Feedstock recycling of plastic wastes/oil mixtures in cokemaking

Two lubricating oils, a plastic waste composed mainly of polyolefins (95%) and their mixtures (1:1 w/w) were assessed for possible use as minor components of coal blends for metallurgical coke production. The addition of 2 wt% plastic waste causes a decrease in the maximum fluidity of the coal developed during thermal heating between 400 and 500 °C. At the same addition rate, the two oils are good additives for mixing with coal/plastic blends in order to partially restore the caking ability of the co-carbonizing systems. Co-carbonizations of the coking blend with the different wastes were carried out in a movable wall oven of 15 kg capacity. Although the bulk density remained unchanged, the addition of the plastic waste produced an increase in coking pressure to values that were too high for it to be considered as a safe blend. At the same time the mechanical strength of the partially gasified coke was improved as reflected by the CSR index. The oils, however, had the effect of reducing bulk density and the coking pressure generated during the process. When blended with the coal and the plastics, the oils appeared to act as good solvents of the polyolefins and also proved to be effective in decreasing coking pressure without negatively affecting coke quality.     

Relevance of the composition of municipal plastic wastes for metallurgical coke production

This study is concerned with the effects of the composition of mixed plastic wastes on the thermoplastic properties of coal, the generation of coking pressure and the quality of the resulting cokes in a movable wall oven at semipilot scale. The mixed plastic wastes were selected to cover a wide spectrum in the relative proportions of high- and low-density polyethylenes (HDPE and LDPE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET). From the results it was deduced that the reduction in Gieseler fluidity in the coal blend is linked to the total amount of polyolefins in the waste. It was also found that these thermoplastics increase the pressure exerted against the wall in the course of the coking process and that coke quality is maintained or even improved. However, when the level of aromatic polymers such PS and PET are increased at the expense of polyolefins, the coking pressure decreases. Thus, the amount of aromatic polymers such as PS and PET in the waste is critical, not only for controlling Gieseler fluidity and coking pressure, but also for avoiding deterioration in coke quality (reactivity towards CO₂CRI and mechanical strength of the partially-gasified coke CSR). An amount of polyolefins in the waste lower than 65 wt.% for a secure coking pressure is established.     

The effect of coal blend fluidity on the properties of coke

The effect of maximum fluidity of coal blends on coke quality was investigated using high fluidity coals and pitch to increase the fluidity of the blends. The results show that high fluidity of the blends could improve the growth of anisotropic carbon in coke. It also improves the coke M₃₀, but this is restricted when using high fluidity coals as additives. There is no significant improvement of the M₁₀ by increasing the fluidity. The reactivity, however, could be reduced to lower than the expected value by increasing the coal blend fluidity.     

废塑料配煤炼焦实验研究

利用2kg焦炉实验,研究废塑料配煤炼焦产物的特性．研究结果表明,废塑料代替瘦煤配煤炼焦对改善焦炭强度效果明显．废塑料代替瘦煤比例为1％～5％,焦炭的反应性和反应后强度呈现劣化趋势,但当废塑料比例为3％时,焦炭的反应性和反应后强度仍优于纯煤焦化所得焦炭,焦油中的芳香环结构物质增加,焦油出现轻质化趋势,焦炉煤气的热值有明显的提高,具有显著的工业应用前景．     

Influence of coal thermoplastic properties on coking pressure generation: Part 2 - A study of binary coal blends and specific additives

