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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Calcium looping | 3/6 | https://en.wikipedia.org/wiki/Calcium_looping | reference | science, encyclopedia | 2026-05-05T10:46:20.922266+00:00 | kb-cron |
=== Sintering === CaO is also prone to sintering, or change in pore shape, shrinkage and grain growth during heating. Ionic compounds such as CaO mostly sinter because of volume diffusion or lattice diffusion mechanics. As described by sintering theory, vacancies generated by temperature sensitive defects direct void sites from smaller to larger ones, explaining the observed growth of large pores and the shrinkage of small pores in cycled limestone. It was found that sintering of CaO increases at higher temperatures and longer calcination durations, whereas carbonation time has minimal effect on particle sintering. A sharp increase in sintering of particles is observed at temperatures above 1173 K, causing a reduction in reactive surface area and a corresponding decrease in reactivity. Solutions: Several options to reduce sorbent deactivation are currently being researched. An ideal sorbent would be mechanically strong, maintain its reactive surface through repeated cycles, and be reasonably inexpensive. Using thermally pre-activated particles or reactivating spent sorbents through hydration are two promising options. Thermally pre-activated particles have been found to retain activity for up to a thousand cycles. Similarly, particles reactivated by hydration show improved long term (after~20 cycles) conversions. Additionally, an optimized make-up strategy can maintain sufficient levels of activity without excessively increasing operating costs.
== Disposal of waste sorbent ==
=== Properties of waste sorbent === After cycling several times and being removed from the calcium loop, the waste sorbent will have attrited, sulfated and become mixed with the ash from any fuel used. The amount of ash in the waste sorbent will depend on the fraction of the sorbent being removed and the ash and calorific content of the fuel. The size fraction of the sorbent is dependent on the original size fraction but also the number of cycles used and the type of limestone used.
=== Disposal routes === Proposed disposal routes of waste sorbent include:
Landfill; Disposal at sea; Use in cement manufacture; Use in flue gas desulfurisation (FGD). The lifecycle CO2 emissions for power generation with CaL and the first three disposal techniques have been calculated. Before disposal of the CaO coal power with CaL has a similar level of lifecycle emissions as amine scrubbing but with the CO2-absorbing properties of CaO CaL becomes significantly less polluting. Ocean disposal was found to be the best, but current laws relating to dumping waste at sea prevent this. Next best was use in cement manufacture, reducing emissions over an unabated coal plant by 93%.
==== Use in lime and cement manufacture ==== The manufacture of lime and cement is responsible for approximately 8% of the world's CO2 emissions. Around 65% of this CO2 comes from the calcination of calcium carbonate as shown earlier in this article, and the rest from fuel combustion. By replacing some or all of the calcium carbonate entering the plant with waste calcium oxide, the CO2 caused from calcination can be avoided, as well as some of the CO2 from fossil fuel combustion. This calcium oxide could be sourced from other point sources of CO2 such as power stations, but most effort has been focussed on integrating calcium looping with Portland cement manufacture. By replacing the calciner in the cement plant with a calcium looping plant, it should be possible to capture 90% or more of the CO2 relatively inexpensively. There are alternative set-ups such as placing the calcium looping plant in the preheater section so as to make the plant as efficient as possible or to indirectly heat the calciner for increased energy efficiency. Some work has been undertaken into whether calcium looping affects the quality of the Portland cement produced, but results so far seem to suggest that the production of strength-giving phases such as alite are similar for calcium looped and non-calcium looped cement.
== Direct Separation Technology == Calix Ltd has developed a new type of kiln that enables the CO2 from the calcination process to be driven off as a pure stream. Calix achieves this by calcining finely ground CaCO3 continuously down vertical reactor tubes. The reactor tubes are heated from the outside using electricity or fuel ensuring the CO2 stream is pure and not contaminated with air or combustion products. This technology has been successfully piloted in Europe by a cooperative industry group with support from the European Union as the Low Emission Intensity Lime And Cement (LEILAC1) reactor project. The study report concluded that the technology could capture C02 from full scale lime and cement kilns at €14 to €24/t. Transport and storage costs are not included in this estimate and will be dependent upon infrastructure available near the cement or lime plant A FEED study is underway for a larger commercial demonstration kiln proposed for the Heidelberg Cement plant in Hannover (LEILAC2). This commercial demonstration kiln is designed to capture 100ktpa CO2. Leilac-2 passed its Financial Investment Decision (FID) in March 2022, and its Front End Engineering Design (FEED) Study Summary was completed and published on 13 October 2023, leading to a new and improved design and revised timeline. The next milestone is procurement of long lead items, currently underway (2023). This type of kiln is also being studied as a potential method to decarbonise shipping through both looping and single use processes. The single use process would involve using CaCO3 to be sown over the ocean, thereby permanently capturing addition carbon from the ocean as the CaCO3 reacts to form Ca(HCO3)2 and reversing ocean acidification.
== Economic implications ==
Calcium looping has several economic advantages.