4.8 Cement Manufacturing & Combustion
Categories 36, 1747, 1748, and 1749
4.8.1 Introduction
The above-mentioned categories include primary emissions of criteria pollutants from cement manufacturing and plant-combustion activities. A summary of all categories and emissions processes covered is shown below:
| Category | Description | Classification |
|---|---|---|
| 36 | Cement Manufacturing | Point |
| 1747 | Cement Plant Combustion (coke) | Point |
| 1748 | Cement Plant Combustion (coal) | Point |
| 1749 | Cement Plant Combustion (natural gas) | Point |
Particulate matter (PM) is the primary pollutant of concern. PM at cement plants is generated during quarrying, crushing, grinding, blending, drying, transfer process, and storage of cement. These process emissions are reported within category 36. The single largest source of PM emissions is the pre-calciner kiln at one Bay Area facility. The cement industry generally uses mechanical collectors, electric precipitators, or bag houses to control emissions. The most desirable method of disposing of the dust collected by an emission control system is injection into kiln burning zone for inclusion in the clinker.
Various fuels are used to produce heat in the kiln for the cement manufacturing process. These fuels have included combustion of coke (accounted for in category 1747), coal (category 1748), and natural gas (category 1749). Since the year 2010, coal is no longer used as a fuel in the kiln. The emissions from these fuels are the five criteria pollutants, namely PM, reactive and total organics (ROG and TOG, respectively), nitrogen oxides (NOx), sulfur oxide (SOx), and carbon monoxide (CO) and are reported in the above-mentioned categories. Cement manufacturing process is a major source of Carbon Dioxide (CO2), a major greenhouse gas (GHG). CO2, methane (CH4), and nitrous oxide (N2O) are GHGs emitted during the combustion of the fuels.
Diesel fuel use in cement plants is mainly limited to emergency generators and portable compressors. These emissions used to be included in category 1750. Category 1750 has now been retired and all diesel fuel combustion emissions (region-wide) are now covered under category 304.
4.8.2 Methodology
Point Sources are operations that emit air pollution into the atmosphere at a fixed location within a facility, for which the Air District has issued a permit to operate, e.g. refinery cooling towers. These could also be a collection of similar equipment / sources located across multiple facilities, e.g. reciprocating engines.
During the permit to operate (PTO) issuance process, the BAAQMD collects information from the operating facility and/or determines from published literature, e.g. EPA’s AP-42, characteristics of a source including maximum throughput, emission factors for emitted pollutants, and control factors associated with downstream abatement devices. These characteristics are then stored for future use in the BAAQMD’s internal database. Facilities that hold a permit to operate are required to renew this permit periodically (this period varies based on facility and source type). Upon renewal, the facilities are requested to provide any updates to source characteristics as well as the source throughput for the last 12 months. This throughput, in combination with the emission factors and controls factors stored in the internal database, are used to estimate annual emissions at the source level. These source level emissions are then sorted and aggregated into categories.
Further speciation and quality assurance of emissions are performed as a part of the inventory process. The BAAQMD staff also perform a systematic crosswalk between CEPAM’s source category classification (Emission Inventory Code - EICs) and the District’s source category classification (category identification number - cat_ids), which ensures consistency in the annual emissions reporting process (CEIDARS) to California Air Resources Board. The last part of the inventory development process includes forecasting and back casting, and aggregation into sub-sectors and sectors for documentation purposes. For those years where no data is available, emissions data are backcasted to year-1990, as well as forecasted to year-2040 using either interpolation or another mathematical approach (see Trends section). Finally, emissions trends spanning from year 1990-2040 for each category and pollutant are evaluated for anomalies that are then investigated and addressed.
Categories 36, 1747, 1748 and 1749 are considered point source categories and follow the above methodology for emissions estimation. Category 1750 has been retired as all diesel-combustion emissions from backup generators and reciprocating engines across any facility in the Bay Area are now aggregated under a single Category 304.
The PM2.5/PM and the PM10/PM ratios for this category(s) are consistent with size fractions of speciation profiles made available by the California Air Resources Board (CARB) on their emissions inventory web-page53. For Category 36, CARB profile number 343 (cement production) is applied. PM2.5 constitutes 62% of the total PM for this profile, while PM10constitutes 92% of the total PM. For Categories 1747 and 1748, CARB profile number 131 (coke/coal combustion) is applied. PM2.5 constitutes 15% of the total PM for this profile, while PM10 constitutes 40% of the total PM. Finally, for Category 1749, CARB profile number 120 (gaseous combustion) is applied where PM2.5 is 100% of total PM.