A number of coal blends and pitch/coal blends were evaluated using rheometry, thermogravimetric analysis and microscopy to confirm and further elucidate the coking pressure mechanism previously proposed by Duffy et al. (2007) [1]. We confirm that blending a low rank, high fluidity, low coking pressure coal, with a high rank, low fluidity, high coking pressure coal can significantly reduce the coking pressure associated with the latter. Interestingly, blending does not necessarily result in a fluidity that is midway between that of the two coals; sometimes the fluidity of the blend is less than that of the low fluidity coal, especially when the coals are significantly different in rank. This occurs because the increase in complex viscosity (η*) through resolidification of the low rank, high fluidity coal counteracts the reduction in η* resulting from softening of the high rank, low fluidity coal. It has also been confirmed that the η* of the resultant blend can be estimated from the η* of each component coal using a logarithmic additivity rule commonly employed for polymer blends.Polarised light microscopy has indicated that the degree of mixing between coals of different rank is minimal, with fusion restricted to the particle surface. It is therefore inappropriate to think of such a coal blend in the same way as a single coal, since each component coal behaves relatively independently. This limited fusion is important for understanding the coking pressure mechanism for blends. It is proposed here that the lower rank coal, which softens at lower temperature, is able to expand into the interparticle voids between the high rank coal that is yet to soften, and these voids can create channels for volatiles to traverse. Then, and importantly, when the high rank coal begins to expand, the pore structure developed in the resolidified structures of the low rank coal can facilitate removal of volatiles, while the resolidified material may also act as a suitable sorbent for volatile matter. This is considered to be the primary mechanism by which coal blending is able to alleviate coking pressure, and applies to addition of inert material also.Addition of a coal tar pitch was found to increase fluidity but also to extend the thermoplastic range to lower temperatures. This caused an increase in the swelling range, which was accompanied by a long plateau in η*, a feature which has previously been observed for certain high fluidity, high pressure coals. Elasticity and η* at the onset of expansion were also higher for both the pitch impregnated coals and the high pressure blends, which supports previous findings for singly charged high pressure coals, and confirms the potential use of such criteria for identifying potentially dangerous coals/blends.     

The mechanism of coking pressure generation I: Effect of high volatile matter coking coal, semi-anthracite and coke breeze on coking pressure and plastic coal layer permeability

One of the most important aspects of the cokemaking process is to control and restrain the coking pressure since excessive coking pressure tends to lead to operational problems and oven wall damage. Therefore, in order to understand the mechanism of coking pressure generation, the permeability of the plastic coal layer and the coking pressure for the same single coal and the same blended coal were measured and the relationship between them was investigated. Then the ‘inert’ (pressure modifier) effect of organic additives such as high volatile matter coking coal, semi-anthracite and coke breeze was studied. The coking pressure peak for box charging with more uniform bulk density distribution was higher than that for top charging. It was found that the coking pressure peaks measured at different institutions (NSC and BHPBilliton) by box charging are nearly the same. The addition of high volatile matter coking coal, semi-anthracite and coke breeze to a low volatile matter, high coking pressure coal greatly increased the plastic layer permeability in laboratory experiments and correspondingly decreased the coking pressure. It was found that, high volatile matter coking coal decreases the coking pressure more than semi-anthracite at the same plastic coal layer permeability, which indicates that the coking pressure depends not only on plastic coal layer permeability but also on other factors. Coking pressure is also affected by the contraction behavior of the coke layer near the oven walls and a large contraction decreases the coal bulk density in the oven center and hence the internal gas pressure in the plastic layer. The effect of contraction on coking pressure needs to be investigated further.     

焦油渣配煤炼焦的实验研究

分析了焦油渣配煤炼焦的可行性,并在20kg实验焦炉上进行了焦油渣配煤炼焦实验,确定了焦油渣在炼焦煤中配入的最佳比例。实验结果表明:焦油渣配煤炼焦是可行的,并可提高焦炭的块度和抗碎强度,同时优化了焦油渣的最佳配量及最佳粒度,分别为焦油渣的添加量以3%～5%为宜、最佳粒度为0.2mm左右的占85%。在此基础上,进行了工业性对比试验,验证了在生产中添加3%～5%焦油渣炼焦的可行性。     

Modification of sub-bituminous coal by steam treatment: Caking and coking properties

A Chinese sub-bituminous Shenfu (SF) coal was steam treated under atmospheric pressure and the caking and coking properties of the treated coals were evaluated by caking indexes (G_RI) and crucible coking characterizations. The results show that steam treatment can obviously increase the G_RI of SF coal. When the steam treated coals were used in the coal blends instead of SF raw coal, the micro-strength index (MSI) and particle coke strength after reaction (PSR) of the coke increased, and particle coke reactivity index (PRI) decreased, which are beneficial for metallurgical coke to increase the gas permeability in blast furnace. The quality of the coke obtained from 8% of 200 °C steam treated SF coal in coal blends gets to that of the coke obtained from the standard coal blends, in which there was no SF coal addition in the coal blends. The removal of oxygen groups, especially hydroxyl group thus favoring the breakage of the coal macromolecules and allowing the treated coal formation of much more amount of hydrocarbons, may be responsible for the modified results. The mechanism of the steam treatment was proposed based on the elemental analysis, thermo gravimetric (TG) and FTIR spectrometer characterizations of the steam treated coal.     

