Cement Kilns: Difference between revisions

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* Stage 3 - '''Pre-heating Raw Material''': a pre-heating chamber using kiln 'exhaust' gases to reduce energy consumption and pre-condition the raw material into oxides.

* Stage 4 - '''Kiln Phase''': the principle phase which produces a '''clinker''', exiting the kiln in marble-sized nodules - it is the binder that is used in cement products.

* Stage 5 - '''Cooling and Final Grinding''': the clinker is rapidly air-cooled and gypsum (and other active ingredients as required) is added to the clinker and ground to a fine power to produce '''cement'''

* Stage 5 - '''Cooling and Final Grinding''': the clinker is rapidly air-cooled and gypsum (and other active ingredients as required up to around 5%) is added to the clinker and ground to a fine power to produce '''cement'''

* Stage 6 - '''Packing and Shipping''': the cement is conveyed from grinding mills to silos where it is then packed in bags.

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{| class="wikitable"

|-

! Category !! Description !! Proportion of clinker !! Proportion of other materials

! Category !! Description of Cement !! Proportion of clinker !! Proportion of other materials

|-

| CEM I || Portland cement || 95 to 100% || 0 to 5%

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| CEM V || Composite cement (incorporating both GGBS and pozzolanic material) || 20 to 64% || 18 to 50% GGBS; 18 to 50% Pozzolanic material

|}

In 2018 the UK produced 7,734,000 tonnes of clinker, leading to to the manufacture and sale of 10,076,000 million tonnes of cement (including 935,000 tonnes of imported cement) by the five main companies in the UK. Imports by others and other cementitious materials (fly ash and GGBS) bought the total UK cementitious materials to 15,188,000 tonnes in 2018<ref>[https://cement.mineralproducts.org/documents/2018-07-23_ANNUAL_Cementitious.pdf MPA Annual Cementitious 2001-2018]</ref>.

==Use of Waste - Historical Context==

The introduction of waste materials - or 'Alternative Raw Materials' as coined by the industry - can be as part of the kiln phase or the final grinding stage and it can be used as an additive or as a fuel in the process.

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* the ability of the clinker to absorb heavy metals into its structure<ref>[https://en.wikipedia.org/wiki/Cement_kiln Wikipedia Entry]</ref>

'''By 2005''' the range of alternative fuels had expanded in Europe to include [[Tyres|tyres]], [[Plastic|plastic]], [[Paper|paper]], [[~~Refuse Derived Fuel~~]], dried [[Sewage Sludge|sewage sludge]], [[MBM|meat and bone meal]] and some other waste streams, with fuel costs typically accounting for 30 to 40% of operating costs<ref>[https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/291569/scho0106bjzn-e-e.pdf Environment Agency Science report on Solid Waste Derived Fuels in Cement Kilns, an International perspective]</ref>. This was driven by the cement industry looking to reduce its costs and carbon emissions, and by changes in the waste sector around the [[Landfill Directive]] and the introduction of the [[Landfill Tax]] which made cement kilns an alternative outlet for suitably prepared waste materials/[[Waste Derived Fuel]].

'''By 2005''' the range of alternative fuels had expanded in Europe to include [[Tyres|tyres]], [[Plastic|plastic]], [[Paper|paper]], [[RDF]]/[[SRF]], dried [[Sewage Sludge|sewage sludge]], [[MBM|meat and bone meal]] and some other waste streams, with fuel costs typically accounting for 30 to 40% of operating costs<ref>[https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/291569/scho0106bjzn-e-e.pdf Environment Agency Science report on Solid Waste Derived Fuels in Cement Kilns, an International perspective]</ref>. This was driven by the cement industry looking to reduce its costs and carbon emissions to make a more sustainable product, and by changes in the waste sector around the [[Landfill Directive]] and the introduction of the [[Landfill Tax]] which made cement kilns an alternative outlet for suitably prepared waste materials/[[Waste Derived Fuel]].

'''By 2010''' the MPA reports that 1,528,315 tonnes of waste by-products were used as fuel and raw materials in UK cement manufacture, accounting for 7.2% of cement production and the proportion of fuel comprising waste was 39.7%<ref name = ''ref1''/>.

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|}

In the table above the [[EWC]] code for the waste is shown as well as the description - [[Hazardous Waste]] is signified by entries where the six-digit [[EWC]] code is marked by an asterisk (*). Note that the two codes [[EWCChap19|19 12 10]] (generally [[SRF]]) and [[EWCChap19|19 12 12]] (generally [[RDF]], but can be used to describe 'process fines' by some operators) which together account for 318,595 tonnes (or 42% of the tonnage recorded) and comes primarily from the processing of [[Residual Waste]]. The other primary codes used as fuel are [[EWCChap19|19 02 08*]] (the solvent based fuels) and [[EWCChap16|16 01 03]] (waste tyres) which together account for 153,474 tonnes (or 20% of the tonnage recorded) meaning that of the 753,783 tonnes recorded in 2018, 62% were from 4 waste types that all were used as fuel in the cement process.

In the table above the [[EWC]] code for the waste is shown as well as the description - [[Hazardous Waste]] is signified by entries where the six-digit [[EWC]] code is marked by an asterisk (*). Note that the two codes [[EWCChap19|19 12 10]] (generally [[SRF]]) and [[EWCChap19|19 12 12]] (generally [[RDF]], but can be used to describe 'process fines' by some operators) which together account for 318,595 tonnes (or 42% of the tonnage recorded) and comes primarily from the processing of [[Residual Waste]]. The other primary codes used as fuel are [[EWCChap19|19 02 08*]] (the solvent based fuels) and [[EWCChap16|16 01 03]] (waste tyres) which together account for 153,474 tonnes (or 20% of the tonnage recorded) meaning that of the 753,783 tonnes recorded in 2018, 62% were from 4 waste types that all were used as fuel in the cement process. Tonnage of [[MBM]] and [[Wood Waste]], which may have been higher in previous years are not shown to be so high in 2018, as alternative [[Biomass Waste EFW]] plants have been developed for them that have competed with the cement kilns.

==List of UK Grinding and Blending Sites==