Over time, gas turbines lose efficiency due to the build-up of foulants. No matter how efficient the system, this build-up in unavoidable. It’s therefore imperative to carry out a regular gas turbine water wash in order to remove foulants and maintain performance. This can be done via an on line or off line method.
Why carry out a gas turbine water washing?
Without regular, thorough cleaning, the build-up of foulants such as scaling, particulates, corrosion and chemical reactions can ultimately lead to costly unscheduled shutdowns. As particles build up, air flow through the compressor is disrupted. In turn, this affects efficiency with symptoms such as reduced output, a drop in compressor discharge pressure, an increase in operating temperature and greater fuel consumption. An inefficient system is more costly to run and, if left for too long, it will eventually have to be shut down.
In financial terms, these shut downs can be extremely expensive, with losses of millions per annum on a typically 100MW sized gas turbine.
What is gas turbine off line washing (also known as crack washing)?
In order to carry out gas turbine off line washing, the turbine must, unsurprisingly, be stopped. Then a thorough cleansing process can begin during which foulants are removed. This is usually carried out in stages including the application of a cleaning solution followed by a series of rinse cycles. Each of these cycles requires the turbine to be accelerated and then left to slowly come to a stop. After this sequence, remaining salts are dissolved by leaving them to soak in the cleaning solution.
The final water rinse of an off line wash means all removed contaminants are cleansed from the system before it starts up again.
Gas turbine off line washing is costly in terms of time with a knock-on effect on profit. For this reason, on line washing was developed to reduce the need to stop the turbine completely.
What is gas turbine on line washing?
Gas turbine on line washing is effective as it reduces the rate at which foulants build up in the first place. While the turbine is still running, atomised cleaning fluid is injected into the system. This is not only effective, but is much gentler than other methods which can erode blades and/or damage coatings.
Importantly, gas turbine on line washing can be effectively carried out without impacting the operation of the unit. Needless to say, this is a bonus in terms of bottom lines!
Although highly effective, on line washing is generally used hand-in-hand with an occasional off line system to ensure optimum results.
For both washing methods, water quality must be carefully monitored in order to prevent the introduction of new contaminants.
How to carry out an on line clean?
In order to avoid frequent, time-consuming manual off line cleaning, a Rochem on line cleaning system can be installed. This system carries out a clean in a few minutes during normal operation.
It requires the installation of a small amount of hardware:
- Rochem injection nozzle system in the process compressor suction pipeline
- Rochem self-contained wash delivery skid (operating at pressures up to 100 barg)
The process of carrying out an on line wash is then very simple. The delivery tank is filled with Fyrewash solution and connected to the injection nozzle system. Typically an injection period of between 10 to 15 minutes followed by a rinse water purge is sufficient.
On line cleans should be supplemented from time-to-time with off line washing in order to maintain optimum performance. Fyrewash can be used in both instances, and is perfectly suited to the task.
Fyrewash is made up of specialist chemicals and designed specifically for this purpose. It is suitable for all types of fouling and removes far more than water alone ever could. It is also less abrasive than other methods.
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