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Changes in ambient temperature have an impact on fullload power and heat rate of a gas turbine, but also on part-load performance and optimum power turbine speed. Manufacturers typically provide performance maps that describe these relationships for ISO conditions.
 
The excerpts are taken from a paper “Gas turbine performance” presented by Rainer Kurz of Solar Turbines and Klaus Brun of Southwest Research Institute at the 2015 Middle East Turbomachinery Symposium.
 
The performance curves are the result of the interaction between the various rotating components and the control system. This is particularly true for DLN engines. If the ambient temperature changes, the engine is subject to the following effects:
 
The air density changes. Increased ambient temperature lowers the density of the inlet air, thus reducing the mass flow through the turbine, and therefore reduces the power output (which is proportional to the mass flow) even further. At constant speed, where the volume flow remains approximately constant, the mass flow will increase with decreasing temperature and will decrease with increasing temperature.
 
The pressure ratio of the compressor at constant speed gets smaller with increasing temperature. This can be determined from a Mollier diagram, showing that the higher the inlet temperature is, the more work (or head)is required to achieve a certain pressure rise. The increased work has to be provided by the gas generator turbine, and is thus lost for the power turbine, as can be seen in the enthalpy-entropy diagram. At the same time NGgcorr (ie the machine Mach number) at constant speed is reduced at higher ambient temperature. As explained previously, the inlet Mach number of the engine compressor will increase for a given speed, if the ambient temperature is reduced. The gas generator Mach number will increase for reduced firing temperature at constant gas generator speed.
 
The Enthalpy-Entropy Diagram describes the Brayton cycle for a two-shaft gas turbine. Because the head produced by the compressor is proportional to the speed squared, it will not change if the speed remains the same. However, the pressure ratio produced, and thus the discharge pressure, will be lower than before. Looking at the combustion process, with a higher compressor discharge temperature and considering that the firing temperature is limited, we see that less heat input is possible, ie., less fuel will be consumed .The expansion process has less pressure ratio available or a larger part of the available expansion work is being used up in the gas generator turbine, leaving less work available for the power turbine.
 
On two-shaft engines, a reduction in gas generator speed occurs at high ambient temperatures. This is due to the fact that the equilibrium condition between the power requirement of the compressor (which increases at high ambient temperatures if the pressure ratio must be maintained) and the power production by the gas generator turbine (which is not directly influenced by the ambient temperature as long as compressor discharge pressure and firing temperature remain) will be satisfied at a lower speed. The lower speed often leads to a reduction of turbine efficiency: The inlet volumetric flow into the gas generator turbine is determined by the first stage turbine nozzle, and the Q3/NGG ratio (i.e., the operating point of the gas generator turbine) therefore moves away from the optimum.
 
Variable compressor guide vanes allow keeping the gas generator speed constant at higher ambient temperatures, thus avoiding efficiency penalties. In a single-shaft, constant speed gas turbine one would see a constant head (because the head stays roughly constant for a constant compressor speed), and thus a reduced pressure ratio. Because the flow capacity of the turbine section determines the pressure-flow-firing temperature relationship, equilibrium will be found at a lower flow, and a lower pressure ratio, thus a reduced power output.
 
The compressor discharge temperature at constant speed increases with increasing temperature. Thus, the amount of heat that can be added to the gas at a given maximum firing temperature is reduced.
 
The relevant Reynolds number changes: At full load, single-shaft engines will run a temperature topping at all ambient temperatures, while two-shaft engines will run either at temperature topping (at ambient temperatures higher than the match temperature) or at speed topping (at ambient temperatures lower than the match temperature). At speed topping, the engine will not reach its full firing temperature, while at temperature topping, the engine will not reach its maximum speed. The net effect of higher ambient temperatures is an increase in heat rate and a reduction in power. The impact of ambient temperature is usually less pronounced for the heat rate than for the power output, because changes in the ambient temperature impact less the component efficiencies than the overall cycle output.

Source : www.turbomachinerymag.com
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JAKARTA – PT Pertamina Internasional Eksploration & Production, the upstream subsidiary of PT Pertamina (Persero), which manages oil and gas assets overseas, successfully undertake the tender offer for Maurel & Prom stocks at the first phase.

The results of the tender offer  has been announced by Autorité des Marchés financiers (AMF) of France on January 25th, 2017 local time. Starting from February 1st, 2017, PIEP will control as many as 125.924.574 stocks and the voting rights of Maurel & Prom, which is equivalent to 64.46% of the stocks and 63.35% of the voting rights of Maurel & Prom.

