not endless. The current supply is for approximately 50 years. That is why the USA wants to trail for oil and natural gas in Alaska. If the USA do this, there are big consequences for the environment.

Alternative energy

The advantage of alternative energy is that the energy source is endless and doesn't give any pollution. Still, there are not many alternative energy forms, because for instance the technique to transform sun-beams into electric energy is very expensive.

Energy density is the amount of energy stored in a given system or region of space per unit volume, or per unit mass, depending on the context, although the latter is more formally specific energy. Hydrogen has a higher energy density per unit mass than does gasoline, but a much lower energy density per unit volume.

In energy storage application the energy density relates the mass of an energy store to its stored energy. The higher the energy density, the more energy may be stored or transported for the same amount of mass.

The highest density sources of energy are fusion and fission. Fusion includes energy from the sun which will be available for billions of years (in the form of sunlight) but humans have not learned to make our own sustained fusion power sources. Fission of U-235 in nuclear power plants will be available for billions of years because of the vast supply of the element on earth. Coal and petroleum are the current primary energy sources in the U.S. but have a much lower energy density. Burning local biomass fuels supplies household energy needs (cooking fires, oil lamps, etc.) worldwide.

Energy density (how much energy you can carry) does not tell you about energy conversion efficiency (net output per input) or embodied energy (what the energy output costs to provide, as harvesting, refining, distributing, and dealing with pollution all use energy). Like any process occurring on a large scale, intensive energy use creates environmental impacts: for example, global warming, nuclear waste storage, and deforestation are a few of the consequences of supplying our growing energy demands from fossil fuels, nuclear fission, or biomass.

Energy Densities Plot

Coal

Coal is a fossil fuel formed in ecosystems where plant remains were preserved by water and mud from oxidization and biodegradation, thus sequestering atmospheric carbon. Coal is a readily combustible black or brownish-black rock. It is a sedimentary rock, but the harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. It is composed primarily of carbon and hydrogen along with small quantities of other elements, notably sulfur. Coal is extracted from the ground by coal mining, either underground mining or open pit mining (surface mining).

Coal is the largest source of fuel for the generation of electricity world-wide, as well as the largest world-wide source of carbon dioxide emissions. Carbon dioxide is a greenhouse gas and these emissions contribute to climate change and global warming. In terms of carbon dioxide emissions, coal is slightly ahead of petroleum and about double that of natural gas.

Types of coalAs geological processes apply pressure to dead biotic matter over time, under suitable conditions it is transformed successively intoPeat, considered to be a precursor of coal. It has industrial importance as a fuel in some countries, for example, Ireland and Finland. Lignite, also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation. Jet is a compact form of lignite that is sometimes polished and has been used as an ornamental stone since the Iron Age. Sub-bituminous coal, whose properties range from those of lignite to those of bituminous coal and are used primarily as fuel for steam-electric power generation. Additionally, it is an important source of light aromatic hydrocarbons for the chemical synthesis industry. Bituminous coal, a dense mineral, black but sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing and to make coke. Anthracite, the highest rank; a harder, glossy, black coal used primarily for residential and commercial space heating. It may be divided further into metamorphically altered bituminous coal and petrified oil, as from the deposits in Pennsylvania. Graphite, technically the highest rank, but difficult to ignite and is not so commonly used as fuel: it is mostly used in pencils and, when powdered, as a lubricant.

Coal is classified into four main types, or ranks (lignite, sub-bituminous, bituminous, anthracite), depending on the amounts and types of carbon it contains and on the amount of heat energy it can produce. The rank of a deposit of coal depends on the pressure and heat acting on the plant debris as it sank deeper and deeper over millions of years. For the most part, the higher ranks of coal contain more heat-producing energy.

