Linz-Donawitz Slag Research Articles

Enriched Linz-Donawitz (LD) slag application for improving grain yield and quality of wheat grown under nutritionally poor degraded soil

Aim: To evaluate the impact of enriched steel slag on the physico-chemical characteristics of soil and yield attributes of wheat under poor quality degraded soil. Methodology: Steel slag was biologically and organically amended with natural sources of phosphorus (P), sulfur (S), potassium (K) and nitrogen (N) and characterized for its nutrient content along with biological activity. The impact of resultant products was assessed on soil quality and yield component traits of wheat for two consecutive years (2021-2022 and 2022-23). Results: Application of slag based products significantly (p<0.05) improved the plant height, biological yield, grain yield and ear bearing tillers (EBT) of wheat even with 80% of recommended fertilizer dose (NPK). Further, in comparison to control, a moderation of soil pH (8.6 to 8.8), EC (0.18 to 0.20 dS m-1), OC (0.22 to 0.24 %) and essential mineral macronutrients viz., N (126 to 130 kg N ha-1), P (8.0 to 13.0 kg ha-1), K (100 to 125 kg ha-1) were observed with the application of amended steel slag products. No significant change with respect to existing heavy metal concentration viz., Co, Ni, Cd and Pb in soil was observed when supplemented with amended slag products. Interpretation: Steel slag can be transformed favorably for on-farm application to improve wheat yield besides serving as an environmentally sustainable alternate of soil conditioner for the management of degraded soil. Key words: Degraded soil, Heavy metals, Steel slag, Waste management, Wheat

Properties of alkali activated masonry units incorporating Linz-Donawitz (LD) steel slag aggregates and Mangalore tile waste (MTW)

Abstract The existing cement masonry units consume cement, natural resources and fuel making it less sustainable. The unrestrained utilization of natural resources and substantial production of industrial wastes has led to reuse and recycling for sustainable development. Among the prevailing industrial wastes, steel slags are presently dumped in landfills. Previous studies have utilized Linz Donawitz (LD) slag aggregates as a partial replacement for natural aggregates. On the other hand, the locally available Mangalore tile waste (MTW) was studied as a natural aggregate replacement. In the current investigation, the LD slag aggregates, and the MTW fine powder, aggregates were incorporated into the masonry system and accessed their fresh properties such as setting time, flow and hardened property -compressive strength, along with microstructural investigations. The masonry mixes indicated that the LD slag type 3 and M sand-based masonry unit exhibited higher compressive strength, around 40 MPa, and can be categorized as heavy-duty bricks according to IS 2180:1988.

Investigation on modified Linz-Donawitz slag for the treatment of Pb2+ ion-laden wastewater - A slag utilization sustainable approach

The present study investigated the adsorptive chemistry of Pb2+ ions eradication using modified Linz-Donawitz slag (LDS), a byproduct of steelmaking industries. The processing of LDS was carried out using a magnetic separation technique followed by planetary micro-crushing. The morphology of surface texture and elemental composition of LDS were examined using SEM and EDS techniques, respectively. XRD and FTIR analysis revealed that the divalent cation of Pb2+ was replaced by Ca2+ to form metal silicate (Pb2SiO4) and ferrite (Pb2Fe2O5) through ion exchange and finally precipitated. The experiment data best fitted Langmuir isotherm and showed excellent adsorption capacity of LDS for Pb2+ adsorption (479 mg/g). Thermodynamic parameters, Gibbs free energy (ΔGo), and enthalpy change (ΔHo) indicated the adsorption was spontaneous and endothermic. The leachability study done by the ICP-OES technique suggested the possibility of immobilizing Ca and Si due to the dissolution of CaO and SiO2. The study demonstrated the potential of LDS for treating Pb2+ ions as part of the waste utilization of the steel industry for a sustainable approach.

Effect of particle size and application rate of steel (Linz-Donawitz, LD) slag on heavy metal built-up in soil and their transfer dynamics in spinach (Spinacia oleracea L.)

