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OAR Box 1784 

Prepped by Ollie Stewart 

Document Number: 

27) ll-B-1 

Docket Number: 

A-84-44 

Printed 10/31/2008 8:05:39 AM Sheet 27 of 143 
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•; f J* ^ 'i UNITED STATES ENVIRONMENTAL PROTECTION AGENCY i* -r\- 1 

"*" I SS2Z * Office of Air Quality Planning and Standards _/6 '-^

 x 

\*<Art Research Triangle Park, North Carolina 27711 

bit A 1983 

MEMORANDUM 

SUBJECT: Trip Report - Inspection of LO-CAT Process at Fletcher Oil , 

Carson, California 

FROM: Charles B. Sedman 

Standards Documentation Section, ISB/ESED (MD-13) 

TO: Ken Durkee, Chief 

Standards Documentation Section, ISB/ESED (MD-13) 

The LO-CAT process at Fletcher Oil & Refining Company, Carson, 

California, was inspected by EPA personnel on September 27, 1983. 

Attendees included: 

Charles Sedman U. S. EPA 

"Gail Lacy U. S. EPA 

Wilson Chapman ' ARI Technologies 

Connie Rutter South Coast APCD 

David Zeiger South Coast APCD 

The purpose of the visi t was to gather information on processes 

which remove and recover sulfur from refinery sour gases for a forthcoming NSPS review. 

Background 

In 1972 a new source performance standard was promulgated which 

limits hydrogen sulfide (H2S) concentrations in refinery fuel gas to 

10 grain per 100 standard cubic feet gas or about 160 ppmv. Refineries 

having large amounts of recoverable H2S have traditionally chosen to 

scrub sour fuel gas with an amine solution, eventually recovering the 

sulfur via the Claus process (with additional clean-up by tai l gas 

treaters where required). Smaller quantities of fuel H2S (perhaps up. 

to 10 long tons per day) may be more economical to recover by other, 

processes, including: 

0

 direct conversion of fuel H2S to elemental sulfur by the 

Stretford process 

0

 direct scrubbing of fuel gas which converts H2S to salable 

sodium hydrosulfide (NaSH) 
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° direct scrubbing of fuel gas and conversion to salable 

ammonium thiosulfate, (NH3)2S203. 

0 use of the LO-CAT process 

As part of the review of the fuel gas NSPS, as required by the Clean 

Air Act, the above options are to be evaluated to determine the performance and cost of fuel gas H2S control. Results would then be used 

to determine if a revision to the-NSP.S is warranted. 

The LO-CAT Process 

The LO-CAT process consists of absorbers, an oxidizer, and sulfur 

separation and storage. The LO-CAT catalyst consists of an aqueous 

solution of chelated iron, which is circulated in a closed loop between 

absorbers and the oxidizer vessel. In the absorbers, the H2S is absorbed 

into the catalyst solution and oxidized to elemental sulfur: 

2Fe+3 + S-2 — > 2Fe+2 + S 

The reduced (FE+ 2) iron is then recirculated to the oxidizer vessel where 

the iron is oxidized to Fe+3 by aereation and recirculated to the absorbers. 

Contaminated air exiting the oxidizer is routed to an incinerator. 

Elemental sulfur, in a slurried form, is first cooled and then 

coalesced in the oxidizer and settles to the bottom. Sulfur is continually 

withdrawn from the oxidizer and pumped to a sulfur melter. The aqueous 

catalyst solution/molten sulfur mixture is then separated by gravity where 

the sulfur is withdrawn to storage and the catalyst solution returned to 

the oxidizer. Normally a slipstream of the clarified solution is withdrawn 

as by-product ammonium thiosulfate solution, once the thiosulfate concentration 

has increased to a predetermined maximum, usually 20 percent by weight. 

Figure 1 shows the LO-CAT process as designed at Fletcher Oil. At 

Fletcher several additional features are incorporated which include 

(1) two-stage absorption of high pressure process gas, and (2) venturi 

expansion chambers on absorber vessels (not shown in Figure 1) to flash 

off hydrocarbon liquids entering the absorbers. 

