MEMORANDUM

DATE: August 2 , 2013

SUBJECT: Approach for Hydrogen Fluoride Continuous Emission Monitoring and

Compliance Determination with EPA Method 320

FROM: Steffan Johnson

Measurement Policy Group, SPPD

TO: Residual Phosphoric Acid Manufacturing and Phosphate Fertilizer Production

RTR and Standards of Performance for Phosphate Processing

A. INTRODUCTION

T echnological advances in stationary source emissions monitoring allow for direct measurement
of fluoride emissions ( hydrogen fluoride ) as an alternative to the measurement of a total fluoride

. A total f luoride test method is currently used for the demonstration of compliance with a t otal

fluoride standard in the Phosphate Fertilizer and Phosphoric Acid rule s (40 CFR, Part 63, Subparts AA and BB)

. Since promulgation of the existing rule s in 1999 , new developments in

emissions measurement using Fourier Transform Infrared ( FTIR ) instrumentation have made direct, real time measurement of specific hazardous air pollutants ( HAP s ) possible. T he use of such technologies requires consideration of instrument stability, instrument calibr ation, calibration standards, daily quality assurance/quality control ( QA/QC ) procedures as well as reporting and recordkeeping requirements

. The purpose of this memo is to discuss and highlight appropriate measurement and monitoring requirements for the u se of this technology in regards to compliance demonstration testing and continuous emissions monitoring.

B. DISCUSSION

Accurate m easurement of hydrogen fl uo ride ( HF ) with FTIR technology

, i n real time , is now a possibility with an EPA Method 320 approach. In the early 2000’s the availability of testers who could perform such testing, as well as the costs of performing these tests, presented challenges to requiring use of this technology. In recent years, more instrumentation and expertise have

bec ome available, as well as a general trend in lower emissions testing costs using these

instruments

. T he EPA is beginning to propose their use as an alternate compliance

demonstration , as well as continuous monitoring approaches in various rules. T he use of such

instrumentation can be expected to provide benefits to the regulated source as well as the regulatory community. Emission measurement results of the specific HAP are available

, on site

, with good accuracy and precision at very low levels. Real time d ata provides for a greater understanding of process to pollutant correlation and provides sources with valuable process

control feedback that is not provided with a manual stack test. This same instrumentation can be used for monitoring of other flue gas constituents if needed.2

Concurrent with requiring such monitoring in rules

, a number of other supporting requirements

must be addressed to provide reliable and q uality a ssured data from these systems. Such underlying concepts are: s election of appropria te equipment, instrument calibration and drift evaluation, r elative a ccuracy determination and p erformance specifications , appropriate calibration standards, and data QA/QC.

Selection of Equipment:

In order to continuously measure HF with a continuous emissions monitor ( CEMS ) equipment

that satisfies basic source CEMS measurement and control equipment criteria needs to be

install ed according to the manufacturer’s specifications and the requirements set out in the soon

to

- be

- proposed Performance Specifi cation 18 ( PS

- 18 ) for hydrogen chloride ( HCl ) CEMS

. Extractive HF CEMS would be expected to include a sample extraction system, sample conditioning module, HF analyzer, diluent analyzer, system controller, data recorder, reference gas system and moisture m easurement system. An in

- situ CEMS would not need a sample extraction system or sample conditioning module, but would need the other above listed

components.

The current draft of PS

- 18 specifies that, for extractive CEMS, the system must be designed to

be able to introduce reference gas flow sufficient to flood the sampling probe and prevent entry of gas from the effluent stream . It also specifies that the sampling conditioning module must be operated in such a way as to keep the particle free gas sample a bove the dew point temperature of its components.

Typical EPA p erformance s pecifications require that CEMS be installed at an accessible location where the pollutant concentration or emission rate measurements are directly representative of

the emissions or can be corrected to be representative of the emissions from the affected facility. With regards to HF CEMS emissions measurement location, the current draft of PS

- 18 specifies

that an HCl CEMS should be (1) at least two equivalent diameters downstream o f the nearest control device, point of pollution generation or other point at which a change of pollutant concentration may occur, and (2) at least half an equivalent diameter (calculated according to Method 1 in appendix A

- 1 to part 60) upstream from the effluent exhaust. The draft PS

- 18, which provides such requirements for HCl CEMS will address a majority of what is necessary to measure HF continuously.

