Carbonization of Coal in Heat Recovery Coke Oven Battery Feb15

Carbonization of Coal in Heat Recovery Coke Oven Battery...

Carbonization of Coal in Heat Recovery Coke Oven Battery One of the present trends in the production of the metallurgical coke is the comeback of non-recovery ovens. The ovens are called non-recovery since the by-products are not recovered and are burnt during the process of coal carbonization. This is driven due to the less interest in by-products, smaller investment per annual ton, and better environmental performance. The development of non-recovery coke ovens took place in 1980s and 1990s. This technology arises from the classic beehive ovens which supplied since the eighteenth century the coke for the industrial revolution. The beehive ovens were manually operated, with small heat recovery, just for heating the oven. Now, non-recovery ovens are modern construction, with highly mechanized operation, and automated to a certain degree. The non-recovery ovens are called heat recovery ovens when the energy of the exit gases is recovered in the form of steam for generation of power. The schematics of the HR coke oven process are shown in Fig 1. Fig 1 Schematics of the process of a heat recovery coke oven The basis for the heat recovery (HR) coke ovens is the so called ‘Jewell-Thomson oven’. These ovens were developed in 1960 when three test ovens were successfully built at Vansant, VA. Several of these ovens are grouped together to form one battery. Gases generated by the combustion of the volatile matter are sent through the down-comers and further burnt to heat the oven bottom and sides. The hot flue gas is used for steam production and power generation. Jewell-Thomson oven is shaped with a rectangular ground area. The oven brick lining is composed of silica refractory material. Coal is charged onto the oven floor at the beginning of the cycle. The carbonization process is...

Recovery of Benzol from Coke Oven Gas Feb09

Recovery of Benzol from Coke Oven Gas...

Recovery of Benzol from Coke Oven Gas Benzol (also called as benzole) is the name normally applied in the chemical industry to a mixture of hydrocarbons of the benzene series, in which benzene itself predominates, in association with certain of its homologues and various impurities. The term is not applied to any particular mixture or quality of the liquids. The recovery of benzol from the coke oven gas implies the removal of vapours of the benzene series, and their subsequent conversion by condensation into different liquid products. The benzene series is the most important group of substances in the class of aromatic hydrocarbons.  It is the series of carbon-hydrogen compounds based on the benzene ring, with the general formula CnH2n-6, where ‘n’ is 6 or more. Examples are benzene (C6H6), toluene (C7H8), and xylene (C8H10). The members of particular interest of this series are the first three namely benzene, toluene and xylene, which at normal temperatures are clear colourless liquids having very similar properties. There are, in fact, three isomeric xylenes, or substances of the composition and molecular weight corresponding to C8H10. The first, in which the methyl groups assume the 1.2 position, is known as ortho-xylene, the 1.3 placing gives meta-xylene, and the 1.4 compound is para-xylene. These three isomers differ slightly in properties, and xylene, as commonly produced, is a mixture of all three, meta-xylene usually predominating. Benzol also known as crude benzol is a product which is produced during carbonization of coking coal. The quantity of benzol in coke oven gas varies considerably with the treatment to which the gas has been subjected during carbonization and its processing, as well as with the type of coal, and the temperature of its carbonization. If a high yield of benzol is desired, it is obviously unwise...

Recovery of Ammonia during Production of Coke from Coking Coal Jan26

Recovery of Ammonia during Production of Coke from Coking Coal...

Recovery of Ammonia during Production of Coke from Coking Coal Ammonia (NH3) is a by-product produced during the production of coke from coking coal in the by-product coke ovens. It is a constituent of the coke oven gas (COG) leaving the coke ovens, with a typical concentration in raw COG of 6 grams per normal cubic meters (g/N cum). The solubility of NH3 in water leads to its presence in the flushing liquor of coke oven battery (COB) with a typical concentration of 5 grams per litre (g/l) to 6 g/l of total NH3. Therefore, due to the net production of flushing liquor in the COB, also sometimes being referred to as excess flushing liquor, there arises a liquid stream as well as a gas stream from which NH3 is required to be removed. The quantity of excess liquor is around 12 % of the dry coal throughput, which depends on the coal moisture content. Removal of NH3 from the gas stream is a universal feature of a coke oven and by-product plant. This is because NH3, in the presence of the other COG contaminants hydrogen cyanide (HCN), hydrogen sulphide (H2S), oxygen (O2), and water, is extremely corrosive to pipelines made of carbon steel. Also, when ammonia is uncontrollably burnt in any combustion chamber, it forms nitrogen oxides (NOx) which causes air pollution. Hence, removal of NH3 from COG and liquid stream is required to be also done due to environmental reasons. The primary NH3 handling process in the coke oven and by-product plant deals with the removal and disposal of the NH3 present in the COG. However, NH3 recovery systems often include facilities to handle the NH3 arising in the excess flushing liquor. For proper understanding of how these facilities are incorporated into...

