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TECHNICAL MEMORANDUM

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

FROM: Eastern Research Group, Inc.

DATE: June 3, 2013

SUBJECT: Applicability Clarifications to the Phosphoric Acid Manufacturing Source 

Category

1.0 INTRODUCTION

The definitions for wet-process phosphoric acid process line and superphosphoric acid 

process line provide a list of emission points, whose emissions must be included when 

determining compliance with the emission limits of the Phosphoric Acid Manufacturing 

NESHAP (40 CFR part 63, subpart AA) and Phosphoric Acid Manufacturing NSPS (40 CFR 

part 60, subparts T and U). We determined that it was unclear whether emissions from clarifiers 

and defluorination systems at wet-process phosphoric acid (WPPA) process lines, and oxidation 

reactors at superphosphoric acid (SPA) process lines, were regulated by the Phosphoric Acid 

Manufacturing NESHAP and NSPS . These emission points are common to phosphoric acid and 

superphosphoric acid processes but were not clearly listed as applicable to subparts AA, T, and 

U. This memorandum examines how oxidation reactors, defluorination processes, and clarifiers

are incorporated into WPPA or SPA process lines and analyzes the available data in relation to 

emission limits.

2.0 OXIDATION REACTORS

Oxidation reactors are used to remove organics by mixing SPA with nitric acid, 

ammonium nitrate, or potassium permanganate. Four facilities currently use oxidation reactors

and information provided for the oxidation processes at these facilities included sufficient detail 

that indicated the processes are integrated into the SPA process line and thus part of their typical 

operations. In fact, one facility already ducts oxidation reactor emissions through the same stack 

as SPA emissions and thus oxidation reactor emissions were included in past performance tests. 
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As part of the section 114 requests, test data were provided by three of the four facilities for their 

oxidation processes.1 We evaluated the inclusion of hydrogen fluoride (HF) emissions or total 

fluoride (TF) emissions, if HF data were not available, from oxidation reactors to determine if 

facilities currently using an oxidation process would be affected by this clarification for 

compliance purposes.

Simplot Don operates an oxidation reactor and its emissions are currently controlled by 

the same control device as their SPA process. Therefore, this facility has already shown it can 

achieve compliance as emissions for EP-401 are below SPA emission limits. 

PCS White Springs has two distinct SPA process lines (36 and 70) and an oxidation 

reactor process line (61) which is associated with SPA process line 36. Test data was available 

for all three processes, although it was noted that process line 36 was not operating with both of 

its evaporators. Because both evaporators were not operating, the emissions were not expected to 

be at their expected maximum value. Summing the total fluoride emissions from process lines 36 

and 61 may not provide an accurate picture of the emissions for compliance purposes, so test 

data for process line 70 was used in place of line 36 (total fluoride emission for process line 70 

were greater than process line 36). When the total fluoride emissions for process lines 61 and 70 

are summed, this summation value falls below the current SPA emission limit, therefore we 

determined that the PCS White Springs combined emissions would meet the SPA process line 

limit.

Agrium Nu-West also incorporates an oxidation reactor into their SPA process. 

Emissions from oxidation reactor feed tanks are currently controlled by the main SPA scrubber 

(EP-522) but the oxidation reactor itself (EP-541) is not controlled by this scrubber. Test data 

were provided for both emission points. The oxidation reactor HF emissions (EP-541) were 

much higher than HF emissions from the SPA scrubber, and emissions from EP-541 exceed the 

proposed HF limit. This may be due to the fact the oxidation reactor emissions are uncontrolled. 

Because the SPA process line exceeds the HF limit, costs were estimated to reduce the oxidation 

reactor emissions; this discussion is presented in a separate memorandum.

2 While Agrium NuWest may incur a cost to comply with the proposed HF limit due to the clarification that 

emissions from oxidation reactors must be included with SPA process line emissions, it would be 

minimal. 
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3.0 DEFLUORINATION

Defluorination of phosphoric acid is performed using diatomaceous earth for at least two 

facilities. Defluorination processes were identified for Agrium Nu-West and Simplot Don. 

Emissions test data was not provided by facilities with these operations and limited information 

was available on the emissions expected from these processes. Simplot Don did provide details 

on their operations, but this information was classified as confidential business information 

(CBI). We can, however, state that the defluorination processes are fed by the phosphoric acid 

process line and are part of the typical operations at the facilities.

4.0 CLARIFIERS

Clarifiers are used at most phosphoric acid facilities as an additional separation step after 

evaporators. The clarifiers separate the phosphoric acid slurry into a lighter stream and a heavier 

stream. The lighter stream from a clarifier continues downstream (e.g., sent to the next 

evaporator in the series). The heavier stream from a clarifier is recycled back to the process 

upstream of the clarifier for further processing (e.g., to the reactor or filter). It is not uncommon 

for facilities to have several clarifiers in their process and their use is part of their typical WPPA 

process line operations. When reviewing facility data, it was also noted that several facilities 

already include clarifier emissions when determining compliance with subpart AA emission 

limits. There are two facilities, however, that do not include emissions from clarifiers when 

determining compliance and instead route their clarifier emissions to a scrubber separate from 

the main WPPA process line scrubbers. These two facilities are Mosaic New Wales and Mosaic 

Bartow. Emissions data were provided by Mosaic New Wales (EP-12 and EP-22) and Mosaic 

Bartow (EP-06) for their clarifiers.1Including emissions from clarifiers would not affect each 

facility’s ability to meet the subpart AA emission limits, based on the data available. 

5.0 CONCLUSION

Phosphoric acid facility operations were reviewed in detail, and in each instance the 

oxidation reactors, defluorination process, and clarifiers were included as a typical part of the 

WPPA or SPA process line. Several facilities already include emissions from these emission 

points when determining compliance with the Phosphoric Acid Manufacturing NESHAP or 

NSPS. When emissions data were available to analyze, each facility’s emissions were also below 

the applicable WPPA or SPA emission limit when emissions from oxidation reactors or clarifiers
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were included, except for one facility’s oxidation reactor. The intention of the current regulations

was not to exclude emissions from certain emission points when facilities were determining 

compliance for WPPA or SPA process lines. Therefore, the clarifications provided to the process 

line definitions will make this easier to understand and ensure that all emission points related to a 

process line will be accounted for in the future.

6.0 REFERENCES

1. Eastern Research Group, Inc. “Emissions Data Used in Residual Risk Modeling: 

Phosphoric Acid and Phosphate Fertilizer Production Source Categories.” Docket ID: 

EPA-HQ-OAR-2012-0522. August 2014.

2. Eastern Research Group, Inc. “Control Costs and Emissions Reductions for Phosphoric 

Acid and Phosphate Fertilizer Production Source Categories.” Docket ID: EPA-HQOAR-2012-0522. June 2014.