AMMONIA PLANT CO2 ABSORPTION PROCESS

Prem BabooSr. manager(Prod)National Fertilizers Ltd, IndiaFIE ,Institution of Engineers( India)Technical Advisor & an Expert for www.ureaknowhow.com

CO2ABSORBER&REGENERATOR

CO2

TO UREA PLANT

.6 Kg/Cm2

43.2KNM3

9.14

P-1307

P1301

(A,B&C)

E302

A&B

48%

48%

IN

CO2-17.10%

Ar-.75%

N2-21.3%

CH4-0.4%

CO-0.11%

H2-60.84%

OUT

CO2-.11%

Ar—0.30%

N2—25.65%

CH4—0.5%

CO--.13%

H2—73.51%

13FIC

20

13-FIC-2 1

8.5

48.

54

FLOW

1135M3

FLOW

345M3

104 M3

104M3

3.94M

PALL

RINGS

1.5”

..01M

TO

TA

L 51

7M32

”PA

LLR

ING

S

L.P. STEAM

30 TON

13 FIC02

P.G.

BENFIELD PROCESS FLOW DIAGRAM

13 FIC0213HIC101

DM WATER FROM TANK

307 MT/Hr.

PROCESS GAS TO

METHENATOR

600C

345M3

FAN COOLER

E 1303

ABSORBER

F 1302

28.45MT/Hr

1100C

PROCESS

CONDENSATETX-1301

CICULATION

PUMP

BOOSTER

PUMP

REGENATOR

F-1301

B-1305E-1302

A/B

B1306-

TO FGR

FLASH GAS

1590C

PROCESS GAS

CO

ND

EN

SA

TE

E1308

E1306

LP STEAM

B13

01

11

30C

11

62

M3/H

r

B-1

303

T0 DE-AERATOR

C.W.

REMOVAL OF CO2:-

PROCESS FOR REMOVAL OF CO2 ARE BASED UPON SCRUBBING OF GAS WITH SOME SOVENT (PHYSICAL OR CHEMICAL)

THE SOLVENT SHOULD HAVE THE FOLLOWING PROPERTIES:-

i. HIGH CO2 SOLUBILITYii. LOW VISCOSITYiii. HIGH STABILITY UNDER OPERATING CONDITIONiv. NO REACTIVITY UNDER OPERATING CONDITIONv. VERY LOW VAPOUR PR UNDER OPERATING TEMP

GENERAL CONSIDERATION IN PROCESS SELECTION

1. PARTIAL PR OF CO2 IN FEED GAS AND TOTAL PR OF ABSORPTION

2. CO2 PURITY

3. GAS CONTAINING CO

4. AVAILABILITY OF UTILITY AND COST

TWO TYPE OF PROCESSESSA. PHYSICAL

PROCESS SOLVENT

1. WATER SCRUBBING WATER

2. LINDE’S RECTISOL METHANOL

3. ALLIED SELEXOL POLYPROPYLENE GLYCOL DIMETHYL

EITHER

4. FLUOR’S PROCESS PROPYLENE CARBONATE

5. PURISOL N METHYL- 2 PYRROLIDINE

6. SULPHINOL TETRAHYDRO THIOPHENE 1, 1 DIOZIDE

B. CHEMICAL ABSORPTION

BEST SUITED FOR LOW CO2 PARTIAL PRESSURE

1. MEA PROCESS:- MONO ETHANOL AMINE (REBOILER ENERGY IS HIGH 2NH2(CH2)2 OH + CO2+H2O=[HO(CH2)2NH3]2CO3

DISADVANTAGE:-

(i)[HO(CH2)2NH3]2CO3+CO2+H2O= 2HO(CH2)2NH3HCO3

(ii) HO(CH2)2NH2+CO2= HO(CH2)2NHCOONH3(CH2)2OH

CARBOMATE IS CORROSSIVE IN HOTER PARTS OF MEA• GV PROCESS • CATACARB PROCESS• BENFIELD PROCESS

C. PHYSIOCHEMICAL PROCESS 1. MDEA PROCESS( METHYLDIETHANOAMINE

BENFIELD PROCESS

OVER 700 BENFIELF PLANTS IN WORLD

ENERGY 660 – 1140 KILO CALORIE PER NORMALM3CO2

45% FOR REGENERATION 55% FOR ABSORPTION

K2CO3+CO2+H2O=2KHCO3+HEAT( MILD EXOTHERMIC)

