33i experiences in upgarding of pgt5 gas turbine pdvsa gas · Experiences in Upgrading of PGT5 Gas Turbines by Carlos Blanca, José Martínez, Luís Vera, ... The PGT 5 gas turbine

Gas Production and Handling Advances

XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29 th, 2008 Page 1

Experiences in Upgrading of

PGT5 Gas Turbines

PDVSA Gas, S.A. - Venezuela

Authors: José G. Martínez – Maintenance Suptte. Carlos D. Blanca – Turbomachinery Suptte. Luis Vera. Turbomachinery Major Technician. Jorge L. González – Maintenance Supv. JANUARY 2008



Experiences in Upgrading of PGT5 Gas Turbines

by Carlos Blanca, José Martínez, Luís Vera, Jorge González

ABSTRACT

Santa Barbara Extraction Plant is located in the Monagas state –Republica

Bolivariana de Venezuela- and it is part of four (04) extraction plants of Natural Gas

Liquid (NGL) which belong to East Criogenic Complex of PDVSA GAS. This Plants

has two (02) trains of processing gas, each train has a system of mechanical

refrigeration with propane and it has centrifugal compressors. Those compressors are

driven by gas turbines, PGT5 model. The Refrigeration system guarantee suitable

temperature to obtain NGL, then it is a very important system.

During 2004 a second cycle of major maintenance (80.000Hrs), for PGT5 gas turbine

was reached and it was a opportunity to improve the mechanical performance in

these gas turbines. This work consisted of upgrading of low pressure rotor and

internal components parts of the system of compression and expansion with the

purpose of increasing power, since 6800 HP to 7300 HP. Additionally, we could

standardize spares part stock in Santa bárbara Extraction Santa Barbara and Jose

Fractionation and shipping Plant, which already had a gas turbine of 7300Hp. Also it

had a project to upgrade two (02) units of 6400 HP and one of 6800 HP to 7300 HP.

The upgrading could guarantee better conditions of operation in the refrigeration

system and more mechanical benefits.

The upgrading consisted in to change some internal components and adjust few

parameters of the system of control gas turbine, with the purpose of increase the

power.



This work will expose aspects in orden to explain the modifications made, as well the

experiences and the present gas turbine conditions.

INTRODUCTION

The upgrading of equipment is not a new idea; it is used in the oil industry since many

years ago; in order to increase the levels of production, to increase reliablity or simply

to improve the conditions of operation, also for obsolesence of spare part. Gas

turbine technology is always improving, with the purpose of increasing the efficiency

of the turbines. Actually this efficiency does not reach 40%, for a simple cycle. In that

way, the manufacturers offer packages of upgrading, which consist of the

replacement of improved internal pieces, with the purpose of obtaining greater

benefits either in the unit and the process. The client is who will decide by an

technical-economic evaluation if it is recommendable to maintain the unit in original

characteristics or to accept the offer.

The Santa Barbara extraction plant was officially inaugurated in 1995 and the gas

turbine model selected -for its refrigeration system- it was the PGT5 gas turbine. This

model of turbine had been used in Jose Fractionation and shipping Plant, which was

inaugurated in 1985. The PGT 5 gas turbine was a improvement made to MS1002

gas turbine of 6400 HP - in Jose there are three (03) MS1002. After that a PGT5 had

other modification and now it can develop a power of 7300 Hp. This turbine is called

PGT5A.

MAINTENANCE PLAN REVIEW

When PDVSA overcome the strike in 2002, a review of gas turbine maintenance´s

plans and strategies was possible in the East Cryogenic Complex . The results were

not encouraging because of a lot of maintenance pending for next years and few

thechnicians in that area to supervise this work. Additionally, It was necessary to

continue with a revamping of control sytems which had been starting years ago.

However, the greater challenge was a situación with a gas turbine in refrigeration



systems. Those turbines had 80.000 hrs working and its manufacture recommended

major maintenance rotors, replacement of axial compressor blades and other internal

parts. This work had to be made in Italy and it was important a good strategy to have

that rotors on time for each maintenances.

The East Cryogenic complex had two (02) set of rotors (2 rotors of low pressure and

2 rotors of high pressure), but they were not interchangeable due to differences in

models in each Plant.

Figure N° 1. Equipments summary in Jose and Santa Brabra Plants

Figure N° 1 shows the turbines by models in each plant mentioned and control

systems which were updated to Mark V and those that had SUVIMAC. It required

replacement of four (04) systems of control (3 in Santa Barbara and 1 in Jose) and to

do five (05) major maintenances (4 in Santa Barbara and 1 in Jose), during a

estimted of 3 years approximately.

