There's also newer integrated gasification combined cycle IGCC technology, which sends the gas through a combustion turbine to generate electricity, and then routes excess heat from that process to generate even more electricity through a traditional steam turbine.
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In either process there are multiple points at which CCS technology could intervene. One such point is called pre-combustion. At this stage, an air separation unit produces a stream of almost-pure oxygen, which flows into a coal gasifier. Gasifiers are essentially tanks that produce synthetic gas mixtures known as syngas. The oxygen in this coal gasifier reacts with fuel to create a syngas made up of hydrogen, carbon monoxide, water, and CO2.
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This form of syngas is nothing new: invented in the s by William Murdoch , in the 19th century it was used to power gas lights in many towns and gained the nickname "town gas. CCS technology sends the syngas to a shift reactor, where it encounters steam. That steam transforms the carbon monoxide that's present into hydrogen and even more CO2.
The CO2 is then captured from the gas stream, compressed, and dehydrated. That leaves it ready for transport and storage. Ideal spots for this include old oil and gas fields, which have already dug into the earth, but any deep saline formation, filled with porous rock and salty water, will do. Ships could also send the CO2 to refineries in the ocean. The idea is that the CO2 stays there for millions of years and eventually chemically binds with the surrounding rock. The technology can also be used post-combustion and with oxygen-based fuel. Post-combustion uses a solvent to bind with CO2, which then drives it off into storage.
That plant, Petra Nova , is the world's first post-combustion plant and is about 30 miles southwest of Houston, where it captures 1. The question is mostly one of cost and efficiency. CCS plants are expensive to build and maintain, and retrofitting the technology onto older plants requires an increase in power and costs.
That number goes up to 38 if you include projects under construction or in developmental planning, which takes some time. The only way costs can decrease is by installing a large number of CCS projects worldwide. However, the high cost of CCS is challenging project development.
Carbon and Coal Gasification
The evolution of electric lighting made available from public supply extinguished the gas light, except where colour matching was practised as in haberdashery shops. During gasification, the coal is blown through with oxygen and steam water vapor while also being heated and in some cases pressurized. If the coal is heated by external heat sources the process is called "allothermal", while "autothermal" process assumes heating of the coal via exothermal chemical reactions occurring inside the gasifier itself. It is essential that the oxidizer supplied is insufficient for complete oxidizing combustion of the fuel.
During the reactions mentioned, oxygen and water molecules oxidize the coal and produce a gaseous mixture of carbon dioxide CO 2 , carbon monoxide CO , water vapour H 2 O , and molecular hydrogen H 2. Some by-products like tar, phenols, etc. This process has been conducted in-situ within natural coal seams referred to as underground coal gasification and in coal refineries.
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The desired end product is usually syngas i. If the refiner wants to produce alkanes i.
If, however, hydrogen is the desired end-product, the coal gas primarily the CO product undergoes the water gas shift reaction where more hydrogen is produced by additional reaction with water vapor:. Although other technologies for coal gasification currently exist, all employ, in general, the same chemical processes. For low-grade coals i.
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As well, some coal gasification technologies do not require high pressures. Some utilize pulverized coal as fuel while others work with relatively large fractions of coal. Gasification technologies also vary in the way the blowing is supplied. In this case the oxidizer passes through coke and more likely ashes to the reaction zone where it interacts with coal. The hot gas produced then passes fresh fuel and heats it while absorbing some products of thermal destruction of the fuel, such as tars and phenols.
Thus, the gas requires significant refining before being used in the Fischer-Tropsch reaction. Products of the refinement are highly toxic and require special facilities for their utilization. As a result, the plant utilizing the described technologies has to be very large to be economically efficient. It was built due to embargo applied to the country preventing it from importing oil and natural gas.
RSA is rich in Bituminous coal and Anthracite and was able to arrange the use of the well known high pressure "Lurgi" gasification process developed in Germany in the first half of 20th century. In this case there is no chemical interaction between coal and oxidizer before the reaction zone.
