Online Monitoring of Recip Compressors, 2004

8/13/2019 Online Monitoring of Recip Compressors, 2004

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NPRA Maintenance ConferenceMay 25-28th, 2004. San Antonio

On-line Monitoring of Reciprocating

Compressors

By

Alberto Guilherme Fagundes Schirmer, Dresser-Rand

Nelmo Furtado Fernandes, PetrobrasJos Eduardo De Caux, Petrobras


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"ONLINE" MONITORING OF RECIPROCATING COMPRESSORSNPRA Maintenance Conference May 25-28th, 2004

Alberto Guilherme Fagundes Schirmer (1)

Nelmo Furtado Fernandes (2)Jos Eduardo De Caux (3)

AbstractContinuous monitoring of critical rotating machinery is widely accepted by users ofstrictly rotating machinery such as centrifugal and screw compressors. However,continuous monitoring of reciprocating machinery such as compressors and internalcombustion engines has not achieved the same level of acceptance. Significant

progress has been achieved recently in narrowing this acceptance gap. This paperdescribes the pilot installation of a RECON C-GUARD monitoring system on aWorthington BDC-2 reciprocating compressor at PETROBRAS Gabriel PassosRefinery in Betim, MG, Brazil. This system, developed by Windrock Inc. Technologyand marketed exclusively by Dresser-Rand, is the first system of its kind everinstalled in Brazil. This paper also includes the theory of Reciprocating CompressorDynamic Analysis using practical examples of common compressor defectsdiagnosis. The results of the pilot project at Gabriel Passos Refinery are assessedregarding both process and refinery profitability improvements.

(1) Mechanical Engineer. Senior Maintenance & Reliability Engineer at Dresser-Rand Company, Houston, TX.(2) Chemical Engineer. Senior Process Engineer at PETROBRAS Gabriel Passos

Refinery, Betim. MG, Brazil.(3) Maintenance Technician. Technical Consultant at PETROBRAS Gabriel Passos

Refinery, Betim, MG, Brazil.


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1. Introduction

Reciprocating compressors are the most common type of compressors found inindustrial applications. Worldwide installed reciprocating compressor horsepower isapproximately three times that of centrifugal compressors and maintenance costs ofreciprocating compressors are approximately three- and- a- half times greater thanthose for centrifugal compressors [1].

Continuous monitoring of critical rotating machinery is widely accepted by strictlyrotating machinery users such as centrifugal and screw compressors. However,continuous monitoring of reciprocating machinery such as compressors and internalcombustion engines has not yet achieved the same acceptance level. Recently,there has been good progress in this field. This paper presents the pilot installationof a RECON C-Guard monitoring system, developed by Windrock Inc. Technologyand marketed exclusively by Dresser-Rand, on a Worthington BDC-2 compressor atPETROBRAS Rafael Passos Refinery in Betim, MG, Brazil.

Large reciprocating machinery users such as gas transmission and storage

companies in the United States and Europe use condition-based maintenance. Thismaintenance strategy allows not only cost reduction by reducing the number ofmaintenance interventions to only those actually needed, but also provides efficiencyimprovements by dynamic analysis of the equipment as well.

Condition-based maintenance has become more prevalent in refineries andpetrochemical plants because of the increased criticality of these machines as plantcapacity increases to the point that compressors previously spared are now pressedinto full-time service. Achieving higher reliability requires continuous monitoring ofthe reciprocating compressors.

Reciprocating compressor dynamic analysis is based on the interpretation ofdeviation of its operation parameters from ideal conditions. Parameters to beanalyzed include cylinder internal pressures, volumes, temperatures, phase,vibrations and rod drop. The analysis also includes calculated parameters such aspower, efficiency, rod loads and losses.

Continuous online monitoring of reciprocating compressors through dynamicanalysis allows malfunction diagnosis improving the time and cost to repair andprovides continuous protection from catastrophic events such as rod or cylinderrupture.


