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MEMORANDUM

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

FROM: Eastern Research Group, Inc.

DATE: June 9, 2014

SUBJECT: Comparison of 40 CFR Part 60, subpart W and subpart X (Standards of 

Performance for the Phosphate Fertilizer Industry: Triple Superphosphate Plants 

and Granular Triple Superphosphate Storage Facilities) and 40 CFR Part 63, 

subpart BB (National Emission Standards for Hazardous Air Pollution from 

Phosphate Fertilizers Production Plants)

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

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

NSPS 40 CFR Part 60, subpart W and subpart X, and NESHAP 40 CFR Part 63, subpart BB

(hereafter referred to as subpart W, subpart X, and subpart BB, respectively). Subparts W and X 

were last amended on October 17, 2000 and subpart BB 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 TRIPLE SUPERPHOSPHATE 

(TSP)

Two process descriptions, run-of-the-pile-TSP (ROP-TSP) and granular TSP (GTSP), are 

provided in chapter 8, Volume I, Fifth Edition of AP 42. It is noted in AP 42 that no U.S. 

facilities are currently producing ROP-TSP. From Section 8.5.2.21:

The ROP-TSP material is essentially a pulverized mass of variable particle size 

produced in a manner similar to normal superphosphate. Wet-process phosphoric acid 

(50 to 55 percent P2O5) is reacted with ground phosphate rock in a cone mixer. The 

resultant slurry begins to solidify on a slow moving conveyer en route to the curing 

area. At the point of discharge from the den, the material passes through a rotary 

mechanical cutter that breaks up the solid mass. Coarse ROP-TSP product is sent to a 

storage pile and cured for 3 to 5 weeks. The product is then mined from the storage pile 

to be crushed, screened, and shipped in bulk.

GTSP yields larger, more uniform particles with improved storage and handling 

properties. Most of this material is made with the Dorr-Oliver slurry granulation 

 

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http://www.epa.gov/ttnchie1/ap42/ch08/final/c08s05-2.pdf
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process, illustrated in Figure 8.5.2-1. In this process, ground phosphate rock or 

limestone is reacted with phosphoric acid in 1 or 2 reactors in series. The phosphoric 

acid used in this process is appreciably lower in concentration (40 percent P2O5) than 

that used to manufacture ROP-TSP product. The lower strength acid maintains the 

slurry in a fluid state during a mixing period of 1 to 2 hours. A small sidestream of 

slurry is continuously removed and distributed onto dried, recycled fines, where it coats 

the granule surfaces and builds up its size.

Slurry-wetted granules are then discharged onto a rotary dryer, where excess water is 

evaporated and the chemical reaction is accelerated to completion by the dryer heat. 

Dried granules are then sized on vibrating screens. Oversize particles are crushed and 

re-circulated to the screen, and undersize particles are recycled to the granulator. 

Product-size granules are cooled in a countercurrent rotary drum, then sent to a storage 

pile for curing. After a curing period of 3 to 5 days, granules are removed from storage, 

screened, bagged, and shipped.

2.0 COMPARISON OF NSPS 40 CFR PART 60, SUBPART W AND SUBPART X TO 

NESHAP 40 CFR PART 63, SUBPART BB

The following sections provide a brief comparison of subpart W and subpart X to subpart BB 

standards for TSP.

2.1. Applicability

Both subpart W and subpart BB apply to TSP production; however, subpart BB only applies to

the production and storage of GTSP (see Table 2.1a). Subpart W appears to apply to both ROPTSP and GTSP production as 40 CFR 60.230(a) reads “...the provisions of this subpart appl[ies 

to] each triple superphosphate plant...” However, subpart W excludes the storage of GTSP as 40 

CFR 60.230 only addresses ROP-TSP in regards to product storage. Storage of GTSP is covered 

under subpart X (see Table 2.1b).

Table 2.1a. Applicability Provisions in 40 CFR Part 60, Subpart W and

40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart W 40 CFR Part 63, Subpart BB

Each TSP plant[a] w/ design capacity >15 tons P2O5

feed per day [§60.230(a)] and facilities which store 

ROP-TSP [§60.230(b)]

Each new or existing GTSP process line[a] at a 

major source [§63.620(a)(2) and §63.620(c)]

No R&D exemption Includes R&D exemption [§63.620(d)]

No SSM exemption Includes SSM exemption [§63.620(e)]

[a] For both subpart W and subpart BB, requirements apply to: mixers, curing belts (dens), reactors, granulators, dryers, coolers2, 

screens, and mills.