The CO2 emission factor used in the cement manufacturing process was obtained from the California Climate Action Registry’s Cement reporting Protocol. The combustion sources (coke, natural gas and diesel) GHG emission factors for CO2, CH4, and N2O were obtained from the Department of Energy (EIA) and the California Energy Commission (CEC).
4.8.3 Changes in Methodology
Beginning in year 2017, major updates have been introduced to the methodology by which PM emissions for this sector are computed. The traditional approach of estimating PM emissions from combustion sources has been known to be not comprehensive, since it accounts for only the filterable portion of PM and not condensable PM. Condensable PM (PM-CON) are ultra-fine particles that are emitted from a high-temperature source in the gas phase and condense to sub-micron particles after cooling54. PM-CON is not typically captured by standard filter-based source tests that are used to calculate emission factors commonly used in emissions inventory calculations (e.g. AP-42).
The US Environmental Protection Agency (USEPA) codified the requirement to measure PM-CON as part of New Source Review (NSR) Implementation Rule in 2008, and the rule became enforceable in 2011. Method 202 is the EPA’s reference test method for quantifying the PM-CON fraction of primary PM55. Until the development and application of alternative Method 201a (for ambient sources)56, most air quality regulatory organizations did not require or enforce the PM-CON standards or measurement requirements.
The current methodology includes emission factors generated from source-specific District-approved source tests (mostly based on USEPA Method 201a) that account for the condensable portion of PM. The mass of PM-CON can often be several times the filterable component of PM emissions. Thus PM-CON has been estimated and included in PM10 and PM2.5 for this category since the year 2017 but not prior to that.
No other changes in methodology were made to this version of the base year emissions inventory.
4.8.4 Emissions
A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.
For most of 2000s and 2010s, the annual PM emissions within Category 36 averaged ~50 tons/year, but following the inclusion of PM-CON from year 2017 onwards, PM emissions have averaged ~500-600 tons/year. A similar spike has been observed in TOG (~450-650 tons/year) and CO (~3000-4000 tons/year). Category 1747 is a big regional source of NOx (~1300 tons/year) and SOx (~1000 tons/year) emissions in 2015. Category 1748 used to be a big source of criteria pollutants in the past (see ‘Trends’ section). Thus, these categories can be deemed to be large sources of criteria pollutant emissions in the Bay Area.
4.8.5 Trends
The PM emissions from Category 36 are heavily impacted by inclusion of condensable PM (PM-CON) into the inventory, starting at year 2017.
(a) Historical Emissions / History
Historical emissions for point source emissions are derived from source-specific throughputs provided by the permitted facility, compiled/reported emission factors, and regulation-based control factors. This information is archived in the BAAQMD’s internal database which is queried to retrieve the data for historical and current years. Interpolation techniques to account for missing data are used when necessary, this is the case for years 1991-1992.
Prior to year 2017 when PM-CON began to be accounted for within category 36, PM emissions from cement manufacturing processes remained fairly stable in spite of some specific rules (see below). Emissions of NOx, CO and SO2 from category 1747 (coke combustion) follow a distinct increasing pattern going from the 2000s to 2010s, as coke became an increasingly used fuel for cement manufacturing combustion. Emissions of the same pollutants within category 1748 (coal combustion) abruptly stop after year 2009 as coal was prohibited from being used as a fuel in 2010. Emissions of all pollutants are relatively minor to negligible for category 1749 (natural gas combustion) compared to category 1747 and 1748 in spite of its increasing use in 2010s.
Two federal rules address air emissions from Portland cement manufacturing, namely New Source Performance Standards (NSPS) and National Emission Standard for Hazardous Air Pollutants (NESHAPS). For specific industrial operations (such as cement manufacturing), EPA addresses criteria pollutants from new, modified and reconstructed sources through NSPS. NESHAP address emissions of hazardous air pollutants from both new and existing sources.
The cement manufacturing operations are subject to District regulations regarding permitting e.g. Rule 2-157 and Rule 2-258, emissions of toxic or hazardous compounds like Rule 2-559 and some regulations for individual pollutants. For example, Rule 6-160 reduces particulate emissions from the control imposed by Ringleman requirements.
The District adopted Rule 9-1361, Nitrogen Oxide, Particulate Matter, and Toxic Air Contaminants from Portland Cement Manufacturing, on September 17, 2012. This rule became effective on September 9, 2013 and limits the emissions of NOx, PM, and toxic air contaminants.
