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MEMORANDUM

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

FROM: Eastern Research Group, Inc.

DATE: June 4, 2014

SUBJECT: Comparison of 40 CFR Part 60, subpart T (Standards of Performance for the 

Phosphate Fertilizer Industry: Wet-Process Phosphoric Acid Plants) and 40 CFR 

Part 63, subpart AA (National Emission Standards for Hazardous Air Pollution 

from Phosphoric Acid Manufacturing Plants)

This document presents a general comparison between the applicability, definitions, emission 

standards, monitoring and operating requirements, and testing and compliance requirements of 

the current NSPS 40 CFR Part 60, subpart T, and NESHAP 40 CFR Part 63, subpart AA

(hereafter referred to as subpart T, and subpart AA, respectively). Subpart T was last amended on 

October 17, 2000 and subpart AA was last amended on April 20, 2006. This document does not 

encompass recordkeeping or reporting requirements: each subpart references the respective 

general provisions.

1.0 PROCESS DESCRIPTIONS FOR PRODUCING PHOSPHORIC ACID

Two process descriptions, the wet-process and thermal process, are provided in Chapter 8, 

Volume I, Fifth Edition of AP 421. In the wet-process, beneficiated ground phosphate rock is 

reacted with sulfuric acid and weak phosphoric acid to produce phosphoric acid and 

phosphogypsum, a waste product. In most cases, the phosphoric acid is concentrated in vacuum 

evaporators. In the thermal process, elemental phosphorus is oxidized to form phosphorus 

pentoxide, which is subsequently hydrated to form strong phosphoric acid. Based on industry 

responses to the April 2010 Section 114, no facility currently uses the thermal process. 

2.0 COMPARISON OF NSPS 40 CFR PART 60, SUBPART T TO NESHAP 40 CFR 

PART 63, SUBPART AA

The following sections provide a brief comparison of subpart T to subpart AA standards for 

phosphoric acid manufacturing.

 

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http://www.epa.gov/ttn/chief/ap42/ch08/final/c08s09.pdf
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2.1. Applicability

Both subpart T and subpart AA apply to wet-process phosphoric acid (WPPA) manufacturing 

operations; however, subpart AA also applies to superphosphoric acid process lines and purified 

acid process lines. While NSPS 40 CFR Part 60, subpart U applies to superphosphoric acid 

plants, there does not appear to be any NSPS standards applicable to purified acid process lines.

Because subpart T only applies to WPPA plants, the remaining sections of this document do not 

discuss superphosphoric or purified acid process lines. The applicability of each subpart to 

WPPA manufacturing is presented in Table 2.1. Subpart T references design capacity, while 

subpart AA applies to major sources.

Table 2.1. Applicability Provisions in 40 CFR Part 60, Subpart T and 40 CFR Part 63, Subpart AA

40 CFR Part 60, Subpart T 40 CFR Part 63, Subpart AA

Each WPPA plant[a] having a design capacity of 

more than 15 tons P2O5 feed per calendar day 

[§60.200(a)]

Each phosphoric acid manufacturing plant 

[§63.600(a)], including the following new or 

existing affected sources at a phosphoric acid 

manufacturing plant:

Each WPPA process line[a] [§63.600(b)(1)]

Each evaporative cooling tower [§63.600(b)(2)]

Each phosphate rock dryer [§63.600(b)(3)]

Each phosphate rock calciner [§63.600(b)(4)]

Does not apply to a new or existing phosphoric 

acid manufacturing plant this is not a major source 

[§63.600(c)]

No R&D exemption Includes R&D exemption [§63.600(d)]

No SSM exemption Includes SSM exemption [§63.600 (e)]

[a] For both subpart T and subpart AA, requirements apply to reactors, filters, evaporators, and hot wells.

[b] 40 CFR Part 60, subpart U applies to superphosphoric acid plants.

2.2. Definitions

Subpart T defines a WPPA plant. Subpart AA defines a WPPA process line. Subpart AA also 

includes several additional definitions related to WPPA manufacturing. Refer to Table 2.2 for 

details.
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Table 2.2. Definitions in 40 CFR Part 60, Subpart T and 40 CFR Part 63, Subpart AA

40 CFR Part 60, Subpart T 40 CFR Part 63, Subpart AA

WPPA plant: any facility manufacturing 

phosphoric acid by reacting phosphate rock and 

acid. [§60.201(a)]

WPPA process line: any process line 

manufacturing phosphoric acid by reacting 

phosphate rock and acid. [§63.601]

Definitions in Subpart AA related to WPPA

manufacturing not in Subpart T

Evaporative cooling tower: an open water 

recirculating device that uses fans or natural draft 

to draw or force ambient air through the device to 

remove heat from process water by direct contact. 

[§63.601]

Phosphate rock calciner: equipment used to remove 

moisture and organic matter from phosphate rock 

through direct or indirect heating. [§63.601]

Phosphate rock dryer: the equipment used to reduce 

the moisture content of phosphate rock through 

direct or indirect heating. [§63.601]

Phosphate rock feed: all material entering any 

phosphate rock dryer or phosphate rock calciner 

include moisture and extraneous material as well as 

the following ore materials: fluorapatite, 

hydroxylapatite, chlorapatite, and carbonateapatite.

[§63.601]

2.3. Standards

Subpart T contains a single standard for total fluorides from a WPPA plant. Subpart AA contains 

total fluoride standards for new and existing WPPA lines, particulate matter standards for 

phosphate rock dryers and calciners, and standards for evaporative cooling towers. Refer to

Table 2.3 for details.

