The Role Gas Turbines Play in Power Plant Reliability

Gas turbines play a huge role in power plant reliability. In most cases—whether it be simple-cycle or combined-cycle applications for gas turbines—the gas turbine is the first major piece of equipment in the process that needs to start. So, without a reliable control system or a well-maintained and cared-for control system, your primary piece of major equipment is out of the game or unavailable.

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In this article, we will explain the role of gas turbines a little more, and why they so important for the reliability of your power plant.

Start Permissives: Ready to Start or Not?

Typically, when most frames 7FA, 6FA, 5A, or any industrial frame size gas turbine owner starts the plant with the gas turbine control system, there is typically a page with start permissives, indicating the system is ready to start or not ready to start. Start permissives are conditions on the unit that need to be met before it can start.

In many cases, the rest of the equipment at the plant depends on the gas turbine control system because it is often the first thing that plant managers will start before the other equipment. 

Therefore, if you receive the “not ready to start” indication, then you won’t be able to start your gas turbine—or the rest of your plant at all, especially if there are other drivers behind the gas turbine. 

How the Control System Works

A control system is made up of a bunch of subsystems, pretty much like everything in a power plant. So, the control system as a whole has subsystems under it, and that can kind of be broken down and analyzed in an engineering mind state. 

The primary parts of the control system are the software and logic, which are really reliable. They don’t typically break; they are just computer code that is programmed.

Typically when we see problems, malfunctions, abnormalities in logic or software, it’s because of some type of human interaction. Most control systems or any other equipment for that matter don’t fail on their own. Of course, failures without human interaction can happen, but they are rare.  

The relays in the system that bring the logic from the software are typically control cards and other communication devices. These devices can fail. In these cases, when the devices can fail, the logic and software fails as well.

Why Reliability is So Important

If you don’t have a reliable gas turbine control system, then you usually can’t even get the plane off the ground, so to speak. You can’t even really gain any momentum!

Therefore, it is important to perform check out and regular inspections of your control system equipment. At TC&E we like to call these inspections “reliability assessments”. To put it simply, it involves a clean and inspect of the system. 

At TC&E, our team checks the control system, cleans it out, performs some file management, and ensures that there aren’t any warning lights and that everything looks healthy and functional.

Contact our team today to learn more about our reliability assessments and what we can do to help ensure your plant’s reliability. 

Cogeneration of Bagasse

Cogeneration of bagasse is one of the most attractive and successful biomass energy projects that have already been demonstrated in many sugarcane producing countries such as Mauritius, Reunion Island, India and Brazil. Combined heat and power from sugarcane in the form of power generation offers renewable energy options that promote sustainable development, take advantage of domestic resources, increase profitability and competitiveness in the industry, and cost-effectively address climate mitigation and other environmental goals.

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According to World Alliance for Decentralized Energy (WADE) report on Bagasse Cogeneration, bagasse-based cogeneration could deliver up to 25% of current power demand requirements in the world’s main cane producing countries. The overall potential share in the world’s major developing country producers exceeds 7%. There is abundant opportunity for the wider use of bagasse-based cogeneration in sugarcane-producing countries. It is especially great in the world’s main cane producing countries like Brazil, India, Thailand, Pakistan, Mexico, Cuba, Colombia, Philippines and Vietnam. Yet this potential remains by and large unexploited.

Using bagasse to generate power represents an opportunity to generate significant revenue through the sale of electricity and carbon credits. Additionally, cogeneration of heat and power allows sugar producers to meet their internal energy requirements and drastically reduce their operational costs, in many cases by as much as 25%. Burning bagasse also removes a waste product through its use as a feedstock for the electrical generators and steam turbines.

Most sugarcane mills around the globe have achieved energy self-sufficiency for the manufacture of raw sugar and can also generate a small amount of exportable electricity. However, using traditional equipment such as low-pressure boilers and counter-pressure turbo alternators, the level and reliability of electricity production is not sufficient to change the energy balance and attract interest for export to the electric power grid.

On the other hand, revamping the boiler house of sugar mills with high pressure boilers and condensing extraction steam turbine can substantially increase the level of exportable electricity. This experience has been witnessed in Mauritius, where, following major changes in the processing configurations, the exportable electricity from its sugar factory increased from around 30-40 kWh to around 100–140 kWh per ton cane crushed. In Brazil, the world’s largest cane producer, most of the sugar mills are upgrading their boiler configurations to 42 bars or even higher pressure of up to 67 bars.

Technology Options

The prime technology for sugar mill cogeneration is the conventional steam-Rankine cycle design for conversion of fuel into electricity. A combination of stored and fresh bagasse is usually fed to a specially designed furnace to generate steam in a boiler at typical pressures and temperatures of usually more than 40 bars and 440°C respectively. The high pressure steam is then expanded either in a back pressure or single extraction back pressure or single extraction condensing or double extraction cum condensing type turbo generator operating at similar inlet steam conditions.

Due to high pressure and temperature, as well as extraction and condensing modes of the turbine, higher quantum of power gets generated in the turbine–generator set, over and above the power required for sugar process, other by-products, and cogeneration plant auxiliaries. The excess power generated in the turbine generator set is then stepped up to extra high voltage of 66/110/220 kV, depending on the nearby substation configuration and fed into the nearby utility grid. As the sugar industry operates seasonally, the boilers are normally designed for multi-fuel operations, so as to utilize mill bagasse, procured Bagasse/biomass, coal and fossil fuel, so as to ensure year round operation of the power plant for export to the grid.

Latest Trends

Modern power plants use higher pressures, up to 87 bars or more. The higher pressure normally generates more power with the same quantity of Bagasse or biomass fuel. Thus, a higher pressure and temperature configuration is a key in increasing exportable surplus electricity.

In general, 67 bars pressure and 495°C temperature configurations for sugar mill cogeneration plants are well-established in many sugar mills in India. Extra high pressure at 87 bars and 510°C, configuration comparable to those in Mauritius, is the current trend and there are about several projects commissioned and operating in India and Brazil. The average increase of power export from 40 bars to 60 bars to 80 bars stages is usually in the range of 7-10%.

A promising alternative to steam turbines are gas turbines fuelled by gas produced by thermochemical conversion of biomass. The exhaust is used to raise steam in heat recovery systems used in any of the following ways: heating process needs in a cogeneration system, for injecting back into gas turbine to raise power output and efficiency in a steam-injected gas turbine cycle (STIG) or expanding through a steam turbine to boost power output and efficiency in a gas turbine/steam turbine combined cycle (GTCC). Gas turbines, unlike steam turbines, are characterized by lower unit capital costs at modest scale, and the most efficient cycles are considerably more efficient than comparably sized steam turbines.