The overall control efficiencies (CE) of various pollutants as a result of this rule are listed below:
For Category 36, the overall CE of PM increases slightly, to over 99%.; the overall CE of organics is approximately 14%.
For Category 1747, the overall CE of NOx is 42%; the overall CE of organics is approximately 45%.
For Category 1749, the overall CE of NOx is 42%; the overall CE of organics is approximately 62%
(b) Future Projections / Growth
Forecasting of point source emissions is done based on calculations as shown in the equation below using recently updated growth profiles and a base year of 2020. The growth profiles for this base year inventory have been verified and updated to represent the most likely surrogate for growing emissions for a given category up to year 2040. Forecasting for point source emissions includes impact of in-place regulations, but does not include estimation of controls that will theoretically be implemented as part of future policy emission targets or proposed regulation and legislation.
\[ \text{PE} = \text{Gr} * \text{Ci} * \text{Ei} \] \(PE\) = projected emissions of pollutant i in a past or future year
\(Gr\) = growth rate by economic profile of industry or population
\(Ci\) = control factor of pollutant i based on adopted rules and regulations
\(Ei\) = base year emissions of pollutant i
The future projection of emissions does not take into account the known impact of COVID pandemic related changes to consumption demand and production estimates, as these throughput changes are not part of the business-as-usual scenario or expected to be permanent. In April 2020, the global COVID pandemic and reduction in demand led to Plant 17 ceasing the cement kiln operations and in November 2022, it was announced that the plant is shutting down permanently and will not resume operations. This will have a significant impact to the future emissions trend for these categories, although in this iteration of the current base year inventory, we project emissions without taking the current plant 17 closure into account.
Projections of emissions to year 2040 for Category 36 is based on a growth curve derived from the extrapolation of throughput from year 2011 through 2018. For Category 1747, NOx emissions are used for projections and a growth curve is derived and extrapolated for future years. A growth profile developed using CARB and CEC data to represent natural gas consumption in the Industrial sector is used to estimate future emissions from Category 1749 (natural gas combustion).
4.8.6 Uncertainties
Although PM-CON is now being accounted for in the cement manufacturing sector (from year 2017 onward), historical backcasting of PM-CON for prior years is not included in this iteration of the base year inventory. Consequently there is an order of magnitude difference in the total PM emissions from Category 36 in pre-2017 and post-2017 years. This leads to a huge discrepancy and uncertainty attached to the majority of the emissions estimates from this category. Inclusion of PM-CON emissions in the historical estimates of category 36 remains one of the major inventory updating and improvement projects going forward.
4.8.7 Contact
Author: Abhinav Guha
Reviewers: Tan M. Dinh and Yuan Du
Last Update: November 06, 2023
4.8.8 References & Footnotes
CARB. 2022. PMSIZE. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎
WVDEP. 2013. Particulate Matter Overview: Supplement to the Emission Inventory Guidance for Pollutant Reporting CY2013. West Virginia Department of Environmental Protection. https://dep.wv.gov/daq/planning/inventory/Documents/Filterable%20and%20Condensable%20PM.pdf↩︎
USEPA. 2016. Method 202. https://www.epa.gov/sites/default/files/2020-08/documents/m202-best-practices-handbook.pdf↩︎
USEPA. 2017. Method 201a. https://www.epa.gov/sites/default/files/2017-08/documents/method_201a.pdf↩︎
BAAQMD. 2021. Regulation 2 Rule 1. https://www.baaqmd.gov/rules-and-compliance/rules/reg-2-rule-1-general-requirements?rule_version=2021%20Amendment↩︎
BAAQMD. 2017. Regulation 2 Rule 2. https://www.baaqmd.gov/rules-and-compliance/rules/reg-2-rule-2-new-source-review↩︎
BAAQMD. 2021. Regulation 2 Rule 5. https://www.baaqmd.gov/rules-and-compliance/rules/reg-2-rule-5-new-source-review-of-toxic-air-contaminants?rule_version=2021%20Amendment↩︎
BAAQMD. 2018. Regulation 6 Rule 1. https://www.baaqmd.gov/rules-and-compliance/rules/reg-6-rule-1-general-requirements?rule_version=2018%20Amendment↩︎
BAAQMD. 2016. Regulation 9 Rule 13. https://www.baaqmd.gov/rules-and-compliance/rules/reg-9-rule-13--nitrogen-oxides-particulate-matter-and-toxic-air-contaminants-from-portland-cement-ma↩︎