Fletcher Experience 

At Fletcher Oil several operating problems were experienced, including: 

(1) higher than design levels of H2S in sour gas 

(2) sul fur floating 

(3) solution foaming 

(4) corrosion, erosion 

(5) plugging 

(6) biological growth (weakening of catalyst) 
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The higher concentrations of H2S in the sour gas resulted in 

higher levels of H2S in the product fuel gas. Since it was determined 

that the existing system would accommodate the increased catalyst 

recirculation and sulfur melting demands, addition of a second absorber 

(preabsorber) in series with the original absorber solved the problem. 

Sulfur floating is caused by contamination of sulfur particles with 

liquid hydrocarbon carryover from process units. This also results in 

a lower purity sulfur product. This problem was partially solved by 

the addition of venturi expanders to flash off hydrocarbons in the absorber 

liquor and partially by the judicious use of wetting agents in the catalyst 

solution to sink sulfur in the separator. 

Solution foaming in both absorbers and oxidizer vessel was alleviated 

by the continuous addition of small amounts of anti-foaming agent to the 

fresh catalyst solution. 

Corrosion and erosion problems in piping and valves were mitigated at 

Fletcher by replacing all carbon steel valves and pipes with stainless steel. 

Plugging or bridging of the oxidizer cone with sulfur was solved by 

addition of an intermittent air sparging system. Plugging in the small 

diameter slurry pipes has been controlled by addition of a strainer to 

remove compacted sulfur slugs. In the molten sulfur circuit, steam jacketed 

piping replaced steam traced and insulated piping. 

Finally, catalyst degredation due to biological growth has been controlled by the addition of biocides to the fresh catalyst charge. The use 

of biocides has been lessened by operating the system at higher temperatures -

125°F versus 110°E originally. 

Process Controls 

The Fletcher LO-CAT is operated outdoors with no central control panel. 

In addition to safety alarms for high temperatures, pressures, or mechanical 

failures, process control is also maintained by intermittent-sampl ing of 

the catalyst solution. On a 2-hour basis, redox potential, and pH are 

sampled and measured by Fletcher's laboratories. PH is generally maintained 

between 6.9 and 7.5. Once a week a sample of catalyst solution is taken 

and sent to the LO-CAT licensor, ARI Technologies, for determination 

of chelated Fe+ 3 . Also, H2S in the product fuel gas is sampled and analyzed 

ewery 2 hours. 

Successful operation is, therefore, dependent on catalyst iron and 

chelate concentration, pH, and catalyst circulation rates, controlled within 

narrow range. Also, the addition of small amounts of additives is critical 

in the control of adverse chemical and biological phenomena. Also, as 

discussed earlier, the temperature of the solution is important in controlling 

biological activity. 
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Emission Reduction 

The LO-CAT process at Fletcher handles up to 2-3 volume percent 

of H2S (20,000-30,000 ppmv) in entering sour gas. During my visit, I 

observed process and analytical log books showing outlet H2S concentrations 

ranging from 0-30 ppmv H2S in product gas for a 99.9+ percent removal • 

efficiency. The design guarantee given is 150 ppmv H2S. 

Other Discussion -

I asked refinery operators about the reliability of the LO-CAT 

process. The general consensus was that it was one of the less troublesome process units in the refinery. The attending inspectors from 

the South Coast APCD added that the Fletcher LO-CAT unit had never 

presented a compliance problem due to high reliability and complete 

emission control redundancy in the NaSH.unit. [In case of failure, the 

NaSH process can handle the entire process gas H2S loading normally routed 

to the LO-CAT.] 

Also worth mentioning is that the ammonium thiosulfate (ATS) purge 

has never been used at Fletcher, indicating that oxidation of the solution 

is not a problem. 

Summary and Conclusions 

1. The LO-CAT process at Fletcher has experienced, and apparently 

solved, a number of process problems and now operates reliably and with 

high (99.9%+) H2S removal efficiencies. 

2. Time permitting, follow-up with ARI Technologies is recommended 

to study the economics of the LO-CAT as compared to other alternative 

processes, as a function of H2S amounts removed. 
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