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Effects of impurities on phase equilibrium in quicklime and cement clinker production
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
2024 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Effekter av orenheter på kemisk jämvikt vid produktion av bränd kalk och cementklinker (Swedish)
Abstract [en]

The production of quicklime and cement clinker are energy-intensive processes resulting in significant CO2 emissions. Fuel switching, electrified heating, and carbon capture have gained attention as means of addressing this. Conventional production processes are direct-fired, meaning that the impurities, which originate from either quarries or fuels, interact with the product, influencing process performance and product quality. The suggested strategies for addressing CO2 emissions will alter the process conditions. For example, introducing electrified heating using plasma would shift the process atmosphere to primarily CO2, possibly affecting volatilisation and recirculation. The overall aim of this thesis was to generate new knowledge on the impact of impurities under process conditions in the context of the shift towards more sustainable quicklime and cement clinker production. 

Limestone surface impurities and their effects on quicklime product quality were evaluated. Ash-quicklime interactions were studied both on a laboratory scale and using multicomponent chemical equilibrium calculations (MECs). The volatilisation of minor elements in cement clinker production was investigated on a laboratory scale, and using a counter-current MEC-model with both a conventional combustion atmosphere and high-CO2 atmosphere. 

The detailed analysis of the limestone surface layer showed enrichment of impurities. However, quicklime sampled from a parallel flow generative kiln (PFR) showed low amounts of reactants from surface impurities, which were suggested to contribute to build-ups and increased levels of lime-kiln dust instead. Laboratory-scale studies of coal ash and quicklime interactions and MECs showed that typical cement clinker phases are thermodynamically stable at the coal ash-quicklime interface. Porosity and pore-size distribution were evaluated in pure quicklime samples and quicklime samples exposed to olive pomace, pine bark, and wheat straw ash. Olive pomace ash affected quicklime microstructure severely by increasing porosity and pore size. The laboratory study on the volatilisation of minor and trace elements in cement clinker formation showed higher retention of K, Na, and S in a high CO2 atmosphere, likely explained by low H2O partial pressure and high CO2 partial pressure. Counter-current MECs showed lower enrichment of K, Na, and S in a high CO2 atmosphere.

Future work is suggested to investigate the fate of surface impurities entering industrial PFR kilns. Further, the effect of biomass ash on quicklime microstructure should be evaluated in a complete combustion atmosphere, as should the effects of the rolling bed and recirculation of volatile elements in the rotary kiln. The effects of an altered process atmosphere on cement clinker quality and the volatilisation of minor and trace elements are interesting topics for further studies, e.g. in a pilot-scale rotary kiln.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2024. , p. 76
Keywords [en]
Thermodynamic equilibrium calculations, thermal process chemistry, olive pomace, pine bark, wheat straw, microstructure, porosity, linear intercept method, electrification, combustion atmosphere
National Category
Chemical Engineering Energy Engineering
Identifiers
URN: urn:nbn:se:umu:diva-223880ISBN: 9789180703963 (electronic)ISBN: 9789180703956 (print)OAI: oai:DiVA.org:umu-223880DiVA, id: diva2:1855537
Public defence
2024-05-31, BIO.E.203 - Aula Biologica, Biologihuset, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2024-05-08 Created: 2024-05-02 Last updated: 2024-05-02Bibliographically approved
List of papers
1. Impact of limestone surface impurities on quicklime product quality
Open this publication in new window or tab >>Impact of limestone surface impurities on quicklime product quality
2024 (English)In: Minerals, E-ISSN 2075-163X, Vol. 14, no 3, article id 244Article in journal (Refereed) Published
Abstract [en]

Quicklime is produced through the thermal processing of limestone in industrial kilns. During quarry operations, fine particulate quarry dust adheres to limestone lump surfaces, increasing the bulk concentration of impurities in limestone products. During thermal processing in a kiln, impurities such as Si, Mg, Al, Fe, and Mn react with Ca, reducing quicklime product quality. Which reactant phases are formed, and the extent to which these result in a reduction in quality, has not been extensively investigated. The present study investigated as-received and manually washed limestone product samples from two operational quarries using elemental compositions and a developed predictive multi-component chemical equilibrium model to obtain global phase diagrams for 1000–1500 °C, corresponding to the high-temperature zone of a lime kiln, identifying phases expected to be formed in quicklime during thermal processing. The results suggest that impurities found on the surface of the lime kiln limestone feed reduce the main quality parameter of the quicklime products, i.e., calcium oxide, CaO (s), content by 0.8–1.5 wt.% for the investigated materials. The results also show that, in addition to the effect of impurities, the quantity of CaO (s) varies greatly with temperature. More impurities result in more variation and a greater need for accurate temperature control of the kiln, where keeping the temperature below approximately 1300 °C, that of Hatrurite formation, is necessary for a product with higher CaO (s).