Industrial utilization of spent ion-exchange resin in the coke battery

Experimental coking with spent ion-exchange resins as an additive in the coal batch is considered; rammed batch is employed. Both box coking and large-scale coking are considered; the resin content in the batch is 1–5 wt %. The influence of the resins on coke quality is assessed. The coal blend used in industrial coke production is employed. Adding small quantities of resin (<5 wt %) to the batch improves the coke’s cold strength M ₈₀ and M ₄₀, without impairment of CRI and CSR. The quality of the coal tar and the organized gas emission remains unchanged. Hence, spent ion-exchange resins may be recycled by adding small quantities (3%) to the coal batch in coke production.     

Using polymer waste in coke production

The utilization of solid domestic waste—plastic, rubber, leather, textiles, wood, and paper—in coking batch after mixing with residues from coal-tar stores at coke plants is investigated. All the solid domestic waste considered—especially plastic waste—increase the yield of coke in the >80 and >60 mm class and the yield of tar and benzene. The introduction of plastics and a mixture of solid domestic waste with up to 1% of tar-storage residues does not impair the quality of the coke produced.     

The mechanism of coking pressure generation II: Effect of high volatile matter coking coal, semi-anthracite and coke breeze on coking pressure and contraction

One of the most important aspects of the cokemaking process is to control and limit the coking pressure since excessive coking pressure can lead to operational problems and oven wall damage. Following on from a previous paper on plastic layer permeability we have studied the effect of contraction of semi-coke on coking pressure and the effect of organic additives on contraction. A link between contraction (or simulated contraction) outside the plastic layer and coking pressure was demonstrated. The interaction between this contraction, local bulk density around the plastic layer and the dependence of the permeability of the plastic layer on bulk density was discussed as possible mechanisms for the generation of coking pressure. The effect of blending either a high volatile matter coal or one of two semi-anthracites with low volatile matter, high coking pressure coals on the coking pressure of the binary blends has been explained using this mechanism.     

Co-carbonization of hard coals and coal extracts 1. The co-carbonization of low rank coals with extracts

Studies on the influence of an additive derived from coal on the coking properties of lower-rank coals and on the structure of cokes obtained from blends have been undertaken in our laboratory since 1978. The two coal extracts from flame coal (Int. Class. 900) and gas-coking coal (Int. Class. 632) were used as additives. The results indicate that the blends prepared from low-rank coals — flame coal (Int. Class. 900), gas-flame coal (Int. Class. 721) and the extracts possess better coking properties in comparison to the parent coals. The optical texture and the degree of structure ordering of the cokes obtained from blends is related to the amount of extract in the blend. With increasing extract content in the blend, increases were observed in the amount of optically anisotropic areas in cokes from low-rank coal/extract blends and the crystallite height (L_c) of cokes from the blends. The isotropic optical texture of cokes from low-rank coals can be modified by coal extracts to an anisotropic optical texture. The non-fusible coal is the most difficult to modify. An explanation of the observed phenomena is given.     

Influence of polyethylene terephthalate on the carbonisation of bituminous coals and on the modification of their electric and dielectric properties

The purpose of this research was to study the influence of 2 wt% of polyethylene terephthalate (PET) on carbonization of two bituminous medium-volatile coals being different in maximum fluidity (MF). During the research into consideration were taken the structure of the coal plastic layer, the value and the distribution of the intralayer pressure, the changes in volume of the heated coal charge and in the development of the porous structure of the coke, so the changes in electric and dielectric properties of the solid residues obtained from the co-carbonisation of the coals with PET and a coal-tar pitch.The investigations were carried out in a laboratory unit using X-raying and tracing the coal charge with markers of copper foil. Changes in the porous structure of the carbonized coals were estimated on the basis of micrographs taken with a scanning electronic microscope (SEM). It was established that under the influence of PET the thickness of the plastic layer of coals decreases; its zone structure modifies, value and the distribution of the intralayer pressure in the heated charge of bituminous coals changes. PET can change the mechanism of formation of coke obtained from coals with a lower MF index, which leads to appearance of a less dense coke. PET facilitates the formation of a denser coke when blended with a coal with higher MF.The change of electric and dielectric properties of co-carbonisation products of coals with PET and coal tar pitch is analysed. The analysis shows that PET reacts with coals with distinct MF indices in a different way and has an influence on them opposite to that of pitch. Namely: when blended with a coal of low MF, PET facilitates the formation of cross-links between the macromolecules, and with high MF—the processes of macromolecular chains' growth due to the increase in their length.     