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2. Reciprocating Compressor Dynamic Analysis Basic Concepts

The Pressure x Volume diagram is the best way to represent the energy cycle in areciprocating machine. Although the theory is relatively simple, getting actualdiagrams online presents technological challenges that only recently were overcome.Solutions to these challenges are addressed in Section 4.

For simplification, only one side of the compressor cylinder is shown in Picture 2.1.which is used as reference for the reciprocating compressor energy cycle descriptionthat follows.

At A, also known as top dead center (TDC), both suction and discharge valves areclosed. During expansion, the piston movement increases the volume occupied bythe gas that originally occupied the clearance volume. This volume increase for thesame gas mass causes reduction of the cylinder internal pressure.

As the piston reaches B, cylinder internal pressure is equal to suction line pressure.

A small additional piston movement is enough to reduce the cylinder internalpressure below suction line pressure causing the suction valve(s) to open.

As the piston moves from B to C, suction line gas at a pressure higher than thecylinder internal pressure is admitted into the cylinder. The portion of the totalcylinder volume occupied by the admitted gas is called suction volume [2].

At C, the piston begins to move in the opposite direction. As it begins this movement,the piston reduces the volume of gas contained in the cylinder, increasing itspressure and forcing the suction valves to close.

After the suction valves close, the original clearance volume gas and the gasadmitted during the suction cycle are reduced in volume by the piston movement.Consequently, the cylinder internal pressure increases until reaching the dischargeline pressure in D.

A small additional piston movement is enough to raise the cylinder internal pressureabove the discharge line pressure causing the discharge valve(s) to open.

From D to A, gas in the cylinder at pressures exceeding the discharge line isdischarged. The volume of gas discharged is called discharge volume [2].

The shaded zones on Picture 2.1 represent the additional work done to force the gasthrough the suction and discharge valves. The area of the shaded zones represents(approximately) the valve losses. Theoretical P x V diagrams superimposed on theactual diagrams supply important compressor diagnostic information. Section 3presents examples of this use of P x V diagram feature.


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Picture 2.1 Typical Pressure x Volume (P x V) diagram

Because of manufacturing and assembly tolerances, reciprocating compressorsmust have some clearance volume. Because there is some gas remaining in theclearance volume at the end of the entire discharge stroke (swept volume), thisremaining gas must expand during the suction stroke. The ratio between suctionvolume and the swept volume is called suction volumetric efficiency and isexpressed by the equation [3]:

eSweptVolum

umeSuctionVolVES =

In a similar manner, only part of the piston stroke is used to discharge gas. The ratiobetween the discharge volume and the swept volume is called discharge volumetricefficiency and is expressed by the equation [3]:

VolumeSwept

VulomeeDischVED

arg=

All the mass of gas admitted into the cylinder, except that remaining as describedabove, is discharged. The ratio between the gas mass admitted and gas mass

discharged (flow balance) is a function of the ratio of volumetric efficiencies which isequal to 1. This ratio is one of the most representative parameters of thecompressors condition. As an example, leaking discharge valve(s) will cause a flowbalance lower than 1. Leaking suction valves will cause a flow balance higher than 1.The flow balance concept will be discussed in detail later this paper.

VolumeClearanceVolume

Swept Volume

Total Cylinder Volume

Ps

PdDischarge

Pressure

Suction

Pressure

Ex

pansion

Com

pression

Suction Volume

Discharge Volume

A

B C

D


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3. Reciprocating Compressor Dynamic Analysis Diognostic Examples

The components that most frequently cause reciprocating compressor shutdownsare listed in Table 3.1 below [4].

Table 3.1 Components that causes reciprocating compressor shutdown

Component Percent (%)

Compressor Valves 36Packing 17.8Process 8.8

Piston Rings 7.1Rider rings 6.8

Unloads 6.8Cylinder Lubrication 5.1

Instrumentation 5.1Other 6.5

Table 3.2 shows the distribution of reciprocating compressor failures [4].