Linz-Donawitz (LD) slag is a solid industrial waste generated during the production of steel. In general, the amount of LD slag produced varies from 300 to 400 kg ton-1 of steel. Presently only 25 % of the steel slag, which is also rich in various macro and micro-nutrients, is being reused in India compared to 70–100 % in other countries. The present study deals with the possibility of utilizing LD slagas a nutrient rich low-cost soil conditioner in agriculture. An experiment was thus conducted to determine the effect of LD slag application at rates 0.25, 0.50 and 1 t ha-1 in two particle sizes i.e., <50 and <100 microns (µ) on spinach (Spinacia oleracea L.). Physico-chemical, biological characteristics and heavy metals in soil and latter’s transfer from soil to the foliage was also determined. The results showed that an application of LD slag @1 tha-1 and 100 µ particle size significantly improved the soil microbial count and activity of enzymes such as dehydrogenase and phosphatase while at a smaller particle size of LD slag (50 µ) @ 1 tha-1, a significant increase in the foliage yield of spinach was observed. The risk due to heavy metals present in the steel slag as evidence by indicator of heavy metal content in plants i.e. transfer factor (TF), hazard quotient (HQ) and hazard index (HI) was within the permissible range. However long-term effect of steel slag application on ecotoxicity and phytotoxicity levels must be deciphered. In conclusion the application of LD slag in spinach does not negatively impact the soil health and in fact causes an increase in the economic yield of spinach.

Effect of bioaugmented Linz-Donawitz slag and biochar on physiological and yield attributes of wheat (Triticum aestivum)

Industrial wastes and agricultural by-products are increasingly used in crop production as supplements along with fertilizers. An experiment was conducted during the winter (rabi) seasons of 2021 and 2022 at the research farm of the ICAR-Indian Agricultural Research Institute, New Delhi to determine the individual and combined effects of bioaugmented Linz-Donawitz (LD) slag and biochar on physiological and yield attributes of wheat (Triticum aestivum L.) variety HD 2967. Bioaugmented products with cow-dung, LD slag and biochar in different combinations were prepared in laboratory scale and applied in crates. All the treatments were applied with 100%RDF except control. Growth parameters such as total leaf area, chlorophyll content, NDVI; and leaf photosynthetic attributes such as net photosynthetic rate, stomatal conductance and transpiration rate were affected by bio-augmentation. Our study reported an increase in total leaf area (18.2–21.3%), chlorophyll content (26.5–31.0%), net photosynthetic rate (93.2%), stomatal conductance (61.3%), transpiration rate (24.7%) in bioaugmented treatments with LD slag and biochar over 100%RDF. A yield increase of 25.6 and 27.1% was found in bioaugmented treatments with a combination of LD slag (2 t/ha) and biochar (1 t/ha) over 100%RDF during 2021 and 2022, respectively. No. of spikes, grains per spike and dry biomass weight were positively influenced by bioaugmentation. The bioaugmented treatments with a combination of LD slag and biochar gave significantly higher grain yield, followed by bioaugmented LD slag compared to bioaugmented biochar alone in the respective application rate of treatments.

Indirect Aqueous Mineral Carbonation of Samples of Linz–Donawitz Slag from the Steel Industry in Eastern India

Indirect Aqueous Mineral Carbonation of Samples of Linz–Donawitz Slag from the Steel Industry in Eastern India

Performance assessment of Linz–Donawitz slag as alternative coarse aggregate in concrete: a comprehensive study on mechanical and durability properties

Performance assessment of Linz–Donawitz slag as alternative coarse aggregate in concrete: a comprehensive study on mechanical and durability properties

Use of marble dust and linz-donawitz slag for the production of pervious concrete