In addition, PIEP also controls many as 6,845,626 ORNANE (Obligation remboursable en numéraire et en actions nouvelles et existantes / Obligations Remboursable for cash and shares) of 2019, equivalent to 46.70% of the outstanding ORNANE of 2019 . PIEP will also hold  3.848.620 ORNANE of 2021, which is equivalent to 36, 88% of the outstanding ORNANE of 2021.

Payments to the owners of ORNANE will be conducted on transaction completion and at once handing over the ORNANE to companies with a value of 17.28 euros per ORNANE of 2019 (i.e. the nominal value plus interest by 0.03 euros), and 11.05 euro per ORNANE of 2021 (i.e. nominal value plus interest by 0.03 euro).

In accordance with article 232-4 from AMF General Regulations, the tender offer will be automatically re-open for 10 working days period. The tender offer schedule will be published soon by AMF.

President Director of Pertamina Dwi Soetjipto says the success of the first phase of tender offer is a good momentum for Pertamina to be more aggressively expand abroad amid the improving global crude oil prices. According to him, after Pertamina become the controlling stockholder (minimum of 51% stockholding), it can further consolidate the Maurel and Prom’s production to PIEP’s production.

“It certainly will improve the performance of Pertamina’s upstream. In addition, ISC is currently also reviewing and preparing  the possibility to make oil production which not only increase Pertamina’s production value, but also strengthen the supply to Indonesia, “said Dwi.

Director of Upstream of Pertamina Syamsu Alam added that the prospect of Maurel and Prom oil and gas assets is very potential to be developed by Pertamina through PIEP, where at the end of 2015 the oil and gas reserves listed has reached 205 million barrels of oil equivalent. With assets spread across Europe, America, Africa and Asia, it can become prove the company’s capabilities in the upstream business on a global scale. “Pertamina is more optimistic to be able to develop its upstream business faster,” said Syamsu Alam.

Meanwhile, Vice President Corporate Communication of Pertamina Wianda Pusponegoro says, “With the success of the first phase of this tender offer, we hope and optimistic that the next stage of the tender offer will run properly and the results will be optimum for PIEP and Pertamina.”

Source From : pertamina.com
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In a fully enclosed gas turbine installation, the enclosure sides and roof include panels and access doors supported on a heavy-duty frame. The side and roof panels are easily removed individually for complete access to the major components for inspection and maintenance and for component removal by forklift and overhead crane. The panels are treated with fiberglass material for noise attenuation and thermal insulation, and weather stripping is installed between all panels for sealing and sound attenuation.
This article contains excerpts from the paper, “Gas turbine packaging options and features” presented at the Second Middle East Turbomachinery Symposium by Klaus Brun of SouthWest Research Institute, Rainer Kurz of Solar Turbines and Marybeth G Nored of Apache, Inc.
Fully enclosed gas turbine installation

