Electrified externally heated rotary calciner for calcination of cement raw meal

publishedVersio

The Use of Amine Reclaimer Wastes as a NOx Reduction Agent

AbstractAmine reclaimer wastes (ARW) generated in carbon capture and sequestration (CCS) is categorized as a hazardous waste which needs proper disposal. The proposal described in this paper can bring about a multi-effective solution to the problem of CCS waste handling. Both the pilot scale and the full scale experimental trials carried out in this study using ARW and pure monoethanolamine (MEA) confirmed the possibility of utilizing ARW as a potential reagent for the selective non-catalytic reduction (SNCR) of NOx in combustion flue gases. Even though the effectiveness of ARW is lower than that of aqueous ammonia, i.e. the most common SNCR chemical reagent used in industry (above 60% NOx reduction efficiency), ARW is nonetheless shown to possess valuable SNCR qualities (at least 20% NOx reduction efficiency) considering its availability as a waste product which has to be safely disposed. A series of thermo-gravimetric analyses provided important information on vaporization characteristics of amine reclaimer bottom wastes. The proposed methodology can lead to simultaneous energy and material resource recovery while primarily solving two environmental pollution problems, i.e. toxic ARW wastes generated in CCS, and emission of NOx a class of highly active greenhouse gases

Fluidized bed calcination of cement raw meal: Laboratory experiments and CPFD simulations

The chemical and thermal processes associated with the decarbonation and fuel combustion in the cement kiln process produce a large amount of carbon dioxide (CO2) contributing with around 8 % of the global CO2 emissions. Utilizing green electricity instead of fossil fuels to decarbonate the raw meal in the calciner can eliminate the CO2 emissions produced through fuel combustion and also provide a basis for simple capture of the CO2 generated through calcination because CO2 is the only gaseous product exiting from the electrified calciner. In the current work, an electrically heated fluidized bed (FB) reactor is being developed to calcine the raw meal. The FB may replace the traditional entrainment calciner used in many plants. The purpose is to enable efficient indirect heat transfer in the bubbling bed and hence obtain pure CO2 as the gaseous product from the calciner. The minimum fluidization velocity and pressure drop of the particle bed are important characteristics in the design of a bubbling fluidized bed, and these have been measured in a cold-flow lab-scale fluidized bed unit. The particle size distribution of the meal ranged from 0.2 – 180 µm, with a median particle size of 21 µm. The experimental results revealed that the regular cement raw meal is difficult to fluidize due to the large fraction of Geldart C particles in the meal. Based on experimental observation, this may be explained by inter-particular electrostatic forces forming particle clusters. The fluidization process has also been simulated with the commercial computational particle and fluid dynamics (CPFD) software Barracuda® (version 17.4.1). The purpose of using CPFD was to be able to simulate the process at cold-flow conditions and then, based on this, simulate the process at large-scale hot-flow conditions. The simulation results complied quite well with the lab-scale experiments and confirmed the difficult fluidization of the meal.acceptedVersio

Combined calcination and CO2 capture in cement clinker production by use of electrical energy

The technical feasibility of electrifying the calcination process in a precalciner cement kiln system was assessed by studying different electrification concepts. Resistance-based heating was selected as it requires no CO2 recycling, has a high electricity-to-heat efficiency and has no major safety concerns. Resistance-based heating may be implemented in different types of calcination reactors. In this study, a rotary calciner was selected because the material flow can be readily controlled, it appears to be technically feasible to implement heating elements with a sufficiently high surface temperature to perform calcination, and rotary kilns are already in use in the cement industry, hence can be regarded as well-known technology. It is possible to integrate the electrified calciner with an existing cement kiln system in such a way that minimum disturbance of the production process is obtained. Hence, no negative impacts on the process, product quality or emissions are expected. The required electrical energy input for calcination in a kiln system producing 1 Mt of clinker per year, is about 85 MW. An early-phase cost estimate was conducted resulting in total annualized costs of 67 € per ton of CO2 avoided. The net avoided CO2 emission was 72 % (using a CO2 footprint of 47 g/kWh for electrical energy). The described CO2 capture concept was technically and economically compared with amine-based absorption of CO2 from the preheater exhaust gas. Two amine-based cases were calculated, one using electrical energy as the source of solvent regeneration (85 % net CO2 reduction) and another one using only available waste heat as the energy source (48 % net CO2 reduction). The annualized costs of these two cases were 75 and 40 € per ton of CO2 avoided, respectively. Hence, in cement plants where large amounts of waste heat are available, aminebased absorption appears to be the least expensive option for reduction in CO2 emissions. However, in systems with no such waste heat available, electrified calcination, for example in the form of electrified rotary calciners, may be a competitive alternative to post-combustion capture technology.publishedVersio