Table 3.2 Reciprocating compressor failure causes

Cause Percent (%)

Overload 28Liquid or foreign object ingestion 18

Lubrication 12Fatigue 9

Freezing 6Other or undetermined causes 27

Maintenance costs of repairable items are distributed as per Table 3.3 [1].

Table 3.3 Maintenance costs per repairable item

Component Cost Percent (%)

Valves 50Packing 20

Piston Rings 20Rider Bands 7Piston Rods 2

Cylinder Liners 0.5Bearings 0.5

Systems that monitor only parameters such as rod drop or valve cover temperatureare able to diagnose only a small portion of the failures listed in the above tables.

The dynamic analysis concepts, previously presented in this paper, enablediagnosing most common defects in reciprocating compressors. In this paper, thesecapabilities will be exemplified by identification of suction and discharge valve leaksas well as piston rings.


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3.1. Suction and Discharge Valve Leak Diagnosis

In the case of leaking suction valves(s), faster than ideal pressure reduction occursduring the suction stroke. This happens because the gas in the cylinder is at apressure higher than the pressure of the suction line. Because the suction valve(s) isleaking, the gas flows toward the suction line, causing the cylinder internal pressure

to equalize with the suction line pressure sooner than would occur in the ideal cycle.This faster expansion can be easily noticed when the actual P-V diagram issuperimposed to the ideal diagram as seen in Picture 3.1.

Picture 3.1 Leaking Suction Valve P-V Diagram

In a similar manner, the cylinder internal pressure would rise slower in case ofleaking suction valve(s). Superimposing the ideal P-V diagram to the actual P-Vdiagram as in Picture 3.1 can easily show this.

Picture 3.1 also shows that leaking suction valve(s) increase the suction volumetricefficiency and reduce discharge volumetric efficiency. As a result, the flow balance is

higher than 1.

In case of leaking discharge valves, the gas expansion is slower than ideal becausethe higher pressure gas from the discharge line is admitted into the cylinder throughthe leaking discharge valves. As shown in Picture 3.2, the slower expansion causesthe reduction of the suction volumetric efficiency.

Similarly, for leaking discharge valve(s), the cylinder internal pressure will increasefaster during the compression. Superimposing the actual P-V diagram to the ideal P-V diagram easily shows this. Picture 3.2 shows the superimposed diagrams and also

Volume

Pressure

Clearance

Volume

Swept Volume


Suction Volume big ger than ideal

Discharge Volume smaller than

Ideal Volume

Ideal PV Diagram

Com

pression

slower than Ideal

Exp

ansionfaster

than

ideal

Actual PV

Diagram

Ps

Pd


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how the discharge volumetric efficiency increases. The flow balance is consequentlyhigher than 1.

Realistically, 100 percent leak-proof valves do not exist and the flow balance isalmost never exactly 1. Typically flow balances between 0.95 and 1.10 areconsidered acceptable. A more precise assessment can be done calculating the costof the valve losses. A better discussion on this is available in Section 5 of this paper.

Picture 3.2 Leaking discharge valve P-V Diagram

Picture 3.3 Discharge Valve with extreme leak

In extreme cases, discharge valve leaks can be so large that the volume increaseduring the expansion is not enough to reduce the cylinder internal pressure belowthe suction line pressure. In this case the suction valves do not open, thus no gas isadmitted into the cylinder. Picture 3.3 shows a typical example of this condition.

Volume

Pressure

Clearance

Volume

Swept Volume


Suction Volume smaller than Ideal

Discharge Volume bigger than Ideal Volume

Ideal PV Diagram

Com

press

ion

faste

rthanIde

al

Exp

an

sionSlower

than

ideal

Actual PVDiagram

Ps

Pd


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3.2. Piston Ring leak diagnosis

Most industrial compressors are double effect, meaning that the compressionhappens in both sides of the piston. Small clearance piston rings are installed toimpede the flow from one side of the piston to the other. Well-designed piston ringsshould stop this leakage and move with minimum friction. Even the best-designed

rings, including lubricated designs, will show some type of wear over time.