Peat is an organic material that forms in the waterlogged, sterile, acidic conditions of bogs and fens. These conditions favour the growth of mosses, especially sphagnum. As plants die, they do not decompose. Instead, the organic matter is laid down, and slowly accumulates as peat because of the lack of oxygen in the bog. A little over 3% of the earth's land surface is covered in peat.Lignite is also known as brown coal and is an intermediate stage between peat and coal. Lignite was formed about 50 million years ago. It is the lowest rank of coal with the lowest energy content.  Lignite coal deposits tend to be relatively young coal deposits that were not subjected to extreme heat or pressure. Lignite is crumbly and has high moisture content. Lignite is mainly burned at power plants to generate electricity.Sub-bituminous coal has a higher heating value than lignite. Sub-bituminous coal typically contains 35-45 percent carbon, compared to 25-35 percent for lignite. Most sub-bituminous coal in the U.S. is at least 100 million years old. About 44 percent of the coal produced in the United States is sub-bituminous.Bituminous coal contains 45-86 percent carbon, and has two to three times the heating value of lignite. Bituminous coal was formed under high heat and pressure. Bituminous coal in the United States is between 100 to 300 million years old. It is the most abundant rank of coal found in the United States, accounting for about half of U.S. coal production. Bituminous coal is used to generate electricity and is an important fuel and raw material for the steel and iron industries.Anthracite contains 86-97 percent carbon, and has a heating value slightly lower than bituminous coal.  

Coking and use of coke

Coke is a solid carbonaceous residue derived from low-ash, low-sulfur bituminous coal from which the volatile constituents are driven off by baking in an oven without oxygen at temperatures as high as 1,000 °C (1,832 °F) so that the fixed carbon and residual ash are fused together. Metallurgic coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Coke from coal is grey, hard, and porous and has a heating value of 24.8 million Btu/ton (29.6 MJ/kg). Some coke-making processes produce valuable by-products that include coal tar, ammonia, light oils, and "coal gas".

Petroleum coke is the solid residue obtained in oil refining, which resembles coke but contains too many impurities to be useful in metallurgical applications.

Gasification

Coal gasification can be used to produce syngas, a mixture of carbon monoxide (CO) and hydrogen (H2) gas. This

syngas can then be converted into transportation fuels like gasoline and diesel through the Fischer-Tropsch process. Currently, this technology is being used by the Sasol chemical company of South Africa to make gasoline from coal and natural gas. Alternatively, the hydrogen obtained from gasification can be used for various purposes such as powering a hydrogen economy, making ammonia, or upgrading fossil fuels.

During gasification, the coal is mixed with oxygen and steam (water vapor) while also being heated and pressurized. During the reaction, oxygen and water molecules oxidize the coal into carbon monoxide (CO) while also releasing hydrogen (H2) gas. This process has been conducted in both underground coal mines and in coal refineries.

(Coal) + O2 + H2O → H2 + CO

If the refiner wants to produce gasoline, the syngas is collected at this state and routed into a Fischer-Tropsch reaction. If hydrogen is the desired end-product, however, the syngas is fed into the water gas shift reaction where more hydrogen is liberated.

CO + H2O → CO2 + H2

High prices of oil and natural gas are leading to increased interest in "BTU Conversion" technologies such as gasification, methanation and liquefaction.

In the past, coal was converted to make coal gas, which was piped to customers to burn for illumination, heating, and cooking. At present, the safer natural gas is used instead.

Liquefaction - Coal-To-Liquids (CTL)

Coals can also be converted into liquid fuels like gasoline or diesel by several different processes. In the direct liquefaction processes, the coal is either hydrogenated or carbonized. Alternatively, coal can be converted into a gas first, and then into a liquid, by using the Fischer-Tropsch process.

In the Bergius process, coal is liquefied by mixing it with hydrogen gas and heating the system (hydrogenation). This process was used by Germany during World War I and World War II and has been explored by SASOL in South Africa. Another hydrogenation process which was patented by Wilburn C. Schroeder in 1976. The process involved dried, pulverized coal mixed with roughly 1wt% molybdenum catalysts. Hydrogenation occurred by use of high temperature and pressure synthesis gas produced in a separate gasifier. The process ultimately yielded a synthetic crude product, Naphtha, a limited amount of C3/C4 gas, light-medium weight liquids (C5-C10) suitable for use as fuels, small amounts of

NH3 and significant amounts of CO2.

