Process Analyzer Applications

The Claus sulfur recovery unit (SRU) and tail gas treating unit (TGTU) require a suite of process gas analyzers to operate safely, protect the catalyst/amine at high efficiency and meet environmental regulations for sulfur dioxide (SO2) emissions.

The development of sulfur recovery for oil refining, gas processing and coke oven plants was largely driven by environmental regulations in the early 1970s, resulting in AMETEK's development of the SRU tail gas analyzer. Optimization of the process and further enhancements gave genesis to numerous other analyzer applications. This application note covers the seven possible analyzer tags that are addressed by AMETEK (see Figure 1, simplified process flow diagram).

The hydrogen sulfide (H2S)/SO2 SRU tail gas (air demand) analyzer (AT3) is the one constant – every SRU will employ this critical analytical measurement. If the SRU is followed by a TGTU, there is at least one, and possibly two, additional analyzers located at sample point locations AT4, AT5 and/or AT6.

The feed gas/acid gas analyzer (AT1) is becoming more prevalent, as recent developments provide real-time full composition analysis to mitigate hydrocarbon (HC) upsets. In addition to measuring H2S, ammonia (NH3)

IPS-4 UV/IR ANALYZER

888 PIT AND TAIL GAS ANALYZER

931 TGTU ANALYZER

930 H2S IN SULFUR PIT ANALYZER

900 TAIL GAS ANALYZER

914 CEMS

SULFUR RECOVERY AND TAIL GAS TREATING UNIT

and total HC, the feed gas analyzer can quantify the acid gas contaminants (BTX, methanol, CO2).

To identify a potentially explosive environment in the sulfur pit or tank, an analyzer (AT2) measuring H2S should be permanently installed.

Finally, the emissions analyzer (AT7), in its simplest form, reports the SO2 emission but can also be used as a process optimization tool if the emission is expressed in mass basis terms.

ametekpi.comTo find out more or request a quote visit our website

APPLICATION NOTE

AT3. TAIL GAS ANALYZER

IPS-4 UV/IRA full composition, real-time analyzer accounts for all O2 consuming species in acid gas streams. Using a combined ultraviolet (UV) and infrared (IR) “full spectrum” technique, total hydrocarbon (THC) is measured in the IR as “methane equivalent” and H2S is measured in the UV so the exact amount of air can be added (or subtracted) from the reaction furnace for steady state control.

Benefits of acid gas analyzer include:• Where transient spikes of HC cause sudden increase in air

demand – resulting in an H2S spike at the tail gas – and when the event is over, SO2 breakthrough into the TGTU, (see Figure 2)

• NH3 measurement for (refinery) sour water stripper (SWS) acid gas. • Additional measurements for quantification of

benzene-toluene-xylene (BTX) and methanol (MeOH) contamination in (natural gas processing) acid gas

• Material balance and mass emission calculations • Heated Acid Gas (HAG) probe offers a single connection for sample

extract and return to process. Always consider adding the HAG probe and sample point at feed stage or SRU outage

• Rated NEMA-4X (IP65) for outdoor installation; a cabinet or shelter is not required

888/930 Pit GasLiquid sulfur contains ~350 parts per million (ppm) of dissolved H2S and spontaneous degassing results in accumulation in the head space. If the sweep gas is interrupted, H2S can reach the lower explosive limit (LEL) (~3.25 %), (see Figure 3).

Benefits of the pit gas analyzer include: • Computational fluid dynamics (CFD) modeling confirms

localized H2S concentrations can be 16 times the mean value, indicating values of ~2,000 ppm H2S which may constitute an imminent hazard

• SO2 is monitored to alarm for a smoldering pyrophoric sulfur fire

• The pit gas analyzer can also be used for mass balance purposes as a sulfur pit vent routed to the incinerator accounts for approximately one-third of the emissions

888/900 Tail Gas

2 3

Amine and SWS acid gas

Reaction furnace & waste heat exchanger

Reduction gasgenerator Reduction reactor

Quench column Absorber & stripper columns

H2S recycle to Claus inlet

Thermal oxidizerConverters & condensersCobalt-molybdenum

Sulfur pit (tank)

AT1

AT2

AT3AT4

AT5 AT6

AT7

ametekpi.com

AT1. ACID GAS ANALYZER (SRU Feed Forward Control) MEASURES: H2S + Total HC (NH3, CO2, BTX)

AT2. SULFUR PIT (TANK) ANALYZER (Lower Explosive Limit)

(Refer to application note F-0299 Feed Forward Analysis for Sulfur Recovery Units for additional details).