Place, publisher, year, edition, pages
MDPI, 2024
Keywords
calcium oxide, chemical equilibrium calculations, thermal process chemistry
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:umu:diva-223093 (URN)10.3390/min14030244 (DOI)2-s2.0-85189068374 (Scopus ID)
Funder
Swedish Energy Agency, 50224-1Vinnova, 2015-04541
Available from: 2024-04-11 Created: 2024-04-11 Last updated: 2024-05-02Bibliographically approved
2. Characterization of limestone surface impurities and resulting quicklime quality
Open this publication in new window or tab >>Characterization of limestone surface impurities and resulting quicklime quality
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-223876 (URN)
Available from: 2024-04-30 Created: 2024-04-30 Last updated: 2024-05-02
3. Coal ash and limestone interactions in quicklime production
Open this publication in new window or tab >>Coal ash and limestone interactions in quicklime production
2021 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 300, article id 120989Article in journal (Refereed) Published
Abstract [en]

This paper reports on results from detailed studies on coal ash and limestone interactions during calcination. Industrially produced quicklime from a coal-fired rotary kiln was analyzed and compared with laboratory-scale studies of surface interactions between two coal ashes and limestone. Exposure tests were performed at 1,100 °C and 1,350 °C, in a high CO2 atmosphere. SEM-EDX analyses of the ash-quicklime interface were performed to detect and quantify changes in microstructure, as well as the depth of ash interaction into quicklime. Stable phases in the ash-quicklime interface were assessed by multi-component chemical equilibrium calculations based on local EDX analysis. The industrially produced quicklime showed intrusion by extraneous elements, mainly Al and Si, up to 800 µm into the quicklime, in accordance with expected ash composition, based on the ash analysis of coal fuel used. In laboratory-scale and 1,100 °C, ashes appeared solid to a large extent, and no distinctive microstructure difference of quicklime was observed underneath the ash-quicklime interface. At 1,350 °C, the ashes appeared molten to a large extent, and the quicklime microstructure was affected compared to at 1,100 °C, resulting in densification. For both temperatures and both coal ashes, the interface reactions reduced the amount of reactive CaO, thereby resulting in a decrease in product quality. The laboratory methodology was shown to be useful to increase mechanistic understanding of the ash-quicklime interactions. The method could be expanded to test other limestone qualities and fuels, e.g. renewable biofuels.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Ash-quicklime interactions, Coal ash, Quicklime product quality, Quicklime production
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:umu:diva-183786 (URN)10.1016/j.fuel.2021.120989 (DOI)000659195600005 ()2-s2.0-85106278311 (Scopus ID)
Available from: 2021-06-02 Created: 2021-06-02 Last updated: 2024-05-02Bibliographically approved
4. Solid biofuel combustion or electrification for limestone calcination: Effects on quicklime surface microstructure
Open this publication in new window or tab >>Solid biofuel combustion or electrification for limestone calcination: Effects on quicklime surface microstructure
2022 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 326, article id 124955Article, review/survey (Refereed) Published
Abstract [en]

Net CO2 emissions from the production of quicklime can be reduced by introducing renewable solid fuels or sustainably produced electricity for heating of the process. This paper reports the results of a study examining the effects of new heat sources on quicklime surface reaction products and on quicklime microstructure. Limestone was heated to 1100 °C and 1350 °C in high CO2 atmosphere under three conditions: i) an ash mixture representing conventional coal and a solid biofuel (olive pomace); ii) olive pomace ash, and iii) no ash representing an electrically heated process. The ash-quicklime interfaces of the samples were analyzed for elemental composition and microstructure using SEM-EDX. Multi-component chemical equilibrium calculations were used to assess the stable chemical phases in the interface. Coal-olive pomace ash mixture resulted in coarsening of the quicklime microstructure; this effect was less severe compared to that of pure olive pomace ash. The calculations indicated that the potassium in olive pomace ash was bound to Si- and Al-rich coal ash phases. Exposure to potassium-rich olive pomace ash resulted in severe coarsening of the quicklime microstructure. The difference was most obvious at 1,350 °C, and was probably the result of intrusion of a potassium-rich salt melt. For limestone without ash, the quicklime showed enhanced sintering and reduced porosity at the higher temperature, in agreement with previous studies. Interface reactions and microstructure coarsening, here most apparent for the case with olive pomace, could be problematic in industrial quicklime production since they may contribute to decreased available CaO and reactivity.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Quicklime microstructure, Ash-quicklime interactions, Available CaO, Limestone calcination, Coal ash, Biomass ash
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-199585 (URN)10.1016/j.fuel.2022.124955 (DOI)000824761700004 ()2-s2.0-85132932615 (Scopus ID)
Funder
Swedish Energy AgencyUmeå University
Available from: 2022-09-20 Created: 2022-09-20 Last updated: 2024-05-02Bibliographically approved
5. Microstructural characterization of quicklime exposed to biomass ash at high temperature
Open this publication in new window or tab >>Microstructural characterization of quicklime exposed to biomass ash at high temperature
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-223877 (URN)
Available from: 2024-04-30 Created: 2024-04-30 Last updated: 2024-05-02
6. Influence of a high-CO2 atmosphere on the volatilization of minor and trace elements during cement clinker formation
Open this publication in new window or tab >>Influence of a high-CO2 atmosphere on the volatilization of minor and trace elements during cement clinker formation
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-223878 (URN)
Available from: 2024-04-30 Created: 2024-04-30 Last updated: 2024-05-02

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7891011121310 of 18
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