Piston ring leaks can be diagnosed and quantitatively assessed through dynamicanalysis. An increase and reduction of pressure during expansion and compressiontypify these leaks when compared to the ideal cycle.

Head end (HE) and crank end (CE) sides are separated by half a cycle (180o). Thismeans that when HE is compressing, HE is expanding and vice-versa. When oneside reaches the discharge pressure the other side is at suction pressure, thus theseare the maximum leak points. However, there is a moment in which both sides are atthe same pressure and no leak occurs. Leak direction changes at this point. In a

single side P-V diagram (Picture 3.4) a piston ring leak shows the actualcompression or expansion crossing the ideal line.

Picture 3.4 Leaking ring P-V diagram

4. Reciprocating Compressor Online Monitoring

Although the concepts presented in the previous section are relatively simple, theactual pressure and volume measurements are challenging because a large numberof pressure x volume correlated points must be collected during each compressioncycle to allow effective compressor diagnosis.

The system installed at PETROBRAS-REGAP collects pressure measurements atevery degree of revolution for each side of the cylinder, resulting in 360measurements per revolution or 3570 measurements per second for the 595-RPM

Volume

Pressure

Ideal PV Diagram

Actual PVDiagram

Ps

Pd

Actual and IdealPV Diagrams

crossing


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compressor speed. Specialty pressure transducers are designed for this application.Pressure transducers used in regular process controls are not suited for this service.

The volume associated with the pressure is calculated using the crankshaft angularposition in relation to TDC and is a direct function of this angle for a givencompressor geometry.

Temperature transmitters collect suction and discharge temperatures for eachcylinder. Temperatures are needed for the compressor thermodynamic performanceassessment.

Vibration impulse signals with crankshaft phase reference are also collected for eachcylinder. Vibration information can confirm P-V diagram diagnoses as well as monitormechanical looseness.

Although not absolutely necessary for compressor dynamic analysis, rod drop canalso be collected. Rod drop can supply additional piston ring, rider ring andcrosshead shoe wear information [5].

The following parameters can be calculated and monitored:

Power Power required to complete the gas compression cycle and is used todetermine if the compressor is overloaded. It is also used in conjunction with idealisentropic power to calculate isentropic efficiency. Unless the compressor load orgas composition is changed, the isentropic efficiency should not vary significantlyover time and any significant deviation should be investigated.

Capacity Capacity is calculated as the average of suction and discharge conditionsand also can be calculated at standard conditions.

Flow Balance As previously discussed, flow balance is the ratio between theadmitted and discharged masses. Flow balance is used as the first indication ofcompressor anomalies. A detailed analysis of other parameters will diagnose theproblem effectively.

Rod Load The reciprocating compressor rod is subjected to a combination of loadsbecause of cylinder internal pressures and inertia of the moving parts. Rod load canbe influenced by changes in suction and discharge pressure, compressor unloading,valve(s) leaks, and other causes. Overloading a compressor rod is very dangerousand must be avoided because of potential catastrophic failure, including risk of

personal injury.

Rod Reversal The rod load varies from compression to tension and vice-versaalong the piston stroke. To assure adequate lubrication of the crosshead pin, theload vector should change direction during the piston stroke. API Std 618 [6]recommends that the duration of this reversal shall not be less than 15 degrees ofcrank angle, and the magnitude of the peak combined reversed load shall be at least3 percent of the actual combined load in the opposite direction. Somemanufacturers have even more rigorous design criteria.


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Picture 4.1 shows a typical diagram of rod load and rod reversal for a reciprocatingcompressor.

Cylinder Maximum Pressure Cylinder overpressure indicates presence of liquids orrestrictions to the gas flow.