Nowadays, the development of infrastructure is in full swing, which exploits natural resources and causes environmental pollution. Furthermore, cement is the most essential commodity for construction material mainly concrete, and its production is rapidly increasing to fulfil the demand for construction. The cement production is regarded as the one of the key causes of CO2 emissions, which adversely affect the atmosphere by causing global warming. In addition to this, the ecosystem may suffer from marble quarrying and construction material processing. Nonetheless, waste marble can be used as a by-product if managed in accordance with regional, national, and international environmental laws. On the other hand, Currently, LD slag is disposed of in landfills, which exacerbates the scarcity of available land and contaminates groundwater through the leaching of heavy metals. The waste materials have the potential to be used in the development of infrastructure materials. The infrastructure development has aggravated the issue of rainwater runoff and flash flooding in rainy seasons because of inappropriate drainage. The elimination of sand in pervious concrete reduces its strength performance its practical applications are still limited. This study is aimed toward the permeability improvement of conventional pavement concrete by the implementation of pervious concrete and also to improve its strength characteristics. In this study, an attempt has to be made to replace the cement with marble dust up to a replacement level of 0% to 20% with an interval of 5%. Also, natural aggregate is replaced with Linz-Donawitz (LD) slag by 5%, 15%, 25%, and 35%. From the study, it is found that the use of marble dust and LD slag improves the strength properties, but reduces the permeation properties.

Durability assessment of concrete with natural and Linz Donawitz slag as coarse aggregates

Rapid growth of infrastructure has resulted in incessant consumption of natural aggregates in cement concrete leading to its depletion. Efforts have been made to utilize industrial by-products such as steel slag aggregates in concrete as partial replacement for natural aggregates. However, the utilization of Linz Donawitz (LD) slag aggregates in concrete is very limited compared to other slag aggregates. The limited utilization could be attributed to the expansive nature of LD slag aggregates, which may result in durability issues. In this study, the compressive strength and durability characteristics of concrete with 100% LD slag coarse aggregate are investigated considering three different cement types, including Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC) and Portland Slag Cement (PSC) for all the mixtures. LD slag and control concrete were examined for durability by conducting water permeability, electrical resistivity, drying shrinkage, rapid chloride penetration (RCPT) and water absorption tests. X-Ray Diffraction (XRD) analysis along with the microstructural investigations using SEM-EDS was carried out to supplement durability results. The compressive strength results indicated that LD slag concrete depicted higher strength than control concrete and there was a steady increase in strength with curing duration. Interestingly, PSC concrete depicted higher rate of strength gain compared to other cements. Further, LD slag concrete depicted low permeability and water absorption compared to control concrete, where it can be anticipated lower freeze–thaw damage. RCPT results indicated lower penetration of chloride ions representing delayed corrosion of steel in LD slag concrete. Overall, LD slag concrete depicted enhanced durability than control concrete.

Synthesis of precipitated calcium carbonate from LD-slag using CO2

The waste Linz-Donawitz (LD) slag produced in the steel industries is known to have high calcium oxide (CaO) content along with other inorganic salts. There is an untapped potential for the valorization of the waste LD-slag, where the constituent calcium oxide can be converted to valuable calcium carbonate and subsequently contributes to the sequestration of carbon dioxide. In this study, table sugar was introduced as a promoter to enhance the conversion of CaO to CaCO3. The valorization of the LD-slag process was conducted in a CO2 atmosphere by varying the temperature over 25–55 °C. The highest calcium oxide conversion was found at 55 °C. Various techniques were employed in order to assess the crystal growth, textural properties, and thermal behavior of the synthetic CaCO3 formed. The calcite phase is dominated in a temperature range of 25–55 °C, whereas unstable vaterite was identified at 45 °C. Further, at higher temperature ∼55 °C, the needle-like aragonite phase was found to dominate. The reaction kinetic data are well-fitted with the pseudo-second-order model (R2 = 0.99) as compared to other models. The whiteness of the obtained samples was measured via UV-spectrometer and the PCC sample achieved at 55 °C showed significant whiteness characteristics among others. The CO2 sequestration efficiency in this study was found to be ∼17%. It was estimated that 500 g of CO2 could sequestrate by 1 kg of LD-slag. Moreover, the “t” value obtained from the hypothesis test is 49.92, which reveals that the presence of table sugar in the reaction, leads to a higher Ca(OH)2 concentration.

