Gas turbine performance is affected by the environmental challenges of a specific installation. A filtration solution designed to protect the turbine needed to be designed to address each of the conditions faced, including varying amounts of dust, salt, moisture and other contaminants. The spectrum of potential hazards that could be faced at a turbine installation means one filter cannot meet all needs. Even the different forms of dust or moisture present need to be considered within the design of the filter house.
In the Middle East, a mixture of sandstorms, heat, mist and moisture from random fog events, make for a brutal environment for a gas turbine. It is the combination of the moisture in thick fog combined with high dust concentrations that can be particularly challenging for a filter system.
Without the correct design and implementation of a system, the installation is at risk of sudden pressure increases, gas turbine shutdowns, difficult and time-consuming maintenance and greatly shortened filter life. Indeed, as one operator was experiencing, it is not uncommon for pre-filters to require changing every two or three days and final filters to need replacement after just six or seven months, as opposed to a normal life expectancy of over two years. The increased labour and ongoing cost to keep operations running and reduced availability of the gas turbine was having serious impact on the operation’s bottom line.
The gas turbine installation in question was at a power plant in a coastal, desert location in the Middle East. Seasonal fog events and extremely high levels of dust were causing havoc with the system. After careful review of the installation and specific environmental conditions, however, relatively simple changes led to a dramatic improvement in performance.
When to pulse – and when not to…
One of the first areas to be considered was the pulse system settings. A pulse system removes dust build-up on the filter and tends to operate in one of two ways. In the first, it can be set to run continuously without regard for the differential pressure.
Alternatively, however, it can be configured to run when the differential pressure across the filter reaches a certain level. Once this level is seen, the pulse system turns on, cleans the filters and then turns off when a low differential pressure setpoint is met.
The site’s pulse system was set to run continuously. The issue this created, however, was that the fine dust in the area was leaving the filters in a dust cloud and simply becoming re-entrained on the filter. The system was changed to operate only when differential pressure reached a pre-set trigger level. The switching levels were established based on testing with the local environmental conditions and found to be optimized with the system turning on at 1.5” wg (water gauge) and off at 1.0” wg. This meant the filters were cleaned before pressure became an issue but not before a dust cake built up on them that enabled gravity to help the dust move down the filter house. Typical set points for pulse cleaning start around 3.0” wg and stop at 2.5 or 2.0” wg.
Handling the moisture from the fog
The next area to be considered were the coalescers, which were experiencing serious issues. Coalescers are used to remove moisture from the air flow prior to it reaching the filter. If there is a lot of moisture in the air flow when it reaches the filtration stages, small moisture droplets combine with the dust and sand to create blockages and sudden increases in differential pressure. The size of these droplets means they can also work their way into the matrix of the filter media and get stuck. Coalescers usually work to prevent this from happening by combining small moisture droplets to form bigger, heavier ones-many of which will then naturally fall out of the airflow.
The site in question had traditional coalescers installed, known as mat coalescers, which employ media similar to that used in dust filtration. The issue with these, however, was that the high volumes of dust were quickly clogging them and, with no path for the inlet air flow, they were being forced out of place. Once the air was able to completely bypass the coalescers, the moist air and dust were continuing to the filter and creating blockages. Placing the coalescing technology with a modern, fully washable, 100% synthetic mesh resolved this issue and, even after 12 months of operation, the coalescers remain in firmly in place and doing the task for which they are installed.
Unlike the traditional mat equivalents, the new synthetic media coalescers had been specifically designed to allow the sand and dust to pass through. The new units work by using a two-stage coalescence configuration. The first stage is a moisture separator with coalescing efficiency down to 50 microns. The second stage, a clearcurrent TS1000 coalescer, has 99 percent coalescing efficiency for droplets down to 10 microns but which has limited dust removal capability. It is this deliberate limitation of dust removal capability which avoids blockages and significantly reduces the maintenance overheads where high levels of both dust and moisture are present. The dry dust is then easily handled by the filtration system, to prevent it damaging the turbine.
Two simple changes = huge improvements in performance
Following these two changes on site, pulse system settings and coalescer technology employed, the site has experienced no shutdowns because of problems with the filter system or sudden differential pressure increases. The self-cleaning filter life is exceeding the customer requirement of two years and maintenance intervals have been extended. This has reduced operating costs, limited manual labour interventions required, and increased production availability – significantly improving operating profits.
In regions where there are such extreme conditions as found in the Middle East, operators are advised to start the difficult season with new, clean filters. They should evaluate all filtration options and new technologies available, as these may offer a major upgrade to existing technology and save a great deal of time and money. Operators are also advised to proactively plan outages to be in the best position to survive seasonal, tough environmental conditions.
Success is not about ‘on paper’ specifications
Measurement of the success of a filtration solution cannot be measured by specification comparisons or laboratory testing, as these do not portray the real-world conditions of each installation. Instead, success criteria needs to be based on critical factors such as the reduction in turbine downtime and outages for filter replacements.
The example given above shows that, with the correct experience and expertise, significant improvements to turbine performance can be gained with even relatively small solutions and adjustments. System design and settings need to be geared towards the real-world environment in which the solution is installed. Working with filtration experts, other turbine operators can benefit from evaluating total solution management of their inlet systems.
About the author: David Trisante is sales director at Parker Hannifin Filtration division. Trisante earned his engineering degree in the prestigious Universitat Politecnica de Catalunya (Spain) and the Aalborg Univeritet i Esbjerg (Denmark). He holds more than 20 years’ experience in purification and air pollution control markets as well as in a variety of Filtration equipment’s ranging from dust collectors, electrostatic precipitators or Gas Turbines air intake systems. Trisante has developed different roles in engineering services, product management and executive sales in BHA, General Electric and Clarcor Holdings.