Rendering of a new park and a cultural and entertainment complex, which will sit above an underground CHP plant in South Korea (photo courtesy of KOMIPO)[/caption]

By JAMES BERRYOil and gas has been a booming area for heavy equipment sales for many years. But with oil prices plummeting, it appears that combined heat and power (CHP) has emerged as the new growth area. This is confirmed by a Navigant Research study into commercial CHP. It found that interest is growing around the world due to concerns about grid reliability, rising electricity demand and greenhouse gas emissions. As a result, Navigant expects the global CHP market to be worth $14 billion per year by 2024. Most installations have traditionally been in the United States and Northern Europe. But there are many in China, Japan and South Korea, too. South Korea, in particular, has been aggressively adding more CHP. Drivers include strong economic growth, a rise in electricity demand of 3.6% annually and cold winters (temperatures as low as -18°C) calling for the expansion of the district heating network within large cities. “Conditions for district heating and new CHP projects are excellent, due to a high population density in Korean metropolises and a climate with hot summers and cold winters,” says Lothar Balling, head of gas turbine power plant solutions at Siemens Energy. District heating began in Korea in the eighties with heating service being provided to the Yeouido and Banpo districts of Seoul. Since then, its use has expanded throughout the Seoul metropolitan area and into other cities within the Asian nation. Many of these plants utilize CHP. Simple CHP systems deployed for district heat use a boiler to generate steam to be fed into distribution lines for heating purposes, as well as to drive a steam turbine connected to a generator to produce electric power. A more efficient arrangement, however, is to design a CHP plant around a combined cycle system. In this case, the fired boiler is replaced with a gas turbine and a heat recovery steam generator (HRSG). Such combined cycle power plant (CCPP) systems are more efficient for applications in which a higher portion of the input energy goes towards power generation. Efficiency can be further increased by utilizing a synchronous self-shifting clutch to shut down the condensing portion of the steam turbine when power generation demands are low. In this way, steam continues to be produced for district heating. When power generation requirements return or when steam demand falls off, the clutch can reengage the condensing steam turbine to boost power output. As a result, operating point efficiencies in excess of 80% can be achieved economically by district energy systems. CHP-based district heating also offers sufficient operational flexibility so plants can respond to demand and market conditions in the most optimum manner. Korean CHP Origins The first utility scale CHP in South Korea was Ilsan in 1993. It used Westinghouse (now Siemens) W501D5 gas turbines in a 4+1 and a 2+1 CCPP configuration for a total of 140 MW. Since then, the country has added a variety of CHP projects. The 400 MW megawatt Daegu Green Power CHP plant brings district heating to 25.000 households. It features one Siemens SCC6-8000H 1S gas turbine. Siemens worked with Lotte Engineering and Construction to complete the facility. The plant provides 20% of the city of Daegu’s daily power needs. It uses a single-shaft design with an air-cooled H-class gas turbine, 600°C steam cycle technology and a Benson HRSG. The latest CHP facility to come online in South Korea is the 550 MW Sejong district heating plant which is a 2+1 CCPP using Mitsubishi Hitachi Power Systems M701F gas turbines. This 67,007m² site also provides 391 Gcal/hr of heat. Doosan engineered the facility in Sejong, a new Korean administrative city about 100 miles from Seoul. It consists of 2 x 180 MW gas turbines, a 200 MW HP-IP (High Pressure-Intermediate Pressure) and LP (Low Pressure) steam turbine generator train and HRSG. The generator sits at one end followed by the 90 MW HP-IP turbine and the 110 MW LP turbine drives with an automatic synchronous self-shifting overrunning clutch by SSS Clutch in between. When heating demand is high, all of the steam exhausting from the HPIP turbine is directed to the district heating system and the LP turbine is disengaged by the overrunning clutch. This eliminates the need for cooling steam which would be required if the LP turbine was left spinning unloaded. When heating steam demand is low, however, a portion of the HP-IP exhaust stream is sent to the LP turbine which automatically engages with the HP-IP turbine to supply extra power to the generator for electricity production. Producing the steam at higher temperature and pressure than that required by the district heating system allows for efficient production of power in the HP-IP turbine. The clutch between the LP turbine and the generator, in addition to providing operational flexibility and eliminating the need for cooling steam, provides capital savings by eliminating the need for a second generator and switchgear. As well as lowering installation costs, this reduces the footprint of the facility. According to Seong Heon Yang, an engineering manager at Doosan Heavy Industries and Construction who helped lead the effort, the application of the clutched steam turbine is the key technology for flexible operation of CHP with variable demands of heat and power. He said that an appropriate clutch system was designed by close cooperation with the clutch provider. From rotordynamic studies, a clutch system with two jack shafts was designed to ensure dynamic stability to the entire train. This included the use of 5-pad tilting pad journal bearings to prevent bearing instability. Underground CHP While these projects are already impressive, South Korea is taking CHP to another level entirely by doing something no one has ever done before – constructing a utility-scale CHP-based district heating plant beneath a city. Doosan is in the midst of erecting a power plant beneath the Seoul Thermoelectric Power Plant which is operated by Korea Midland Power (KOMIPO). Sited in the Mapo District of Seoul, the existing plant is to be retired in 2017 at which point it will be transformed into a complex consisting of a library, museum, a sports center and a concert hall. Meanwhile, construction work is going ahead below ground to establish the new facility. When completed, the Seoul Combined Cycle Thermal Power Plant will consist of two power islands each producing 400 MW which will provide 10% of the power for Seoul as well as heat for 100,000 houses (heat production of 530 Gcal/hr). Work is already ongoing to establish a platform for the subterranean facility 30 meters deep alongside the Han River. Doosan won the contract from KOMIPO to supply and install two GTs, two STs and two HRSGs. Underground plant Once that plant goes online, South Korea intends to add even more CHP. As well as the underground plant at Mapo, another facility is under construction in Anyang, a suburb of Seoul. Korea’s GS Power is upgrading an aging district heating plant at that location using the GE 7HA.02 gas turbine and associated steam turbine with a clutch operating as part of the district heating system. All the steam generated can be used for district heating in winter months, if necessary. The plant will have the capacity to generate 935 MW in combined cycle mode. Looking ahead, the latest design concept combines a clutched single shaft arrangement such as Daegu and a clutched multi-shaft setup as in Ilsan or Sejong into a combined singleshaft design. This approach offers the small footprint and lower cost of single- shaft along with the flexibility and greater maximum heating flow of multi-shaft. Author: Jim Berry has over 40 years experience in the sales, marketing, application engineering and service of centrifugal and reciprocating compressors, pumps, gas turbines, and diesel and gas engines. He obtained his BSME in Mechanical Engineering from Drexel University in 1963. He currently works as a technical consultant for engineering firms. For more information contact: