We
engage ourselves in offering high performance coke plants, industrial coke
plant, coke process plant. The plant runs with coal, which is a form of
metallurgical coking coal derivative. It is the main heat-sourcing agent in
metallurgical procedure and acts as a reducing agent facilitating the
translation of metallurgical ores into metal involved in the process of
smelting. The coke we offer is produced in oven batteries of integrated
steel plants. There are numeral pig iron plants and integrated steel plants
built in India, which does not have any coke making facility. To make it
available in southern and western part of India, most of the coke is
imported from other nations. Keeping this point in notice we started to
produce met coke and for this purpose and therefore we purchase the
NON-RECOVERY COKE OVEN PROJECT of 100,000 TPA of met coke.
Introduction :| (Power Generation) is given in Figure - 1 | |
| Non Recovery Coke Oven System | By Product Recovery Coke Oven System |
| Application of heat is bi-directional for converting coal to coke from top to bottom and from bottom to top. Refer Figure-2 | Application of heat is bi-directional sideways. Refer Figure-2 |
| Typical scheme of Non recovery coke oven plant with power generation is indicated in Figure-3 | Typical scheme of By product recovery coke oven plant with power generation is indicated in Figure-3A |
| III. Other Features | |
| The oven design is capable of carbonizing coals having high V.M content is which case, coke yield will be lower for obvious reasons. Due to higher oven width and shrinkage of coal charge occurring in vertical direction. Non recovery coke ovens can accept wider base of coal types. | Due to similar width, the acceptance of types of coals is limited |
| Non recovery coke ovens are capable of producing a coke which is large, strong, dense and abrasion resistant. The coarse mosaic microstructure, low porosity, large means cell wall thickness, minimal shrinkage and mino crack development during carbonixation result in coke of low reactivity, high temperature strength and stability and superior post reaction strength. These properties make non recovery oven coke ideal for the optimum performance of the cupola. To obtain blast furnace coke, the type of coal is to be carefully selected. | Will produce approx. ½ of the width of oven and mean size of coke produced will be smaller. The coke will be more porous and less denser. However, by choice of correct coal blend composition, good quality acceptance to BF can be produced. |
| Refer Coaltree Figure-4A | |
| Requires more (extensive) area. (of the coke oven plant proper). | For the same throughput requirement, required lesser area for the coke oven plant proper. |
| IV. Simplicity Features | |
| Simple technology and therefore readily understood or performed | Complex technology but is also understand and performed. |
| Less time to build | Requires more time to build. |
| Fewer brick shapes needed for construction....23 | More brick shapes and also in terms of quality. Brick shapes are more complicated. Approx. over 1000 shapes will be involved. |
| No expense for by products recovery | Expenses due to by product recovery. |
| Lower operating cost | Higher operating cost |
| Lesser manpower requirement.... Requires only one fourth the manpower as compared to conventional by product coke ovens since such elaborate arrangements as the by product recovery ovens are not required. | More man power. Deployment is required. Apply 4 times that of the Non recovery system. |
| BOD plants are not required in the non recovery coke oven plant. | BOD plant is a must. |
| Ease of maintenance..... Operation of bank of coke ovens are not affected during repairs to individual ovens. | More complicated in terms of maintenance and upkeep. |
| Accommodate any coal blend.... Including lesser contracting and expanding coals and therefore can accept wide variety of coals. | Limited variety of coals are accepted. |
| The refractory brick work is not subjected to higher loads and hence ensures increased life. | Refractory work is subject to higher load and wear and tear. |
| No sticker ovens or Green coke occurence together with ease of pushing of coke from the ovens. This will ensure lesser damages to the refractories. | Possiblity of sticker ovens is there. Due to lesser oven width, ease pushing of coke will not be there. |
| Heating control is simpler. | Heating control is more elaborate. |
| V. Clean System Features | |
| Lesser marketing efforts and operations as only coke and power are to be sold. | More marketing efforts are required depending upon extent of by products are recovered. |
| Since the ovens operate under negative pressure, no leakage from oven door charging holes and therefore it will be pollution free. | Oven chamber operates under positive pressure and therefore there is possibility of confines existing from the oven chamber. |
| It does not smell like a coke oven as chemical by products from coking are not recovered. Instead, they are incinerated during the coking process. The result is-clean stack emissions. | Very much smells like a typical coke oven due to the smell of coal chemicals. |
| No hazardous chemicals to be produced and stored. | Hazardous chemicals are used. |
| Technology adopted ensures meeting with stringent EPA standards of USA for visible emissions. | Higher investment for pollution abatement facility are required to meet the stringent EPA stipulations of USA |
| VI. Reliability Aspects | |
