2009 Issue

32 I N MAY, THE UTAH SECTION of the American So- ciety of Mechanical Engineers (ASME) toured Rocky Mountain Power’s Gadsby power plant, located at 1400West North Temple in Salt Lake City. Being mechanical engineers, we were look- ing for examples of things that we understand. But what was also apparent were all of the other engineering disciplines that were represented in the workings of the plant. The Gadsby plant began operation in 1951 with the purchase of the first coal-fired Westinghouse steam turbine, with a peak output of 40-MW. Additional steam turbines were added in 1952, a 60-MW Westinghouse turbine and 1954, a 105- MW General Electric turbine. For years these turbines helped provide for the electrical needs of the Salt Lake valley. Originally, the turbines burned coal dust. The coal was brought in by rail and pulverized into dust at the plant. As you canwell imagine, coal dust was dirty and dangerous. The turbines were converted to burn natural gas in the early 1990’s. In 2002, three natural gas-powered 40-MW turbines were added to the plant. These turbines were GE-built LM6000’s – land derivatives of the engine used to power the Boeing 747 aircraft. The LM6000 turbine consists of a five-stage low- pressure compressor, a 14-stage high-pressure compressor, an annular combustor, a two-stage, air-cooled high-pressure turbine, and a five- stage low-pressure turbine. Electrical power is generated directly by the low-pressure turbine, which rotates at 3,600 rpm (General Electric Energy 2008). While theGadsby plant was once amajor power producer in the valley, it is now used as a “peaker” station – its power comes on-line to handle peak loads. When we visited, a cool day inMay, none of the turbines were running. The dispatch center in Oregon determines when the turbines are started up, depending on capacity and demand. The gas turbines can be generating electricity within 10 minutes, thanks to their aircraft engine heritage. The steam turbines take a couple of hours to get up to speed. The steam turbines are massive, taking up a large multiple-story building. The boilers are natural gas fired. The boilers heat the steam bar- rel, superheating the steam to 1000°F at 1450 psi. The steam then passes through the high- and low- pressure turbines, which in turn rotate a dynamo which generates electricity. The steam then travels through the condenser, wherewater-cooled tubes remove the heat and convert the steam back to water, which circulates back into the boiler. The water-cooled tubes are fed by water from the nearby Jordan River. After passing through the tubes to condense the steam, the water goes out to cooling towers, delivering the heat to the atmosphere before circulating back through the system. A control room monitors the six turbines while in operation, allowing operators to see what is happening. The operators can see at a glance the significant pressures, temperatures, and flow rates, in order to ensure that the systems are functioning properly. Controlling and reducing mono-nitrogen ox- ides (NOx) is an important part of the process. NOx forms when fuel is burned at high tempera- tures, and is a major contributor to smog and acid rain (US Environmental Protection Agency 1998). The boilers contain low NOx burners, which can change angles and dampers to control the NOx output. Our tour guide indicated that if the plant isn’t meeting the state NOx level requirements, then something is wrong and needs to be cor- rected, because the burners, as designed, easily meet the requirements. The Gadsby plant is also being used to control wind farm power, currently coming fromOregon. The wind turbines are very large, with blades 120 feet long and turbine housings the size of a bus. From the control room, they can determinewheth- er the wind is within the speed range of the wind turbines, and if it is, they can generate electricity using wind power and route it into the grid. They can also run diagnostics remotely to see that the wind turbines are functioning correctly. As mechanical engineers, we recognized the thermodynamics involved in running the steam and gas turbines. The gas turbines operate on the Brayton cycle, while the steam turbines operate on the Rankine cycle. Simplified versions of these Generating Power TERRY D. HAWS, JR, PE , ATK LAUNCH SYSTEMS Engineering continues to make our world smaller, faster, and cleaner as the pace of technology continues to accelerate. As it does, communication and interdependence between engineering disciplines becomes more and more important. cycles were the subject of much study in college classes, as we derived the work and efficiency possible from each. Seeing the cycles in action helped those principles come alive. But other engineering disciplines are also necessary to keep the plant operating correctly. Environmental engineering is important to make sure that neither the air nor the water coming from the plant is contaminated beyond acceptable levels. Generating electricity tomeet the growing needs of the valley requires electrical engineering. Using the electricity efficiently to condition homes and offices requires HVAC engineers to create efficient designs. Civil and structural engineers are needed to design and build the enormous buildings required, including the 250 foot smoke stacks that tower over the site. The three gas tur- bines are derivatives of aircraft engines, originally designed by aeronautics engineers. And creating the control systems for the turbines and the wind farm also requires controls engineering. And the pace of technology will only further blur the lines between the engineering disci- plines, requiring us as engineers to have a broad base of knowledge to complement our individual specialties. A recent Mechanical Engineering article talked about the need to be “T-shaped people” – deep in one disciplinary area but with a broad base of knowledge. (Simpson, Barton and Celento 2008) ASME’s stated vision is: “To be the premier organization for promoting the art, science and practice of mechanical and multidisciplinary engineering and allied sciences to our diverse communities throughout the world.” ASME and the other professional engineering organizations will need to continue to work together in new and creative ways to make sure systems small and large, from nanomachines to the Gadsby power plant and beyond, operate efficiently, cleanly, and well. All of us, working together, can generate the power we need to continue to change the world. Mr. Haws, a graduate of Brigham Young University, and a licensed professional engineer. He is affiliated with ATK Launch Systems in Promontory, Utah.