 

2 Listed as “cookers” in §60.230(a): the term “cookers” (as opposed to coolers) is assumed to be a typographical 

error as background literature and ERG’s knowledge of industry does not indicate any equipment referred to 

“cookers” being used in the manufacture of TSP.
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Table 2.1b. Applicability Provisions in 40 CFR Part 60, Subpart X and

40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart X 40 CFR Part 63, Subpart BB

Each GTSP storage facility[a] [§60.240(a)] Each new or existing GTSP storage building[a]

at a 

major source [§63.620(a)(2) and §63.620(c)]

No R&D exemption Includes R&D exemption [§63.620(d)]

No SSM exemption Includes SSM exemption [§63.620(e)]

[a] The following emission points are listed as components of GTSP storage: storage or curing buildings (noted as “piles” in 

subpart x), conveyors, elevators, screens and mills.

2.2. Definitions

The differences in applicability presented in Section 2.1 are reflected in the definitions for each 

subpart. Subpart W generally defines a TSP plant (without regard to run-of-pile or granular) and

ROP-TSP, but not GTSP. Refer to Table 2.2a for details.

Table 2.2a. Definitions in 40 CFR Part 60, Subpart W and 40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart W 40 CFR Part 63, Subpart BB

TSP plant: any facility manufacturing TSP by 

reacting phosphate rock with phosphoric acid. A 

run-of-pile TSP plant includes curing and storing.

[§60.231(a)]

ROP-TSP: any TSP that has not been processed in 

a granulator and is composed of particles at least 

25% by weight of which (when not caked) will 

pass through a 16 mesh screen. [§60.231(b)]

GTSP process line: any process line, not including 

storage buildings, manufacturing granular TSP by 

reacting phosphate rock with phosphoric acid.

[§63.621]

In subpart X and subpart BB, only GTSP and GTSP related terms are defined. Refer to Table 

2.2b for details.

Table 2.2b. Definitions in 40 CFR Part 60, Subpart X and 40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart X 40 CFR Part 63, Subpart BB

Fresh GTSP: granular TSP produced within the 

preceding 72 hours [§60.241(d)]

Fresh GTSP: granular TSP produced within the 

preceding 72 hours. [§63.621]

GTSP storage facility: any facility curing or storing 

fresh GTSP [§60.241(a)]

GTSP storage building: any building curing or 

storing fresh GTSP. [§63.621]

2.3. Total Fluorides Standards

The total fluorides standards differ in both magnitude and applicability between subpart W and 

subpart BB. Subpart BB includes separate standards for GTSP process lines and storage 

buildings, whereas Subpart W contains a single numerical emission limit, but does not 

differentiate between production/process lines and storage. Refer to Table 2.3a for details.
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Table 2.3a. Total Fluorides Standards in 40 CFR Part 60, Subpart W and

40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart W 40 CFR Part 63, Subpart BB

Existing Sources New Sources

Production and Storage: [a]

100 g/Mg of equivalent P2O5

feed (0.20 lb/ton) [§63.232]

Process Line: 75 g/metric ton of 

equivalent P2O5 feed (0.150 lb/ton)

[§63.622(b)]

Process Line: 61.5 g/metric ton 

of equivalent P2O5 feed (0.1230 

lb/ton) [§63.623(b)]

No prohibition on shipping Prohibition on shipping fresh GTSP[§63.622(c)(2) and §63.623(c)(2)]

[a] The single numerical emission limit in subpart W applies to production of ROP-TSP and GTSP and the storage of ROP-TSP, 

based on the applicability provisions in 40 CFR 60.230 (refer to Section 2.1).

Subpart X and subpart BB contain an equivalent numerical emission limit for total fluorides. 

Additionally, subpart X and subpart BB both include a provision prohibiting the shipment of 

fresh GTSP. No such provision is contained in subpart W for the shipment of ROP-TSP. Refer to 

Table 2.3b for details.

Table 2.3b. Total Fluorides Standards in 40 CFR Part 60, Subpart X and

40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart X 40 CFR Part 63, Subpart BB

New and Existing Sources

Storage Facility: 0.250 g/hr/metric ton of 

equivalent P2O5 stored (5.0x10-4lb/hr/ton) 

[§63.242(a)]

Storage Building: 0.250 g/hr/metric ton of 

equivalent P2O5 stored (5.0x10-4lb/hr/ton) 

[§63.622(c)(1) and §63.623(c)(1)]

Prohibition on shipping fresh GTSP [§63.242(b)] Prohibition on shipping fresh GTSP [§63.622(c)(2) 

and §63.623(c)(2)]

2.4. Monitoring and Operating Requirements

The most substantial difference between subparts W and X and subpart BB in regards to 

monitoring and compliance is related to establishing and adhering to parameter monitoring 

ranges for wet scrubbing systems. All three subparts include requirements to operate a 

continuous parameter monitoring system to record pressure drop, but only subpart BB includes a 

requirement to monitor and record the flow rate of scrubbing liquid. Subpart BB also includes 

specific language that facilities must operate within the establish parameters, whereas such 

language is not included in subpart W or subpart X. Subpart X and subpart BB also includes 

requirements to maintain an account of GTSP in storage, but subpart W does not include any 

storage accounting requirements. Refer to Tables 2.4a and 2.4b for details.