Percent Clearance Most users do not have this information. Percent clearance

requires an iterative calculation technique using a variety of methods. Significantdifferences in results may be indicative of inadequate program setup or presence ofliquids in the cylinder.

Picture 4.1 Rod Load and Rod Reversal

Theoretical discharge Temperature It is calculated assuming isentropiccompression of the gas and is a good reference for comparison with the actualdischarge temperature. Generally a difference between theoretical and actualtemperatures above 20oF is indicative of excessive recirculation caused by valve(s),piston rings, or unloader anomalies (among others).

Volumetric Efficiencies As discussed in section 3, the volumetric efficiencies arecalculated from the P-V Diagrams.

Valve Losses The additional energy required to force the gas through the valves is

calculated and can be expressed as total energy percent or cost, provided theunitary energy cost is known.

All the above parameters can be monitored continuously or periodically. Computernetworks greatly enhance the possibility of online monitoring.

Periodic monitoring is done using portable analyzers and instrumentation.Periodically, qualified analysts install temporary pressure, temperature vibration, andphase sensors, connect the analyzer, and collect the necessary data. The analyzer


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is programmed to calculate the parameters mentioned above. Modern analyzers candisplay graphical results that are easier to interpret and diagnose.

The main advantage of periodic monitoring is its flexibility to collect additional data ifneeded. This flexibility is very important for experimental analysis greatly improvingdiagnosis accuracy. Periodic monitoring requires highly qualified analysts with morethan 10 years experience analyzing reciprocating equipment.

The main disadvantage of periodic monitoring is that it cannot provide continuousmachinery protection. As discussed previously, the calculated parameters mustoperate within limits, otherwise there is a risk of catastrophic failure including risk tothe personnel involved in maintenance and operation of the machine(s).

Continuous online monitoring is done using permanently installed intelligenttransmitters for pressure, temperature, vibration and phase signals. Thesetransmitters calculate the parameters mentioned above and, because they areconnected to computer networks, allow remote analysis of the data.

The same intelligent transmitters also can be connected to PLC- based controllersor DCS systems, enabling the machinery protection to be integrated with processcontrols and protection. The intelligent transmitters have also optional relay outputsin case they are used in the plant protection systems.

The main advantage of continuous monitoring is continuous protection of themachine(s). Additionally continuous monitoring allows cross-examination of processinformation and machinery dynamic information increasing diagnostic capabilities.

The main disadvantage of continuous monitoring is the lack of flexibility for additionaldata collection because the sensors cannot be easily relocated. The location and

quantity of sensors must be carefully studied to maximize diagnostic capabilities.

5. Reciprocating Compressor Monitoring System Installation at PETROBRAS-REGAP

Initial discussions between Dresser-Rand and PETROBRAS headquarters indicatedthat although the company was very well positioned regarding centrifugalcompressor monitoring, there was no reciprocating compressor monitored at anyPETROBRAS refinery. PETROBRAS strategy for critical machinery is continuousmonitoring and large investments made in centrifugal compressors, turbines and

pumps.

PETROBRAS reviewed its compressor fleet from all 11 refineries and selected thebest for a pilot project -- Gabriel Passos Refinery (REGAP) in Betim, MG.Compressor Tag number 106-K-2A was chosen because of the critical nature of thehydrogen make-up process.

The 106-K-2A compressor is a two-stage compressor with the operational data listedin Table 5.1:


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Table 5.1 - 106-K-2A Compressor Operational Data

Compressor 1st

Stage 2nd

Stage

Manufacturer Worthington(D-R)

Power (HP) 805 - -Speed (RPM) 595

Service Hydrogen - -

Suction Pressure (psig) - 198 465Discharge Pressure (psig) - 482 796Suction Temperature (oF) - 95.4 110Discharge Temperature - 247 202Cylinder Diameter (in) - 11 1/2 7 1/2

Suction Valves per side 2 1Discharge Valves per side 1 1

Unloaders 2 1

Picture 5.1 shows a schematic diagram of the installation. All field components areapproved for Class 1 Div. 1 Group B (NEC).