Performance Specification Criteria:

A number of QA/QC requirements are necessary to validate the data from any installed CEMS system. With HF CEMS we expect the following to QA/QC requirements to apply:

H F CEMS Measurement Range

An applicable p erformance s pecification will require t hat a documented check of the continuous emissions measurement range of the H F CEMS be performed to verify that the instrument is functioning correctly following installation

. For example, the draft Performance Specification 183

requires that the data collection device output range include zero and the upper limit of the

mea surement range for HCl CEMS, and it is likely to be similar for HF CEMS

.

Interference Test

. A test to detect analyzer response to potential interferences that may cause measurement bias that

are not adequately accounted for in the calibration procedure i s required

. For the current draft of

PS

- 18 t he combined interference response for the analyzer used for the test must not be greater than ± 3.0 percent of the equivalent HCl concentration used for the interference test.

Level of Detection (LOD) Determination

. A determination of the minimum amount of HF that can be detected above the background in a representative gas matrix (the LOD) is necessary

. LOD determination is independent of the span required in applicable regulations. If the LOD determin ation test is performed in a controlled environment, verification of the LOD during the initial field certification test using the DS test procedure ( as included in Appendix A of the soon

- to

- be

- proposed PS 18 ) would be required . The

field verified detectio n level would replace the controlled environment LOD and would become the site or installation specific LOD.

Response Time (RT) Determination

. The response time of a n extractive HF CEMS must be determine d based on the average upscale and downscale respons e time as the response time for the system (the RT). This is the time it takes for the measurement system, while operating normally at its target sample flow rate, dilution ration, or data collection rate to response to a known step change in gas concentra tion (from a low or zero level to high

- level gas concentration or vice versa). The RT must read within five percent of the stable gas response (i.e., the calibration error of the HF CEMS must be less than 5 percent )

.

Calibration Error (CE) Test

. A CE test is the mean difference between the HF calibration gas value and the CEMS response at each calibration point expressed as a percentage of the span. The CE of an HF CEMS must be less than 5 percent.

Seven

- Day Calibration Drift (CD) Test

. Prior to c onducting a n RA test on an HF CEMS, a seven

- day CD test must be conducted . The purpose of the seven

- day CD test is to verify the ability of the CEMS to maintain calibration for each of seven, 24

- hour periods. The zero

- level and high

- level drift for each da y must be less than 5 percent of the span value. Each daily drift check must be performed for seven consecutive days to meet this requirement and each drift check must be recorded and reported for the seven

- day

drift check tests.

R elative A ccuracy (RA) Te st

. Determination of the RA for an HF CEMS is a requirement

. T he RA must be established against

an RM (Reference Method), in this case EPA Method 320 . The RA is the absolute mean difference between the gas concentration determined by the CEMS and the value determined by the RM, plus the 2.5 percent error confidence coefficient of a series of tests divided by the average of the RM or the applicable emission standard.4

There are also specifi c requirements to record and report supporting data for test procedu res and

calculations set out in the draft PS

- 18. Similar requirements would apply to an HF CEMS

installation. For example, for systems that use a gas blender and/or liquid evaporative calibrator

to deliver HF gas standards, the draft PS

- 18 specifies that y our record and report supporting data for these devices, including liquid feed calibrations, liquid standard(s) concentration, feed rate and gas flow calibrations for all diluent and HCl gas flows. Such systems

, when used for HF calibration standards would also require documentation. The draft PS

- 18 also specifies that owners and operators record and report summaries (in tabular form) of the results of CD tests, beyond calibration span linearity tests, RT tests, CE tests, RA tests and optional spike and

recover (dynamic spiking or DS) procedures. Additionally, the draft PS

- 18 specifies that owners and operators record and report supporting dilution system data and LOD and system limitation

verification data for in stalled HCl CEMS. We expect these specifications would also apply to an

HF CEMS installation.

Daily QA/QC Requirements:

Procedure 6 : The draft Performance Specification 18 specifies the minimum QA requirements necessary for the control and assessment of the quality of CEMS data submitted to the EPA. EPA plans to propose QA procedures for HCl (Procedure 6) at the same time it proposes PS

- 18. The draft

Procedure 6 would direct ly applicable to HF CEMS

. The procedure assesses the quality of the CEMS data produced by estimating accuracy. The procedure also assist s in the control and improvement of the quality of the CEMS data by implementing QC policies and corrective

actions. Bot h of these purposes work together to ensure that data quality is acceptable.

Who would comply with Procedure 6 ?

S ource owners and operators required to install HCl or HF CEMs for compliance monitoring would be required to meet the minimum requirements of Procedure 6 once finalized and would

be encouraged to develop and implement a more extensive QA program or to continue such programs where they already exist.

