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Help with modelling CCS technologies for cement industry
#1
Hello,

I am new to TIMES and seeking some advice in order to better capture certain dynamics in my representation of the cement industry. I aim to explore net-zero pathways for the cement industry by 2050, with an emphasis on fuel-switching flexibility, while giving the model an option for incorporating CCS for existing facilities to influence future investment decisions. Given the short timeline (about 25 years), retrofitting existing facilities with CCS appears to be crucial and gives a more consistent picture of how things could go in reality to the model. However, the problem is that the model structure is designed in a way that the burner is divided from the kiln (to capture fuel switch options and reflect the costs, efficiencies, etc., related to each carrier). And this makes modeling carbon capture technologies, in particular, more challenging. I have outlined two different modeling approaches so far, as explained below, and I would appreciate feedback or suggestions for capturing better what could happen in reality.

Please note that in both approaches, the kiln (calcination) is distinct from the burner (furnace), followed by a finishing stage where clinker is mixed with additives to produce cement.


1. Separate Technologies Approach (This seems to be the most common way of modeling CCS in TIMES models): Here, each technology (e.g., burners, kilns) is modeled separately with and without CCS. This complicates capturing CCS's potential for existing technologies and doesn't dynamically account for trade-offs between CCS implementation and fuel switching. The other problem is with the separated burners as, in reality, when you implement a CCS unit, it will capture the emissions coming from the kiln (which includes the fuel emissions, too), and therefore in the model, one should be able also to capture the emissions from burner and to do so I would need to define new technologies for burners again too (let's say with 5 burners and 3 CCS technologies, for each burner 4 (w/o CCS + 3 w CCS)=20 technologies should be added, and same goes for the kiln technologies). Furthermore, assigning CCS costs based on activity unit capacity (Mt for kiln and PJ for burner) and fuel emission factors presents challenges. Also, the type of CCS technology selected for each might differ, while in reality, the fuel combustion and calcination occur in one place.

2. Integrated Plug-in Approach: Here, CCS is treated as a plug-in technology (so the capacity of this is based on kt) (various CCS technologies exist) that is applied across the cement production stages (kiln and burner). This model reduces the number of technologies by channeling all emissions through each CCS technology or a dummy process where no capture occurs. After doing some runs, I noticed that with TIMES where no demand is defined for a commodity, the process won't be active (valid for both CCSs and dummy). To solve this, user constraints are defined based on the activities of host technologies by adjusting the total flow of emissions coming out of (the kiln and burner) to be equal with CCS and dummy accordingly. This way, the CCS technologies would work until there's some activity for kilns. However, the challenge related to this approach would be the compatibility of the CCS capacity with the capacity of each production technology, as there's only one process defined for each CCS technology type (also, in reality, one builds a CCS plant to capture emissions coming from a certain facility, and when the facility expires, there would be no point for the CCS to exist except the host will be renewed too). This way of considering emissions as a pool might also create problems, such as capturing some of the emissions with MEA while the rest go through calcium looping, for example, and both emissions might come from one specific technology. I am not sure how realistic such simplifications would be on a national (one or two countries) or regional (e.g., Nordics) scale. On the other hand, this approach gives the model a handful of options and freedom to choose if it wants to invest in CCS for existing ones or build new ones from scratch, where again it can use it with OR w/o CCS.

Could you provide insights on improving these approaches or suggest alternative methods to capture better the interactions between CCS deployment (for existing stock and new technologies) and fuel switching in the cement industry? I can provide you with more details about my case if needed.


Looking forward to comments.

Thanks!
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#2
Welcome to the Forum.

> I noticed that with TIMES where no demand is defined for a commodity, the process won't be active (valid for both CCSs and dummy).

I don’t think this is a fair statement about TIMES.  I think you are probably just using a commodity balance (which is the default for ENV commodities), whereas it seems to me that you should apparently use a fixed balance for the commodity in this case. Defining user constraints for adjusting the total flow of emissions coming out of the kiln and burner to be equal with the input to the CCS and dummy should be quite unnecessary.

> Could you provide insights on improving these approaches or suggest alternative methods to capture better the interactions between CCS deployment (for existing stock and new technologies) and fuel switching in the cement industry?

It seems to me that the TIMES retrofit / lifetime extension options might suit well for your purpose. You could allow the model to have the option of replacing the existing capacity by a refurbishment add-on technology (with CCS, among any number of different options), with the desired additional investment cost, fixed O&M costs, variable costs and other process characteristics (e.g. with fuel switching). However, when using the retrofit/LE options, the size of the model is likely to increase more than with the simplistic plug-in options you described.

The documentation for the TIMES Retrofits and Lifetime extensions facility is found here.

There are some examples linked on the VEDA Forum, see e.g. the following thread: CCS retrofit file documentation

Of course, fuel switching and CCS can be also combined in any technology in TIMES, with the captured amount of CO2 (and the related electricity consumption for e.g. compression), process efficiency and variable costs all depending on the fuel(s) used.
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#3
Thank you, Antti,  for the prompt reply and helpful links!

> I don't think this is a fair statement about TIMES. I think you are probably just using a commodity balance (which is the default for ENV commodities), whereas it seems to me that you should apparently use a fixed balance for the commodity in this case. Defining user constraints for adjusting the total flow of emissions coming out of the kiln and burner to be equal with the input to the CCS and dummy should be quite unnecessary.


You are right. It makes sense when there's no consumption the process shouldn't be active unless the balance is defined otherwise. As you suggested, the problem with idle processes was resolved after changing the commodity balance to fixed instead of the default balance (without any user constraints).

You could allow the model to have the option of replacing the existing capacity by a refurbishment add-on technology (with CCS, among any number of different options), with the desired additional investment cost, fixed O&M costs, variable costs and other process characteristics (e.g. with fuel switching).

I went through the documentation and ran the example a few times to see how it works. However, since our model is a full energy system and all industries have stock instead of PASTI, I wanted to ask how this could change the results in the retrofit case compared to the latter? I find it challenging to track exactly how much of the stock is refitted. It seems like with stock, by default, the capacity reduces linearly to zero at the end of the lifetime. 

Also, with the salvage cost, I understand that by defining the NCAP_FDR, you can enable the salvage cost for the host process. Apparently, for the retrofit (-1) technology, there’s no salvage cost unless one defines it as a life extension (+1). So, how can one compare the greenfield versus brownfield if it is very close to the end of the time horizon (model end year) and the cost calculations related to the retrofit don’t have a salvage cost?


Another question I have is related to common approaches in the modeling industry sector: Why, usually, in models, is the industry modeled based on STOCK and not PASTI? In the real world, that’s not how industrial units operate. Is it because modelers tend to enforce the model to replace capacities with new technologies, or are there other reasons behind this?

Thank you.
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#4
> However, since our model is a full energy system and all industries have stock instead of PASTI, I wanted to ask how this could change the results in the retrofit case compared to the latter?

The TIMES retrofit options can never create any new capacity. Therefore, if you use PRC_RESID for defining the phase-out of existing capacity, the capacity of a retrofit option will always be at most the original capacity.  For example, if you have defined a linear phase-out of the existing capacity, and at some year the remaining capacity is fully retrofitted, that retrofitted capacity can of course then only follow the subsequent phase-out trajectory. But if only half of the capacity is retrofitted, then the subsequent phase out of the original capacity can be fully allocated to the non-retrofitted portion as long as such remains, and only after the non-retrofitted portion has been fully retired, the retrofitted capacity would need to start following the trajectory. I hope that is understandable?

> I find it challenging to track exactly how much of the stock is refitted.

Why so? The Var_Cap attribute should give you exactly the amount of capacity retrofitted or life-extended. 

> It seems like with stock, by default, the capacity reduces linearly to zero at the end of the lifetime.

No, there is no such default.  But it can be forced to be so when defining existing capacities with a linear phase-out.  Then any fully retrofitted capacity simply must follow the same trajectory, because a retrofit can not not create any new capacity, it can only replace the old capacity with the retrofitted capacity. The lifetime extension options never have such characteristic; while replacing the old capacity they effectively create new capacity with a well-defined lifetime.

> Apparently, for the retrofit (-1) technology, there’s no salvage cost unless one defines it as a life extension (+1).

Yes, as described in the documentation.  In general, it is not possible to define a consistent salvage value for a retrofit, because its lifetime is endogenous. And I guess it is even somewhat questionable whether retrofit costs should have salvage value. But of course, you could annualize the investment costs and thereby add all the investment costs as a fixed O&M costs, which should effectively result in costs equivalent to those with a salvage value. You may ask why there isn't an option available to do that automatically, and the answer is that it is now left to the user if such is wanted, because if doing so, it would make it possible to retire the retrofit investment at any point with a full salvage credit for the remaining lifetime (unless when using the forced retrofit option). And for the annualizing one would need to use some lifetime assumption, not quite known apriori.

> So, how can one compare the greenfield versus brownfield if it is very close to the end of the time horizon (model end year) and the cost calculations related to the retrofit don’t have a salvage cost?

Well, I think in most models retrofits would be deployed for existing capacities that would usually either be retired before the EOH anyway, or the salvage value of the retrofit investment would be very small, and not much affecting the cost-optimal decisions. However, with LE options you could ensure full salvage values.
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