Influence of elevated temperature on compressive strength of LD slag aggregate concrete

PurposeThis study aims to investigate the compressive strength of concretes incorporating Linz-Donawitz slag (LD slag) as partial replacement for natural fine and coarse aggregates and compare them with traditional concrete.Design/methodology/approachThe natural fine and coarse aggregates were replaced by weight simultaneously up to 100% with LD slag aggregates at an incremental increase of 20%. Concrete of grades M20, M25, M30, M35 and M40 were cast, cured and tested with standard cube specimens to study the density and compressive strength of reference and LD slag aggregate concretes (LDSACs). The concrete specimens were exposed to elevated temperatures, i.e. 100 to 900 °C at an equal interval of 100 °C and tested to study the variation in density and residual compressive strength.FindingsThe results from the experiments reveal that the LDSAC yields a higher density than that of the reference concrete and also undergo less density variation when exposed to elevated temperatures. In addition, the residual compressive strength of LDSAC specimens was significantly higher than that of the reference concrete.Research limitations/implicationsLD slag is believed to be stronger and more durable than locally available limestone aggregates or blast furnace slag. Moreover, it is necessary to study its strength and other properties to determine whether it can be successfully used as an aggregate in concrete universally.Practical implicationsUse of LD slag as aggregates in concrete will convert LD slag into a value added product and as an alternative to the existing natural aggregates which will help in maintaining ecological balance and save valuable lands.Social implicationsThe economically weaker section of the society may now use LDSAC as waste utilization will bring down the overall cost and hence it will benefit people on large scale.Originality/valueUse of LD slag as aggregate in concrete can help find an alternative to the existing natural aggregates which will save the ecosystem and at the same time help in reducing the industrial waste on a large scale.

Sustainably produced concrete using weathered Linz-Donawitz slag as a fine aggregate Substitute: A comprehensive study with Artificial intelligence approach

Continuous consumption of natural resources such as river sand and coarse aggregates due to increased industrialization and urbanization has impeded the movement towards green concrete in construction, i.e., utilizing waste materials in its production, steel slag waste being one of them. Accumulation of Linz-Donawitz slag (LD slag) has become cumbersome in India, posing a problem of landfills and environmental degradation, i.e., abating soil and water quality due to the leaching of toxic metals. Fewer experimental studies have examined whether weathered fine LD Slag can substitute for fine aggregates in concrete. Additionally, the research has yet to compare the behavior of concrete comprising weathered fine LD slag in Normal Strength Concrete (NSC) and High Strength Concrete (HSC) containing Metakaolin. The current study aims to establish an optimum replacement quantity for fine aggregates with fine LD slag. The slag replaced fine aggregates by volume at 25, 50, 75 and 100%. The findings that examined the effects of using LD slag on the mechanical behaviour, durability and microstructure of concrete are presented in this study. Furthermore, taking a total of 180 experimental data points, the compressive strength of concrete was predicted using artificial intelligence (AI) methods such as Artificial Neural Networks (ANNs), Decision Trees (DT) and Random Forests (RF). Coefficient of determination R2, Mean Absolute Error (MAE) and Root Mean Square Error (RMSE) were computed to assess the performance of generated models. Besides, a sensitivity analysis technique was employed to determine the most influential parameter among cement, Metakaolin, Fine Aggregate, Coarse Aggregate, LD slag, Superplasticizer, water content and testing age on the compressive strength results. Experimental investigation showed that adding LD slag up to 50% for NSC and 25% for HSC was optimal and showed better results for tested properties than conventional concrete mixes. Among proposed AI techniques, the DT technique was the best-performing model with an R2 value of 0.973 and the least for MAE (3.534 MPa) and RMSE (4.409 MPa). Sensitivity analysis performed on the DT model showed that testing age was the most critical parameter for the prediction of compressive strength.