Five (05) Gas Turbines Tres (03) to 6400 BHP ISO One (01) to 6800 BHP ISO One (01) to 7300 BHP ISO

Control Sytems 4 Mark V 1 Suvimac

Four (04) Gas Turbines 6400 BHP ISO

Control Sytems 1 Mark V 4 Suvimac



The disposition of one (01) of rotors of 6400 HP and one (01) set of rotors of 6800 HP

did not offer any advantage to make the logistics of maintenance in Italy, due to time

since the rotor is sent, repaired and received again, to be installed. This situation was

consulted to the manufacturer and it offered two alternatives:

1) Buy other set of rotors to 6800 HP.

2) Upgrading :

a. Upgrading to 6800 HP.

b. Upgrading to 7300 HP.

PROPOSALS ANALYSIS.

In order to make an analysis of the manufacturer´s proposals, the following aspects

were considerated: storage of spare parts, stock spares, costs, technical aspects.

1) Buy other set of rotors to 6800 HP.

This option represented a simple option, which consisted of buying an additional set

of rotors for Santa Barbara Extraccion Plant with the purpose of having one set

available in each maintenance. It would be made the logistic of transport and repair in

such way that it was always a set of rotor in Italy, and another in Venezuela to be

installated. However differences of spare parts between the units it was keeping,

therefore it would not be possible to use that set in another gas turbines models.

Aditionally a third set of rotors requested of a space to be stored and they had the

same costs by repair of rotors with same power.

2) Upgrading Rotor.

a) Upgrading to 6800 HP.

This option was quite feasible. It does not buy a new set of rotor, old sets are used;



one is repaired and one is upgrading to 6800 HP. But there was the condition of one

gas turbine in Jose with a power of 7300 HP, and it would be keeping in that power.

In consequence the difference in the spare parts would not be eliminated. Additionally

the costs associated to the maintenance of the rotors were greater than the costs to

upgrade to 7300 HP, because of offer supplied by the manufacturer; it will be

exposed in next part of this paper.

b) Upgrading to 7300 HP.

A quite tentative offer was supplied by the manufacturer of the gas turbines, in orden

to upgrade to 7300 HP all units. According to the information provided by the

manufacturer, this offer was motivated they will not manufactured MS 1200 (6400

Hp) and PGT5 (6800 Hp) anymore -only PGT5A (7300 Hp)- they guaranteed the

spare parts but the manufacture costs would be elevated and long time of response in

case of fail.

The offer o package consisted of:

1) Engineering Documentation.

2) Compressors blades.

3) A new antisurge válve and pipelines.

4) Internal Parts (Shourd, nozzles, buckets and bearings).

Costs associated to this package were compared with the prices of spare parts offer

for a Major Maintanance; keeping same power and knowing that five (05) sets of

rotors it would have to be repaired.



Table N° 1. Repair and upgarding rotors sumamry.

Table N°1 presents the costs associated with a can be observed the associated to

maintenance of the rotors without upgrade, the cost was of 2,38 MMBsF and the

upgrading offer (spare parts and services were Incluided) was1,85 MMBsF.

Therefore the offer upgarding represented a saving of 0.54 MMBSF by unit and a

saving total of 2,69 MMBsF. Other advantages to make the upgrade to 7300 HP are:

the possibility of use of spare parts in both plants and the availability of additional

power for the system of refrigeration in the Santa Barbara Extraction plant. In that

sytem the gas turbine always presented control for temperature, since 10:00 a.m. to

4:30 p.m. approximately, it is means that exhaust temperature is up 1050 °F, and

sometimes this casused a trip.



Due to the conditions above mentioned and lack of supervisors, it was approved by

respective instances, the upgrading of gas turbines to 7300 HP. That the process

took approximately 20 months, from the beginning of the process until signature of

the contract. This due to different situations such as: Review of the engineering

specifications, estaimation of cost, economical analysis, approval of PDVSA Gas

Directors, expires of documents of the manufacturer in the National System

Contractors.

ACTIVITIES SCHEDULE.

Activities of Maintenance began in the second quarter of 2005, as soon as the

manufacturer gave the sets of rotors, upgrading to 7300 Hp, and all necessary spare

parts for the Major Maintenance of 80,000 Hrs.

Figure N° 2. Activities schedule.

The figure N° 2, shows the execution of the activities from the phase of engineering to

the implantation of the project, at the present moments the project is going on; in



order to upgrade all the PGT5 gas turbine units in Jose.