煤种适应性及配煤炼焦探讨

讨论了原料煤及煤中显微组分对煤的成焦过程的影响;分析了中温沥青、焦油渣、废塑料、无烟煤、焦粉作为添加剂进行配煤炼焦时的实际情况。选用合适的添加剂进行配煤炼焦,能更好地实现煤炭资源合理有效利用,对工业生产具有重要的理论意义和实用价值。     

A laboratory scale assessment of the utilization potentials of sub-bituminous Nigerian coals as components of coking blends

This paper examines the ability of A240 Petroleum pitch to improve the coking characteristics of sub-bituminous Lafia and Enugu coals of Nigeria. Also examined is the compatibility of Enugu and Lafia coals with a prime coking Ogmore coal in a blend for coke making. The exercise is motivated by the desire to include non-coking Nigerian coals in coal blends for making blast furnace coke.The coking characteristics of Lafia and Enugu coals are highly susceptible to improvement by A240 petroleum pitch. The pitch also interacts with the improves the coking characteristics of a blend of Enugu and Lafia coals.No interaction occurs between Enugu and Ogmore coals. Little interaction occurs between Lafia and Enugu coals. A strong interaction occurs between Lafia and Ogmore coals. Ogmore coking coal tremendously improves the coking characteristics of a blend of Lafia Enugu coals. Optical microscopy, microstrength and reactivity tests reveal that high volatile coking Lafia coal act as a bridging coal between Enugu coal and a prime coking coal in a ternary coking blend.     

Coke quality on adding coking byproducts to the batch

The addition of coking byproducts improves the properties of the coal batch and the coke produced. Adding acidic tar from the sulfate department to the coal batch affects the pyrolysis of the coal’s organic mass, while the ratio of size classes in the coke may be regulated by adjusting the quantity of the additives.     

废轮胎与配煤共焦化产物收率研究

利用2kg级模拟工业高温焦化装置进行废轮胎与煤共焦化实验,考察了共焦化产物分布及产物收率受废轮胎橡胶变化的影响．结果表明,煤与废轮胎共焦化时存在“协同效应”,该效应具有明显的增气、增油和降低热解水的作用．当废轮胎配比为1％～7％时,焦炭收率随配比增加而降低,焦油收率呈增加趋势;与原煤单独炼焦相比,焦炭收率最多减少2．27%,焦油增加幅度至少是焦油总量的3．3％．用小颗粒度废轮胎可提高冶金焦率,当废轮胎颗粒度为D〈0．20mm时,冶金焦率增加幅度至少是原煤单独炼焦的3．6％．在废轮胎粒度D〈0．20mm,配比为3％时共焦化,可得到最大冶金焦率,并使焦油收率有所提高．     

煤与废塑料共焦化研究进展

介绍了煤与废塑料共焦化的机理,分析了影响煤与废塑料共焦化的主要因素:废塑料的种类、配入比例、粒径、预处理方式等,分别讨论了添加废塑料对膨胀压力和焦炭结构的影响。指出煤与废塑料共焦化技术在节约炼焦煤资源和环保方面具有较好的发展潜力。     

顶装炼焦改造为捣固炼焦的生产实践

介绍了JN43-80型焦炉由顶装炼焦改为捣固炼焦的改造工程,对比了改造前后炼焦用煤质量指标、配煤煤种和比例、用煤量、焦炭质量指标、化工产品回收率等。顶装炼焦改为捣固炼焦具有减少主焦煤配入量、增加气煤的配入量、提高焦炭产量等优势,通过改造,可使焦化企业降本增效。     

基氏流动度在配煤炼焦中的应用

针对迁安中化炼焦煤采用常规煤质指标分析出现的单种煤常规指标较好,配煤炼焦后焦炭强度下降的问题,采用基氏流动度分析了常用两种中强黏结性炼焦煤A煤和B煤的煤质,探讨了其与常规煤质指标的关系,介绍了基氏流动度在配煤炼焦中的应用情况及存在问题。结果发现,A煤和B煤的常规煤质指标接近,最大基氏流动度分别为7209 ddpm和829 ddpm,可以较好区分两种煤;基氏流动度特征指标中的软化温度、塑性温度区间及最大流动度可反映炼焦煤的基本性质;炼焦煤的最大流动度的对数值在2.2~3.0、挥发分在23%~27%时,焦炭M40>87%、M10<7%。