The most difficult issue for this installation was the absence of cylinder pressureports. Drilling ports would not be feasible because the time needed for themandatory hydrotest of the cylinders. To avoid drilling the cylinder, there weredifferent solutions for the first and second stages.

Picture 5.1 Online Monitoring Schematic Diagram

The first stage cylinder is fitted with plugged recirculation ports. The compressorOEM designed modified plugs in order to pipe the internal pressure to the externalpressure transducer. Picture 5.2 shows detail of this modification. Isolating valveswere installed to allow easy maintenance and calibration of the pressuretransducers.


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The second stage cylinder in not fitted with recirculation ports. The adopted solutionwas to pipe the pressure through the discharge valves. The discharge valves werechosen to avoid the additional difficulty caused by suction valve unloaders. TheOEM markets the modification design. Picture 5.3 shows a schematic diagram of themodification.

The OEM supplied modified MAGNUM valves as well as the design of themodification, which were executed and installed by PETROBRAS - REGAP.

Picture 5.2 First Stage Pressure Port

1ststage beforemodification

1stStage aftermodification (isolatingvalve and pressuretransducer installed)

Picture 5.3 2ndStage Pressure Port Schematic Diagram

Assembly detailsAdapter tube


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Picture 5.4 shows details of the 2ndStage assembly. Isolating valves were installedfor pressure transducer maintenance and calibration.

Picture 5.4 Second Stage Pressure Port Assembly

2ndStage isolating valvesand transducer installationdetail

2ndstage beforemodification

2ndstage aftermodification

Temperature transmitters were installed at suction and discharge pulsation bottles.Picture 5.4 shows details of the installation.

Picture 5.4 Temperature transmitters installation

Adapter tube Assembly details

Discharge

Suction


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The phase sensor (pickup) was installed on the electric motor fan because of betteraccess. The phase reference is precisely correspondent to TDC. Picture 5.5 showsdetails of the installation.

Picture 5.5 Phase sensor installation details

Phase sensor installed on the electricmotor fan OD

Phase sensorassembly detail

The field instrumentation was connected to intelligent transmitters by shieldedcables. The transmitters were connected to a dedicated microcomputer in the controlroom. Because this microcomputer is connected to the PETROBRAS computernetwork, dynamic data from the compressor are available throughout most of thePETROBRAS organization.

Intelligent transmitters controlling the software can be programmed to send dataperiodically either by email or FTP(?) if additional security is necessary.

6. Achieved Results

6.1. Diesel Hydrotreating Units at REGAP

Brazil currently has two main specs for diesel fuel. Diesel B, or "inland" diesel with.35 percent sulfur and diesel D or "metropolitan" with 0.20 percent sulfur for majorurban centers. REGAP (Refinaria Gabriel Passos) produces diesel for the MinasGerais State in order to comply with both specs.

In order to comply with market specs, REGAP has two hydrotreating units: Unit-108and U-110. U-110 operates at pressures around 50 kgf/cm, and up to 57kgf/cm. U-108 operates at lower pressures around 45 kgf/cm.

One of the main quality items required by diesel specs (besides sulfur content) is theASTM color specification which is directly related to product stability. The mainchemical characteristic linked to color is the diesel nitrogen and aromatics content.


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Picture 6.2 - P-V Diagram, second stage

After compressor shutdown and valve inspection, it was evident that the diagnosiswas correct. Figure 6.3 shows details of the second stage suction valves. Themarking of the unloader fingers is very clear as well as the shadowed area due togas passage.

Figure 6.3 - Second Stage Suction Valve Details

The maintenance intervention was restricted to suction valve replacement andcorrecting the unloader finger setting. The compressor was tested after theintervention and operated at discharge pressure above 60Kg/cm2Figure 6.4 showsthe P-V diagram during the test.