Development of low heavy metal − Linz-Donawitz slag for safe spinach cultivation

Linz-Donawitz Slag is regarded as a soil conditioner and can be exploited for its mineral and nutritional value in agriculture, however, it is necessary to check the Potentially Toxic Elements (PTEs) which could impact the soil rapidly and crop production adversely. Environmental hazards associated with mounting piles of Linz-Donawitz slag emanating from the steel producing industry and its sustainable management are a major challenge. A research study was carried out using different chemical chelating agents to achieve reduction in PTEs' concentration in Linz-Donawitz slag and to study the effect of transfer of PTEs’ from the treated and untreated LD Slag applied to the spinach. Optimization was done using response surface methodology, and the highest extraction efficiency for Cadmium (Cd) and Lead (Pb) removal was observed using a concentration of 10 mM, liquid-to-solid ratio of 5:1, and shaking time of 60 min to obtain Low heavy metal Linz-Donawitz slag (Low HM-LD Slag). The highest chelation was observed while using the chelating agent Ethylene diamine-N, N'-Di succinic acid (EDDS) followed by Ethylene diamine tetra acetic acid (EDTA) then Diethylene triamine penta acetate (DTPA), and the least extraction was observed using the Citric acid (CA). The Low HM-LD Slag so obtained was assessed for its response on Spinach under the varied level of Recommended Dosage of Fertilizer (RDF) under field soil in pot culture. A significant difference in the growth of spinach was observed between 100% RDF treated Low HM-LD Slag and 50% RDF treated Low HM-LD Slag derived using different chelating agents The PTE analysis of soil and plant showed an undetectable level of Cd, Pb in both the shoot and root samples Under Low HM-LD Slag treatments @ 100% and 50% RDF condition. The present work advocates the use of chemical chelators reducing PTEs' load in Linz-Donawitz slag before using it for application in agriculture as a soil conditioner or as a fertilizer.

Effect of Linz-Donawitz slag addition on the hot stage slag mineralogy and fuming conditions: Output slag modification during the industrial Zn fuming operation

Up to 39.35 wt% of CaO-rich Linz-Donawitz (LD) slag was gradually added to copper slag during an industrial Zn fuming process to investigate the influence of CaO content on the Zn fuming efficiency and slag high-temperature mineralogy. Multiple slag samples were taken from a standard fuming process and an LD slag modified fuming process. Microstructure analysis revealed that the fuming bath was primarily composed of the liquid phase and a small number of spinel particles prior to LD slag addition. In contrast, an additional wustite phase was observed after the LD slag addition. According to the FactSage simulation, the bath temperature in the standard fuming process was between 1139 and 1180 °C and the oxygen level was around 1 × 10−13 - 5 × 10−14 atm. Upon the addition of LD slag, the temperature decreased to 1085–1140 °C, while the pO2 increased to 1 × 10−12 - 5 × 10−13 atm. An increase in LD slag content facilitated the decomposition of fayalite and spinel phases, the generation of metallic Fe under pO2 of 1 × 10−13 atm, the formation of wustite under pO2 of 1 × 10−12 atm, and the precipitation of melilite. The optimal fuming conditions for Zn recovery and slag modification without Fe formation were pO2 of 1 × 10−12 atm, the temperature of 1168–1210 °C and an LD slag content of 28.6 wt%. Under these conditions, the CaO content in the liquid phase can reach approximately 20 wt% and ensure that the fumed slag is a suitable raw material for cementitious materials production.

Utilization of Linz-Donawitz slag and brick bat for the production of sustainable paver blocks

Due to the unplanned and uncontrolled exploitation of mineral resources and the massive production of industrial trash, waste is now being reused and recycled for sustainable development. The production of cement and concrete in the building industry has been enhanced by the recycling and reuse of waste. Construction provides a lot of opportunities for recycling. These by-products can produce better outcomes and can raise concrete quality. There are about 120,000 brick kilns in India. Each year, 250 billion bricks are manufactured, of which 5% are waste. On the other hand, the buildup of Linz-Donawitz slag (LD slag) in India has become problematic, leading to a problem with landfills and environmental deterioration. Nowadays, paver blocks have become quite popular and are utilized to pave vacant spots in front of homes as well as parking lots, businesses, and enterprises. One of its key advantages is that damaged individual blocks can be replaced. The current study concentrates on utilizing these waste materials to create Paver Blocks that can be used by pedestrians. Paver blocks comprising LD slag at a replacement level of 50% for fine aggregate and brick bat at a maximum replacement of 30% with coarse aggregate were tested for properties such as compressive strength, flexural strength, water absorption and abrasion resistance. Out of the proposed mixes, the mix with 20% Brick Bat and 50% LD Slag is the best as it qualifies the necessary quality and strength requirements.