Fluidized bed calcination of cement raw meal: Laboratory experiments and CPFD simulations

The chemical and thermal processes associated with the decarbonation and fuel combustion in the cement kiln process produce a large amount of carbon dioxide (CO2) contributing with around 8 % of the global CO2 emissions. Utilizing green electricity instead of fossil fuels to decarbonate the raw meal in the calciner can eliminate the CO2 emissions produced through fuel combustion and also provide a basis for simple capture of the CO2 generated through calcination because CO2 is the only gaseous product exiting from the electrified calciner. In the current work, an electrically heated fluidized bed (FB) reactor is being developed to calcine the raw meal. The FB may replace the traditional entrainment calciner used in many plants. The purpose is to enable efficient indirect heat transfer in the bubbling bed and hence obtain pure CO2 as the gaseous product from the calciner. The minimum fluidization velocity and pressure drop of the particle bed are important characteristics in the design of a bubbling fluidized bed, and these have been measured in a cold-flow lab-scale fluidized bed unit. The particle size distribution of the meal ranged from 0.2 – 180 µm, with a median particle size of 21 µm. The experimental results revealed that the regular cement raw meal is difficult to fluidize due to the large fraction of Geldart C particles in the meal. Based on experimental observation, this may be explained by inter-particular electrostatic forces forming particle clusters. The fluidization process has also been simulated with the commercial computational particle and fluid dynamics (CPFD) software Barracuda® (version 17.4.1). The purpose of using CPFD was to be able to simulate the process at cold-flow conditions and then, based on this, simulate the process at large-scale hot-flow conditions. The simulation results complied quite well with the lab-scale experiments and confirmed the difficult fluidization of the meal

Fluidized bed calcination of cement raw meal: Laboratory experiments and CPFD simulations

The chemical and thermal processes associated with the decarbonation and fuel combustion in the cement kiln process produce a large amount of carbon dioxide (CO2) contributing with around 8 % of the global CO2 emissions. Utilizing green electricity instead of fossil fuels to decarbonate the raw meal in the calciner can eliminate the CO2 emissions produced through fuel combustion and also provide a basis for simple capture of the CO2 generated through calcination because CO2 is the only gaseous product exiting from the electrified calciner. In the current work, an electrically heated fluidized bed (FB) reactor is being developed to calcine the raw meal. The FB may replace the traditional entrainment calciner used in many plants. The purpose is to enable efficient indirect heat transfer in the bubbling bed and hence obtain pure CO2 as the gaseous product from the calciner. The minimum fluidization velocity and pressure drop of the particle bed are important characteristics in the design of a bubbling fluidized bed, and these have been measured in a cold-flow lab-scale fluidized bed unit. The particle size distribution of the meal ranged from 0.2 – 180 µm, with a median particle size of 21 µm. The experimental results revealed that the regular cement raw meal is difficult to fluidize due to the large fraction of Geldart C particles in the meal. Based on experimental observation, this may be explained by inter-particular electrostatic forces forming particle clusters. The fluidization process has also been simulated with the commercial computational particle and fluid dynamics (CPFD) software Barracuda® (version 17.4.1). The purpose of using CPFD was to be able to simulate the process at cold-flow conditions and then, based on this, simulate the process at large-scale hot-flow conditions. The simulation results complied quite well with the lab-scale experiments and confirmed the difficult fluidization of the meal

CPFD simulation of enhanced cement raw meal fluidization through mixing with coarse, inert particles

In the current work, computational particle and fluid dynamics (CPFD) simulations are used to study an electrically heated bubbling fluidized bed (BFB) used as a calciner in a cement manufacturing process, applying a binary-particle fluidization system. Owing to the fine particle size (0.2 – 180 µm) of the limestone used as a raw meal in the cement kiln process, a conventional bubbling fluidized bed may be difficult to apply due to particle cohesion causing poor fluidizability of the particles smaller than 30 µm. In the current study, to enhance the fluidization of the raw meal particles, they are mixed with coarse (550 – 800 µm), inert particles. The aggregation and clustering of the fine particles will decrease due to collisions with inert coarse particles, and hence a more homogeneous distribution of raw meal particles may be achieved. The inert particles will also provide a thermal energy reservoir through their heat capacity and thereby contribute to a very stable bed temperature, which is advantageous in the control of the process. After the raw meal particles have been calcined, they have to be separated from the coarse, inert particles. This can be done by increasing the velocity of the CO2 used for fluidization to a value sufficiently high to entrain the raw meal particles, but still sufficiently low that the coarse, inert particles are not entrained. The commercial CPFD software Barracuda was used for simulations to investigate suitable operational conditions at 1173 K, such as the particle size distribution of the inert particles and the fluidization gas velocity. The impact of gas velocity variation on the fluidization of the particle mixture was studied, and an appropriate range of velocities for the calcination and entrainment modes could be determined. The simulations revealed that mixing raw meal particles with inert coarse particles can enhance the flowability in the FB reactor indicating that it is possible to apply the concept in a full-scale calcination process

Improved multi-stage cross-flow fluidized bed classifier

In the present work, improvements to a novel fluidized bed solids classification system previously published by Jayarathna et al. are discussed (Jayarathna et al., 2018 [1]). The system is designed for a high temperature application, namely solids classification in a CO2 capture plant incorporated with a coal-fired power plant. The capture plant is proposed to be equipped with the latest calcium looping technology, fully integrated calcium looping (FICaL). The classifier will be fed with a mixture of sorbent and heat transfer (inert) particles in the real plant at the operating temperature in between 910 °C and 600 °C. Due to the higher temperature it is not possible to use any sensitive process equipment such as filters or metal screens or any mechanically moving parts. Stepwise development of a such a system is explained in the previous publication by the authors (Jayarathna et al., 2018 [1]). In this work, the system is down-scaled into a smaller cold flow system, and zirconia and steel particles are used to mimic the sorbent and heat transfer solids particles in the hot flow system, respectively. Experiments and CFD simulations are carried out for the cold flow classification system. The previous fluidized bed design (Jayarathna et al., 2018 [1]) reached an efficiency of 90% and 99% recovery (10% and 1% loss) of the lighter (zirconia) and heavier (steel) components, respectively, but a 10% loss of sorbent particles in the real system would not be economical. The new modified system reached recovery efficiencies of 97% and 98% (3% zirconia loss and 2% steel loss) of the lighter and heavier component, respectively. CFD is used as a supporting tool in the design process, and also in making improvements to the design. Improvements are made by modifying the classifier geometry such as shape, height and internal design features. The experimental results from the improved classifier are compared with the CFD predictions made by the commercially available CFD software Barracuda® 17.1. Discrepancies between the experimental and simulated results are discussed, and the Barracuda CFD model is recommended as a good simulation tool for such studies and for upscaling the simulations for the hot flow system. The improved solid classifier design obtained good enough classification performances to proceed with upscaling and continue to make further improvements in the hot flow system. The iterative design and modeling effort from this research work has produced a functional, high-efficiency classification concept that can be used for the 1000 μm HT-solids particles and the 175 μm sorbent particles in the full-scale hot-flow system

Experimental Study of Thermal and Catalytic Pyrolysis of Plastic Waste Components

Thermal and catalytic pyrolysis of virgin low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and mixtures of LDPE/PP were carried out in a 200 mL laboratory scale batch reactor at 460 °C in a nitrogen atmosphere. Thermogravimetric analysis (TGA) was carried out to study the thermal and catalytic degradation of the polymers at a heating rate of 10 °C/min. The amount of PP was varied in the LDPE/PP mixture to explore its effect on the reaction. In thermal degradation (TGA) of LDPE/PP blends, a lower decomposition temperature was observed for LDPE/PP mixtures compared to pure LDPE, indicating interaction between the two polymer types. In the presence of a catalyst (CAT-2), the degradation temperatures for the pure polymers were reduced. The TGA results were validated in a batch reactor using PP and LDPE, respectively. The result from thermal pyrolysis showed that the oil product contained significant amounts of hydrocarbons in the ranges of C7⁻C12 (gasoline range) and C13⁻C20 (diesel range). The catalyst enhanced cracking at lower temperatures and narrowed the hydrocarbon distribution in the oil towards the lower molecular weight range (C7⁻C12). The result suggests that the oil produced from catalytic pyrolysis of waste plastics has a potential as an alternative fuel