Table 2.4a. Monitoring and Operating Requirements in 

40 CFR Part 60, Subpart W and 40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart W 40 CFR Part 63, Subpart BB

P2O5 Feed Accounting

 Install, calibrate, maintain, and operate a 

monitoring device which can be used to 

determine the mass flow of phos-bearing 

 Install, calibrate, maintain, and operate a monitoring 

device which can be used to determine and 

permanently record the mass flow of phos-bearing 
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Table 2.4a. Monitoring and Operating Requirements in 

40 CFR Part 60, Subpart W and 40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart W 40 CFR Part 63, Subpart BB

feed to process within an accuracy of ±5% 

over operating range. [§60.233]

 Maintain a daily record of eq. P2O5 feed 

according to procedures in subpart.

[§60.233]

feed to process within an accuracy of ±5% over 

operating range. [§63.625(a)]

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

procedures in subpart. [§63.625(b)]

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). [§60.233]

Install, calibrate, maintain, and operate a monitoring 

system which continuously measures and permanently 

records:

A) the pressure drop across [§63.625(c)(1)], and 

B) the flow rate of scrubbing liquid to [§63.625(c)(2)],

Each scrubber in the process scrubbing system in 15-

min block averages (accuracy of ± 5% over operating 

range). [§63.625(c)(2)]

Establish allowable ranges, maintain daily averages 

within the established ranges, for pressure drop and 

flow rate. [§63.624 and §63.625(f)]

Table 2.4b. Monitoring and Operating Requirements in 

40 CFR Part 60, Subpart X and 40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart X 40 CFR Part 63, Subpart BB

Product Storage Accounting

 Maintain an accurate account of TSP in 

storage to permit the determination of the 

amount of eq. P2O5 stored. [§60.243(a)]

 Maintain a daily record of eq. P2O5 stored 

according to procedures in subpart.

[§60.243(b)]

 Maintain an accurate account of TSP in storage to 

permit the determination of the amount of eq. P2O5

stored. [§63.625(d)]

 Maintain a daily record of eq. P2O5 stored according 

to procedures in subpart. [§63.625(e)(1)]

Scrubbing Systems

Install, calibrate, maintain, and operate a 

monitoring device which continuously 

measures and permanently records the total 

pressure drop across any process scrubbing 

system (accuracy of ± 5% over operating 

range). [§60.243(c)]

Install, calibrate, maintain, and operate a monitoring 

system which continuously measures and permanently 

records:

A) the pressure drop across [§63.625(c)(1)], and 

B) the flow rate of scrubbing liquid to [§63.625(c)(2)],

Each scrubber in the process scrubbing system in 15-

min block averages (accuracy of ± 5% over operating 

range). [§63.625(c)(2)]
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Table 2.4b. Monitoring and Operating Requirements in 

40 CFR Part 60, Subpart X and 40 CFR Part 63, Subpart BB

40 CFR Part 60, Subpart X 40 CFR Part 63, Subpart BB

Establish allowable ranges, maintain daily averages 

within the established ranges, for pressure drop and 

flow rate. [§63.624 and §63.625(f)]

2.5. Testing and Compliance

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

subpart X, and subpart BB. Subpart W and subpart X only require an initial performance test, 

whereas subpart BB requires initial and annual testing. Subpart BB also allows facilities a 

broader choice of test methods than subpart W and subpart X in determining P2O5 content of 

feed and product stored.

Subpart X and subpart BB are identical in restrictions regarding the testing of GTSP storage 

buildings in relation to the amount of GTSP being stored. Refer to Table 2.5 for details.

Table 2.5. Testing and Compliance in 40 CFR Part 60, Subparts W and X, and

40 CFR Part 63, Subpart BB

40 CFR Part 60, Subparts W and X 40 CFR Part 63, Subpart BB

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. [§63.626(a)(1)]

New Sources: Within 180 days of compliance date and 

then annually. [§63.626(a)(2)]

Sampling and Analysis Methods

Total Fluorides: Method 13A or 13B with 60 

minute sampling time and 0.85 dscm (30 dscf) 

sample volume. [§60.234(b)(2) and 

§60.244(c)(2)]

P2O5 Content of Feed and Product 

Stored[a]: The Association of Official 

Analytical Chemists (AOAC) Method 9.

[§60.234(b)(3)(ii) and §60.244(c)(3)(ii)]

Total Fluorides: Method 13A or 13B with a 1 hour 

sampling time and 0.85 dscm (30 dscf) sample volume.

[§63.626(c)(2)]

P2O5 Content of Feed and Product Stored: Various 

methods from the Association of Florida Phosphate 

Chemists, Seventh Edition 1991 and the Official 

Methods of Analysis of AOAC International, sixteenth 

Edition, 1995. [§63.626(c) and (d)]

[a] Storage only applies to subpart X.