JAYA RAWAT, DHANEESH VS, P.V.C. RAO & N.V. CHOUDARY

BPCL, Corporate R&D Center Greater Noida

Paper ID: 20100982

IMPROVING ENERGY EFFICIENCIES OF CRUDE PREHEAT EXCHANGERS BY SEQUENCING OF CRUDE OILS – A STUDY

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

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.

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

FOULING MECHANISM

CAUSES OF FOULING Organic

Insoluble Asphaltenes

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.

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

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.

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.

TOOLS FOR IMPROVING ENERGY EFFICIENCIES OF CRUDE PREHEAT EXCHANGERS

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 oilsCASE-3 Crude exchanger’s fouling reduction by reversing the

crude blend ratios

METHODOLOGY

1. TLC-FID analysis

CII values > 0.9 and higher is considered as indication for instability

0.6-0.9 is good stable range.

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

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

With antifoulant, no deposits, fully dispersed

Without antifoulant, deposits seen at the bottom

DISPERSION STABILITY OF ANTIFOULANT

METHODOLOGY- …… CONTD

CASE STUDIES -1

PropertiesProperties Crude blend-1Crude blend-1 Crude blend -2Crude blend -2 Crude blend -3Crude 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:-1 Typical properties of crude blend

Fouling behavior of three crude blends 1,2 & 3 were studied

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

Table -2:- Comparison of Fouling parameters of crude oils

Crude blend-3 has shown the maximum fouling tendency among the studied crudes.

Crude exchangers fouling reduction by aromatic solvents

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.

CASE STUDIES -2

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.

Crude exchangers fouling reduction by sequencing of crude oils

CASE STUDIES -2. ………CONTD

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

Table 3:- Typical crude properties of cleaning crudes

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.

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

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.

CASE STUDIES -3

Crude exchangers fouling reduction by reversing the crude blend ratios

Property Crude A Crude BoAPI 39.2 23.9

Sulphur, %wt 0.158 0.142

Pour point, oC 7 <-20

Viscosity @ 40oC, cSt 3.5 8.5

Table-5: Physical properties of crude oil A & B

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.

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.

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.

CASE STUDIES -3. ………CONTD.

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

Table-6: CII values of crude blends

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.

REDUCE CORROSION

THANKS FOR YOUR KIND ATTENTION

REDUCE FOULING

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