The process of low temperature carbonization (LTC) can also convert coal into a liquid fuel. Coal is coked at temperatures between 450 and 700°C compared to 800 to 1000°C for metallurgical coke. These temperatures optimize the production of coal tars richer in lighter hydrocarbons than normal coal tar. The coal tar is then further processed into fuels.

In the Fischer-Tropsch process, an indirect route, coal is first gasified to make syngas (a balanced purified mixture of CO and H2 gas). Next, Fischer-Tropsch catalysts are used to convert the syngas into light hydrocarbons (like ethane) which

are further processed into gasoline and diesel. This method was used on a large technical scale in Germany between 1934 and 1945 and is currently being used by Sasol in South Africa. In addition to creating gasoline, syngas can also be converted into methanol, which can be used as a fuel, or into a fuel additive.

Refined Coal

Refined coal is the product of a coal upgrading technology that removes moisture and certain pollutants from lower-rank coals such as sub-bituminous and lignite (brown) coals. It is one form of several pre-combustion treatments and processes for coal that alter coal's characteristics before it is burned. The goals of pre-combustion coal technologies are to increase efficiency and reduce emissions when the coal is burned. Depending on the situation, pre-combustion technology can be used in place of or as a supplement to post-combustion technologies to control emissions from coal-fueled boilers.

Environmental effects of coal

Environmental effects

There are a number of adverse environmental effects of coal mining and burning, specially in power stations.

These effects include:

•release of carbon dioxide and methane, both of which are greenhouse gases, which are causing climate change and

global warming. Coal is the largest contributor to the human-made increase of CO2 in the air.

•generation of hundred of millions of tons of waste products, including fly ash, bottom ash, flue gas desulfurization

sludge, that contain mercury, uranium, thorium, arsenic, and other heavy metals

•acid rain

•interference with groundwater and water table levels

•impact of water use on flows of rivers and consequential impact on other land-uses

•dust nuisance

•subsidence above tunnels, sometimes damaging infrastructure

•rendering land unfit for other uses

•coal-fired power plants without effective fly ash capture are one of the largest sources of human-caused background

radiation exposure

•coal-fired power plants shorten nearly 24,000 lives a year, including 2,800 from lung cancer.

•coal-fired power plant releases emissions including mercury, selenium, and arsenic which are harmful to human

health and the environment.

Underground fires

There are hundreds of coal fires burning around the world. Those burning underground can be difficult to locate and many cannot be extinguished. Fires can cause the ground above to subside, their combustion gases are dangerous to life, and breaking out to the surface can initiate surface wildfires. Coal seams can be set on fire by spontaneous combustion or contact with a mine fire or surface fire. A grass fire in a coal area can set dozens of coal seams on fire. Coal fires in China burn 109 million tons of coal a year, emitting 360 million metric tons of CO 2. The Australian

Burning Mountain was originally believed to be a volcano, but the smoke and ash comes from a coal fire which may have been burning for over 5,500 years.

Energy value of coalThe energy value of coal, or the fuel content, is the amount of potential energy in coal that can be converted into actual heating ability. The value can be calculated and compared with different grades of coal or even other materials. Materials of different grades will produce differing amounts of heat for a given mass.

The calorific value Q of coal is the heat liberated by its complete combustion with oxygen. Q is a complex function of the elemental composition of the coal. Q can be determined experimentally using calorimeters. Dulong suggests the following approximate formula for Q when the oxygen content is less than 10%:

Q = 337C + 1442(H - O/8) + 93S,

where C is the mass percent of carbon, H is the mass percent of hydrogen, O is the mass percent of oxygen, and S is the mass percent of sulfur in the coal. With these constants, Q is given in kilojoules per kilogram.

Coal assayCoal assay techniques are specific analytical methods designed to measure the particular physical and chemical properties of coals. These methods are used primarily to determine the suitability of coal for coking, power generation or for iron ore smelting in the manufacture of steel.