The gas produced in the reaction zone passes solid products of gasification coke and ashes , and CO 2 and H 2 O contained in the gas are additionally chemically restored to CO and H 2. As compared to the "direct blowing" technology, no toxic by-products are present in the gas: those are disabled in the reaction zone. The reason for reviving the interest in this type of gasification process is that it is ecologically clean and able to produce two types of useful products simultaneously or separately : gas either combustible or syngas and middle-temperature coke.
The former may be used as a fuel for gas boilers and diesel-generators or as syngas for producing gasoline, etc. Combustion of the product gas in gas boilers is ecologically cleaner than combustion of initial coal. Thus, a plant utilizing gasification technology with the "reversed blowing" is able to produce two valuable products of which one has relatively zero production cost since the latter is covered by competitive market price of the other. As the Soviet Union and its KATEKNIIUgol' ceased to exist, the technology was adopted by the individual scientists who originally developed it and is now being further researched in Russia and commercially distributed worldwide.
Industrial plants utilizing it are now known to function in Ulaan-Baatar Mongolia and Krasnoyarsk Russia. Pressurized airflow bed gasification technology created through the joint development between Wison Group and Shell Hybrid. For example: Hybrid is an advanced pulverized coal gasification technology, this technology combined with the existing advantages of Shell SCGP waste heat boiler, includes more than just a conveying system, pulverized coal pressurized gasification burner arrangement, lateral jet burner membrane type water wall, and the intermittent discharge has been fully validated in the existing SCGP plant such as mature and reliable technology, at the same time, it removed the existing process complications and in the syngas cooler waste pan and [fly ash] filters which easily failed, and combined the current existing gasification technology that is widely used in synthetic gas quench process.
It not only retains the original Shell SCGP waste heat boiler of coal characteristics of strong adaptability, and ability to scale up easily, but also absorb the advantages of the existing quench technology. Underground coal gasification UCG is an industrial gasification process, which is carried out in non-mined coal seams. It involves injection of a gaseous oxidizing agent , usually oxygen or air, and bringing the resulting product gas to the surface through production wells drilled from the surface.
The product gas can be used as a chemical feedstock or as fuel for power generation. The technique can be applied to resources that are otherwise not economical to extract. It also offers an alternative to conventional coal mining methods. Compared to traditional coal mining and gasification, UCG has less environmental and social impact, though environmental concerns exist, including the potential for aquifer contamination.
Carbon capture, utilization, and sequestration or storage is increasingly being utilized in modern coal gasification projects to address the greenhouse gas emissions concern associated with the use of coal and carbonaceous fuels. In gasification , on the other hand, oxygen is normally supplied to the gasifiers and just enough fuel is combusted to provide the heat to gasify the rest; moreover, gasification is often performed at elevated pressure. The resulting syngas is typically at higher pressure and not diluted by nitrogen, allowing for much easier, efficient, and less costly removal of CO 2.
All coal gasification-based conversion processes require removal of hydrogen sulfide H 2 S; an acid gas from the syngas as part of the overall plant configuration. Typical acid gas removal AGR processes employed for gasification design are either a chemical solvent system e.
Process selection is mostly dependent on the syngas cleanup requirement and costs. For significant capture of CO 2 from a gasification plant e. The syngas produced by the gasifiers needs to be treated through various processes for the removal of impurities already in the gas stream, so all that is required to remove CO 2 is to add the necessary equipment, an absorber and regenerator, to this process train.
In combustion applications, modifications must be made to the exhaust stack and because of the lower concentrations of CO 2 present in the exhaust, much larger volumes of total gas require processing, necessitating larger and more expensive equipment. The CO 2 will be sent by pipeline to depleted oil fields in Mississippi for enhanced oil recovery operations.
Ninety percent of the CO 2 produced will be captured using Rectisol and transported to Elk Hills Oil Field for EOR, enabling recovery of 5 million additional barrels of domestic oil per year. Plants such as the Texas Clean Energy Project which employ carbon capture and storage have been touted as a partial, or interim, solution to climate change issues if they can be made economically viable by improved design and mass production.
There has been opposition from utility regulators and ratepayers due to increased cost; and from environmentalists such as Bill McKibben , who view any continued use of fossil fuels as counterproductive. The by-products of coal gas manufacture included coke , coal tar , sulfur and ammonia ; all useful products. Dyes , medicines, including sulfa drugs, saccharin and many organic compounds are therefore derived from coal gas. Coke is used as a smokeless fuel and for the manufacture of water gas and producer gas. Coal tar is subjected to fractional distillation to recover various products, including.