CO2+H2O=HCO3-+H+

CO3--+H2O=HCO3-+OH-

CO2+CO3--H2O=2HCO3

1M3 30% K2CO3 SOLN ABSORBED 10M3 CO2 WITHOUT ANY ACTIVATOR

ACTIVATOR ACTION:- DEA (R2NH) R=CH2CH2OH

R2NH+CO2=R2NCOOH (INTERMIDIATE PRODUCT)

R2NCOOH+K2CO3+H2O= R2NH+2KHCO3

K2CO3+CO2+H2O=2KHCO3

PROPERTIES OF DEAMW = 105.14, SP GR = 1.0966, MELTING PT = 28OC , BP = 10/100/760MMHG= 150/205/260ANALYSIS OF LEAN SOLUTION / RICH SOLNK2CO3 KHCO3 EQ K2CO3 F/C TV V+5 DEA FE17.22 15.32 27.80 .38 10.4 .4 2.42 42.110.67 25.52 28.30 .67 .85 .67 2.8 ----CALCULATION OF F/C 1 _ _%AGE K2CO3 %EQ K2CO3 % EQ K2CO3 = % K2CO3+(MW KHCO3)100 % KHCO3

MW K2CO3)138 17.22+(0.69)X15.32=27.8016 1- FC 1_ (17.22) = 0.38 IN LEAN SOLN

27.8016

F/C IN RICH / LEAN SOLN = 0.858/0.352 (DESIGN VALUE)

F/C = F/C RICH – F/C LEAN (ACTUAL) .

F/C RICH – F/C LEAN (DESIGN)

COMPARISON BETWEEN PLANTS

RECTISOL PHYSICALABSORPTION. LOWER ENERGY.REMOVAL OF ALLIMPURITIES SUCH ASORGANICS, H2S, BENZENE, GUMFOAMING AND HYDROCARBON.PRODUCTION OFGAS WITH NEGLIGIBLE WATERGAS SOLVENT METHANOL. HIGH CO SLIP FROMCO SHIFT SECTION.FINAL REMOVAL OF CO,CO2 BY N2 WASHINI

BENFIELD CHEMICAL ABSORPTION612KCAL/NM3 CO2B-1306 YESLP BOILER AFTER REBOILER NOREGN SINGLEACTIVATOR SINGLEDEAHYDROLLIC TURBSINGLE( POWER GENERATION)AERATION OF SOLN NO FAVOURABLECO2 BLOWER NO