Important Properties of CoalThe most important properties of coal to the combustion engineer are as follows:

· Proximate analysis - to determine the moisture, ash, volatile matter and fixed carbon· Ultimate or elementary analysis - to determine the elemental composition of the coal· Calorific value · Caking properties - for bituminous coals only· Grindability - where the coal is to be pulverised

Proximate and Ultimate analysisProximate analysis is the simpler of the tests and is used to determine the moisture, ash, volatile and fixed carbon content. Ultimate analysis is used to determine the elemental composition in terms of Carbon, Hydrogen, Sulphur, Nitrogen and Oxygen by difference.

The percentages can be reported by weight in a variety of different ways:

As sampled (as received) - exactly as the sample came to the labDry - based on the air dried sample (not completely dried)Dry, Ash free - based on the air dried sample with ash removedDry, Mineral Matter Free (DMMF) - based on the air dried sample with all mineral (inorganic) matter removed

MoistureMoisture is an important property of coal, as all coals are mined wet. Groundwater and other extraneous moisture is known as adventitious moisture and is readily evaporated. Moisture held within the coal itself is known as inherent moisture and is analysed. Moisture may occur in four possible forms within coal:

•Surface moisture: water held on the surface of coal particles or macerals •Hydroscopic moisture: water held by capillary action within the microfractures of the coal •Decomposition moisture: water held within the coal's decomposed organic compounds •Mineral moisture: water which comprises part of the crystal structure of hydrous silicates such as clays Total moisture is analysed by loss of mass between an untreated sample and the sample once analysed. This is achieved by any of the following methods;

1.Heating the coal with toluene 2.Drying in a minimum free-space oven at 150 °C (300 °F) within a nitrogen atmosphere 3.Drying in air at 100 to 105 °C (210 to 220 °F) and relative loss of mass determined Methods 1 and 2 are suitable with low-rank coals but method 3 is only suitable for high-rank coals as free air drying low-rank coals may promote oxidation. Inherent moisture is analysed similarly, though it may be done in a vacuum.

Volatile matter

Volatile matter in coal refers to the components of coal, except for moisture, which are liberated at high temperature in the absence of air. This is usually a mixture of short and long chain hydrocarbons, aromatic hydrocarbons and some sulfur. The volatile matter of coal is determined under rigidly controlled standards. In Australian and British laboratories this involves heating the coal sample to 900 ± 5 °C (1650 ±10 °F) for 7 minutes in a cylindrical silica crucible in a muffle furnace. American Standard procedures involve heating to 950 ± 25 °C (1740 ± 45 °F) in a vertical platinum crucible. These two methods give different results and thus the method used must be stated.

Ash

Ash content of coal is the non-combustible residue left after coal is burnt. It represents the bulk mineral matter after carbon, oxygen, sulfur and water (including from clays) has been driven off during combustion. Analysis is fairly straightforward, with the coal thoroughly burnt and the ash material expressed as a percentage of the original weight.

Fixed carbon

The fixed carbon content of the coal is the carbon found in the material which is left after volatile materials are driven off. This differs from the ultimate carbon content of the coal because some carbon is lost in hydrocarbons with the volatiles. Fixed carbon is used as an estimate of the amount of coke that will be yielded from a sample of coal. Fixed carbon is determined by removing the mass of volatiles determined by the volatility test, above, from the original mass of the coal sample.

Chemical analysis

Coal is also assayed for oxygen content, hydrogen content and sulfur. Sulphur is also analysed to determine whether it is a sulfide mineral or in a sulfate form. This is achieved by dissolution of the sulfates in hydrochloric acid and precipitation as barium sulfate. Sulfide content is determined by measurement of iron content, as this will determine the amount of sulfur present as iron pyrite.Carbonate minerals are analysed similarly, by measurement of the amount of carbon dioxide emitted when the coal is treated with hydrochloric acid. Calcium is analysed. The carbonate content is necessary to determine the combustible carbon content and incombustible (carbonate carbon) content.Chlorine, phosphorus and iron are also determined to characterise the coal's suitability for steel manufacture.

