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TECHNICAL MEMORANDUM

TO: Tina Ndoh, U.S. EPA/OAQPS/SPPD - Minerals and Manufac turing Group

FROM: Eastern Research Group, Inc.

DATE: June 9, 2015

SUBJECT: Maximum Achievable Control Technology (MACT) Floor Ana lysis for

Phosphate Rock Calciners at Phosphoric Acid Manufacturing Plants – Final Rule

1.0 INTRODUCTION
This memorandum presents the methodology and results of the maximum achievable control technology (MACT) floor determinations for mer cury (Hg) and total fluoride for phosphate rock calciners in the final rule for phosphoric a cid manufacturing plants (40 CFR part 63, subpart AA). The proposed rule included emissions limits f or hydrogen fluoride, instead of total fluoride, but these limits were not finalized. Tot al fluoride emission limits, as a surrogate for hydrogen fluoride, were determined; see the preamble for discussion regarding total fluoride versus hydrogen fluoride limits for phosphoric acid manufac turing plants. The organization of this memo is as follows:

2.0 Summary of Existing Limits

3.0 MACT Floor Determination Methodology for Phosphate Rock C alciners

3.1 Use of Non-Detect Values 3.2 Phosphate Rock Calciners – Hg Emission Limit 3.3 Phosphate Rock Calciners – Total Fluoride Emission Limi t

4.0 References Appendix A: Hg UPL Calculations Appendix B: Total Fluoride UPL Calculations

2.0 SUMMARY OF EXISTING LIMITS
The existing National Emissions Standard for Hazardous Air Pollutants (NESHAP) for phosphate rock calciners in the phosphoric acid manufacturi ng plants source category (40 CFR Part 63, subpart AA) established emission limits for parti culate matter (as a surrogate for hazardous air pollutant (HAP) metals). Table 2-1 summarize s this emission limit.2 Table 2-1. Existing Emissions Limits for Particulate Mat ter from Phosphoric Acid Manufacturing Plants under 40 CFR Part 63, Subpart AA

Equipment Description Particu late Matter (gr/dscf) Existing Sources New Sources Phosphate rock calciner 0.080 0.040 gr/dscf – grains per dry standard cubic foot

3.0 MACT FLOOR DETERMINATION METHODOLOGY FOR PHOSPHATE ROCK CALCINERS Section 112(d) of the CAA requires EPA to set emissions standards for HAP emitted by major stationary sources based on performance of the M ACT. The MACT standards for existing sources must be at least as stringent as the average e missions limitation achieved by the best performing 12 percent of existing sources (for which the Admi nistrator has emissions information) or the five best performing sources for sou rce categories or subcategories with less than 30 sources (CAA section 112(d)(3)(A) and (B)). For new sources, MACT standards must be at least as stringent as the control level achieved in practice by the best controlled similar source (CAA section 112(d)(3)). These requirements constitute the MACT floor for new and existing sources. EPA may not consider costs or other impacts i n determining the MACT floors. EPA must consider cost, non-air quality health and environmenta l impacts, and energy requirements in connection with any standards that are more stringent than the MACT floor (beyond-the-floor (BTF) controls).

In order to determine the MACT floor, the EPA calculat es the upper prediction limit (UPL). Justification for using the UPL and the UPL calc ulation procedures are discussed in the UPL memorandum 1 . The UPL represents the value the mean of future test run observations can be expected to fall below, based on the results of the i ndependent sample of size (n) from the same population. Therefore, should a future test condition be selected randomly from any of these sources (e.g., average of three runs), one can b e confident (99 percent confident in the case of a 99 percent UPL) that the reported level will fall below a MACT floor emission limit calculated using a UPL.
The UPL is the appropriate statistical tool to use to acc ount for variability in the concentration data from phosphoric acid manufacturing pl ants. For these emission points, where there is a limited sampling of the source category and E PA does not have test data from all of the emission points for a pollutant in the subcategory, the predictive aspect of the UPL calculation is especially important.
Only one facility currently operates phosphate rock calcine rs; PCS Aurora. In response to an April 2010 CAA section 114 request, PCS Aurora provided Hg (by US EPA Method 30B) and total fluoride (by US EPA Method 13B) emissions testing results for one of the six calciners to the EPA. In addition, the facility provided Hg emission s testing results (by US EPA Method 30B) for another, previously untested calciner in response t o a January 2014 CAA section 114 request. For additional information, refer to the separat e Information Collection memorandum 2

. The following sections describe the methodology used to c alculate MACT floors for total fluoride and Hg for phosphate rock calciners at phosphoric a cid manufacturing plants.3

