The Generation of Electricity
Redbud (A combination plant)
The Generation of Electricity
Redbud (A combination plant)

The Redbud Plant Driving up to the plant was remarkable in that the plant occupied so much space that it was practically inconceivable that I had never seen it before. The sheer amount of steam pouring off the cooling towers provided an easily seen waymark upon the approach to the plant and from a distance it appeared to be a manufacturer facility for clouds. Upon the drive up, security was quickly notated as they requested my ID and provided me a pre-printed name tag indicating that our presence had already been vetted and accounted for. Key note, it was very very cold outside. I’m curious whether the steam generation would have been as spectacular from a viewing perspective if it had been a lot warmer outside. That being said, they quickly split us up into groups and we had the great fortune of both going inside (mmm warmth) and we got to learn about the integral pieces of what we were about to see which gave us some perspective on what we’d observe. In this case we were observing a combination cycle power plant which combines the Rankine (steam) power cycle with a Brayton (gas turbine) cycle. In order to combine these two processes, the combustion gases from the Brayton cycle are actually funneled into a Rankine cycle system. The efficiency gains of the combination were compared and in their presentation they notated that a steam power plant users 11,500 Btu/KWh and a gas turbine uses about 10,500 Btu/KWh but the combination only uses 7,000 Btu/KWh providing them what was somewhere in the vicinity of 30% efficiency by either alone but combined rising to somewhere around 50% efficiency. The single greatest loss of efficiency appears in the cooling towers where heated water vapor (the clouds of steam you see on your approach to the plant) escape from the cooling tower which accounts for an approximate 37% loss of energy. Looking at the gas turbine first, they notated that most turbines are comprised of a compressor, combustor, and turbine. In our discussion through the central command station, it was interesting to note that the turbines could all be spinning at the same speed (RPM) but actually producing different levels of megawatts based on their current needs/ascribed levels they were contracted to produce. For instance turbine one was spinning at a similar 3600 RPMs but producing 176.7 MW versus the average 185 MW produced by the other three turbines. This is a function of modifications made in the compressor that control how much fuel is being delivered to the turbine. The hot exhaust gases are then channeled into the HRSG which heats water and the resultant steam is channeled into differing levels of pressure at the top of the HRSG (high, intermediate, and low). Each HRSG was noted to have a capacity to produce 1 million pounds of steam per hour. The steam from the HRSG hits the steam turbine which turns a series of blades that rotate providing rotational energy. The energy from the steam is expended as it flows across these blades and reaches a point of saturation as it exits the steam turbine which leads to the use of the condenser. “Wet” steam was explained as very corrosive to the internals of the steam turbine and thus they superheat the steam as it enters the turbine in order to “dry” it out. As it exits, the remaining heat is removed from the steam and the steam is converted back to water. Along with this entire conversion process is an emissions monitoring process that makes sure that the plant reduces its impact on the environment. Per the presentation, the Redbud facility is permitted for 3.5ppm NOX and 17.2 ppm CO. This requires a catalytic reduction system which uses aqueous ammonia which transforms NOX into nitrogen and water vapor. Another interesting part of the tour was the introduction to the chemical treatment facility. As the equipment producing all of this electricity is extremely sensitive, they need to keep constantly aware of the makeup of the chemicals flowing through the system. A cyclical system of testing the major liquid components of the system were observed and it was interesting to note that the plant workforce tested much of the systems themselves as they did not always have chemist on site. Some of this apparently is a legacy from when the plant was operated independently so each person could take on the responsibilities of most others to account for vacations, sicknesses, etc… The last portion of the presentation detailed how their electric production quota is derived. The Redbud is a member of the SSP South sub-region and they utilize algorithms to determine the most cost-efficient production of electricity for the region while maintaining capabilities to spool up additional resources in the event of a disaster. One of the most meaningful bits of information was the relative times associated with the spool up of certain turbines. Because many of these turbines would take hours to bring online, the SPP must take all of this into account as it may not simply be a matter of making a call and suddenly being able to produce an extra 1000 MW of energy in the event that another plant goes down. This balancing act is a sensitive issue as simply bringing up lots of spare power is a waste of resources, but the inability to bring on power in the event of a disaster could be calamitous for those involved. It is very much an instance of weighing the outside influences (weather, type of plant, speed to deployment, etc…) versus the capabilities that are currently online. I quite enjoyed the visit to this plant and appreciated the opportunity to see its inner workings. I was surprised I had never truly seen a plant of its magnitude before in Oklahoma even in passing.