GVCHEMICAL ABSORPTION713.5KCAL/NM3 CO2B-1306 NOYES

DOUBLEDUAL (DEA+GLYCINE)DUAL PUMP DRIVEN

AVAILABLE

CO2 BLOWER

VENEZEULACHEMICAL ABSORPTION700KCAL/NM3 CO2B 1306 YESYESYESDOUBLEDUALDEA+GLYCINE)DUAL PUMP DRIVEN

AVAILABLE

CO2 BLOWER NO

contd

CO2 BLOWER YESDISADVANTAGE NO PGRNO OF PUMP AND COLUMN MORE INITIAL COST HIGHCO2 EXCESS VENT NO CO2 EXCESS

PGR AMMONIA PRODUCTION

NO CO2 EXCESSUTILIZE

CO2 EXCESS VENTPGR AVAILABLE

CORROSION

CO2 ITSELF WEAKLY ACIDIC

HOT POTASSIUM CARBONATE SOLN AGGRESSIVE FOR CORROSION

COMPOUND MAY FORM WITH THE SCRUBBING SOLN CORROSIVE TO STEEL

THEREFORE, A VANADIUM SALT V+5 IS USED IN THE SOLN AS A CORROSION INHIBITOR

THE VANADIUM OXIDISES THE IRON ON MET AL SURFACES

(VANADATION) BY ADDING V2O5

THE RESULTANT OXIDES FE3O4 MAGNETITE PRODUCE A TIGHT ADHERENT FILM ON THE

SURFACE WHICH RESULTS IN ESSENTIALLY NO CORROSION DURING OPERATION UNLESS

THE FILM IS DISTURBED V+5 +Fe2e = V+4 +Fe3e

FERRIC Fe2O3 MOST STABLE FORM

V2O5 CONVERTS Fe2O3 TO Fe3O4

2FeO +V2O5 = Fe2O3 + V2O4

FeO + Fe2O3 = Fe3O4 (MAGNETITE)

MAINTAIN PENTAVALENT VANADIUM NOT LESS THAN 0.2 WT % INCREASE V+5 CONTENT

BY ADDITION FRESH V2O5 (VANADIUM PENTAOXIDE)

ADDITION OF KNO2 IS RECOMMENDED FOR OXIDATIION METHOD

KNO2 +V2O4 = V2O5 +KNO

CORROSION AND PROBLEMS IN PLANTS

• 1 – 1986 AND 1992 IN RCF ( HALDOR TOPSOE PLANT)• 2 – 1986 : PRECIPITATED BICARBONATE PEELS-OFF THE PASSIVATIION LAYER IRON• AND VANADIUM IN THE SOLN CO-PRECIPITATE WITH THE BICARBONATE FORMING

• A SLURRY PLANT WAS SHUT DOWN 30 DAYS CIRCULATION PUMPS REPAIRED • NOV 1994 – HYDRO AGRI TRINIDAD’S TRINGEN II – 33 DAYS SHUT DOWN • PROTECTIVE MAGNETITE LAYER IN THE ABSORBER BOTTOM AND DISTRIBUTER

BECOME DAMAGED FORMATION OF IRON CARBONATE CORROSION RATE INCREASED COMPLETE DEPLETION OF VANADIUM

• 1992 – KRIBHCO HAZIRA – KELLOG’S DESIGN • FOLLOWING A NUMBER OF CRASH SHUT DOWN DUE TO NG AND MAINTENANCE JOB

• THE CO2 PRODUCT PURITY OF BOTH UNITS CAME UP TO 97.96% DUE TO FAILURE OF FLOATING HEAD GASKET IN THE FLOATING HEAD TYPE EXCHANGER (REBOILERS)

• SUSPECTABLE FAILURE AND THIS ALLOWED LEAKING PROCESS GAS TO ATTACK AND DESTROY THE PASSIVATION LAYER OF CS WALL OF REGENATOR

• 2001 – VENEZUELA JOSE FERTILISERS . AFTER REDUCTION OF LT CO SHIFT CONV CATALYST – CATALYST DUST BEFORE LINE UP TO GV DID NOT BLOW / REMOVE PROPERLY Fe CONTENT IN GV SOLN -~ 5000 PPM VISCOSITY OF SOLN INCREASED FREQUENT CHOCKING OF STRAINERS AND DRAIN LINES OCCURS WHOLE SOLN FILTERS THROUGH Fe CONTENT CAME DOWN AND VISCOSITY NORMALISED

BENFIELD SYSTEM: START UP

CHECK LIST :-1. TRIP SYSTEM: IS-4, IS-5, IS-301A, B, C, IS 303, IS 304 ARE IN RESET CONDITION

2. STROKE CHECKING OF ALL CONTROL VALVES3. CHECK a. 13 HV- 10 ------------CLOSEb. 13 HIC 101-------------CLOSEc. 13 FCV 02 -------------BY PASS & CV F/Cd. ISOLATION VALVES OF 13 FIC -01, LIC -01, 13LIC-20- I/2, 13PV 28 13 LCV- - 26-1/2