Weathering resistance of Linz–Donawitz (LD) slag as ballast material using freeze-thaw and sulfate soundness

As nonrenewable natural aggregates with acceptable geotechnical properties become scarce, costly, and entail negative environmental impacts, the study of alternatives remains a first-order challenge for sustainable railway design. This paper focuses on the physical and chemical weathering effects of the industrial byproduct Linz–Donawitz (LD) slag as a ballast material. For this purpose, 75 freeze–thaw (F-T) and 40 sulfate soundness (SS) cycles were carried out on the byproduct. We present a series of laboratory experiments involving particle characteristics, durability and strength for different F-T and SS cycles. To benchmark the performance of LD slag, we also performed our experiments on two natural aggregates: gneiss and basalt. Our main findings reveal that: (i) the shape of LD slag ballast and its particle size distribution are unnafected by the F-T and SS cycles, (ii) the basalt exhibits higher magnitudes of fouling after SS cycles, (iii) losses in Los Angeles abrasion and shock resistance were much more pronounced in SS tests for all ballast materials, (iv) LD slag is more resistant and less susceptible to the degrading effects of freezing and thawing, (v) point load tests indicate that the loss of resistance of basalt is small compared to that of gneiss, (vi) the byproduct showed a decrease in strength of 87% after 40 SS cycles, suggesting that chemical weathering exerts a dominant control on the performance of LD slag. The findings are relevant to elucidate the physical and chemical weathering effects of LD slag and to promote its sustainable use.

Utilization of steel plant waste and by-products in reactive coke making

Coke is used in the blast furnace as a fuel. To produce the coke, metallurgical coals are blended in the coal blend. But the reserves of the coking coals are limited in India. Hence, there is a need to use the non-coking coals in the blast furnace. However, there is a limitation for use of non-coking coals in the coal blend for coke making. So, an attempt was made in this study to increase the amount of non-coking coals in the coal blends. In the present work, briquetting technique was used for producing briquettes having non-coking coal up to 40%, and rest is slightly coking coal along with reactive materials and binders. Those samples were compressed in a hydraulic press to form briquettes which were then carbonized. The strength and reactivity tests of those coal briquettes were carried out to determine the optimum addition proportion of reactive materials and binders. It was found that 10% of reactive material was optimum for briquette making. The use of coal tar pitch and petroleum pitch binders were also studied, and their optimum values were obtained as 3%. It was also found that coal briquettes comprising of LD (Linz-Donawitz) slag and iron oxide exhibited higher reactivity as compared to other reactive materials.

Mechanical and durability properties of concrete incorporating weathered coarse Linz-Donawitz (LD) steel slag