Sulfur is used in the manufacture of sulfuric acid and ammonia is used in the manufacture of fertilisers. Most of them use coal as feedstock. As of large scale expansion of the coal gasification industry was occurring only in China where local governments and energy companies promote the industry to provide jobs and a market for coal. For the most part, the plants are located in remote, coal-rich areas. The central government is aware of the conflicts with environmental goals: in addition to producing a great deal of carbon dioxide, the plants use a great deal of water in areas where water is scarce.
From its original development until the wide-scale adoption of natural gas, more than 50, manufactured gas plants were in existence in the United States alone. The process of manufacturing gas usually produced a number of by-products that contaminated the soil and groundwater in and around the manufacturing plant, so many former town gas plants are a serious environmental concern, and cleanup and remediation costs are often high. In the earliest days of MGP operations, coal tar was considered a waste and often disposed into the environment in and around the plant locations.
While uses for coal tar developed by the lateth century, the market for tar varied and plants that could not sell tar at a given time could store tar for future use, attempt to burn it as boiler fuel, or dump the tar as waste. Commonly, waste tars were disposed of in old gas holders, adits or even mine shafts if present.
Over time, the waste tars degrade with phenols , benzene and other mono-aromatics — BTEX and polycyclic aromatic hydrocarbons released as pollutant plumes that can escape into the surrounding environment. Other wastes included " blue billy ",  which is a ferroferricyanide compound—the blue colour is from Prussian blue , which was commercially used as a dye. Blue billy is typically a granular material and was sometimes sold locally with the strap line "guaranteed weed free drives".
The shift to the Carburetted Water Gas process initially resulted in a reduced output of water gas tar as compared to the volume of coal tars. The advent of automobiles reduced the availability of naphtha for carburetion oil, as that fraction was desirable as motor fuel. MGPs that shifted to heavier grades of oil often experienced problems with the production of tar-water emulsions, which were difficult, time consuming, and costly to break.
The cause of tar change water emulsions is complex and was related to several factors, including free carbon in the carburetion oil and the substitution of bituminous coal as a feedstock instead of coke. The production of large volumes of tar-water emulsions quickly filled up available storage capacity at MGPs and plant management often dumped the emulsions in pits, from which they may or may not have been later reclaimed.
Even if the emulsions were reclaimed, the environmental damage from placing tars in unlined pits remained. The dumping of emulsions and other tarry residues such as tar sludges, tank bottoms, and off-spec tars into the soil and waters around MGPs is a significant factor in the pollution found at former manufactured gas plants known as "FMGPs" in environmental remediation today. Coal tar and coal tar sludges are frequently denser than water and are present in the environment as a dense non-aqueous phase liquid.
In the UK, a number of former gasworks sites have been redeveloped for residential and other uses including the Millennium Dome , being seen as prime developable land within the confines of city boundaries. Such development opportunities are now leading to problems associated with planning and the Contaminated Land Regime and have recently [ when? Coal gasification processes require controls and pollution prevention measures to mitigate pollutant emissions.
Non-slagging gasifiers produce dry ash similar to that produced by conventional coal combustion, which can be an environmental liability if the ash typically containing heavy metals is leachable or caustic, and if the ash must be stored in ash ponds. Slagging gasifiers, which are utilized at many of the major coal gasification applications worldwide, have considerable advantage in that ash components are fused into a glassy slag, capturing trace heavy metals in the non-leachable glassy matrix, rendering the material non-toxic.
This non-hazardous slag has multiple beneficial uses such as aggregate in concrete, aggregate in asphalt for road construction, grit in abrasive blasting, roofing granules, etc. Ash is formed in gasification from inorganic impurities in the coal. Some of these impurities react to form microscopic solids which can be suspended in the syngas produced by gasification. Typically coal contains anywhere from 0. These "acid gases" are removed from the syngas produced by the gasifiers by acid gas removal equipment prior to the syngas being burned in the gas turbine to produce electricity, or prior to its use in fuels synthesis.
Coal usually contains between 0.