re Carbon capture from a cement plant

Thanks for your respond. You are right, almost same quantity of CO2 is produced, but the CO2 is separated in a concentrated form from the calciner, which will be ready for subsequent storage.

 I would like to ask another concern if you are available to answer it. Approximately 60% of the heat input is supplied into the pre-calciner in a cement process while the rest in the kiln. Is 60% a requirement? What happens if 80% instead of 60% is supplied into the calciner? Furthermore, do you think it is possible to reach 100% calcination efficiency in the calciner if it operates at 930 C? According to equilibrium of CO2 over CaO, it is possible. Moreover, can the precalciner in a cement plant be replaced with an circulating fluidized bed calciner? Sorry for the questions but I am not able to discuss those ideas with experts like you everyday. Thanks.

Regards

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re Carbon capture from a cement plant

Reaction of the decomposition of CaCO3 is the endothermic,   the majority of reactions of clinker formation is exothermic. Look the table of calculating the standard enthalpies of X. Taylor. Based on these data, calculate the heat balance. For a more accurate calculation the differential thermal analysis of the raw mix must be done.  Differential thermal analysis also give you information about   Reaction of the decomposition of CaCO3. It begin at 720 oC, max speed at 850 oC,  final at 920 OC. At 930 oC delete of CO2 is possidle.

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re Carbon capture from a cement plant

Hello Can1043,

As Michail has indicated, the energy 'split' of 60% to calcination and 40% to main burner is a thermodynamic requirement. The strongly endothermic reaction CaCO3 -> CaO + CO2 requires 60% of the total thermal energy.

Does your proposed process include fine grinding (~90% <90um) of the limestone and clay/sand/iron ore?  If so, this will require at least two separate raw material grinding systems.

Separating the limestone from the clay & corrective components below 1000deg C also has chemical implications;-

Chemical reactions start to occur between free CaO and SiO2, Al2O3 & Al2O3 at temperatures well below 930 degC. For instance, Belite starts to form by solid-solid reaction of CaO with ultrafine clay silicates as low as 600 degC.

The presence of clay minerals is also known to facilitate the calcination of limestone to CaO and CO2 at lower temperatures than for pure CaCO3.

 I suspect that separating the limestone from the clay & corrective components until later in the process and using different heating mechanisms for each stream will no doubt be more inefficient and costly.

Wouldn't it be better to simply extract the CO2 from the exhaust gases coming out of the stack? There is a large amount of waste heat produced by a clinker kiln which could be used to generate electricity to power a CO2 separation/capture plant. That way you also capture the CO2 from the fuels as well.

Regards,

Ted.

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re Carbon capture from a cement plant

Dear Ted,

Thanks for your answer. Actually, the idea was proposed by Dr Abanades from CSIC, Spain, and the research paper was titled "analysis of a process for capturing the CO2 resulting from the precalcination of limestone in a cement plant". You can find the article online but it requires a subscription.

I simulated reference cement process initially with a capacity of 115 ton clinker/h and calculated 60% energy requirement in the calciner whereas the rest of heat is supplied into the kiln. However, while the calcination efficiency is taken as 90% in the base cement plant, it is assumed to be 100% in the capture plant where CFB calciner is in use. Therefore, the heat requirement in calciner increases and more than 60% of heat is required in the CFB calciner for this case. I was asking if there are any problems when more than total 60% of heat input, for example 65%, is provided into the calciner. Of course, the other question is the use of CFB calciner in the cement process. 

I am aware of the reactions between CaO and clay minerals below 900 C. Unfortunately, the separation of limestone and clay is a requirement in the proposed system. However, according to my calculations, no additional heat is required compared to the reference plant whereas up to 56% CO2 is separated in pure form. I thought that partial belite formation which normally occurs below 900 C, takes place in the kiln with either longer kiln or higher solid residence times. Do you agree?

I agree that compared to the reference cement plant, two raw material grinding systems and a twin preheater are necessity but their total sizes should be similar to the ones in the reference plant.

In my simulation, the kiln gases at 320 C is sent to raw material and fuel drying units and leave the system at 110 C. There is a possibility to recover heat from excess air from the clinker cooler, which is at 279 C but the heat requirement in a post-combustion amine process is much higher than the possible heat recovery. Even the kiln at 320C is used for steam generation instead of used for raw material drying, I believe additional heat source is necessity.

I have been investigating the integration of a cement plant with different carbon capture processes such as calcium looping, amine-scrubbing, membrane separation process and oxy-combustion and would be happy to have any discussions on the subject. Thanks.

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