Ironmaking by Blast Furnace and Carbon di Oxide Emissions Jan14

Ironmaking by Blast Furnace and Carbon di Oxide Emissions...

Ironmaking by Blast Furnace and Carbon di Oxide Emissions It is widely recognised that carbon di-oxide (CO2) in the atmosphere is the main component influencing global warming through the green-house effect. Since 1896 the concentration of CO2 in the atmosphere has increased by 25 %. The iron and steel industry is known as an energy intensive industry and as a significant emitter of CO2. Hence, climate change is identified by the iron and steel industry as a major environmental challenge. Long before the findings of the Inter-governmental Panel on Climate Change in 2007, major producers of iron and steel recognized that long term solutions are needed to tackle the CO2 emissions from the iron and steel industry. Therefore, the iron and steel industry has been highly proactive in improving energy consumption and reducing greenhouse gas (GHG) emissions. In the present environment of the climate change, within the iron and steel industry, there is a constant drive to reduce energy costs, reduce emissions and ensure maximum waste energy re-use. In the traditional processes for producing iron and steel, emission of CO2 is inevitable, especially for the blast furnace (BF) process, which requires carbon (C) as a fuel and reducing agent to convert iron oxide to the metallic state, and hence is the main process for the generation of CO2 in an integrated iron and steel plant. Climate policy is in fact, an important driver for further development of the ironmaking technology by BF. Critically, amongst the challenges facing the BF operation is decarbonization. Significant steps have been made by the iron and steel industry to increase the thermal efficiency of the BF operation, but ultimately there is a hard limit in decarbonization, associated with the need for C as a chemical reductant. Since the 1950s,...

Coal Tar and its Distillation Processes Dec26

Coal Tar and its Distillation Processes...

Coal Tar and its Distillation Processes Coal tar, also known as crude tar, is the by-product generated during the high temperature carbonizing of coking coal for the production of the metallurgical coke in the by-product coke ovens. It is a black, viscous, sometimes semi-solid, fluid of peculiar smell, which is condensed together with aqueous ‘gas-liquor’ (ammoniacal liquor), when the volatile products of the carbonization of coking coal are cooled down. It is acidic in nature and is water insoluble. It is composed primarily of a complex mixture of condensed-ring aromatic hydrocarbons. It can contain phenolic compounds, aromatic nitrogen (N2) bases and their alkyl derivatives, and paraffinic and olefinic hydrocarbons. In the process of coal carbonization the constituents of the tar escape from the coke ovens in the form of vapour, with a little solid free carbon (C) in an extremely finely divided state. The tar is precipitated in the hydraulic main, in the condensers, and scrubbers etc., in a liquid state, at the same time as the ammoniacal liquor is formed. The tar formed in the hydraulic main is, of course, poorer in the more volatile products than that formed in the condensers and scrubbers, and is consequently much thicker than the latter. The normal yield of coal tar during the coal carbonizing process is around 4 %. Coal tar has a specific gravity normally in the range of 1.12 to 1.20, but exceptionally it can go upto 1.25. It depends on the temperature of carbonization. The lower specific gravity tars are generally produced when low carbonization temperatures are used. Viscosity of tar affected similarly. The heavier tars contain lesser benzol than the lighter tars, and more fixed carbon. The nature of the raw material and the temperature of carbonization affect the chemical composition,...

Coking Pressure Phenomena and its Influencing Factors Dec17

Coking Pressure Phenomena and its Influencing Factors...

Coking Pressure Phenomena and its Influencing Factors Coking pressure is a phenomenon which has become important because of the use of the double-heated wall, vertical, slot-type coke ovens. In the round beehive ovens as well in the heat recovery coke ovens, which are also being used for coke production, the coal can freely expand upwards and thus the swelling of the charge is accommodated by this free expansion. On the other hand, in the slot-type coke ovens, the expansion of the coal horizontally to the heated wall is restricted. There are several cases of premature failure of oven walls during the coal carbonization process. The erection of the new, larger and taller coke ovens has been accompanied by undesirable occurrences of distorted walls due to the coking pressure resulting in several studies regarding the expansion behaviour of coal during carbonization. The efforts have been focused on developing a reliable test so that coal blends can be tested for safety prior to their use in the coke ovens. Development of coking pressure During carbonization process, coal passes through the plastic stage and volatile matter (VM) evolves during and, to a lesser extent, after that stage. It is normally accepted that coking pressure arises in the plastic stage. In a coke oven chamber, two vertical plastic layers parallel to the heating walls are formed from the beginning of carbonization. As the carbonization proceeds these layers move towards the centre of the oven. At the same time, similar horizontal layers are formed at the top and bottom of the charge. These are joined with the two vertical layers and the whole forms a continuous region that surrounds the uncarbonized coal and it is usually referred to as the ‘plastic envelope’. The permeability of the plastic layers is...