p.1 

OAR Box 1784 

Prepped by Ollie Stewart 

Document Number: 

57) ll-D-10 

Docket Number: 

A--84-44 

Printed 10/31/2008 8:05:40 AM Sheet 57 of 143 
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2-D-

'. 1. TECHNOLOGIES INC. 

Octobe r 18 , 1985 

Mr. Larr y Elmore 

U.S. Environmenta l Protectio n Agency 

MD-1 3 

Research Triangl e Park , North Carolin a 27711 

Dear Mr. Elmore : 

Pleas e excus e th e dela y in sendin g you th e preferre d flow 

diagram fo r th e LO-CAT® Hydrogen Sulfid e Oxidatio n process 

f o r refiner y fue l gas treating . 

The flow diagram was correct , bu t th e attache d process 

descriptio n had an erro r in it , and i t took longe r t o corren t tha n I though t i t would. 

Yours ver y truly , 

ARI TECHNOLOGIES INC. 

L. C. Hardiso n 

Presiden t 

LCH.nn 

Attachments 

600 N. First Bank Drive • Palatine, Illinois 60067 

(312) 359-7810 • TWX 310-693-1591 

'M 

•\o 

I 
P.3 

J ~ Y 

PROCESS DESCRIPTION 

CONVENTIONAL LO-CAT® 

HYDROGEN SULFIDE OXIDATION PROCESS 

FLOW DESCRIPTION 

Sour gas passes through an inlet gas scrubber to remove entrained 

liquids and enters the absorber at line pressure through a specially 

designed venturi prescrubber. The gas passes upward through a low 

liquid-filled vessel in which it contacts the LO-CAT catalyst solution flowing downward. The H2S is absorbed in the solution and 

converted immediately to solid sulfur. Sweet gas with less than 

100 ppm H2S leaves the absorber vessel and passes through a sweet 

gas scrubber to guard against mist carryover before entering the 

fuel system. 

The following chemical reactions take place in the absorber vessel: 

(1) H2S Absorption 

H2S + H20 -*• H2S (aqueous) + H2O 

(2) First Ionization 

H2S (aqueous) •*• H+ + HS" 

(3) Second Ionization 

HS"+ H+ + S= 

(4) Oxidation of Sulfide 

2Fe+++ + S= •*• 2Fe++ + S°l 

Active LO-CAT solution enters the absorber column at the top and 

flows downward through the vessel counter-current to the gas flow. 

The spent solution leaves the vessel through an internal cone 

bottom. Partially reduced solution runs by gravity or pressure 

difference through a solution cooler.and into the oxidizer vessel, 

in which it is regenerated by direct contact with compressed air. 

Regeneration of the LO-CAT solution in the oxidizer involves the 

following reactions: 

v_. .M 

/ 
P.4 

(5) 

(6) 

ari 

TEOWXOQtSfC 

Oxygen Absorption 

O2 + H2O -»• 20 aqueous) + H2O 

Regeneration of Iron 

2Fe

 + + + 0 (aqueous) + H2O + 2Fe+++ + 2 (OH)" 

Overall, the reaction is 

(7) H2S + 1/2 O2 -»• H20 + S° + 

The spent air, with a small fraction of the oxygen removed, leaves 

the top of the oxidizer vessel and discharges to the atmosphere. 

Sulfur formed in the Absorber vessel circulates with the solution 

and the particles grow to the 10-20 micrometer range. The larger 

particles settle out of the bulk solution flow in the bottom of the 

Oxidizer vessel and are flushed out of the cone-bottomed settling 

area as a slurry at 10 to 20 wt% sulfur. 

The sulfur slurry is pumped at approximately 100 psig through a 

special non-plugging heat exchanger or melter, where it is heated 

to 270°F by 50 psig steam. The solution and molten sulfur phase 

formed in the melter flow through steam jacketed piping to a steam 

jacketed separator vessel, where a liquid-liquid interface is maintained. 

Molten sulfur is withdrawn from the separator vessel on level control 

to a molten sulfur storage tank or a sulfur pit where it is stored 

for ultimate shipment by truck or rail car. 

The solution return leaves the sulfur settler through a back pressure 

control valve set at about 75 psig. The bulk of the solution is returned to the settler vessel and then to the absorber/oxidizer circuit. 

CHEMICAL REQUIREMENTS 

In the oxidation of H2S to sulfur, some side reaction takes place 

which may be represented by the equation: 

(8) 2HS" + 1-1/202 + H2S203 

This reaction reduces the pH of the scrubbing solution, and Na2C03, 

KOH or other alkaline salt must be added to maintain the pH of the 

solution in the 8-8.5 pH range. This leads to a gradual buildup of 

Na2S203 or similar water-soluble sulfur-containing salts in the 

solution. These have no deleterious effect at concentrations below 

30 wt% or so. 

The solution composition is maintained at a stable level by continuous additions of the following chemicals: 
P.5 

ARI-310 Concentrate is added to replace any solution which may be 

lost with the sulfur cake. 

ARI-310M Chelate-rich Makeup solution is added to replace Type A and 

Type B chelate compounds lost from the solution by slow oxidation 

reactions. ARI provides a complete analytical service and catalyst 

samples on a weekly or semiweekly basis which are sufficient to 

maintain economical'addition rates. 

N____2____(__3 Buffering Solution is added to replace losses with the sulfur 

coke and to neutralize thiosulfate ions formed in the process. 

Adjustments in the addition rate are based on daily measurements of 

the solution pH. 

ARI-400 Biochem Biostat is added at about 10 ppm by weight per day. 

This prevents biological damage to the chelate system. 

Wetting Agent and Anti-Foam Additives may be added continuously in 

small amounts if the gas stream contains oily materials which interfere with sulfur settling, or surface active materials which can 

otherwise cause foaming. 
SOUR GAS VEiNITURl LIQUID FILLED 

SCRUBBER PRE-CO.NTACTOR ABSORBER 

OXIDIZER AIR 

COMPRESSOR 

X 

SOUR 

GAS 

l*M= 

CWM6 

J 

. 1 

SULFUR 

LOADOUT 

STATION 

MOLTE N 

SULFU R 

STORAGE 

SULFU R 

SEPARATOR 

SWEET GAS OUT 

SOLUTION 

CIRCULATION 

PUMP 

NOTE : 

CHEMICAL ADDITION EQUIPMENT NOT SHOWN. 

an TBOHN0L0G6S HC 

ANAEROBIC 

LO-CAT*'** HYDROGEN SULFIDE 

OXIDATION PROCESS 

A