| Reliability in obtaining good quality coke. For obtaining good quality coke, good quality raw material, coking coal is essential. Carbonizing conditions play only a little role. In other words, coke making follows the rule – GARBAGE In – GARBAGE OUT principle. As such, even with non recovery coke ovens, good quality coke can be produced which can be used for larger size blast furnaces with hi-quality low ash coking coals from Australia, this aspect is ensured. | Reliable in obtaining good quality coke |
| The machineries, mechanisms etc involved are much simpler and are subjected to lesser abuses and hence are more reliable for operation. | The machine and modules involved are more complicated and are subject to increased abuses. |
| VII. Environmental Aspects | |
| Non recovery coke ovens operate on negative pressure in the oven chamber, the down comers, sole flues and whole of gas dust. As such, emissions from the ovens are eliminated. | By product ovens operate under positive pressure. As such continuous emissions from oven chambers will occur. In order to avoid this, flexible type oven doors, cleaning mechanisms are to be provided. |
| During charging of oven with coal charging car, due to many number of down comers to send the waste gases from crown to sole flues, no charging emissions take place. | Charging emissions will occur. In order to eliminate this, high pressure ammonical liquor aspiration system at the stand pipes are to be provided. |
| Due to controlled introduction of primary air through the oven doors into the oven chamber and secondary air into the sole flues, the potential thermal Nox generation is restricted. Inherent in the TKEC/PACTII Non recovery coke oven process is a staged combustion technique to generate minimum amounts of Nitrogen Oxide | To control Nox emissions, staged air heating is to be provided. |
| (Nox). The selective admission of primary air into the oven cavity (crown) and the admission of secondary air into the sole flues, provide a "low temperature" environment for combustion. This minimizes the potential of "thermal Nox" generation and restricts Nox formation to less than 60ppm vdc. This technique is generally recognized as being approximately 50% less than most low Nox combustion techniques. | |
| The design quenching car that receives the coke is in a trough form thereby any fall of coke during pushing is avoided. This is to a very large extent avoids particulate emission during pushing. Refer Figure-5 | Due to incorporation and design of quenching car and coke guide car, fall of hot coke occurs from oven chamber to Quenching car which causes heavy pollution on the coke side. Refer Figure-5 |
| The quenching tower is provided with baffles and grit arrestors in the chimney which suppresses the emissions of dust from the quenching tower chimney. | The quenching tower is provided with baffles and grit arrestors in the chimney which suppresses the emissions of dust from the quenching tower chimney. |
| The fine particles and coke breeze is washed down from the trough of the quenching car into the drain leading to the breeze settling pond. | The fine particles and coke breeze is washed down from the trough of the quenching car into the drain leading to the breeze settling pond. |
| There is no liquid effluent originated from the plant since the quenching water has to have make up water only which is available through admission service water into the pond. The quenching cycle is a closed one. Refer Figure-6 | Due to cumulative generation of By product waste water, liquid effluent is generated from the By product plant. This water is to be treated through BOD plant and ultimately discharged into the stream. Refer Figure-6A. If this water is recycled for quenching of coke, plume of steam let out will contain harmful chemicals viz. Phenol, Thiacyanide etc and pollute the atmosphere. |
| The non recovery coke oven unit as offered by Thyssen will fully satisfy the environmental norms. It is not out of place to metnion here that the American Environmental Agencies (U.S Environmental Protection Agency, EPA, the National Resources Defence Council NRDC and The American Iron and Steel Institute AISI) have declared the non recovery coke oven technology to be the technical standard in environmental protection. This is of relevance, since in USA, the clean AIR Act Regulations are much more stringent than in any other country. The non recovery technology as operated as TKEC currently the only coke making process that has been issued a "Green Field" license by the EPA for the new construction of coke ovens plants in USA. Refer Figure-7A & 7B | By product recovery coke ovens do not qualify as a "Green Field" technology and as Clean Development Mechanism under Kyoto Protocol. Refer Figure-1A |
| No pollution due to recovery of coal chemicals, since ovens are operated under negative pressure, unlike by product ovens, there will be no continuous emission from the door leaks or leaks from the charging holes etc. and therefore ensure pollution free process. | Heavy pollution due to recovery of coal chemicals. Ovens operate under positive pressure and therefore there is continuous visible emissions from the coke oven. |
| No liquid effluents are generated since, for coke quenching the quenching water is recirculated and fresh water is added to make up the evaporation loss. This quenching water will not contain any hazardous chemical such as phenol or thiocyanate etc. Refer Figure-6 | It shall be noted that huge quantity of by product waste water is generated in the by product recovery coke ovens plant and hence waste water treatment in the form of BOD plant is required to eliminate hazardous chemicals such as phenol, thicyanate etc. before discharging into the sea or outside. Refer Figure 3A & 6A In many plants, this water is recycled and used for quenching. The plume of steam discharged into atmosphere through quenching tower will contain chemicals such as phenol, thiocyanate etc. thereby polluting the atmosphere. |
