Table of Contents
1.1 The choice of a gas turbine
The purchase of a car is pending. Now the question arises, what should it be? A spartan new car or a used luxury model? Demand the scheduled tasks a sports car, an off-road vehicle or a tractor? Do we feel ourselfs bound to a special brand? Should we benefit from a bargain, even when it does not fit exactly to the required profile? Should we buy an attraktive product due to it’s technical data, even when the label does not apply as reliable? Are the additional costs worth, which are justified with new technologies like nonmetallic brake discs or a distance warning system? Isn’t here rather to count with novel problems or malfunctions? At all, doesn’t the whole electronic monitoring lead to breakdowns and uncertainity? Are the extra equipments which are avised to me worth it’s money? And, by the way, what about the repair shop and the maintenance costs? How about the spare parts, its costs and availability? And, if I and my car have to separate, what about the resale? Depending from how we decide, the coming years together with our car will be pleasant, stressful or even frustrating. Naturally even with a consultation of neutral specialists, the analysis of tests and the breakdown statistic, a remaining risk will stay.
Very similar questions can be asked during the selection of a gas turbine. So we will utilise all sources to minimise our risk, respectively to get an advantage as high as possible.
Should we have several types of gas turbines from one or more manufacturers at our disposal? The question arises as to the proper technical choice. Apart from one’s own requirements, it is valid to consider or evaluate a number of sources and informations, some of which will be mentioned below:
- The expected operator -specific operation conditions ( "Ill. 1.1-4") , e.g. start/shut off cycles, power output, quick starts, necessary availability, standstill periods.
- Information regarding reference addresses and operators of special types of gas turbines.
- Visits to maintenance and overhaul shops that have offers of service.
- Technical discussion with the customer service department of the manufacturer.
- Assessment and evaluation of technical papers, e.g., maintenance regulations, operation instructions , overhaul handbook, technical literature, technical drawings, production data.
- Location survey in order to detect potential problems: air contamination, potential dust load, recirculation risk, danger of icing ( "Ill. 1.1-2").
- Existing foundations and support structures: bearing capacity, vibrations , elasticity, etc.
- Special utility demands of the operator such as pollutant disposal , e.g., solvents,
- Special environmental demands that necessitate e.g., water or steam injections, low - NOX - combustors or exhaust gas noise suppressor. ( "Ill. 1.1-2").
The future operator should, perhaps, consult an expert, when, prior to the procurement, operation specific questions are to be cleared, e.g., with the manufacturer or the repair shop. Some examples of such queries are:
- Components determining length of life ( "Ill. 2.3-3" and "Ill. 2.3-4") and associated failure mechanisms, e.g., cyclic limited, rotor components or especially creep stressed, high pressure, turbine blades.
- Time dependent changes of the operation performance ( "Ill. 1.1-1" and "Ill. 2.5-2"), e.g., to be expected drop in efficiency, temperature increases as a result if need be?
- Which parts contribute in which manner to the drop in efficiency, e.g., erosion of the abradables in the casings, abrasion on labyrinth seals, increasing roughness of blades at turbine and compressor?
- Are there particular weak spots or susceptibilities, e.g., during operation, maintenance, hardware? How are new technologies to be evaluated?
- Do the expected hardware characteristics suit the specific features of operation, e.g., by special corrosion conditions, erosion, frequent start/shut down - cycles or ( "Ill. 1.1-4", "Ill. 2.2-1 and 2" and "Ill. 2.5-2"), perhaps, necessary quick-starts?
- Is it possible to reach a bonus on service life through favorable operating conditions?
- Should one recommend a special monitoring system (Chapter 5.1.1), e.g., vibration monitoring, regular oil analysis, evaluation of the filter residue and magnetic chip detector deposits (chapter3.5)?
- Does the repair shop come up to the expectations of the operator? (see Chapter 4)
- Choice of an appropriate suction filter (principle, materials)
It is clear that the consent and concessions of the manufacturer (OEM), with regard to technical papers, procedure in case of failure, access to failed parts etc., is more easily attainable before rather than after a procurement.