Process for capturing CO2 arising from the calcination of the CaCO3 used in cement manufacture

Enflamed CO2 emissions from cement production in Nepal

Cement industry is one of the main contributors to greenhouse gas (GHG) emissions, specifically carbon dioxide (CO₂). This paper presents the cement production and the CO₂ emissions from the cement industry in Nepal. We compute emissions for the process-related, combustion-related (fuel use), and electricity-related activities during the cement production. We used eight emission factors (EFs) for the process-related, two EFs for the combustion or fuel-related, and two for the electricity-related activities using the previous researches. We computed the emissions as a product of the activities and the EFs. The estimated CO₂ emission in 2019 from the cement production is 3.45 ± 0.50 million metric tons (mMt) for Nepal. In 2019, the emissions are 1.87 ± 0.16 mMt from the process-related, 1.52 ± 0.34 mMt from the combustion-related, and 0.062 ± 0.004 mMt from the electricity use activities during the cement production in Nepal. Cumulative CO₂ emission was 22.73 ± 3.82 mMt from 1987 to 2019. Per capita CO₂ emission is 0.12 mMt for Nepal in 2019. Nepal contributes about 0.06% CO₂ emission from cement production to the global CO₂ emission (2.08 Gt) from the cement industry. By evaluating per capita gross domestic product (GDP) (from 1987/1988 to 2019/2020) and the human development index (HDI) (from 1990 to 2019) with the cement production, the result shows that cement production increases significantly (p < 0.01) with an increase in the GDP and the HDI. We emphasize that the study's outputs are directly relevant to the country's emission inventory, mitigation planning, and developing a strategy for cleaner production.

From Unavoidable CO2 Source to CO2 Sink? A Cement Industry Based on CO2 Mineralization

The cement industry emits 7% of the global anthropogenic greenhouse gas (GHG) emissions. Reducing the GHG emissions of the cement industry is challenging since cement production stoichiometrically generates CO₂ during calcination of limestone. In this work, we propose a pathway towards a carbon-neutral cement industry using CO₂ mineralization. CO₂ mineralization converts CO₂ into a thermodynamically stable solid and byproducts that can potentially substitute cement. Hence, CO₂ mineralization could reduce the carbon footprint of the cement industry via two mechanisms: (1) capturing and storing CO₂ from the flue gas of the cement plant, and (2) reducing clinker usage by substituting cement. However, CO₂ mineralization also generates GHG emissions due to the energy required for overcoming the slow reaction kinetics. We, therefore, analyze the carbon footprint of the combined CO₂ mineralization and cement production based on life cycle assessment. Our results show that combined CO₂ mineralization and cement production using today's energy mix could reduce the carbon footprint of the cement industry by 44% or even up to 85% considering the theoretical potential. Low-carbon energy or higher blending of mineralization products in cement could enable production of carbon-neutral blended cement. With direct air capture, the blended cement could even become carbon-negative. Thus, our results suggest that developing processes and products for combined CO₂ mineralization and cement production could transform the cement industry from an unavoidable CO₂ source to a CO₂ sink.

Characterization of a Marl-Type Cement Raw Meal as CO2 Sorbent for Calcium Looping

The use of cement raw meals as sorbent precursors for CO₂ capture can reinforce the synergies between the cement production process and calcium looping CO₂ capture technology. In this work, we measure the CO₂-carrying capacity of different calcined samples of a particular marl, which were obtained under very different calcination conditions and setups (a thermogravimetric analyzer, a drop tube furnace, and an industrial calciner). We find that the reactivity toward CO₂ of these calcined materials displays a strong sensitivity to the calcination conditions, in particular to calcination time. A pronounced competition between the belite (Ca₂SiO₄) formation reaction and the formation of free CaO needed for CO₂ capture is detected. As the calcination of the raw meal approaches flash conditions (i.e., >90% calcination conversion in less than 10 s), the belite formation is shown to be minimized, leading to sorbents with CO₂-carrying capacities of approximately 0.4 mol CO₂/mol CaO.

Selecting CO2 Sources for CO2 Utilization by Environmental-Merit-Order Curves

Capture and utilization of CO2 as alternative carbon feedstock for fuels, chemicals, and materials aims at reducing greenhouse gas emissions and fossil resource use. For capture of CO2, a large variety of CO2 sources exists. Since they emit much more CO2 than the expected demand for CO2 utilization, the environmentally most favorable CO2 sources should be selected. For this purpose, we introduce the environmental-merit-order (EMO) curve to rank CO2 sources according to their environmental impacts over the available CO2 supply. To determine the environmental impacts of CO2 capture, compression and transport, we conducted a comprehensive literature study for the energy demands of CO2 supply, and constructed a database for CO2 sources in Europe. Mapping these CO2 sources reveals that CO2 transport distances are usually small. Thus, neglecting transport in a first step, we find that environmental impacts are minimized by capturing CO2 first from chemical plants and natural gas processing, then from paper mills, power plants, and iron and steel plants. In a second step, we computed regional EMO curves considering transport and country-specific impacts for energy supply. Building upon regional EMO curves, we identify favorable locations for CO2 utilization with lowest environmental impacts of CO2 supply, so-called CO2 oases.