Table 2.3. Standards in 40 CFR Part 60, Subpart T and 40 CFR Part 63, Subpart AA

HAP/Pollutant 40 CFR Part 60, 

Subpart T

40 CFR Part 63, Subpart AA

Existing Sources New Sources

Total Fluorides (lb/ton 

of equivalent P2O5 feed)

Affected Facility: 

0.020 [§63.202(a)]

WPPA Process Line:

0.020 [§63.602(a)]

WPPA Process Line:

0.01350 [§63.603(a)]

Particulate Matter 

(lb/ton of phosphate rock 

feed)

NA

Rock Dryer: 0.2150 

[§63.602(c)]

Rock Dryer: 0.060 

[§63.603(c)]

Particulate Matter 

(gr/dscf) NA Rock Calciner: 0.080 [§63.602(d)]

Rock Calciner: 0.040 

[§63.603(d)]

None Specified NA

Prohibition on introduction of wet scrubber liquid 

effluent into any evaporative cooling tower. 

[§63.602(e) and §63.603(e)]
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2.4. Monitoring and Operating Requirements

The most substantial differences between subpart T and subpart AA in regards to monitoring and 

compliance is related to establishing and adhering to parameter monitoring ranges for wet 

scrubbing systems. Both subparts include requirements to operate a continuous parameter 

monitoring system to record pressure drop, but only subpart AA includes a requirement to 

monitor and record the flow rate of scrubbing liquid. Subpart AA also includes specific 

requirements that facilities must operate within the established parameters: such requirements are

not included in subpart T. Additionally, subpart AA includes specific monitoring requirements 

for phosphate rock dryers and calciners: subpart T contains no such requirements. Refer to Table 

2.4 for details.

Table 2.4. Monitoring and Operating Requirements in 

40 CFR Part 60, Subpart T and 40 CFR Part 63, Subpart AA

40 CFR Part 60, Subpart T 40 CFR Part 63, Subpart AA

P2O5 Feed Accounting –WPPA Plant/Process Line

 Install, calibrate, maintain, and operate a 

monitoring device which can be used to 

determine the mass flow of phos-bearing 

feed to process within an accuracy of ±5% 

over operating range. [§60.203(a)]

 Maintain a daily record of eq. P2O5 feed 

according to procedures in subpart.

[§60.203(b)]

 Install, calibrate, maintain, and operate a monitoring 

device which can be used to determine and 

permanently record the mass flow of phos-bearing 

feed to process within an accuracy of ±5% over 

operating range. [§63.605(a)(1)]

 Maintain a daily record of eq. P2O5 feed according to 

procedures in subpart. [§63.605(b)(1)]

P2O5 Feed Accounting –Rock Dryer/Rock Calciner

 NA

 Install, calibrate, maintain, and operate a monitoring 

device which can be used to determine and 

permanently record either the mass flow of phosbearing feed to the dryer/calciner, or the mass flow of 

product from the dryer/calciner within an accuracy of 

±5% over operating range. [§63.605(a)(2)]

 Maintain a daily record of phosphate rock feed or 

product (depending on monitoring choice) using the 

monitoring system which meets the requirements of 

§63.605(a)(2). [§63.605(b)(2)

Scrubbing Systems

Install, calibrate, maintain, and operate a 

monitoring device which continuously 

measures and permanently records the total 

pressure drop across the process scrubbing 

system (accuracy of ± 5% over operating 

range). [§60.203(c)]

Install, calibrate, maintain, and operate a monitoring 

system which continuously measures and permanently 

records:

A) the pressure drop across [§63.605(c)(1)], and

B) the flow rate of scrubbing liquid to [§63.605(c)(2)],

Each scrubber in the process scrubbing system in 

15-min block averages (accuracy of ± 5% over operating 

range). [§63.605(c)(1) and (c)(2)]

Establish allowable ranges, maintain daily averages 

within the established ranges, for pressure drop and 

flow rate. [§63.604 and §63.605(d)]
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2.5. Testing and Compliance

The testing and compliance requirements vary in frequency and method between subpart T and 

subpart AA. Subpart T only requires an initial performance test, whereas subpart AA requires 

initial and annual testing. Subpart AA also allows facilities a broader choice of test methods than 

subpart T in determining P2O5 content of feed.

Table 2.5. Testing and Compliance in

40 CFR Part 60, Subpart T and 40 CFR Part 63, Subpart AA

40 CFR Part 60, Subpart T 40 CFR Part 63, Subpart AA

Frequency of Performance Test

Within 60 days of max production rate, but no 

later than 180 days after initial startup [§60.8]

Existing Sources: On or before applicable compliance 

date and then annually. [§63.606(a)(1)]

New Sources: Within 180 days of compliance date and 

then annually. [§63.606(a)(2)]

Sampling and Analysis Methods

Total Fluorides: Method 13A or 13B with at 

least a 60 minute sampling time and 

0.85 dscm (30 dscf) sample volume.

[§60.204(b)(2)]

P2O5 Content of Feed: The Association of 

Official Analytical Chemists (AOAC) Method 

9. [§60.204(b)(3)(ii)]

Total Fluorides: Method 13A or 13B with at least a

60 minute sampling time and 0.85 dscm (30 dscf) 

sample volume. [§63.606(c)(2)]

Particulate Matter: Method 5 (40 CFR part 60, 

appendix A) with at least a 60 minute sample time and 

0.85 dscm (30 dscf) sample volume for rock dryers and 

a 1.70 dscm sample volume for rock calciners. 

[§§63.606(d)(2) and 63.606(e)(1)]

P2O5 Content of Feed: Various methods from the 

Association of Florida Phosphate Chemists, Seventh 

Edition 1991. [§63.606(c)(3)(ii)]