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:
Jos G. Martnez Maintenance Suptte.
Carlos D. Blanca Turbomachinery Suptte.
Luis Vera. Turbomachinery Major Technician.
Jorge L. Gonzlez Maintenance Supv.
JANUARY 2008
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 2
Experiences in Upgrading of PGT5 Gas Turbines
by Carlos Blanca, Jos Martnez, Lus Vera, Jorge Gonzlez
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 brbara 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.
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 3
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 maintenances
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 situacin with a gas turbine in refrigeration
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 4
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 N1. 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
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 5
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 manufacturers 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;
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 6
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 vlve 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.
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 7
Table N1. Repair and upgarding rotors sumamry.
Table N1 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.
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 8
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 N2. Activities schedule.
The figure N2, 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
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 9
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 N3. 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.
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 10
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 N4. Old antisurge Valve Figure N5. New Antisurge Valve
2) Replacement of internal
parts.
Figure N6. Internal Part upgrading.
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 11
Figure N6 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 presin 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 %.
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 12
2) Test N2. 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 N1 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
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 13
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.
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 14
ANEXOS
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 15
Annex N 1. Operacional Parameters
Gas Production and Handling Advances
XVIII Gas Convention, AVPG, Caracas, Venezuela, May 27 - 29
th
, 2008 Page 16
Annex N 2. Pictures
Tubine Area Accesory compartment
Centrifugal compressor Combustin Chamber
Axial Compressor Housing Axial Compressor
