1. JAYA RAWAT, DHANEESH VS, P.V.C. RAO & N.V. CHOUDARY
Paper ID:
IMPROVING ENERGY EFFICIENCIES OF CRUDE PREHEAT EXCHANGERS BY SEQUENCING OF CRUDE OILS – A STUDY
JAYA RAWAT, DHANEESH VS, P.V.C. RAO & N.V. CHOUDARY
BPCL, Corporate R&D Center Greater Noida

2. OUTLINE OF PRESENTATION
Fouling problems in crude pre-heat exchangers
Fouling - chemistry
Reasons for fouling
Remedial measures for fouling
Sequencing of crude oils for improving crude pre-heat efficiency
Case Studies
Case -1
Case-2
Case-3
Conclusions

3. FOULING CHEMISTRY
Fouling is defined as the formation of an unexpected phase (solid, liquid or gas) hydrocarbon-based deposits on heat exchanger surfaces that interferes with processing.
First fouling layer has low thermal conductivity, which increases the resistance to heat transfer and reduces the effectiveness of the heat exchangers.
Second, as deposition occurs, the cross-sectional area is reduced, which causes an increase in pressure drop across the apparatus and creates inefficient flow in the heat exchanger.

4. FOULING MECHANISM Mechanism Effect on heat transfer surface
Particulate deposition
Accumulation of particles
Crystallization
Precipitation of dissolved salts (Scale formation)
Chemical reaction
Insoluble products formation
Corrosion
Corrosion products accumulation
Biological activity
Growth of living matter
Freezing
Process fluid solidification

5. CAUSES OF FOULING Organic Insoluble Asphaltenes Inorganic
Incompatible Oils on Mixing
Self-Incompatible Oils
Coke: Insoluble Asphaltenes at Thermal Cracking Temperatures
Polymerization of Conjugated Olefins
Inorganic
Sea Salts: Sodium, Calcium, and Magnesium Chloride
Iron Sulfide and Iron Oxide: Corrosion Products
Ammonium Chloride from units
Aluminum Silicate: Clay or Catalyst Fines
Assuming desalter functioning proper, there can be two causes for fouling; first is incompatibility & second is fouling tendency of crude itself.

6. FOULING MITIGATION STRATEGY
Diagnosis: Determine the cause of fouling.
Process conditions/history
Analysis of Foulant
Analysis of oil flowing through fouling unit
Investigation: Trace the cause to the source.
Determine each step in the progression from incoming crude oil through upstream units until the foulant is deposited in the fouled unit.
Innovation: Device ways to interrupt/reduce foulant precursors at each step.
a range of ideas of how to stop or interrupt each step in the progression from precursor in the crude oil to deposited foulant.
Mitigation: Select the best of these ways for the particular refinery to implement.
establish a quantitative measure of success to evaluate and to test the preferred mitigation action and make a recommendation

7. WAYS ADOPTED TO MINIMIZE FOULING
Off-line cleaning of heat exchanger tube bundles by chemical or mechanical cleaning. However, off-line cleaning interrupts regular services and also results in to period of non-production.
Online is a better strategy to address the fouling problems proper selection of crude oils which have cleaning properties so that foulants created by one crude can be cleaned by another crude oil.
Role of aromatic solvents and aromatic component of the crude oils play a significant role in this study.
Reversal of crude blend ratios has also been depicted here as one of the important step in order to reduce fouling in crude –preheat exchangers.

8. SEQUENCING OF CRUDE OILS FOR IMPROVING CRUDE PRE-HEAT EFFICIENCY
Selection of sequence of crude oil processing in such manner so that foulants created by one can be cleaned by next one
This strategy involves
Determination of fouling nature of crude oils
Assessment of nature of foulants by SARA analysis
Identification of cleaning crude
Lab/pilot scale trials for the crude sequencing
Chemicals analysis of foulants at each step.

9. TOOLS FOR IMPROVING ENERGY EFFICIENCIES OF CRUDE PREHEAT EXCHANGERS

10. WORK PLAN
Recommended strategy is to use key indicators and knowledge of the most common causes of refinery fouling to determine the cause of fouling
Once the cause is determined, the foulant precursors are traced to the source.
By stopping the foulant precursors from forming, the unexpected foulant phase can be eliminated from the refinery completely.
CASE -1 Crude exchanger’s fouling reduction by aromatic solvents
CASE -2 Crude exchanger’s fouling reduction by sequencing of crude oils
CASE-3 Crude exchanger’s fouling reduction by reversing the crude blend ratios

11. METHODOLOGY 1. TLC-FID analysis
The SARA (asphaltenes, saturates, resins and aromatics) analysis of crude oils and fouling deposits were with Thin Layer Chromatography-Flame Ionization Detection (TLC-FID) technique.
Asphaltene + saturates
CII =
Resins + Aromatics
CII values > 0.9 and higher is considered as indication for instability
is good stable range.