3.1 Use of Non-Detect Values As part of the MACT floor methodology, we compare the UPL to non-detect data, in the form of three times the representative detection limi t (RDL), an as additional UPL check. At very low emission levels where emission tests result ed in ND values, the inherent imprecision in the pollutant measurement method has a large influence on the reliability of the data underlying the regulatory floor emission limit. Because of sample and emission matrix effects, laboratory techniques, sample size and other factors, method detecti on levels normally vary from test to test for any specific test method and pollutant measurement. Th e confidence level that a value measured at the detection level is greater than zero is about 99 percent. The expected measurement imprecision for an emission value occurrin g at or near the method detection level is about 40 to 50 percent. Pollutant measurement imprecision de creases to a consistent level of 10 to 20 percent for values measured at a level about three times the method detection level.
The procedure for determining a representative detection li mit (RDL) starts with identifying all of the available reported pollutant specific method detection levels for the bestperforming units regardless of any subcategory (e.g., existin g or new, fuel type, etc.). From that combined pool of data, the arithmetic mean value is calcul ated. By limiting the dataset to those tests used to establish the floor or emissions limit (i. e., best performers), the result is representative of the best-performing testing companies a nd laboratories using the most sensitive analytical procedures. The outcome should minimize the e ffect of a test(s) with an inordinately high method detection level (e.g., the sample volume wa s too small, the laboratory technique was insufficiently sensitive, or the procedure for determining the minimum value for reporting was other than the detection level). The resulting mean of the method detection levels is designated as the RDL as characteristic of accepted source emissions measurement performance.
The second step in the process is to calculate three ti mes the RDL to compare with the calculated floor or emissions limit. The multiplicati on factor of three is used to reduce the imprecision of the analytical method until the imprecisi on in the field sampling reflects the relative method precision as estimated by the Reference Method Accuracy and Precision (ReMAP) study. 3 That study indicates that such relative imprecision re mains a constant 10 to 20 percent, over the range of the method. For assessing th e calculated floor results relative to measurement method capabilities, if three times the RDL were less than the calculated floor or emissions limit (e.g., calculated from the UPL), it w ould be determined that measurement variability was adequately addressed. The calculated floor or emissions limit would need no adjustment. If, on the other hand, the value equal to thr ee times the RDL were greater than the UPL, it would be concluded that the calculated floor or e missions limit does not account entirely for measurement variability. Where such was the case, t he value equal to three times the RDL would be substituted for the calculated floor or emissio ns limit, which results in a concentration where the method would produce measurement accuracy on the order of 10 to 20 percent, which is similar to other EPA test methods and the results f ound in the ASME ReMAP study.
We used a procedure similar to the one discussed above to c alculate the three times RDL value for Hg measured by US EPA Method 30B and for total fluor ide measured by US EPA Method 13B. Facilities submitted US EPA Method 30B and US E PA Method 13B concentration data (including non-detect values) in response to the April 13, 2010 section 114 request and PCS Aurora submitted additional US EPA Method 30B concentration data in response to the January4

24, 2014 section 114 request. The concentration data included test ing from phosphate rock calciners, WPPA, SPA, and phosphate fertilizers process l ines. First, we identified the method detection levels reporting by the facilities. Second, we then treated the average of the method detection levels as the RDL value for Hg and total fluori de. Finally, we calculated three times the RDL value and compared to the UPL values.

3.2 Phosphate Rock Calciners – Hg Emission Limit For Hg, we calculated MACT floors for phosphate rock cal ciners after evaluating the variability in the concentration data reported by PCS Aurora. Hg emissions data were available for two phosphate rock calciners, see Table 3-1 for the ave rage Hg concentration for each. Calciner Hg emissions are the result of Hg contained in th e fuel and raw materials. Because the six phosphate rock calciners are designed to be identica l and use the same raw materials and fuels, Hg emissions from the six calciners are expecte d to be identical. Therefore, all Hg data from the calciners were combined into one dataset to deter mine both new and existing MACT floors.

Table 3-1. Average Concentration of Mercury from Phosphat e Rock Calciners (as Measured by US EPA Method 30B)

Facility and Process Line Average Hg Concentration (mg/dscm @ 3% O 2 ) PCS Aurora (202) 9.87E

- 02 PCS Aurora (203) 9.92E

- 02 mg/dscm @ 3% O 2 – milligrams per dry standard cubic meter corrected to 3 percent oxygen

We performed skewness and kurtosis tests, and determined the Hg data have a normal distribution. The normal distribution UPL equation was t hus applied; see the UPL memorandum 1 for additional background. Results of the UPL analysis o f Hg emissions data from phosphate rock calciners, including the final existing source limit, are presented in Table 3-2. The complete UPL analysis for Hg is presented in Appendix A. As previousl y discussed, the data used to determine the MACT floor for existing and new sources are the same.