| Due to protracted (long) coking time, charging and pushing emissions (if any) will be approximately less than 50% of that of equivalent By product recovery ovens. | Due to narrower width of ovens, the coking time is shorter thereby resulting in higher emissions occurring due to charging and pushing of coke from the ovens. |
Met-coke Making Through High Temperature Carbonization Of Coal Comparison
Between Low Temperature & High Temperature Carbonization
| Low Temperature Carbonisation (LTC) | High Temperature Carbonisation (HTC) | |
| (a). | It is carried at 700°C. | It is carried at 1000°C. |
| (b) | It produces semi-coke which is used as a smokeless domestic fuel. It can sometimes be used in boiler also to avoid smoke. | It produces metallurigical coke for use blast furnace and cupolas in foundry etc. |
| (c) | Yield of coke oven gas is less in LTC. It is about 150-160 Nm3 gas/ton dry coal. Less gas yield is due to less devolatalisation of coal and less cracking of hydrocarbons at lower temperature of carbonisation. | Yield of coke oven gas is more in HTC due to more cracking of hydrocarbons (maintain methane in coke oven gas) at higher temperature. Yield is about 270-300 Nm3/to of dry coal. |
| (d) | Yield of tar is high in low temp carbonisation. It is about 10% of dry coal. | Tar yield is less here. It is 3% of dry coal charged. |
| (e) | Ammonia yield is low. | Ammonia yield is more (10-15gm/N coke oven gas). |
| (f) | Calorific value of coke oven gas produced in LTC is more due to higher percentage of methane and unsaturated hydrocarbons in it. C.V. Is about 6000-6500 kcal/Nm3. | C.V. Of coke oven gas produced in H.T.C is less. It is about 4200-4400kcal/Nm only due to lesser percentage of hydrocarbons resulting from its cracking at higher temperature of carbonisation. |
| (g) | The tar produced is aliphatic in nature. It contains less quantity of aromatic ring compunds like benzene, toluene, naphthalene, phenol, anthracene etc. However, tar acid content is higher. | Tar produced has more of aromatic ring compounds (due to crystalisation reaction of straight chain compounds being favoured at higher temperature). |
| (h) | After carbonisation, discharging of coke is difficult as it swells a lot but does not shrink much finally at the end of coking due to lower temperature of carbonisation. | Discharging of coke is easier as it shrinke finally to a more extent comparatively due to higher temperature of carbonisation. |
| (i) | Free carbon in tar (which results from the cracking of hydrocarbons) is less. It is about 5-10% of tar. Since cracking (HC-H+C) is less severe at lower temperature. | Free carbon in tar is more (due to more intense cracking of hydrocarbon at higher temperature. It is about 15-20% of tar. Higher carbon in tar chokes the hydraulic main and other tar flow pipelines). |
| (j) | Coke produced is weaker (due to less shrinkage) bigger in size and more reactive (due to higher porosity). | Coke produce is stronger (i.e shalter index micum index, abrasion index are more) smaller in size and less reactive (due to low porosity) due to higher amount of shrinkage of coke at higher temperature. |
| (k) | Volatile matter content in coke is more (5-7%) hence it is easier to ignite it because of lower ignition temperature of high volatile matter containing coke. Ignition temperature of LTC coke is about 425°C. | V.M in coke is less (1-2%) hence the ignition temperature is more. Ignition temperature of high temp coke is about 605°C. |
| (l) | Hydrogen content in coke oven gas is less (35-40%) Hence, difference in gross and net calorific value is less. | (l) H2 content in coke oven gas is more (55-60%). It is beneficial for an adjoining nitrogeneous fertiliser plast attached to steel plant (as in the case of Rourkela Steel Plant) which gets hydrogen (for ammonia making) from oven gas by its cryogenic cooling. |
| (m) | Coke yield is more. It is about 77% of coal. | (m) Coke yield is less (about 70% of dry coal). |
| Temperature °C | Effect | High Temperature Carbonisation (HTC) | ||
| Carbonaceous residue (solid) | Tar and Oil | Gas | ||
| 300 | Initial decompositon temperature | Coal | Nil | Some CO+CO2, H2O |
| 320 | Slight appearance of oil | Coal | Thin, light coloured oil | Above plus some CH4 and unsaturated |
| 360 | Marked evolution of thick coal, oils and hydrocarbon gases, coal residue begins to soften | Partially Softened | Darker, red or brown oil | More CH4 and higher parafins, some H2. |
| 430 | Evolution of viscous oil and tar. Coal residue becomes softer and swells. Pronotned gas evolution causes bubble formation, rapid decomposition of coal. | Soft carbonaceous mass of maximum volume and hubble structure | Darker brown more viscous oil | Maximum evolution of paraffin and unsaturated hydrocarbons with some CO, H2 and H2O. |
| 460 | Oil and tar yield reduces, plastic expanded mass solidifies to semi coke | Solid semicoke with maximum bubble structure and weak cell walls. | Nearly viscous oil or tar | Diminishing yield of hydrocarbons water, une in CO and H2O |
| 600 | Oil and tar cease, hard semi-coke starts to shrinks | Semi-coke is harder and shrunken, color is still black. | Non evolved | Gasses namely CO, H2 and CH4. |
| 900-1050 | Continued shrinkage hardness the coke, structure changes with commencement of formation of graphite lattice. | Hard, silvery grey appearance. | Non evolved | |
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