Advanced Valve Solutions, Start-Stop Operation, OTV Valves in GE/Alstom GT24/26 Units
The worldwide introduction of wind, solar power and other renewables create an increasingly flexible demand on gas fired power stations to balance the grid.
To operate in a reliable, quick, modulating and start/stop regime, some improvements are necessary.
To start and to stop a modern CCGT installation takes time and cannot be done instantaneously. The gas turbine needs to be warmed through as well as the rest of the power plant, the HRSG, (Heat Recovery Steam Generator) downstream of the gas turbine, the interconnecting steam pipework, the steam turbine and all other balance of plant items.
This all must be done as quickly as possible to limit the starting costs and to supply as soon as possible to the grid. In the European markets the driving factor is high fuel costs, reducing the need for full speed no load, however in the USA the driving factor is to reach emission values as soon as possible.
For all CCGT plants the demand for being reliable and the need to be able to start the installation, to supply to the grid, is the single most important driving factor.
The AVS Solution
Advanced Valve Solutions has a bespoke package of dedicated products to solve these problems, based on our specific and extensive experience in these types of operating regimes. With this package in place, it leads to reduced maintenance costs, to reduce starting time and to upgrade the reliability of you existing installation. With many years of experience and a group of high qualified European manufactures supporting our performance, we deliver a complete solution.
OTC level control valves are primarily used in CCGT installations based on GE/Alstom GT 24 and GT 26 gas turbines. These valves are controlling the water level in the OTC (Once through Cooler, used to cool GT compressor air before being used to cool the GT Blades and Veins. The range of operation that the valve is required to operate in is enormous. Often staggered trim designed valves are used. However, due to an uncontrolled gap flow, staggered trims are failing.
We developed a ridged multi-staged control valve with continuous flow control and an exact, defined pressure drop per stage to avoid any cavitation and unstable control.
The first part of the stroke does not control any flow but is just used to energise the different control stages, moreover is also avoiding any hammering within the valve during opening.
It is our experience, that these valves will now last between C-inspections. Furthermore, the spares prices are cheaper than that of a staggered trim design, and in most cases, the entire valve is more cost effective than replacing parts in a staggered trim design valve.
This makes Commercial justification a very simple one. An entire new Valve, with a predicated 4-year life cycle, against spare parts only, in an old valve, with an undefined service life.
Tel: 01270 586 944
Published in Valve User Magazine Issue 49
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