Concrete usage in recent decades has skyrocketed, which has led to immense pressure on the natural resources such as sand and aggregates involved in its production. The circular economy concept, i.e., usage and recycling of waste products, can be incorporated into concrete production to alleviate the overutilization of natural resources. LD slag is presently dumped as a landfill, aggravating limited land availability and polluting groundwater by leaching heavy metals in it. Previous studies employed Linz-Donawitz (LD) Slag as an alternative to natural aggregates in concrete production. However, none of the studies has focused on the comparative behavior of weathered LD slag incorporated in normal concrete (NC) and metakaolin-based high-strength concrete (HSC). The present experimental study focuses on determining the optimum replacement level of coarse aggregates with LD Slag. Coarse aggregates were replaced with LD Slag at 25, 50, 75 and 100%. Mechanical and durability properties such as hardened concrete density, ultrasonic pulse velocity, compressive strength, split tensile strength, flexural strength, modulus of elasticity, drying shrinkage, water absorption, sorptivity and abrasion resistance were evaluated. Results showed that replacing 75% of coarse aggregates with LD Slag displayed better results for said properties compared to the control mix, both for NC and HSC. Compressive strength, split tensile strength, flexural strength and modulus of elasticity were improved in the range of 7–9%, 19–29%, 6–11% and 7–16% for 75% replacements at 90 days of testing, respectively. Along with lower water absorption, abrasion, and drying shrinkage, the sorptivity coefficient was also reduced compared to control mixes at all testing ages. The usage of LD slag in concrete will result in waste elimination and management and prevent soil contamination.

Steel Converter Slag as an Oxygen Carrier—Interaction with Sulfur Dioxide

Steel converter slag, also called Linz-Donawitz (LD) slag, has been considered as an oxygen carrier for biofuel chemical looping applications due to its high availability. In addition to its content of iron which contributes to its oxygen-carrying capacity, LD slag also contains a significant amount of calcium. Calcium, however, is known to interact with sulfur, which may affect the usability of LD slag. To get a better understanding of the interaction between sulfur and LD slag, batch scale experiments have been performed using solid and gaseous fuel with or without sulfur dioxide, together with LD slag as an oxygen carrier. The reactivity and sulfur interaction were compared to the benchmark oxygen carrier ilmenite. Sulfur increases the gasification rate of biofuel char and the conversion of CO for both LD slag and ilmenite. However, no effect of sulfur could be seen on the conversion of the model tar species benzene. The increased gasification rate of char was suspected to originate from both surface-active sulfur and gaseous sulfur, increasing the reactivity and oxygen transfer of the oxygen carrier. Sulfur was partly absorbed into the LD slag particles with calcium, forming CaS and/or CaSO4. This, in turn, blocks the catalytic effect of CaO towards the water gas shift reaction. When the SO2 vapor pressure was decreased, the absorbed sulfur was released as SO2. This indicates that sulfur may be released in loop-seals or in the air reactor in a continuous process.

Fate of NO and Ammonia in Chemical Looping Combustion─Investigation in a 300 W Chemical Looping Combustion Reactor System

Chemical looping combustion (CLC) is a novel combustion concept that transfers oxygen from air to fuel using an oxygen carrier that circulates between an air reactor and a fuel reactor. Thus, the combustion products, H2O and CO2, are obtained in a separate flow, and ideally, a pure CO2 gas stream is obtained after condensation of H2O. Consequently, CLC has a unique potential for avoiding the high costs and energy penalties of CO2 capture. Further, NO emissions can potentially be avoided. CLC is flameless, and the temperature is too low for the formation of thermal NOx. Moreover, fuel NOx and prompt NOx do not form in the air reactor in the absence of fuel. In the fuel reactor, the absence of oxygen prevents normal NOx formation. However, when using fuels containing nitrogen, NO may form in the fuel reactor because the oxygen carrier can oxidize fuel nitrogen compounds. To achieve a CO2 stream suited for storage, NO must be removed. Dependent upon how NO is removed, the process could be free from any NO emissions. NO formation and NO reduction were investigated in a 300 W CLC reactor by adding either NH3 or NO. The work involved two different oxygen carriers, Linz–Donawitz (LD) slag and ilmenite, two temperatures, 850 and 900°C, two circulation rates, and different flows of syngas fuel. Further, operation without fuel with a fully and partially oxidized oxygen carrier was studied. For LD slag, lower fuel flow promoted the formation of NO and decreased the reduction of NO. Likewise, higher temperatures raised NO formation and lowered NO reduction. Ilmenite, however, was by far more superior with respect to NO. Thus, NO formation only occurred in the absence of fuel and with a fully oxidized oxygen carrier. Likewise, NO was fully reduced to N2 for all conditions, except in the absence of fuel and with fully oxidized ilmenite.