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Figure 6.4 - P-V Diagram after correction

The actual curves are very close to the ideal cycle. Since this intervention, Dresser-Rand has analyzed the compressor weekly to alert PETROBRAS of anyperformance degradation.

6.3. Achieved Results

As previously discussed, process improvements come from discharge pressuremaximization. Higher discharge pressures allow treating low value streams, whichcan be incorporated, to the diesel stream after treatment.

Operating U-110 at higher pressures increases nitrogen removal and allows theincorporation of hard-to-treat streams into the diesel stream increasing dieselproduction and reducing production of low- added -value products.

U-110 was typically operated at 49 kgf/cm2 at reactor inlet and the high-pressureseparator was controlled at 42kg/cm2. Plant design allows reactor inlet pressures upto 57 kgf/cm, thus the pressure can be raised to 57 kgf/cm at reactor inlet and up to52 kgf/cm at the high-pressure separator. The pressure can be raised 7 to 8kgf/cm.

Raising the pressure improves catalyst activity, sulfur and nitrogen removal, andsaturation of aromatic rings improves at high hydrogen partial pressures. Becausethe product color is related to the reduction of nitrogen and aromatics, operating athigher pressures improves diesel quality. [7].

The refinery expects to process an additional 100 m/d of coker gas oil, which is hardto incorporate to the diesel stream due to the high sulfur, nitrogen and aromaticscontent. With this additional processing, the sale of low value gas oil will decreaseand the sale of high- value diesel will increase.


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For each m/d of coker gas oil incorporated into the diesel stream, there will be anestimated additional margin of US$20.00 when producing diesel B. This representsan estimated addition of US$720,000.00/year from diesel B production.

7. Acknowledgements

The authors are thankful for the support received from PETROBRAS, Dresser-Randand Windrock Inc. Within these organizations the following people deserve to bementioned: Fbio Dutra (PETROBRAS-REGAP); Manoel Simes (PETROBRAS-Tecnologia de Equipamentos Dinmicos); Rogrio Campos (PETROBRAS -Tecnologia de Equipamentos Dinmicos); David Scheef (Dresser-Rand); Rod Gunn(Dresser-Rand); Dalmo Barros (Dresser-Rand); Ed Flanagan (Windrock Inc.) eWarren Liable (Windrock Inc.)

BIBLIOGRAFY

[1] Griffith, W. A., Flanagan, E. B., ONLINE, CONTINOUS MONITORING OFMECHANICAL CONDITION AND PEORFORMANCE FOR CRITICALRECIPROCATING COMPRESSORS, Proceedings of the 30t TurbomachinerySymposium, Texas A&M University, Houston, TX, 2001

[2] Rodrigues, P. S. B., COMPRESSORES INDUSTRIAIS, Editora Didtica eCientfica : PETROBRAS, Rio de Janeiro, RJ, 1991

[3] GPSA, ENGINEERING DATA BOOK VOLUME 1, Gas Processors SuppliersAssociation, Tulsa, OK, 1998

[4] Leonard, S. M., INCREASING THE RELIABILITY OF RECIPROCATINGCOMPRESSORS ON HYDROGEN SERVICES, National Petroleum Refiners

Association Maintenance Conference, New Orleans, LA, 1997[5] Schultheis, S. M., Howard, B. F., ROD DROP MONITORING, DOES IT

REALLY WORK?, Proceedings of the 29thTurbomachinery Symposium, TexasA&M University, Houston, TX, 2000

[6] API Standard 618, RECIPROCATING COMPRESSORS FOR PETROLEUM,CHEMICAL, AND GAS INDUSTRY SERVICES, 4th Edition, AmericanPetroleum Institute, Washington, DC, 1995

[7] Topsoe, H., Cluasen, B.S., Massoth, F.E., HIDROTREATING CATALYSYS,Science and Technology, Springer 1996.

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Online Monitoring of Recip Compressors, 2004