Ash fusion testThe behaviour of the coal's ash residue at high temperature is a critical factor in selecting coals for steam power generation. Most furnaces are designed to remove ash as a powdery residue. Coal which has ash that fuses into a hard glassy slag known as clinker is usually unsatisfactory in furnaces as it requires cleaning. However, furnaces can be designed to handle the clinker, generally by removing it as a molten liquid.Ash fusion temperatures are determined by viewing a moulded specimen of the coal ash through an observation window in a high-temperature furnace. The ash, in the form of a cone, pyramid or cube, is heated steadily past 1000 °C to as high a temperature as possible, preferably 1600 °C (2900 °F). The following temperatures are recorded;•Deformation temperature: This is reached when the corners of the mould first become rounded •Softening (sphere) temperature: This is reached when the top of the mould takes on a spherical shape. •Hemisphere temperature: This is reached when the entire mould takes on a hemisphere shape •Flow (fluid) temperature: This is reached when the molten ash collapses to a flattened button on the furnace floor.

Crucible swelling index (free swelling index)The simplest test to evaluate whether a coal is suitable for production of coke is the free swelling index test. This involves heating a small sample of coal in a standardised crucible to around 800 degrees Celsius (1500°F). After heating for a specified time, or until all volatiles are driven off, a small coke button remains in the crucible. The cross sectional profile of this coke button compared to a set of standardised profiles determines the Free Swelling Index.

Caking Properties of Coals

This is a unique property of coals in the bituminous group of coals and is an essential property for coals which are required for coking. As a caking coal is heated it passes through a region where it becomes very plastic, softens, swells and then re-solidifies. The residue is a cellular coke mass. Coals which do not cake simply form a non coherent or weakly coherent char.

The caking behaviour is critical to coke making. A successful coke must be strong and not powdery.

Grindability

This is particularly important if a coal is to be burnt in the pulverised state. In this case, significant work must be done in order to reduce the coal down to particles of sufficient size for combustion. The Hardgrove grindability index is calculated by applying a standard amount of work on a sample of coal and determining the increase in surface area. 

Coal CleaningCoal cleaning is a process by which impurities such as sulfur, ash, and rock are removed from coal to upgrade its value. Coal cleaning processes are categorized as either physical cleaning or chemical cleaning. Physical coal cleaning processes, the mechanical separation of coal from its contaminants using differences in density, are by far the major processes in use today. Chemical coal cleaning processes are currently being developed, but their performance and cost are undetermined at this time. Therefore, chemical processes are not included in this discussion.

Diagram of froth flotation cell. Numbered triangles show direction of stream flow. A mixture of ore and water called pulp [1] enters the cell from a conditioner, and flows to the bottom of the cell. Air [2] or nitrogen is passed down a vertical impeller where shearing forces break the air stream into small bubbles. The mineral concentrate froth is collected from the top of the cell [3], while the pulp [4] flows to another cell.

Elements of a conventional flotation cell

THE MANUFACTURE OF COKE

Coke is manufactured from the carbonisation of prime coking coals. Carbonisation is performed for three main reasons: To make a smokeless fuel for domestic/industrial applications: to provide a coke for some other process (most importantly blast furnaces); to produce a combustible gas. However other important products are formed including coal tar which in the past was a very important chemical feedstock.

Raising the temperature of coking coals in the absence of oxygen results in their devolatilisation and the formation of a solid fuel, coke, which has a porous structure. Two types of coke can be made, hard and soft. The difference is in the temperature of carbonisation. Soft coke is carbonised at lower temperatures 600-700C. This results in a product with a reduced volatile content of the order 9% and hence better combustion characteristics.

Hard coke is carbonised at higher temperatures and resulting in devolatilisation and loss of porosity. Combustion characteristics are reduced making these cokes only suitable for more specialist purposes such as manufacture of carbon electrodes or in blast furnaces.

High Temperature Carbonisation of coal 

Coking process is the most important aspect to make comprehensive usage of coal. It shows that coal gets carbonized and becomes coke under high temperature with generation of coke oven gas and various chemical products. A coking plant mainly comprises of coal preparation, coking, coke quenching and screening, and gas purification, etc.

