1.2 Coal Technology Industry.pdf

Chemical Process Technology CPT150X Coal Technology Lecturer: Dr Debbie De Jager 2024  Mining Preparation for blasting at an A Sasol Mining initiators- Underground mining open-cast mine using explosive develo...

Chemical Process Technology CPT150X Coal Technology Lecturer: Dr Debbie De Jager 2024  Mining Preparation for blasting at an A Sasol Mining initiators- Underground mining open-cast mine using explosive developed electronic initiation accessories system Coal plants Alpha olefins distillation columns at Secunda Sasol Olefin octene plant (Secunda) Coal formation link  Classification of coal Material Carbon content Graphite 100% Anthracite 90-95% Bituminous 80-90% Lignite ±70% Peat ±60% Bituminous Coal Anthracite Coal  Coal Processing Coal is not pure carbon. It is a mixture of a large # of complex organic compounds. On heating strongly in the absence of air, coal produces many useful products. Destructive distillation of coal (cf. fractional distillation) Coal is thermally pyrolysed by heating without contact with air and converted into a variety of solids, liquid and gases. The process entails the "cracking" (breaking up) of macromolecules into smaller, more volatile components such as coke, charcoal, oils, and gases. Main products: coke (solid), coal tar (liquid), coal gas (gas) Low-temp carbonisation (450 – 700 °C): more liquid, less gas. Liquids such as tar acids & bases [coal used: lignite, bituminous and sub-bituminous] High-temp carbonisation (900 °C): more gases (hydrogen, methane, ethylene, CO etc), less liquid (water and crude light) Carbonisation (conversion) takes place in steps 1. Initiation stage: C-C bonds broken with T°C. 2. C-H bonds broken @ T°C ≤ 600°C. 3. Elimination of heterocycle complexes & progressive aromatization. 4. Average mol. weight of volatile intermediate products decrease with an increase in temperature. 5. Final decomposition between 600 and 800°C.  Coke Largest product from destructive distillation Coal is converted to coke by driving off impurities to leave almost pure carbon. Coking coal must be low-ash, low-sulfur bituminous coal and also have low phosphorous content. The physical properties of coking coal cause the coal to soften, liquefy and then resolidify into hard but porous lumps when heated in the absence of air. Global steel production is dependent on coal. Metallurgical coal – or coking coal – is a vital ingredient in the steel making process. Coke is used mainly to smelt iron ore and other iron bearing materials in blast furnaces, acting both as a source of heat and a chemical reducing agent, to produce pig iron, or hot metal.  Coking of coal Beehive, main product is coke [OBSOLETE]. By-product (also known as co-product) produces coke and a large variety of coal chemicals (e.g. tar, ammonia, benzole, naphthalene etc). The coking process consists of heating coking coal to around 1000-1100 °C in the absence of oxygen to drive off the volatile compounds (pyrolysis). This process results in a hard porous material - coke. In coking of coals, the particles fuse together, coalescing to form a coherent mass called coke. Coke is produced in a coke battery which is composed of many coke ovens stacked in rows into which coal is loaded.  Coking ovens Beehive coking ovens By-product coking ovens One of the most elaborate and costly structures and is erected with attention to engineering detail. Ovens are used for the carbonisation of coal. By-product coking of coal Ovens are built in batteries of 10 – 100 ovens. Individual ovens operate intermittently, each oven started and stopped at different times so that operation continuously produce gas. Ovens have to withstand severe strain in their use and must remain gas-tight. Narrow chambers: ±11-12m long, 0.5m wide and 5m high. Ovens hold ±15-25 tons of coal. Finely crushed coal dropped through charging holes on top of the ovens and left in the oven until the evolution of volatiles stops. Walls ±1100°C and centre ±980°C. Average flue gas temperature ±1290°C. Flue gases are reused. Gas and entrained liquid passes upward to a steel pipe (hydraulic main) connected to all the ovens in a series. Temp. vary with operating conditions, coking time, oven width, type of coal, moisture content, size. Operated to produce best quality coke for steel mills.  Coke At the end, red-hot mass is pushed out of the oven. Coke falls into a quenching car. Once pushed out of the vessel the hot coke is then quenched with either water or air to cool it before storage or is transferred directly to the blast furnace for use in iron making.  Coal tar Coal tar is a by-product from the destructive distillation of coal. Quantity and quality vary depending on rate of production of the ovens and nature of coal. Mixture of many chemicals, mostly aromatics Black oily material resulting from the destructive distillation of bituminous coal. The fractional distillation of coal tar yields light oil, middle oil, heavy oil, and anthracene oil. The residue from this process is called pitch.  Coke oven gas Is a by-product from the destructive distillation of bituminous coal. Composition ±55-66% H2 ±20-30% CH4 Including N2, CO2, high paraffins and unsaturated hydrocarbons (e.g. ethane, propane etc.) and O2. Coke oven gas has a heating value of about 20,000 kJ/m3. Normally used in the heating of coke oven battery’s, heating in other furnaces of the steel plant and for power generation. Can potentially be used to produce other chemicals (e.g. ammonia) or recycled into hydrogen. Coal gasification and liquefaction Most reactions start by converting coal to CO and H2. CTG = Coal-To-Gas GASIFICATION: Steam is passed over hot coal to obtain a fuel gas called synthesis gas (i.e. syngas) composed of a mixture of CO2, CO, H2, CH4 and water vapour. This can be transformed by various methods into useful products (e.g. CH4). CTL = Coal-To-Liquids LIQUEFACTION (indirect/direct): Indirect liquefaction involves the gasification of coal to syngas. Using the Fischer–Tropsch process, syngas is converted into liquid hydrocarbons. [SASOL] Direct liquefaction converts coal directly into liquids directly. Coal gasification and liquefaction  Synthesis gas (Syngas) Syngas is a CO-H2 mixture produced by either: 1. Gasification of organic material like coal and biomass, or 2. Steam reforming of natural gas. Producer Gas Syngas Coal or coke Coal Air (O2 + N2) O2 Steam Steam H2, CH4, CO, CO2 and N2 Mainly H2 and CO Sasolburg: Sasol (South African Coal, Oil & Gas Corporation) Sasol Secunda Synthetic fuel plant  Sasol Gas production Sasol produces synthesis gas from low-grade coal. Feedstock for the FT conversion processes. Process starts in the gasification plant where coal under pressure and at high temperature in the presence of steam and oxygen is converted into crude gas. After cooling, the gasification condensates yield co-products such as tars, oils and pitches. Other co-products, such as nitrogenous compounds, sulphur and phenolics are recovered as ammonia, sulphur, cresols and phenols respectively, with the pitch being converted into coke in the anode coke plant. The purified synthesis feed gas is then available for conversion to automotive fuels and oils, as well as a range of petrochemical compounds. Sasol Technologies and Processes Proprietary GTL Fischer-Tropsch (FT) technology is at the heart of Sasol's innovative advances into new frontiers. With the start-up of Oryx GTL in Qatar, Sasol operates three proprietary and distinct types of FT processes, namely; 1. Low temperature cobalt, for Oryx GTL fuels production; 2. Low temperature iron, for Sasolburg wax and chemicals production; and 3. High temperature iron, for Secunda fuels and chemicals production. Sasol GTL Process Sasol Process