can1043
5 posts
TimePosted 26/12/2013 23:14:46
can1043 says

Carbon capture from a cement plant

Dear all,

I am a PhD student and have been working on CO2 capture from cement plants. I need your comments and suggestions for a process available in the literature. The title of reference study is "Analysis of a Process for Capturing the CO2 resulting from the Precalcination of Limestone in a Cement Plant". In this process, in a place of pre-calciner, two reactors are occupied, which are calciner and external combustor. The calciner operates at 930 C and that is for the combustor is 1050 C. The system use circulating fluidized bed, and the solids from the combustor is circulated back to the calciner to satisfy heat requirement. Therefore, the CO2 from calcination of limestone can be captured in pure form. In summary, it separates combustion and calcination reactions into two different chambers. Since it is a conceptual design, process integration of this idea has not been proposed yet. First of all, I would like to ask your opinion for the idea, what do you think? What are the challenges for this process? I have been working on the process integration of this design into a cement plant. In the reference paper, only CaO is circulated between the reactors but in real cement process, the raw material contains limestone, clay and quartz. To prevent circulation of clay between the reactors, I thought that there would be a possibility of separate limestone from the other raw materials and use of a twin preheater. The limestone and clay minerals will be heated up in two different preheaters and only CaO will be circulated. They will be then mixed after the calciner. At this point, I am not sure how this change in cement plant affects the cement chemistry. I know that partial belite formation at the last stage of preheater and in the precalciner but I do not know what would happen actually.

I appreciate all your contributions in the forum where more realistic issues have been discussed. I also know that many of you may not agree with the idea proposed here but I would really appreciate of you can share your comments and suggestions. Thanks.

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Silastman
80 posts
TimePosted 28/12/2013 04:47:18
Silastman says

re Carbon capture from a cement plant

Dear can1043 !

Without the concept of and chemical reactions underlying your proposal, it is not entirely clear. If you can provide, please concept and chemical reactions with the calculation of enthalpy and Gibbs energy. In addition, a calculation of the balance of energy and mass of the material.

 

With The Best Regards !

Dr. Michail A. Miheenkov

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can1043
5 posts
TimePosted 28/12/2013 09:30:26
can1043 says

re Carbon capture from a cement plant

Dear Dr Miheenkov (Silastman),

I can explain the concept better.I solved mass and energy balances in a commercially available process simulator called UniSim. I did it for both reference cement plant and the proposed configuration.

In the proposed design, limestone and clay are fed into two different preheaters. The flue gases heat them up to ~750 C. Only partially calcined limestone is fed to a calciner at 930 C in which I assumed full calcination. The calciner is coupled with a circulating fluidized bed combustor which operates at 1050 C. There is no combustion in the calciner but in the combustor. Solids from the combustor (97 wt% CaO) are circulated back to the calciner and provide heat required in this reactor. The only reaction occurring in this CFB system is the calcination reaction.

The CaO leaving the calciner is mixed with preheater clay and sent to the kiln. All the clinkerization reactions, the formation of alite, belite, aluminate and ferrite, are completed in the kiln. This is the concept which provides up to 56% CO2 avoidance from a cement plant with same amount of total thermal energy requirement with the reference cement plant.

I was asking, first of all, the comments of experts. I did mass and energy balances already and may publish them if we feel that it works. What is not clear for me the clinker chemistry. In the reference cement plant, I normally assume that partial belite formation occurs in the last stage of the preheater and calciner but in the proposed design the limestone and clay are mixed after the calciner. Will it affect the clinker composition significantly? Thanks.

Regards

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Silastman
80 posts
TimePosted 28/12/2013 12:10:00
Silastman says

re Carbon capture from a cement plant

 

From the basics of Thermodynamics the reaction of formation of belit in  mixture is  happens when the temperature at which it is possible (Gibbs energy is negative). If the mixture is heat up to that temperature in the kiln, the belit and other minerals of  cement clinker also emerge in the kiln. More fundamentally, the amount of heat required to remove CO2 from pure CaCO3 more than in mixed with clay. Also it is not clear what reduced CO2 emissions. Regardless, you burn pure CaCO3 or burn it mix with clay, at equal quantity CaCO3 , the same quantity CO2 will be allocated.

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