Coal Preparation It is the preparation stage of coking. This stage includes coal receiving, blending, crushing and mixing. Coal is stored in coal yard separately as per different categories and delivered to different coal blending hoppers by belt conveyor. Several categories of coal will be proportioned in blending hopper, then, crushed and mixed in crushing house and delivered to coal tower.

Coking is the process of blended coal being carbonized under high temperature in carbonization chambers to produce coke and crude gas. The process is composed of coal stamping, charging, coking, coke discharging. After stamping, formed cake will be charged to the carbonization chamber by charging car for softening, melting, solidification, shrinkage, and then forms coke. The final coke will be pushed out of the carbonization chambers by pushing and charging car and transfer to the next stage treatment. Abundant crude gas produced during carbonization process will be cooled down to around 830C at high line by spraying ammonia water and then via header delivered to gas purification shop for treatment.

Quenching & Screening Temperature for carbonization chamber is around 10000C. Wet quenching method is the most popular method to be used at present. Hot coke will be delivered to quenching tower, cooling water will quench and cool down coke to environment temperature, then it will be discharged onto wharf and remained for 30 minutes, then delivered to screening tower. After screening, coke grade will meet client requirement. Cold Condensation & Air Blowing Temperature of crude gas in the header is around 830C. It is mingled with abundant tar and gas. To facilitate the utility and delivery, crude gas needs to be cooled down to 250C. Tar and ammonia water are condensed and drawn out. In order to induce crude gas from coke oven smoothly and maintain gas pressure which is required by the sequential process of coal gas purification, cooled gas needs to be pressurized by compressor. Pressurized coal gas will be brought to desulphurization section for desulphurization treatment. ●     Equipment in this section is mainly composed of cooler, electrical tar trapper, air blower.●     Main product: Tar

DesulphurizationThe content of sulfur in gas shall be de-sulfured below 200mg/m³ to meet the requirements of gas users and recovering consequent chemical products. Presently, wet-type oxidation desulphurization process is adopted, which was widely accepted with the following salient features: Green, Compact, and Easy operation, High efficient desulphurization, etc. In addition, sulfur will be produced in the section of desulphurization, which can be used to produce sulfuric acid. ●     The major equipment of desulphurization section shows as follows: Desulphurization tower, Regenerating tower, Ammonia vaporizing tower ●     Main product: sulfur Sulfur-Ammonium SectionThe content of ammonia in  gas shall be purified below 100mg/m³  to meet the requirements of gas users and gas transportation. Presently, there are two widely adopted and applied technologies: sulfur-ammonium process and ammonia decomposition process. However, the former one  is more widely used, due to the reason that it can produce sulfur-ammonium products with low cost, and it is more economic and practicable. The principle of sulfur-ammonium process is to use sulfuric acid to absorb  ammonia in the gas, and then produce sulfur-ammonium products. ● The major equipment of sulfur-ammonium section :   saturator ●     Main product: ammonium sulfate Benzene ScrubbingBenzene is an important chemical material, which has high economic value. Benzene Scrubbing means to use washing oil (tar or petroleum) to absorb  benzene in  gas. After passing through scrubbing tower, benzene can be separated and made into semi-finished benzene products, which can be further refined or for sale Washing oil can be recycled  after benzene scrubbing . ●     The major equipment of washing-removing benzene section shows as follows: Benzene scrubbing tower, Benzene removing tower. ●     Main products: semi-finished benzene products, pure gas. Crude gas from coke oven can be purged into high caloric coke oven gas after purification process and chemical products recovering. It can be used for both industrial and civil usage, and can also be sent to chemical plant as  materials of chemical synthesis.

The main steps in the coal carbonisation process

Bituminous coal was crushed and fed to the retort, where high temperatures carbonised the coal to produce gas and coke. 

The coke was sold or used to manufacture 'producer gas' that provided heat for the coal carbonisation process. 