The enclosure is constructed to support adequate roof load (usually 50 lb/sqft) and to withstand a wind load of 120 mph (or more, if specified). The following standard features are usually included in a basic enclosure:
  • Inlet and exhaust ventilation silencers: The enclosure ventilation openings are equipped with vent silencers with weather louvers.
  • Single fan ventilation system: Enclosure ventilation is provided by a single motor-driven fan. This motor is typically 3-phase AC, high efficiency, with Class F insulation. The fan is sized to provide the airflow required to ensure that the internal air temperature arounGasd the enclosed equipment remains within acceptable limits. Sometimes, for additional ventilation or certification requirements, a dual fan ventilation system may be required.
  • Pressurization system: The enclosure is positive pressurized to prevent the ingress of external hazardous atmospheres through the enclosure seams. A differential pressure transmitter is provided for enclosure low pressure alarm and shutdown.
  • AC lighting: 110-VAC or 220-VAC lights are provided to illuminate the enclosure interior, with on/off switches located at the interface panel.
  • Trolleys: Internal movable trolley rails located over the turbine for turbine maintenance and removal are included.
  • Door Hardware: All enclosure doors are equipped with a heavy duty stainless steel door locking mechanism, including handles, hinges, latching mechanism, internal lock override release, restraining device, and attaching hardware. The enclosure doors are equipped with door position switches to initiate an alarm whenever any of the enclosure doors are not securely closed.
Computational Fluid Dynamic (CFD) tools are used in both on- and off-shore applications to validate design criteria. Previously, this data was only occasionally requested for offshore applications. Now, however, it is becoming more of a requirement. We will focus on the application of this tool for the acoustic enclosures. The CFD tool is used to apply the surface temperature to the turbine, understand the temperature distribution within the enclosure, and determine the required flow distribution and proper size of the ventilation fans and motors. Understanding the flow distribution within the enclosure allows the optimization of the package design to minimize stagnant volumes where gas, if present, could be trapped, as well as position package components away from identified hot areas so the component temperature limits are not exceeded.
The test rig is used to match the analysis with actual test data to validate the accuracy of the CFD tool. The colored streamlines represent airflow velocity throughout the enclosure with dark blue representing the lowest velocity flow and the light blue, green, and yellow representing progressively higher velocities. This CFD model represents a full size package with all of the major components. The dashed lines represent the flow direction. Again, the dark blue color being the lower velocity air; while green, yellow, and red represent increasing velocities.
Beyond the above described features, manufacturers often provide the following options for the enclosure:
Sound Attenuation
The sound-attenuated enclosure is intended for use with suitable turbine air inlet and exhaust silencing systems in environments where low noise levels are a requirement. Ventilation openings are equipped with suitable silencers to achieve maximum sound attenuation. Sound levels at a specific site will depend on existing walls, barriers, equipment in close proximity, multiple units, and other installation considerations.
Enclosure Barrier Filter
The enclosure ventilation inlet is equipped with a singlestage, disposable, barrier-type filter unit equipped with a deltaP alarm switch. The ventilation exhaust opening is equipped with back-draft dampers to prevent ingress of dust when the unit is not running.
Fire and Gas Detection and Monitoring System
Usually, an automatic, electronically controlled fire and combustible gas detection and monitoring system is installed in the enclosure. A typical system description is provided below: The primary fire detection system uses multi-spectrum infrared (MIR) detectors. The system includes an automatic optical integrity feature to provide a continuous check of the optical surfaces, detector sensitivity and electronic circuitry of the detector-controller system, and automatic fault identification with digital display of system status in numerical code.
The secondary fire detection system consists of rate compensated thermal detectors. The two detection methods act independently in detecting and reporting a fire. The fire and gas system control panel provides system supervision (for open circuit, ground fault, or loss of integrity), initiates alarm, release of fire suppression agent, and visual display of system status. The suppression system agent release is activated automatically with release solenoids located on the fire suppression skid. The suppression system can also be activated by an electrical push button on the turbine enclosure or manually at the suppression skid. If a fire is detected, the detectors transmit an electrical signal to the fire and gas system control panel to activate the fire alarm and suppression system. The enclosure is equipped with two gas detectors: one at the turbine enclosure ventilation air inlet and one at the ventilation exhaust to provide continuous monitoring for combustible gases at the enclosure ventilation inlet and outlet.
The detectors are diffusion-based, point-type infrared devices that provide continuous monitoring of combustible hydrocarbon gas concentrations. The turbine start signal is interlocked with the fire and gas monitoring system to ensure the atmosphere is safe prior to initiating turbine engine start.
Most commonly, the enclosure is equipped with a CO2 fire suppression system consisting of a primary total flooding distribution system and a secondary metered distribution system. In the United States, the system is designed in accordance with the U.S. National Fire Protection Association Code 12. On detection of fire, the detectors transmit an electrical signal via the fire control panel to activate the fire suppression system release solenoids located on the fire suppression skid. On receipt of this signal, the solenoid actuated control heads activate the discharge valves on the primary and extended extinguishing cylinders, releasing the extinguishing agent into the enclosure.
CO2 pressure actuates the pressure trip operated dampers that close all vent openings. CO2 release control heads are also provided with manual release levers.
Additionally, a weatherproof fire suppressant cylinder cabinet is sized to house the CO2 extinguishant cylinders and is equipped with doors for servicing. The manual pull levers are routed, by cable, to break glass pull stations on the exterior wall of the cabinet. CO2 cylinders are mounted on a weight scale with a preset alarm.
Another frequently used fire suppression system uses water mist.
Equipment Handling System
An equipment handling system is provided, consisting of external trolley beams and movable chain-fall hoists for removal of major equipment from the package. A trolley beam extension allows turbine removal through the side of the enclosure. One end of the beam extension attaches to the inside trolley rails; the other end is a floor-standing A-frame. The gas turbine or other heavy equipment is then removed through the enclosure side and placed on a truck bed or cart.

Source from : turbomachinerymag.com
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Gas turbine corrosion is a common phenomenon experienced by operators. It can be traced to contaminants through the air inlet system, water systems (from evaporative cooler carryover, compressor wash solutions, NOx control injection water, and dual fuel injector purging), and fuel (gaseous and liquid).
 
