The energy intensive nature of lime and dolime production and the chemical reactions that occur when the quarried rock is heated at high temperature, have long been known to cause significant production of carbon dioxide which in many cases is emitted to atmosphere.
The British lime industry is working hard to be at the forefront of the decarbonisation of lime production and has come together to set out an ambitious plan to accelerate decarbonisation and deliver ‘net negative’ carbon emissions by 2040. The MPA Lime Net Negative 2040 Roadmap explains how the sector can go beyond net zero a decade ahead of the UK’s overall 2050 target by deploying technologies such as fuel switching and carbon capture as well as recognition of lime’s natural carbon-absorbing properties. The roadmap also outlines the enabling actions required by Government and other industries in the supply chain.
In addition, international research confirms that around one third of the carbon dioxide from lime production is naturally reabsorbed from the atmosphere back into lime products – a process known as carbonation – though this is yet to be recognised in carbon accounting methodologies. Combining the industry proposed developments with the enabling action by Government and the natural effects of carbonation, means the production of British lime could become net negative by 2040, and make a positive and ongoing contribution to addressing climate change.
The deployment of five key levers are how lime production could be decarbonised by 2040:
Examples of enabling action by Government and other industries in the supply chain could include:
During 2022 MPA Lime and its members achieved a world first and took the bold step of trialling hydrogen as an alternative fuel for existing kiln systems with a view to clearly indicating whether hydrogen fuel is possible or desirable within the sector. The £2.82m project had been approved and funded through the UK Government Department for Business, Energy and Industrial Strategy (BEIS) Energy Innovation Programme, Industrial Fuel Switching competition phase 3. The project, titled: Alternatives to Natural Gas for High Calcium Lime Manufacturing: Hydrogen FS4243 was designed to provide fundamental knowledge that will inform the future strategic direction of the lime industry, in the UK and across the globe.
Demonstrating the viability of hydrogen as an alternative fuel for lime manufacturing, accompanied by the challenges conversion presents, enables future operational and capital investment to prepare the sector to be ‘hydrogen-ready’.
This project assessed short-term impacts, for example, implications on production and product quality. Longer term implications of hydrogen use will require longer term studies – for example, in process monitoring and control systems, emissions control, and in maintenance schedules.
The demonstration project showed that at low levels of hydrogen substitution (20% by volume) there is limited impact on kiln operation, lime product or emissions to air. However, at increasing substitution levels there are significant challenges in terms of kiln operation – risking sintering and kiln blockages. NOx emissions appeared to be lower than predicted by the CFD modelling, and manageable without the need to install additional abatement equipment.
The potential to produce lime with 100% hydrogen fuel would require significant, costly adaptations and installation changes to address all of the practical and safety related challenges, though it is considered that there is a pathway that can make this a reality.
View the BEIS Fuel switching report.
MPA Lime members are already actively involved in the development of carbon capture, utilisation and storage (CCUS) for their production sites:
MPA Lime members are all owned by international businesses, which are already involved, either as individual companies or as members of consortia, in the urgent research and development of transport and storage systems both in the UK and internationally. There is also UK and international research and development of existing and novel carbon capture and processing technologies, to provide efficient, safe and sustainable solutions.
What is also known is that the carbonation of lime and dolime products is the natural and desired outcome of many of the historic and still common applications of lime products. Carbonation is the natural absorption of carbon dioxide by lime and dolime products. Lime or dolime products are used in many essential applications from treatment of drinking water to abatement of polluting emissions and for key industries that are helping address climate change. Therefore, stopping production of lime and dolime products as they are currently manufactured is not a viable option, as alternative materials with lower emissions profiles for the applications that rely on lime and dolime products, are simply not available for a range of reasons. Accepting that lime production is to continue, the decarbonisation of the lime and dolime industry is clearly an urgent challenge to help address climate change and worldwide efforts are seen to be being aimed at achieving this as quickly as possible, whilst maintaining product availability and quality. Emissions of carbon dioxide from modern lime and dolime production arise from two sources, the combustion of the hydrocarbon fuels which causes around 25% of the emissions and from the process of the calcination of the rock which creates around 75% of the emissions.
In the case that all of the lime produced ends up being carbonated, then the amount of carbon dioxide released would be limited to that which occurs through the combustion process and the consequences of that depends on the fuel type used. Early production will have been with biomass or perhaps with bio-oils and it is not until the use of coal, crude oil and natural gas, and the expansion of lime use through the industrial revolution, that the impacts of carbon dioxide from lime products began to accelerate. Many of the current applications of lime products also cause them to be exposed to carbon dioxide in the atmosphere either immediately during use, or over a more extended period of time. With this exposure, the lime will chemically react with carbon dioxide present in the atmosphere, permanently capturing it as the lime returns back to a form of limestone. Recent international research has determined that across all modern lime product applications, approximately 33% of the total process carbon dioxide emitted during production is reabsorbed, with much of this occurring within the first year after lime production.
Image: Partly restored chalk quarry at Singleton Birch, North Lincolnshire. Image courtesy of Tom Gardner, Singleton Birch.
Two key applications of lime products have always involved the capture and use of the Carbon Dioxide emitted in the lime manufacturing process and this can mean that up to 100% of the CO2 liberated from the stone is not emitted to atmosphere. These applications are in the manufacture of Precipitated Calcium Carbonate (PCC) and in the processing and production of sugar.
PCC is produced for a wide variety of uses including in the paper, food, nutritional supplements and pharmaceutical industries, as well as in the production of many sealants, paints and polymers.
The production of PCC is carried out by production of quicklime that is then carefully mixed with water to produce a hydrated lime slurry and the slurry then has the captured CO2 bubbled through it in a carefully controlled process to form PCC products with specific designed characteristics.
The use of naturally abundant Calcium Carbonate, namely limestones and chalks cannot be a substitute for the PCC products as the natural forms of the rocks are very different to the controlled, processed forms and thus cannot replicate the designed characteristics of PCC. The production of sugar involves a carbonation process stage in sugar refineries to purify and clarify the sugar liquor. It involves the same production processes as for PCC up to the point of producing the hydrated lime slurry and then the precipitation of Calcium Carbonate is used by adding the slurry to the sugar liquor and then bubbling the CO2 through it which causes impurities in the sugar to be captured by formation of Calcium Carbonate as it precipitates out of solution by the addition of the CO2.