re Carbon capture from a cement plant

Hello Can1043,

Thanks for the information.     To answer your questions;

(1)  In a normal suspension preheater/calciner kiln, supplying more than 60% of the total heat input to the calciner would most likely be disastrous. Since all of the necessary ingredients to produce clinker are present in exactly the right proportions and in a finely-divided state, there is always a delicate balance between calcination (900 -1050C) and clinkerisation (>1150C).

As long as the endothermic calcination reaction is absorbing heat, the hot meal does not reach a sufficient temperature to melt and form clinker. However, as soon as there is more than enough heat to balance the calcination reaction, there is the likelihood of a large temperature increase and the very real danger of producing clinker in the calciner.

Such an outcome would be catastrophic. The calciner, bottom cyclones and/or kiln inlet would become totally blocked by a mass of clinker that would take days or weeks to jack-hammer out.

However, in your proposed process such an outcome would be highly unlikely since you are only calcining relatively pure limestone, so there is little danger of producing clinker in the calciner.

(2)   Yes, without a preheater/calciner, a longer kiln would be required to ensure preliminary belite formation. But this would be a backward step for the cement industry. In the past, kilns were much longer and thermally inefficient. The innovation of suspension preheaters and pre-calciners allowed the kiln to be shortened and significantly lowered the specific heat consumption (MJ/t clinker), cutting production costs dramatically. These days cost effectiveness is absolutely essential for the survival of a cement plant, so my guess is that, in the foreseeable future at least,  it will be almost impossible to convince cement producers to go back to longer kilns.

You mentioned longer kiln residence times as an alternative solution. Unfortunately material residence time within the kiln has both production and quality implications which, again, would be costly to solve.

I wish you well with your project and if you have any technical questions regarding cement manufacture or process chemistry etc. I would be only too happy to answer them if I can..

Regards,
Ted.

 

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re Carbon capture from a cement plant

I agree with Ted. The benefits of your proposal are not clear, the disadvantages are obvious. I advise you to consider the option of a single flow in fluidized bed. In fluidized bed ratio solid/gas more than in ciclon. Thus in the fluidized bed you will get a higher concentration of CO2 & in the single flow will be gases from the decomposition of the CaCO3 and from burning fuel.

 

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re Carbon capture from a cement plant

Dear Ted and Silastman,

Thanks for the replies. In order to explain the proposed design and its benefits in details, I tried to attached couple of schematic diagrams with mass and energy balances but it did not allow me to upload a zip file. Please find the file here  https://www.dropbox.com/s/al05mz31mc54uir/D_Ozcan.zip . The zip-file is confidential and password protected so if you can send me an email to shareonly_cemnet@outlook.com I will send you the password asap.

I did proper mass and energy balances considering all major reactions in a cement plant. The CFB calciner temperature is set to 930 C rather than 915 C in the reference plant, and complete calcination is assumed. Thus, temperature never reaches over 930 C in the calciner of proposed system. The CaO from the calciner is mixed with clay and then fed to the kiln. The temperature of CaO+clay mixture is 845 C. The hot solid particles are circulated between the calciner and an external combustor which operates at 1050 C. The heat requirement in the calciner is met by hot solid (CaO) from the combustor. Therefore, the gas stream from the calciner only contains CO2 in pure form.

If you have any time to give your comments on the attached schematic diagram, I would appreciate. The benefit is high concentrated CO2 removal from calcination of limestone, 56% avoidance without a CO2 capture unit. I am willing to discuss disadvantages of the system as well as suggestions from you, by respecting your experience.Thanks.

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