Below are excerpts from a paper “Gas turbine durability in harsher environments” by Zaher Mutasim of Solar Turbines Incorporated at the first Middle East Turbomachinery Symposium held in Qatar.
 
Ingested contaminants can result in corrosion to the compressor, combustion, and turbine sections of gas turbine engines if proper product design and mitigation solutions are not applied. In most applications, corrosion of compressor components is unlikely during engine operation because the compressor is dry. However, during shutdowns where cold surfaces condense water, chemical species such as hydrochloric acid and sulfur trioxide can be absorbed in the water producing an acidic, corrosive liquid. This liquid phase can result in aqueous corrosion of compressor components through a variety of mechanisms, e.g., generalized, pitting, and crevice corrosion, and stress corrosion cracking. In cases where hydrochloric acid and sulfur trioxide are present and the relative humidity is high, the high velocity of the air at the compressor inlet causes the temperature of the air to drop due to conversion of internal energy to kinetic energy. The temperature drop can result in the formation of a liquid phase in the forward stages of the compressor during operation.
    
Liquid Fuel Flow Divider Aqueous Corrosion
Corrosion in some instances has resulted in the binding of variable stator vanes and subsequent high cycle fatigue failure of compressor airfoils. Combustion Section Two main types of corrosion are known to affect components within the combustion section. Aqueous / acidic corrosion of fuel delivery system components such as fuel manifolds and fuel flow dividers, and fuel injector braze joints can occur in much the same way as the aqueous corrosion of compressor components, except that the contaminants can also be fuel borne. Corrosion to these components can result in fuel leaks and fires, and malfunction of fuel injectors.
Fuel Injector Tip Sulfidation
Sulfidation, which is the reaction between a metal and a sulfur/oxygen-containing atmosphere to form sulfides and/or oxides, can affect fuel injector tips. In essence, sulfidation attack is a form of accelerated oxidation resulting in rapid degradation of the substrate material due to loss of corrosion protection. Whereas during oxidation protective oxide scales can form, the metallic sulfides formed are not protective. This accounts for the rapid rate of degradation produced by sulfidation attack.
Type I Hot Corrosion Attack to Turbine Blade
Airfoils and Tips
Turbine section hot corrosion is the most serious form of corrosion experienced by the turbine section components. To better understand hot corrosion, it is useful to first discuss oxidation. Oxidation is the chemical reaction at high temperatures between a component and the oxygen in its surrounding gaseous environment. Oxidation of turbine section components is relatively easy to predict and measures can be taken to control it since it primarily involves relatively simple metal/oxygen reactions. The oxidation rate increases with temperature. Metal loss due to oxidation can be reduced by the formation of protective oxide scales. Chromium, aluminum, and silicon are the only chemical elements known to form protective oxide scales at the temperatures encountered in gas turbine engine hot sections. The presence of these elements in turbine engine alloys and coatings results in improved oxidation resistance.
Type II Hot Corrosion Attack to Turbine Blade Shank
Hot corrosion is a form of accelerated oxidation that is produced by the chemical reaction between a component and molten salts deposited on its surface. Hot corrosion comprises a complex series of chemical reactions, making corrosion rates very difficult to predict. Sodium sulfate is usually the primary component of the deposit and degradation becomes more severe with increasing concentration levels of contaminants such as sodium, potassium, vanadium, sulfur, chlorine, fluorine, and lead. The rate and mechanism of hot corrosion attack is influenced by temperature.
There are two types of hot corrosion. Type I or high temperature hot corrosion, occurs at a temperature range of 730 to 950°C. Type II or low temperature hot corrosion occurs at a temperature range of 550 to 730°C. These types of hot corrosion attack feature distinct mechanisms and exhibit unique features. Both types can occur in the turbine section. Because of the varying service temperatures experienced by turbine section components, both corrosion types can occur on the same component. For example, Type I hot corrosion may occur on first and second stage turbine blade airfoils and tips, whereas Type II hot corrosion may occur under the platform of first and second stage turbine blades.
To achieve higher power density, gas turbines must run at higher firing temperatures. This can be achieved with advanced alloys that can withstand the higher operating temperatures. To achieve the alloy’s desired high temperature mechanical properties, alloy compositions must be altered. For example, refractory elements are added to alloys to increase their mechanical strength, but at the expense of other elements such as chromium, which is essential for hot corrosion resistance.







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