Measurement of H2S/SO2 in SRU tail gas for feedback (trim) control of the process air. Reliability has evolved to the point where the analyzer anticipates and reacts to adverse process conditions. With an installed operating base in excess of 2,000 units, AMETEK offers two types of tail gas analyzers, the Model 888 and Model 900.

Benefits of the 888 Tail Gas:• Close-coupled (no sample line), mounts directly on the pipe

• Does not require climate-controlled shelter, rated for 60°C (140°F) without external cooling, and automatic flow control

Benefits of the 900 Tail Gas:• Extractive (sample line) – for installation in an analyzer house in

extreme climates, or if the sample point location is compromised due to piping design, or for measurement ofcarbonyl sulfide and carbon disulfide (COS and CS2)

• Sample handling is close-coupled but external to the process, at a safe and accessible distance

• Optional double-block isolation from the process

APPLICATION PROCESS

Amine and SWS acid gas

Reaction furnace & waste heat exchanger

Reduction gasgenerator Reduction reactor

Quench column Absorber & stripper columns

H2S recycle to Claus inlet

Thermal oxidizerConverters & condensersCobalt-molybdenum

Sulfur pit (tank)

AT1

AT2

AT3AT4

AT5 AT6

AT7

Figure 1. Simplified process flow diagram showing eight process analyzer tags

CO

NC

ENTR

ATI

ON

%

H2S THC SO2 H2S

TIME

9:36

0.000 0.000

-0,1

-0,4

-0,9

-1,4

-1,9

-2,4

2,0

3,5

-0,1

-0,4

-0,9

-1,4

-1,9

-2,4

2,0

3,5

0.050

0.100

0.150

0.200

0.250

10.000

20.000

30.000

40.000

50.000

60.000

70.000

80.000

90.000

100.000

10:36 11:36 12:36 1:36 2:36 3:36

Transient Hydrocarbon Upset:12 fold increase in total HC,6 minutes in duration causes an increase in H2S.

29/04/2014 16:12:11.289 28/07/2014 16:12:11.28990,00 days

H2S values above the LEL:Simultaneous SO2 values indicatinga smoldering (pyrophoric) fire.

~400 ppm COS + 100 ppm H2Sresulting in ~350 ppm SO2

emission exceedance.

COS

H2S

Figure 2. Field data/HC process upset

CO

NC

ENTR

ATI

ON

%

H2S THC SO2 H2S

TIME

9:36

0.000 0.000

-0,1

-0,4

-0,9

-1,4

-1,9

-2,4

2,0

3,5

-0,1

-0,4

-0,9

-1,4

-1,9

-2,4

2,0

3,5

0.050

0.100

0.150

0.200

0.250

10.000

20.000

30.000

40.000

50.000

60.000

70.000

80.000

90.000

100.000

10:36 11:36 12:36 1:36 2:36 3:36

Transient Hydrocarbon Upset:12 fold increase in total HC,6 minutes in duration causes an increase in H2S.

29/04/2014 16:12:11.289 28/07/2014 16:12:11.28990,00 days

H2S values above the LEL:Simultaneous SO2 values indicatinga smoldering (pyrophoric) fire.

~400 ppm COS + 100 ppm H2Sresulting in ~350 ppm SO2

emission exceedance.

COS

H2S

Figure 3. Sulfur pit high H2S and SO2 values (just prior to an incident)

MEASURES: H2S/SO2

MEASURES: H2S/SO2 (COS, CS2)

ametekpi.comTo find out more or request a quote visit our website To find out more or request a quote visit our website

AT4/AT5/AT6. TAIL GAS TREATING UNIT (TGTU) ANALYZER

931/932 TGTUThe TGTU increases sulfur recovery efficiency up to 99.99% (<100ppm SO2 emissions) by combining a reduction stage and amine treating to recycle H2S back to the SRU.

The primary purpose of measuring excess hydrogen (H2), (0 to 5%) is to ensure full conversion of all sulfur compounds to H2S.

The secondary function is the measurement of the residual sulfur compounds. The sample point can be in one of three locations. As H2 does not essentially change after the reduction reactor, the utility of the sulfur gas measurement varies according to design needs and sample point location. 931 and 932 analyzers, both use UV spectroscopy to measure single, and multiple species, respectively.