CLOSEe. DM WATER CIRCULATIION – NORMALf. CW TO E -1308 A/B – OPENg. F 1302 PR NORMAL WITH NG > 15KG/CM2h. N2 TO F 1301 OPEN j. PUMPS – P-1307/ P- 1301 PROPERLY LINED UP k. PUMPS ELECTRICALLY ENERGISED l. PUMPS L.O. CIRCULATION & SEALING WATER SYSTEM NORM

Contd.m. LEVEL IN B 1305 LESS THAN 100%n. O2 CONTENT IN THE SYSTEM LESS THAN 100PPM4. START CIRCULATION KEEP E 1303 FANS IN STOPPED CONDITION5. KEEP 13HV 10 CLOSE AND START INDIRECT HEATING BY SM STEAM PR LESS THAN 5 KG/ CM2 , TEMP LESS THAN 1800C F 1301 PR 2 KG/CM2 (N2) OBTAIN BENFIELD SOLN TEMP 105OC

PASSIVATION A. STATIC – E 1302 A/B FLOODED CONDITION TEMP=130OC DURATION 48 HRS B. DYNAMIC – CIRCULATION RATE 80% DURATION 36 HRS MAINTAIN V+5 EQUAL 0.5% K2CO3 KHCO3 EQ K2CO3 F/C V+5 DEA FE 20.96 6.37 25.33 0.172 0.47 2.18 66.74PPM LOCAL DRAINING B 1303 ON R1205 BY PASS MOV45 FULL CLOSED

FOR INDIRECT HEATING STOPPED CONDITION

NG FLOW TO PRIMARY REF 6000NM3, STEAM FLOW 30 TE/HR

RECYLE GAS FLOW ( 12FIC 02 +12 FIC 17) EQUAL 4000NM3

( 800 +2200)

12TJR 1/12, 06 =5000C / 7500C

13 PI C11= 0.6KG/CM2

B 1305 STEAM EJECTORS , X 1301 A/B/C/D I/VS OF VAPOURS AND

SL STEAM I/V MOTIVE STEAM TO BE OPENED FOR LINING UP SEQ

1. X 1301D

2. X 1301C

3. X 1301B

4. X 1301A FROM CCR 13 HIC O4, O5, O6, O7, INITIALLY TO BE

CLOSED AND TO BE OPENED AFTERWARDS.

13 FIC O2 I/VS TO BE OPENED

contd

13 HIC 101 TO BE OPENED

LINE UP 13 TIC O9

STOP NG TO F 1302 AND N2 TO F 1301 BLIND TO BE PROVIDED

STOP LOCAL DRAINING OF 1303 AND LINE UP TO PC HEADER

BENFIELD THEORY

a. FAVOURABLE PARAMETERS FOR ABSORPTION1. HIGH PRESSURE ( LIMITATION REF PRESSURE)

2. BETTER ACTIVATOR ( DEA, IN LINE II GLYCINE ALSO)

3. LOWEST F/C

4. BETTER FILTERATION ( 10 MICRONS OR LESS)

5. OPTIMUM SPLIT STREAM TEMP

6. IMPROVED PACKED BEDS AND INTERNALS

b. FAVOURABLE PARAMETERS FOR REGENERATION1. LOW PRESSURE

2. PROPER DISTRIBUTION OF RICH SOLN

3. IMPROVED PACKED BED AND INTERNALS

4. REGN STEAM FLOW/ PR / TEMP OPTIMUM

FOAMING CAUSES: IMPURITIES

i. SODIUM:- <1.0 % Na LIMITED NaHCO3 SOLUBILITYii. CHLORIDE:- AS CL- >100PPMiii. INERTS SALTS:- FORMATE, THIOSULPHATE ETC. CAN JOLERATE UPTO

MINIMUM INNNERTS IN SOLUTION DEENSITY AND ABSORPTION AFFECTED.