To remove impurities, the raw gas (containing tars and other by-products) was: scrubbed with weak ammonia liquor in the hydraulic and foul mains cooled in the primary condenser blown through the exhauster treated by the tar extractor to remove tars from the gas scrubbed to remove ammonia from the gas diverted through iron oxide purifiers to remove hydrogen sulfide and other impurities, including cyanide.

The purified gas was metered, stored and distributed to consumers. Tars and condensates collected during gas production were combined and fed to a tar-liquid separator. Weak ammonia liquor was separated from the tar. The tar was either processed further, recycled as an alternative fuel, or sold as raw coal tar.

Dry Charcoal

Charcoal burning

Wood pile before covering it by turf or soil, and firing it (around 1890)

Modern charcoal retorts

Charcoal

Charcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen. The resulting soft, brittle, lightweight, black, porous material resembles coal and is 85% to 98% carbon with the remainder consisting of volatile chemicals and ash.

Historically, production of wood charcoal in districts where there is an abundance of wood dates back to a very ancient period, and generally consists of piling billets of wood on their ends so as to form a conical pile, openings being left at the bottom to admit air, with a central shaft to serve as a flue. The whole pile is covered with turf or moistened clay. The firing is begun at the bottom of the flue, and gradually spreads outwards and upwards. The success of the operation depends upon the rate of the combustion. Under average conditions, 100 parts of wood yield about 60 parts by volume, or 25 parts by weight, of charcoal; small scale production on the spot often yields only about 50%, large scale was efficient to about 90% even by the 17th century.

The modern process of carbonizing wood, either in small pieces or as sawdust in cast iron retorts, is extensively practiced where wood is scarce, and also for the recovery of valuable byproducts (wood spirit, pyroligneous acid, wood tar), which the process permits. The question of the temperature of the carbonization is important; according to J. Percy, wood becomes brown at 220 °C, a deep brown-black after some time at 280 °C, and an easily powdered mass at 310 °C. Charcoal made at 300° is brown, soft and friable, and readily inflames at 380 °C; made at higher temperatures it is hard and brittle, and does not fire until heated to about 700 °C.

Types of charcoalCommercial charcoal is found in either lump, briquette, or extruded forms:

•Lump charcoal is made directly from hardwood material and usually produces far less ash than briquettes. •Briquettes are made by compressing charcoal, typically made from sawdust and other wood by-products, with a binder and other additives. The binder is usually starch. Some briquettes may also include brown coal (heat source), mineral carbon (heat source), borax, sodium nitrate (ignition aid), raw sawdust (ignition aid), and other additives like paraffin or petroleum solvents to aid in ignition. •Extruded charcoal is made by extruding either raw ground wood or carbonized wood into logs without the use of a binder. The heat and pressure of the extruding process hold the charcoal together. If the extrusion is made from raw wood material, the extruded logs are then subsequently carbonized.

UsesOne of the most important historical applications of wood charcoal was as a constituent of gunpowder. It was also used in metallurgical operations as a reducing agent, but its application has been diminished by the introduction of coke, anthracite smalls, etc. For example, charcoal may be used to smelt a variety of metals from aluminum to copper as it burns at the necessary temperature (2000 degrees Fahrenheit/1100 degrees Celsius). A limited quantity is made up into the form of drawing crayons; but the greatest amount is used as a fuel, which burns hotter and cleaner than wood. Charcoal is often used by blacksmiths, for cooking, and for other industrial applications.

Purification/FiltrationThe porosity of activated charcoal accounts for its ability to readily adsorb gases and liquids ; charcoal is often used to filter water or adsorb odors. Its pharmacological action depends on the same property; it adsorbs the gases of the stomach and intestines, and also liquids and solids (hence its use in the treatment of certain poisonings). Charcoal filters are used in some types of gas mask to remove poisonous gases from inhaled air. Wood charcoal also to some extent removes coloring material from solutions, but animal charcoal is generally more effective.Animal charcoal or bone black is the carbonaceous residue obtained by the dry distillation of bones; it contains only about 10% carbon, the remainder being calcium and magnesium phosphates (80%) and other inorganic material originally present in the bones. It is generally manufactured from the residues obtained in the glue and gelatin industries.