Benefits of the TGTU analyzer include:AT4 – AbsorberMeasurement of SO2 breakthrough from the reduction reactor to the quench column. SO2 values in excess of 5ppm can deactivate the amine

AT5 – Quench OutletMeasurement of H2S (0 to 5%) to quantify the load to the amine treater and provide a material balance on the SRU

AT6 – Absorber Outlet The most common sample point for H2S (0 to 250 ppm), which

(Refer to application note F-0229 Reduction/Amine Tail Gas Treaters with Model 931/932 Analyzers).

MEASURES: H2/H2S (SO2, COS, CS2)

CO

NC

ENTR

ATI

ON

%

H2S THC SO2 H2S

TIME

9:36

0.000 0.000

-0,1

-0,4

-0,9

-1,4

-1,9

-2,4

2,0

3,5

-0,1

-0,4

-0,9

-1,4

-1,9

-2,4

2,0

3,5

0.050

0.100

0.150

0.200

0.250

10.000

20.000

30.000

40.000

50.000

60.000

70.000

80.000

90.000

100.000

10:36 11:36 12:36 1:36 2:36 3:36

Transient Hydrocarbon Upset:12 fold increase in total HC,6 minutes in duration causes an increase in H2S.

29/04/2014 16:12:11.289 28/07/2014 16:12:11.28990,00 days

H2S values above the LEL:Simultaneous SO2 values indicatinga smoldering (pyrophoric) fire.

~400 ppm COS + 100 ppm H2Sresulting in ~350 ppm SO2

emission exceedance.

COS

H2S

Figure 4. COS upset data from TGTU absorber

is a measure of the amine absorber efficiency and the primary contribution to SO2 emissions. COS can be measured at the absorber outlet. COS is typically <5ppm but process upsets in the reduction reactor can result in hundreds of ppm, (see Figure 4). A valuable tool to isolate process problems and quantify the contributions to emissions. CS2 can also be measured at this sample point

TAIL GAS TREATING UNITCLAUS SULFUR RECOVERY UNIT

ametekpi.comTo find out more or request a quote visit our website

USA - Pennsylvania 150 Freeport Road Pittsburgh PA 15238 Tel: +1 412 828 9040 Fax: +1 412 826 0399

USA - Delaware 455 Corporate Blvd. Newark DE 19702 Tel: +1 302 456 4400 Fax: +1 302 456 4444

Canada - Alberta 2876 Sunridge Way NE Calgary AB T1Y 7H9 Tel: +1 403 235 8400 Fax: +1 403 248 3550

USA Tel: +1 713 466 4900 Fax: +1 713 849 1924

Brazil Tel: +55 19 2107 4100

France Tel: +33 1 30 68 89 20 Fax: +33 1 30 68 89 99

China Beijing Tel: +86 10 8526 2111 Fax: +86 10 8526 2141 Chengdu Tel: +86 28 8675 8111 Fax: +86 28 8675 8141 Shanghai Tel: +86 21 5868 5111 Fax: +86 21 5866 0969

WORLDWIDE SALES AND SERVICE LOCATIONSSALES, SERVICE & MANUFACTURING

Germany Tel: +49 2159 9136 0 Fax: +49 2159 9136 39

India Tel: +91 80 6782 3200 Fax: +91 80 6780 3232

Singapore Tel: +65 6484 2388 Fax: +65 6481 6588

© 2018, by AMETEK, Inc. All rights reserved. Printed in the U.S.A. A-0478 Rev 2 (0718) One of a family of innovative process analyzer solutions from AMETEK Process Instruments. Specifications subject to change without notice.

AT7. CONTINUOUS EMISSIONS MONITORING (CEM) SYSTEM

909/910/919/920/914 CEM

• If SO2 is reported on a mass basis, requires a stack gas flow rate and “hot-wet” analysis of SO2

• If the SRU is followed by a TGTU, the measurement base is typically “dry” basis

• If the TGTU can be bypassed, the SO2 analyzer can be dual-ranged (0 to 500 ppm/0 to 1% SO2)

• The 914 is a built-to-order CEM that includes all the components needed for a compliance monitoring and reporting project, using a dry extractive sampling technique

• The 909 and 910 analyzers incorporate gas flow rates. The 919 and 920 do not

SO2 emission, measurement base, and parameters vary according to:

MEASURES: SO2/O2 (NOx, TRS, Mass Emission, Dual Range)

SERVICES Our in-house service centers provide after-sales services to ensure you get the best performance from your system. This includes technical support, certification, calibration, commissioning, repairs, servicing, preventative maintenance and training. Our highly trained technicians can also attend your site to cover planned maintenance schedules and repair emergency breakdowns.