Calcium looping spent sorbent as a limestone replacement in the manufacture of portland and calcium sulfoaluminate cements

The calcium looping (CaL) spent sorbent (i) can be a suitable limestone replacement in the production of both ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement, and (ii) promotes environmental benefits in terms of reduced CO2 emission, increased energy saving and larger utilization of industrial byproducts. A sample of CaL spent sorbent, purged from a 200 kWth pilot facility, was tested as a raw material for the synthesis of two series of OPC and CSA clinkers, obtained from mixes heated in a laboratory electric oven within temperature ranges 1350°-1500 °C and 1200°-1350 °C, respectively. As OPC clinker-generating mixtures, six clay-containing binary blends were investigated, three with limestone (reference mixes) and three with the CaL spent sorbent. All of them showed similar burnability indexes. Moreover, three CSA clinker-generating blends (termed RM, MA and MB) were explored. They included, in the order: (I) limestone, bauxite and gypsum (reference mix); (II) CaL spent sorbent, bauxite and gypsum; (III) CaL spent sorbent plus anodization mud and a mixture of fluidized bed combustion (FBC) fly and bottom ashes. The maximum conversion toward 4CaO·3Al2O3·SO3, the chief CSA clinker component, was the largest for MB and almost the same for RM and MA.

Influence of microwave power, metal oxides and metal salts on the pyrolysis of algae

The work was to investigate the influence of microwave power, metal oxides and metal salts onto the pyrolysis of algae (4.55 wt.% moisture). It was found that the heating rate and the final temperature would increase as enhancing the microwave power. When microwave power increased from 750 W to 2250 W, the yield of solid residue decreased by 22.05%, and gas yield increased 39.45%. After adding 5% (mass basis) CuO and MgO, the yield of solid residue and bio-oil appeared the greatest decreasing ranges of 14.35% and 11.04%, respectively. Electrical energy consumption increased by 1.44% and reduced by 40.76% after CuO and MgO was added, separately. When algae was mixed with 5% (mass basis) MgCl2, ZnCl2 and NaH2PO3, respectively, the yield of solid residue increased by 3.98%, 1.13% and 2.31%, and the bio-oil yield increased by 6.3%, 16.92% and 0.71%, respectively. The effect of microwave absorption was ZnCl2>NaH2PO3>MgCl2.

Spray water reactivation/pelletization of spent CaO-based sorbent from calcium looping cycles

This paper presents a novel method for reactivation of spent CaO-based sorbents from calcium looping (CaL) cycles for CO(2) capture. A spent Cadomin limestone-derived sorbent sample from a pilot-scale fluidized bed (FBC) CaL reactor is used for reactivation. The calcined sorbent is sprayed by water in a pelletization vessel. This reactivation method produces pellets ready to be used in FBC reactors. Moreover, this procedure enables the addition of calcium aluminate cement to further enhance sorbent strength. The characterization of reactivated material by nitrogen physisorption (BET, BJH) and scanning electron microscopy (SEM) confirmed the enhanced morphology of sorbent particles for reaction with CO(2). This improved CO(2) carrying capacity was demonstrated in calcination/carbonation tests performed in a thermogravimetric analyzer (TGA). Finally, the resulting pellets displayed a high resistance to attrition during fluidization in a bubbling bed.

CO₂ capture from cement plants using oxyfired precalcination and/or calcium looping

This paper compares two alternatives to capture CO(2) from cement plants: the first is designed to exploit the material and energy synergies with calcium looping technologies, CaL, and the second implements an oxyfired circulating fluidized bed precalcination step. The necessary mass and heat integration balances for these two options are solved and compared with a common reference cement plant and a cost analysis exercise is carried out. The CaL process applied to the flue gases of a clinker kiln oven is substantially identical to those proposed for similar applications to power plants flue gases. It translates into avoided cost of of 23 $/tCO(2) capturing up to 99% of the total CO(2) emitted in the plant. The avoided cost of an equivalent system with an oxyfired CFBC precalcination only, goes down to 16 $/tCO(2) but only captures 89% of the CO(2) emitted in the plant. Both cases reveal that the application of CaL or oxyfired CFBC for precalcination of CaCO(3) in a cement plant, at scales in the order of 50 MWth (referred to the oxyfired CFB calciner) is an important early opportunity for the development of CaL processes in large scale industrial applications as well as for the development of zero emissions cement plants.