Table 3-2. MACT Floor Analysis and Existing Source Limit for Mercury (by US EPA Method 30B) – Phosphate Rock Calciners

Parameter Value Distribution Normal 99.0% UPL (mg/dscm @ 3% O 2 ) 1.40E-01 3x RDL (mg/dscm @ 3% O 2 ) 5.71E

- 03 Existing Source MACT Floor Emission Limit for Hg [1] (mg/dscm @ 3% O 2 ) 1.40E-01
[1] - MACT floor limits were rounded up to two significant f igures (e.g., 100.1 would be rounded to 110). mg/dscm @ 3% O 2 – milligrams per dry standard cubic meter corrected to 3 percent oxygen RDL – representative detection limit

At proposal, Hg emission limits for existing and new sour ces were set equal to a more stringent BTF limit. After additional consideration, w e are not finalizing the BTF limit for5

existing phosphate rock calciners, but instead finalizing flo or level limits based on feedback received during on the proposed rule. The MACT floor calcu lated limit for Hg emissions from existing phosphate rock calciners is shown in Table 3-2. W e are, however, finalizing the BTF limit for new phosphate rock calciners. See the preamble and a separate BTF Analysis memorandum

4 for additional discussion regarding the BTF limits. The BTF new source limit was determined by estimating the emissions which would be achieva ble using a Hg control device (e.g., activated carbon injection) at phosphate rock cal ciners. Based on the available data, it was determined that 90 percent Hg reduction is achievable. Theref ore, the BTF limit for Hg, as seen in Table 3-3, is 10 percent of the calculated MACT limit.

Table 3-3. New Source BTF Mercury Limit – Phosphate Rock Ca lciners

Parameter Value New Source BTF Limit for Hg (mg/dscm @ 3% O 2 ) 1.40E-02

mg/dscm @ 3% O 2 – milligrams per dry standard cubic meter corrected to 3 percent oxygen

3.3 Phosphate Rock Calciners – Total Fluoride Emission Limit Total fluoride data were available for one phosphate rock c alciner at PCS Aurora, with three test runs. Therefore, we have a limited dataset f or the pollutant total fluoride from phosphate rock calciners. The first step in the UPL meth odology involves determining the distribution. Because there are only three test runs, the kurtosis function in Excel does not work; it requires at least 4 values in order to avoid dividing by zero. Therefore, a separate kurtosis estimator and distribution methodology is used. This metho dology compares the ratio of skewness to the standard error of the skewness for both the raw and log transformed data. The lower of the two ratios identifies the data distributio n that best represents the sample set. After applying these equations, we determined the total fluoride data are normally distributed.
We evaluated this specific dataset to determine whether it i s appropriate to make other modifications to the UPL approach used to calculate the MACT floor as a result of the limited data. For the phosphate rock calciner dataset, we perfor med the following steps: we selected the data distribution that best represents the dataset; ensur ed that the correct equation for the distribution was then applied to the data; and compared i ndividual components of the limited dataset to determine if the total fluoride standard based on the limited dataset reasonably represents the performance of the units included in the da taset. The results of this analysis are presented below.

The MACT floor dataset for total fluoride from new and existing phosphate rock calciners includes three test runs from one phosphate ro ck calciner. After determining that the dataset is best represented by a normal distribution and e nsuring that we used the correct equation for the distribution, we considered the selecti on of a lower confidence level for determining the emission limit by evaluating whether the calculated limit reasonably represents the performance of the unit upon which it is based. In thi s case, the calculated emission limit is about twice the short-term average emissions from the best performing source, indicating that the emission limit is not unreasonable compared to the actua l performance of the unit upon which the limit is based and is within the range that we see wh en we evaluate larger datasets using our6

MACT floor calculation procedures. Therefore, we determ ined that no changes to our standard UPL floor calculation procedure are warranted for this po llutant and subcategory. Additional details and background on the MACT floor calculation and l imited datasets are provided in separate memorandums. 1, 5 Results of the UPL analysis of total fluoride emissio ns data from phosphate rock calciners, including the final limits, are pr esented in Table 3-4. The complete UPL analysis for total fluoride is presented in Appendix B

. Table 3-3. MACT Floor Analysis and Limit for Total Fluoride ( by US EPA Method 13B) – Phosphate Rock Calciners

Parameter Value Distribution Normal 99.0% UPL ( lb TF/ton phosphate ore feed ) 8.93E

- 04 3x RDL ( lb TF/ton phosphate ore feed ) 5.47E

- 04 MACT Floor Emission Limit for total fluoride [1] 9.0E

- 04

[1] - MACT floor limits were rounded up to two significa nt figures (e.g., 100.1 would be rounded to 110). RDL - representative detection limit

4.0 REFERENCES

1. Ndoh, Tina. EPA. “Use of the Upper Prediction Limit for Calculating MACT Floors.” Docket ID: EPA-HQ-OAR-2012-0522. July 30, 2014.

2. Eastern Research Group, Inc. “Information Collection and Additional Data Received for the Phosphoric Acid and Phosphate Fertilizer Production Source Categories.” Docket ID: EPA-HQ-OAR-2012-0522. May 2014.

3. “Reference Method Accuracy and Precision (ReMAP): Phase 1, Precision of Manual Stack Emission Measurements” American Society of Mech anical Engineers, Research Committee on Industrial and Municipal Waste. February 2001.

4. Eastern Research Group, Inc. “Beyond-the-Floor Analys is for Phosphate Rock Calciners at Phosphoric Acid Manufacturing Plants.” Docket ID: EPA -HQ-OAR-2012-0522. June 8, 2015.

5. Ndoh, Tina. EPA. “Approach for Applying the Upper Prediction Limit to Limited Datasets.” Docket ID: EPA-HQ-OAR-2012-0522. June 8, 2015.