The draft Procedure 6 specifies that the program include written procedures and manufacturer’s information that describes in detail, complete, step

- by

- step procedures and operations for specified activities (e.g., calibration drift checks of all H F CEMS and temperature and pr essure

measurement accuracy for in

- situ CEMS ). The draft P rocedures specify that records of these written procedures be maintained and available for inspection by enforcement agencies

.

Calibration Drift Assessment

. Source owners and operators required to install H F CEMS would be required to check, record and quantify the CD at two concentration values at least once daily in accordance with the method prescribed by the manufacturer and by the applicable performance specification . The H F

CEMS calibration must, at a minimum, be adjusted whenever the daily zero (or low

- level) CD or daily high

- level CD exceeds two times the drift limits of the applicable performance specification (e.g., PS

- 18).5

The draft Procedure 6 specifies that the accuracy of each CEMS b e audited at least once each calendar quarter by a relative accuracy test audit ( RATA ) , DS audit (DSA), a cylinder gas audit (CGA) or other acceptable alternative approved by the Administrator. Hydrogen fluoride audit

gases are expected to be National Inst itute of Standards and Technology ( NIST ) certified or

NIST

- traceable. The draft Procedure 6 also specifies that RATAs be conducted once every four

calendar quarters unless the affected facility is off

- line.

Excessive Audit Inaccuracy

. The draft Procedur e 6 defines what constitutes an out

- of

- control CEMS and specifies corrective actions to eliminate problem(s) when a CEMS is deemed out

- of

- control. The draft p rocedure also specifies that owners and operators of the out

- of

- control CEM S verify that the probl em(s) has been eliminated by documenting and reporting the results of the audit following corrective action showing the CEMS to be operating within specifications. For purposes of excessive audit inaccuracy, a CEMS is considered out of control when (1) RAT A is less than 5 percent of span, (2) the DSA allowable RA is ± 15 percent of the average spike value or ± 20 percent of the applicable emission standard, whichever is greater, or (3) CGA is less than 5 percent of span. CEMS data collected during out

- of

- co ntrol periods must not be used in calculating emission compliance nor be counted towards meeting minimum data availability as required under an applicable regulation or permit.

Criteria for Acceptable QC Procedures

. In situations where a CEMS experiences excessive out

- of

- control conditions resulting from the quarterly audits for two consecutive quarters, according to the draft Procedure 6 source
, owner or operator s would need to revise their QC procedures, or modify or replace their CEMS.

Criteria for Optional QA Test Frequency

. The draft Procedure 6 states that i f a CEM is determined to be in

- control for eight consecutive quarters that include a minimum of two RATA, owners or operators of the CEMS may revise their auditing procedures to use CGA or DSA each quarter for seven subsequent quarters. Under

this proposed scenario, the CEMS owner would only be required to perform a RATA that meets the acceptance criteria once every two years. Conversely, an owner or operator of a CEMS that fails a RATA, CGA, or DSA would need to revert to their original auditing schedule until the

audits results meet in

- control criteria to start re

- qualifying for the optional QA test frequency again.

Calculations for CEMS Data Accuracy

. The draft Procedure 6 specifies RATA calculation, CGA accuracy calculation and DSA accuracy calculation requirements.

O wners and operators of affected HCl CEMS must report for each CEMS the accuracy and CD

assessment results and the drift and accuracy information as a Data Assessment Report (DAR) (an example of a DAR format is provided in Procedure 6; section 9.0, Figure 1). At a minimum, the DAR must contain source owner and operator information; identification and lo cation of monitors in the CEMS; manufacturer and model number of each monitor in the CEMS; and assessment of CEMS data accuracy and date of assessment. The DAR is required to be submitted with the report of emissions required under the applicable regulatio n or permit that requires6

continuous emission monitoring.

C

. SUMMARY

The above discussion outlines our expectations for what constitutes an acceptable HF CEMS monitoring system, as well as QA/QC criteria for assessing the performance of the system and quality of the reported data. HF CEMS technology is currently on the cusp of development, and a number of technical requirements have yet to be put in pla ce to fully implement such systems (i.e. specific p erformance s pecifications, NIST calibration standards, and d aily QA/QC requirements). Yet at least one appropriate technology exists, as described in EPA Method 320, and we envision a growing need for thes e systems in the future. This measurement approach has significant advantages in terms of being able to directly and continuously measure HF, versus current compliance demonstrations that require annual testing for t otal fluoride as a surrogate for

HF. The EPA will be soliciting and accepting public comment on the proposed PS

- 18 and Procedure 6, therefore this is subject to future change.

We expect that where HF CEMS will be installed, the points discussed in this memo will need to

be addressed and resolve d.