12. METHODOLOGY …………CONTD
2. THERMAL FOULING TEST
Hot Liquid Process Simulator (HLPS) – a useful tool for predicting heat exchanger performance and the fouling tendencies of specific process fluids
HLPS was operated in single-pass mode and the data was generated at constant heating medium temperature of 380ºC temperature, 700 psi pressure for duration of 5 hours at 3.0 ml/minute flow rate

13. METHODOLOGY- …… CONTD DISPERSION STABILITY OF ANTIFOULANT
Without antifoulant, deposits seen at the bottom
With antifoulant, no deposits, fully dispersed

14. Tube weight increase (g)
CASE STUDIES -1
Crude exchangers fouling reduction by aromatic solvents
Fouling behavior of three crude blends 1,2 & 3 were studied
Table:-1 Typical properties of crude blend
Properties
Crude blend-1
Crude blend -2
Crude blend -3
Density at 150C g/ml
0.8131
0.8347
0.8121
Sulphur, %W
0.163
0.228
0.152
Asphaltene %W
0.240
0.166
0.155
Table -2:- Comparison of Fouling parameters of crude oils
S.No.
Sample
Tube weight increase (g)
DT (ºC) 1.
Crude blend -1
0.0052 8 2.
Crude blend -2
0.0078 12 3.
Crude blend -3
0.0115 38
Crude blend-3 has shown the maximum fouling tendency among the studied crudes.

15. CASE STUDIES -1 . ………CONTD
The deposits obtained from crude blends1, 2 and 3 fouling test were collected and analyzed for their foulants characteristics. The fouling in case of all the three crude blends was mainly due to high paraffinic components.
Cleaning experiments were carried out in HLPS with aromatic solvents mixture (in-house prepared) for their suitability for the dissolution of deposits on fouled tubes.
It has been observed that with aromatic solvent blend-1 the circulation time and temperature (3.5 hr & 900C) required are higher than aromatic solvent blend -2 (2 hr & 800C). The mixture of these two has shown comparatively good results in less circulation time.

16. Crude exchangers fouling reduction by sequencing of crude oils
CASE STUDIES -2
Crude exchangers fouling reduction by sequencing of crude oils
SELECTION OF CLEANING CRUDE
Based on the results obtained from CASE-1, It was observed that the aromatic fractions contribute a lot in fouling reduction, so that if crude are selected in such manner so that the deposits created by one crude can be cleared by another one, similarly aromatic rich crudes may be processed to reduce the fouling in heat exchanges and it expected to clear the deposits created by the earlier processed crudes.

17. CASE STUDIES -2. ………CONTD
Table 3:- Typical crude properties of cleaning crudes
S.No.
Properties
Cleaning crude -1
Cleaning crude -2 1.
Density at 150C g/ml
0.8612
0.8382 2.
Sulphur, %Wt
2.12
1.02 3.
Asphaltene %Wt
0.37
0.19 4.
Aromatics %Wt
21.93
30.20
The crude blends 1-3 lie are low in sulphur and asphaltene and their fouling deposits are highly paraffinic.
It is evident from Table-4 that cleaning crude-2 is more aromatic and less asphaltenic as compared to cleaning crude-1.

18. CASE STUDIES -2. ………CONTD
Table: 4 HLPS test run with cleaning crudes for dissolution of deposits on tube
Test Parameters
Crude blend -3
Cleaning crude-1
Cleaning crude-2
1st run cycle
2nd run cycle
Increase in tube weight (g)
0.0406
0.0044
0.0020
0.0012
0.0003
D T (ºC) 38 20 11 10 4
Based on the above study it was observed that crude oils with low sulphur, less asphaltene and higher aromatics content should be preferred as cleaning crude.
The cleaning property can be successfully achieved by alternately charging with non-fouling or cleaning crude in order to minimize fouling in the heat exchangers.

19. CASE STUDIES -3
Crude exchangers fouling reduction by reversing the crude blend ratios
Table-5: Physical properties of crude oil A & B
Property
Crude A
Crude B
oAPI
39.2
23.9
Sulphur, %wt
0.158
0.142
Pour point, oC 7
<-20
40oC, cSt
3.5
8.5
Crude A and B are non-fouling crude when processed neat
whereas higher blends of crude A such as A70 and A80 have shown very high fouling.

20. CASE STUDIES -3. ………CONTD.
Fouling behavior of crude blends with different blend ratios
Crude A and B are non-fouling crude when processed neat, whereas higher blends of crude A such as A70 and A80 have shown very high fouling.
During the experiments it was observed that, when ratio of crude B was increased in the blend -the fouling mitigation trends was observed.

21. CASE STUDIES -3. ………CONTD.
A20 and A30 blends are less than 0.9, which means that these blends are stable, whereas the CII values obtained for A50, A70 and A80 blends are higher than 0.9 indicating instability of these crude blends.
Further it was also observed that this phenomenon has been observed in case of crude blend with high and low pour point, where if percentage of low pour crude is increased in crude it further helps in fouling reduction.
Table-6: CII values of crude blends
Sr. no.
Crude Blends
CII 1.
A20
0.674 2.
A30
0.797 3.
A50
1.220 4.
A70
1.325 5.
A80
1.414

22. CONCLUSIONS
Fouling in crude pre-heat exchangers can be managed through the proper sequencing of crude oils
Low sulphur, less asphaltene and higher aromatics content crudes can be selected as cleaning crude in case of fouling of paraffinic crudes.
Crude oils with cleaning behavior can prevent or even reverse the fouling caused by other crude oils.
Fouling can also be reduced by proper managing the crude blend ratios. In some cases it can be reversed even by changing the crude blend ratios
By alternately charging non-fouling or cleaning crude and fouling crudes, heat exchangers of crude pre-heat train can be maintained in the clean condition.
ACKNOWLEDGEMENTS
The authors are grateful to ED (MR/R&D), BPCL for his constant encouragement and guidance in publishing this work.

23. THANKS FOR YOUR KIND ATTENTION
REDUCE FOULING
REDUCE CORROSION

25. H/C Atomic Foulant
1.4 – 1.9 Wax
1.0 – 1.2 Unconverted Asphaltenes
0.7 – 1.0 Thermally Converted Asphaltenes
0.3 – 0.7 Coke