Typical Coalbed Methane Well

Coalbed methane (CBM) is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy in United States, Canada, and other countries. Australia has rich deposits where it is known as coal seam gas.

Also called coalbed gas, the term refers to methane adsorbed into the solid matrix of the coal. It is called 'sweet gas' because of its lack of hydrogen sulfide. The presence of this gas is well known from its occurrence in underground coal mining, where it presents a serious safety risk. Coalbed methane, often referred to as CBM, is distinct from a typical sandstone or other conventional gas reservoir, as the methane is stored within the coal by a process called adsorption. The methane is in a state lining the inside of pores within the coal (called the matrix). The open fractures in the coal (called the cleats) can also contain free gas or can be saturated with water.Unlike much natural gas from conventional reservoirs, coalbed methane contains very little heavier hydrocarbons such as propane or butane, and no natural gas condensate. It often contains up to a few percent carbon dioxide.

Permeability of coal bed methane reservoirsPermeability is key factor for CBM. Coal itself is a low permeability reservoir. Almost all the permeability of a coal bed is usually considered to be due to fractures, which in coal are in the form of cleats. The permeability of the coal matrix is negligible by comparison. Coal cleats are of two types: butt cleats and face cleats, which occur at nearly right angles. The face cleats are continuous and provide paths of higher permeability while butt cleats are non-continuous and end at face cleats. Hence, on a small scale, fluid flow through coal bed methane reservoirs usually follows rectangular paths. Porosity of coal bed reservoirs is usually very small ranging from 0.1 to 10%.

Adsorption capacityAdsorption capacity of coal is defined as the volume of gas adsorbed per unit mass of coal usually expressed in SCF (standard cubic feet, the volume at standard pressure and temperature conditions) gas/ton of coal. The capacity to adsorb depends on the rank and quality of coal. The range is usually between 100 to 800 SCF/ton for most coal seams found in the US. Most of the gas in coal beds is in the adsorbed form. When the reservoir is put into production, water in the fracture spaces are drained first. This leads to a reduction of pressure enhancing desorption of gas from the matrix.

ExtractionTo extract the gas, a steel-encased hole is drilled into the coal seam (100 - 1500 meters below ground). As the pressure within the coal seam declines, due to the hole to the surface or the pumping of small amounts of water from the coalbed, both gas and 'produced water' escape to the surface through tubes. Then the gas is sent to a compressor station and into natural gas pipelines. The 'produced water' is either reinjected into isolated formations, released into streams, used for irrigation, or sent to evaporation ponds. The water typically contains dissolved solids such as sodium bicarbonate and chloride.

As production occurs from a coal reservoir, the changes in pressure are believed to cause changes in the porosity and permeability of the coal. This is commonly known as matrix shrinkage/swelling. As the gas is desorbed, the pressure exerted by the gas inside the pores decreases, causing them to shrink in size and restricting gas flow through the coal. As the pores shrink, the overall matrix shrinks as well, which may eventually increase the space the gas can travel through (the cleats), increasing gas flow.

The gas composition must be considered, because natural gas appliances are designed for gas with a heating value of about 1000 BTU per cubic foot, or nearly pure methane. If the gas contains more than a few percent non-flammable gasses such as nitrogen or carbon dioxide, it will have to be blended with higher-BTU gas to achieve pipeline quality. If the methane composition of the coalbed gas is less than 92%, it may not be commercially marketable.

Environmental impactsCBM wells are connected by a network of roads, pipelines, and compressor stations. These structures can compromise the scenic quality of the landscape, fragment wildlife habitat, and displace local wildlife populations . Over time, wells may be spaced more closely in order to extract the remaining methane. Additionally, the produced water may contain undesirable concentrations of dissolved substances. Water withdrawal may depress aquifers over a large area and affect groundwater flows.

In Australia, produced water is typically evaporated in large ponds due to the high salinity of the water. Recently a number of gas companies have commenced operating or developing plant to treat the product water for use as domestic supply, cooling water for power stations or discharge to streams. These plant typically use reverse osmosis to treat the product water.