iv. HEAVY METALS:- POTENTIAL FOR LOSS OF PASSIVATION. v. SOLUBLE Fe CONTEST:- CONTENT UPTO 150PPM (NORMAL) MAX

SOLUBLE 200 – 250 PPM – CORROSION OCCURING. vi. SOLIDS IN SOLUTION:- ABRASIVE, LOSS CORROSION PROTECTION,

FOAMING OF SOLUTION. vii. SOLUBLE INORGANIC CONTAMINATES:-

- TOTAL SALTS HIGH- PROCESS TEMP INCREASES- LOSS OF ABSORPTION EFFICIENCY

viii. SOLUBLE ORGANIC CONTAMINATES:-- FREQUENT CAUSE OF FOAMING OF SOLUTION- SOME LOSS OF ABSORPTION EFFICIENCY

ix. GREASE AND OIL.. x. INTERNALS DISTURBES

FOAMING CAUSES

i. DUST OF ACTIVATED CARBONii. SUSPENDED METALLIC COMPOUNDS, WHICH MAY DISTURB

SURFACE TENTIONiii. DECOMPOSITION PRODUCTSiv. ORGANIC SUBSTANCES, GREASE, LUBEOIL, PAINT BITUMIN

EPOXY RASINS.v. SULPHIDES

FOAMING IS INDICATED BY :-1. HIGH PDI OF ABSORBER, REGENERATOR2. SOLUTION CARRY OVER3. SOLUTION HOLD UP IN PACKINGS4. LEVEL INSTABILITY5. INCREASE IN CO2 SLIP

FOAMING CONTROL

1. SIDE STREAM FILTRATION – A) MECH FILTER~ 10 MICRONS

FLOW – 5% TO 10% OF CIRCULATION RATE.

(CONTINUOUS REMOVAL OF SOLIDS )

B) ACTIVATED CARBON FILTER:- TO REMOVE

i. ORGANIC MATTER AND CONTEMINANTS

ii. DECOMPOSED COMPOUNDS

iii. IF COLOUR OF SOLN IS DARK, IMPROVE TRANSPARENCY

2. LIMITED USE ( 20ML) OF ANTIFOAM AGENT (UCON 50 HB 5100, POLYGLYCOLS , SILICONES.

3. DEMISTERS OF ABSORBER AND REGENERATOR FLUSHING BY BFW

FOAMING TEST

50 ML FILTERED BENFIELD SOLUTION AT 90OC

SHAKEN VIGOROUSLY OR N2 IS BUBBLED FOR ONE MINUTE

HIGHT OF FOAM > 40 MM

COLLASPE TIME > 10SEC

CAUSE OF INCREASE IN CO2 SLIP

1. INCORRECT SOLUTION FLOW RATE.

2. HIGH Fe OF HPC SOLUTION.

3. INCORRECT LEAN/ TOP SOLUTION TEMP.

4. INCORRECT SOLN COMPOSITION

5. FOAMING

6. INCORRECT SOLN / GAS – DISTRIBUTION IIN BEDS

7. DDISTURBANCE IN PACKING ARRANGEMENTS

8. DAMAGE / DISLOCATE INTERALS OF ABSORBER/ REGENERATOR

CAUSES OF BAD REGENERATION

1. LOW REGENERATION STEAM FLOW / TEMP / PR2. HIGH SOLUTION FLOW RATE3. ABSORBER GAS INLET TEMP LOW4. REGENERATOR PR HIGH5. INCORRECT STEAM / SOLUTION TEMP

PROCESS FOR REMOVAL OF CO2 ARE BASED UPON SCRUBBING OF GAS WITH SOME SOVENT (PHYSICAL OR CHEMICAL)

THE SOLVENT SHOULD HAVE THE FOLLOWING PROPERTIES:-i. HIGH CO2 SOLUBILITYii. LOW VISCOSITYiii. HIGH STABILITY UNDER OPERATING CONDITIONiv. NO REACTIVITY UNDER OPERATING CONDITIONv. VERY LOW VAPOUR PR UNDER OPERATING TEMP

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