Energy Balance

The process requires energy: energy to quarry the limestone, energy to crush it into pieces, energy to calcine it into lime and energy to dispose of the lime in seawater. This section examines how much energy is required. If that energy is supplied by a carbon-containing fuel, then carbon dioxide will be generated – the amount of carbon dioxide generated will depend upon the type of fuel used.

  • How much energy is used in the production of lime in current industrial processes? How much heat energy is used (to heat the limestone) and how much electrical energy is used (to drive machinery)?
  • How much carbon dioxide is generated during the production of lime (both from the calcining of the limestone and from the combustion of the fuel)? How does this amount vary dependant on the calcining method used and the type of fuel used?
  • Are there any methods of calcining limestone that produce a pure stream of carbon dioxide from the calcination of the limestone (i.e. physically separating the calcination of the limestone from the heating (see diagram), as opposed to co-firing the fuel/air mix with the limestone in a kiln)? If so, how energy efficient are they?

If you are able to help answer any of these questions, please get in touch with us.  This project cannot progress without your input.

 

5 people have left a comment

Alberto says: July 22nd, 2009

Please let me give you some Thermodynamics topics concerning your idea, how you talk about it.

1-You mine CaCO3 (let’s say 1 tonn) … spending energy…
2-You heat CaCO3 to extract CaO (you’ll need to heat to over 900°C… a lot of energy, at least 6 MegaJoules per 100g)
3-Once heat, CaCO3 will absorb 176 KJoules/100g (about 1760 Megajoule for 1 tonn) to decompose to CaO and CO2… producing CO2
4-…now you propose to use this CaO to trap some new CO2 on water… some CO2 that will be less than you’ve already spent!!!

First problem: what you have been doing is get free one CO2 molecule to absorb another CO2 molecule… not so smart…
Second problem: In order to decompose CaCO3 you’ll have to spend 1760 MJ or energy per 1 tonn of CaCO3, the equivalent you might produce burning 53 kg of carbon and producing 196 kg of CO2… all of that to trap 440 kg of CO2… and I didn’t count the energy needed for heating and all other operations!!!

Short: you are proposing to take a substance, spend a lot of energy (and produce a lot of CO2) to extract its CO2 and send it into the atmosphere so that you’ll be able to re-trap some of the CO2 you have just been producing… on thermodynamics, it doesn’t make sense…

Alberto

Ps: as you wanted numbers…
1-Energy needed to calcinate CaCO3: 176 Kjoule/100g CaCO3, equivalent to producing AT LEAST 19,6 g of CO2; heating CaCO3 to 900°C: 6 MJoule/100g CaCO3 theoric (based zero loss efficiency)
2-CO2 generated during the production of lime: 44g CO2 from 100g CaCO3 decomposition, 19.6 g CO2 due to you need to give energy to decompose 100g CaCO3… at least 180g CO2 for heating of 100g CaCO3 based on Carbon rich fuel
3-CaCO3 calcination is a process that is thermodynamically possible only at very high temperature (900°C or more); no way of proceeding without heating.

limexpert says: January 4th, 2010

I want to communcate you the right value of CO2 that will be retained for the life cycle analysis of lime concerning France and that has been published by the french Lime Association: One metric ton lime is produzing 1059 kg of CO2 from the quarry up to silo before loading. You can use this value to calculate the CO2 balance of your project for production of bicarbonate. The produced lime is evaluated with 98% of purity. That means that to produce bicarbonate with one metric ton of such lime you can absorb : 1000 X 0,98 / 56 X 44 X 2 = 1500 kg of CO2. There is a favorable balance of 441 kg of absorbed CO2 by 1 metric ton of lime.

limexpert says: January 4th, 2010

The french lime assosciation calculated the CO2 impact of lime by using a high percentage of fossil energies. If you produce the lime with solar energy or biomass energy we can gain a great part of CO2 due to energy.
My opinion is that it could be possible to produce the lime directly by attaking the limestone with a concentrated sunray – solar kiln – without extraction of limestone in a quarry.

Dennis says: October 27th, 2010

In your detailed proposal, you mention reacting the lime with water to form calcium hydroxide, before putting it in the ocean. That reaction is exothermic. Could that heat be used to reduce the overall energy requirement?

varun gor says: April 12th, 2011

how to calculate heat balance in vertical gas based regenerative kiln? from where i could start calculation for it?

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