ACTIVITIES EXECUTED IN MAINTENANCE.

From the beginning of the maintenances, five (05) Major Maintenances of 80,000

hours were executed and six (06) set of rotors were upgraded. Those activities were

contained in a Contract called “ Gas Turbine Major Maintanance and upgrading, East

Criogenic complex”. The activities incluided in that contract and costs are show in

next figure.

Figure N° 3. Activities included in the Gas Turbine major Maintenance and Upgrading,

East criogenic Complex.

In the first quarter of 2008 a second contract for 18 MMBsF is going to be signed, it is

important highlight that one disadvantage was the export and import of rotors, which

were not on time with a previuos schedule time.



In order to increase the power, the next specific activities were executed:

1) Replacement of the axial compressor antisurge valve

An old antisurge valve was replaced for a fast action one and greater capacity to vent

air. In the following figures, the differences are showed:

Figure N°4. Old antisurge Valve Figure N° 5. New Antisurge Valve

2) Replacement of internal

parts.

Figure N° 6. Internal Part upgrading.



Figure N° 6 shows internal parts replaced to increase the power to 7300 hp and they

were: 0 to 5th blades stages in the housing of the axial compressor, variable nozzle

or 2nd nozzle stage and rotors buckets.

3) Changes in the control curves.

Due to air flow increases, the curves of heating and acceleration change. Parameters

in control system are modified to fit them; some conditions that can be mentioned are:

Increase of gas combustible pressure, variation in constants of control of curves

heating and acceleration, however, control exhaust temperature is keeping. But, in

next part it will show that it is not a problem.

TEST AND RESULTS.

In order to demonstrate the benefits obtained with the upgarding a "Perfomance test”

is neccesary. This test takes some parameters of gas turbine and compressor

process, after they are sending to the manufaturer and through computation software

it can determinate the performance of the machine. But, due to lack of a flow meter in

the gas combustible pipeline, it was not possible to do a test. That value is quit

importance for do the calculations. However, some tests were made and through

observations of process parameters before and after. Therefore it was possible

determined qualitatively benefits in the refrigeration system.

1) Test N° 1. Gas turbine 7300 hp (PGT5A) hp working and Gas turbine 6800 hp

PGT5 stopped.

The operational parameters observed are better. The system has better pressure in

first stage suction, because of that; it can handle greater flow through the centrifugal

compressor. The presión can arrive to 20 PSI, in the other hand with a PGT5 gas

turbine the pressure was around the 28 PSI, being the normal pressure 14, 5 PSI.

That value represents an improvement of 55 %.



2) Test N° 2. Both units working at the same time. ( PGT5 and PGT5A).

This test was made in two parts:

a) Both gas turbines at the same Speeds.

In this condition the centrifugal compressors associated to the PGT5A can handle

greater flow than the compressor associated to the PGT5. Also, some time the

procces antisurge valve is open. Annex N°1 shows that conditions.

b) Both gas turbines at different Speeds.

This condition is the normal operation - when the system has one PGT5 gas turbine

and one PTG5A. With a review of parameters data since the first upgrading, it was

determinated that the gas turbine has never been in temperature control. Even when

the filter house was with a high pressure differential, because of the exhaust

temperature exaust were lower than ever before.

CONCLUSIONS AND RECOMMENDATIONS.

The tests made and the results give some benefits, obtained through the upgrading;

in conclusion a PGT5A Gas turbine improves the conditions in the refrigeration

system. The benefits are:

• Better succion pressure with a unit is stopped, around 55%.

• More flexibility

• Better conditions of exhaust temperatures.

• Now it possible to have only one spare part stock.

It is important mentioned that the time in exporting and importing rotors was longer

than scheduled, for that reason it was recommended, in meeting of high directors of

the manufacturing company, to develop an infrastructure in Venezuela, to make the

maintenance of rotors here. Additionally with the new vision of the company in the



social matter, socila project were maden and this also was exposed in that meeting.

It is recommended to install the necessary instrumentation in order to make a

"Perfomance Test". Then, it will be possible quantified how much power was gained.

Finally, it is recommended to continue with the upgrading and to make the same tests

in Jose.



ANEXOS



Annex N° 1. Operacional Parameters



Annex N° 2. Pictures

Tubine Area Accesory compartment Centrifugal compressor Combustión Chamber Axial Compressor Housing Axial Compressor

Documents

33i experiences in upgarding of pgt5 gas turbine pdvsa gas · Experiences in Upgrading of PGT5 Gas Turbines by Carlos Blanca, José Martínez, Luís Vera, ... The PGT 5 gas turbine