Controls retrofit for gas turbines

Innovations in control systems

Whereas developments on the mechanical side are fairly steady, control systems have made quantum leap improvements compared to systems of 15 to 30 years ago and still advance every year. Yet a control system only cost a fraction compared to the turbine it is controlling. It is this combination which makes it so attractive to consider upgrading the control system: the investment-effect ratio is high. In fact in quite a few cases it will reduce the stress on the turbine itself and thus lengthens its life beyond the cost of a controls upgrade. This is possible by achieving fewer trips from high power and operating closer to the limits without exceeding these.

 

 

It is however important to ensure that the control system is truly modernized; a like-for-like retrofit as seen so often should be avoided at all cost. This requires specialist knowledge of the turbine application itself instead of generic automation methods.

Consider investing in an upgrade of your control system and take advantage from some of the advancements in the industry, like:

  • Visualisation and trending of all engine parameters on a large screen in a comfortable control room
  • High speed trending with low hysteresis and storage over many years
  • Pre & post event-triggered trending with resolutions up to 10 ms for special conditions such as starts and trips
  • No more missed events, no need for that spurious fault to re-occur to properly diagnose it. The order of events is accurate, leaving no doubt as to what came first. Compare the stored data with data of 1, 2 or 3 years ago, or longer if desired
  • Distinction of events is dramatically better. Whereas older systems contain one indication light to indicate ‘a’ fault, current systems will point you exactly to the faulty device – further supported with a historical trend of that device
  • Current PLCs are much more accurate. Self-calibrating high definition analog to digital conversion is the norm nowadays. This makes it possible to operate gas turbines closer to their limits – safely. Examples are exhaust gas temperature limit and compressor surge limit. You are less likely to burn an engine out. Or you can operate with one engine less because you know you are safely on that limit. Think of the savings in fuel costs and CO2 emission!
  • Modern components have a much higher reliability compared to their predecessors
  • More intelligence can be put in the control system if needed when compared with discrete systems. Changes are easy to program. For example, stopping the engine with a cooling-down cycle instead of just cutting the fuel reduces the number of overhauls on your engine while keeping its performance. The gas compressor does not have to be depressurised on each stop saving on CH4 emission. Be green and safe money at the same time
  • All modern PLCs support safety levels up to SIL-3. This is much better than the average trip-relay string your current system might still use. This means that with one single system it is now possible to carry out both the control and safety functions. It is now also possible to carry out certain control functions such as engine purging in safety logic. This is very important if there is a boiler located in the exhaust stack. With conventional systems and architectures this is complicated to accomplish
  • Availability can be increased by adding redundant field instrumentation which is then processed by the CPU using intelligent voting. Notorious problematic sensors no longer shut you down
  • Coupling to DCS or remote systems is easy to accomplish. There is no more need to limit dispatching with only a subset of the information available locally

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